US2647188A - Electrical switch contact means - Google Patents

Description

July 28, 1953 E. J. POITRAs 2,647,188

mamon. swrrcH CONTACT mms original Filed April 19, 1 946 INVEN TOR.

' makers and breakers.

Patented July 28, l 1953 ELECTRICAL SWITCH CONTACT MEANS Edward J. Poitras, Holliston, Mass.

Original application April 19, 1946, Serial No. 663,281. Divided and this application January 12, 1950, Serial No. 138,130

1 This invention relates tov electrical circuit More particularly it aims to improve the construction, arrangement and `operation of contact elements or means having general utility in connection with electrical Claims. (C1. 200-122) switches of various types and including especially those of the thermal responsive class.

certain embodiments of the invention:

Fig. 1 is a longitudinal sectional view of a switch embodying the contact means of the invention, the switch in this instance having a thermally responding actuator;

Fig. 2 is a generally similar view of a further embodiment of the invention including additional features which are applicable' also in connection with the embodiment of Fig. 1; and

Figs. 3 and 4 are respectively an enlarged and partly schematic bottom plan view of a portion of one of the contact leafs of Fig.' 2, and a wiring diagram pertaining to Fig` 2.

As above noted the invention here is particularly concerned with novel construction, arrangement and manner of operation for the contact elements proper, such as the pair `of leafs 30, 40 of Figs. 1 and 2 having electric contacts or buttons 3|, 4| respectively riveted or otherwise fastened in normal opposed relation atV or adjacent Athe leaf ends remote from the supportedf'ends. .These contacts proper 3l, 4I may be of silveror tively away from each other in the illustrated example; that is, the longer leaf 46 for example is biased downward, while theupper and shorter leaf 36 is oppositely spring biased against a reference element 52.

f In addition' to the properties of electrical conductivity, longitudinal rigidity and lateral spring bias for the respective leafs 30 and 40, and as a main feature of the present invention, the materials'thereof are also selected to provide a distinct expansion differential as between the two leafs, taking into account the coefficient of ex-l pansion of the ceramic or other insulating locator 23. The lower leaf 46 preferably has the higher expansion coeflicient.

The locator or precision mounting element23 is in the example of Fig. l fixed at the inner face of a cover 2B for the metallic case or body of the switch, designated generally at l and including a bottom 2 and a peripheral wall 3 defining a cavity or compartment 4 within which several operating parts are enclosed.

The leaf mounting element or locator 23 is of electrical insulating and heat resistant material, preferably a ceramic. This locator`23 is positioned and aligned on and relative to the cover 20 and hence also to the case l as by bosses 24 at the upper face of the locator 23 and fitted into apertures provided for the purpose on the cover 28. Further positioning of the locator 23 relative to the case body may be had by abutment with the adjacent end portion of the peripheral wall 3.

The inner or lower portionfof the locator 23 of the examples has two levels respectively presenting vertically spaced aligned longitudinal positioning'channels 25 and 26 for the pair of switch leafs 38 and 40. These extend length- Wise of the case in the portion of the cavity 4 above a button I4 of the actuator or bridge 5, again referred to later. The two leafs 30, 4D and the corresponding channels 25, 26 of the locator 23 are relatively proportioned in width and length for firm fitted reception of the corresponding ends of the leafs in the channels. The leafs 30, 40 are thus keyed against lateral swinging or misalignment and are further held against displacement by individual threaded studs 21, 2'8 headed at their lower ends and extending through apertures in the respective leafs and in the locator 23 centrally of the bosses 24 thereof. At the outside of the cover 2] the studs 21, 28 project through insulation 29 and are held by lock nuts 21a, 28a.. The projecting portions of the studs constitute terminals for connecting `electric conductors, being provided for the purpose with washers and hex nuts as at 2lb, 28fb. As above noted the switch leafs 36, 4i) are constrained frcm angular motion about their respective studs 2'1, 28 by reason of the channels 25, 26 of the locator, thus precluding them from inadvertent shorting or grounding against the sides of the case as might otherwise occur under the turning torque attendant on screwing down the hex nuts 2lb, 28h in attaching lead wires when installing the device. The studs 21, 28 rigidly hold -the locator 23 with respect to the cover 20 and hold the leafs 30, 40 in the channels of the locator. On assembly of the parts, with the cover held on the case end walls and abuttively between the side wall margins and with the case and cover interwelded as at 22 the entire enclosure and contained parts become in effect a unitarily rigid structure. Also as noted, the locator 23 is of a ceramic .or other insulating Imaterial preferably vadapted to 4withstand both high temperatures and high voltages.

The described construction of the leafs 30, 40 of materials selected to provide a distinct Qei(- pansion dierential as between the two leafs affords a differential weld-shearing v:action `for and at the contacts 3|, M This is .obtained through the novel structural .combinationas .illustrated and described, including the longitudinal stiffness of the contact-bearing leaf members 30 and 40 and the differential expansion provided for them through the use of metals having differ- ;ing .Icoeicients of expansion. v'Hence vwhen :the .switch heats up a relative movement of the contacts 3|, 4i takes place inthe direction lengthiwise of the leafs. This produces Va shearing motion'at the contact points and separates any J`weld that imay have occurred .between them. Such shearing `.motion is one of substantial force .asnapplied by Zt'hedifferent-ial change of length -of the longitudinally :sti leafs 3D, lll'l. Otherwise the only force to :break contact welds lwould fbe the spring force-of :the longer leaf 4D coming into lplay when Athe .button I4 the strut :5 withdrawsrom the leaf runder expansion of the case, andsuch spring fforce is generally inadequate to .insure separation of 'the contacts.

iin accordance-with the invention,xhowever, the differentially expanding leafs 3.0, :40, Vbeing sub- -stantia'lly straight and longitudinally rigid members, without ciset, exert va shearing force which :is fsubstantial Ieven for relatively ysmall temperature excursions above the setting. 4This shearing force `:is 'additive to -theespring .force lat 'the con- .tacts resultant from the initial spring :bias of the leaf 410 and insures a clean opening of the contacts, in :spite of welding at Vthe contacts. yThis markedly #contrasts 'with prior devices :in which the only `separat-ing force at the contacts is had by spring -gradient of the contact carrying strips, 4under which :relatively large 'temperature excursions above a set point may occur -without separative opening of the contacts. .weld-shearing Yaction at the :contacts lis indicated in Fig. 1 by the dotted lining representative of a :longitudinally :shifted Yas well as lowered position .of Ythe -under contact 4l As stated, the novel contact .elements 30, 3l `and 11D, 4I .having the self-shearing action by reason of the expansion differential as fbetween the 4respective leafs may be :employed fin .connec- =tion -with various actuating means of switches of vdifferent types. The actuator means here Villustrated fby -way of example comprises the bridge .or strut element :5 previously referred to and which is more fully described in my parent application above identified. It is sufficient here to Ynote .that the strut 5` comprises opposed levers or varms E united in lengthwise angular relation ,at a peak where the insulator button I4 is mounted, the strut arms having the Aopposite ends fixed flatwise upon the case rbottom -2. Adjacent the fixed ends and at the central lpeak the strut 5 has flexure hinges whereby rthe button vI4 vvreceives .transverse motion -as the angle at the central v.peak region of thestrut is increased or .decreased under differential thermal actionas between the strut 5 vand the bottom .2 of the case,

The Adescribed these parts being fabricated from materials chosen for a substantial differential in characteristic thermal expansion. In the examples of Figs. 1 and 2 the switches are illustrated in a form for circuit breaking on heating and with the peak of the strut 5 directed toward the contact leafs. For such .operative .arrangement the material of the strut '5 is selected `for a relatively low thermal expansion while the material of the case -I has a relatively higher expansion characteristie. Thus .in :the presence of a critical high temperature expansive lengthening of the case 'bottom s2, greater than that of the strut, tends to hinge the latter toward a flatter position and to move the peak 'button I4 toward the case bottom 2. VAs :explained :in the parent application, an inverse application of the actuator means may be'had, to provide a switch which normally is open and which is closed in response to a predetermined tempera-ture rise, either by reversing the relativeexpansibility of the strut and vthe case, making the strut of the more expansive material yand the :ca-se of a material of lower .expension coeflicient, or ythe -similar result may be .had 4by inverting the -strut itself. In the latter instance, with .the peak A,of the strut -5 pointed .downwardly heat-eiected motion -of the latter will be 1awa-y from the bottom 2 .of the case "when the latter is of the -expansible material. Or a reverse inverseaction of circuit-breaking in response to temperature lrise may be had byinterchanging the case Aand the strut materials lwith respect vto their expansibility, similarly -as in the instance of 4the `upwardly inclined strut as in Figs. 1 and 2.

Fig. 2 shows a further embodiment of the invention in which the ggeneral construction may :be lregarded as lsimilar "to that of Fig. -1. For illustration .the switch is here shown as of the normally closed type designed to break the cir- .cuit :on heating, as in Fig. 1, but it may be of .any of .the typesfpreviously mentioned. In this instance the case I-ib -is represented as fabri- .ca-ted from ysheet metal -stock shaped -to a lgen- .erally rectangular enclosure lform including up- -turned side walls, one of which lhas -end portions bent transversely Vto provide end walls 3y. Two mutually perpendicular walls, herein the bottom 2b and one of the side wallsare extended to form -mounting ears i e, le and I f, lf, `having mounting apertures I g. These latter, Aproviding :for either yside or 'bottom mounting of the switch device, desirably are elongated .for ease in .attachment and to allow for shift of the case lrela-- tive to 4the Isupporting means in the .course of thermal expansion and contraction. Similar integraler other mounting ears may .be provided -for .the Aswitch of 'the preceding figure.

In .the instance of :Fig 2, the switch Abody Aincluding the case Ib and the cover 20h .are Ylongitudinally proportioned to accommodate an additional and alternatively available terminal stud .60. The contact-bearing leafs 30, 40 and the ldisplacement-magnif-ying strut element 5b .are correspondingly proportioned. The third ter- .minal 60 of Fig. 2 provides for alternative electrical connection .of -certain auxiliary means providing the switch with either or 4both features .of a snap action and Iof -nn anticipatory' Aaction .compensating :for fprocess lag in the system or apparatus for circuit `control of which :the switch is to be employed.

Referring -still toFig. 2, .ieafs ASi). 40 .may be in all respects not `otherwise mentioned the same .as .in Fig. 1, `including J.the differential expansion germes capacity and resulting weld-shearing function as already described. One of the contact-carrying leafs, herein the upper and shorter leaf 30 carries an electro-magnetic device comprising an inverted U-shaped piece 65 of magnetic material at the inner face of this leaf and having the legs 69 extended toward the other leaf 40. A coil 6l' of fine insulated conductive wire is wrapped about the yoke of the magnetic U-piece 65 and also about the leaf 36 itself, the construction desirably being such that this entire electro-magnetic device may be adjustably shifted lengthwise of the leaf 39.

The number of turns and the resistance of the coil 61 is determined in accordance with the desired magnitude of two characteristics, namely the magnetic field desired and the heat-creating capacity desired from the coil as a resistive element. One end of the coil is fiexibly connected electrically to the leaf 30 as at 61a.. The other end of the coil is flexibly extended and connected as at Glb to the stud 60 as by anchorage and electrical union beneath the riveted end 60' thereof, the stud being insulated from the cover b as by extensions of the locator 23D and of the exterior insulation 29b. For A. C. installations to smooth the magnetic force fluctuation otherwise tending to cause chatter of the contacts 3|, 4|, the electromagnetic device 65 may be provided in known manner with shading rings 68 each encircling about a one-half portion of the respective leg 66 of the magnetic piece or core 65.

When the described electro-magnetic means is to be employed the connections for the circuit in which the switch is installed are made at the end terminal stud 28 and the auxiliary stud 60, with no connection at the terminal stud 21. Thus the coil 61 of the electro-magnetic device is placed in series with the switch contacts 3|, 4|, the circuit being through the stud 99, the coil 61, the leaf 30, the contacts 3|, 4| and the leaf 40 and Via it to the outer terminal stud 28.

In operation, with the contacts 3|, 4| closed, the coil 67 is energized. The resulting magnetic flux in piece 65 and the immediately adjacent portion of the opposite leaf 40, which in this instance also is of magnetic material, tends to maintain the contacts closed against force conditions acting in the separating direction. When the operative force condition overcomes the magnetic holding force sufiiciently to compel a break of the electric circuit the magnetic eld is destroyed. Consequently the previously magnetically held leaf 49 snaps open under the extreme force unbalance. Conversely, at the moment of establishment of the magnetic field upon circuitclosing engagement of the contacts 3|, 4| the supplemental magnetic holding force thereof tends to seal the electric circuit. Thus as illustrated in Fig. 2 a snap action is afforded in a thermostat having capacity for temperature differential as to the selective temperature setting. Further, through the described electro-magnetic means and herein by utilizing one and the same coil 6l a pre-heating lag-compensating anticipatory effect is had. During the period of contact closure and magnetic field energization the current passing through the coil 6l causes resistance heating within the thermostat case and effective upon the latter and the strut 5. The result is an effect known in other connections in this general art as antcipation, that is, an operative preparation of the thermostat 6. to take into account a time lag in the associ'- ated system or apparatus. Further, by shifting the position of the electro-magnetic means 65--68 lengthwise of the leafs 30, 40 the thermal differential action is modified, as a function of the position of the magnetic circuit along the contact leafs.

My invention is not limited to the particular embodiments thereof illustrated and described herein, and I set forth its scope in my following claims:

I claim:

1. An electrical switch having in combination with an insulating support a pair of electrical contact-carrying metallic leafs of longitudinal columnar rigidity, said leafs relatively movable laterally to and from each other to close and to open the contacts, actuating means external to the leafs controlling said leaf movement, said leafs respectively being of such markedly different thermal expansibility as to effect a shearing action between the contacts under heat change at and commonly ambient alike to both leafs.

2. In a thermostatic switch, electrical contactcarrying spring metallic leafs relatively movable to and from each other to close and to open the contacts, thermal-responsive means for effecting said leaf movement, one leaf having a portion of magnetic material, the other leaf carrying opposite said portion a dual function electro-magnetic element including a magnetic core piece and a surrounding coil connected to energize the electro-magnetic element when the contacts are closed thereby to afford a holding action and also a resistance heating action modifying the operational temperature status at the thermostatic switch.

3. An electrical switch having in combination with an insulating support a pair of electrical contact-carrying metallic leafs of longitudinal columnar rigidity, the leafs respectively of such different thermal expansibility as t0 effect under heat change thereat a shearing action between the contacts, and electro-magnetic holding means on and in series connection with the leafs and correlated with said shearing action.

4. An electrical switch according to claim 3 wherein the electro-magnetic means is variably positionable lengthwise the leafs for adjusting the effective extent of the shearing action.

5. An electrical switch according to claim 3 wherein the electro-magnetic means includes a coil which is also constituted as a heater element.

EDWARD J. POITRAS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 666,764 Lindstrom Jan. 29, 1901 1,651,408 Peacock Dec. 6, 1927 1,978,065 Twombly Oct. 23, 1934 2,242,971 Glennon May 20, 1941 2,286,375 Ray June 16, 1942 2,334,897 Baker Nov. 23, 1943 2,389,686 Reingruber et al. Nov. 27, 1945 2,444,745 Mosley July 6, 1948 2,492,023 Whittaker Dec. 20, 1949 2,496,917 Poitras Feb. 7, 1950 FOREIGN PATENTS Number Country Date 214,325 Great Britain Apr. 17, 1924

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