US2278990A - Thermal switch - Google Patents

Description

April '1, 1942.

c l. HALL THERMAL SWITCH Filed Oct. 21, 1941 1 liq vv z Inventor: Ch e stew" I. H 8| His Attorn ey.

Illlllll" lgwunnlq l Patented Apr. 7, 1942 THERMAL SWITCH Chesterl. Hall, Bexford, N. Y., assignor to General Electric Company, a corporation of New York Application October 21, 1941, Serial No. 415,929

' (c1. Mil-122) K Claims.

My invention relates to thermal switches and particularly to manually or automaticallyreset thermo-responsive relays for interrupting an electric circuit in response to excessive heat developed by a predetermined excessive current flowing therethrough.

One of the principal objects of my invention is to provide a new and improved relay of the above character which is simple and inexpensive to manufacture and which will give long and dependable service with a-minimum of attention.

It is a further object of my invention to provide a relay of the above character which is rugged in construction and which will accurately maintain its temperature adjustment despite considerable rough usage.

It is a still further object of my invention to provide such a thermal relay with a snap action in opening and closing its contacts and with a simple and easily accessible means to change over the relay from manual to automatic reset operation.

It is a specific object of my invention to provide a thermal relay having a snap acting movable switch member arranged to disengage the contacts with a hammer blow.

rear side elevation of the device in Fig. 1; Fig. 4 is a sectional view taken along the lines 4-4 of Fig. 1; and Fig. 51s a sectional view taken alon the lines 5-5 of Fig. 1.

Referring now to the drawing, I have shown my thermal relay supported within a box-like base In of suitable insulating material, such as a molded plastic compound. The sides of the insulating base iii are irregularly shaped and provided with a plurality of bosses, bores, slots, and the like to accommodate the various parts of the operating mechanism, as will be more fully de- To the attainment of the above and other objects of my invention I provide a movable switch member, spring pressed into pivotal engagement with a pair of substantially parallel rods mounted upon .a suitable base. The rods are made of materials having substantially diiferent temperature coefficients of expansion, and means are provided for heating the rod having the higher coefllcient of expansion in response to the magnitude of the current flowing in a circuit to be protected. Unequal-expansion or contraction of the supporting rods causes pivotal movement of the contact carrying movable switch member and consequent opening or closing of a pair of circuit controlling contacts. Preferably, the movable switch member also carries a keeper of magnetic material cooperable with a small permanent magnet of high coercive force for the purpose of endowing the contact movement with snap action in both directions. 7

My invention itself will be better understood and its objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing, in which Fig. 1 is a side view, partly in section, of a thermal switch embodying my invention, the casing cover being removed to disclose the operating parts; Fig. 2 is a plan view of the device of Fig. 1; Fig. 3 is a scribed hereinafter. Adjustably threaded into one side of the casing III is a rod ll having a substantially spherical end I! arranged to support a right angular switch member or contact arm l3 having a complementally shaped recess I4 engaging the spherical end l2 of the rod I l.

. As shown, the rod H is threaded into a metallic bushing I 5' which is in turn threaded into a tapped hole in the side of the casing l0. To maintain the supporting rod II in laterally fixed position, the casing I0 is preferably provided with a pair of integrally formed upstanding bosses l6 and I1 spaced apart just sufiiciently to permit interposition of the rod. I Disposed substantially parallel to the rod II and extending between the switch arm l3 and the side of the casing I0 is a second rod l8 having" conically shaped'end portions arranged for pinpoint engagement with both the switch arm l3 and the side of the casing Ill. The switch arm i3 is biased into engagement with both the rods II and I8 by means of an arcuate spring strip l8 positioned between the switch arm l3 and an opposite side of the base It. Preferably, the supporting rod II is formed of a metallic alloy having an exceedingly small temperature coeflicient of expansion, while the temperature sensitive rod I8 is formed of a metal having a relatively large temperature coefllcient of expansion. For example, a suitable material for the supporting rod is an alloy composed of approxir mately 36 per cent nickel, 0.2 per cent carbon,

and the remainder iron, while a suitable material for the expansible rod I8 is aluminum. Although in the preferred form of my invention the supporting rod II is substantially no'nexpansible, I wish it to be understood that my invention is not limited to such an arrangement, for it will be evident to those skilled in the art that the 1 device will operate entirely satisfactorily so long as the temperature coeflicient of expansion of the supporting rod H is substantially smaller than the temperature coeflicient of expansion of the expansible rod i5.

The switch member I3 is in the form of a substantially right angular lever having a transverse rigid portion 25 disposed substantially at right angles to the rods II and |5. and a channelshaped metallic rigid portion 2| disposed substantially parallel to the rods. Connected to the rigid portion 29 of the lever by means of a bolt 22, I also provide a pair of cantilever leaf springs 23 and 24 arranged in substantially parallel spaced relation to the rigid portion 2|. The leaf spring 23 is .a contact spring carrying at its outer extremity a movable contact 25 arranged in normal engagement with a stationary contact 25. The leaf spring 24 is an armature spring and arranged to carry at its outer end a keeper 21 of magnetic material for cooperation with a small permanent magnet 28. The rigid portion 2| of the switch member is shorter than the armature spring 24 and has at its end an in-turned projection 2|a arranged to engage the armature spring adjacent the magnet keeper 21. Similarly, the armature spring is shorter than the contact spring 23 and carries at its end an in-turned projection 24a arranged to engage the contact spring 23 adjacent the contact 25.

piece or spring wir 52.

The snap action magnet 25 is preferably of the type exerting a relatively high coercive force in proportion to the physical dimensions of the magnet. While I do not wish to be limited thereto, a suitable material, and one which I prefer to use for the magnet, is an alloy comprising of 6 to 15 per cent aluminum, 12 to per cent nickel, about 5 per cent copper if desired, and the remainder iron, such as is described and claimed in Patents 1,947,274 and 1,968,569, issued February 13 and July 21, respectively, 1934, to William E. Ruder.

The fixed contact 25 is mounted upon a conducting strip 29 which passes through a slot in the wall of the casing ill to form with a bolt an external contact terminal. A second external contact terminal 3| is connected to the movable contact 25 by means of a flexible conducting lead 32 attached to the terminal 3| and to the bolt 22. The bolt 22 is in electrically conducting engagement with the flexible contact spring 23 and with the flexible conducting lead 32.

According to the preferred form of my invention illustrated in the drawing, the expansible rod I5 is disposed in heat conducting relation to a hairpin type resistance heater 35. As shown, the resistance heater 35 is closely adjacent and substantially parallel to the expansible rod l8 and has its electrically remote-ends extending through an aperture ,in the wall or the casing l5 for electrical connection to a pair of heater terminals 35 and 31. For electrical connection and mechanical support one end of the heater 35 is welded to a plate 38a connected to the heater terminal 35 and the other end of the heater 35 is welded to a conducting strap 33 connected to the heater terminal 31. In order to preclude accidental short circuiting oi the heater 35 a small strip of insulating material 39 may be inserted between the electrically remote ends 01' the heater 35 in the region of their connection to the external terminals 35 and 31. The heater 35 is preferably connected in circuit with a motor or other apparatus to be protected, so that it carries the same current as that flowing through the protected circuit or a current proportional thereto. The contacts 25, 25 are preferably arranged in a control circuit, as for example, in

, magnet will attract its keeper.

series with the actuating coil of a line contactor.

In order to provide adequate electrical insulation between separate circuits as required by present day commercial standards. a strip of flexible insulating material 49 may be sprung into position between suitable bosses formed on the casing I5 and arranged to isolate the heater terminal 31 from the contacts 25, 26.

Simple means are provided for selectably arranging my thermal relay for either manual or automatic reset. To this end I pivotally mount a reset lever or plate upon a screw 46 attached to the side wall oi! the casing I0. One end of the lever 45 is provided with an abutment 41 arranged to engage a slidable and manually operable reset pin 48 which projects through one wall or the casing Ill. The opposite end of the lever 45 is arranged to provide a pair oi forwardly extending projections 45 and 49 between which the spring strips 23 and 24 and the rigid portion 2| 0! the switch member i3 are disposed in spaced relation. The reset lever 45 is also provided with a pin 50 extending through a slot 5| in the rear wall of the casing l9 and connected to one end of a substantially straight The wire 52 has in a slot 53 formed in the rear side of the casing l5 and has its other end fixedly connected to the casing by means of a screw 54. Within the slot 53 is moulded an upright boss 55 having an appreciable thickness.

By comparing now Fig. 3 with Fig. 1, it will be observed that when the spring 52 is arranged upon the right side of the boss 55, as viewed at Fig. 3, the reset lever 45 of Fig. 1 will be biased to its extreme clockwise position, as viewed in Fig. 1. In its tripped position the switch member i3 is rotated counterclockwise so that the contact spring 23 approaches the projection 45 of the reset lever 45 and the air gap between the magnet 25 and its keeper 21 is sufficiently great so that the force of magnetic attraction is unable to return the switch member to contact closing position even though the rod l8 contracts. To reset the relay the button 45 is depressed to rotate the reset lever 45 counterclockwise until the pro ection 49 engages an adjustable stop screw 55 mounted in the side of the base I5. I! the rod l5 has cooled sumciently to allow the switch member l3 to return to contact closing position, the projection 45 on the reset lever 45 by engag mg the spring 23 will move the switch member clockwise sufficiently to bring the keeper 21 within the effective fleld of the magnet 25 and the If, however, the reset button 45 is depressed before the rod II has cooled and contracted sufficiently to permit the switch member i3 to return to contact closing position, no reclosure will result. In this case the projection 45 oi! the reset lever 45 will engage the contact spring 23 between its point of support and the projection 24a and force the spring 24 into engagement with the projection 2|a. Since the rigid portions of the switch member are held in fixed position by the expanded rod l5, the projection 45 will bend the spring 23 into reverse configuration between the bolt 22 and the projection 23, thereby preventing reclosure oi the contacts. By the means described, reclosure of the contacts is prevented until the rod l5 has cooled sufllciently to permit the keeper 21 to move into engagement with the magnet 25. This is true even though the reset button 45 is held continuously depressed.

In order to" convert the relay for automatic reset operation it is merely necessary to remove the screw 54 of Fig. 3 thereby to release the spring 52, and then to reconnect the spring 52 after placing it on the other side of the boss 55.

with the permanent magnet 28. v

In operation my thermal overload relay is normally in the position shown in Fig. l in which the expansible rod I8 is contracted and the switch member i3 is rotated about the end l2 of the supporting rod II to its extreme clockwise position in which the keeper 21 is in engagement with the magnet 28 and the contacts 25 and 26 are also in engagement. Upon the occurrence of an excessive current in the heater v 35 and the consequent generation of an excessive amount of heat thereby, the expansible rod l8 elongates and exerts a force tending to rotate the angular switch member IS in a counterclockwise direction about its pivot point upon the end l2 of the supporting rod ll. Such counterclockwise movement is initially resisted by the magnetic attraction between the permanent magnet 21 and its keeper 25. Eventually, however, the force exerted upon the armature spring 24 by means of the small in-turned projection 2la on the rigid portion 2i of the switch member I3 is suflicient to pull the keeper 21 away from the magnet 28, thereby permitting the switch member l3 to rotate in a counterclockwise direction. Since the magnet and keeper are disengaged with a snap action. the armature spring 24 will move sufiiciently far when released so that the in-turned projection 24a on the end of the spring will engage the contactspring 23 with a hammer blow to disengage the movable contact 25 from the stationary contact 26.

If the relay has been set eration the reset lever 45 will be biased in a clockwise direction and the movable switch member I! will remain in its extreme counterclockwise position regardless of subsequent cooling and contraction of the expansible rod l8. As has been previously explained, the device may be reset under these conditions by depressing the button 48. If, on the other hand, the relay has been adjusted for automatic reset operation the reset lever 45 will be biased to its counter clockwise position as soon as the expansible rod i8 is sufliciently cooled to permit such movement.

While I have described but one preferred embodiment of my invention by way of illustration,

many further modifications will occur to those skilled in the art, and I therefore wish to have it understood that I intend by the appended claims to cover all such modifications as fall within the true spirit and scope of my inventi-"n What I claim as new and desire to secure by Letters Patent of the United States is:

l. A thermosensitive switch comprising a support, a switch member including a pair of fiex ible portions and a rigid portion connected together in substantially parallel spaced relation, pivotal means for mounting said switch member upon said support, circuit controlling means carried by a first of said flexible portions, snap acting means carried by a second of said flexior manual reset op-' ible portions for releasably retaining said second flexible portion in a predetermined normal position, and t hermoresponsive means operable in conjunction with said rigid portion to release said snap acting means and to'move said second flexible portion into striking engagementwith said first flexible portion thereby to actuate said circuit controlling means.

2. A thermosensitive switch comprising a base, a fixed contact mounted upon said base, a switch memberincluding a pair of flexible portions and a rigid portionvconnected together in substantially parallel spaced relation, pivotal supporting means for said switch member, a movable contact carried by a first of said flexible portions and arranged to engage said fixed contact, magnetic means carried by the second of said flexible portions, second magnetic means 'on said base arranged normally to releasably retain said first magnetic means and to bias said contacts into engagement, and an expansible member arranged to rotate said switch member about said pivotal supporting means, whereby said rigid portion engages said second flexible portion to release said first magnetic means with a snap action and to move said second flexible portion intostriking engagement with said first flexible portion thereby to disengage said contacts.

3. A thermosensitive switch comprising a base, a fixed contact mounted upon said base, a movable switch member pivotally supported upon said base, said switch member including a pair of flexible portions and a rigid portion connected together at one end and extending in substantially parallel spaced relation, a movable contact mounted upon the outer end of a first of said flexible portions and arranged to engage said fixed contact, magnetic means m'ounted upon the outer end of a second of said flexible portions, the outer end of said second flexible portion being formed to provide a first projection arranged to engage said first flexible portion adjacent said movable contact, second magnetic means on said base arranged to engage and releasably to retain said first magnetic means thereby to bias said contacts into engagement, a second projection on the outer end of said rigid portion for engaging said second flexible portion adjacent its end, and thermosensitive expansible right angular switch member having one leg including a pair of flexible portions and a rigid portion connected together in substantially parallel spaced relation, a pair of relatively expansi'ble rods disposed in substantially parallel spaced relation with each other and with saidone leg between said base and the other leg of said switch member, means for biasing said switch member into pivotal engagement with said rods, circuit controlling means carried by a first of said flexible portions, snap acting means carried by a second of said flexible portions for releasably retaining said second flexible portion in a predetermined normal position, and means for heating atleast one of said relatively expansible rods in proportion to the value of the current in said circuit, whereby when said current attains second flexible portion to release said snap acting means and to move said second flexible por-- tion into engagement with said first flexible portion with a hammer blow to actuate said circuit controlling means.

5. A thermosensitive switch for protecting an electric circuit comprising a base of insulating material having a plurality of side walls, a fixed contact mounted upon one of said walls, a substantially right angular movable switch member having a rigid leg pivotally mounted upon a pair 01 relatively expansible rods, said rods being disposed in substantially parallel spaced relation between a second of said walls and said transverse leg and at least one of said rods being adjustably mounted upon said second wall, the other leg of said switch member including a pair of flexible portions and a rigid portion connected together at one end and extending in substantially parallel spaced relation, a movable contact mounted upon the outer end of a first or said flexible portions and arranged to engage said fixed contact, a keeper of magnetizable material mounted upon the outer end of the second of said flexible portions, the outer end 01' said second flexible portion being formed to provide a first projection arranged to engage said first flexible portion adjacent said movable contact, a permanent magnet mounted upon said one wall and arranged to engage and releasably to retain said keeper thereby normally to bias said contacts into engagement, a second projection on the outer end 01' said rigid portion engaging said second flexible portion adjacent said keeper, and means responsive to the current in said circuit for heating one of said rods to rotate said switch member, whereby said rigid portion presses said keeper out 01 engagementwith said magnet with a snap action and said first projection is moved into striking engagement with said flrst flexible membar to disengage said contacts.

6. A thermosensitive switch ior protecting an electric circuit comprising a base of insulating material having a plurality oi side walls forming a container, a flxed contact mounted upon one of said walls, a substantially right angular movable switch member having a pair 01' legs disposed in substantially parallel spaced relation to adjacent walls of said container, a substantially nonexpansible supporting rod adjustably mounted in a wall adjacent said one wall of said base and extending inwardly therefrom, spring means for biasing one of said legs into pivotal engagement with said supporting rod, an expansible rod disposed in substantially parallel spaced relation to said supporting rod and pivotally engaging said base and said one leg, the other leg or said switch member including a pair 01' flexible portions and a rigid portion connected together at one end and extending in substantially parallel spaced relation, a movable contact mounted upon the outer end of a first of said flexible portions and arranged to engage said flxed contact, a keeper o1'.magnetizable material mounted upon the outer end of the second 01' said flexible portions, the outer end of said second flexible portion being formed to provide a first projection arranged to engage said first flexible portion adjacent said movable contact, a permanent magnet mounted upon said base and arranged to engage and releasably to retain saidkeeper thereby to bias said contacts into engagement, a second projection on the outer end of said rigid portion engaging said second flexible portion adjacent its end, and electric heating means responsive to the current'in said circuit for heating said expansible rod, whereby said keeper is released from said magnet by pressing engagement of said second projection with said second flexible portion and said second flexible portion is moved with a snap action to strike said first flexible portion and to disengage said contacts.

7. A thermosensitive switch comprising a support, a switch member including a pair of flexible portions and a rigid portion connected together in substantially parallel spaced relation, pivotal means for mounting said switch member upon said support, circuit controlling means carried by a first of said flexible portions, snap acting means carried by a second of said flexible portions for releasably retaining said second flexible portion in a predetermined normal position, thermoresponsive means operable in conjunction with said rigid portion to release said snap acting means and to move said second flexible portion into striking engagement with said first flexible portion thereby to actuate said circuit controlling means, resetting means arranged to engage said flexible portion and to move said switch member to reset said circuit controlling means, and means operable in conjunction with said rigid portion of said switch member and with said resetting means positively to prevent resetting of said circuit controlling means until s aid thermoresponsive means have cooled to a predetermined temperature.

8. A thermosensitive switch comprising a support, a switch member including a pair of flexible portions and a rigid portion connected together in substantially parallel spaced relation, pivotal means'for mounting said switch member upon said support, circuit controlling means carried by a first of said flexible portions, said first flexible portion having a predetermined normal curvature, snap acting means carried by a second of said flexible portions for releasably retaining said second flexible portion in a predetermined normal position, thermoresponsive means operable in conjunction with said rigid portion to release said snap acting means and to move said second flexible portion into striking engagement with said flrst flexible portion thereby to actuate said circuit controlling means, resetting means arranged to engage said flrst flexible portion intermediate its ends and thereby to move said switch member to reset said circuit controlling means, and means including said rigid portion for engaging the ends ofsaid flexible portion to prevent resetting of said circuit controlling means until said thermoresponsive means has cooled to a predetermined temperature, whereby actuation of said resetting means prior to said predetermined cooling of said thermoresponsive member produces a reversal of the curvature of said flrst flexible member thereby positively to prevent the resetting of said circuit controlling means.

9. A thermosensitive switch comprising a support, a switch member including a pair of flexible portions'and a rigid portion connected together in substantially parallel spaced relation, pivotal means for mounting said switch member upon said support, circuit controlling means carried by a first of said flexible portions, snap acting means carried by a second of said flexible portions for releasably retaining said second flexible portion in a predetermined normal position, thermoresponsive means operable in conjunction with said rigid portion to release said snap acting means and to move said second flexible 'portion into striking engagement with said first flexible portion thereby to actuate said circuit controlling means, manually operable resetting means ar-' away from said first flexible portion thereby to' provide automatic or manual resetting, respectively, of said circuit controlling means.

10. A thermosensitive switch comprising a support, a switch member including a pair of flexible portions and a rigid portion connected together in substantially parallel spaced relation, pivotal means for mounting said switch member upon said support, circuit controlling means carried by a first of said flexible, portions, snap acting for releasably retaining said second flexible por I tion in a predetermined normal position, thermoresponslve 'means operable-in c'orLiunction' with said rigid ,portionto release said snap acting means and to move said'second flexible portion into striking engagement with said first flexible portion thereby to actuate said circuit controlling means, manually operable resetting means arranged to engage first flexible portion and to move said switch member to reset said circuit controlling means, spring means arranged selectably to bias 'said'resetting means toward or away 7 means carried by a second of said flexible portions from said first flexible portion, and'a boss formed upon said casing and engaging said spring means

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