US1538938A - Switch construction - Google Patents

Description

May 26, 1925.

G. E. HULSE SWITCH CONSTRUCTION Filed Feb. 15, 1922 41 44 V 2Q 25 21 3- p L, 52 34 i f 19 6'6, 59 4'0 5 I I. 56 55 1: 16 l v {Y/X/I/X/X/ 3'4 5 52 15 10 13 9? M anvemto'c Patented May 26, 1 925.

"um'ran STATES PATENT OFFICE.

GEORGE E HULSE, OF NEW HAVEN, CONNECTICUT, ASSIGNOB TO SAFETY CAR HEAT- ING & LIGHTING COMPANY, A CORPORATION OF NEW JERSEY.

SWITCH CONSTRUCTION.

Application filed February 15, 1922. Serial No. 536,611.

To all whom it may concern:

Be it known that I, GEORGE E. HULsE, a citizen of the United States, and a resident of the city of New Haven, in the county'of New Haven and State of Connecticut, have invented an Improvement in Switch Con struction, of which the following is a specification.

This invention relates to switches for controlling electrical circuits and, more particularly, to thermostatically controlled switches.

One of the objects of this invention is to provide a simple and practical switch construction of positive and reliable action. Another object is to provide a switch con struction capable of quickly interrupting or closing an electric circuit in response to a gradually or progressively varying operating force and, more particularly, to provide a switch construction of this nature in which arcing at the circuit-closing contacts is prevented from resulting in detrimental effects. Another object is to provide a switch of the above nature in which the opening of the switch in response to a slowly varying force is made positive, de-

endable and quick in action. ther obects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the tfeatures of construction, combination of elements and arrangement of parts as will be exemplified in the structure to be hereinafter descrlbed, and the scope of the application of which will be indicated in thc following claims.

In the accompanying drawings in which is shown one of various possible embodiments of this invention,

Figure 1 is a plan view of the switch proper; and

Figure 2 is a side elevation, partly in section, of the switch showing also diagrammatically the electrical circuits associated therewith.

As conducive to a clearer understanding of this invention, it may at this point be noted that in .any switch construction for controlling electric circuits it is of practical importance that the circuit-closing members be moved relatively to one another quickly and abruptly in order that arcing at the separation of the active contacts be avoided. Where switches for controlling electric circuits are employed and adapted to be controlled or operated by a force which increases or decreases relatively slowly, provision must be made for maintaining the circuit-closing contacts in contact with one another with a substantial pressure since, as the gradually varying operative force approaches a critical value. the coacting contacts are relieved of the pressure exerted therebetween preliminary to'the operative force exceeding the critical value required for operating the switch. As the contacts are relieved of the desired pressure, there arises a tendency for arcing to take place between the contacts and this I arcing will be maintained until the operative force passes the critical value and actually separates the contacts. It is particularly an object of this'inventio-n to preclude such arcing from taking place and from resulting in destruction of, the coacting contacts.

Thus, for example, where it is desired to control an electric circuit in response to temperature changes, the conditions above 8 briefly mentioned are met with and the embodiment of this invention herein described will be considered in connection with an electric circuit controlled in accordance with temperature changes.

Referring now to the drawings, there is shown a main base plate 10 upon which the several mechanisms may be mounted or assembled. In Fig. 2 of the drawings thereis shown at 11 an electric motor by way of example whose connection to the storage battery 12 and whose operation therefore it is desired to control in predetermined manner.

The circuit of the motor 11 is carried through the conductors 13 and 14 to two terminals or binding posts 15 and 16 respectively mounted upon the contact-supporting arm 17 suitably secured and mounted upon the base plate 10, as by means of the screws 18. The binding posts 15 and 16 are associated with contacts 19 and 20 respectively to be more clearly hereinafter described, adapted to be placed in electrical connection with one another by means of an electrically conductive bridging member 21 mounted upon 105 R 1 f he lever or arm 22 pivotally mounted at substantially its center upon a suitable pin 23 supported in the post 24 suitably secured to the base plate 10. Pivotally mounted at its center upon the pin 23 and adjacent the arm 22is a second arm or lever 25 to the respective ends of which as at 26 and 27 are pivotally connected the springguiding rods 28 and 29. The spring-guiding rods 28 are in slidable connection with the projecting lugs 30 and 31, respectively, suitably mounted upon the side and at the ends of the arm 22, suitable openings being provided in the lugs 30 and 31 for slidably supporting and guiding the rods 22 and 29 respectively. Upon the guiding rods 28 and 29 are mounted the coil springs 32 and 33 respectively adapted to form with the rocker arm 25 a toggle for operating the arm 22 and its associated bridging member 21.

The toggle formed by the rocker arm 25 and the springs 32 and 33 is operated or controlled by means of a diaphragm 34 suitably mounted in a housing 35 preferably secured to the under side of the base plate 10. The chamber formed between the diaphragm 3t and the housing 35 is connected by means of a tube 36 to a thermostatic vessel. generally indicated at 37. The thermostatic vessel 37 contains a suitable volatile liquid such as. for example. ethylchloride. so that upon a rise in temperature adjacent the thermostatic vessel 37 the vapor tension of the ethyl chloride rises and. acting against the diaphragm 34. becomes effective' to move the latter in an upward direction as seen in Fig. 2. Vice versa. should a decrease in temperature adjacent the thermostatic vessel 37 take place. the vapor tension in the system will be decreased so that the diaphragm 34 may be moved in the opposite or downward direction as viewed in Fig. 2 by the atmospheric pressure exerted thereon.

A stem 38 is suitably connected to the diaphragm 34 and extends upwardly through the base plate 10. Surrounding the stem 38 is an expansible spring 39 acting. between the base plate 10 and a thumb nut 40 suitably threaded upon the stem 38. The tension of the spring 39 against which the atmospheric pressure upon the diaphragm 34 operates may thus be adjusted to the vapor tension. and hence the temperature limits between which the diaphragm 34 becomes operative, may be balanced or adjusted against the atmospheric pressure.

The upper end of the stem 38 passes loosely through a suitable opening in a lever 41 pivotally mounted at its one end as at 42 to a supporting post 43 suitablv mounted upon the base plate 10. The other end of the lever 41 is pivotallv connected as by means of the pin 44 to one end of the rocker arm 25 forming part of the toggle. A pair of nuts 45 and 46 threaded upon the stem 38, one upon each side of the lever 41, make the operative connection between the stem 38 and the lever 41 and it will be noted that this connection may be readily adjusted so that the operative parts may be adjusted with respect to one another for most efficient operation.

In Fig. 2 of the drawings the bridging member 21 is shown in circuit-closing relation with respect to the contacts 19 and.20 so that the circuit of the motor 11 is closed. Assuming now, for example, that the motor operates a suitable cooling mechanism whose operation it is desired to control within predetermined temperature limits, it will be seen that as the temperature surrounding the thermostatic vessel 37 decreases, the vapor pressure within the associated pressure system is progressively decreased. The atmospheric pressure thus becomes progressively more effective to move the diaphragm 3t and its associated stem 38 in downward direction as viewed in Fig. 2 against the decreasing vapor pressure operative upon the diaphragm 34 within the chamber 35. This movement takes place relatively slowly and the corresponding swinging of the rocker arm 25 in a clockwise direction as viewed in Fig. 2 through the lever 41 takes place at a substantially correspondingly slow rate. The springs 32 and 33 act by their tension to hold the bridging member 21 either in or out of circuit-closing relation with respect to the contacts 19 and 20. and during the progressive clockwise rotation of the rocker arm 25 the latter. together with the springs. is gradually brought into substantially straight-line position. During this action the springs are compressed and, because of their being placed in substantially straight-line relation to the rocker arm 25, the pressure with which they are effective to hold the bridging member 21 in desired position is materially decreased. Hence. for example. the bridging member21 is held in circuit-closing relation to the contacts 19 and 20 at a very much less pressure than is necessary for the maintenance of good electrical contact. and hence arcing will take place between the contacts and the bridging member and this arcing will continue until the pressure operative within the chamber 25 is sufficiently decreased to permit the rocker arm 25 to be moved further in a clockwise direction to break the toggle formed by the rocker arm 25 and the springs out of straight-line position. Since the forces acting upon the toggle arm 25 vary relatively slowly. a material period of time may elapse before the above action takes place .and during which time the arcing would tend to continue with destructive effects upon the contacts. f

In order to prevent destructive arcin taking place and to make the operation 0% the switch positive, there is mounted upon the base member 10 a U-shaped iron core 17 upon the two vertical legs of which are mounted the windings 48 so that the core forms part of the magnetic circuit therefor. The core 47 and its windings -18 are mounted adjacent the one end of the lever or arm 22 so that an armature 49 mounted upon the end of the arm 22 may be operated upon by the electromagnet 48. The windings 48 are connected by one conductor 50 to the binding post 15 associated with the contact 19 and by another conductor 51 to a third binding post 52 in electrical connection with a contact 53 preferably interposed between. the contacts 19 and 20 hereinbefore described. The contacts 19, 20 and 53 are preferably yieldingly mounted upon the supporting arm 17 and may, for example, be of cylindrical construction slidably mounted in a housing 54 threaded upon the head 55 of the binding posts, as 16 for example. A spring 56 is interposed between each contact and the head 55 of the associated binding post and tends to urge the contact, as 20 for example, in an upward direction. A collar 57 preferably integrally formed with the contacts is associated with each contact 19, 20 and 53 andlimits the upward movement of the contacts in response tothe action of the springs 56.

As will be seen from Fig. 2, the supporting arm 17 is inclined slightly so as to maintain the contacts 19, 20 and 53 in substantial alignment with the bridging member 21 when the latter is swung downwardly into circuit-closing relation therewith, Contact members 20 and 53 are preferably of such length that they are substantially simultaneously engaged by or disengaged from the bridging member 21. Contact member 19,

, however, is somewhat shorter and its upper end lies normally slightly below the plane passing through the upper ends of the contacts 20 and When the bridging member 21 is swung in clockwise direction and into circuit-closing relation to the several contacts, the springs 32 and 33 forming with the rocker arm 25 the operating toggle, oppose the action of the springs 56 associated with the contacts 19, 53 and 20 so that the springs 56 are compressed and so that the bridging member 21 is held in electrical contact with the associated contact members at a substantially predetermined pressure, and p the several parts will assume the positions substantially as shown in Fig. 2 of the drawings.

Turning now to the action of the progressively or slowly varying force operating upon the toggle or rocker arm 25, it will be seen as above mentioned, that as the rocker arm 25 is brought into straight-line relation with respect to the springs 32 and 33, the latter become less effective to hold the bridg- .bers tend to maintain within the limits of their operation a good electrical contact between the respective or associated parts and tend to cause the contacts 19, 53 and 20 to follow up the slight retrograde movement of the arm 22 due to the relative ineffectiveness of the springs 32 and 33 to maintain them positively in circuit-closing position. Before, however, the operating toggle is broken or brought out of straight-line relation by the progressive or slow movement in a clockwise direction of the rocker arm 25 in response to the diaphragm 34, a material period of time will elapse and the resultant decrease in the pressure of contact would tend to cause destructive arcing to take place. It will be seen, however, that contact 19 being shorter than the contacts 53 and 20 will be the first of the three contacts at which such decrease in pressure of contact takes place and that, therefore, the arcing will take place at the contact 19. The windings 48 of the electromagnet, however, in being connected to the binding posts 15 and 52, are in eflect bridged across the arc gap formed bet-ween the bridging member 21 and the contact 19. As soon,

therefore, as arcing takes place, the potenline relation 01', in other words, the toggle is broken and the compressed springs and 33 are at once free to snap the arm 22 in counter-clockwlse direction thus to move the bridging member 21 quickly and rapidly away from its associated contacts.

Thus it will be seen that the lapse of time required for the slowly varying force operative upon the toggle to bring the same out of straight-line position is avoided and that destructive arcing which tends to take place during this lapse of time is avoided. Furthermore, it will be seen that whatever arcing of a destructive nature tends to take lace is concentrated at a predetermined contact and that as soon as this arcing takes place the electromagnets become instantaneously effective to bring about the opening of the switch in a rapid and abrupt manner to prevent further arcing from taking place. It will also be noted that upon the operation of the electromagnets, as hereinbefore described, they are after operation at once the windings; furthermore, also, so thatthe diaphragm and its associated mechanisms are freeto move the switch into circuitclosing position without opposition by the magnets themselves.

It will thus be seen that there has been provided in this invention a switch construction in which the several objects hereinbefore set forth, as well as others, are achieved and in which many advantages are attained. It will further be seen that there has been provided a switch construction of dependable and inexpensive construction and one'that is well adapted to meet the conditions of practical use.

As many embodiments might be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In construction of the general nature of that herein described, in combination, a pair of contacts adapted to control the opening and closing of an electric circuit, means for moving one of said contacts into and out of circuit-closing relation with respect to the other, an electromagnet connected across said contacts, thereby to be energized by the potential drop across the are formed between said contacts as said operating means moves one of said contacts out of circuit-closing position with respect to the other, means responsive to the energization of said electromagnet for relatively rapidly moving said contact away from the other, and means responsive to the actuation of said last-mentioned means by said electromagnet for disconnecting said electromagnet from one of said contacts.

2. In construction of the general nature of that herein described, in combination, a pair of contacts adapted to control the opening and closing of an electric circuit, means for moving one of said contacts into and out of circuit-closing position with respect to the other, and means operated by an electromagnet energized by the potential drop across the are formed between said contacts as said operating means moves one of said contacts out of circuit-closing position with respect to the other for rapidly withdrawing said contact from the other.

3. In construction of the gene :11 nature of that herein described, in combination, a

air of contacts adapted to control the opening and closing of an electric circuit, toggle means for moving one of said contacts into and out of circuit closing position with respect to the other, and means controlled by the are formed between said contacts as said toggle means upon its operation begins to move one of said contacts away from the other for assisting said toggle means to rapidly move said contact away from the other.

4. In construction of the general nature of that herein described, in combination, a pair of contacts adapted to control the opening and closing of an electric circuit, toggle means including a spring link for moving one of said contacts into and out of circuit-- closing relation with respect to the other, said spring link acting to hold said contact in circuit-closing relation with respect to the other after operation of said toggle means, an electromagnet connected across said contacts and adapted to be energized by the potential drop across the are formed therebetween as said toggle means is operated into substantially straight-line relation, thus making said spring link ineffective to hold said contact in circuit-closing relation to the other, an armature associated with said electromagnet. and connections between said armature and said toggle means whereby upon energization of said magnet said toggle means is operated thereby out of straight-line position to move said contact out of circuit-closing relation with respect to the other.

5. In construction of the general nature of that herein described, in combination, a pair of contacts adapted to control the opening and closing of an electric circuit, toggle means including a spring link for moving one of said contacts into and out of circuitclosing relation with respect to the other, said spring link acting to hold said contact in circuit-closing relation with respect to the other after operation of said toggle means, an electromagnet connected across said contacts and adapted to be energized by the potential drop. across the arc formed therebetween as said toggle means is operated into substantially straight-line relation, thus making said spring link ineffective to hold said contact in circuit-closing relation to the other, an armature associated with said electromagnet, and mechanical connections between said armature and said contact whereby upon energization of said magnet said contact is rapidly moved away from its cooperating contact.

6. In construction of the general nature of that herein described, in combination. a pair of contacts adapted to control the opening and closing of an electric circuit. means mechanically connected to one of said contacts and responsive to a relatively slowly varying force for controlling the movement of one of said contacts toward or away from the other. and means controlled by the are formed between said contacts as said contacts are relatively slowly separated by said operating means for initiating a rapid movement of one of said cont-acts away from the other.

7. In construction of the general nature of that herein described, in combination,

a pair of contacts ada ted to control the opening and closing 0 an electric circuit, means responsive to a relatively slowly varying Pressure for controlling the movement of one of said contacts toward or away from the other, an electromagnet. connected across said contacts and adapted to be ener- 'ized by the otential drop across the arc iormed there etween as said pressure-responsive means begins the movement of one of said cont-acts away from the other, an armature associated with said electromagnet, and mechanical connections between said armature and said moving contact for initiating a rapid movement thereof away from the other contact.

8. In construction of the general nature of that herein described, in combination. a pair of contacts adapted to control the opening and closing of an electric circuit, one of said contacts being movable with re-' spect to the other, toggle means including a spring link for moving said movable contact into or out of circuit-closing relation with respect to the other, said sprin link being adapted upon operation of sai toggle to hold said movable contact in or out of circuit-closing relation with respect to the other contact respectively, means responsive to a relatively slowly varying pressure for operating said toggle means, and

I auxiliary means operative to assist said toggle means to move said movable contact away from its cooperating contact and operative upon said toggle-operatin means having placed said toggle means into substantially straight-line position.

9. In construction of the general nature of that herein described, in combination, a pair of contacts adapted to control the opening and closing of an electric circuit one of said contacts being movable with respect to the other, toggle means including a spring link for moving said movable contact into or out of circuit-closing relation to the other, said spring link acting to hold said movable contact in or out of circuit closing relation respectively upon operation of said toggle means, means responsive to a slowly varying pressure for operating said toggle means, and electromagnetic means operative to initiate the operation of said toggle means to movesaid movable contact away from its cooperating contact when said pressure-responsive tog le-operating means has progressively brought said toggle means into substantially straight-line position thereby to make said spring link ineflfective to hold said movable contact in circuit-closing relation to said other contact and con- ;trolled substantially by said spring link.

10. In construction of the general nature of that herein described, in combination, a pair of contacts adapted to control the opening and closing of an electric circuit one of said contacts being movable with respect to the other, toggle means including a spring link for moving said movable contact into or out of circuit-closing relation to the other, said spring link acting to hold said movable contact in or out of circuit-closing relation respectively upon operation of said toggle means, means responsive to a slowly varying pressure for operating said toggle means, an electromagnet connected across said contacts and adapted to,be energized by the potential drop across the are formed therebetween when said pressure-responsive toggle-operating means has operated said toggle means into substantially straight-line position thereby to make inefl'ective said spring link to hold said movable contact in close circuit-closin relation to the other, 'an armature associate with said electromagnet, and connections between said armature and said toggle means adapted in response to the energization of said magnet to complete the operation of said toggle means to move said movable contact out of circuit-closing relation to the other contact.

11. In construction of the general nature of that herein described, in combination, a pair of contacts adapted to control the opening and closing of an electric circuit, one of said contacts being movable with respect to the other, means for mov ing said movable contact into circuit-closing relation with respect to the other,

spring means associated with said movable contact for maintaining said contact in circuit-closing relation to the other, means opposing the action of said spring means and operative to cause said spring means to maintain said movable contact in electrical connection with said other contact at a predetermined pressure, and means controlled by said last-mentioned means and operative when said spring means fails to maintain said movable contact in electrical connection with said other contact at less than said predetermined pressure for moving said movable contact out of circuitclosing relation to said other contact.

12. In construction of the general nature of that herein described, in combination, a pair of contacts adapted to control the opening and closing of an electric circuit, one of said contacts being movable with respect-to the other, .means for moving said movable contact into circuit-closing relation to the other contact, means adapted to hold said movable contact in circuit-closing relation to the other with a predetermined pressure, a spring tending to oppose said holding means and operative to cause a separation between said contacts when said holding means exerts a pressure therebetween less than said predetermined pressure, and

Lil

means controlled by the separation of said contacts for moving said movable contact away from said other contact.

13. In construction of the general nature of that herein described, in combination, a pair of contacts adapted to control an electric circuit, one of said contacts being movable with respect to the other, means for holding said movable contact in circuitclosing relation to the other and adapted to hold said contacts together at a predetermined pressure, a spring tending to oppose said holding means and operative upon said holding means exerting a pressure less than said predetermined pressure to cause a separation between said contacts, and electromagnetic means energized by the potential drop across the arc formed between said contacts upon their separation for relatively rapidly moving said movable contact out of circuit-closing relation to the other contact.

14. In construction of the general nature of that herein described, in combination, a pair of contacts for controlling an electric circuit, toggle means including a spring link for moving one of said contacts into or out of circuit-closing relation to the other, said spring link being adapted to hold said contacts in circuit-closing position, means responsive to a relatively slowly varying force for operating said toggle means, means opposing said spring link and operative to separate said contacts when said spring link holds said contacts in circuitclosing relation to one another with a pressure less than a predetermined pressure as said toggle-operating means gradually places said spring link in substantially straight-line relation to its associated toggle members, and means controlled by the separation of said contacts for moving one of said contacts substantially rapidly away from said other contact.

15. In construction of the general nature of that herein described, in combination, a pair of contacts for controlling an electric circuit, toggle means including a spring link for moving one of said contacts into or out of circuit-closing relation to the other, said spring link being adapted to hold said contacts in circuit-closing position, means responsive to a relatively slowly varying force for operating said toggle means, means opposing said spring link and operative to separate said contacts when said spring link holds said contacts in circuit-closing relation to one another with a pressure less than a predetermined pressure as said toggle-operating means gradually places said spring link in substantially straight-line relation to its associated toggle members, and electromagnetic means controlled by said spring link opposing means for moving said toggle means out of straight-line relation thereby to permit said toggle means to move said contact away from the other contact.

16. In construction of the general nature of that herein described, in combination, a pair of contacts for controlling an electric circuit, toggle means including a spring link for moving one of said contacts into or out of circuit-closing relation to the other, said spring link being adapted to hold said contacts in circuit-closing position, means responsive to a relatively slowly varying force for operating said toggle means, means opposing said spring link and operative to separate said contacts when said spring link holds said contacts in circuit-closing relation to one another with a pressure less than a predetermined pressure as said toggle-operating means gradually places said spring link in substantially straight-line relation to its associated toggle members, and electromagnet means energized by the potential drop across the are formed between said contacts upon their separation by said spring link opposing means adapted to assist said toggle means in relatively rapidly.

moving said movable contact away from the other contact.

17. In construction of the general nature of that herein described, in combination, a relatively fixed contact, a second contactmounted adjacent thereto, means yieldingly mounting said second contact and tending to hold said second contact above the plane of said first contact, a circuit-closing member adapted to bridge said two contacts, means for moving said circuit-closing member into bridging relation to said two contacts, spring means operative upon the circuit-closing member and adapted to hold said member in bridging relation to said two contacts and in opposition to said yielding mounting means of said second contact whereby said member is held in circuit-closing relation to said two contacts with a predetermined pressure, and whereby said yielding mounting means of said second contact becomes effective to separate said member from said first contact upon said spring means exerting a force on said circuit-closing member less than said predetermined pressure, and means controlled by the separation of said circuit closing member from said first contact for moving said circuit-closing member away from both of said contacts.

18. In construction of the general nature of that herein described, in combination, a relatively fixed contact, a second contact adjacent thereto, means, yieldingly mountin said second contact and tending to hold sai second contact above the plane of said first contact, a bridging member adapted to place said two contacts in circuit-closing relation, toggle means including a spring link for moving said bridging member into and out of circuit-closing relation with respect to said two contacts, said spring link being operative to oppose said yielding mounting means of said second contact thereby to hold said bridging member in circuit-closing relation with respect to said two contacts and with a predetermined pressure, means controlled by a relatively slowly varying force adapted to operate'said to gle means, said yielding mounting means 0 said second con tact being operative to move said bridging member away from said first contact when said spring link exerts a pressure less than said predetermined pressure as said toggle operating means places said toggle means in substantially straight-line position, and means controlled by the separation of said bridgin member and said first contact for relative y rapidly moving said bridging member away from both of said contacts.

19. In construction of the general nature of that herein described, in combination, a relatively fixed contact, a second contact adjacent thereto, means yieldingly mounting said second contact and tending to hold said second contact above the plane of said first contact, a bridging member adapted to place said two contacts in circuit-closing relation,

toggle means including a spring link for,

moving said bridging member into and out of circuit-closing relation with respect to said two contacts, said spring link being operative to oppose said yielding mounting means of said second contact thereby to hold said brid ing member in circuit-closing relation wit respect to said two contacts and with a redetermined pressure, means controlled y a relatively slowly varying force adapted to operate said toggle means, said yielding mounting means of said second con-' tact being operative to move said bridging member away from said first contact when said spring'link exerts a pressure less than said predetermined pressure as said toggleoperatingmeans places said toggle means in substantially straight-line position, and means controlled by the separation of said brid ing member from said first contact for moving said toggle means out of straightline position thereby to permit said means to move said bridgin member out of convtact with both of said contacts.

second contact above the plane of said first contact, a bridging member adapted to place said two contacts in circuit-closing relation, toggle means including a spring link for moving said bridging member into and out of circuit-closing relation with respect to said two contacts, said spring link being operative to oppose said yielding mounting means of said second contact thereby to hold said bridging member in circuit-closing relation with respect to said two contacts and with a predetermined pressure, means controlled by a relatively slowly varying force adapted to operate said toggle means, said yielding mounting means of said second contact being operative to move said bridging member away from said first contact when said spring link exerts a pressure less than said predetermined pressure as said toggle-operating means places said toggle means in substantially strai ht-line position, an electromagnet connecte across said bridging member and said. first contact adapted to be energized by the otential drop across the are formed there etween, and an armature connected to said toggle means and adapted upon the energization of said electromagnetto move said to 'gle means out of straight-line position thereby to permit said to gle means to move said brid g member relatively rapidly away from 0th of said contacts.

21. In construction of the general nature of that herein described, in combination, a pair of contacts adapted to control the opening and closing of an electric circuit, means for moving one of said contacts into and out of circuit-closing relation with respect to the other, an electromagnet connected across said contacts, thereby to be energized by the potential across said contacts as said operating means moves one of said contacts out of circuit-closing position with respect to the other, means responsive to the energization of said electromagnet for relatively rapidly movin said one contact away from the other, an means operative upon said contacts being moved into circuit opening position to disconnect said electromagnet rom said contacts and operative upon said contacts being moved 1nto circuit-closing position to connect said electromagnet across said contacts.

In testimony whereof, I have signed my name to this specification this 9th day of February, 1922.

GEORGE HULSE.

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