US3259727A

US3259727A - Low-resistance connector

Info

Publication number: US3259727A
Application number: US317110A
Authority: US
Inventors: William A Casler
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-10-16
Filing date: 1963-10-16
Publication date: 1966-07-05
Anticipated expiration: 1983-07-05

Description

July 5, 1966 w. A. CASLER 3,259,727

LOW-RESISTANCE CONNECTOR Filed Oct. 16. 1963 3 s s 1 23 FIG- /C'IG'8 L [i /7 if 7 9 /9 H a INVENTOR. W/u/AM ,4. (451.5?

July 5, 1966 w. A, CASLER 3,259,727

LOW-RESISTANCE CONNECTOR Filed Oct. 16. 1965 2 Sheets-Sheet 2 53 I FIG. 3

INVENTOR.

WILLIAM A. CASLER BY 6! a F IG. H

ATTORNEYS United States Patent 3,259,727 LOW-RESISTANCE CONNECTOR William A. Casler, 3487 Barhite, Pasadena, Calif. Filed Oct. 16, 1963, Ser. No. 317,110 11 Claims. (Cl. 200-155) This is a continuation-in-part of my application for Low Resistance Connector, Serial No. 98,443, now abandoned, filed March 27, 1961, which was a continuation of my application for Low-Resistance Rotary Contact, Serial No. 670,470, now abandoned, filed on July 8, 1957.

This invention relates to electrical contacts, and more particularly to low-resistance contacts for maintaining or breaking low amplitude circuits.

In circuits where both current and voltage values are relatively low, even small-changes in contact resistance cause noise that obscures if it does not totally mask the low amplitude signals. As a result, the need for lowresistance contacts exists in many types of service. Principal applications, however, are to close circuits between non-rotating parts or to at least periodically connect rotating parts. Virtually every circuit breaker illustrates the former application. Many examples of the latter are also at hand. For example, to carry indications from strain gauges or other sensing equipment mounted on rotating parts to auxiliary instrumentation where such signals are interpreted, to carry error signals for the control of servo motors, and to carry signals from rotary position indicators, navigational instruments or radio signals to or from rotating antennas where high fidelity of reproduction must be continued during rotation of the equipment. For any of the services mentioned and for many others, either the effective impedance of the apparatus supplying the signals may be very low, of the order of perhaps 2 or 3 ohms, or the changes in impedance which effectively generate the signal currents may be of this order. In these and other cases, minute variations in resistance at points of electro-mechanical contact can introduce errors which greatly reduce the performance of a system. Furthermore, metal oxides, minute contaminants, vibration, wear, and other deleterious factors can, in some applications, so greatly increase resistance between contacting surfaces that operating life and reliability are significantly reduced.

The principal purpose of the present invention is to provide electrical contacts for connecting and/or controlling electrical circuits, particularly where small voltage or current signals or other factors (as discussed above) make it desirable or mandatory to provide low, constant resistance circuit paths through circuit controllers. This purpose is accomplished in the instant case by a construction which provides wiping action between the contacting surfaces as they engage and thereafter maintains a plurality of high unit pressure contact points between the contacting parts. For purposes of clarity the invention may be considered in the environment of rotating contactors and switches and conventional multi-pole (stationary) switches. The problems are to some extent different but the broad concept of utilizing high unit pressure contact points and wiping the contacting surfaces is common to both. These construction features more particularly includes a flexible transfer contactor that mechanically and electrically engages one or more contactor elements along extended lengths of groove or wedge seating surfaces formed therein thereby to provide the desired wiping action and high unit pressure contact points.

This broad purpose may be first discussed in connection with rotary contacts requiring minimum variation in contact resistance and consequent noise generation during rotation of the parts between which contact must be established. Objects are to provide a rotary contacting 3,259,727 Patented July 5, 1966 means wherein the unit pressure between the contacting parts can be made very high and the contact resistance correspondingly low and invarient; to provide such means for establishing high uni-t pressure which are nonetheless of themselves light, compact, and easy to handle; to provide contacting means where a major portion of the current transferred between the rotating and stationary parts is carried between contact elements that are themselves stationary relative to each other but wherein a wiping action, tending to clean the contacting surfaces, nonetheless takes place constantly as contact is established and broken between successive relatively minute areas of the parts in contact; to provide a contacting device which is equally applicable to high or low rotational speeds, and to conditions where the rotation is either continuous or intermittent; and to provide a device composed of light and easily fabricated parts and which is simply and easily assembled or disassembled.

In addition to these objects that relate primarily to the electrical aspects, objects relating to mechanical features are to provide a contact that is simple to fabricate, is insensitive to misalinement, vibration and dirt and is low in cost.

Considered broadly, the rotating contact embodiment of the present invention comprises a circular contact member mounted on the inner one of two relatively rotatable parts (for convenience hereinafter referred to as the rotor) this member having a generally V-shaped groove formed in its outer periphery. Surrounding the inner contact member is a contact ring mounted on the outer member (hereinafter referred to as the stator), this ring being substantially concentric with the inner member and also having a generally V-shaped groove formed in its inner periphery. It is to be understood that the distinction between rotor and stator is purely arbitrary; the rotor may actually be the stationary member about which the stator rotates.

I Held between the circular contact and the ring is a transfer contact or armature which, when not so held and there distorted, is a spring of toroidal form whose diameter is greater than the radial separation between the grooves in the rotor and stator contacts. For most applications this spring or transfer contact is preferably in the form of an electrically continuous, helically wound spring, although for some purposes it may be one or more circular loops of spring material. Owing to its diameter, when it is sprung into place to engage the grooves in both rotor and stator contacts, it is distorted into a generally kidneyshaped form that contacts a material are within the groove of both the rotor and stator contacts. The inherent resilience of this spring contact wedges it into the V-shaped grooves so that the unit pressure between the sides of the grooves and the lines of contact formed between the sides of the grooves and the spring can be greatly in excess of the diametric force exerted by the spring in its tendency to assume its natural form as a circular toroid. The excess in diameter of the undistorted spring over the separation between the rotor and stator contacts also insures that a material are of both the rotor and stator contacts is in contact with the spring. When rotation occurs the spring rolls around the periphery of both contacts at a rate dependent upon the relative diameters of the rotor and stator contacts and no slippage occurs between the two arcs of contact. At each end of these arcs, however, where the spring is entering and leaving the respective grooves as it rolls, a minute wiping action occurs. This wiping action under high unit pressure tends to keep the lines of contact clean, removing dust particles and penetrating oxidation so that by the time any portion of the spring has entered the arc of contact with either of the two grooves the parts are in firm and low-resistance engagement, with many paths in parallel between the contacting parts.

Nearly all metals exposed to the atmosphere acquire at least a minute film of oxide. All materials are subject to contamination by oil, dust and other foreign substances. The high unit pressure as the coils turn to enter the grooves causes them to cut through and wipe off any of these contaminants, and as the coils wedge into the grooves the metal-to-metal contact is maintained during the period throughout which the coils are stationary relative to the grooves. There are thus many parallel, lowresistance paths between the relatively rotating parts. It is only the entering and leaving turns that are changing in resistance in opposite senses and are but a small proportion of the total conductance.

Moreover, because of the flexibility of the contacting loop, mutual vibrational movement between the rotating parts is absorbed and does not disturb the 'wedged-in contacts, so that the circuits in which the contacts are employed is free of microphonic interference from such vibration. Similarly, the flexibility of the spring loop makes the device substantially shockproof.

Turning next to a consideration of the less demanding stationary switch embodiment, it comprises a pair of parallel disposed contacts and a resilient transfer contact or armature biased to jam partially between facing surfaces of the contacts and along a substantial length thereof. This provides a low resistance path between the contacts (by virtue of the high unit pressures developed at the multiple points of contact) which follows the scraping action as the armature snaps into contacting position.

In the illustrative embodiment disclosed, the parallel contacts are a pair of flat strips disposed in planes that intersect at an acute angle outwardly from the location of the transfer contact; the V-shaped groove so formed is quite similar to those formed in the rotor and stator of the other embodiment. Cooperating with these circuit terminals is the transfer contact in the form of a section of a helically wound spring that is compressed end to end and operated by a toggle that snaps it off center to a position bridging the contacts or to an open part of the switch body. The inherent resilience of the spring contact wedges it in the V-shaped groove. The unit pressure, here too, is high which assures a low resistance path for signals transmitted thereover. The length of contact between the transfer contact and strips may be controlled by the relative location of the parts and by using arcuate shaped contact strips. In all cases, as the helical spring wedges between the fixed contacts, it scrapes the surfaces thereby removing oxidized particles, dust or other foreign materials that cause variable and/or high contact resistances.

The preferred forms of the invention, together with several modifications applicable to various somewhat different services will next be described. In the drawings, illustrative of these descriptions:

FIG. 1 is an axial sectional view illustrating the rotating contact embodiment of the invention as applied to a double contact for carrying both sides of an instrumentation circuit such as that including a strain gauge;

FIG. 2 is a plan view of the apparatus shown in FIG. 1, partly in section, illustrating more clearly the kidneyshaped contour taken by the spring transfer-contact when in place;

FIG. 3 is a partial plan view taken along line XX of FIG. 1 to illustrate one embodiment in which the rotor and stator might be segmented to complete circuit paths other than as illustrated in FIG. 2;

FIG. 4 is a partial plan view taken along line XX of FIG. 1 to illustrate another embodimentin which the rotor and stator might be segmented to complete circuit paths other than as illustrated in FIGS. 2 and 3;

FIG. 5 is a fragmentary drawing illustrating a helicalspring type of transfer contact and indicating one method of forming continuous helical springs for the rotating contact embodiment;

FIG. 6 is an isometric View showing the manner of bending the ends of the wire forming a helical spring preparatory to joining them to form a toroid;

FIG. 7 is a view similar to FIG. 6 showing the wires connected;

FIG. 8 is a radial cross-section view through one of V-grooved contacting members of the rotating contact embodiment showing a number of generally rectangularshaped leaf springs in contact therewith;

FIG. 9 is a similar view showing a helical toroidal spring in engagement with a slightly different, contoured form of a V-groove utilized in the rolling contact embodiment;

FIG. 10 is a side sectional view illustrating the stationary switch embodiment of the invention as applied to a two-pole switch for opening or closing an electrical path; and

FIG. 11 is an end cross section taken along line 1111 of FIG. 10.

FIG. 1 of the drawing shows a small portion of the frame .1 of the stator of a device wherein it is desired that both sides of a circuit be carried to the rotor. The portion shown of the frame 1 carries a bearing 3 in which the rotor-shaft 5 turns. An insulating sleeve 7 is forced, keyed or otherwise secured on the shaft and a pair of circular contacts 9 are securely fixed to this sleeve. Conveniently the sleeve 7 may be of an insulating plastic, preferably one of the thermo-setting plastics such as Bakelite or other phenolic, and the contacts 9 may be molded into the sleeve, forming a single integral unit. In the outer periphery of each of the contacts there is for-med a V-shaped groove 11.

An insulating cylinder 13 is secured to the frame 1, for example, by screws 15, so that its inner periphery is concentric with the shaft 5 and circular contacts 9. Like the sleeve 7, the cylinder 13 may also be formed of one of the plastics. The sleeve carries a pair of contact rings 17, each of which has a V-shaped groove 19, similar in shape to the grooves 1 1, formed in its inner periphery, Each of the grooves 19 is substantially coplanar with a corresponding groove 11.

The

elements

9 and 17 are preferably formed of one of the good conductors, such as brass, copper or silver, which are fairly resistant to corrosion, so that contact resistance to it is low. For the type of service wherein the present invention is likely to be used gold would Work; coin silver is one of the best materials because of its resistance to both corrosion and wear, but the other materials mentioned are very nearly as satisfactory. For light duty silver-plated bronze. or copper is satisfactory but for high-speed rotating machinery solid metal is preferred because even though the wear is slight, with continuous rotation a thin plating will soon wear through since plated coatings are ordinarily soft. On the other hand, high speed operation and the wear resulting from it tend to keep contacting surfaces clean. For such purposes beryllium-copper is preferred, but the other materials mentioned are quite satisfactory.

Leads 21 and 21' are schematically shown as connected to the circular contacts 9 and leads23 and 23' are similarly shown as connected to the contact rings 17. These leads represent the two sides of the circuit through which contact is to be established. Contact between leads 21 and 23 and 21 and 23' respectively is made through intermediate spring contacts 25. FIGS. 3 and 4 show alternative Ways in which circuits might be completed.

For example, it might be desirable to complete a path.

between two segments of the stator (01' rotor). In this case, an insulating separator 51 may form segments 52-54 on the stator 17. Any two of these will be bridged by contact 25 as it revolves (FIG. 3). Another circuit arrangement is provided by segmenting the stator into small conducting sections 5557 as illustrated in FIG. 4.

In the latter, the transfer contact 25 will commutate a signal at the rotor 9 sequentially to

segments

55, 56 and 57 of the stator 17. Numerous variants may be perceived inasmuch as the location of the contacts isnot critical, only the use of the wedging action along extended portions of the contacts through which the low resistance circuit must be established. This being the case, whenever the claims refer to contacts between the rotor and stator, it is intended that they include circuits established between segments on the rotor or stator as well as commutating arrangements. Additionally, the sides of the stator forming the V-shaped groove may be insulated to form circuit terminals through which a path is closed by the transfer contact or armature.

A preferred form of the intermediate or transfer contacts is best illustrated in FIGS. 2-5. FIGS. 2-4 show the form assumedby them when in place as shown in FIG. 1 while FIG. 5 shows such a contact in undistorted form, prior to being snapped into place. Each of the contacts 25 is in the form of a continuous loop or toroid of spring material. The preferred form, shown in FIG. 5, is a helically wound spring of highly resilient wire, such as beryllium-copper, with its ends brought together so that electrically and mechanically the spring forms a continuously toroidal helix. It is important that the joint, shown in FIG. 5 at 26, should not materially aifect the flexibility of the spring or weaken it, at the point where it is formed. It has been found that this can be accomplished by bending the end of the wire, of which the helix is formed, at right angles so that it projects radially inward toward the center of the toroid at both ends of the spring. The two inwardly projecting ends are abutted and connection between them is made in any suitable fashion, as by twisting, welding or soldering, or preferably by both twisting and welding or soldering. The projecting ends might also be fastened inside the helical windings in cases where such construction might be superior to the projecting joint illustrated.

The diameter of the toroid 25 must exceed the separation between the grooves 11 and 19, and preferably it is much greater than their separation; it may be equal to or greater than the diameter of the grooves in the contact ring 17, the upper limit being that when the toroid is distorted and snapped into place as shown in FIG. 2, the two ends of the loop formed by it do not come into contact, although they may nearly surround the inner contact 9. In general it is desirable that a large number of turns of the toroid come into contact with each of the grooves, so that a fairly large diameter is indicated but too large a diameter will sometimes cause the loop to pull away from the central portion of its contact with the inner groove 11. The preferred diameter is such that when in place the spring is distorted from its originally toroidal form into the somewhat kidney-shaped form shown in FIG. 2. Here and in the claims that follow, however, kidney-shaped is intended to be construed broadly to include cases where the spring nearly surrounds the inner contact.

The winding of the helical spring must be sufficiently open so that where it is bent most sharply, which may either be around the inner contacts 9 or at the ends of the loops where it is inflected between the inner and outer contacts, the adjacent turns do not quite come into actual abutment, since such abutment sets a limit to the flexibility of a spring of the character described.

When the spring is distorted as shown in FIG. 2, its natural tendency is, of course, to straighten out, thus exerting a radial pressure tending to force it into the V-shaped grooves between which it is held. As the rotor turns it carries the spring with it, and as a result the spring rolls around the inner periphery of the stator contact so that additional turns of the spring are continually entering the groove 19 and continually advancing point 27 at the advancing end of the loop and leaving the groove 19 at the corresponding point 29 at the trailing end. Similarly new turns are entering the grooves 11 at the point 31 and leaving at the point 33. It is at these points that the spring is most strongly flexed and the pressure is greatest. The actual contact pressure is materially greater than the radial force exerted by the spring in its attempt to straighten at its point of entry and leaving the grooves because of the mechanical advantage given by the wedging action. The more acute the angle of the V the greater the mechanical advantage and the higher the contact pressure, so that even though the radial pressure may be relatively light the contacting pressure is several times as great.

As the turns of the spring enter and leave the grooves their planes are changing. Between the points of entering and leaving the grooves, where the turns are in stationary contact with the

elements

9 and 17 respectively, the planes of these individual turns are very nearly radial with respect to the device as a whole. At the two ends of the loop the planes of the individual turns are substantially at right angles to the radius. As the turns enter and leave the grooves the planes of the turns are changing and as a result there is added to the wedging action a turning or rubbing action which cleans the contacting surface and gives the advantages of a wiping contact. This action constantly takes place as the spring rolls around both inner and outer elements; it speeds the drop in resistance with the individual turns as contact takes place with each successive turn. As the turns of the spring wedge into the grooves at the advancing of the loop their circular form is itself slightly distorted so that they :make a short line-contact with each side of the groove instead of the theoretical point contact, and this also serves to decrease the contact resistance.

If the angle at the apex of the groove is acute and the sides correspondingly steep, so that the mechanical advantage is great and the contact pressure high, the wellknown irreversible property of a wedge comes into play and the turns remain firmly seated throughout the arcs around the inner and outer grooves where they are relatively at rest, the contact pressure being exerted by the turns themselves in their efforts to resume their truly circular form. There is therefore no measurable change in the contact resistance throughout the portion of their paths where they are relatively stationary with respect to the inner and outer grooves.

There are, of course, numerous modifications that are possible in the construction of the various parts of the device. For example, the sides of the grooves in either or both of the

contacts

9 and 17 can be contoured, somewhat as shown through the section 17 of a contact ring illustrated in FIG. 9. Such contouring increases slightly the area of contact at the expense of contact pressure. The apex of the groove need not be carried to a sharp point. It may be rounded as shown in this same figure, as long as the groove is carried deep enough and the radius at the apex is enough smaller than that of the helical turns so that contact takes place at the sides and not at the bottom of the groove.

It is also possible to use a toroidal spring formed of a single endless wire loop or a number of leaf springs. The springs need not be of circular cross-section; they may be elliptical or substantially rectangular in cross-section as indicated at 25' of FIG. 8, wherein the groove 19" is also shown with a rounded apex. If the loop is a solid wire or a group of leaf springs of non-circular cross-section it should be sufliciently thick, measured radially of the toroid, to be resistant enough to torsion so that, in the case of a loop of rectangular cross-section it will not tend to twist and make a flat contact against the sides of the groove, thus defeating the wedging action upon which much of effectiveness of the device depends. Coiled-spring toroids with non-circular turns can be formed and used but they are diflicult to make and unless they are carefully designed do not have sufficient torsional rigidity to be as satisfactory as helically-wound springs with circular turns.

If solid wire loops are used, of either circular or noncircular cross-section, the action that takes place at the point of make or break differs onlyin degrees from that V which occurs to a helically wound loop. In the case of a solid, single-turn spring, each differential length around its periphery acts like a turn of a helical spring and forms a rubbing or sliding contact as it enters or leaves the groove. The individual turns or elements of such a solid spring are not as readily deformable as are those of a helix and the contact area, measured circumferentially around each individual turn is correspondingly less. On the other hand the elementary turns are closer together, so that the over-all area may be just as great. It is a matter of individual choice, depending upon the service to which the individual device is adapted, which form of loop will be used. One factor in making the choice may be the frequency of currents carried by the contacts; for very high frequencies the additional inductance of a coil may make a solid-section toroid preferable.

The relative radii of the inner and outer contacts, 11 and 19 respectively, are unimportant, the criteria for satisfactory operation of the invention being that the loopdiameter of the'transfer contact be greater than the separation of the grooves and that this separation be constant throughout the extent of the grooves. It follows that the invention may be used to connect reciprocating parts, for example, which move in parallel paths, since such paths form the limiting case of circles of infinite radius. In this case either contact can be considered the centra one.

It is recognized that rolling spring-contacts are not new per se. For example, Patent No. 2,467,758, issued to N. E. Lindenblad, discloses fiat circular spring contacts that roll around an inner cylindrical'surface to make bridging contacts between adjacent conducting sectors. Devices of this character are intended to carry high currents and high voltages and large contact areas are necessary for the purpose. While satisfactory for use in highcurrent circuits they are not adapted for use in low-current low-voltage circuits such as those to which the present invention is primarily directed. For one thing, fiat springs rolling on cylindrical surfaces exert no wiping action. Instead of dust particles, oxide, or the like being scraped off as the advancing edge of the loop engages, the flat contact springs merely roll up and over such particles. High voltages and high currents will burn away the intercontact material so that it is usually of no moment; lowvoltage circuits, carrying small current do not have this effect. Another reason why such rolling contacts. are not good low current transfer devices is that they are incapable of developing the high unit pressures required.

Additionally, experiment has proved that a rolling contact between flat surfaces, while it gives large contact area, is noisier than is a conventional brush-and-slip-ring engagement. The present invention is obviously not intended to carry heavy power but in the service for which it is designed it may reduce interferent noise generated by the contacts by as much as 20 db, in comparison with conventional brushes and slip-rings.

The stationary switch embodiment can take many forms, one of which is illustrated in FIGS. 10 and 11. The switch includes a pair of

contacts

61 and 62 supported along one side of an insulated body member 63. The transfer contact 64 is a section of a helical spring supported at one end 66 at the end of the body member 63 and attached at its other end to a toggle or actuation lever or device 67. The lever 67 is pivotally supported by pin 66 to the body member 63 and the transfer contact 64 is axially compressed when disposed along a line between its two points of restraint. As a result, as the toggle 67 is moved away from the side of body member 63 to which contact strips 61 and 62 are afiixed, the helical spring 64 snaps into the V-shaped groove formed by the strips 61 and 62 (see FIG. 10). In closing a path between

contacts

61 and 62, the helices scrape the sides of the contact strips thereby assuring clean, low resistance contacts. The degree of compressing normally carried by the transfer contact 64 along with the angle of the V-groove and its depth permits the area of contact to be controlled. As noted above, the

strips

61 and 62 can be arcs of circles to increase the area of contact, hence the number of high unit pressure points. When the path through the contacts is to be interrupted, the toggle 67 is moved the opposite way to cause the spring 64 to snap to the blank or open side of the body member 63. As is the case with the rotary contact embodiment, rather than completing a circuit between

parallel strips

61 and 62, the circuit path may be completed between the transfer contact 63 and one or both of the

strips

61, 62.

It should be apparent that a number of different actuating means can accomplish the same salutory result. For example, a slide lever or push button can push the compressed helix over the center point. All have in common that they cause the transfer contact to wedge between the contact strips. Another variation may be the shaping of the

contact elements

61 and 62. While illustrated as fiat strips, they can be wires or the like. Similarly, the transfer contact 64 can be varied as suggested in connection with the rotary transfer contact described above.

Yet other variations should be apparent. The exemplary embodiment of FIGS. 10 and 11 is for a single throw, single pole switch, whereas the principle is equally applicable to more versatile switches. For example, parallel contact strips might be aflixed in each quadrant of a switch body so that a circuit can be closed between any one of four pairs of connectors. Yet another example is a switch wherein one toggle will close a number of parallel circuits. The variants mentioned here are not inclusive but designed to illustrate the wide application of the inventive concept forming the nexus of the present invention.

Besides those shown and mentioned, other modifications embodying the principle of wedging contact and wiping engagement upon which the present invention depends are possible. Those illustrated are therefore not intended as limiting the scope of the invention, all intended limitations being specifically set forth in the accompanying claims.

What is claimed is:

1. Means for establishing a low resistance electrical connection between mutually rotatable parts comprising an outer contact ring having a generally V-shaped groove formed in the inner periphery thereof, a circular contact member mounted substantially coaxially within said contact ring for rotation relative thereto and having a generally V-shaped groove formed in its outer periphery substantially coplanar with and facing the groove in said contact ring, and an endless loop intermediate transfer contact including a spring of generally toroidal form distorted into a generally kidney shaped form and wedged between the V-shaped grooves facing each other, the cross section of the spring being less than the radial separation between said ring and said circular member and the diameter of the undistorted loop being greater than the radial separation between said ring and said circular member so that when so distorted there is an appreciable arc of contact between said spring and each of said ring and said circular contact member.

2. Apparatus as defined in claim 1 wherein said transfer contact comprises an endless multi-turn helically wound spring.

3. Apparatus as defined in claim 1 wherein said transfer contact comprises a single endless loop of spring wire.

4. Means for forming electrical contact between mutually movable parts comprising a pair of contact members mounted in substantially coplanar relationship on said parts respectively, each of said contact members having a V-shaped groove formed therein so that said grooves face each other and are spaced by a substantially constant distance throughout their extent, and a transfer contact comprising a continuous spring forming a loop the diameter of which when undistorted is greater than the spacing between said grooves and a cross section of which is less than the spacing between said grooves, said spring being distorted into a generally kidney-shaped form and wedged into each of the facing grooves.

5. The invention as defined in claim 4 wherein said spring is a helically-wound toroid.

6. Means for completing a low resistance path between terminals comprising, in combination, at least one contact member having sections forming a generally V-shaped groove having an acute angle, a transfer armature adapted to cooperate with said contact member, terminals associated with selected ones of said sections and said armature, and means for moving the armature from a first position out of contact with at least a portion of said contact member to a second position in contact with said portion of said contact member operable to close a path between at least a pair of said terminals by wedging the armature between the sections forming the contact member, said armature in engaging the contact member wiping the contacting surfaces and establishing a plurality of high pressure points of contact along extended parts of said armature and said contact members, said transfer armature being a multi-turn, helical wound spring, the planes of the turns of said spring changing with respect to the contacting surface upon engagement and disengagement and the compressive biasing of said helical spring in part urging the armature to wedge between the sections defining said V-shaped groove.

7. Means for completing a low resistance path between contact members comprising, in combination, at least one pair of fixed contact members forming a generally V-shaped groove therebetween and forming an acute angle, a resilient movable contact flexibly supported adjacent the opening of said V-shaped groove, means biasing said movable contact to urge it to equilibrium positions outwardly from an imaginary axis through its point of support, the movable contact in one of said equilibrium positionsbeing wedged between the sides of said V-shaped groove to complete a path between at least a pair of said contact members and in another one of the equilibrium positions being out of contact with said fixed contact members, said movable contact in wedging between said fixed contact members wiping the contacting surfaces and 1t) establishing a plurality of areas of high pressure contact along extended portions of the contact members, and means operable to selectively direct said movable contact to open and closed path equilibrium positions.

8. A switch for completing a low resistance path between a pair of terminals comprising, in combination, a switch body, at least one pair of contact strips supported in said body in spaced apart relation to form a generally V-shaped groove therebetween and forming an acute angle, a resilient transfer armature attached to the body adjacent each set of ends of the fixed contact strips for movement between a closed position in wedged contacting relation with and interior of said groove and an open position out of contact therewith, said armature in wedging between the strips wiping the contacting surfaces and creating a plurality of high pressure contacting points along extended parts of said armature and said contact strips, terminals associated with said strips and said armature to permit at least one path to be closed when the armature is in said closed position, means biasing said armature towards one of said open and closed positions, and means to selectively control the movement of said armature to the open and closed positions.

9. A switch for completing a low resistance path between a pair of terminals in accordance with claim 8 wherein said transfer armature is a multi-turned, helically wound spring biased to assure one of said open and closed positions.

10. A switch for completing a low resistance path between a pair of terminals in accordance with claim 8 wherein the attachment points for said armature lie in a line substantially parallel to the ends of said fixed contact strips, said transfer armature is a multi-turned helically wound spring, and the armature is biased toward the open or closed position by compressing the helix between the points of attachment.

11. A switch for completing a low resistance path between a pair of terminals in accordance with claim 10 and including a lever pivotally supported on the switch body to initiate and control movement of the transfer armature between the open and closed positions.

No references cited.

KATHLEEN H. CLAFFY, Primary Examiner.

J. R. SCOTT, Assistant Examiner.

Claims

1. MEANS FOR ESTABLISHING A LOW RESISTANCE ELECTRICAL CONNECTION BETWEEN MUTUALLY ROTATBLE PARTS COMPRISING AN OUTER CONTACT RING HAVING A GENERALLY V-SHAPED GROOVE FORMED IN THE INNER PERIPHERY THEREOF, A CIRCULAR CONTACT MEMBER MOUNTED SUBSTANTIALLY COAXIALLY WITHIN SAID CONTACT RING FOR ROTATION RELATIVE THERETO AND HAVING A GENERALLY V-SHAPED GROOVE FORMED IN ITS OUTER PERIPHERY SUBSTANTIALLY COPLANAR WITH A FACING THE GROOVE IN SAID CONTACT RING, AND AN ENDLESS LOOP INTERMEDIATE TRANSFER CONTACT INCLUDING A SPRING OF GENERALLY TOROIDAL FORM DISTORTED INTO A GENERALLY KIDNEY SHAPED FORM AND WEDGED BETWEEN THE V-SHAPED GROOVES FACING EACH OTHER, THE CROSS SECTION OF THE SPRING BEING LESS THAN THE RADIAL SEPARATION BETWEEN SAID RING AND SAID CIRCULAR MEMBER AND THE DIAMETER OF THE UNDISTORTED LOOP BEING GREATER THAN THE RADIAL SEPARATION BETWEEN SAID RING AND SAID CIRCULAR MEMBER SO THAT WHEN SO DISTORTED THERE IS AN APPRECIABLE ARC OF CONTACT BETWEEN SAID SPRING AND EACH OF SAID RING AND SAID CIRCULAR CONTACT MEMBER.