US2420300A

US2420300A - Electric overload protective device

Info

Publication number: US2420300A
Application number: US467956A
Authority: US
Inventors: John B Cataldo; Jr William E Stilwell
Original assignee: John B Pierce Foundation
Current assignee: John B Pierce Foundation
Priority date: 1942-12-05
Filing date: 1942-12-05
Publication date: 1947-05-13
Anticipated expiration: 1964-05-13
Also published as: GB573135A

Description

May 13, 1947- J. B. CATALDO ETAL ELECTRIC OVERLOAD PROTECTIVE DEVICE Filed Da e. 5. 1942 2 Sheets-Sheet 1 B. CATALDO LIAM E. STILWELLJR.

ORNEY May 13, 1947. I J. B. CATALDO ETAL ELECTRIC OVERLOAD PROTECTIVE DEVICE 2 Sheets-Sheet 2 Filed Dec. 5. 1942 FVAH iii ILL

\AM .STILWELLJR Patented May 13, 194? UNITED STATES PATENT GFFICE 2,420,3ilh

ELECTRIC Q'VERLOAI) PROTEC'IEVE DEVKJE John B. Cataldo, Summit, N. 3., and William E. Stilwell, J12, Cincinnati, Ohio, assignors to John B. Pierce Foundation, New York, N. Y., a corporation of New York Application December 5, IS IZfSerial No. 467356 6 Claims. 1

It is also an object of the invention to provide electric protective apparatus of the character de-- scribed which may be employed in place of conventional plug fuses and the like.

It is an object of the invention to provide apparatus of the class described which will be trip free, that is, which cannot be held in closed circuit position during the pendency of the overload or other abnormal condition in the electric circuit.

It is an object of the invention to provide overload protective apparatus which embodies a simple, conveniently arranged manual re set to return the apparatus to operative position.

In a preferred form of the invention, we em ploy a snap-acting spring member, desirably in the form of a snap spring or disk, capable of assuming two positions of stable equilibrium, that is, capable of being snapped or upset from a concave form to a convex form, and vice versa, and maintaining such position. The snap spring is preferably mounted on an axially movable shaft, in connection with which elements there is a coil spring which urges the snap spring or disk in the direction of an organization of load-line contacts disposed at the ends of a preferably tri-legged bimetallic structure adapted for connection. into an electric circuit. Most preferably. the snap spring is provided with silver button contacts for engagement with the contacts on the bimetallic element, although said snap spring contacts may, if desirable, be supplanted by an electro plating or other coating of silver on one surface of the rim of the snap spring.

The snap spring assembly is desirably cor1- tained within a housing configurated internally to provide a shoulder immediately above the rim of the snap spring. I

A manually operable push-pull button,-or a bell crank pivoted within the housing is operatively associated with the aforesaid shaft to draw the latter and the snap spring respectively up wardly in the direction of and into engagement with the shoulder. Manual release of the button or hell crank, as the case may be, permits the coil spring to move the assembly, including the shaft and snap spring, back to its original posi tion, namely, such that the snap acting mem ber contacts the aforesaid bimetal element.

Preferably one of the load-line terminals is connected to the snap spring. When the ap- 5 paratus is in normal operating status, the snap spring, or the contacts thereof, are in electrical. engagement with the contacts of the bimetallic element, which latter, in turn, are connected to the other load-line terminal. By suitable design or calibration of the bimetallic member, the legs thereof. will start to warp upwardly, under the heating effect of overload electric current passing therethrough or short circuit. The upward movement or continuedwarping of the bimetal ele-- ment exerts a continually increasing pressure against the rim of the snap spring until its overthrow or upset point is reached, whereupon the spring will reverse its position of equilibrium, and the contacts thereof will be drawn away from engagement with the contacts of the bimetallic member, with great rapidity. The circuit will then be broken the legs of the bi; etallic member, upon 300 n will return to their initial. position.

ecause of the mint charac teristic of the st spi \Vlli remain in inverted position, in which position the rim will engage, or be closely proximate, the aforesaid shoulder of the at said housing. To return the closed circuit position, 1, the shaft upon which ved upwardly, where- 4 spring will be brought lder and the snap spring pressure, be inverted to its accomplished by manual push-pull button or hell orrnal position. However, till be elevated or out of contact with respect to the contacts of the bimetallic element long as said manual displacement is imposed; so long as the snap spring is thereby held in its retracted position, it will be impossible to re-close the electric circuit. In other words, it is impossible to hold the circuit t ailer in closed circuit position.

wever, immediately upon release of the man element, the coil spring will drive the snap g assembly downwardly a unit and the spring into contact with the biznetal them-=- ital condition causing the overload or short has not been remedied, th cyc e of operor not the snap s ring is in circuit position. Such indicator, se a rod or pin the housing of again t the riin o1" nap spring in normal er end of the pin is housing: When the to open circuit poe rim lifts the indiits upper end prohe device, thereby operative status ends itself conveng connectors, such as on ectcr of an electric iron ctors to afford indir a; iaratus equipped with "achment plugs. advantages will hereinl sectional View or" a circuit the present invention; tion similar to Fig. i, but talzen hereto;

1 the device of 1 detail showing,

of th operating the invention in the form of an liustrated in Figs. 1 llustrated as applied Which may be aite. the repositioned, by Welding the known man- S rig. o, e n depth to r the base i section showing another 4 there is positioned a circuit breaker organization, an essential element thereof being a snap spring 21, preferably in the form of a threespoked annular disc, said snap spring being so dished that it assumes either a convex form as shown in section in Fig. l, or a concave form, as shown in Fig. 7, each of said forms being a position of stable equilibrium of the spring.

For engaging the respective contacts 26 of the bimetallic structure, the snap spring 21 may have similar silver button contacts 28, see Fig. l, or if pr ferred, the entire face of the rim of the snap spring may be silver plated or otherwise provided to function as a contacting surface of suitable conductive material, Fixed to the center of the snap spring, see Fig. 6, is a shaft 30, a reduced diameter end of which passes through the snap spring. The tip of said shaft is flared and engaged by a collar 3!, which bears against the central portion of the disk and between which and a Washer 32 the disk is secured to the shaft 3. Surrounding said shaft 30 and preferably bearing against washer 32, is a coil spring 33jthe other end of which bears ag: inst the shoulder 3! of the intermediate body portion 2|. Suitably electrically connected to the structure of the snap spring 21 is a conductor 35 which is of relatively flexible material and connected by means of a solder joint or equivalent to the outer shell conductor member 35 of the device, as illustrated in Fig. 1.

It will be seen that when employed in lieu of a conventional plug fuse, the contact 25 is arranged to make electrical connection with one of the lines of an electrical circuit, and the shell 36 provides the connection with the other or return line of the circuit. It will be seen also that with the elements in their Fig. 1 position, the path of electric current is through the respective legs of the bimetallic structure, thence to the snap etallic structure 23 is formed of materials of suitable character and current carrying capacity, to "Warp under the heating influence of electric currents of predetermined values. Since the bimetallic structure is secured only at its center point, and with the materials of the bimetal structure suitably arranged with respect to their coefficients of expansion, the increase in temperature in such a bimetallic structure is utilized to warp the legs thereof upwardly, in which circumstance they will press against the snap spring 2?. After the exertion of a suitable pressure, which may be determined in advance from the warning response of. the bimetal element and the throw characteristic of the snap spring, said snap spring 2! will invert or upset, and in so doing, will lift its contacts 28 out of engagement With the contacts 28 of the bimetallic structure, thereupon break a the circuit.

a. previously the snap spring 21 is so red that it has two positions of stable equllh brium, and therefore. it will remain in its inverted position indefinitely. The body portion 2| has a shoulder see Fig. 2, adjacent which the r'm of the snap spring 21 rests, see Fig. 7, when It will obvious, therefore, that by moving the snap spring bodily upward, as by lifting the shaft 30, the reaction pressure of the rim of the snap spring against shoulder 31 will cause it to snap back into its ori inal position. To manually accomplish such a reverse movement of the spring, we provide in the instant embodiment a bell s a es-o crank lever 38, the free end of which passes through a suitable aperture in the cap 22 and the opposite end of which is pivotall connected to the shaft 30 as shown in Figs. 1 and 2. The bell crank lever is iulcrumed on the upper sur face of the shoulder ti l by the illustrated lug 38a. Lateral displacement of the free end oi said lever causes said bell crank to raise the shaft 3G to eiiect the snapping of the spring ill to its ini tial convex position.

Th displacement of the snap spring 2? and the contacts thereof relative to the bimetal struc= ture 23 is such, under the stated condition, that when the snap spring is returned to its original convex position under the action of the bell crank the respective contacts of the snap spring and the bimetallic structure do not meet and the cir cult is not closed. Therefore, it is not possible to hold the circuit breaker closed by continued manual displacement of the bell. crank; lever 38. It is only when the lever is released that the snap acting disk is enabled to make contact with. the bimetal element.

As illustrated in Fig. 2, an indicator to reveal the relative position of the snap spring il may comprise a light, flexible rod 39 resting, under the influence of a light coil spring 39a, upon the rim of the snap spring 21. With the apparatus in normal closed circuit position, the upper end of the rod 39 is flush with, or beneath, the surface or" the cap 22, thus being unnoticeable. When the snap spring throws to open circuit position, however, the rising of the rim of said snap spring causes the rod 39 to be driven upwardly. in which circumstance its upper end appears above the surface of the cap 22, thereby im dicating that the circuit breaker has been thrown to open circuit position.

Fig. '7 is representative of the various embodia ments of our invention described herein, in depicting the action of the overload protection afiorded by our invention immediately after the of the bimetallic structure 23 have risen under the influence of temperature generated by the passage of excess electric current therethrough, and have exerted such pressure upon the snap spring 21 that the snap spring is di placed to its inverted, i. e., concave position of stable equilibrium. It will be noted that in such position, the contacts 28 of th snap spring are displaced from the contacts 28 of the bimetallic member, and that the rim of the snap spring is raised against or closely adjacent to the shoulder ill of the body member 2i. In such position, the circuit has been broken. l

in Fig. 8, it is shown how the action of the bell crank 38. is effective to draw the shaft til upwardly against the tension or the coil spring 33, and has caused the snap spring to invert itself to its original convex position. Fig. 8 also shows that such inversion of the snap spring is not oi. itself suihcient to restore electric contact between the contacts is and 2s respectively or the snap spring and bimetallic member. There" fore, even if the bell crank 38 were actuated be. fore the bimetallic structure had cooled suhh ciently to bring its legs back into normal posi tion against the base fill, the electric circuit could not be closed. because the raised position of the snap spring 2? resulting from manual displacement on the bell crank lever 38 and consequent upward movement of the shaft 30 prevents the snap spring from moving into engagement with the bimetallic element The circuit breaker may not, therefore. be held in closed circuit posh til ill

tion. However, upon releasing the lever the shaft and. the snap disc spring are automatically projected by the coil spring to effect electrical connection of the snap disc spring with the contacts of the bimetallic clement Referring to Figs. 9 and fill, our invention is illustrated respectively as applied to an attachment plug and an outlet plug tap.

In the embodiment of Figs. Si and ll, an outer shell all contains an assembly housing the spring and bimetallic members, the lower por tion of the housing provides a chamber for con.- nection of the cord C. Said housing includes a cup at, the base of which is channelled as previ ously described with respect to the base of the Fig. l embodiment, to receive the trl-leggecl bi metallic member secured at its central point to the cup ll by a rivet serving also to con nect the bimetallic element with a terminal for connection with a conductor of the electrical cord C.

The snap spring i l, in. this embodiment shown with an overlaid continuous contacting surface 5, i carried by a spring biased shaft the coil spring 33 thereof and elements supporting the shaft on the snap spring as being arranged as shown in Fig. 6. Instead of the bell crank 38, however. the shaft Bill is provided with. a button-head as which may be manually grasp-ed to raise the shaft Cal against the tension of coil spring Snap spring is is electrically connected to a plug blade ll by means of a flexible connection The snap spring assembly is carried by a plug portion all molded with a coarse' male thread to permit its easy and permanent securement to and within the cup If desired, suitable adhesive may be applied to rigidity the connection b tween the plug t t? and the cup ii.

The second plug blade is the termination of a bns-bar havin c 'nnnal serving a connector for the ot' uctor of the electric cord C; a central portiol of said bus oar lies within a channel 1p me r it, see Fig. ii. The intermediate angulc. offset elements. respectivel overlie end. surfaces of the plug 59 and the cup ll, in tight engagement therewith.

' lllu ctors of the electric s iii, as by con mbodiment, the plug l snap spring organizlc cup ll, see Fig. ll,

. sibling the 51' id therewith associ is screwed into a d central oortio of the bus-bar is laid in tl'l-e channel. being held in position by the tight engagement of oiiset portions with the end. surfaces of the plug and cup it.

in connecting the in tale of the cord C, the shell id is removed by merely unscrewing it from the inner assembly. The end of the cord 0 is passed through the illustrated aperture in the shell and the wires of the cord (3 connected as show" wh upon the shell may be re screwed to e illustrated in 16 corresponds ,r that of Fi 9 except with respect to s in: contacts and the rovision of p l blade slots in shell The shell ltlc, when initially secured to the cup at the completion of manufacture, need not again be removed.

The op merits e ill a "ation of the Figs. 8-

. to that previous).

When bile under the action of is disposed be" whereupon grasp ng it outwardly is pring to its initial u ten 45 is released, by the coil spring 33 bimetallic element to had been plugged, to impossiblather e ic 'ic circu pre be operator s from associaludes any possihandling the e described our invention by c forms thereof, it will be up changes and modifications a they do not depart from spring means posof stability movably posiusing and disposed in opert said thermostatic metal means for urging id snap 'ricity conductive cor act with metal when said tal structure in series in an thermostatic structure havaole under increase in temagainst cuit, housing dly extending abutment means pos ioned proximate the rim of said snap disc spr means when said snap disc means in its second position of staaccessible external of said means 1 inn p";-

re invert being provided ly i a said snap dwc Yr ant m ans to the ans to its aid initial spring 2 disc clam 1, wh rein cl eely inorabl of said comp metal structur substantia said substantially circular Spring member into electrical contact with said thermostatic metal structure when said substantially circular spring member is in one of its positions of stability, means for connecting said substantially circular spring member and said thermostatic metal structure in series in an electrical circuit, said thermostatic structure having a portion displaceable under increase in temperature and arranged to exert pressure against said substantially circular spring member whereby under the heating effect of predetermined values of the electrical current of such electrical circuit said thermostatic structure causes said substantially circular spring member to be thrown out of engagement with said thermostatic metal structure and to its second position of stability to thereby interrupt such electrical circuit, abutment means disposed within said housing arranged to engage the rim of said substantially circular spring member when the latter is in its position of interrupting such electrical circuit, and means for displacing said substan' ally circular spring member when in its said c1 cult interrupting position to engage said abutment means to thereby cause said substantially circular spring member to invert to its opposite position of stability.

5. Apparatus as defined in claim 4 wherein said resilient means is a coil spring for urging said substantially circular spring member into electrical contact with said thermostatic metal structure.

6. An overload protected attachment plug, comprising a cup member having a thermostatic member secured at the base thereof, a hollow plug member insertable with said cup member, said plug member having a snap disc spring disposed therein, said snap disc spring having two positions of stability, in one of which positions said snap disc spring is in contact with said thermostatic member, means for connecting said snap .isc spring and said thermostatic member into electric circuit, a housing for said assembly up and hollow plug member, said housing being provided with inwardly extending abutment means positioned proximate the position of the rim of said snap disc spring when said snap disc spring is in its position out of contact with said thermostatic member; shaft means extending into said hollow plug member; a coil spring engaging said shaft means and abutting at its one end with said snap disc spring and at its opposite end against a fixed support; and means extending exteriorly of said housing for operating said shaft means to thereby move said snap disc spring to engage at its rim with said abutment means waereby such engagement with said coil spring auses said sn p spring to invert to its opposite .osition. of stability.

JOHN CATALDO.

W'I' IAIlE E. STILWELL, JR.

'tENoEs CITED The following references are of record in the file of this patent:

UNFTED STATES PATENTS