US2834854A - Temperature responsive spring actuated switch for electrical heating devices - Google Patents

Description

May 13, 1958 T. H. sTlEBEL ET AL 2,834,854

TEMPERATURE RESPONSIVE SPRING ACTUATED SWITCH FOR ELECTRICAL HEATING DEVICES A7' TORNEV May 13, 1958 TEMPERATURE RESPONSIVE SPRING ACTUATED SWITCH FOR Filed July 25, 1956 T. H. sTlEBl-:L ET Aa. 2,834,854

ATTORNEY May 13, 1958 T. H. STIEBEL ET AL 2,834,854

TEMPERATURE RESPONSIVE SPRING ACTUATED SWITCH FOR ELECTRICAL HEATING DEVICES Filed July 25, 1956 4 Sheets-Sheet 5 A r TORNEY May 13, 1958 T. H. sTlEBEL ET AL 2,834,854

TEMPERATURE RESPONSIVE SPRING ACTUATED SWITCH FOR ELECTRICAL HEATING DEVICES Filed July 25, 1956 4 Sheets-Sheet 4 F IG. /0

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:im hl-mw 6l L I H||IIIIHITHIHI6J sua s, a6- 78 az 6r zm/ l lwHIimlllum/ orro msu/vaak /WENTS rfv/500m? H. sr/EBEL United States Patent TEMPERATURERESPONSIVE SPRING ACTUAT ED SWITCH FOR ELECTRICAL HEATING DEVICES Theodor H. Stiebel and Otto I. Irslinger, Holzminden (Weser), Germany Application July 25, 1956, Serial No. 600,051

Claims priority, application Germany July 29, 1955 12 Claims. (Cl. 200--140) The instant invention relates to spring actuated switches for connecting and disconnecting a source of electric power to .and from electrical heating devices of which the actuation is initiated yby a temperature or pressure responsive element on reaching a predetermined temperature.

An object of our invention is to provide a spring actuated switch in which the movement of a temperature or pressure responsive element with increasing temperature or ypressure produces increased tension in initially tensioned and elastically deformed plate springs, of which springs the tension yon reaching a maximum magnitude corresponding to the predetermined temperature initiates va quick restoration of the spring tension to its initial value accompanied by the movement of at least'one switch eleyment to open the line supply circuit.

Another object of our invention is to provide a spring actuated switch in which, as contrasted to prior art spring switches, the pressure between the engaged switch contacts increases as the switch elements move toward the switch opening position, and of which the engaged line closing contacts are opened positively and suddenly at high speed with minimum Wear on the contacts due to heating and pitting by electric arcing.

Still another object of our invention is to provide a spring switch -for which, while the effective throw of the switch is increased, the spatial requirements are a minimum, and the switch assembly requires a minimum of parts all relatively simple in structure.

We accomplish the foregoing, and other obvious, objects by providing at least two prebiased plate springs which each are resiliently sprung by supporting their ends between two spaced support points movable relative to each other under the action of a temperature or pressure responsive element, such as a piston or plunger. in a first embodiment, the two plate springs have each a supporting point for one end at substantially the same distance from the, for example vertical, center line of a movable cradle and in the same horizontal plane, while the other supporting point of each is in an arm of a bridge of insulating material on the upper yface of which is the conductive `plate for closing the line circuit. In the line circuit closing position, the spring supporting points in the bridge are positioned in a plane parallel to and above the plane of the spring support points in the cradle, The bridge arms are of such length that in the circuit closing position they are at a predetermined distance from the bottom of the housing enclosing the switch. The springs preferably cross each other as installed so that the cradle support point of each spring is to the opposite side of the center line relative to its bridge support point, with each spring of such, and like, shape as not to interfere with any movement of the other vertically. The cradle is so dimensioned that it can freely move into the recess between the bridge arms, that is, each bridge spring support point is further from the center line than its cooperating cradle spring support point. It follows that 2,834,854 `Patented May 13, .1958

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' 2 since each spring is sprung betweenits support points and thus flexed under tension therebetween, each spring is of a length exceeding the distance between itsvsupport points with .the bridge and cradle spaced furthest from each other in each the circuit closing and circuit opening positions. The distance along the center line between the lower .faces of the ixed terminals of the line circuit, which project through the cover of the switch housing, and the bottom of the housing against which v the base of the cradle is pressed in the circuit closing position of the switch, is such -that alike in the circuit opening and closing positions, both plate springs have la residual tension, an appropriately positioned stop being provided to limit the distance the cradle can move under spring tension oncircuit opening. In the circuit closing position the base of the cradle, with increasing pressure or temperature, -is engaged by the temperature or pressure responsive element to move the cradle, and the cradle spring support points, toward the bridge and the plane of the bridge spring support points. Thus the tension of the springs is increased in accordance with the increase in temperature to which the heat responsive element is subjected, -and the contact plate carried by the bridge is forced with increasing pressure against the fixed contacts' of the line terminals. Whenthe cradle spring support points reach the plane of the bridge spring support points, each spring is at its maximum tension. Just beyond such coplanar position of the supports points, the cradle under the increased tension of the springs quickly-moves away from the heat responsive element, in the same direction as it moved due to the pushing action of the heat responsive element, to engage the appropriately positioned stop. Simultaneously the bridge ends of the plate springs move the bridge in the opposite direction until the bridge arms r engage the `bottom of the housing, thus disengaging the conductive plate carried by the bridge from the fixed line terminals and opening the circuit. Thus the increased spring tension is dissipated in the movement of the cradle and the bridge, and the electric circuit opened instantaneously at high speed. To restore the switch to the circuit closing position, we provide a rod connected to the cradle and extending through the housing cover by which, with the temperature responsive element having suiciently cooled to be withdrawn to at or below the housing bottom, the cradle may be pushed against the tension of the plate springs to engage the housing bottom simultaneously moving the bridge toward the housing cover to engage the conductive plate to the line terminals. Obviously the temperature at which the switch opens may be adjusted by appropriately varying the bias of the plate springs, for example by changing the distance between the spring support points in the direction of the relative ymovement of the cradle and bridge. To have the switch ofy this embodiment function as a controller, that is, asa device -for automatically reclosing the switchafter it has opened and repeating this cycle of opening and closing the circuit, the push rod may be replaced by a tension spring braced between the housing cover and the cradle. In such modification, as the heat responsive element cools after the line circuit has been opened, the cradle follows the withdrawing movement ofthe element and ultimately will reclose the switch and circuit when the heat responsive element has sutciently withdrawn.

In. a second embodiment of our invention which we deem preferable for higher current magnitudes and for polyphase systems, we use `a pair vof plate springs which are not mutually crossed and of each of which the supporting points for both its kends are to the same side of the vertical center line. A dat carrier plate, preferably of rectangular or hexagonal shape, has a spring supporting groove in each of two opposite end surfaces and is -carried by a rod positioned centrally of the housing and guided in the cover thereof for movement substantially aligned with the pressure or temperature responsive element. A disc of insulating material has resiliently mount ed thereon a plurality of conductive plates, each of which is capable of engagement with one pair of a plurality of pairs of fixed terminals in the line supply circuit and extending through the cover of the housing, in the circuit closing position of this embodiment of the switch. A plurality of notches spaced about the periphery of the disc engage with guide members integral with the housing wall so that the disc may slide therealong without undesired tilting or inclination between the ends of the guides, the ends being appropriately spaced from each other and constituting stops in each direction of disc movement. One of a pair of plate springs is sprung between one of the edge spring supporting grooves of the carrier plate and a spring support point in a bracket spaced from the vertical center line such that in the circuit closing position of the disc, this bracket spring support point lies in f a plane above that in which the carrier plate support point lies. The other of the pair of plate springs is tensioned between the -other edge spring support groove of the carrier plate and a spring support point in a formed lever. The formed lever is pivoted at the end thereof remote from the center line and diametrically to the opposite side of the center line relative to the bracket, and its free end extends upwardly and inwardly so that at all times a portion thereof bears against the lower face of the disc. The spring support point in the formed lever is closely adjacent to the pivot pin of the lever and is coplanar with the bracket support point for the other plate spring, lying above the carrier plate spring support groove in the circuit closing position. It thus is apparent that in such circuit closing position the free end region of the formed lever is biased to its uppermost position resiliently against the disc, the disc in turn being resiliently pressedv against the lever by a tension spring braced between the housing cover and thecentral region of the disc.

The operation ofthe second embodiment is similar to that of the rst in that, as the temperature responsive element with increasing temperature, pushes the carrier plate ahead of it, the spring supports increasingly tension both plate springs until the maximum deection and tension is reached when all four spring support points are in the same plane. On passing beyond this coplanar phase, the carrier plate under the releasing tension of both plate springs is quickly moved upwardly in the same direction it has been moving while simultaneously the tension of the plate spring having its one end supported in the lever support point exerts a force in the opposite direction, quickly moving the free end region of the lever quickly moving downward the distance determined by the guides engaged by the disc notches as the force of the tension spring braced between the housing cover and the disc become effective against the disc. To vary the temperature at which the instant switch embodiment opens, the lower portion of the rod supporting and carrying the carrier plate is preferably threaded, and the rod screwed further or less far into the carrier plate thus varying `accordingly the distance the carrier plate spring support grooves must move to become coplanar with the bracket and formed lever spring support points. To enable manual restoration of the instant switch to its line closing position, the rod on which the carrier plate is supported extends through the cover, and is pressed downwardly as in the case of the rst embodiment. By the simple expedient of interconnecting the carrier plate and the temperature `responsive element this embodiment can likewise be converted into a controller switch.

The various objects and features of our invention will be better understood from the following more detailed description taken in conjunction with the accompanying drawing, in which:

Figure 1 shows the rst embodiment of the switch mechanism of our instant invention with the switch housing partially broken away, the switch elements being in the circuit closing position;

Figure 2 is a section along line 2-2 of Figure l;

Figure 3 is a section along line 3--3 of Figure l;

Figure 4 is a simpliiied showing of the active switch elements of Figure l in the position just before the plate springs open the heating circuit;

Figure 5 is a simplified showing of such active elements of Figure l in the position they assume immediately after passing just beyond the position shown in Figure 4;

Figure 6 is a modification of the first illustrative embodiment of Figures l through 5 to constitute the mecha nism an automatically rreclosing switch when the temperature of the heating enclosure drops to a predetermined lower temperature;

Figure 7 shows the second illustrative embodiment for simultaneously disconnecting a plurality of pairs of line terminals, for example three pairs of a three-'phase line supply, in elevation with the switch housing partially broken away and the active switch elements in the circuit closing position just at, and for some time after, closure;

Figure 8 is Figure 7 rotated 90 about its vertical axis;

Figure 9 is a top view of the second illustrative embodiment, and

Figures 10 and ll are highly simplified schematics of the active switch elements just before the circuit is opened and immediately after circuit opening, respectively.

Referring to the drawing and more particularly to Figures 1 through 5 showing the first illustrative embodiment of the switch mechanism of our instant invention, the switch housing 1 has a fitted bottom 2 having an integral externally threaded projection 3 of a smaller diameter, which in turn has a probe 4 of still smaller diameter and relatively long, extending therefrom into the enclosure heated by the heating device and into the wall of which the projection 3 is tightly screwed. The interior of the hollow probe 4, which is closed at its free end, houses a material free to move relative to the probe and having a temperature coefficient of expansion greater than the material of the probe, which first mentioned material moves a plunger 5 in response to the temperature of the probe upwardly and through a centrally disposed aperture in a formed recess 7 of the housing bottom 2 with increasing probe temperature and downwardly (Figure l) with decreasing probe temperature.

The recessed portion 7 is formed to receive the base 8 of a channel or cradle member 9 in which one end of each of the two crossed plate springs 10 and 1l is pivotally braced, the other end of each spring being supported in a ceramic, electrically non-conductive, bridge 12 movable relative to the cradle or channel 9. The bridge i2 stradclles the channel 9 lengthwise and has a pair of depending end arms, 13 and 14, which are partially overlapped by the end regions of the spaced lengthwise anges, 15 and 16, of channel 9 thus to act as guides for the channel and arms. The upper face of the ceramic bridge carries a conductive strip 17, which in the line to heating element circuit closing position as in Figure l, interconnects the terminals i8 and 19 extending through the top of switch housing i, for example. Each of the springs 10, il, which preferably are of the same contiguration for manufacturing and assembly reasons, has a narrow tongue portion 2t), a wider central body portion 2, and a forked portion 22 at its other end region, the tongue 20 being of such width as to readily pass through the gap of the forked portion 22, and each tongue 20 and the forks of the forked portion 22 being of such length that neither will interfere with the other when the two springs, with their central portions substantially superimposed, have the tongue of each flexed through the forked portion of the other (Figure 3). Each tongue 20 at its free end has a pair of spaced longitudinal projections, 23 and s 24, adapted to be engaged into the grooves, 25 and'26, in the lateral faces of the ` bridge end arms 13 and 14 and pivotally supporting the other end of each spring and 11. Each such spring is of a length that it at all times remains ilexed and bowed intermediate its end support points. The grooves and 26 are somewhat wider than the thickness of the material of sheet metal springs 10 and 11 at the inner surface of each bridge arm, thus allowing the projections slight upward and downward movement within the grooves as the springs 10 and 11 move from a curvature resulting from a given initial tension to that produced by a maximum tension and back to that of the initial tension as the bridge and cradle are moved in relative opposite directions, as below explained. The forked portion 22 of each spring has an integral, laterally outwardly extending projection, 27 and 28, on each fork adapted to be pivotally engaged in the, preferably triangular shaped, apertures 29 and 30, respectively 29 and 30', through the flanges 16 and 15 of the cradle 9. The apertures 29 and 30', while of the same basic triangular shape as apertures 29 and 30 transversely aligned therewith, are open to the top of flange 15, away from the angle against which the projection 27 of the respective springs is braced kon assembly thereof with the cradle, thus facilitating such assembly. Each lateral pair of apertures 29, 29 and 30, 30f is spaced equally from the vertical center line of the bridge 12, which spacing is obviously less than the spacing therefrom of the grooves 25, 26 in the bridge arms 1,3, 14. The position vertically (in Figure 1) of the apertures 29, 3G, 29', 30 in the cradle flanges is such that with the switch just connected to close the circuit, these pivotally bracing spring apertures lie in a horizontal plane below that in which the grooves 25 and 26 hold the other ends of the springs and braced by the tongue ends against the inner surfaces of the respective bridge arms, 13, 14. The body portion 21 of each spring 10, 11 has an elongated aperture therethrough of such diameter that even on relative displacement of the superimposed crossed springs while flexing, such displacement is not interfered with by a formed restoring rod 32 which extends from the channel base 8 through the springs 10, 11, through the bridge 12 and conductive plate 17, and through a projection 33 on the cover. The rod 32 is biased downwardly toward the cradle base 8 by a helical spring 34 about it and braced between a shoulder on it and a shoulder in the bore through the projection 33.

Each of the cradle flanges 15, 16 has integral with, for example the central portion of its upper face, a lateral projection 35, 36 forked at its free end. Each forked free end of such projection 35, 36 straddles a guide rod 37, 38 between a lower stop surface 39 and an upper stop surface 40. The guide rods 37, 3S simultaneously affix the fitted bottom 2 to switch housing 1 by any known means, such as4 threaded end portions with nuts screwed down to clamp the housing and the fitted bottom to the rods. The pair of lower stop surfaces 39 are so positioned that when engaged by the projections 35, 36 the cradle base 8 rests in the recessed portion '7 ofthe housing bottom 2, while the upper stop surfaces 40 are so positioned that the springs 10 and 11, in the contact opening position of the switch, cannot move the cradle 9 upward after the lower surfaces of the bridge arms 13, 14 have engaged the housing bottom 2 to have the cradle push the bridge upwardly beyond stops 40 thus re-engaging the plate 17 with the contacts 18 and 19. Thus the lower stops limit the throw of the cradle downward, the plate 17 engaging the line terminals 18 and 19 and the bridge being spaced from housing bottom 2, while the upper stops limit the throw of the cradle upward, the plate 17 having disengaged from line contacts 18 and 19 and the bridge resting on housing bottom 2.

The switching mechanism having been positioned as shown in Figure 1 to the circuit closing position, by depressing tne upper end of rod 32 extending ab'ove the housing projection 33 thus engaging the conductive plate 17 with the line contacts 18 19, the temperature or' pressure responsive plunger 5 is just below, or at most in contact with, the cradle base 8 as the cradle rests on the recessed portion 7 of the housing bottom. Current thus flows through the heating element, not shown, and as the region about the probe 4 is heated, the heat responsive material within the probe expands and moves the plunger 5 correspondingly upward. It will be noted that throughout the circuit closing position the lower faces of the bridge arms 13, 14 are spaced from the housing bottom 2, while the cradle base 8 rests on the recessed portion 7 thereof initially and only so long' as the plunger 5 does not move it upwardly ahead of the plunger. The projections 27, 28 of each plate spring 10, 11 are vertically below the projections 23, 24 of the tongue free end of each, one of the springs, for example spring 10, beingftensioned so as to curve convexly upward between its bracing points 29, 29' in the cradle and those, the groves 25, 26, in the bridge arm 14, while the other spring 11 is tensioned to be flexed downwardly between its bridge end support grooves in arm 13 and its cradle supports points 30, 30. 'Ihat is, the cradle and bridge would, in the absence of the stops provided by the bottom recessed portion 7 and the stop surfaces 39 for the cradle and those provided by fixed terminals 18, 19 for the conductive plate 17 on the bridge, tend to move completely away from each other until both springs were completely unilexed and without tension. The just named stop elements being spatially predetermined fixed points to stop movement of the bridge and cradle before the springs 10, 11 become untensioned, both springs remain flexed and under residual tension.

As the temperature communicated to the probe increases, the plunger 5 moves increasingly upwardly, and the corresponding upward movement of the cradle increasingly tensions and flexes the springs 10, 11 until such time as the spring end support points 29, 29', 30, 30 in the cradle are in the same horizontal plane as the support grooves 25, 26 in both bridge arms 13, 14, as is shown in Figure 4. In this position, the springs 10, 11 are flexed a maximum and hence their tension is at a maximum. As follows from the detailed description of the shapes and dimensioning of the springs, each spring freely moves to this increased curved or iiexed position without inter- Y ference from the other due to the length of both tongues 20 and of both forks of the forked ends 22 and the tongues being of less width than are the gaps between the forks of the forked ends 22.

Now when the temperature of the probe increases slightly more, which temperature is readily predetermined to be any desired value for a particular switch, the tern- .perature responsive plunger 5 moves the cradle 9 up a slight additional amount so that the pivot and support points 29, 29', 30, 30 in the cradle are above the support grooves 25, 26 of each spring in the bridge arms 13, 14 and the vertically directed components of the spring tension at the grooves 25, 26 are now directed downwardly. Since the bridge is free to move downwardly, due to the gap heretofore between its arms 13, 14 and housing bottom 2, the bridge is quickly and suddenly propelled downwardly against the housing bottom, thus moving the conductive plate downwardly with it and breaking the engagement between the plate and the line contacts 18, 19 and opening the circuit. Simultaneously, as the result of the spring tension component at the knife edge support and pivot points of the springs at their other ends, namely at cradle apertures 29, 29', 30, 30', now being directly upward, the cradle 9 continues its upward travel but now under releasing tension of the springs and moves quickly and suddenly upward until the forked ends of the projections 35, 36 strike against the upper stops 40 on thel guide rods 37, 38. Again, if it were not for the stop provided for the bridge by the housing bottom 2, and that for the cradle by surfaces `40, the bridge and the i cradle would separate from each other until the springs 10, 11 were completely unflexed and without tension. The distances to the respective stops are, however, so predetermined that in the circuit opening position the springs 10, 11 remain under a residual tension. It is to be noted that with the above described construction neither the application of the motion producino force from the ternperature responsive plunger in a direction other than perpendicular to the cradle base 3 nor apossible unequal elasticity in the springs 10, 11, will adversely aifect the -switching operation of the instant embodiment-it will always be sudden and quick and positive.

The circuit having been opened, the restoring rod 32 was carried up by the cradle base and, against the tension of its coiled spring 34, the rod has moved its upper end, which preferably is flush with the top of projection 33 while the circuit is closed, up beyond the projection. By pressing the projecting rod end down into the projection manually, the lower end of the rod forces the cradle 9 downward, and reversing the disconnecting operation just described, the lower face of the ceramic bridge arms remains resiliently pressed against the housing bottom 2 until the support points 29, 29', 3), 30 are moved to a plane below that then occupied by the bridge spring support grooves 25, 26. Now the spring tension moves the arms and the bridge suddenly and quickly upward, engaging the conductive plate 17 to the line contacts 18, 19, while the cradle is propelled downward suddenly and quickly until it strikes the recessed bottom position 7, providing of course that the plunger 5 has receded and moved down sufficiently on the cooling of the probe and the thermally expansive material therein contained.

In Figure 6 there is shown a modification of the first illustrative embodiment which will function as a temperature controller. A pair of compression springs, 41 and 42, are braced between the cradle projections 35, 36 and the housing cover, tending at all times to press the cradle down against the movable temperature responsive plunger 5. Obviously, the cradle base 8 will thus at all times rest against the upper surface of the plunger. The tension of springs 4t), 41 is such as not to interfere with the above described disconnect operation, but is sucient to cause the cradle to follow the downward movement of the plunger as the heat expansible material within the probe 4 contracts on cooling. Thus without manually pushing the rod 32 down, the above described circuit closing operation will take place at such times, and each time, the cradle spring support points of the springs 10, 11 are again moved by the springs 41, 42 to a plane below that then occupied by the bridge spring support grooves thereof, as the cradle follows the plunger to its low, and circuit closing, position. Hence the contents of the electrically heated enclosure or vessel are automatically maintained at a desired temperature above room temperature without any manual attendance.

Referring now to Figures 7 through ll showing our second illustrative embodiment, the tted housing bottom 2 with its integral and external threaded projection 3, the long integral probe 4, the movable plunger 5 entering the recessed housing bottom 7 through central aperture 6 under the control of the heat expansible material in the probe, are as in the lirst embodiment. Housing Sil, of electrical insulating material, is essentially a cylinder closed at its top 51 and open at its base to receive the tted bottom 2, and has a plurality of radially inwardly extending guide ribs 52, integral with the top and the cylindrical wall of the housing and enclosing the bolts 53 by which the tted bottom 2 is aixed to the housing. In Figures 7 through 9, the housing has three ribs 52 equally spaced from each other, and a pair of terminals 54, 55 and 56, 57 and 53, 59 extends through the cover between the successive ribs, each pair of terminals being engageable in the circuit closing position with an electrically conductive plate 60, 61, 62 spring mounted on a disc 63 of insulating material. The disc 63 has a plurality of notches into which the guide ribs 52 extend, and an integral upward projection 64 of insulating material be tween each of the spring mounted plates 60, 61, 62 prevents any vibration of the mounting springs from accidentally causing contact between adjacent conductive plates. To prevent accidental electrical contact between the terminals of a pair on the exterior of the housing cover 51 it is provided with a relatively thin integral radial rib 65 between the terminals of each pair, and to prevent such contact between terminals of different pairs, an outwardly flaring rib 66 between successive terminal pairs.

The disc 63 is provided with a central aperture 67 through which extends a rod 68 of electrical insulating material about the upper portion of which there is a coiled spring 69 biased against the cover 51 and the disc 63 tending to displace the disc 63 downwardly. The upper portion of the rod 68 extending through the projection 70 integral with the cover 51, is preferably of a hexagonal or square cross-section, and is held against rotation in a correspondingly shaped aperture 71 through a ring 72 threaded into the projection 70. The lower end region 73 of the rod 63 is threaded and has screwed thereon a carrier plate 74 having at least one pair of parallel sides each having a knife- edge groove 75, 76 therein. The vertical position of the carrier plate 74 on the threaded lower rod portion 73 may be varied, thus regulating the temperature at which the switch will open the heating circuit, but is generally quite close to the fitted housing bottom 2 in the circuit closing position. A formed bracket 77 supported in the central recessed portion 7 of the housing bottom has a knife-edge groove 73 positioned above, in such circuit closing position as shown in Figure 7, the plane of the grooves 75, 76 in the carrier plate, and a plate spring 79 is tensioned between the grooves 76 and 78 so that, for example, it is tlexed with a curvature convex upward. A second arm 80 of the bracket 77 and diametrically opposite the arm having groove 78, has pivoted thereto at the end thereof remote from the central aperture 6 through the housing bottom, a formed lever 81 which has a knife-edge support 82 near such pivoted end. The support 82, in the circuit closing position, is above the grooves 75, 76 in the carrier plate 74 about the same distance as is the groove 78 above the grooves 75, 76, the grooves 75, 76 being in the same horizontal plane. The lever 81 has an aperture 83, relatively elongated lengthwise thereof, through its upper and curved free end region, the threaded portion 73 of the rod 68 passing therethrough. Thus the rod 68 with its threaded end 73 does not interfere with the movements of the lever 81 under the tension of the plate spring 84 which is sprung between the grooves 75 and 82 to flex it with a curvature convex downward, for example. At all times then, the lever 81 has its free end region resiliently pressed against the disc 63. At right angles to the bracket 77 and its arm 80,` is positioned a pair of angle members of which the upper faces 86 of the upright arms thereof are in the path of downward movement of the disc 63, limiting such downward movement to a predetermined distance to assure that both plate springs 79 and 84 remain under tension when the present embodiment is in the circuit opening position. Similarly the distance the disc may move upwardly is predetermined by appropriate positioning of the lower ends of xed terminal pairs 54, 55 and 56, 57 and 58, 59 so that on circuit closure the conductive plates 60, 61, 62 and hence disc 63 can only move such a distance that the springs 79, 84 likewise remain under a residual tension. The operation of the second embodiment in opening thev circuit after manual closure is in general similar to that of the iirst embodiment, with the exception that the disc 63 is not propelled downwardly directly by the plate springs 79 and S4, as is the bridge 12 of the first embodiment by the releasing of the maximum tension of its plate springs 10, 11, but by the action of spring 69. In brief, in the second embodiment with the plunger 5 9 moving upward with increasing heat, the spring ends in support points 75 and 76 in the carrier plate 74 are moved upwardly by the plunger to reach the position shown in Figure 10 in which each end of both springs 79, 84 is in the same horizontal plane and both springs are at maximum exure and maximum tension. On the slightest further upward push of the plate 74 by the plunger 5, the springs 79, 84 tend to unflex and untension and as, relative to the spring 79 only its end in the groove 76 is free to move, the carrier plate 74 is quickly snapped upwardly in the relief of the maximum tension of spring 79. With the carrier plate 74 so moving, the groove 75 obviously carries its end of the spring 84 upward also, and the opposite end of the spring 84 in the groove 82 presses downward to pivot the lever 81 clockwise about the pivot 80. The free endof the lever 81 thus moves down, permitting the spring 69 to push the disc 63 down a distance sufficient to break the engagement between the terminals 54, 55 and 56, 57 and 58, 59 and the conductive plates 60, 61, 62 respectively, as shown in Figure l1, and against the stop surfaces 86. To close the circuit, the rod 68, like rod 32 of the first embodiment, is pressed down manually to move the plate 74 down against the springs 79, 84 of which the tension again reaches a maximum when all the spring end supports are coplanar and then unflex to force the plate 74 down as far as possible and the free end of the lever 81 upwardly carrying the disc 63 to the circuit closing position. Obviously the temperature at which the spring support points will be coplanar, that is the temperature at which the second embodiment will open the circuit, may be adjusted by threading the carrier plate 74 higher or lower on the threaded portion 73 of rod 68. To convert the second embodiment into a controller of the type shown in Figure 6 in respect ofthe first embodiment, the threaded rod end 73 or the plate 74 is connected to the adjacent end of the,

plunger 5.

It is to be expressly understood that the embodiments and the modifications thereof which we have described in detail are by way of illustration only and in no manner limitative. Various modifications will suggest themselves to the worker in the art without departing from the spirit and scope of the instant invention.

What we claim is:

1. A switching mechanism for lines supplying electrical energy to heat an enclosure comprising a movable element responsive to the temperature of the enclosure, at least one fixed terminal in the line, a first and a second switch element, at least one movable terminal on the first switch element engageable to the fixed terminal to close the line circuit, a first stop limiting the motion of each switch element in the direction away from the fixed terminal, a pair of prebiased plate springs having one end of each spring pivotally supported in the second switch element, a second stop, a pair of supports for the other ends of the plate springs positioned above the second switch element in the line closing position of the mechanism, the second switch element being moved toward the first switch element by the heat responsive element with increasing temperature to position such one ends of the springs coplanar with the other ends of the springs and slightly therebeyond and being rapidly propelled in such direction thereafter by the plate springs to engage the second stop, the first switch element simultaneously with the spring propelled movement of the second switch element moving in the opposite direction by the plate springs to disengage the movable terminal from the fixed line terminal until it engages the first stop, and means connected to the second switch element to restore the first and second switch elements to the circuit closing position.

2. A switching mechanism according to claim 1 in which the distance between the first and second stops is Cil so predetermined that with the first switch element against the first stop and the second switch element against the second stop, the springs of the pair are flexed and tensioned.

3. A switching mechanism according to claim 2 in which the distance between the first and second stops is so predetermined that with the movable terminal engaging the fixed line terminal and the second switch element against the first stop, the springs of the pair are exed and tensioned.

4. A switching mechanism according to claim 1 in which the first switch element is a bridge of ceramic electrical insulating material having a pair of arms depending from its ends, the second switch element is a cradle positionable between the bridge arms, said one ends of the springs being pivotally supported in the cradle, and the supports for said other ends of the springs are in the bridge arms, respectively.

5. A switching mechanism according to claim 4 in which a third spring at all times biases the cradle against the movable temperature responsive element.

6. A switching mechanism according to claim 4 in Awhich the prebiased springs of the pair are superimposed on and cross each other, and are pretensioned to bulge in opposite directions.

7. A switching mechanism according to claim 6 in which the means to restore the switch elements to the line closing position is a rod movable along its own axis and connected to the second switch element, the rod being manually operable in the direction opposite to that of the motion of the heat responsive element with increasing temperature.

8. A switching mechanism according to claim 6 in which the means to restore the switch elements to the line closing position is a third spring biasing the second switch element at all times in the direction opposite to that of the motion of the heat responsive element with increasing temperature.

9. A switching mechanism according to claim 1 in which the first switch element is a. disc of electrical insulating material, the second switch element is a flat carrier plate supported on a rod, which rod constitutes the switch element restoration means, the said one ends of the springs are pivotally supported in the carrier plate, the support for the said other end of the one spring is a spatially fixed point, the support for the said other end of the other spring is in a pivoted lever, and a third spring resiliently urges the disc in the direction opposite to that of the motion of the temperature responsive movable element with increasing temperature.

l0. A switching mechanism according to claim 9 in which the pivoted lever has its free end resiliently bearing against the disc, and the lever free end on the propelling movement of the carrier plate is propelled away from the disc, and the disc is simultaneously moved by the third spring in the direction of the free end lever movement.

1l. A switching mechanism according to claim 10 in which the end of the rod carrying the carrier plate is threaded to enable variation in the position of the carrier plate along the rod to adjust the temperature at which the temperature responsive element initiates the spring propelled motion of the second switch element.

12. A switching element according to claim 10 in which the temperature responsive movable element is a plunger, and the end of the rod supporting the carrier plate is connected directly to the plunger.

References Cited in the file of this patent UNITED STATES PATENTS 2,639,352 Watson May 19, 1953 2,666,108 Brown Jan. 12, 1954 2,691,084 Miller Oct. 5, 1954

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