US3218426A - Magnetic electrical contacts having a nonmagnetic sector therein - Google Patents

Description

,1965 P. c MONTOYA ETAL 3,2 8, 26

MAGNETIC ELECTRICAL CONTACTS HAVING A NONMAGNETIC SECTOR THEREIN Filed June 26, 1964 22 22 2 minim-5 (a) (b) Rau/ C Momoya A Char/es E. Jackson E 3 Ber) 1 Neumon ZFKM KM United States Patent 3,218,426 MAGNETIC ELECTRICAL CONTACTS HAVING A N ONMAGNETIC SECTOR THEREIN Paul C. Montoya, 3613 Stardust Drive NE.; Charles E. Jackson, 3554 San Pedro NE.; and Bert P. Neumon, 1605 California NE, all of Albuquerque, N. Mex. Filed June 26, 1964, Ser. No. 378,131 7 Claims. (Cl. 200166) Our invention relates generally to the switching of electrical currents, and more particularly to electrical contacts used in such switching.

In switching electrical currents, the contacts usually are driven together by an outside force, such as an electromagnetic force derived from a signal, from a pressure, or by manual means. In any case, it is usually important and frequently quite important that once the contacts come together they stay together with a minimum of resistance between them. However, it has been found through experience that almost always some intercontact resistance results. Static contact resistance is determined by the materials and the geometry of the contacts, while dynamic contact resistance may be the result of several factors. One factor is believed to be a vapor pressure caused by the vaporization of a microscopic amount of contact material at initial contact. This vapor pressure physically forces the contacts apart, causing the intercontact resistance to be a function of the resistance of the metal vapor between the contacts.

Another factor in dynamic contact resistance is magnetic repulsion of the contacts resulting from magnetic fields created by the conduction of current through the contacts from several different directions within the contacts.

Another form of contact resistance is caused by the contacts bouncing rather than remaining closed upon initial contact. Still another form of contact resistance may be caused by contamination of the contact surfaces.

It is a general object of our invention to minimize all forms of contact resistance by creating a contact closing force from a magnetic field produced by the current flowing through the contacts.

Briefly, our invention accomplishes this and other objects to become apparent by means of a pair of contacts each of which is divided into a central, current-carrying portion and a non-current-carrying portion surrounding the first portion. The non-current-carrying portion is constructed of both magnetic and nonmagnetic materials, each type of material taking up a certain section of the contact and arranged so that the nonmagnetic section will interrupt circular lines of magnetic flux created by electrical current carried by the contacts. Proper orientation of the two contacts with respect to each other forces the flux to cross between the contacts two or more times, thus attracting the contacts to each other and minimizing intercontact resistance, regardless of whether the current is alternating or direct. Our invention should not be confused with prior devices using permanent magnets which accelerate the contacts as they approach each other, actually increasing contact bounce beyond that present in contacts without magnetic aid. Since our invention does not produce magnetic attraction until the contacts initially close, there is no such acceleration.

A better understanding of our invention may be had by reading the more detailed description to follow in conjunction with the appended claims and the attached drawing, in which:

FIG. 1 is an enlarged perspective view of a pair of contacts constructed in accordance with our invention, showing the travel of magnetic flux between the contacts;

FIG. 2 shows a side view of the contacts of FIG. 1 in a closed position;

3,218,426 Patented Nov. 16, 1965 "ice FIG. 3 shows spherical surfaces of a pair of contacts, each with two nonmagnetic portions shaped to provide constant-reluctance-ratio flux paths between contacts;

FIG. 4 is a side view of a pair of closed contacts having generally conical surfaces; and

FIG. 5 is a sectional view of the contacts of FIG. 4, taken along the lines 55 and showing the preferred shape of the nonmagnetic section for providing a constantreluctance-ratio path between contacts.

Referring now to the drawing, FIGS. 1 and 2 show a preferred embodiment of our invention, electrical current being conducted into contact 10 by means of conductor 11, and out of contact 12 by means of conductor 13. It is assumed that the contacts are driven together by some external means not shown, at the time intercontact conduction is desired. The contacts are shown slightly apart so that the contacting surface of contact 12 might be shown, but in the description to follow it is assumed that the contacts have touched during the closure action to the extent that current has begun to flow.

By the right-hand rule, current flowing through conductor 11 in the direction shown will create circular lines of magnetic flux 14 around conductor 11. Similar lines of flux will be present in contact 10, as indicated by the line A-B in magnetic section 15 of contact 10. The flux lines will be interrupted by a narrow, radial nonmagnetic section 16, and, assuming this section has a greater reluctance than the alternate flux path from contact 10 to contact 12, the flux will proceed from B to C, jumping the intercontact space. The flux then continues its circular path, this time within contact 12, from C to D. Here it encounters another narrow radial nonmagnetic section 20, causing the flux to jump from contact 12 back to contact 10 where it resumes its circular path. It is realized that this description is somewhat idealized, since in practice the intercontact magnetic flux will be distributed throughout the facing magnetic sections rather than being concentrated at the edge of each section as shown.

This transfer of magnetic flux back and forth between contacts continues as long as there is current flowing between the contacts, and results in an attractive magnetic force which draws the contacts together, minimizing intercontact resistance. To facilitate the conduction of current, there may be provided a central current-carrying portion 21 on contact 12 and a similar portion (not shown) on contact 10. These portions may be made from silver or other good conductive material, or in some cases may be of the same material as the magnetic sections of the contacts. The term current-carrying portion as used herein means that portion of a contact which conducts current from that contact to another when the contacts are closed.

Good magnetic design practices should be followed in designing the magnetic and the nonmagnetic sections of the contacts. Among other things this means that the intercontact magnetic paths B-C and D-A should have a reluctance approximately one-tenth that of the magnetic path across nonmagnetic sections 16 and 20 at any radial location beyond the current-carrying portion 21. This assures maximum attraction between contacts. Also, the nonmagnetic sections preferably should be shaped to provide intercontact paths the reluctance of which has a constant ratio to the reluctance of the nonmagnetic sections, regardless of radial location. As shown in FIG. 3, when the contact surfaces are spherical the boundary lines 22 between the magnetic and nonmagnetic sections should be approximately arcs of circles.

'For a balanced attraction between contacts, and to avoid interference between flux paths, the contacts should be oriented with their respective nonmagnetic sections nonaligned. The preferred orientation of maximum nonalignment is shown in FIG. 1 where each contact has only one radial nonmagnetic section, and in FIG. 3 where each contact has two radial nonmagnetic sections.

FIGS. 4 and 5 show an alternate contact shape, being generally conical except that central current-carrying portions 23 are flat or rounded to provide good contacting surfaces. It is seen that, with conical surfaces, the boundaries 24 between the magnetic and nonmagnetic sections will be straight rather than curved.

The magnetic force of attraction between contacts can be calculated by known formulas. The calculation shows that, for contacts each having only one radial nonmagnetic section properly designed, a contact having a diameter of one-quarter inch and conducting thirty amperes will have an attractive force fifty to one hundred times the weight of each contact. Comparative tests of conventional nonmagnetic conducting contacts and contacts designed in accordance-with our invention show some contact damage after three closures, and considerable contact damage after fifteen closures, of the conventional contacts, the damage apparently being due to intercontact resistance and arcing. Fifteen closures of contacts designed in accordance with our invention showed little or no damage when used to conduct heavy currents in the same non-inductive circuitry. Other tests made using inductive circuitry in the conducting line showed conventional contacts substantially ruined after eighteen closures, while our contacts operated for sixty closures without any noticeable damage.

A preferred embodiment of our invention has been shown, and evidence submitted to prove its unquestioned superiority over conventional contacts. It is assumed that those skilled in the art will make improvements and variations on the embodiments shown without departing from the sphere and scope of the invention as defined by the claims below. i

We claim as our invention: 1. A pair of electrical contacts, each comprising: a first, generally central, current-carrying, portion; a second, non-current-carrying, portion surrounding said first portion; said second portion being magnetic except for at least one narrow radial nonmagnetic section; and said contacts being oriented with their respective nonmagnetic sections nonaligned, whereby said contacts are attracted to each other by a magnetic force when current flows between them. 4 2. The apparatus of claim 1, wherein at any radial location beyond the current-carrying portions the reluctance of each nonmagnetic section is large compared with intercontact reluctance when the contacts are closed. 3. The apparatus of claim 2, wherein the current-carrying portion of at least one contact extends beyond the remainder thereof toward the current-carrying portion of the other.

4. The apparatus of claim 3, wherein at least one contact is convex.

5. The apparatus of claim 4, wherein the contacts 'are oriented for maximum nonalignment of their nonmagnetic sections.

6. The apparatus of claim 5, each contact having only one radial nonmagnetic section.

7. The apparatus of claim 5, each contact having more than one radial nonmagnetic section, said sections being equally spaced.

No references cited.

KATHLEEN H. CLAFFY, Primary Examiner.

Claims (1)

1. A PAIR OF ELECTRICAL CONTACTS, EACH COMPRISING: A FIRST, GENERALLY CENTRAL, CURRENT-CARRYING, PORTION; A SECOND, NON-CURRENT-CARRYING, PORTION SURROUNDING SAID FIRST PORTION; SAID SECOND PORTION BEING MAGNETIC EXCEPT FOR AT LEAST ONE NARROW RADIAL NONMAGNETIC SECTION; AND SAID CONTACTS BEING ORIENTED WITH THEIR RESPECTIVE NONMAGNETIC SECTIONS NONALIGNED, WHEREBY SAID CONTACTS ARE ATTRACTED TO EACH OTHER BY A MAGNETIC FORCE WHEN CURRENT FLOWS BETWEEN THEM.

Images