US2302399A - Thermal relay - Google Patents

Description

NOV. 17, 1942. $T|M5QN 2,302,399

THERMAL RELAY Filed Feb. 15, 1942 Fjg. I.

Inventor: Allen 6. Stimson,

yfwyf M4 His Atborngg.

rmaduov. 11,1942

THERMAL RELAY Allen G. Stimson, Lynnfleld, Mass., assignor to General Electric Company, a corporation or New York Application February 13, 1942, Serial No. 430,784

15 Claims.

, structure and are subject to the disadvantage of high cost.

Accordingly, it is an object of my invention to provide a thermal relay which shall be emcient and reliable in operation and simple andinexpensive to manufacture in quantity.

It is a further object of my invention to provide a thermal relay having relatively long time delay in operation and capable of exerting a relatively large force over a wide range of movement.

It is a still further object of my invention to provide an ambient temperature compensated thermal relay which shall operate to increase the pressure of normally closed contacts immediately prior to separation of the contacts.

It is a specific object of my invention to provide a thermal time delay starting for electric discharge lamps which shall operate efllciently and which shall be simple and inexpensive to manuiacture.

My relay comprises essentially a pair of movable bimetallic members disposed in parallel spaced relation and connected together at one end. The other end of one of the members is fixed to the base, the adjacent end of the other bimetallic member being free and carrying a movable switch contact. Upon unequal heating of the bimetal members they will deflect unequally so that the free end of the member carrying the movable contact will move relative to the juxtaposed fixed end of the other member. On the other hand, if the members are equally heated or cooled, as by a change in the ambient temperature, they will deflect synchronously so that there will be no relative movement between the fixed end of the one member and the juxtaposed iree contact carrying end of the other member.

My invention will be better understood by referring now to the following detailed description taken in conjunction with the accompanying drawing, in which Fig. 1 is a schematic perspec- 55 tive view of a relay embodying one form of my invention and connected in circuit with an electric discharge lamp; Fig. 2 is a side elevation of the relay in its deflected position immediately before tripping; and Fig. 3 is a side view of the relay in its position of deflection immediately after tripping.

In the drawing I have represented at iii an electric discharge lamp such, for example, as the sodium vapor lamp, having at the ends thereof the anodes II and H and the filamentary cathodes IZ and I3, each cathode being connected at one end with the adjacent anode and at the other end with one of the lamp terminals by which the energy is supplied to the lamp. The source of energy supply is represented at H as being an alternating current circuit of the constant current type such as is commonly used in series lighting systems. Energy is shown taken from the circuit It by means of a series transformer I5 between the ends of the secondary of which and the lamp I have shown the usual film cutout Hi, the radio frequency capacitor 11 and the radio frequency choke l8.

In order that the lamp cathodes may be heated to the desired temperature and suitably activated before the discharge starts in the lamp I connect them at starting by a low resistance circuit for a predetermined time after which the circuit is automatically opened and the discharge starts. For this purpose I have provided a thermal relay comprising a pair of switch contacts 19 and 20 and an operating element in the form of a sinuous bimetallic member 25. The fixed contact I9 is mounted upon a base member of the relay indicated at 26 and the movable contact 20 is carried at the end of a resilient cantilever spring strip 21 which is attached to and extends from the connected free ends of an inner pair of movable leg portions of the bimetallic element 25.

The bimetallic operating member 25 comprises a juxtaposed pair of inner leg portions 28, 29 and a pair of outer leg portions 30, 3|. The leg portions are disposed in edge-to-edge parallel spaced relation and are connected together at alternate juxtaposed ends to form a sinuous current path through all the legs in series circuit relation. The inner bimetallic members 28 and 29 are of substantially the same length as the outer members 30 and 3| but are of considerably smaller crosssectional area. Hence, each inner leg member 28, 29 has a greater electrical resistance and a smaller heat dissipating capacity than each outer leg member 30, 3|. The bimetallic element 25 may easily be fabricated from an E-shaped punching by slotting the central leg of the punching longitudinally for substantially its entire length, the slot falling somewhat short of the free end of the center leg, thereby to form in eilect a pair of juxtaposed U-shaped bimetallic members connected together at the free ends of their parallelly disposed smaller inner legs. The bimetal 25 is supported upon the relay base at the extremities of the relatively large outer legs. As shown, the extremities of the outer leg portions 38 and 3| are rigidly connected to terminal conductors 32 and 33 which form part of the relay base. The bimetallic member 25 is arranged so that in its unheated position the contacts l9 and 28' assume a normally closed position. The contacts are further held in this position and are provided with a snap action in operation by providing at the free ends of the inner leg portions 28 and 29 a magnetizable keeper 34 disposed for operation in conjunction with a small permanent magnet 35 mounted upon the relay base.

In the form of my invention shown by way of illustration in the drawing the bimetallic element 25 is permanently connected in series circuit relation with the discharge lamp I8. In operation, when energy is supplied to the circuit M an alternating current passes through the sinuous bimetallic element 25 in series circuit relation with the filamentary cathodes i2 and I3 and the anode short circuiting relay contacts [9 and 28. The inner and outer legs of the bimetallic element 25 are heated by the current passing through them, so that the lower end of the element 25 moves to the right, and away from the relay base, as viewed in the drawing, as the entire element assumes a curved shape. Due to the fact that the inner legs 28 and 29 are of higher resistance than the outer legs 38 and 3i and due also to the fact that the inner legs have a smaller heat dissipating capacity than the outer legs, the inner and outer legs are unequally heated and the inner legs will attain a temperature higher than that of the outer legs. Be-

cause of the higher temperature of the inner legs these legs will tend to curl to a greater extent than the outer legs 38 and 3!. The tendency of the inner legs 28 and 29 to deflect to a greater extent than the outer legs is initially restrained by the snap action magnet 35 and its keeper 34. tion before the central leg portions 28 and 29 have built up by their higher temperature suflicient internal stress to pull the keeper 34 away from the magnet 35 both the inner and outer leg portions are constrained to deflect in a substantially synchronous manner, since the upper ends of the outer leg members are fixed to the base and the upper end of the inner leg members is magnetically held in substantially its initial position while the lower ends of the inner and outer leg members are firmly connected together During this initial period of defiecby transverse portions of the bimetal. The position of the bimetallic member immediately before opening of the contacts is shown at Fig. 2. It is important to note that during the initial period of substantially synchronous deflection of the inner and outer legs the movement of the lower end of the bimetal 25 away from the relay base causes the free end of the inner legs 28 and 29 to pivot about the upper end of the magnet keeper 34, as shown at Fig. 2. This pivotal movement tends to pull the lower end of the magnet keeper 3| away from the magnet but does not of itself sumciently diminish the magnetic force to permit the center leg portions 28 and 23 to snap to their open circuit positions. It is evident that the pivotal movement Just described will increase the contact pressure between the fixedcontact l9 and the movable contact 28. When finally the inequality in the heating of the inner and outer leg portions of the bimetallic element 25 has attained a predetermined degree the internal strain built up in the inner leg portions 28 and 29 tending to deflect these leg portions farther than the outer leg portions 38 and 3! will be suflicient to pull the keeper 34 away from the magnet 35 and thereby separate the relay contacts l9 and 28 with a snap action. The position of the bimetallic member immediately after separation of the contacts is shown at Fig. 3. Separation of the relay contacts initiates a discharge current in the lamp I8 by removing the short circuit across the anodes H and II.

Ambient temperature compensation of my thermal relay is inherent due to the fact that the movable contact 28 is mounted at the same end of the bimetallic member 25 at which attachment of the bimetallic member to the relay base is made. Thus, under changing ambient temperature conditions, the inner and outer legs of the bimetal 25 are equally heated and deflect equally so that the free end of the inner leg portions 28 and 29 to which the movable contact 28 is attached does not move with respect to the extremities of the outer leg portions 38 and 32 which are attached to the relay base.

By reason of the construction of the bimetallic device which I have provided the time delay between its energization and its movement to open circuit position is suiiicient to permit the cathodes l2 and i3 to become heated to the desired temperature and thus to become activated. This time delay may be of the order of 25 to 45 seconds. A bimetallic member of the configuration which I have provided is particularly adapted to applications requiring such a relatively long time delay and also provides a substantial operating force eifective over a wide range of movement.

While for convenience of fabrication I prefer to form my bimetallic element 25 from an E- shaped punching having three legs of substantially the same size so that when the center leg is slotted it forms two central leg portions having both a higher electrical resistance and a lower dissipating capacity than the outer legs, it will be understood by those skilled in the art that it is in the scope of my invention to provide a, sinuous bimetallic member in which any desired means is provided for unequally heating a pair of parallelly-disposed connected leg portions. For example, this may be eflected by supplying to both leg portions equal amounts of heat but constructing the leg portions to have dissimilar heat dissipating characteristics. On the other hand, the same eil'ect may be obtained by providing leg portions havingsimilar heat transfer characteristics but to which unlike quantities of spect to the inner leg portion the greater will be the transfer of heat from the inner leg to the outer leg and hence, the greater will be the time delay before the inner leg assumes a sufficiently high temperature to assume its independent open circuit position of greater deflection with respect to the outer leg,

While I have shown only one preferred embodiment of my invention by way of illustration, many other modifications will occur to those skilled in the art and I 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 invention.

What I claim as new and desire to secure by Letters Patent 01 the United States is:

1. A thermal relay comprising a base, a fixed contact mounted upon said base, a pair of thermal responsive movable members in parallel spaced relation, one of said thermal responsive members being mounted at one end upon said base and having its other end connected to the juxtaposed end of the other of said thermal responsive members, a movable contact mounted upon the free end of said other thermal responsive member for cooperation with said fixed contact, means for unequally heating said thermal responsive members to separate said contacts, and snap acting means operable in conjunction with said free end of said other thermal responsive member releasably to retain said contacts in engagement.

2. A compensated thermal relay comprising a base, a fixed contact mounted upon said base, a pair of thermal responsive movable members in parallel spaced relation, said thermal responsive members being arranged for deflection in the same direction upon similar changes in temperature thereof and one of said members being mounted at one end upon said base and having its other end connected to the juxtaposed end of the other of said thermal responsive members, a movable contact mounted upon the free end of said other thermal responsive member for cooperation with said fixed contact, means for unequally heating said thermal responsive members to separate said contacts, and snap acting means operable in conjunction with said free end of said other thermal responsive member releasably to retain said contacts in engagement.

3. A compensated thermal relay comprising a base, a fixed contact mounted upon said base, a pair of thermal current responsive movable members in parallel spaced relation, one of said current responsive members being mounted at one end upon said base and having its other end mechanically and electrically connected to the juxtaposed end of the other of said current responsive members, said current responsive members having dissimilar thermal transfer characteristics and being arranged to deflect in the same direction upon the application of heat thereto, a movable contact mounted upon the free end of said other current responsive member for cooperation with said fixed contact, means for supplying substantially equal heating currents to said current responsive members thereby unequally to heat said members and to separate said contacts, and snap acting means for releasably retaining said contacts in engagement.

4. A compensated thermal relay comprising a base, a fixed contact mounted upon said base, a pair of thermal current responsive movable members in parallel spaced relation one of said current responsive members being mounted at one end upon said base and having its other end mechanically and electrically connected to the juxtaposed end of the other of said current responsive members, said current responsive members having substantially the same length but being of dissimilar electrical resistance, a movable contact mounted upon the free end of said other current responsive member for cooperation with said fixed contact, means for supplying substantially similar heating current to said current responsive members thereby unequally to heat said members and to separate said contacts, and snap acting means for releasably retaining said contacts in engagement.

5. A thermal relay comprising a base, fixed and movable switch contacts, a U-shaped movable member having two thermal responsive leg portions arranged for deflection in the same direction upon similar changes in the temperature thereof, the free end of one of said leg portions carrying said movable contact and the juxtaposed end of the other of said leg portions being fixedly attached to said base, means for unequally heating said leg portions to separate said contacts. and snap acting means for releasably retaining said contacts in engagement.

6. A compensated thermal relay comprising a base, a fixed contact mounted upon said base, a U-shaped bimetallic movable member having two leg portions of dissimilar cross sectional areas, a movable contact mounted at the free end of one of said leg portions for cooperation with said fixed contact, means for rigidly attaching the juxtaposed end of the other leg portion to said base, means for supplying a heating current to said bimetallic movable member with said leg portions connected in series circuit relation thereby unequally to heat said leg portions and to separate said contacts, and snap acting means operable in conjunction with said free end of said one leg portion for releasably retaining said contacts in engagement.

'7, A compensated thermal relay comprising a base, a fixed contact mounted upon said base, a U-shaped bimetallic movable element comprising a pair of leg portions of substantially equal length lying in edge-to-edge parallel spaced relation, said leg portions having dissimilar cross-sectional areas and being electrically connected in ,series circuit relation, a movable contact mounted upon the free end of one of said leg portions for cooperation with said fixed contact, means for rigidly connecting the juxtaposed end of the other of said leg portions to said base, means for supplying a heating current to said U-shaped bimetallic element thereby unequally to heat said leg portion and to separate said contacts, and snap acting means operable in conjunction with the end of said other leg portion releasably to retain said contacts in engagement.

8. A compensated thermal relay comprising a base, a fixed contact mounted upon said base, a pair of bimetallic'members disposed in parallel spaced relation, a first of said bimetallic members being mounted at one end upon said base and having its other end mechanically and elecirically connected to the juxtaposed end of the second of said bimetallic members, said bimetallic members being of substantially the same length but of dissimilar cross-sectional areas and being disposed to deflect in the same direction upon the application of heat thereto, a resilient contact spring extending from the free end of said second bimetallic member and carrying at its end a movable contact for cooperation with said fixed contacts, means for supplyin a heating current to said bimetallic members in series circuit relation thereby unequally to heat said members and to separate said contacts, and snap acting means engaging said free end of said second bimetallic member releasably to retain said-contacts in engagements and to increase the contact pressure prior to their separation.

9. A compensated thermal relay comprising a base, a fixed contact mounted upon said base, a lJ-shaped thermal responsive bimetallic element comprising a pair oi leg portions of substantially equal length lying in edge-to-edge parallel spaced relation, said leg portions having dissimilar cross-sectional areas and being electrically connected in series circuit relation, a resilient contact spring connected to and extending from the free end of one of said leg portions and carrying at its end a movable contact disposed normally to engage said fixed contact, supporting means for rigidly connecting the juxtaposed end of the other of said leg portions to said base, a magnet mounted upon said base adjacent said free end of said one leg portion, a keeper ior said magnet connected to said free end of said one leg portion, means for sup plying a heating current to said U-shaped blmetallic element for unequally heating said leg portions thereby to produce unequal deflections of said portions and to separate said contacts, said magnet releasably retaining said keeper in engagement therewith over a portion of the heating period and constraining said one leg portion to pivot about its free end thereby to increase the contact pressure prior to the separation of said contacts.

10. A thermal relay comprising a base, a fixed contact mounted upon said base, a bimetallic element of sinuous configuration comprising an interconnected pair of inner legs and a juxtaposed pair of outer legs connected to said inner legs, said pairs of legs being disposed in sub stantially edge-to-edge parallel spaced relation, a movable contact mounted upon the interconnected ends of said inner legs for cooperation with said fixed contact, supporting means for connecting the juxtaposed ends of said outer legs to said base, means for unequally heating said inner and outer legs to separate said contacts, and snap acting means operable in conjunction with the free end of said inner legs releasably to retain said contacts in engagement.

11. A. thermal relay comprising a base, a fixed contact mounted upon said base, a bimetallic element of sinuous configuration comprising an interconnected pair of inner legs of relatively small cross section and a juxtaposed pair of outer legs connected to said inner legs and having a relatively large cross section, said pairs of legs being disposed in substantially edge-to-edge parallel spaced relation, means for mounting said bimetallic element upon said base at the ends of said outer legs lying adjacent the interconnected ends of said inner legs, said interconnected ends carrying a movable contact for cooperation with said fixed contact, means for supplying a heating current to said bimetallic element, said heating current passing through said legs in series circuit relation thereby unequally to heat said inner and outer pairs of legs, the unequal heating of said pairs of legs tending to produce a greater deflection of said inner legs than of said outer legs and to separate said contacts,

and magnetic means mounted upon the free ends aa oaaco of said inner legs releasably to constrain both said pairs of less to substantially synchronous deflection during an initial portion oi their movement and thereafter to release said inner legs with a snap action for movement to an open circuit position.

12. A compensated thermal relay comprising a base, a fixed contact mounted upon said bas a bimetallic element of sinuous configuration comprising an interconnected pair of inner legs and a juxtaposed pair of outer legs connected to said inner legs, said legs being disposed in substantially edge-to-edge parallel spaced relation and said pairs of legs having dissimilar crosssectional areas, a resilient contact spring connected to and extending from the interconnected ends of said inner legs and carrying at its end a movable contact disposed normally to engage said fixed contact, supporting means for rigidly connecting the juxtaposed ends of said outer legs to said base, a magnetic keeper mounted upon said interconnected ends of said inner legs, a

magnet mounted upon said base adjacent said keeper releasably to restrain movement of said inner legs, means for supplying a heating current to said bimetallic element traversing said legs in series circuit relation, said heating current unequally heating said inner and outer legs thereby to produce unequal deflections thereof to separate said contacts, said magnet releasably retaining said keeper in engagement therewith over an initial portion of the heating period and constraining said inner and outer legs to defiect substantially synchronously during said initial period while said inner legs pivot upon said keeper thereby to increase the contact pressure prior to the separation of said contacts.

13. A thermal relay comprising a base, a fixed contact mounted upon said base, a U-shaped bimetallic member having a pair of leg portions in parallel spaced relation, said bimetallic member being mounted upon said base at the extremity of one 'of said leg portions and carrying a movable contact at the free end of the other of said leg portions, said movable contact being disposed to engage said fixed contact in the unheated positlon of said bimetallic member, means for unequally heating said leg portions to separate said contacts, and magnetic means operable in conjunction with said free end of said leg portion initially to constrain said leg portions to deflect synchronously and subsequently to permit said contacts to separate with a snap action.

14. A thermal relay comprising a base, a fixed contact mounted upon said base, a pair of thermal responsive movable members in parallel spaced relation, one of said thermal responsive members being mounted at one end upon said base and having its other end connected to the juxtaposed end of the other of said thermal responsive members, a movable contact mounted upon the free end of said other thermal responsive member for cooperation with said fixed contact, and means for unequally heating said thermal responsive members to separate said contacts.

15. A compensated thermal relay comprising a base, a fixed contact mounted upon said base, a pair of thermal current responsive movable members in parallel spaced relation, one of said current responsive members being mounted at one end upon said base and having its other end mechanically and electrically connected to for cooperation with said fixed contact, and means for supplying substantially equal heating currents to said current responsive members thereby unequally to heat said members and to 5 separate said contacts.

ALLEN G. STDESON.

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