US 2743428 A
Description (OCR text may contain errors)
April '24, 1956 MARTINES 2,743,428
ELECTRICAL CONTACT ELEMENT FOR RECEIVING A MALE FIN Filed Nov. 8, 1954 INVENTOR.
- R 49119 Marzjnes ATTORNEYS United States Patent ELECTRICAL CONTACT ELEMENT FOR RECEIVING A MALE PIN This invention relates to improvements in an electric plug, particularly the electric contact elements for plugs used for connecting and disconnecting electric heating devices and/or the like with a source of electricity.
An electric contact element of the above character in common use in the trade is formed of a single length of suitable material concave in cross section at both ends and bent back upon itself at the midpoint to provide a pair of resilient jaws. The jaws are made to converge towards the free end thereof to form a restricted opening thereto in an attempt to provide the necessary frictional engagement with the round terminal contact pin received between the jaws. A disadvantage of this general type of contact element is that the engagement between the terminal pin and the jaws is had only at line contact crosswise of the jaws. This permits a lateral shifting and wiggling action between the jaws and the terminal pin which is objectionable.
An object of the invention is to provide a contact element of the above character which is so constructed as to overcome the disadvantages heretofore mentioned.
A more specific object of the invention is to provide a contact element which is so constructed as to provide a positive contact with the terminal pin at many spaced transverse cross sections of the contact element.
Another object is to provide a contact element in which there will be a four point contact engagement with the terminal pin at any given transverse cross section of the contact element.
Another object is to provide a contact element which will, under pressure of the engagement of the terminal pin, yield along a line extending parallel to the axis of the terminal pin.
With these and other objects in view, the invention consists of certain novel features of construction as will be more fully described and particularly pointed out in the appended claims.
In the accompanying drawings:
Figure 1 is a plan view of a connector plug with one half thereof removed and showing the electric contact elements embodying my invention;
Figure 2 is a plan view on a larger scale of one of the contact elements shown in Figure 1;
Figure 3 is a similar view of the opposite side of the contact element;
Figure 4 is an edge view of the contact element; and
Figure 5 is a sectional view taken substantially along line 5-5 of Figure 1 and showing a terminal pin of an electrical appliance engaged with the contact element.
The connecting plug shown is of conventional design comprising an insulating casing preferably made of two similar parts 11, only one of which is shown. The parts 11 are held together as by means of screws 12 passing through the central wall portion 13 and engaged by clamp nuts 14. The casing has spaced longitudinal recesses 15 which extend inwardly from one end of the casing to a common cavity 17, bore 16 extending inwardly from the other end of the casing into the cavity.
I 2,743,428 Patented Apr. 24, 1956 The cable or electric cord 18 passes through the bore 16 into the cavity 17 and. branches therefrom to recesses 15 to be attached. to the contacting elements 20 which are received and held in position by engagement between adjacent wall portions of the casing as will here inafter appear.
According to the present invention the contact element 20 is made from a single strip of suitable flat sheet resilient electrical conducting material which is subjected to a sequence of severing, stamping, and bending operations to form a socket portion 21 which is joined by a flat shank 22 to a pair of arms 23 which. are adapted to be bent and crimped about the wire of the cord 18 received between the arms. The socket portion 21 is generally circular in cross section but out of round with reference to the axis thereof as will hereinafter appear. Between the oppositely disposed longitudinai ribs 24 which extend from adjacent the free end of the socket to adjacent the shank 22 on a plane generally contiguous to the plane of shank 22 there is an arcuate wall portion 25. This wall portion is formed on a radius which is smaller than the radius of the terminal contact pin P to be received in electrical engagement therewith. Because of the dilference in radii. two spaced longitudinal contact areas will result (see Figure 5). The arcuate wall portions 26 of the socket extending from the ribs 24 are formed on a radius greater than the radius of pin P and are provided with reinforcing ribs 27. These wall portions are free of the shank 22and have an inherent resiliency along the axial extent of rib 24 to give a hinging spring action. The edges 28 of the portions 26 are spaced from each other a substantial distance and are turned inwardly to provide two longitudinal areas of contact 26'. The edges 28 also, by virtue of their spring action, maintain the pin P in firm contact with the points of contact in the portion 25. Thus, four longitudinal points of contact are secured between the walls of the socket and the terminal pin P received therein as well as a firm embracing relationship therebetween. This em bracing relationship, it will be noted, is enhanced by the long hinging line along arcuate rib 24 which reduces the chance of fatigue under repeated bending, the stress on the material being distributed in two senses.
The socket walls are made straight in the longitudinal direction, and the wall portions 26 are resilient, yielding outwardly at the junction thereof with the ribs 24. In order to enhance this resiliency, the wall portions 26 are separated from the wall 25 in a longitudinal direction as by means of a slot 29 (see Figure 4). Wall portions 25 and 26 are flared at the entrance end of the socket as at 30 to facilitate the entering of the terminal contact pin P. The shank 22 extends beyond the sides of the socket and provides tabs 31 to engage in recesses 32, 33 formed in the walls of the casing so as to be held in position by the walls thereof.
From the above description it will be apparent that the socket is made with a slightly smaller interior diameter than thcdiameter of the terminal contact pin P so that the bore of the socket 21 will engage at four points at any given transverse cross section thereof. It will be further apparent that the tension of the walls 26 exerted on the terminal contact pin P will tend to move the pin into further engagement with the points of engagement with wall 25. This in turn tends to cause a spreading of said wall 25 and thus places said wall under tension to further increase the grip of the socket walls on the said pin P and provide for a good electrical engagement between contacts.
1. In an electric attachment plug, a contact element for receiving a male pin formed from one piece of resilient electrical conducting material bent to form a straight socket with a wire connecting shank, said socket having in cross section an out of round wall with two spaced longitudinal edges removed from said shank and resiliently yieldable along a line substantially parallel to the longitudinal axis of the socket, the bottom half of said wall being formed on a first radius and the top half of said wall being formed on a second radius whose center is above the center of the first, said wall having four longitudinal spaced points of engagement crosswise thereof equal distances from the axis of said socket whereby a round terminal contact received in said socket will engage at four points at many transverse cross sections of the contact.
2. A one piece contact member for attachment to a plug comprising a substantially tubular body adapted to receive a cylindrical contact pin, said body being open at one side longitudinally of the body and provided with opposite outer ribs extending lengthwise of the body, said body having a wall portion between said ribs extending crosswise on an arc of a first radius having a center midway of said ribs, said wall portion having a wire connecting shank extending therefrom, and resilient wall per tions extending from said ribs toward each other on a curvature with a second radius having a center midway of said ribs and further removed from said wall portion than the center of said first radius to provide with the said first wall a four point contact engagement with a contact pin at many transverse cross sections through said body, said resilient wall portion free of said shank and yielding along a line extending parallel and adjacent said ribs.
References Cited in the file of this patent UNITED STATES PATENTS 1,649,305 Hartmann Nov. 15, 1927 1,921,745 Grace Aug. 8, 1933 2,086,522 Bergstrom July 13, 1937 2,151,226 Ogle Mar. 21, 1939 2,453,826 Adams Nov. 16, 1948 FOREIGN PATENTS 564,889 Germany Nov. 24, 1932 758,099 France Oct. 23, 1933