US3358099A - Bimetallic-strip and rockable-spring actuated snap-acting switch device - Google Patents

Description

Dec. 12, 1967 M. DE BELLOMAYRE BIMETALLlC-STRIP AND HOCKABLE-SPRING ACTUATE SNAP-ACTING SWITCH DEVICE Filed Dec. 23, 1965 2 Sheets-Sheet l D 1 1967 M. DE BELLOMAYRE 3,358,099

BIMETALLIC-STRIP AND ROCKABLE-SPRING ACTUATED SNAP-ACTING SWITCH DEVICE Filed Dec. 23, 1965 2 Sheets-Sheet 2 I7 Fig..-5

18 7 I 19 Fig :6 1

i I 5 I 185.. a I I 5 I I I I Flg..'7 I 0! United States Patent 3,358,099 lHMETALLIC-STRIP AND ROCKABLE-SPRING ACTUATED SNAP-ACTING SWITCH DEVICE Michel de Beliomayre, 69 Ave. R. Poincare, Paris, France Filed Dec. 23, 1965, Ser. No. 516,004 Claims priority, application France, Dec. 30, 1964, 468 5 Claims. (Cl. 200-113) ABSTRACT OF THE DISCLOSURE A system for actuating a snap-acting switch is described. The system comprises a hairpin-shaped bimetallic strip having two prongs extending from a mutual junction to two free ends, one of which carries a movable contact stud. The bimetalic strip pivots at the junction. An arcuate-shape leaf spring having an end hinged to the free end of the other of said prongs pivots at the opposite end of thespring.

This invention relates to a manually or automatically operating electric switch device. Its object is to eliminate the detrimental effect of the gradually reduced pressure between the contact studs which occurs with conventional switch, microswitch or circuit-breaker devices immediately before said contact studs separate.

Considering for example a snap-acting microswitch of the conventional type in which a pushbutton moves an actuating arm connected to the movable contact through a spring, it will be noted that as this actuating arm moves to the position in which the movable contact stud trips, the pressure exerted by the latter against the fixed contact stud gradually diminishes until it becomes zero just before separation. Clearly, if the actuating arm moves slowly, then, as it approaches the position referred to, additional electrical contact resistance harmful to the circuit will be set up due to the lack of pressure against the fixed contact stud. Further, the sparks which occur as a result when the actuating arm reaches this critical zone will rapidly wear out the contact studs until they become unserviceable.

The present invention provides for the introduction of a flexible member which stores the energy exerted on the actuating arm and then restores it abruptly and instantaneously when said arm reaches a given position, whereby the movable contact stud is abruptly tripped, the contact pressure having remained constant until the actuating arm reaches the triggering position.

The invention accordingly provides for replacing the rigid actuating arm utilized on presently known devices by a flexible blade made, for instance, of spring steel or beryllium bronze.

The invention has more specifically for its object to provide a tumbler or snap-acting electric switch device the movable contact stud of which is acted upon simultaneously by a spring furnishing the required contact pressure to said movable stud in the contact-making position thereof and by a flexible actuating arm against a point of which thereon said spring bears and the deformations of which take place against the opposing force of said spring, said flexible actuating arm and said spring being so devised in relation to each other that said bearing point remains stationary as long as, during the initial deformation phase of said flexible arm, the tension in said spring dominates the countering force which is exerted by said flexible arm by reason of the deformation thereof, whereby said tension and hence said contact pressure remain constant during said first phase, and, as the deformation of said flexible arm continues, said spring tension ceases to be dominant and separation of said movable contact stud is abruptly triggered.

The spring referred to is a rocking arcuate-shape spring, as customarily used in light electrical switchgear.

The flexible actuating arm associated to said spring is a bimetallic strip which warps as its temperature varies. These variations may be produced by a Joule effect due to current flowing through the bimetallic strip when the same is connected into the electric circuit in series with the contact studs of the switch device, whereby the latter functions as a cut-out that can be substituted with advantage for an ordinary fuse or circuit-breaker, or embodied in a switch. Alternatively, the bimetallic strip may be exposed to the temperature fluctuations of its surrounding atmosphere, whereby it performs the func tion of a thermostat.

I11 addition to the applications hereinbefore cited, to wit as a cut-out, switchcircuit-breaker, thermostat, or relay, the present invention may be usefully carried into practice wherever it is required to break electric power circuits of the kind commonly employed for the electrical installations of domestic or other consumers.

In the accompanying drawings:

FIGURE 1 is a highly schematic illustration of the switch;

FIGURE 2 shows an alternative constructional form for use as a thermostat;

FIGURES 3 and 4 are longitudinal sectional views of a form of embodiment of a cut-out,.shown respectively in the circuit-making and circuit-breaking positions thereof;

FIGURES 5 and 6 are corresponding sectional views of an alternative constructional form usable as a switch/ circuit-breaker, shown in the positions corresponding to FIGURES 3 and 4; and

FIGURE 7 is a sectional view of another alternative constructional form usable as a thermostat.

The switch shown diagrammatically in FIGURE 1 is a microswitch of the type comprising a lever 1 one end section of which is pivotally connected as at reference numeral 2. and the other end section of which bears a movable contact stud 3 shown as being pressed against a fixed contact stud 4 but which is adapted to separate therefrom and move against a stop 5. A rocking arcuateshape spring 6 has one end section thereof in hinged engagement connection with lever 1 and the other end section thereof in similar hinged connection with the end 7 of an actuating arm- 3 pivotally connected as at reference numeral 9, which control arm is operable by a pushbutton 10, against the opposing urge of a return spring 11, and is movable between tWo facing stops 12, 13.

Instead of being rigid as in conventional microswitches, the actuating arm 8 according to the invention is flexible, i.e. resilient and elastic.

In its normal circuit-making position, movable contact stud 3 exerts against fixed contact stud 4 a pressure P dependent upon the tension in spring 6, While the latter exerts against stop 12 a force P1 through its thrust point 7 on arm 8.

It will be seen that displacement of pushbutton 10' will cause arm 8 to bend without initially shifting the end section 7 thereof which bears against stop 12. Only when the force component P2 due to the internal tension in flexible arm 8 is equal to the component P1 of the force exerted by rocking spring 6 on stop 12 will arm 8 be able to straighten and move into abutment against its other stop 13, whereby lever 1 carrying movable contact stud 3 will be caused to trip from its position in contact with fixed stud 4 to its position in contact with stop 5.

It will be manifest that until arm 8 straightens and thereby trips the whole assembly, the pressure P exerted 3 by movable contact stud 3 against fixed contact stud 4 will not have diminished.

Whilst the subject device of the invention has been considered with reference to a microswitch, it goes without saying that the invention is likewise applicable to a switch wherein return spring 11 is dispensed with and pushbutton ltl is positively connected to flexible arm 8.

The invention is furthermore applicable to a thermostat wherein the force exerted by pushbutton and spring 11 is replaced by a force exerted, by reason of the Warping of a bimetallic strip 14, against flexible arm 8 (see FIGURE 2).

In the examples hereinbefore referred to, flexible arm 8 was a controlled member to which external means (10 or 14) impart the deformation needed to operate movable contact stud 3 In accordance with this invention, however, the flexible arm and the control means thereof are merged into one and the same member, to wit a bimetallic strip.

Said strip is hairpin-shaped and designated by reference numeral 15 on FIGURES 3 and 4, which illustrate a cutout. The bimetallic strip comprises a lower prong 15a carrying movable contact stud 3 and a slightly longer upper prong 15b hingedly connected to one end section of rocking arcuate-shape spring 6. An insulating stirruppiece 16 has the end section of prong 15a fixedly inserted thereinto and the second prong 15b freely threaded therethrough. The assembly comprising spring 6 and bimetallic strip 15 is hingedly engaged as at 17, at the junction of bimetallic strip prongs 15a and 15b, and as at 18, at the free end section of spring 6. The hinge point 17 formed in an insulating boss 19 is fixed, whereas the hinge point 18 formed in a conducting blade 20 is adjustable by a set-screw 21 extending through the insulating enclosure 22 of the device.

Said enclosure is shaped substantially as an ordinary fuse-box and comprises two contact pins 23, with the internal electric circuit therebetween closing through fixed contact stud 4 which is connected to one of pins 23, movable contact stud 3, bimetallic strip 15, spring 6, and blade 20 which is connected to the other pin 23 via an auxiliary circuit-breaker 24. The front face of enclosure 22, i.e. that remote from pins 23, comprises a rearming button 25 urged into a protruding position thereof by a return spring, and a slit opening 26 behind which an indicator 27 shows the device to be in the circuit-breaking position thereof (FIGURE 4), whereas disappearance of said indicator shows the device to be in the active circuit-making position thereof (FIGURE 3). Indicator 27 may be coloured red and is fast with a moulded member 28 pivotally mounted on a pin 29 and hingedly connected to spring 6 via fork-forming dual tracking pegs 30, whereby to follow the movement of assembly 6-15.

These movements are limited by fixed contact stud 4 and by a stop 31 fast with the enclosure. On being depressed, rearming button 25 thrusts against bimetallic strip 15 and causes the assembly to shift from its position against stop 31 (FIGURE 4) to its position of abutment against fixed contact 4 (FIGURE 3), at the same time as auxiliary circuit-breaker 24 opens and remains open until button 25 is released.

The cut-out hereinbefore described operates in the fol lowing manner:

In its normal operative position shown in FIGURE 3 movable contact stud 3 is applied against fixed contact stud 4 with a certain pressure (designated precedingly by P) exerted by spring 6 which is hingedly engaged at 18 and reacts against end section 7 of the upper prong 15b of the bimetallic strip, the latter being in hinged abutment as at 17 and the hinged connection 6-15b lying below the straight line joining hinge points 17-18, whereby the internal electric circuit is closed and current flows through the device between pins 23.

If the intensity of this current reaches an excessive level, bimetallic strip 15, which heats up by the Joule effect since it is connected into the circuit in series undergoes warp through the spreading apart of its prongs 15a, 15b and causes the device to trip (FIGURE 4). This operation can be broken down as follows:

(1) In the initial stage of war-ping of bimetallic strip 15, the end section 7 of its prong 15b hingedly connected to spring 6 tends to rise and to exert an opposing force on said spring. As long as the tension in spring 6 remains dominant, i.e. greater than this opposing force exerted by the bimetallic strip, end section 7 cannot in fact lift and remains pressed against the body of stirrup-piece 16, whereby the contact pressure between studs 3 and 4 remains constant as stated precedingly.

(2) As the degree of warp in bimetallic strip '15 increases, a stage is reached when the opposing force engendered thereby reaches and then exceeds the tension in spring 6. End section 7 then begins to lift while movable contact stud 3 still remains pressed by reaction against fixed contact stud 4.

(3) The hinged connection 6-15 then crosses the straight line joining hinge points 17 and 18, and the spring 6, which is under tension, suddenly relaxes and roc$s bimetallic strip 15 about its hingepoinLlTTIntil it butts against stop 31. In the course of this motion, movable contact stud 3 lifts off fixed contact stud 4-, and this separation is effected by snap-action through the sudden restoration-of the energy stored as a result of the warping of himetallic strip 15, with movable contact 3 being pulled hard off fixed contact stud 4 by the upward impulse produced by upper prong 15b and transmitted via stirruppiece 16 to the lower prong 15a carrying movable contact stud 3.

Manifestly, in the event of a short-circuit or a notable increase in current flow, the three functional stages listed precedingly take place in an extremely short time of the order of a fraction of a second. The hinged connection 615 is in fact designed to be located adjacent to and on one side of the straight line joining hinge points 17, 18, whereby as soon as a raising of the hinged connection point 6-15 is initiated, said point crosses said straight line and causes tripping.

The configuration of the device is then as shown in FIGURE 4, with the internal circuit having been opened. To reclose this circuit, rearming button 25 must be depressed. It is to be noted that, as stated precedingly, this will in turn be effective in breaking said internal circuit through opening of auxiliary circuit-breaker 24. This is designed as a safeguard to prevent unsafe reclosing of the internal circuit due say, to a protracted pressure on rearming button 25 preventing the device from tripping when this might be vital. In order to reclose the circuit, button 25 must be released, thereby allowing auxiliary contact-breaker 24 to close and reverting to the initial configuration shown in FIGURE 3.

The alternative constructional form shown in FIG- URES 5 and 6 relates to a swtich with an incorporated circuit-breaker comprising the same basic component parts, to wit an assembly hingedly connected at 17 and 18 and consisting of an arcuate spring 6 and a hairpinshaped bimetallic strip 15 which are hingedly interconnected at 7, with said bimetallic strip bearing the movable contact stud 3 (shown in its circuit-making position pressed against fixed contact stud 4 in FIGURE 5, and in its circuit-breaking position separated therefrom in FIGURE 6). The switch proper is an ordinary tumbler switch of which the contact points are designated by reference numeral 32 and the rocking operating lever by numeral 33. In accordance with a specific feature of the invention, said lever may also operate on bimetallic strip 15 through the agency of a finger 34 serving as a returning member.

In the operative position shown in FIGURE 5, current flows in through terminal 35, passes through fixed and movable contact studs 4 and 3, then through bimetallic strip '15 and spring 6, reaches the switch points 32 via a connection 36 (shown as being external to enclosure 22 for greater clarity), and finally issues through terminal 37. If bimetallic strip 15 heats up excessively, due, say to a short-circuit, the circuit-breaker will trip by the process described in the case of the preceding form of embodiment, thereby opening the circuit (see FIGURE 6).

in order to reclose the circuit it is first necessary to depress operating lever 33 in order to rock it from its on position to its off position. The resulting downward movement of finger 34 exerts a thrust on bimetallic strip 15, causing the circuit-breaker assembly 6-15 to revert to the circuit-making position of contacts 3, 4 and the switch contact points 32 to open. All that is then necessary is to rock lever 33 back to the on position whereby to close contact points 32 and thereby close the circuit.

The constructional form shown in FIGURE 7 relates to a thermostat. In this case the bimetallic strip 15 is not crossed by electric current and thereby subjected to the Joule effect, but is instead merely subjected to the ambient temperature. In order precisely to avert any risk of heating by the Joule effect, which would impair the sensitivity of the thermostat, the lower prong 15a of the bimetallic strip is lined with a brass plate 38 which shorts out prong 15a, movable contact stud 3 being mounted directly on this brass plate and the flow path through hinge point 17 being likewise provided by said brass plate.

When contact studs 3, 4 are in their circuit-making position, current flows through one of the inputs 39, contact studs 3-4, brass plate 38, hinge point 17 and the other terminal 40. When the ambient temperature exceeds a predetermined threshold, the resulting warp in bimetallic strip 15 causes the contact studs to snap apart and the electric circuit to be broken.

The thermostat device hereinbefore described is supplemented by a rearming button 41 which is pivotally connected at 42 and operates on prong 15b of the bimetallic strip, and also by an adjustable stop 43 for modifying the operating threshold of the device.

What I claim is:

1. An electric snap-acting switch device of the abutting contact type comprising a fixed contact stud and a movable contact stud, the latter stud being movable in a plane through the former stud and substantially normal to contact engaging faces thereof, a switch actuating system for controlling said movable contact stud comprising a bimetallic strip having a hairpin shape with two prongs extending from a mutual junction portion to two end portions spaced from each other in said plane and movable therein toward and away from each other angularly about said junction portion upon temperature variations affecting said bimetallic strip, one of said prongs being adjacent said fixed contact stud and carrying said movable contact stud while the other prong is remote from said fixed contact stud, means for pivotally supporting said bimetallic strip at said junction portion thereof about an axis substantially perpendicular to said plane, an arcuate-shape leaf spring having a first end in hinged engagement with the end portion of said remote prong and a second end opposite said first end, and further means for pivotally supporting said leaf spring at said second end thereof about an axis substantially perpendicular to said plane, whereby said bimetallic strip is bodily movable in said plane and said prongs thereof are further individually movable in said plane with respect to each other.

2. Switch device as claimed in claim 1 further comprising a backing abutment member interposed between said spaced end portions of said bimetallic strip, whereby the force exerted by said leaf spring on the end portion of said remote prong is transmitted through said backing abutment member to said movable contact stud to press the same against said fixed contact stud.

3. Switch device as claimed in claim 2 wherein said backing abutment member is fast with the end portion of said adjacent prong carrying said movable contact stud and is freely engaged by the end portion of said remote prong.

4. Switch dbvice as claimed in claim 3 further comprising a stirrup-piece integral with said backing abutment member and spaced therefrom, the end portion of said remote prong, which is hingedly connected to said spring, being freely threaded through the space between said stirrup-piece and said backing abutment member.

5. Swtich device as claimed in claim 1 further comprising a terminal connected to said fixed contact stud, another terminal connected to said junction portion, and a plate of low electric resistance mate-rial coating the prong which carries said movable contact stud and extending between said movable contact stud and said junction portion, whereby said prong is electrically short-cireuited by said plate and is substantially free of Joule effect.

References Cited UNITED STATES PATENTS 2,191,588 2/1940 Sattler 200-116 2,508,637 3/ 1950 Bolesky 200-113 X 2,783,330 2/1957 Casey 200-116 2,952,758 9/1960 Ellenbereger 200-122 BERNARD A. GILHEANY, Primary Examiner. H. A. LEWITTER, Assistant Examiner.

Claims (1)

1. AN ELECTRIC SNAP-ACTING SWITCH DEVICE OF THE ABUTTING CONTACT TYPE COMPRISING A FIXED CONTACT STUB AND A MOVABLE CONTACT STUD, THE LATTER STUD BEING MOVABLE IN A PLANE THROUGH THE FORMER STUD AND SUBSTANTIALLY NORMAL TO CONTACT ENGAGING FACES THEREOF, A SWITCH ACTUATING SYSTEM FOR CONTROLLING SAID MOVABLE CONTACT STUD COMPRISING A BIMETALLIC STRIP HAVING A HAIRPIN SHAPE WITH TWO PRONGS EXTENDING FROM A MUTUAL JUNCTION PORTION TO TWO END PORTIONS SPACED FROM EACH OTHER IN SAID PLANE AND MOVABLE THEREIN TOWARD AND AWAY FROM EACH OTHER ANGULARLY ABOUT SAID JUNCTION PORTION UPON TEMPERATURE VARIATIONS AFFECTING SAID BIMETALLIC STRIP, ONE OF SAID PRONGS BEING ADJACENT SAID FIXED CONTACT STUD AND CARRYING SAID MOVABLE CONTACT STUD WHILE THE OTHER PRONG IS REMOTE FROM SAID FIXED CONTACT STUD, MEANS FOR PIVOTALLY SUPPORTING SAID BIMETALLIC STRIP AT SAID JUNCTION PORTION THEREOF ABOUT AN AXIS SUBSTANTIALLY PERPENDICULAR TO SAID PLANE, AN ARCUATE-SHAPE LEAF SPRING HAVING A FIRST END IN HINGED ENGAGEMENT WITH THE END PORTION OF SAID REMOTE PRONG AND A SECOND END OPPOSITE SAID FIRST END, AND FURTHER MEANS FOR PIVOTALLY SUPPORTING SAID LEAF SPRING AT SECOND END THEREOF ABOUT AN AXIS SUBSTANTIALLY PERPENDICULAR TO SAID PLANE, WHEREBY SAID BIMETALLIC STRIP IS BODILY MOVABLE IN SAID PLANE AND SAID PRONGS THEREOF ARE FURTHER INDIVIDUALLY MOVABLE IN SAID PLANE WITH RESPECT TO EACH OTHER.

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