US2879355A

US2879355A - Snap action device

Info

Publication number: US2879355A
Application number: US664034A
Authority: US
Inventors: James W Welsh
Original assignee: HODA CORP
Current assignee: HODA Corp
Priority date: 1957-06-06
Filing date: 1957-06-06
Publication date: 1959-03-24
Anticipated expiration: 1976-03-24
Also published as: FR1207044A; GB863041A; DE1155185B

Description

March 24, 1959 J. w. WELSH 2,879,355

SNAP ACTION DEVICE Filed June s, 195'? 2 Sheets-Sheet 1 FIG.1

I J l FIG. 2

INVENTOR.

ATTORNEY March 24, 1959 J. w. WELSH SNAP ACTION DEVICE 2 Sheets-Sheet 2 Filed June 6, 1957 FIGS 9 LZV%TOR.

ATTORNEY SNAP ACTION DEVICE James W. Welsh, Summit, N.J., assignor, by mesne assignments, to Hoda Corporation, Great Neck, N.Y., a corporation of New York Application June 6, 1957, Serial No. 664,034

9 Claims- (Cl. 200113) This invention relates to electric switches or circuit controllers using a snap action vane actuated by a thermostatic or thermodynamic opera-tor to control the operation of circuit controlling contacts. More particularly, the invention is directed to switches of this type in which the thermostatic operator is an integral or unitary part of the snap action vane.

In my US. Patent No. 2,756,304 of July 24, 1956, I have illustrated and described a novel type of snap action vane, and a switch or flasher incorporating the same, in which a vane of relatively stifi spring metal 'is given an initial set by providing a pair of aligned and longitudinally spaced deformations extending from diagonally opposite corners of the vane toward the center thereof, the central area of the vane being left undeformed. This gives the vane an initial bend about a first diagonal extending along the deformation.

The vane is pre-stressed to bend about the other diagonal by attaching a thermostatic wire or ribbon to the corners at the ends of the first diagonal, the wire or rib bon being attached in the cold, contracted condition with the vane bent about the second diagonal. When the wire or ribbon is heated and expands, the vane snaps to its initial bent condition about the first diagonal. When the Wire or ribbon cools and contracts, the vane snaps back to its condition of being bent about the second diagonal.

If such a vane is supported in a certain zone adjacent its center, there is a considerable amplitude of movement of the vane about such mounting point during the snapping action, particularly at the corners of the vane. This characteristic has been advantageously utilized in providing vane-operated switches controlling circuits preferably including electric heating circuits for the thermostatic operator, and flashers or other snap action switches incorporating such a vane have gone into extensive commercial use.

In accordance with the present invention, it has been found that the manufacture of such snap action vane switches can be greatly simplified and reduced in cost by making the thermostatic operator integral with the vane in a single vane forming operation. This eliminates the time and labor hitherto necessary in pre-stressing the vane and holding it pro-stressed while the pull ribbon or wire is attachedto the Vane by spot welding or brazing. Even more importantly, the contact making and breaking operation of the vane is greatly improved, as the contact pressure is maintained fully or even increased during a contact opening cycle right up to the instant when the contacts snap open. This characteristic greatly increases the contact life by minimizing arcing or burning of the contacts.

In making the vane, a piece of preferably electrically conductive spring metal is used, the metal being selected for high elasticity and resistance to creep under static or dynamic stresses. Other factors important in the selection of the metal are its specific temperature resistance, coefficient of electrical resistance, and coefiicient of expansion, all of which factors must be considered with paratent ticular reference to external or ambient operating conditions.

The metal piece is formed with a closed-end slot extending along and parallel to an edge so as to provide a narrow strip of metal along such edge integral at each end with the much larger main body section of the vane. At least the main body section of the vane is then deformed into a shallow V-shape with the apex of the V extending perpendicularly to the narrow strip and preferably bisecting the latter. Such deformation may be effected by providing or forming a narrow rectangular flat section along such apex, with the wings of the V extending at a small angle to such section.

If the main body of the vane is now fixedly supported at a point along or immediately adjacent the apex of the V, and the vane is heated, as by passage of an electric current therethrough, the narrow strip along the vane edge, due to its much smaller cross-section, will expand longitudinally at a rate much greater than the rate of expansion of the main body of the vane. Such expansion of the thermostatic operator or strip results in outward forces on the main body at the junctures of the strip thereto, and this tends to flatten the V. Suchfiattening, in turn, tends to lower the strip relative to the vane mounting point and, if such lowering is resisted as explained hereinafter, further heating and expansion of the strip causes the latter to snap to an upwardly bowed position. If the heating is now dsicontinued, the heater wire section of the vane cools and the resulting contraction of the strip brings the material to its new equilibrium point and thus snaps the latter back to its original position.

As applied to an electric switch, a first contact secured on the undersurface of the strip at or immediately adjacent its mid-section is normally engaged with a second contact fixed relative to the vane mounting point, these two contacts forming part of an electric heating circuit including the vane. When this circuit is closed, with resultant heating of the vane due to electric current flow therethrough and consequent expansion of the integral strip as explained above, the second contact resists or prevents lowering of the strip relative to the vane mounting point. Thus the contact pressure is maintained and even increased during the heating cycle right up to the instant the strip snaps to the upwardly bowed position disengaging the contacts and opening the heating circuit. This maintenance of the contact pressure, in combination with the snap opening of the contacts, greatly prolongs the contact life. Such prolongation of contact life is enhanced by the snap re-closing of the contacts.

The vane may have any desired shape in plan, such as a square, a rectangle, a circle, or a semicircle, dependent upon the desired parameters and intended use of the switch.

For an understanding of the invention principles, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings. In the drawings:

Figs. 1, 2 and 3 are plan views of three pieces of metal slotted to form snap action vanes in accordance with the invention but before deformation of the main body into a shallow V-shape;

Fig. 4 is a plan view of the vane of Fig. 1 after deformation of the main body of the vane;

Fig. 5 is a side elevation view of the vane of Fig. 4, the V-shape of the main body being exaggerated;

Fig. 6 is a bottom plan view of the vane attached to a mounting bracket carrying, in insulated relation, a contact engageable with a contact on the undersurface of the strip;

Fig. 7 is a front elevation view of an automotive type flasher unit embodying the vane of Figs. 1 and 4, the circuit controlled thereby being schematically illustrated;

Fig. 8 is a side elevation view of the flasher unit; and

Fig. 9 is a view similar to Fig. 7 showing the flasher contacts open. Referring to Fig. 1, a vane 15, in accordance with the invention, may be formed by taking a rectangular piece of thin, relatively stifi, resilient metal and forming a. closed-end slot 16 along one edge so as to divide the vane into a relatively narrow thermostatic operator strip 20 integral at each end with a main body section 21. The metal preferably has highelectrical resistance.

While, for most applications, a rectangular shape vane is desirable, the vane shape is dictated by external parameters. In some cases a circular or semicircular shape, such as the vane 15' of Fig. 2 or the vane 15" of Fig. 3 is desirable. Vanes of circular or semi-circular shape may be useful, for example, as circuit breakers installed in lamp sockets. In some other instances, a square shape or an, arcuate shape may be preferred.

Irrespective of the shape of the vane, the cutting of the slot 16 (16', 16") provides a narrow thermostatic operator strip 20 (20', 20") along an edge of the vane and separated by the slot from the main body section 21 (21', 21") of the vane. This strip, which is integral with the main body section at each end 17 (17, 17"), has a cross-sectional area only a fraction of that of the main section, and acts as the usual resistance wire or strip hitherto separate from and mechanically attached to the vane along a diagonal.

Either during the formation of slot 16, or after the slot is formed, the vane, preferably including strip 20, is given a shallow V-shape with the apex 22 of the V extending normal to strip 20 and preferably bisecting the latter. This may be efiectively accomplished by providing a rectangular flat section 23 along the apex of the V as shown in Fig. 4. The angle of the V in section 21 is greater than any angle of the V in strip 20.

For effective action of vane 15 as a snap action switch, body section 21 must be secured or supported at a fixed point on or immediately adjacent the apex of the V. Referring to Fig. 6, this is accomplished, in practice, by spot welding or brazing section 21 to one end 31 of an electrically conductive bracket 30 having a center section 32 ofi'set vertically from end 31 and extending beneath strip 20. Bracket 30 has an outer end 33 offset vertically from mid-section 32. Mid-section 32 has a band 34 of dielectric material therearound, and astrip 36 of conductive material is wound about band 34 and carries a contact 35 normally engaged with a contact 25 on the undersurface of strip 30.

To form a flasher, the vane and bracket combination 15-30 is mounted on a dielectric base 40 carrying receptacle

engaging prongs

41, 42, as shown in Figs. 7-9. In this assembly, the outer end 33 of bracket 30 is welded, brazed, or soldered to a rivet securing prong 41 to base 40, and the outer end of conductor 36 is welded, brazed or soldered to a rivet securing prong 42 to base 40. In making this assembly, the mechanics of assembly are such that strip 20 has a shallow V-shape'and firmly presses its contact 25 against the contact 35 mounted in insulated relation on the mid-section 32 of bracket 30.

' Before describing the operation of the vane, reference is made to the schematic wiring diagram of Fig. 7. As therein illustrated, one terminal of agrounded battery 43, which may be an automotive battery, is connected through a switch 45 to a receptacle (not shown) in which prong 41 is engaged. Prong 42 is engaged in a receptacle (not shown) connected to a grounded load such as lamps 44. When switch 45 is closed, current will flow from battery 43 to prong 41, bracket 30, and vane 15. The current in vane 15 flows over two parallel paths to the opposite ends of strip 20, through the strip and

closed contacts

25, 35 and thence into strip 36, from whence the circuit is completed through prong .42 and lamps 44 to ground.

- As strip 20 has a cross-section much less than that of body section 21, it is heated much more rapidly than the 4 body section, when the heating circuit is completed by closing switch 45. Consequently strip 20 expands longitudinally relative to body "section 21. As strip 20 expands, it is restrained at its ends by the V-shape body 21, so that the center of strip 20 is forced downwardly to increase the pressure of contact 25 against fixed contact 35. The continued expansion of strip 20, with downward movement of the strip thus-restrained, results in a straightening force being exerted on body section 21.

This results in a toggle action wherein, when the out ward force of strip 20 and the constraint exerted by section 21 reach an equilibrium point, strip 20 is snapped to an upwardly bowed position as shown in Fig. 9. This results in a snap separation of contacts 25-35 which, until the exact moment when they are snapped apart, are maintained under increasing contact pressure. The toggle action resulting in snapping of strip :20 to a new position is due to the inward force of section 21 on the ends of strip 20 asa result of section 21 tending to return to its initial V-shape.

When contacts 25-35 are thus snapped apart, the heating circuit is opened and strip 20 starts to cool and contract. As strip 20 passes through the equilibrium point, the pressure of section 21 on its ends snaps strip 20 back to the position of Figs. 7 and8, thus re-engaging contacts 25-35 witha snap action and under the initial contact pressure. j

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without departin from such principles.

What is claimed is: I r i 1. In an electric switch, a snap action vane comprising a substantially flat piece of a single resilient metal having a relatively elongated closed-end slot extending along and adjacent an edge thereof to divide the vane into a main body section and a-strip-separatedfrom said body section by said slot and integral with the body section at each end, with the strip having a cross-sectional area only a fraction of that of the body section; whereby, upon cyclic heating and cooling of said strip the latter will cyclically expand and contract-relative to the body section and, due to the reaction of the body section on the ends of the strip, the intermediate portion of the strip will move substantially, relative to the body section, out of co-planar relation with the latter; an electric heating circuit for said stripincluding said strip;.afixed support secured to said body section;- a first contact fixed relative to said support; and a second contact carried by said strip and movable into and .out of engagement with said first contact by such relative movement of said strip. x i

2. In an electric switch, a snap action vane comprising a substantially flat piece of a single resilient metal of relatively high electrical resistance having a relatively elongated closed-end slot extending along and adjacent an edge thereof to divide the vane into a main body section and a strip separated from said body section by said slot and integral with the body section at each end,

with the strip having a cross-sectional area only a fracportion' of the strip will move substantially relative to 1 the body section, out of co-planar relation with the latter;

a fixed support secured to said body section; a first contact fixed relative to said support; a second contact carried by said strip and movable into and out of engagement with said first contact by such relative movement of said strip; and an electric heating circuit for said strip including said contacts and said strip.

3. A snap action vane comprising a substantially fiat piece of a single resilient metal having a single relatively elongated closed-end slot extending along and adjacent one edge thereof to divide the vane into a main body ection and a strip separated from said body section by said slot and integral with the body section at each end, with the strip having a cross-sectional area only a fraction of that of the body section; at least the main body section of said vane being bent to form a shallow V; whereby, upon heating of said strip the latter will expand relative to the body section and, due to the reaction of the body section on the ends of the strip, the intermediate portion of the strip will move substantially relative to the body section.

4. A snap action vane comprising a substantially fiat piece of a single resilient metal having a single relatively elongated closed-end slot extending along and adjacent one edge thereof to divide the vane into a main body section and a strip separated from said body section by said slot and integral with the body section at each end, with the strip having a cross-sectional area only a fraction of that of the body section; at least the main body section of said vane being bent to form a shallow V having an apex extending normal to said strip; whereby, upon heating of said strip the latter will expand relative to the body section and, due to the reaction of the body section on the ends of the strip, the intermediate portion of the strip will move substantially relative to the body section.

5. A snap action vane comprising a substantially flat piece of a single resilient metal having a single relatively elongated closed-end slot extending along and adjacent one edge thereof to divide the vane into a main body section and a strip separated from said body section by said slot and integral with the body section at each end, with the strip having a cross-sectional area onlya fraction of that of the body section; at least the main body section of said vane being bent to form a shallow V having an apex extending normal to said strip and substantially bisecting said strip; whereby, upon heating of said strip the latter will expand relative to the body section and, due to the reaction of the body section on the ends of the strip, the intermediate portion of the strip will move substantially relative to the body section.

6. In an electric switch, a snap action vane comprising a substantially flat piece of a single resilient metal having a relatively elongated closed-end slot extending along and adjacent an edge thereof to divide the vane into a main body section and a strip separated from said body section by said slot and integral with the body section at each end, with the strip having a cross-sectional area only a fraction of that of the body section; at least the main body section of said vane being bent to form a shallow V; whereby, upon cyclic heating and cooling of said strip the latter will cyclically expand and contract relative to the body section and, due to the reaction of the body section on the ends of the strip, the intermediate portion of the strip will move substantially relative to the body section; a fixed support secured to said body section substantially at the apex of the V; a fixed support secured to said body section; a first contact fixed relative to said support; and a second contact carried by said strip and movable into and out of engagement with said first contact by such relative movement of said strip.

7. In an electric switch, a snap action vane comprising a substantially flat piece of a single resilient metal of relatively high electrical resistance having a relatively elongated closed-end slot extending along and adjacent an edge thereof to divide the vane into a main body section and a strip separated from said body section by said slot and integral with the body section at each end, with the strip having a cross-sectional area only a fraction of that of the body section; at least the main body section of said vane being bent to form a shallow V; whereby, upon flow of electric current through the strip, the strip will heat and expand relatively to the body section and will cool and contract relative to the body section when the current flow is interrupted and, due to the reaction of the body section on the ends of the strip, the intermediate portion of the strip will move substantially rela' tive to the body section; a fixed support secured to said body section substantially at the apex of the V; a first contact fixed relative to said support; a second contact carried by said strip and moveable into and out of engagement with said first contact by such relative movement of said strip; and an electric heating circuit for said strip including said contacts.

8. In an electric switch, a snap action vane comprising a substantially flat piece of a single resilient metal of relatively high electrical resistance having a relatively elongated closed-end slot extending along and adjacent an edge thereof to divide the vane into a main body section and a strip separated from said body section by said slot and integral with the body section at each end, with the strip having a cross-sectional area only a fraction of that of the body section; at least the main body section of said vane being bent to form a shallow V having an apex extending normal to said strip; whereby, upon flow of electric current through the strip, the strip will heat and expand relatively to the body section and will cool and contract relative to the body section when the current flow is interrupted and, due to the reaction of the body section on the ends of the strip, the intermediate portion of the strip will move substantially relative to the body section; a fixed support secured to said body section substantially at the apex of the V; a first contact fixed relative to said support; a second contact carried by said strip and moveable into and out of engagement with said first contact by such relative movement of said strip; and an electric heating circuit for said strip including said contacts.

9. In an electric switch, a snap action vane comprising a substantially flat piece of a single resilient metal of relatively high electrical resistance having a relatively elongated closed-end slot extending along and adjacent an edge thereof to divide the vane into a main body section and a strip separated from said body section by said slot and integral with the body section at each end, with the strip having a cross-sectional area only a fraction of that of the body section; at least the main body section of said vane being bent to form a shallow V having an apex extending normal to said strip and substantially bisecting said strip; whereby, upon flow of electric current through the strip, the strip will heat and expand relatively to the body section and will cool and contract relative to the body section when the current flow is interrupted and, due to the reaction of the body section on the ends of the strip, the intermediate portion of the strip will move substantially relative to the body section; a fixed support secured to said body section substantially at the apex of the V; a first contact fixed relative to said support; a second contact carried by said strip and moveable into and out of engagement with said first contact by such relative movement of said strip; and an electric heating circuit for said strip including said contacts.

References Cited in the file of this patent UNITED STATES PATENTS 2,363,280 Arnold Nov. 21, 1944 2,425,717 Bean Aug. 19, 1947 2,533,274 Matulaitis et al. Dec. 12, 1950 2,708,697 Welsh May 17, 1955 2,716,682 Franklin Aug. 30, 1955 2,720,568 Bletz Oct. 11, 1955 2,825,960 Protz Mar. 11, 1958 2,834,853 Hood May 13, 1958