US2137001A - Circuit breaker and energy absorber therefor - Google Patents

Description

Nov. 15, 1938. G. A. HEALIS 2,137,001 v CIRCUIT BREAKER AND ENERGY ABSORBER THEREFOR Filed Aug. 29, 1936 2 Sheets-Sheet l INVEN TOR.

A TTORN E Y.

Nov. 15; 1938. V G, A HEAL|$ 4 2,137,001

CIRCUIT BREAKER AND ENERGY ABSORBER THEREFOR Filed Aug. 29, 1936 2 Sheets-Sheei .INVENTOYR. w 'M ATTORNEY.

Patented Nov. 15, 1938 PATENT OFFICE CIRCUIT BREAKER sun ENERGY ABSORBER THEREFOR George A. Healis, Philadelphia, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of New Jersey Application August 29, 1936, Serial No. 98,582 21 Claims. (Cl. 200-166) My invention relates, to circuit interrupters, "particularly to automatic high speed circuit breakers, and has for an object the provision of a simple, reliable and inexpensive means operable in accordance with the amount of kinetic energy of the circuit breaker parts for absorbing their energy to prevent rebound of the contact structure and deformation of the parts.

My invention is an improvement upon the arrangement described in co-pending application Serial No. 98,276, filed August 28, 1936, by William Deans and assigned to the assignee of the present invention.

In accordance with my invention, the energy stored in the movable parts of the circuit breaker is absorbed by friction developed between members movable relatively to each other. By absorbing their energy, the movable parts are rapidly decelerated and brought to standstill. The

20 time required to open the circuit is not decreased since the deceleration of the parts occurs only after the movable contact structure has moved substantially to its open circuit position.

My invention is particularly useful in connection with circuit breakers of relatively large current-carrying capacity where the parts, because of the masses of metal necessary to carry the normal, and to withstand overload, currents, are necessarily heavy, and the opening speed is high. 30 Accordingly, with relatively heavy parts moving at high speed, the energy dissipated by suddenly arresting movement of the parts, as by striking a fixed stop, which may be a part of the frame or one of the pivot pins of the circuit breaker, produces an impact force whose magnitude is many times that developed by a graduated but rapid deceleration of the members to standstill. As a result of the foregoing phenomena, exemplifled by the use of the ordinary hammer, the repeated hammer-blows on the stopping member not only caused its deformation but also transmitted the hammer blows to the other parts of the circuit breaker, causing rapid deformation and excessive wear of their pivot pins and associated parts.

Further in accordance with my invention, hammer blows or impact forces are eliminated by securing to one of the switch members suitable friction material and arranging a second member provided with friction material for sliding movement thereover as the circuit breaker is opened. A spring normally biases one member in a position to'be engaged by a movable part of the circuit breaker, the engagement taking place along an inclinedsurface which serves the double function of displacing one friction member withrespect to the other and of developing a substantial force which presses them against each other to increase the friction between them. My invention is particularly characterized by the provision of a crank arm one end of which is operativeiy associated with a friction surface in such manner as to increase with displacement the opposition offered by the friction members.

In one form of my invention the crank arm supports one end of a spring which serves to transmit and to apply to the friction members the force of the spring developed in part by their relative displacement so that the opposition to movement increases with increase of displacement and with increase in the kinetic energy of the parts.

For a more complete understanding of my invention reference may now be had to the accompanying drawings in which:

Figure 1 is a side elevational view of'a circuit breaker embodying my invention with certain parts in section and certain partsomitted;

Fig. 2 is a front elevation of a three-pole circuit breaker formed by three units of the type shown in Fig. 1;' i i Fig. 3 is a perspective view of the actuating member of Fig. 1;

Fig. 4 is a fractional side elevational view of the circuit breaker of Fig. 1 with some of the parts omitted and illustrates the position of the energy absorbing means after opening movement of the circuit breaker has been completed;

Fig. 5 is a perspective view of the brake blocks of Figs. 1 and 4;

Fig. 6 is a side elevation of a modified form of the brake block.

Referring to Fig. 1, I have shown my invention in one form as applied to a circuit breaker mounted upon an insulated base or panel Ill through which extend studs or terminal connectors II and I2 respectively connected to stationary contacts I! and II. To complete a circuit between contacts II and H, a bridging member l5, consisting of a plurality of resilient or spring laminations, preferably of copper, is supported on a movable arm l6, itself pivotally mounted on a pivot pin H for movement between open and closed circuit positions. The pin I1 is supported by a pair of side plates i8, only one of which is shown. To relieve the bridging member l5 from the duty of interrupting the circuit, the upper end of the arm i8 is provided with an arcing contact l9 formed of arc resistance material arranged to cooperate with an arcing con tact 20 electrically connected to the stationary contact i3. The arrangement is such that the contacts I9 and 20 are separated after separation of bridging member I! from its associated contacts 13 and I4.

The switch or circuit breaker operating mechanism may be of the type described in U. S. Letters Patent No. 2,025,781, granted December 31, 1935, upon application of W. M. Scott, Jr.

More specifically, the arm i6 is biased for movement from a closed circuit position to an open circuit position by means of a powerful spring 22 connected at one end to a pivot pin 23 and at its other end to a suitable fixed point, as shown, to the pivot pin H. A double system of toggles, comprising toggle links 24, 25 and 23 pivotally connected together at corresponding ends by a pivot pin 21, cooperate to hold the switch member It in its closed circuit position and also serve to operate it from its open to its closed circuit position. The ends of toggle links 24 and 25 remote fromthe pin 21 are, respectively, pivotally connected at 23 and 23 to an actuating member 29 and to the arm I. The ends of the links 26 remote from the pin 21 are supported from fixed pivot pins 30 supported by the side plates i8.

With the parts in their closedv circuit positions, as illustrated in Fig. 1, the pivot pins 21, 28 and 30 are in substantial alignment; the spring 22 tends to rotate the links 26 in a clockwise direction but their movement is prevented by the link 24, the actuating member 23 pivoted at 32, and by v a latch 33 pivotally connected at 34' to member 29 and engaging a stop 35 carried by a switch operating member 33. The pivot pin 23 occupies aposition just short of alignment with pivot pins 21 and 32.

The force directly applied by the spring 22 to the actuating member 23 is resisted by the latch 33 but a component thereof tends to rotate the latch 33 to its unlatchedposition against the'bias of a relatively weak spring 33a. An auxiliary latch 31 pivotally mounted at" to the main latch 33 has a shoulder 33 engaging a stop 40, carried by operating member 33, to prevent release of the main latch. A second relatively light spring 31a tends toretain the auxiliary latch 31 in its latching position.

The operating member 33, biased by spring 22 through member 23 and latch 33 for rotation in' a counterclockwise direction, is latched into the position shown in-Fig. 1 by a latching member I pivoted thereto at a and engaging the hookshaped end of a member 42 secured to one of the side plates i3.

To open the circuit breaker, a tripping member 43 may be manually rotated about its pivot 43a to release the latch 31 or it may be operated automatically in response to an electrical condition of the circuit. If the circuit breaker is to be opened in response to overload current of predetemiined magnitude, an arm 44 pivoted at 45 may be attracted by a U-shaped magnetic structure l3 surrounding the stationary contact ll. Accordingly, when sufllcient magnetic flux is produced by the flow of current through the circuit breaker, the arm 44 is rotated in a clockwise direction to move the tripping member 43 against the auxiliary latch 31. Upon exertion of the slight amount of force'necessary to release the 1 auxiliary latch, the main latch 33, already biased to a releasing position, frees the movable contact structure for movement to its open circuit position. 1

Upon release of the latch 33 the powerful spring position. Combined with the opening force of the spring 22, to produce extremely high speed movement of arm i6 and contacts I! and is to open circuit position, are the forces due to the resilience of the movable contacts and/or their supports. I

' Circuit breakers of the type here under consideration may be designed to carry current of magnitudes upwardly of 8000 amperes at 600 volts and to interrupt a possible short-circuit current of 400,000 amperes. Consequently the parts are relatively heavy to provide sufficient mechanical strength and to carry or withstand large values of current.

Because of the relatively heavy mass of the arm l6 and its associated movable parts, it will be readily understood the kinetic energy of those parts during opening of the switch is proportional to the square of their respective speeds. Moreover, since the maximum speed occurs as the movable contact structure l5, l6, l9 reaches its fully open position, the kinetic energy of the movable structure is greatest as it reaches its limit of movement. Heretofore the impacts, or blows, delivered to stationary stops, in arresting 'movement of the contact structure, have caused deformation of the stop members as well as deformation or excessive wear'of the pivoted portions of the movable parts. The result was a shortened life of the mechanism. There was also a tendency of the parts to rebound, in' some cases sufliciently to return the contact structure substantially to its closed circuit position. The rea suit was rapid burning of the contact surfaces and a failure of the circuit breaker to interrupt the overload or short circuit current in a time short enough to prevent damage to the conductors or to devices connected in the circuit.

In accordance with the present invention, the energy of the moving parts of the circuit-breaker as they approach their limit of movement towards circuit opening position is'rapidly dissipated as work required to move friction surfaces relative toeach other. In this manner the moving parts are rapidly decelerated and brought to standstill without decreasing the opening speed of the circuit breaker. Deformation of parts, excessive wear, and tendency of the parts to rebound are substantially and effectively eliminated. The latter feature, as pointed out above, becomes important when short circuit currents are interrupted because any return movement of the contact members toward closed position decreases j the air gap between the contact structures and may delay extinguishment of an are drawn between the contacts, or may result in re-ignition of an arc.

As shown, the energy absorber and dlssipater comprises a brake block or friction member I] having secured to its upper and lower surfaces friction elements 5| and 52 formed of woven fabric impregnated with a phenolic condensation product though a good grade of automobile, or other type of, brake lining material may be used. The block 50 is arrangedfor sliding movement between two upstanding armsgll and I, Fig. 3, formed integrally with the actuating member 20, the surface 29a between the upstanding arms being machined to provide a smooth surface with which the friction element II cooperates. If desired, however, the surface Ila may be rough or otherwise formed to increase the frictional resistance. is a a One end of the block ll is wedge-shaped,

V that is to say, it has an inclined face 80a while its opposite end is recessed to form a spring-seat for one end of thecompression spring ll. The opposite end of the compression spring is mounted upon a spring seat carried by the lower end 51a of a crank arm 51 pivotallysecuredatjl to the arms 54 and 55. The opposite end, 51b of the crank arm nests within. a notch provided in a plate 59 which slidably engages the friction element 52. It will be observed the spring .il normally biases the block 50 to a position in spaced relation from the end 51a of the crank arm, or to 'a position near one, the forward, end of the surface 29a. I

The surface We is preferably inclined at an angle of approximately 52 with respect to the plane friction surfaces of elements i and 52, although the angle of surface liia may vary substantially; for example, it may have a value between 40 and 770,though for special cases .it may be selected either above or below these limits. As shown in Fig. 6, the block 50 may be provided with a curved surface 500 formed so that lines tangent thereto form angles with the friction surfaces which vary from about 70 to about, 40 as ,they approach the lower part of member 50.

Again referring to the operation of the circuit breaker to the openposition, it will be remembered that as pivotpins 23 and 21 move inwardly "toward the panel III, the actuating member ll ".rotates in a counterclockwise direction, and the switch arm I6 moves rapidly in a clockwise direction towards its open circuit position. As the rounded. surface Ila approaches the brake block or friction member 50, the parts are arranged so that engagement between the twosurfaces Ila fof inclined faceor surface "a.

and 50a occurs at the upper. or rearward portion a Subsequent movement of surface. Ila; upon the inclined face We displaces the brake block 50 and applies to it a substantial force in a direction topress it against the plane surface 29a of the actuating the force of the drag whichfenergizes the crank.

The spring 58, by displacement of the brake block W, is compressed. and by means of crank arm l1 applies a pressure to the plate 59 simultaneously to increase the frictional resistance offered by the energy dissipater. Accordingly, the block is self-energized; that is, large friction forces are produced which do not depend upon the inclinationof surfaceliia. Moreover, when the parts are moving at greater speed, greater forces are exerted between the friction surfaces to increase the amount of energy absorbed. Specifically, the component of force, due to the inlined surface lilo, which presses block 50 against member" increases with increase in kinetic energy. Thus higher speeds of the parts result in greater rates of acceleration of block ll caused by an increased force applied by surfaceils to surface lla.

Energy absorbing and dissipating devices constructed as aforesaid have proved to be entirely satisfactory to bring the moving parts of a circuit breaker to astandstill with minimum shock. Impact forces or hammer-blows upon the pivotal connections were substantially entirely elimi-' nated.

Continuing. with the operation of the circuit breaker, as the switch arm Il reachm its fully opened position, the brake block ll, by reason of its displacement, has so greatly increased the pressure uponthe friction surfaces, it is den-u way affected. Moreover, when necessary, the

block ll may be readily and economically replaced, although such replacement is seldom necessary. I I i As shown in Fig. 6, the inclined surface lle is to advantage curved somewhat at its upper end so that the surface Ila initiallycauses a' relatively small displacement of block ll. The same result may be approximated by selecting the spring ll with characteristics such that substantial initial compression of the spring does not transmit forces to the. crank arm as large as for later compression of the spring. For example, several turns of the spring. particularly those within the recessed end of the .block ll,

of the spring. Withsuch an arrangement the initial force transmitted would be much less per unit of change of displacement than after the time the smaller turns of the spring engage each other to start compression of the turns of the spring having the larger diameter.

The aforesaid selection of the angle of. the inclined surface lls rests upon the assumption the surface Ila' moves in a substantially straight line across and normal to the surface 500. If the cooperating surface, as surface Ila, approaches through a different path, the angle of surface No is selected to produce the desired displacement.

Preparatory to reclosure of the circuit breaker the latch ll of the operating member ll is rel leased. during opening of the circuit breaker, by movement of a projection or roller 8!, carried by member", over a cam surface lib.

In order to reclose the circuit breaker an cper-.

ating handlell, secured to the operating member ll, is rotated in a counterclockwise direction until the stop ll is moved into a position again to be engaged, by the main latch ll. this engagement being effected by the bias of the spring Ila. At the same time the auxiliary latch 81 and the operating member ll are effectively secured to the actuating member I! so that by returning the handle ll and member ll to their original positions, the circuit breaker is reclosed.

Upon initial movement of the actuating member" in a clockwise direction, the spring ll is effective to move the. friction member of brake block ll towards its original or normal position. In this connection, movement of block ll towards its original position exerts a drag on the crank may be ofless diameter thanthe remaining turns II in a direction tending to decrease the pressure by the crank applied to the' block.

If the spring 56 is sufficiently strong; it may,

after openingof the circuit breaker, rotate the actuating member 29in a clockwise direction to return the brake block 50 to its original position. At any rate the brake block W is returned tofits original position prior to reclosure of the circuit breaker. Thus the energy absorber and, dissipater is effective, should the circuit breaker be tripped during the reclosing operation, to prevent shock and injury to the parts.

-The circuit-closing operation is complete as soon as the latch 4i engages the member 42, although, as indicated, the circuit breaker is tripfree; that is, it may be automatically opened irrespective of, and without interference from,

each pole being identical with the one shown in Fig. 1. The actuating members 29 of each pole are connected together by a common crossmember 65. Similarly the trip members N are secured together by a cross-member 66. The foregoing arrangement insures that an overload upon one of the poles of the circuit breaker is effective to trip all of the poles thereof to open circuit position.

The circuit breaker may be manually opened by means of a tripping member 61 secured to the cross-member 66.

While I have shown a particular embodiment of my invention, itwill be:understood, of course, that I do not wish to be limited thereto, since many modifications may be made, and I therefore contemplate by the appended claims to cover any such modifications as fall within the spirit and scope of my invention.

What I claim is:

1. In a circuit breaker having contact structures one of which is-moved relative to the other from a closed to an open circuit position, the combination of friction means comprising solid bodies insliding contact with each other for opposing opening movement of said movable structure, and mechanical means for increasing as a function of the speed and displacement of said movablestructure the opposition offered by thefriction produced by the sliding contact between said solid bodies to said opening movement of said movable structure.

2. In a circuit breaker having contact'structures one of whichis moved relative to the other from a closed to an open circuit position, the combination of friction means comprising solid bodies in sliding contact with each other for opposing opening movement of said movable structure, and mechanical means operable by said movable structure for continuously increasing the opposition to said opening movement of said movable structure by the friction produced bythe sliding contact between said solid bodies.

3. Means for absorbihg the energy of the movable parts of a circuit breaker incident to their movement from'a closed to an open circuit position compris..1g a pair of relatively movable members one of which is provided with a friction surface slidable with respect to the surface of the other member, means operable by one of the parts of said circuit breaker for displacing one ofsaid members with'respect to the other, and

mechanical means operable in accordance with the displacement of said one member for pressing said surfaces against each other with a pressure which rises with the extent of displacement I of said one member.

f 4. Means for absorbing the energy of the movable parts'of a circuit breaker incident to their movement froma closed to'an open circuit position comprising relatively movable members, one of which is provided with a friction surface slidable over a surface of the other member, means operable by one of the parts of said circuit-breaker for displacing one of said members with respect to the other, means operable with a wedging action by one of'said members to press said friction surfaces against each other, and means for further increasing the pressure upon said surfaces in accordance with the displacement between said members.

5. Means for absorbing the energy of the movable parts of a circuit breaker incident to their movement from a closed to an open circuit position comprising a pair of switch members having friction surfaces, one of which is slidable with respect to the other, and mechanical means energized from one of said members for applying a pressure on said friction surfaces which increases in accordance with the extent of displacement between said members.

6. Means for absorbing the energy of the movable parts of a circuit breaker incident to their movement from one position to another comprising a member provided with a friction surface, means slidably mounting said member upon one of the partsof said circuit breaker, said member being provided with an inclined surface arranged to be engaged by another part of said circuit breaker for displacement ofsaid member as the crank arm against said member to increase the pressure between said surfaces.

7. I Means for absorbing the energy of the movable parts of a circuit breaker incidenttotheir movement from one position to another comprising a memberprovided with friction surfaces on opposite sides thereof, means having a cooperating surface overwhich one of said friction surfaces is slidable, a brake block engaging the other of said friction surfaces, a crank arm, one end of which cooperates with said block, a spring associated with: the opposite end of said crank arm and operable by displacement of said. member for simultaneously pressing said brake block and said adjoining friction surfaces against each other. I

8.In a circuit breaker provided with a movable swltch member, actuating means therefor, the combination of means for absorbing the energy of the movable parts of the circuit breaker incident to their movement from a closed to an open circuit position, comprising a member having a surface slidable along a surface of said actuating member, at least one of said surfaces comprising friction material, means operable by one of the partsof said circuit breaker for displacing ,said member with respect to said actuating member, and mechanical means for pressing said surfaces against each other with a pressure which increases during displacement of said member and which is substantially reduced upon disengagement of said member and said displacing means.

movement from one switching position to another comprising a switch member having a friction surface, a second switch member having a cooperating friction surface andan inclined face adjacent one end thereof engageable by one of said parts of said circuit breaker for displacement of said friction surfaces, and means for pressing said surfaces against each other with a pressure which increases with relative displacement of said surfaces.

10. Means for absorbing the energy of the movable parts of a circuit breaker incident to their movement from one switching position to another comprising a switch member having a friction surface, a second switch member, having a cooperating friction surface and an inclined face adjacent one end thereof engageable by one of said parts of said circuit breaker for displacement of said friction surfaces, a crank arm having its respective ends cooperatively associated with said switch members, and a compression spring interposed between one end of said crank arm and said second switch member for increasing the pressure between said surfaces in accordancewith the extent of displacement of said second switch member relative to said first-named switch member.

11. Means for absorbing the energy of the movable parts of a circuit breaker incident to their movement from one switch position to another comprising a switch member having a friction surface, and an inclined face adjacent one end thereof engageable by one of said parts of said circuit breaker for displacement of said friction surfaces, a crank arm having its respective ends cooperatively associated with said switch members, and a compression springinterposed between one end of said crank arm and said second switch member for increasing the pressure between said surfaces in accordance with the extent of displacement of said second switch member relative to said first-named switch member, said spring. upon disengagement of said inclined face from said part of said circuit breaker returning said second switch member to its original position.

12. In a circuit breaker, an operating member for closing the circuit breaker, a means for opening the circuit breaker, said operating member having a friction surface, a brake block having a cooperating friction surface, a crank arm, one end of which cooperates with said block to press said surfaces against each other, one end of said block having an inclined face engageable by a movable part of said circuit breaker for displacing one of said surfaces relative to the other, and a compression spring supported between the opposite end of said block and the opposite end of said crank arm.

13. In a circuit breaker having movable contact structure movable to an open circuit position, an operating member, a toggle interposed between said member and said structureand movable to a collapsed position, means operable, upon movement of said contact structure to open position, to move said operating member towards said structure, the combination of means for absorbing the energy of the moving parts of said circuit breaker comprising a brake block having one end of said block having an inclined surface, means biasing said block to a position where an upper portion of said inclined surface is engaged by said contact structure as the latter approaches its open circuit, position, further movement of said structure displacing one of said friction surfaces relative to the other, and a crank arm pivoted to said operating member, one end of said arm cooperatively engaging said brake block and the other end of said arm disposed adjacent the end of said brake block opposite its inclined surface, said biasing means including a compression spring interposed between said brake block and said last-named end of said crank arm.

14. In a circuit breaker having contact structure movable at high speed from one position to another and an operating member for operating said contact structure to said one position, the combination of means for absorbing the energy of the movable parts of said circuit breaker during its high speed operation comprising abrake block having a pair of friction surfaces and an incined surface at one end thereof and between said friction surfaces, said operating member having a plane surface disposed between upwardly which are lined with friction material, one end portion of which is wedge-shaped and a spring seat at the opposite end thereof, a movable part of said circuit breaker having at least one surface over which said brake block is slidable, a crank arm pivoted to said movable part, a spring supported between said spring-seat and one end of said crank arm for biasing the opposite end of said crank arm against said block, and means engaging saidwedge-shaped end to move said friction surfaces relative to said movable part and to compress said spring, said crank arm transmitting the force of said spring to said block to increase the pressure upon said surfaces in accordance with the extent of relative movement of said surfaces.

16, A circuit breaker comprising fixed contact structure, a movable system including cooperating contact structure movable to open circuit position, means for braking said movable contact structure comprising a braking member frictionally engaging and movable with respect to a cooperating member, brake-actuating means included in said movable system engaging and actuating said first-named braking member with application thereto of a force having a component acting upon said first-named braking member in direction substantially corresponding with the direction of its movement with respect to its said cooperating member, and mechanical means actuated by said first-named braking member for transmitting said force component and redirecting application thereof to said first-named braking member to increase its pressure upon its said cooperating member.

17. A circuit breaker comprising fixed contact structure, a movable system including cooperating contact structure movable to open circuit position, 7;

means for braking said movable contact structure comprising a braking member frictionally engaging and movable with respect to a cooperating member, brake-actuating means included in said movable system engaging and actuating said firstnamed braking member with application thereto or a force having components, one of which acts its'movement with respect to its said cooperating member, and'mechanical means actuated by said first-named braking member for transmitting said second-named force component and redirecting application thereof to said first'named braking member to increase its pressure upon its said cooperating member.

18. A circuit breaker comprising fixed contact structure, a movable system including cooperating contact structuremovable to open circuit position, means for braking said movable contact structure comprising a braking member frictionally engaging and movable with respect to a cooperating member, brake-actuating means included in said movable system engaging and actuating said first-named braking member with application thereto of a force whose magnitude is dependent upon the speed at which said movable system moves to open circuit position and having a component acting upon'said first-named braking member indirection substantially corresponding with the direction of its movement with respect to its said cooperating member, and mechanical means actuated by said first-named braking memberfor transmitting said force component and redirecting application thereof to said first-named braking member to increase its pressure upon its said cooperating member.

19. A circuit breaker having fixed contact structure, a movable system including cooperating contact structure movable to open circuit position, means for braking saidmovable contact structure comprising a braking member frictionally engaging and movable with respect to a cooperating member, brake-actuating means included in said movable system engaging and actuating said firstnamed braking member with application thereto or a force whose magnitude is dependent upon the speed at which said movable system moves to Patent No. 2,157,001.

GEORGE: A. HEALIS open circuit position and having components, one of which acts upon said first-named braking member in direction to increase its pressure upon its said cooperating member, and another of which acts upon said first-named braking member in direction substantially corresponding with the direction of its movement with respect to its said cooperating member, and mechanical means actuated by said first-named braking member for transmitting said second-named force component and redirecting application thereof to said firstnamed braking member to increase its pressure opposing opening movement of said system, and

means operable during circuit-closing movement of said system for producing a return movement of said first-named member, said means including said pivoted arm upon initiation of said return movement being effective greatly to reduce the braking efiort opposing said return movement.

21. In a circuit breaker having a movable system including contact structure biased to open circuit position, the combination of cooperating braking members at least one of which is displaceable with respect to the other member, brake-actuating means included in said system engaging and producing said displacement of said one member, and means for increasing the braking effort quickly to bring said system to standstill comprising a pivoted arm for pressing said members against each other, means exerting a frictional drag upon one end of said arm to produce with respect to its pivot a toggle-like or wedging action greatly to increase with said displacement the pressure of said members, one against the other.

GEORGE A. HEALIS.

November l5, 1958.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 57, claim 11, afterthe comma and before the word "and" insort --'a second switch nemberhavingacooperatingfriction surf'ace-; page 6, second column, line 58, claim 21, for "member" read membersand that the said Letters Patent should be read with this correction therein that the s ame may conform to the record of the case in the Patent Office.

Signed and sealed this 28th day of January, 1,1.

(Seal) Henry Van Arsdale,

Acting Commissioner of Patents.

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