US2272496A - Switching device - Google Patents

Description

Feb.'1o, 1942. F. E. WOOD 2,272,496

swITcHING DEVICE v Filed April 24, 1939 Y jmj /0 INVENTOR. FREDR/C E. WOOD YBYM,M,M%

ATTORNEYS Patented Feb. 1o, 1942 SWITCHING DEVICE Fredric E. Wood, Oak Park, Ill., assigner to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware- Application April 24, 1939, Serial No. 269,689

11 Claims. (Cl. 200-1) The present invention relates to switching devices and, more particularly, to electrical switch devices of the electromagnetic relay type.

A switching device of the electromagnetic relay type conventionally comprises a eld structure including a core provided with a winding, a movable armature carried by the field structure, and a set of switch springs operatively as-k associated contacts carried by the switch springs 4 and which accommodates equalization of the Contact pressure among the pairs o associated contacts.

In brie, the objects set forth above are in part realized in accordance with one feature of -the present invention by providing a switching device which comprises a pair of associated switch springs, each of the switchsprings being provided with two spaced-apart and independently flexible portions and a plurality of contacts respectively carried by the flexible portions of the switch springs, the contacts respectively carried by the em'ble portions of one of the switch springs respectively cooperating with the contacts respectively carried by the flexible portions of the other of the switch springs. Also, means is provided for moving one of the switch springs, thereby to effect a change in the relative positions of Athe contacts respectivelycarried by the iexible portions of the switch springs. More particularly, each of the switch springs is formed of nat metallic stock and is provided v with a base end and a free end; and a cantilever mounting is provided at the base end of each of the switch springs, the base ends of the switch springs being insulated from each other.

The two independently exible portions provided on one of switch springs are'formed by an elongated slot provided in the one switch spring adjacent the free end thereof. Also, the contacts respectively carried by the iiexible portions of the one switch spring are `carried thereby substantially at the points along the lengths of the exible portions of the onel switch spring whereat the flexible portions have a maximum movement with respect to. the base portion of the one switch spring, thereby t0 insure selfequalization of contact pressure between the respective engaging contacts when the contacts carried by the iiexible portions of the one switch spring are respectively forced into engagement with the contacts respectively carried by the flexible portions of the associated switch spring. Furthermore, the means for moving the one switch spring comprises an operating member carried by the one switch spring adjacent the free end and intermediate the two flexible portions thereof and an element operative to engage the operating member.

In accordance with another feature of the invention, the operating member is secured to the one switch spring adjacent the free end and intermediate the two iiexible portions thereof by a drive screw extending through aligned open ings respectively provided in the free end of the one switch spring and the operating member. Also, the operating member is subjected to some wear incident to the operation thereof by the associated element, whereby dust wearing from the operating member accumulates upon the cooperating metallic contacts. The material of the operating member comprises an inactive organic substance, whereby 'the dust wearing therefrom and accumulating upon the cooperating metallic contacts does not react with the metallic contacts to provide electrical insulating compounds upon the outer surfaces of the metallic contacts. More specifically, the material of the operating member comprises an inactive `organic acetate, such, for example, as a suitable cellulose acetate.

The arrangement for operating the switching device comprises an electromagnetic relay includng rst and second longitudinally extending field elements arranged in spaced-apart relationship, a laterally extending piv'ot pin carried by the rst iield element, means including a clamping member secured to the rst iield element and embracing a portion of the pivot pin disposed intermediate the ends thereof for clamping the pivot pin directly to the outer. surface of the first eld element adjacent the end thereof, and an armature operatively associated with the rst and second eld elements. The armature is provided with two laterally extending arms disposed on opposite sides of the first field element and pivotally mounted on the opposite ends of the pivot pin. The field elements and the armature are so constructed and arranged that the air gap between the rst field element' and the armature is substantially unalof the armature in order to prevent the operating arm of the varmature and the first field element from sticking together due to the magnetic forces therebetween.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing, in which- Figure 1 is a plan view of a switching device of the electromagnetic type constructed and arranged in accordance with the present invention, and a support therefor; Fig. 2 is an exploded side elevational view of the switching device and support shown in Fig. 1, and an enclosing casing therefor; Fig. 3 is an end elevational view of the switching device shown in Fig. 1, and a vertical sectional view of the enclosing casing therefor; Fig. 4 is an enlarged fragmentary longitudinal sectional view of a. portion of the switching device taken along the line 4-4 in Fig. 1, illus'- trating the mounting arrangement for the armature thereof ;-Fig. 5 is an enlarged fragmentary plan view ofa pair of thel switch springs included in the switching device shown in Fig. 1; and Fig. 6v is a longitudinal sectional view of the pair of switch springs taken along the line 6-5 in Fig. 5. .-31

Referring now more particularly to Figs. 1 to 3, inclusive, of the drawing, the switching device there shown comprises an insulating support I0 and an electromagnetic relay II. The relay Il is provided with a field structure including a longitudinally extending core element I2 prothrough aligned openings provided in the Washer 24 and the clamping member 2| and in threaded engagement with a tapped hole provided in the field element I4.

First and second sets of associated switch springs 26 and 21, respectively, are carried by the field element I4 and operatively associated with the operating arms I6 and I1, respectively, of the armature I5. The sets of switch springs 25 and 21 bias the armature I5 in a clockwise direction about the pivot pin 20, as viewed in Fig. 2, into a normal position. When the winding I3 carried by the core element I2 is energized, the electromagnetic flux set up in the core element |2, the field element I4 and the armature I5 causes the armature to be rotated in a counterclockwise direction about the pivot pin 2U, as viewed in Fig. 2, from its normal position to an operated position, thereby to cause the operating arms IE and I1 of the armature I5 to actuate the sets of switch springs 26 and 21, respectively.

The pivotal mounting for the armature I5 closely adjacent both the outer surface and the end of the field element I4 provides a field structure for the relay l I having a minimum electromagnetic reluctance. More specically, the core vided with a winding I3, a longitudinally extending field element I4, and a movable amature I5 operatively associated with the core element I2 and the field element I4.

As best shown in Figs. 1 and 4, the core element I2 and the field element I4 are arranged in spacedapart relationship; and the armature I 5 is carried by the field element I4 adjacent the outer end thereof. More particularly, the armature I5 is pivotally mounted on the outer end of the field element I4 and is provided with two laterally spaced-apart operating arms I6 and I1 projecting over the outer surface of the field element I4 and two upwardly extending and laterally spacedapart supporting arms I8 and I9 disposed on opposite sides of the field element I4 and pivotally mounted on the opposite ends of a laterally extending pivot pin 20 carried by the fieldelement I4 adjacentthe end thereof. 'I'he pivot pin 2|) is clamped directly to the outer surface of the fieldl element I4 by an arrangement including a clamping member 2| provided with two spacedapart clamping arms 22 and 23 embracing a portion of the pivot pin 20 disposed intermediate the ends thereof, The clamping member 2| is securely fastened to the outer surface of the field element I4 by an arrangement comprising a washer 24' and a screw 25, the screw 25 extending element I2, the field element I4 and the armature I5 are so constructed and arranged that the air gap between the armature i5 and the end of the field element I4 is substantially unaltered as the air gap between the end of the core element I2 and the armature I5 is altered incident to the operation of the relay.

An arrangement is provided for preventing the armature I5 from sticking to the end of the core element I2 due to the residual magnetic forces therebetween, which comprises an adjustable screw 28 arranged in a threaded hole provided in the 'armature I5 adjacent the end of the core element I2, the screw 28 being formed of a nonmagnetic material, such as brass. Furthermore, a locking nut 29 is arranged in threaded engagement with the screw 28 in order to lock the screw 28 in any desired adjusted position. Also, an arrangement is-provided for preventing the ends ofthe operating arms I6 and I1 of the armature I5 from sticking to the adjacent portions of the outer surface of the field element I4A due to the residual electromagnetic forces therebetween, which comprises two portions 30 and 3| of the clamping member 2 I, the portion 30 of the clamping member 2| being disposed between the operating arm I6 of the armature I 5 and the adjacent portion of the outer surface ofthe field element I4; and the portion 3| of the clamping member 2| being disposed between the operating arm I1 of the armature I5 and the adjacent portion of the outer surface of the field element I4. Preferably, the clamping member 2| comprises a onepiece construction and is formed of a suitable nonmagnetic material, such as brass.

The arrangement for pivotally mounting the armature of the relay upon the field element thereof and for preventing the operating arm of the armature from sticking to the associated field element due to the magnetic forces therebetween is disclosed and claimed in the oopending application of Fredric E. Wood, Serial vNo. 310,300, filed December 21, 1939, which application is a division of the present application.

As best shown in Figs. 1 .to 3, inclusive, the set of switchsprings 26 comprises two cooperating individual switch springs 32 and 32 arranged in superimposed relationship; while the set of switch springs 21 comprises four cooperating individual switch springs 34, 35, 36 and 31 arranged in superimposed relationship. Each of the switch springs comprises a4 base end and a free end, and is provided with a cantilever mounting at its base end. Also, the switch springs are insulated from each other and from the field element I4 at theirv base ends. The arrangement for mounting and' for insulating the base ends of the set of switch springs 26 comprises a base plate 38 carried by the field element I4, a clamping plate 39 and a plurality of insulating strips 40 disposed between the base plate 38, the clamping plate 39 and the switch springs 32 and 33. Also, two screws 4I are Provided which extend through aligned openings provided in the base plate 38, the clamping plate 39, the insulating strips 40 and the switch springs 32 and 33 and threaded into tapped holes provided in the field element I4. The arrangement for mounting and for insulating the base ends of the set of switch springs 21 is substantially identical to the arrangement for mounting and for insulating the base ends of the set of switch springs 26 and includes a clamping member 42, two screws 43, a base plate, not shown, carried by the field element I4, and a number of interposed insulating strips, not shown.

Each of the switch springs 32, 34 and 36 comprises a first switch spring; while each of the switch springs 33, 35 and 31 comprises a second switch spring. The first switch springs are of identical construction; and the second switch springs are of identical construction; while the construction of each of the rst switch springs is substantially similar to the construction of each of the second switch springs. For example, the rst switch spring 32, as best shown in Figs. and 6, has an elongated longitudinally extending slot or eyelet 44 formed therein adjacent the free end thereof which provides the first switch spring 32 with two elongated laterally spaced-apart and independently iiexible portions 45 vand 46 connected together at the free end of the first switch spring 32 by a curved operating portion 41; while the second switch spring 33 has an elongated longitudinally extending slot 48 formed therein adjacent the free end thereof which provides the second switch spring 33 with two elongated laterally spacedapart and independently flexible portions 49 andy 50. Accordingly, the rst switch spring 32 has an elongated eylet formed therein adjacent the free end thereof; while the second switch spring 33 has a substantially Y-shaped configuration. The second switch spring 33 vis arranged in superimposed relationship with respect to the first switch spring 32,` the flexible portions 49 and 50 of the second switchspring 33 being respectively superimposed with respect to the flexible portions 45 and 46 of the first switch spring 32.

The flexible portions 45 and 46 of the first switch spring 32 carry two longitudinally extending metallic contacts v5I and 52, respectively; while the exible portions 49 and 50 of the second switch spring 33 carry two laterally extending metallic contacts 53 and 54, respectively. The metallic contacts 5I and 53 are arranged in cooperating relationship; while the metallic contacts 52 and 54 arearranged in cooperating relationship. More particularly, each of the sets of metallic contacts 5I, 53 and 52, 54 are arranged in crossing relationship, thereby to insure properv contact between the cooperating pairs of contacts in spite of slight mechanical variations in the positions of the first and second switch springs 32 and 33, respectively. Each of the metallic contacts 5I to 54, inclusive, is formed of a precious arc-resisting metal, has a substantially obelisk configuration, and is welded to the associated exible portion of the switch spring. More particularly, each of the metallic contacts 5I to 54, inclusive, is carried substantially at the point along the length of the associated flexible portion of the switch spring whereat the exible portion has a maximum movement with respect to the base end or body portion of the switch spring, thereby to insure self-equalization of contact pressure between the respective engaging contacts when the contacts respectively carried by the flexible portions of the first switch spring 32 are forced into respective engagements with the contacts respectively carried by the flexible portions of the second switch spring 33.

In order to facilitate movement of the rst switch springs 32, 34 and 36 with respect to the respectively associated second switch springs 33, 35 and 31, operating members 55, 56 and 51 are respectively carried by the first switch springs 32,

-34 and 36 adjacent the free ends thereof. More specifically, the operating member 55 is secured to the operating portion 41 of the rst switch spring 32 by an arrangement comprising a drive screw 58 extending through aligned openings provided in the operating portion 41 of the first switch spring 32 and in the operating member 55. Preferably, the drive screw 58 is of the Parker- Kalon type; while the operating member 55 is formed of an inactive organic insulating material, for a purpose more fully described subsequently. Furthermore, the operating member 55 is provided with a semispherical operating end. Also, it is noted that the operating members 5.6 and 51 are substantially identical to the operating member 55 and are respectively secured to I -55 is secured to the first switch spring 32.

Referring more particularly to Fig. 3, it will be noted that the operating end of the operating member 55 carried by the first switch spring 32 is arranged in direct engaging relationship with the operating arm I6 of the armature I5; the operating end of the operating member 56 carried by the rst switch spring 34 is arranged in direct engaging relationship with the operating arm I1 of the armature I5; and the operating end of the operating member 51 carried by the first switch spring 36 is arranged in direct engaging relationship with the head of the driving screw retaining the operating member 56 to the first switch spring 34.

During the operation of the relay II, when the winding I3 is energized, the armature I5 is rotated about the pivot pin 20 in a counterclockwise direction, as viewed in Fig. 2, as previously noted, thereby to cause the armature I5 to be. moved from its normal position to its operated position. When the armature I5 is moved from its normal position to its operated position, the arm I6 carried thereby engages the operating member 55, thereby to cause the first switch spring 32 to be bent toward the cooperating second switch spring 33; while the arm I1 carried thereby engages the operating member`56, thereby to cause the first switch spring 34 to be bent toward the second switch spring 35. Also, the movement of the operating member 56 carried by the first switch spring 34 is transmitted to the operating member 51 carried by the first switch spring 36, thereby to cause the first switch spring 36 to be bent toward the cooperating second switch spring 31. More particularly, the two pairs of metallic contacts carried by the switch springs 32, 33 are moved into engagement; and the two pairs of metallic contacts respectively carried by the switch springs 3|, 35 and 36, 31 are moved into engagement.

Incident to the operation of the sets of switch springs 26 and 21 by the relay Il, the operating members 55, 55 and 51 are subjected to some wear, whereby dust wearing from the operating members accumulates upon the cooperating metallic contacts carried by the switch springs. In conventional switching devices of this character, theoperating members 55, 56 and 51 are formed of hard rubber which contains some sulphur. The sulphur contained in the dust accumulating upon the cooperating metallic contact members carried by the switch springs reacts with the metallic contacts to produce certain metallic electrical insulating compounds of 'the sulphide type upon the outer surfaces of the metallic contacts, which metallic electrical insulating compounds disposed upon the outer surfaces of the cooperating metallic contacts prevent proper electrical contact therebetween. In order to obviate this inherent defect in conventional switching devices of this type, the operating members 55, 58 and 51 are formed of an inactive organic material in accordance with a feature of the present invention, whereby the dust wearing therefrom and accumulating upon the cooperating metallic contacts carried by the switch springs does not react with the metallic contacts 'to produce metallic electrical insulating compounds upon the outer surfacesof the metallic contacts. For example, the operating members 55, 58 and 51 may be formed of a suitable phenol formaldehyde or cellulose ester resin. However, it is preferable that these operating members are formed of the cellulose acetate compound known as Tonite The relay ii and the sets of switch springs 25 and 21 carried thereby are provided with an elongated casing 59 which cooperates with the support I to enclose the relay II and the sets of switch springs 25 and 21. More particularly, the enclosing casing 59 is provided with a handle 50 and anopen end 5| and is slidably carried by the relay Il. The arrangement for slidably supporting the casing 59 upon the relay il comprises a guide member 62 carried by the relay Il and disposed between the eld element Il and the sets of switch springs 26 and 21. More particularly, the screws Il and 43 which are utilized to secure the sets of switch springs 26 'and- 21, respectively, to the field element Il also extend through aligned openings provided in. the

` laterally projecting guiding beads 53 and 5I disposed on opposite sides thereof adjacent the opposite sides of the field element il, which guiding beads cooperate with two aligned guiding beads 55 and 85 provided in the opposite side walls of the casing 58. Also, the guide member 52 carries two laterally and downwardly extending locking tabs 51 and 88 on the opposite sides thereof which cooperate with two locking beads I8 and 10, respectively, provided in the opposite side walls o! the casing 59. 'I'he arrangement of the guiding beads 33 and 84 and the locking tabs 51 and 8l carried by the guide member 52; and the arrangement of the guiding beads 55 and'i and the locking beads 69 and 10 provided in the opposite side walls of the casing 59 provide for ready placement and removal of the casing 53. Furthermore, it is noted that the interfitting guiding parts carried by the guide member 52 and provided in the opposite side walls of the casing 59 facilitate the sliding movement of the casing 55 and securely lock the casing 5B in position when it is placed upon the relay il.

.It is noted that any reasonable number of individual switch springs may be included in the sets of switch springs 26 and 21 carried by the field element il of the relay Il and that during assembly of the switch springs carried by the ileldelement I4, a suitable number of first and second switch springs are selected and arranged in stacked relationship upon the guide member 62 `carried by the field element Il. The stacked switch springs carried by the field element I4 are aligned by a suitable jig and then securely clamped to the field element Il, the alignment of the switch springs by the jig being facilitated by virtue of the fact that the slots provided in the switch springs are normally disposed in alignment with each other,` thereby to accommodate the jig. Preferably, the side walls of the jig are tapered toward the' forward edge thereof, thereby to insure that the stacked switch springs are aligned both in a lateral and in a longitudinal direction. After the sets of switch springs 2l and 21 have been assembled upon the relay ii, the relay Ii and the sets of switch springs 2B and l21 carried thereby are suitably secured upon the insulating support I0, the support i0 being provided with openings therein through which the terminals for the winding i3 of the relay Il and for the individual switch springs extend. The casing 59 is then slidably placed uponth'e relay li, the casing being guided in place by the guide member 62. When the casing 59 occupies its normal position upon the relay ii it cooperates with the support I0 to provide an enclosing casing for the relay i I and the sets of switch springs 26 and 21 carried thereby, in order to prevent the accumulation of dust and other foreign matter upon the cooperating sets of metallic contacts carried by the sets of switch springs.

In view of the foregoing, it is apparent that an improved switching device of th'e electromagnetic relay type is provided which is of rugged and economical construction and which is reliable and positive in operation.

While there hasbeen described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a switching device, a number of switch' springs formed of nat metallic stock and disposed with their fiat sides opposite each other in substantially parallel planes, each of said switch springs having a base end and a free end, means for providing each of said switch springs with a y cantilever mounting at its base end and for insulating said switch springs from each other at their base ends, each of said switch springs -being provided with two spaced-apart and independently exibl'e portions disposed adjacent the free end thereof, a plurality of contacts respectively car ried by the flexible portions of said switch springs. the contacts respectively carried by the flexible portions of each of said switch springs respectively cooperating with the contacts respectively carried by the flexible portions of adjacent ones of the switch springs, at least one of said switch springs being provided with an operating portion at the free end thereof extending between the two flexible portions thereof, an operating member carried by the operating portion of said one switch spring substantially intermediate the two flexible portions thereof, and means cooperating with said operating member for bending said one switch spring, thereby to effect la change in the relative positions of the contacts respectively carried by the flexible portions of at least two adjacent ones of said switch springs, said member having a semibulbous operating. surface in order to facilitate both lat-eral and longitudinal flexing of said one switch spring.

2. In a switching device, a pair of associated switch springs, each of said switch springs being provided with two spaced-apart and independ-v ently flexible portions disposed adjacent the free end thereof, a plurality of contacts respectively carried by the flexible portions of said switch springs, the contacts respectively carried by the flexible portions of one of said switch springs respectively cooperating with the contacts respectively carried by the flexible portions of the other of said switch springs, at least one of said switch springs being provided with an operating portion at the free end thereof extending between the two flexible portions thereof, an operating member carried by the oper-ating portion of said one switch spring substantially intermediate the two flexible portions thereof, and means cooperating with said operating member for bending said one switch spring toward the other, thereby to force the contacts respectively carried by the fiexible portion of said one switch spring into respective engagements with the contacts respectively carried by the flexible portions of the other of said switch springs, each of the contacts being carried substantially at the point along the length of the associated flexible portion of the switch spring whereat the fiexible portion has a maximum movement with respect to the body portion of the switch spring, thereby to insure self-equalization of contact pressure among the respective lengaging contacts.

3. In a switching device, first and second associated switch springs, said first switch spring including a base end and a free end and having an elongated eyelet provided therein forming two elongated spaced-apart and independently flexible portions and a connecting portion disposed at the free end thereof, said second switch spring including a base end and a, free end, means for providing each of said switch springs with a mounting at its base end and for insulating said switch springs from each other at their base ends, two contacts respectively carried by the flexible portions of said first switch spring, two contacts carried by said second switch spring adjacent the free end thereof, the two contacts respectively carried by the exible portions of said first switch spring respectively cooperating with the two contacts carried by said second switch spring, an operating member carried by the connecting portion of said first switch spring intermediate the two flexible portions thereof, and means for moving said operating member thereby to bend said first switch spring in order to effect a change in the relative positions of the two contacts respectively carried by the flexible portions of said-first switch spring and the two contacts carried by said second switch spring, said member. having a semian elongated eyelet provided therein forming two elongated spaced-apart and independently flexible portions and a connecting portion disposed at the free end thereof, said second switch spring including a base end and a free end, means for providing each of said switch springs with a mounting at its base end and for insulating said switch springs from each other at their base ends,

two contacts respectively carried by the flexible portions of said rst switch spring, two contacts carried by said second switch spring adjacent the free end thereof, the two contacts respectively carried by the flexible portions of said first switch spring respectively cooperating with the two contacts carried by said second switch spring, an operating member carried by the connecting portion of said first switch spring intermediate the two flexible portions thereof, said operating member being provided with a head having a substantially semispherical configuration, an element operative to engage the head of said operating member, thereby to bend said'rst switch spring in order to move the two contacts respectively carried by the flexible portions of said first switch spring into respective engagements with the two contacts carried by said second switch spring, the semi-spherical configuration of the head of said operating member accommodating self-equalization of the contact pressures between the respective engaging contacts, and means for operating said element.

`5. In a switching device, an operating contact spring having a free end and a stationary base end, means for rigidly securing said base end, di- A verging portions and converging portions of said spring forming a closed ovate-lanceolate slot near its free end, contacts on said diverging portions intermediate said base and free ends, and an operating member secured to the extreme free end of said spring at the converging point of said converging portions.

6. In a switching device, an operating contact spring having a free end and a stationary base end, means for rigidly securing said base end, diverging portions and converging portions of said spring forming a closed ovate-lanceolate slot near its free end, contacts on said diverging portions intermediate said base and free ends, and an operating member secured to said spring on the longitudinal center line of said spring.

7. In a switching device, an operating contact spring having a free end and a stationary base end, means for rigidly securing said base end, said spring having a closed elongated hole thereby forming two flexible portions near its free end, a contact on each of said flexible portions located on opposite sides of said hole and intermediate the base and free ends, and an operating member secured to said spring on the longitudinal center line of said spring.

8. In a switching device, an operating contact spring having a free end and a stationary base end, means for rigidly securing said base end, said spring having a closed elongated hole thereby forming two flexible portions near its free end, a contact on each of said flexible portions located on opposite sides of said hole and intermediate the base and free ends, and an operating member secured to the extreme free end of said spring on th'e' longitudinal center line of said spring, said member having'a semibulbous operating surface in order to facilitate both lateral and longitudinal iiexing of said spring, whereby self-equalization of contact pressure between said contacts is lnsured.

9. In a switching device. an operating contact spring having a free end and a stationary base end, means for rigidly securing said base end, said spring having a closed elongated hole thereby forming two flexible portions near its free end, a contact on each of said exible portions located on opposite sides of said hole and intermediate the base and free ends, an operating member secured to said spring on the longitudinal center line of said spring, and other contact springs having contacts for cooperating with said operating spring contacts.

140. In a switching device, an operating con tact spring having a free end and a stationary base end, means for rigidly securing said base end, said spring having a closed ovate hole near its free end thereby forming two flexible portions near its free end, a contact on each' exible portion located opposite the widest portion of said hole and intermediate the free and base ends whereby said contacts are located on said spring at the most iiexible point, and an operating mem ber secured to said spring on the longitudinal center line of said spring thereby ensuring movement of one flexible portion and its contact in case the other nexible portion and its contact is held against movement.

11. In a switching device, an operating contact spring having a free end and a stationary base end, means for rigidly securing said base end, said spring having a closed ovate hole near its free end thereby forming two exible portions near its free end, a contact on each flexible portion located opposite the widest portion of said hole and intermediate the free and base ends whereby said contacts are'located on said spring at the most iiexible point, and an operating member so shaped and secured to said spring on the longitudinal center line of said spring as to ensure the closure of the contact on one flexible portion with a mating contact even though movement or the contact on the other flexible portion is retarded or prevented.

' FREDRIC E. WOOD.

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