US3256406A

US3256406A - Single-curved vane-type thermally actuated switch

Info

Publication number: US3256406A
Application number: US275718A
Authority: US
Inventors: Wojcik Edward
Original assignee: Ideal Corp
Current assignee: Parker Hannifin Corp
Priority date: 1963-04-25
Filing date: 1963-04-25
Publication date: 1966-06-14
Anticipated expiration: 1983-06-14
Also published as: NL6404354A; GB1041368A; SE321885B; DE1465723A1

Description

June 14, 1966 E. WOJCIK 3,256,406

SINGLE-CURVED VANE-TYPE 'IHERMALLY AGTUATED SWITCH Filed April 25, 1963 INVENTOR.

EDWARD WOJC lK A NEY United States Patent 3,256,406 SINGLE-CURVED VANE-TYPE THERMALLY ACTUATED SWITCH .Edward Wojcik, Astoria, N.Y., assignor to Ideal Corporation, a corporation of New York Filed Apr. 25, 1963, Ser. No. 275,718 9 Claims. (Cl. 200113) This invention relates to new and improved switches and elements thereof, particularly of the type useful in flasher circuits or for analogous purposes.

One important object of the invention is to provide a snap action switch suitable for use as a flasher switch or the like, having desired operating characteristics which are not substantially affected by normally occurring variations in the dimensions or properties of the component materials or in the processing and assembly of these materials to produce the switch, so that the switch may be manufactured reliably in large quantities by automatic machinery and with minimum need for adjustments by hand.

Another object of the invention is to provide a switch construction for use in flasher circuits or the like which enables improved control of the relative duration of the flash and olf times of the circuits and will operate advantageously with little or no perceptible difference between the duration of the first flash and that of succeeding flashes.

A further object is to provide a snap action switch which may be readily adjusted to vary its operating characteristics.

Still another object is to provide a snap action switch of the vane type having a simple and yet durable construction giving is a relatively long service life.

The switches provided according to the present invention make use of an electro-thermally or thermally actuated switching element composed of a resilient vane member of distinctive construction coacting with a thermally expansible pull member so as to be constrained to one switching position when the pull member is cool and to switch itself to another position when the pull member is suitably heated, as by the passage of an electrical current through it to heat it by electrical resistance.

The vane member comprises a body leaf of suitably thin and resilient sheet metal or the like, which by being suitably pre-stressed or formed to a naturally curved shape is intrinsically biased toward a natural posture in which it is bowed relative to one axis only into a curvature, preferably having substantially the form of a minor sector of a cylinder, that protrudes to one side of a plane intersection opposite end portions of the leaf. Instead of being allowed to hold this natural posture, the resilient leaf has the thermally expansible pull member so tensioned over its naturally convex side that the pull member normally constrains it, against its intrinsic bias, into an inverted posture in which it is bowed elastically relative to one axis only into a curve protruding to the other side of a plane intersecting said end portions.

The intrinsic bias of the leaf and the expansibility of the pull member are selected so that upon a heating of the pull member to relax its tension, such as by passing an electrical current through it, the pull member no longer can constrain the inversely bowed leaf to its inverted posture; so the leaf then inverts itself toward its natural posture.

The motion attending each inversion of the leaf is readily utilized to effect a switching action. Through electrical heating of the pull member, the switching element can be caused to switch quickly from a normal or cool position to a second position in which the leaf has assumed or approached its natural posture. When the leaf approaches that posture the pull member lies flush against the naturally convex side of the leaf; so the pull member is then cooled and contracted quickly by conduction of heat into the relatively cool body of the leaf. In this way the leaf is returned quickly to its inverted posture for the completion of a switching cycle that can 'be repeated reliably time after time over prolonged periods of time.

According to another important feature of the invention, the inversions of the bowed leaf and the attendant switching motions are caused to take place in each instance with an advantageous snap or toggling action, by providing the vane member with suitable means acting on the opposite ends of the leaf to resist spreading of the leaf so that it must buckle or toggle upon being inverted across the plane intersecting its ends. For this purpose, the vane member may be formed with a side strip joining the ends of the bowed leaf in chordal relation to the leaf at a location adjacent to at least one of its side edges. The strip can be formed out of the same piece of sheet metal as the leaf.

The action of the switching element can be easily modified or controlled by making the side strip or strips stretchable under a certain tension applied thereto by the leaf so that a certain desired resistance will be imposed to each inversion of the leaf.

The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description of a preferred embodiment there of and from the accompanying illustrative drawing in which:

FIGS. -1 and 2 are isometric views taken from opposite sides of a snap action switch embodying the invention;

FIG. 3 is a schematic edge view of the vane member employed in the switch of FIGS. 1 and 2; and

FIGS. 4-7 are schematic views illustrating successive stages in the snapping movement of the switching element between contact open and contact closed positions.

Referring to the drawing, the basic switching element of the switch shown includes a vane member 10 made from a generally rectangular piece of relatively stiff thin sheet metal such, for example, as spring steel in sheet or strip form of about .005 inch thickness. The piece is slotted along one side edge thereof to provide therealong a side strip 16 separated from a relatively wide body leaf 14 by a slot 12, with the side strip joined integrally at its ends to

opposite end portions

15 and 17 of the leaf.

The body leaf 14 is permanently stressed or set to a substantially cylindrically curved natural posture toward which it is always biased by its intrinsic resiliency. In that posture it is bowed relative to one axis only into a curve protruding to one side of a plane intersecting the

end portions

15 and 17, for example, to one side of the plane occupied by strip 16 as indicated schematically in FIG. 3. The side strip 16 is crimped as indicated at 18, so that its normal length corresponds substantially to that of a chord joining the ends of the bowed leaf 14.

Thus, when the vane member is in its natural or unconstrained condition indicated in FIG. 3, it resembles an archery bow having a relatively thin and wide bowed body with the bowstring disposed at one edge of the body, but with the body holding itself bowed instead of being bowed by tension in the string, or side strip 16. The side strip resists spreading of the end-

portions

15 and 17 where it joins them together but does not prevent inversion of the curvature of the body leaf 14.

The basic switching element includes also an expansible pull member 20 that is trained over and governs the postures of the vane member 10. The pull member preferably is a thin narrow band or wire of an electrical resistance alloy, such, for example, as a flat chromiumnickel alloy wire of the type known as Nichrome, havcurvature inverse to the pre-set natural bowing or curvature thereof.

The pull member 20 normally lies substantially in a chordal plane interconnecting the end portions and 17 of the inversely bowed leaf, thus extending over the side 14B thereof substantially as illustrated in FIG. 4 and acting, much as the string of an archery bow, to hold the leaf bowed elastically in the direction opposite to the natural or pre-set bowing thereof, against the intrinsic bias thereof.

The length and the electrical resistance and thermal expansion properties of the pull member are readily selected so that when the temperature of this member is increased, as by the passage of an electrical current through it, the pull member Will expand to relax its tension and the bending moment which it exerts upon the ends of the body leaf. The pull member then will no longer overpower the intrinsic bias or shape restoring force of the body leaf, whereupon the latter inverts itself and returns to its own natural or preferred posture.

As the pull member becomes relaxed the intrinsic bias of the body leaf applies an increasing tension to the side strip 16, which strip by resisting this tension resists spreading of the

end portions

15 and 17 and flattening of the leaf 14 in the course of the return of the latter to its normal posture. The return movement of the leaf therefore is accompanied by a buckling of its thin body, which begins on one side of the plane of the tension of strip 16, as illustrated schematically in FIG. 5, and which upon progressing sufliciently to the other side of that plane causes the leaf to snap with a toggling action to its natural posture, whereby the switching element shown is moved to its preferred position illustrated schematically in FIG. 6.

A similar buckling and toggling action in reverse direction, as illustrated schematically in FIG. 7, occurs upon a contraction of the length of the pull member 20, such as that brought about by a cooling of it from the elevated temperature at which it allowed the body leaf to assume its natural posture. curvature of the leaf is inverted, again with a snap action, and the switching element takes the position to which it is biased by the pull member 20, as illustrated schematically in FIG. 4.

The vane member 16 and pull member 20 constitute an effective snap action switching element suitable for many uses. It is particularly suitable for use as the working element of an improved flasher switch such as that shown in FIGS. 1 and 2.

As there shown, the flasher switch includes a circular frame or base 26 of electrical insulating material, to which are secured a prong or terminal 28 and also, as by a rivet 29, a bracket 30 having one end bent downwardly and passed through the base 26 to form a second prong or terminal 32. The other end 34 of bracket 30 is enlarged and supports a mounting element 38. This mounting element is electrically insulated from the bracket, as by suitable dielectric sheet material 36, and is formed with an upstanding arm 40.

The switching element is mounted on the free end of the upstanding arm 40, as by a rivet or a spot weld at 42 which fixes the body leaf 14 to the arm at a point disposed toward One end of the leaf 14, considerably to one side of the apex or center of the pre-set curvature thereof.

An electrical contact element 48 is fixed to the leaf 14 at a location thereon disposed away from the mounting point 42, advantageously toward the other end of the In this way the bowing or l leaf at a considerable distance to the other side of the apex or center of said curvature. The contact element 48 coacts with a mating contact element 46 which is mounted on the free end of a finger 44 struck upwardly from one side of the bracket 30. The finger 44 so positions contact element 46 that when the pull member 20 is in its normal or cold condition, the body leaf 14 then being held in its reversely bent or inverted posture, the two

contact elements

46 and 48 are pressed firmly together in circuit closing relation to form a closed path for conducting electrical current between the

terminals

28 and 32 through the thermally expansible pull member 20.

The contact elements then connect the vane member 10 with bracket 30, thus with terminal 32. The vane member is at all times connected electrically with terminal 28 through the expansible pull member 20, as by a conductor 50 of low electrical resistance which is secured at one end, as by welding, to substantially the midpoint of the pull member 20 and is secured at its other end, as by welding, to a finger 28a on the upper end of the prong or terminal 28.

Instead of securing the conductor 50 to the pull member by welding, one end of the conductor may be secured to a tab formed integral with the pull member; or a conductor formed as one piece with the pull member may be provided to connect member 26 with terminal 28.

It will be evident that when the switch is in the position indicated in FIG. 1 and the

terminals

28 and 32 are connected into an electrical circuit, electrical current will flow between the terminals by passing through the high resistance pull member'Zt). The pull member then heats and expands until it no longer restrains the leaf 14 to the inverted circuit closing posture illustrated in FIGS. 1 and 4. Thet leaf then begins to buckle or unbend, as illustrated in FIG. 5, toward its own natural or preferred posture, under its own bias which it exerts continuously while it is bent elastically out of that pre-set posture. In the course of this buckling or unbending action, the leaf snaps to its natural posture and thus snaps the switching element to its hot or circuit opening position illustrated in FIG. 6, through a rocking or deflection of the switching element about its mounting point 42 whereby the portion of the 'body leaf carrying contact element 48 is moved away from contact element 46 to break the circuit through the switch.

When the switch reaches its hot or open position, the contact carrying side 1413 of leaf 14, although having been held concave by the pull member while that member is cool, is inverted to its intrinsically convex curvature;

.if desired a lesser length of the pull member may be caused to contact the leaf surface, as by forming the

end portions

15 and 17 with raised corner portions over which the pull member will extend from its

fixed ends

22 and 24.

Since the leaf is highly heat conductive, relatively massive and cold compared to the expanded pull member, the heat of the pull member lying in contact with side 14B is quickly drawn away by conduction through the leaf. Thus the pull member is quickly cooled and contracted, and as it contracts it buckles the leaf against the pre-set bowing thereof so as to move it back to its inverted, circuit closing posture of FIGS. 1 and 4. A probable condition in the course of this invention is indicated in FIG. 7.

When the

contact elements

48 and 46 again come together, they reestablish the circuit through the pull member, and the cycle is repeated. The switch thus continues to open and close the circuit at regular intervals for as long as the actuating electrical circuit into which it is connected is maintained.

The described coaction of the hot pull member and the relatively cold leaf provides important advantages in the use of the switch. The time required for the cooling or open circuit stage of the switch operation can be made shorter than would otherwise be the case. Moreover, the length of this interval can be selected and kept in any of various desired relationships to the time provided for the flashing or closed circuit stage of the operation. In other words, various desired combinations of flash and off times can be provided. Further, the switch will operate in the first of its cycles with very nearly the same flash and off times as in succeeding cycles, which contributes to the effectiveness of its use as a flasher switch for the control of warning signals of atuomobiles or other vehicles.

Since the leaf of the vane member is devoid of vpre-set crimps or bosses and undergoes its inverting move- The crimping of the side strip 16, in addition to shortening it to approximately the chordal length of the bowed body leaf, gives the side strip longitudinal stretchability and the effect of a tension spring imposing, a certain resistance to the inversions of the curvature of the leaf. The magnitude of this resistance can be set at any of a variety of desirable values by control of the stretch resistance of the crimped side strip. In this way the operating characteristics of the switch can be readily fixed and controlled, as desired in manufacturing practice, without being substantially altered by minor variations commonly encountered in the dimensions or properties of the materials used for the manufacture of the switch or in the precision of assembly of its parts. The switch, therefore, can be manufactured to high performance standards with the use of automatic machinery.

Moreover, the crirnped construction of the side strip 16 provides a convenient and easy means of adjusting the operating characteristics of a given switch. When a switch made according to the invention is found to operate otherwise than in accordance with prescribed specifications, it may be made to meet such specifications by an alteration of the crimping of the side strip.

Since the leaf 14 is uniformly curved and undergoes its inversion movements over substantially its entire length, the mounting point 42'and the contact element 48 may be located at any of a variety of points over its area, provided only that they are spaced apart longitudinally of the vane member so as to give the required separating movement of the two contact elements. The extent of{ this movement can be selected as desired by selection of the longitudinal spacing of point 42 and element 48 on the leaf 14.. The pressure of element 48 against element 46 in the closed position of the switch and the motion of element 48 relative to element 46 as these elements make and break contact, can each be similarly selected and controlled.

It has been found, for example, that by locating the mounting point 42 and element 48 toward opposite ends of the leaf, substantially as illustrated, several desirable attributes are attained. Contact element 48 undergoes an advantageous rocking movement while engaging or disengaging element 46, whereby pitting or fusing of the contact elements is avoided or inhibited. The contact elements are held together, when engaged, under a pressure sutficient to assure a large area of mutual contact and a low resistanceto the flow of current through them. And when the elements are disengaged they are spaced apart far enough to prevent bridging of the gapby fused material that commonly tends to build up on the face of one of the contact elements in the course of long service of the switch.

The snap action switch of the invention will thus be seen to provide many distinct advantages in ease and cost of production and in efficiency and durability of operation.

Although an illustrative embodiment of the invention has been described in detail herein with reference to the accompanying drawing, it is to be understood that the invention is not limited to the illustrated embodiment and that various changes and modifications may be effected therein without departing from the scope or spirit of the invention.

What is claimed is:

1. A switching element including a vane member comprising a resilient leaf intrinsically biased over substantially its entire area between opposite end portions of the leaf toward a natural posture in which it is bowed in a single-curved form only to one side of a plane intersecting said opposite end portions, and

a thermally expansible pull member tensioned between said end portions over the naturally convex side of said leaf and normally constraining said leaf against its intrinsic bias into an inverted posture in which it is bowed elastically to the other side of said plane in a single-curved form only from one to the other of said end portions,

the intrinsic bias of saidleaf and the expansibility of said pull member being sufficient that upon a heating of said pull member to relax its tension said leaf will invert itself toward said natural posture.

2. A switching element including a vane member comprising a resilient leaf intrinsically biased over substantially its entire area between opposite end portions of the leaf toward a natural posture in which it is bowed in a single-curved form only to one side of a plane intersecting said opposite end portions, and

a thermally expansible pull member tensioned between said end portions over the naturally convex side of said leaf and normally constraining said leaf against its intrinsic bias into an inverted posture in which it is bowed elastically to the other side of said plane in a single-curved form only from'one to the other of said end portions,

the intrinsic bias of said leaf and the expansibility of said pull member being sufficient that upon a heating of said pull member to relax its tension said leaf will invert itself toward said natural posture,

said pull member lying flush against said naturally convex side when the leaf reaches its natural posture, whereby the pull member is then cooled and contracted quickly by conduction of heat into the leaf so as to return the leaf quickly to its inverted posture.

3. A switching element including a vane member comprising a resilient leaf intrinsically biased over substantially its entire area between opposite end portions of the leaf toward a natural posture in which it is bowed in a single-curved form only to one side of a plane intersecting said opposite end portions, and

a thermally expansible pull member tensioned between said end portions over the naturally convex side of said leaf and normally constraining said leaf against its intrinsic bias into an inverted posture in which it is bowed elastically to the other side of said plane Y in a single-curved form only from one to the other of said end portions,

the intrinsic bias of said leaf and the expansibility of said pull member being sufiicient that upon a heating of said pull member to relax its tension said leaf will invert itself toward said natural posture,

said pull member comprising a wire stretched diagonally over said leaf between diagonally opposite corners of the leaf.

4. A switching element including (a) a vane member comprising (1) a resilient leaf intrinsically biased over substantially its entire area between opposite end portions of the leaf toward a natural posture in which it is bowed in a single-curved form only to one side of a plane intersecting said opposite end portions, and (2) strip means extending between said end portions in chordal relation to said bowed lea-f adjacent to at least one side edge thereof to resist spreading of the leaf so that the leaf will buckle upon being inverted across said plane, and (b) a thermally expansible pull member tensioned between said end portions over the naturally convex side of said leaf and normally constraining said leaf against its intrinsic bias into an inverted posture in which it is bowed elastically to the other side of said plane in a single-curved form only from one to the other of said end portions,

the'intrinsic bias of said leaf and the expansibility of said pull member being sufficient that upon a heating of said pull member to relax its tensionsaid leaf will invert itself by toggle action and thereby snap toward said natural posture.

5. A switching element according to claim 4, said strip means being stretchable by the tension applied thereto by said leaf as said pull member expands, whereby the in version of the leaf is controlled by the stretch resistance of said strip means.

6. A switching element including a vane member in the form of a unitary piece of uniformly thin resilient sheet metal slotted along a side edge thereof to provide therealong a side strip joining opposite end portions of a relatively wide body leaf formed by the remainder of said piece,

said leaf having from end to end thereof an intrinsic substantially uniform curvature biasing it toward a natural posture in which it is bowed between its ends in a single-curved form only protruding to one side of said side strip, said side strip being crimped to shorten it and render it stretchable elastically by the intrinsic bias of the bowed leaf, and a thermally expansible electrical resistance wire tensioned over the naturally convex side of said leaf between opposite end portions thereof and normally constraining said leaf against said bias into an in- Y verted posture in which it is bowed elastically in a single-curved form only protruding to the opposite side of said strip,

said bias and the expansibility of said wire being sufficient that upon a heating of said wire by passage of an electric current through it said leaf will invert itself and snap toward said natural posture. 7. A switching element according to claim 6, said wire being flat and lying in face to face contact with said naturally convex side when said leaf approaches said natural posture, whereby the Wire is then cooled and contracted quickly byconduction o-f heat into the leaf so as to return the leaf quickly to said inverted posture.

8. A snap action switch comprising a switching element as defined in claim 6,

a base,

first and second terminals, a first contact element and a mounting element, all carried by said base,

said first contact element being electrically connected to said first terminal and said mounting element being electrically insulated from said terminals,

said switching element being fixed to said mounting element at a point on said leaf toward one end of said left whereby said switching element is movable angularly relative to said mounting element by inversion of the bowing of said leaf,

said leaf carrying at a point toward the other end thereof a second contact element bearing against said first contact element when said leaf is in said inverted posture,

and means electrically connecting said resistance wire to said second terminal so that when a circuit is closed to said terminals current will flow through said wire to heat and expand it and thereby cause said switching element to break circuit by inversion of said lea-f away from said first contact element.

9. A switching device comprising a resilient vane of electrically conductive material,

a thermally expansible electrical resistance member tensioned between opposite portions of said vane and normally holding said vane bowed to one posture,

the material of the said vane being itself biased so that said vane will deflect toanother posture upon an expansion of said resistance member,

a mounting member having a body portion of said vane fixed thereto,

a first electrical contact element on another body portion of said vane,

a complementary electrical contact element fixed relative to said mounting member in position to be engaged by said first element when said vane is in said one posture,

said contact elements being disengaged by deflection of Said vane to said other posture,

and a flexible electrical conductor fixed to said resistance member for conducting thereto current to heat and expand the same.

References Cited by the Examiner UNITED STATES PATENTS 7 2,363,280 11/1944 Arnold 200-113 2,537,485 1/1951 Stizer et al. 200-137 2,574,869 11/1951 Green 200-67 2,700,083 1/1955 Harmon 200-113 1 2,712,045 6/1955 Welsh 200-122 2,834,853 5/1958 Hood 200-138 2,861,149 11/1958 Hollis et al. 200-113 2,870,292 1/1959 Welsh 200-113 2,878,340 3/1959 Uhl 200-113 3,057,982 10/1962 Grover et al 200-138 3,080,464 3/ 1963 Kurz 200--122 3,098,139 7/1963 Bleiweiss et al. 200-137 BERNARD A. GILHEANY, Primary Examiner. LAURENCE A. WRIGHT, Assistant Examiner.

Claims

1. A SWITCHING ELEMENT INCLUDING A VANE MEMBER COMPRISING A RESILIENT LEAF INTRINSICALLY BIASED OVER SUBSTANTIALY ITS ENTIRE AREA BETWEEN OPPOSITE END PORTIONS OF THE LEAF TOWARD A NATURAL POSTURE IN WHICH IT IS BOWED IN A SINGLE-CURVED FORM ONLY TO ONE SIDE OF A PLANE INTERSECTING SAID OPPOSITE END PORTIONS, SAID A THERMALLY EXPANSIBLE PULL MEMBER TENSIONED BETWEEN SAID END PORTIONS OVER THE NATURALLY CONVEX SIDE OF SAID LEAF AND NORMALLY CONSTRAINING SAID LEAF AGAINST