US3636290A - One-piece sliding contact - Google Patents

Abstract

A one part contact of highly flexible multifinger construction particularly useful for high-current applications.

Description

United States Patent Kucharski 51 Jan. 18, 1972 [54] ONE-PIECE SLIDING CONTACT [56] Refmnc's [7 21 Inventor: Leonard J Kucharski, Chester, Pa. UNITED TATE PATENTS [73] Assignee: I-T-E Imperial Corporation, Philadel hia, 2,176,718 10/1939 Linde ..200/l66 E X Pa. 3,087,038 4/1963 Bethke ....200/166 BA 3,127,492 3/1964 Date ..200/166 BA [22] Filed: June 2, 1970 pp No 42 734 FOREIGN PATENTS OR APPLICATIONS 1,179,394 12/1958 France ..200/163 (g1. ..200/166 M21; Prima'y Examin H 0. Jones 581 Field 6: Search ..2o0/166 E, 166 D, 166 BB, 1 6 BA,

200/166 57 ABSTRACT A one part contact of highly flexible multifmger construction particularly useful for high-current applications.

4 Claims, 18 Drawing Figures Pmmmmm EJ636290 SHEET 30F 4 r, d if! 17/4 ONE-PIECE SLIDING CONTACT This invention relates to a one part sliding contact and, more particularly, to a tulip-clip contact which is more economical to produce than presently known tulip-clip assemblies.

As will become clear hereinafter, the present invention describes a female contact having a plurality of highly flexible contact fingers. The individuality of these fingers is obtained by fabricating a substantially cylindrical contact casing to have a number of equally spaced elongated slots. These slots extend in alternating direction along the length of the casing, from one end of the casing towards the other opposite end. While the slots have generally parallel sides, their ends which are remote from the beginning of the slot construction are of substantially circular section.

Such a contact has been found to be more economical to produce than presently known tulip-clip assemblies, and at the same time exhibits a radial force per finger and undergoes a maximum fiber stress at least comparable to that associated with conventional arrangements. The one piece contact to be described is substantially symmetrical about its horizontal and vertical axis and gives the appearance that the slotted construction constitutes, in essence, a saw cut separating adjacent contact fingers.

Objects and advantages of the present invention will become more understandable from a consideration of the following discussion taken in connection with the drawings in which:

FIGS. 1-3 represent front, top, and side views of a tulip-clip assembly known in the prior art;

FIGS. 46 represent corresponding front, top and side views of an assembly constructed in accordance with the present invention;

FIGS. 7-12 are expanded presentations of selected views of FIGS. 46 which are helpful in an understanding of the present invention;

FIGS. 13a-c illustrate the manner in which the assembly of FIGS. 46 may be constructed; and

FIGS. 14-16 show uses to which the contact assembly of the present invention may be put.

Referring now to FIGS. 1-3 of the drawing, the prior are tulip-clip assembly there shown will be understood as consisting of four separate and independent sections -13. Each such section is designed to correspondingly mate with its two adjacent sections and to exert, by means of a pair of coiled springs 15, 16, uniform pressure on a cylindrical conductor inserted at the opposite ends of the assembly. When generally used, the openings of the female tulip-clip assembly is selected to be slightly less than the diameter of the inserted male cylindrical conductor, 17, 18 to the extent that insertion of the conductor causes the parts of the assembly to deflect outward until restrained by the springs 15, 16. In such manner, a restraining force is exerted on the corresponding parts 10-13, substantially equal to the outward force imposed by the forcefitting of the conductor. When constructed as in FIGS. 1-3, a pair of bus bars may be electrically connected by insertion into the opposite ends of the tulip-clip assembly, whose parts are made of electrically conducting material to carry current from one bus bar to the other. Alternatively, the tulip-clip may be used in serially connecting current limiting fuses with'an electrical circuit breaker to extend the range of currents over which the breaker may afford protection.

As-will be apparent, the manufacture and deployment of such tulip-clips are somewhat complicatednot only because a plurality of correspondingly shaped sections must be fabricated and coincidentally arranged-but also because some fixture must be used in order to exactly hold the corresponding parts in proper position while attaching the restraining springs. It will be appreciated that these springs also add to the cost of the assembly. As will also be apparent, such problems are substantially compounded as the number of tulip-clip fingers are increased.

However, referring to the corresponding views of FIGS. 46, there is shown a contact assembly which is far more economical to manufacture and deploy. It will be seen that the assembly of FIGS. 46 is essentially a one piece assembly having a plurality of electrically conductive contact fingers. In particular, eight such fingers 20-27 are illustrated, with the arrangement being effected by means of a corresponding number of elongated slots or, in essence, saw cuts 30-37. As will be noted, the assembly is of a substantially cylindrical casing construction and, therefore, symmetrical about its horizontal and vertical axes. The elongated slots will be seen to extend in alternating fashion from one end of the cylindrical casing 40 towards its other, opposite end. The sides of each slot are generally parallel, with the slots being arranged in side-by-side relation, generally ending in a circular section, indicated by the reference notation a."

In constructing the clip assembly of the invention, the end receiving the corresponding cylindrical conductor 41, 42 will likewise be selected of somewhat smaller diameter. However, rather than use additional restraining springs to exert sufficient pressure to secure the conductor in place, such pressure is exerted by the tendency of the individual contact fingers to withstand the deformation caused by such insertion. This withstand is exemplified by the exploded view of FIG. 7, showing the circular section of the elongated slot operating to counteract such deforming forces.

For purposes of discussion, the following mathematical analysis is presented to illustrate the magnitude of the contact pressure forces obtainable with the assembly of FIGS. 46 and, also, the maximum stresses present in its electrically conductive material.

' FIGS. 9 and 10 of the drawings show developed views of the assembly of FIGS. 46 in its unstressed condition. FIGS. 7 and 8 represent the assembly in its stressed condition, such as would be obtained by inserting larger size cylindrical conductors at both its rounded ends. Each contact finger 20-27 in the stressed condition will be seen to deflect by a distance e (FIGS. 7, 8) with the deflection being resisted by equal and opposite forces W at each end, in the tangential direction. Each contact member as thus described may be considered to 'be a cantilevered beam or bar subjected to a concentrated load and a couple at the free end. Such a bar has a fiber stress which is zero at the center of its length, and has a maximum value at the ends of its length I, given by the expression:

S 3Wllhb [lb./in. l)

where W the load, in pounds (essentially comprising the equal and opposite forces resisting deflection of the bar in the tangential direction);

h the height of the bar, in inches (in the radial direction); and

b the mean width of the bar, in inches (in the tangential direction).

In order to open the one-piece tulip-clip device radial forces must be applied to the ends of the bars. These are the contact forces F, and are related to the tangential force W, as shown in the end view of FIG. 11. Such forces can be shown to be represented by the expression:

F= rrlN W [lbs] (2) where F the radial force per contact finger; and

N number of fingers at each end of the device (equal to one-half the number of bars shown by the reference notations 20, 21, 22, etc.).

In the operation of the one-part contact clip, it will be seen that the flow of high current will cause all the segment bars of the assembly to attract one another electromagnetically. These forces result in further radial contact pressure, additive to the pressure due to elastic deformation, as indicated in expression (2) above. These electromagnetic forces may be expressed as:

I 2 2 l ewton a electromagnetic constant which in the MKS system equals 41r l D mean diameter of the bar cluster, in meters; and

I current flowing through the bar members. (See the sectional view of FIG. 12.)

Substituting the value for 11.0 and expressing I in kiloamperes, this last expression can be reduced to:

-With 1 m kiloamperes and n of bars 2N.

it can be further shown that the radial force per finger resulting from an increase (AD) in the mean diameter from its unstressed condition as a result of elastic deformation can be obtained from the following expression:

'rr 3 Eh b 3 Y (AD) [1bs.]

Where E modulus of elasticity in pounds/inch of the contact material.

The maximum fiber stress S in terms of the radial force per finger is:

3L NE These last two expressions apply. to forces and stresses developed by elastic deformation only. When the contact carries a heavy current, additional contact forces are developed, which also stress the contact bars. The contact force per bar is given by expression in terms of the number of bars n. Since every two bars are tied together to constitute a finger, the force per finger clue to current flow is:

Lastly, the maximum stress on each bar is given by the ex- Where F r is the force per finger as represented in expression (8) taking into account the conversion of the kp (kilogram force) to pounds, according to the formula 1 kp=2.2 pounds.

FIG. 13 a-c show corresponding views of a contact assembly according to the invention, made of chromium copper. The modulus of elasticity is:

and the following information is used in the design of a contact assembly according to the illustrated embodiment of the invention.

Number of fingers: 16

Number of bars: rr=2N=32 Radial height of the bars:

h=( 1236-0736) /2=0.25 inches Mean diameter (unstressed condition) Width of saw cut separating bars: a=0.040 inches Mean width of each bar, (tangential direction):

b=(1rD/32 )0,.040=0. l 70.0,40=0.06 l 7 inches Approximate free length of the bars: =0.57 inches I pression:

The drawing shows the part in the unstressed condition. When stressed, the inside diameter is increased from 0.656 inches to 0.694 inches. The diameter increase is AD= 0.6940.656=0.038 inches Radial force per finger. Use expression (6).

Max. Fiber stress. Use expression (7).

Radial force per finger for 200 kA current. Use Expression (8) F=(5.1) (10- (mt-1% (5.1) (32-1) (1.00) 1000 (1.036+0.038) (5.1) (31) (12.5) (1000) (1.074) Reducing to lbs.:

F,=23X2.2=50.6 lbs. Max. fiber stress. due to the electrodynamic forces. Use Expression (9).

3F 1 3 50.6 1.0 wS=W: l;; i==( )%0f0 -Z T =9850 lbs/in! =34000 lb./in.

Besides the advantages of simplified manufacture and the ensuring economy in construction, the flexible one-part contact of the invention offers other advantages, as well. Thus, it has been found that both the length l and the resulting diame-' ter of the assembly can be made much smaller than those for prior tulip-clip constructions without suffering any measurable decrease in contact flexibility. Also, if a short circuit current is passed through the contact, the radial forces produced on the fingers as a result further ensure fast contact. Such contact is enhanced by selecting the thickness of the casing wall (8 in FIG. 14) to be much less than the length of the casing. For high-rated current uses, it ,will be readily apparent that even more contact pressure can be added by further using a one piece garter spring (for example) around the contact unit.

- Such contact unit, furthermore, is capable of being fabricated In particular, FIG. 14 shows the contact assembly being used in the electrical connection of bus bar units 50, 51; FIG. 15 shows the assembly 100 as it might be used for joining an electrical conductor 52 to a grounding switch for current breading switch 53, while FIG. 16 shows the use of the assembly 100 as it might be used in high current circuit breaker interrupting contact constructions.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specificdisclosure herein, but only by the appended claims.

I claim:

1. A contact assembly comprising:

a substantially cylindrical open-ended casing of electrically conductive material; i

said casing being slotted along the surface thereof in a direction corresponding to the direction of insertion of a current carrying electrical conductor to be held thereby;

said casing being effected by a plurality of slots alternatively extending from one open end of said casing and the other open end, and with said plurality of slots having nominally parallel sides joining together in a terminating region by a rounded portion cooperating therewith to withstand deformation of said casing when said conductor is of a diameter in excess of the diameter of said casing; said plurality of slots extending for substantially the full length of said casing;

whereby, said casing represents a one-piece assembly having a plurality of fingers, each of which is flexible to permit insertion of said conductor, but sufficiently elastic to insure securing contact pressure to hold said conductor fast in place.

2. The contact assembly of claim 1 wherein the thickness of the wall of said casing is much less than its length for establishing electromagnetic forces in the radial direction of said casing to supplement the radial pressures applied to said conductor caused by the oversized fitting of said conductor within said smaller diameter casing.

3. The contact assembly of claim 2 wherein the forece applied by said plurality of fingers in the radial direction to resist insertion of said conductor is represented by the expression: F=1r/N W where F equals the radial force per finger, in pounds; N equals the number of fingers operative in applying said contact pressure; and W equals the loading force tending to separate said plurality of fingers (in a tangential direction) upon insertion of said conductor, also in pounds.

4. The contact assembly of claim 2 wherein there is further included spring means wrapped around the outside of said casing to further supplement the contact pressure applied to said conductor due to said deformation withstand and electromagnetic forces.

Claims (4)

1. A contact assembly comprising: a substantially cylindrical open-ended casing of electrically conductive material; said casing being slotted along the surface thereof in a direction corresponding to the direction of insertion of a current carrying electrical conductor to be held thereby; said casing being effected by a plurality of slots alternatively extending from one open end of said casing and the other open end, and with said plurality of slots having nominally parallel sides joining together in a terminating region by a rounded portion cooperating therewith to withstand deformation of said casing when said conductor is of a diameter in excess of the diameter of said casing; said plurality of slots extending for substantially the full length of said casing; whereby, said casing represents a one-piece assembly having a plurality of fingers, each of which is flexible to permit insertion of said conductor, but sufficiently elastic to insure securing contact pressure to hold said conductor fast in place.

2. The contact assembly of claim 1 wherein the thickness of the wall of said casing is much less than its length for establishing electromagnetic forces in the radial direction of said casing to supplement the radial pressures applied to said conductor caused by the oversized fitting of said conductor within said smaller diameter casing.

3. The contact assembly of claim 2 wherein the forece applied by said plurality of fingers in the radial direction to resist insertion of said conductor is represented by the expression: F pi /N W where F equals the radial force per finger, in pounds; N equals the number of fingers operative in applying said contact pressure; and W equals the loading force tending to separate said plurality of fingers (in a tangential direction) upon insertion of said conductor, also in pounds.

4. The contact assembly of claim 2 wherein there is further included spring means wrapped around the outside of said casing to further supplement the contact pressure applied to said conductor due to said deformation withstand and electromagnetic forces.

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