US2692927A

US2692927A - Electrical relay

Info

Publication number: US2692927A
Application number: US265135A
Authority: US
Inventors: Clarence S Snavely
Original assignee: Westinghouse Air Brake Co
Current assignee: Westinghouse Air Brake Co
Priority date: 1952-01-05
Filing date: 1952-01-05
Publication date: 1954-10-26
Anticipated expiration: 1971-10-26

Description

Oct 26, 1954 c. s. sNAvELY 2,692,927

ELECTRICAL RELAY Filed Jan. 5, 1952 3 Sheets-Sheet l 1^, 42 a1 IIT 24a 6b 6a H15' A TTRIYE'Y DCL 26, 1954 c. s. slNAvELY 2,692,927

ELECTRICAL RELAY Filed Jan. 5, 1952 3 Sheets-Sheet 2 Insulalz'on l IN V EN TOR.

@lare/nc@ S, Smlvely BY HIS ATTRTY Oct. 26, 1954 C. s. sNAvELY 2,692,927

ELECTRICAL RELAY Filed Jan. 5, 1952 3 sheds-sheet :s

Fig IN1/EN TOR. v

Clarence S. Snavely w. km.

HIS A TTORNEY Patented Oct. 26, 1954 ELECTRICAL RELAY Clarence S. Snavely,

to Westinghouse Miami Shores, Fla., assigner Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application January 5, 1952,

18 Claims.

My invention relates to electrical relays, and particularly to electrical relays responsive to relatively high currents which prohibit the use of the usual relay magnetizing windings.

Load circuits carrying direct current cf several thousand amperes require conductors of very large cross-sectional area to handle such load currents safely and without excessive heat and voltage losses. Such heavy conductors, or bus bars, are not adapted for winding the usual type of meter or relay coils. To measure the high current flow in a conductor of large cross-sectional area, meters are sometimes used which are connected in shunt with a portion or section of the conductor having a known resistance. Meters which are shunt connected to the conductors have been used to initiate various control functions in response to predetermined values of current fiowing through the conductors, the meters being provided with electrical contacts which are operated at the predetermined values of the load current.

In other control applications it has been found desirable to provide a relay mechanism for a conductor or bus bar of large cross-sectional area, which relay mechanism is operated by the magnetic iiuX due to the current ilow through the conductor, the relay mechanism being operated at a predetermined value of the load current. A bus bar relay mechanism of this type is illustrated and described in my copending application for Letters Patent of the United States, Serial No. 771,024, led on August 28, 1947, for Electrical Relays, now Patent No. 2,584,749 issued February 5, 1952.

The relay mechanism disclosed in my copending application provides two relay structures mounted in housings of conducting material, the two housings being bolted together back-to-back to form a conducting path of suitable cross-sectional area to carry the heavy load currents of the circuit into which the relay housings are connected. In the relay mechanism disclosed in the aforesaid application, a high release to pick up ratio is obtained by features of construction described in said application, a change in the release to pick up ratio being obtained by adjustments in the magnetization of the permanent magnet provided for the relay mechanism.

It is an object of my present invention to provide a self-contained relay unit adapted to be clamped to a conductor or bus bar of large crosssectional area carrying heavy load currents and operable by the magnetic iiux due to the Current flow in the conductor cr bus bar.

Serial No. 265,135

Another object of my invention is to provide a relay mechanism having a high release to pick up ratio wherein mechanical means are incorporated to vary the release to pick up ratio of the relay.

These and other objects of my invention I accomplish by providing a nonmagnetic metal frame or support secured to a base of insulating material for mounting the magnetic and contact structures of the relay mechanism. The insulating base together with a backstrap cover also made of insulating material, form a clamping means whereby the relay mechanism is secured to a conductor or bus bar.

A one-piece molded rotor of insulating material is pivotally supported in the nonmagnetic frame, the rotcr having molded therein a magnetizable armature and spring contact lingers, the spring contact ngers coacting with stationary contacts secured to the insulating base. The nonmagnetic frame of the mechanism also supports two magnetizable cores, the ends of which extend through the insulating base and through slots or openings provided in the associated conductor or bus bar. The cores together with the armature and a backstrap complete the magnetic circuit for the relay, the conductor or bus bar being enclosed by the magnetic circuit.

The armature supporting rotor of the relay mechanism is provided with a spiral return spring, one end of which is secured to the rotor while the other end is secured to an adjustable arm. By means of an adjusting screw coacting with the adjustable arm, the tension of the spiral return spring may be increased or decreased. The tension of the spiral return spring determines the pick up value of the relay.

The rotor is further provided with two diametrically oppositely extending flat springs, the outer or free ends of the springs being received in slots cut into two ears or tabs of insulating material. The tabs or ears are secured to two tapped blocks threaded respectively on the oppositely threaded ends of a long screw confined by the nonmagnetic frame. By turning the long adjusting screw, the insulating tabs or ears are moved toward and away from each other. The varying of the eiiective length of the two flat springs in this manner varies the stiffness of the ilat springs. The adjustment of the long screw controls the ratio of the release to pick up value of the relay.

I shall describe one form of apparatus embodying my invention and shall then point out the novel features thereof in the appended claims.

In the accompanying drawings, Fig. 1 is a side elevational view of my novel relay clamped to a bus bar. Fig. 2 is a sectional view taken along the line II-II of Fig. l. Fig. 3 is a plan view of the relay mechanism with the cover removed and portions of the frame broken away. Fig. 4 is a sectional view taken along the line IV--IV of Fig. 3. Fig. 5 is a perspective view of the relay operating mechanism with portions broken away, while Fig. 6 is a perspective view of the relay rotor assembly, portions of the rotor being broken away to show details of construction.

Similar reference characters designate similar parts throughout the several views.

Referring now in detail to the drawings, the reference character l designates in general a relay mechanism embodying my invention secured to a bus bar 2. The bus bar 2 is of a highly conductive, nonmagnetic material adapted to be connected in series with a load circuit (not shown) carrying several thousand amperes of direct current, by vway of tangs 2a. The bus bar 2 is provided with two openings, or slots, 2b cut into the opposite edges of the bar, the slots leaving a central portion 'ic of reduced cross-sectional area which conducts the entire load current through the magnetic structure of the relay mechanism l which I will now describe.

The relay mechanism l comprises a base plate 3 of insulating material formed with a suitable rectangularly shaped recess 3a in its upper surface and having molded therein two pairs of adjustable contacts; a pair of front contacts da and a pair of back contacts lib. The front and back contacts la and 4b are connected by way of connectors 5 to the terminal posts 5a and (ib, respectively, molded in the base plate 3. Secured within the recess 3a of the base plate is a nonmagnetic frame or bracket 'i comprising a base la and four integral standards lb-le, i

the frame being secured to the base plate 3 by nonrnagnetic screws 8 recessed in the underside of the base plate. Fixed to the upper ends of the legs Eb-le of the frame l by four nonmagnetic screws 9 is a nonmagnetic plate lil formed with a dependent circular boss ict (Fig. Li). The boss ma is provided with a concentric journal opening lb which is in vertical alignment when plate it is secured to the frame legs, with a similar opening 'if provided in the frame base la.

Secured in the base la of the nonmagnetic frame l are two magnetizable cores il and l2 extending downwardly with some clearance through suitable openings 3b provided in the insulating base plate 3. with enlarged upper ends of pole Vpieces ila and lZa, respectively, a portion of each of the pole pieces being milled away to form vertical pole faces Hb and |213 on the respective pole pieces. It will be noted in Fig. 3 that the vertical pole faces are parallel to each other, but angularly disposed with respect to the plane intersecting the axes of the two pole pieces.

Rotatably mounted in the nonmagnetic frame 1 for oscillation about a vertical axis is a rotor assembly I3 (Fig. 6) comprising a molded rotor ill of insulating material having molded therein a vertical shaft l5 and a magnetizable armature I6. In the construction of the rotor assembly, the shaft i5 is press tted into an opening (not shown) in the center of the armature It before the rotor is molded. The shaft may be of a suitable magnetizable metal or it may be of a metal having the least bearing friction and wear. I thus provide a single shaft The cores are formed for the rotor assembly for accurate alignment of the rotor and a low reluctance armature intersecting the shaft at right angles. The ends of the armature are formed with vertical pole faces I6@ and leb, the planes of the pole faces (Fig. 3) being angularly disposed with respect to the longitudinal axis of the armature. As will hereinafter appear, the armature pole faces ita and Ib are so formed and the armature so mounted in the rotor assembly that the armature pole faces will be parallel with the pole faces Hb and 12b of the pole pieces when the armature is in its midstroke position.

Four spring fingers il-Zi are also molded in the rotor ifi in the same plane with the armature i6 but normal thereto, the fingers being arranged in coextensive parallel pairs extending in opposite directions from the rotor. Molded in the rotor in the central portion thereof are two diametrically oppositely extending flat springs 2i and 22, the nat springs being slightly longer than the spring contact fingers Ms, and extending in the same directions. The flat springs 2i and '22 in addition to serving as a biasing means for the rotor itl as will hereinafter be described, also serve as the heel connection for the spring contact fingers Il-Zli. The outer or free ends of the flat springs 2l and 22 are electrically connected by way of connectors 23 to the terminal posts 2da and 2Gb, respectively, molded in the base plate 3. As will hereinafter appear, there is very little exing of the connectors 23 because the free ends of the springs 2i and 22 are held practically stationary. The inner ends of the springs 2! and 22 molded within the rotor are electrically connected to the inner ends of the spring contact fingers, the fiat spring 2i being connected to the contact ngers il and is by conducting strips 25 (Fig. 6) riveted to said spring and fingers, while flat spring '22 is similarly connected to the Contact fingers le and 2li.. A slot or groove 26 is provided in the upper surface of the rotor member for receiving the inner end of a coil tension spring 2l, the coils of which encompass the upper end of the rotor la.

The rotor assembly i3 is mounted within the frame l with the lower end of shaft i5 in the bearing provided by opening lf in the base 'ia and the upper end of the shaft in the bearing formed by the opening im? in plate i@ when said plate is secured to the frame legs. The rotor assembly I3 is adapted to be oscillated about a vertical axis defined by the shaft i5 in a manner to be described, the armature being oscillated in the plane of the pole faces Hb and |219 of the pole pieces and the contact fingers [Lfd being oscillated in the plane of the stationary contacts da. and lib.

Adjustable means are provided for varying the tension of the coil spring 2l to bias the rotor assembly i3 to one extreme position in which the back contacts 1lb are engaged by the spring ccntact fingers i7 and is of the rotor assembly. The tension of the coil spring `2l will determine the flux level o-r current value at which they baci; contacts 1lb are disengaged and the front contacts da engaged by the spring contact fingers I8 and 20.

To this end an arm 28 is pivoted on the dependent boss lila of the frame plate lil (Figs. 4 and 5), the free end of the arm being formed with a dependent ear or abutment plate 29 which is riveted to the free end of the coil tension spring 2l of the rotor assembly. Coacting with the abutment plate 29 of the arm 28 is an adjusting screw 30, threaded through an ear 'Ig offra-me leg lb, the inner end of the screw abutting the plate 29 (Figs. 3 and 5). By threading thescrew 3c inwardly, the arm 2t is pivoted in a counterclockwise direction (Fig. 3), thereby increasing lthe bias of the coil tension spring. To decrease the bias of the coil tension spring the adjusting screw is threaded outwardly of ear 1g.

The bias of the coil tension spring 2l tends to rotate the rotor assembly I3y in a counterclockwise direction (Fig. 3,) To limitv the angular displacement of the rotor assembly I3 due to the bias of the coil tension spring, nonmagnetic stop screws 3Ia and 3Ib are threaded through thev frame legs 'Ib and 1d, the inner ends of which are adapted to abut the armature I6 in one extreme or release position in which the back contacts 1lb-Il and IIb-I9 are closed. It will be noted in Fig. 3 that in the release position of the armature I6 a small air gap exists between the pole faces I Ib and I2?) of the pole pieces and the pole faces ISU. and Ib of the armature. rlhe two sets of pole faces are practically parallel in the release position of the armature, the pole faces of the armature and pole pieces being so constructed and assembled that the two pairs of pole faces will be parallel when the armature is in its mid stroke position. To limit the rotation of the rotor assembly in a clockwise direction, nonmagnetic stop screws 32a and 32D are threaded through the legs lc and le, respectively, of the frame l; the clockwise rotation of the rotor assembly being limited to a second extreme or full-stroke position in which the front contacts la-I8 and 411-20 are closed and the air gaps between the armature pole faces irt, Ib and the pole faces IIb, I2b of the pole pieces are very nearly closed. It will be appreciated that abutment of the pole faces should be avoided to prevent sticking of the armature when magnetic flux threading the armature decays.

The relay mechanism thus far described is mounted on the` bus ,bar 2, the insulating base plate S engaging the top surface of the bus bar and the cores II and I2 extending into and through the bus bar slots v2b. The cores II and I2 are enclosed in sleeves 33 of insulation material (Fig. 2) to insulate the cores from the bus bar. It will be noted in Fig. 2 that the lower ends of the cores extend slightly below the bottom surface of the bus bar. A backstrap 34 of magnetizable material is provided for the lower ends of the cores iI and I2 to complete the magnetic circuit of the relay. The backstrap 34 is enclosed by a backstrap cover 3'5 made of insulation material which also serves as a clamping means for securing the relay mechanism I to the bus bar 2.

The backstrap cover 35 is clamped to the underside of the bus bar 2 by means of four screws 36k preferably made of brass. The heads of the screws 3E are recessed in suitable openings 3c provided in the insulating base plate 3, the screws passing through openings 2d in the bus bar 2 with some clearance, and are threaded into metal inserts 3l' recessed in the backstrap cover 35. A strip 33 of insulation material is interposed between the bottom face of the bus bar and the backstrap cover, the strip being suitably pe forated to accommodate the cores Il and I2, and the clamping screws 35.

The bacastrap cover is formed with a recess 35a to accommodate the ends of the cores I I and I2 and the

magnetizable backstrap

3,4. The backstrap S4 is biased upwardly against the lower ends of the cores by a leaf spring 39 interposed between the backstrap and the bottom of the recess 35a. One or more nonmagnetic shims 4I) may be inserted between the lower ends of the pole pieces I I and I2 and the baclrstrap 34 to vary the reluctance of the magnetic circuit of the relay, whereby an approximate pick up value of flux may be obtained at which the relay will close its front contacts.

A cover III preferably of sheet steel, secured to the top plate IIJ of the frame by two screws 42 and having a gasket 43 (Figs. 3 and 4) interposed between the lower edge of the cover and the base plate 3, seals the relay mechanism against the entry of foreign matter, the steel cover acting as a magnetic shield for the relay structure.

The relay mechanism thus far described will operate to open its back contacts 4in-Il and IIb-I9 and close its front contacts lla-I8 and Ila-*20 in response to a now of current of predetermined value through the bus bar 2. The flow of direct current through the bus bar creates a magnetic eld encircling the bus bar in closed loops. The magnetizable cores I I and I2 being in the magnetic field set up by the current flowing through the central portion 2c of the bus bar, together with the backstrap 34 and the armature I6, offer a relatively low reluctance path for the encircling magnetic lines of force of the magnetic eld. The armature I6, being biased in a counterclockwise direction by the coil spring 2l, will be attracted to the pole faces lib and IZb against the bias of the spring 2l when the flux in the magnetic circuit exerts a force greater than the biasing force of the spring 2l.

The operation of the armature I6 in response to the flux threading the magnetic circuit of the relay may be varied by varying the reluctance of the magnetic circuit by including therein the ncnrnagnetic shims 40, or by varying the tension of the spring 2l biasing the rotor assembly. By varying the reluctance of the magnetic circuit an approximate range of current values at which the relay will close its front contacts is established and by varying the tension of the coil spring 2l the pick up current value of the relay may be accurately determined.

The coil spring 21 biasing the rotor assembly I3 is a long spring, and the biasing force exerted thereby may be considered as remaining constant in any position of the armature from its release position to its full-stroke position. When the magnetic force exerted on the armature is greater than the biasing force of the coil spring, the armature will move toward its full-stroke postion, thereby decreasing the widths of the air gaps between the pole faces of the armature and the pole pieces. The torque exerted on the armature by the magnetomotive force thus increases while the biasing torque of the coil spring remains constant, so that the armature moves to its full-stroke position with a snap action. Since the air gaps between the armature and the pole pieces are narrower when the armature is in its full-stroke position than when in its release position, a lesser magnetomotive force is required to hold the armature in its full-stroke position than to move the armature from its release positiony against the bias of the coil spring. |The current or pick up value at which the relay will close its front contacts is thus greater than the current or release value at which the relay will open its front contacts.

Considering for the moment, a short spring biasing the rotor assembly i3 in place of the long spring 21, and a torque exerted on the armature by the magnetomotive force sufficient to overcome the bias of the short spring, the movement of the armature from its release position toward its fullstroke position will increase the biasing torque of the short spring. The decreasing widths of the air gaps between the armature and the pole pieces will decrease the reluctance of the magnetic circuit so that an increasing torque is exerted on the armature by the magnetomotive force. The increasing torques exerted on the armature tend to balance each other with the result that the armature creeps to its full-stroke position. When the armature is in its full-stroke position, the magnetomotive force acting upon the armature will be at its maximum, but the biasing force of the short spring will also be at its maximum. Thus any small change in the value of the current creating the magnetomotive force will permit the return of the armature to its release position. With a short spring biasing the rotor assembly, the current, or pick up value at which the relay will close its front contacts is thus approximately equal to the current, or release value at which the relay will open its iront contacts.

In providing an electrical relay having a high ratio of release to pick up value I combine the biasing influences of two springs, a long spring such as the coil spring 21 described and a short spring such as the flat springs 2| and 22 which I will now describe in detail; the spring arrangement being such that I retain the snap action or a rotor assembly influenced by a long spring and the high ratio of release to pick up value of a relay having a rotor assembly inuenced by a short spring, the spring arrangement also providing means whereby the ratio of the release to pick up value may be accurately controlled.

To this end, the free ends of the fiat springs 2l and 22 are conned in slots 44a cut in tabs 44 of insulation material. The tabs 44 are secured to threaded blocks 45 which are threaded on the oppositely threaded ends of an adjustment screw 46, the ends of the flat springs being held and tending to bias the armature toward its mid-stroke position. The adjustment screw 46 is rotatably mounted in the frame legs id and le, the screw being conned in the frame by a sleeve or collar 41 pinned to the screw between the supporting frame legs (Fig-s. 3 and 4). By turning the adjustment screw one way or the other, the blocks 45 carrying the confining tabs 44 may be moved toward or away from each other to Vary the effective lengths of the two flat springs 2| and 22. By varying the effective lengths of the springs, the stiiness of the two springs is varied without producing any reaction force which may cause friction and wear at the pivot points.

The general effect of stiffening the flat springs 2! and 22 is to increase the bias of the rotor assembly toward its mid-stroke position. This biasing eiTect of the two iiat springs tends to reduce the force exerted by the spiral spring in holding the rotor assembly in its released position with the armature i6 abutting the stops 3 ia, 3 Ib. The restoring force of the spiral spring 27 in returning the rotor assembly from its full-stroke position is increased by the centering effect of the two flat springs 2l and 22. As a result of this modulating action on the spiral spring torque by the centering torque of the flat springs, the pick up value of the relay will be reduced since the centering torque of the flat springs partially offsets the biasing torque of the coil spring. The release value of the relay will be increased since the centering torque of the flat springs now aids the restoring force of the coil spring. The adjustment of the effective lengths of the iiat springs 2| and 22 by the adjustment screw thus controls the ratio of release to pick up values of the relay.

The relay mechanism herein described may be advantageously used with a bus bar permanently connected in service, any replacement or servicing of the relay being accomplished by handling of the small self-contained relay unit. The calibration of the relay mechanism is also more easily effected, the relay mechanism being removed from the bus bar and reassembled to test coils having a xed number of turns, so that the relay can be calibrated from a low current source. The adjustments of the coil spring and of the flat springs of the rotor assembly are also advantageous in that such adjustments of the tension or stiiness of the springs may be readily and accurately made, the adjustment of the effective lengths of the two flat springs to vary the ratio of release to pick up values of the relay being simpler than methods provided in the prior art. Such adjustments may readily be made without disassembly of the relay unit, and may even be made through a cover or shield suitably provided with openings for insertion of a screw driver.

Although I have herein shown and described only one form of an electrical relay embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a member mounted for movement between two extreme positions, a rst spring biasing said member toward a position intermediate the two extreme positions, the bias of said rst spring increasing as said member is moved from the intermediate position toward either of the two extreme positions, a longer second spring biasing said member to one extreme position against the bias of said rst spring, the bias of said second spring remaining substantially uniform throughout the range of movement of said member, and means for applying a force of predetermined magnitude to move said member from the one extreme position to the other extreme position, said first and second springs coactng to move said member from the other extreme position when the force applied to said member is less than the predetermined magnitude.

2. In combination in accordance with claim l in which means are included to vary the bias of said second spring to vary the magnitude of the force required to move said member from the one extreme position to the other extreme position.

3. The combination in accordance with claim 2 in which means are included to vary the b-ias of said rst spring to vary the ratio of the magnitude of the force applied to said member in its other extreme position which permits movement of said member from the other extreme position by said springs, to the magnitude of the force required to move said member to the other extreme position.

4. The combination in accordance with claim 3 in which the rst spring is a. flat spring and the longer second spring is a coil spring, and in which the means to vary the bias of said rst spring includes a confining member for the spring to vary the eective length thereof.

5. In an electrical relay, the combination comprising, a magne'tizable core structure including a member movable between two extreme positions, and two mechanical force exerting means coacting with said movable member, each exerting a force of different magnitude on said member; the rst of said means tending to move said member to a position intermediate its two extreme positions and the second of said means moving said member to one of its extreme positions, said member being moved from the one extreme position to the other extreme position in response to magnetic flux of a. predetermined level supplied to said core structure, the force exerted by the rst of said means on said member increasing as said member is moved from the intermediate position toward either of its two extreme positions; the force exerted by the second or said means on said member being substantially uniform throughout the range of movement or said member; both of said means coasting to move said member from its other extreme position toward its one extreme position when the magnetic flux level supplied to said Core structure falls below the magnetic ux level at which said member was moved from its one extreme position to its other extreme position.

6. In an electrical relay, the combination comprising, a magnetizable core structure including a member movable between two extreme positions, and two springs coacting with said movable member, each spring exerting a force of different magnitude on said member; one of said springs tending to bias said member to a position intermediate the two extreme positions, the other of said springs biasing said member to one extreme position in opposition to the bias of the one spring; said member being moved from the one extreme position to the other extreme position in response to magnetic flux of a predetermined level supplied to the core structure; the force exerted by the one spring on said member increasing as said member is moved from the intermediate position toward either of its extreme positions; the force exerted by the other of said springs on said member being substantially uniform throughout the range of movement of the member; both of said springs coacting to move said member from the other extreme position toward the one extreme position when the level of the magnetic flux supplied to the core structure falls below the magnetic flux level at which said member was moved from the one extreme position to the other extreme position.

7. In an electrical relay, the combination comprising, a magnetizable core structure including .a member movable between two extreme positions, two Springs coacting with said movable member, each spring exerting a force of different magnitude on said member; one of said springs tending to bias said member to a position intermediate the two extreme positions, the other of said springs biasing said member to one extreme position in opposition to the bias of the one spring, said member being moved from the one extreme position to the other extreme position in response to magnetic ux of a predetermined ,toward the one extreme level supplied to the core structure; the force exerted by the one spring on said member increasing as said member is moved from the intermediate position toward either of its extreme positions; the force exerted by the other of said springs on said member being substantially uniform throughout the range of movement of the member, both of said springs coacting to move said member from the other extreme position position when the magnetic flux level supplied the core structure falls below the magnetic ux level at which said member was moved from the one extreme position to the other extreme position, and means for varying the bias of each of said springs to vary the magnetic flux level at which said member is moved to its other extreme position and the ratio of the magnetic flux level at which said member is moved from its other extreme position to the magnetic flux level at which the member is moved to its other extreme position.

8. In an electrical relay, the combination comprising, a magnetizable core structure including a member movable between two extreme positions, a at spring tending to bias said member to a position intermediate the two extreme positions, and a coil spring biasing said member to one extreme position, said member being moved from the one extreme position to the other extreme position in response to magnetic flux of a predetermined level supplied to the core structure; the force exerted by the coil spring on said member being substantially uniform throughout the range or movement of the member, the force exerted by the ilat spring on said member increasing as said member is moved from the intermediate position toward either of its extreme positions; both of said springs coacting to move said member from the other extreme position toward the one extreme position when the magnetic ux level of the core structure falls below the magnetic flux level at which the member was moved from the one extreme position to the other extreme position.

9. In an electrical relay, the combination comprising, a magnetizable core structure including a member movable between two extreme positions, a. flat spring tending to bias said member to a position intermediate the two extreme positions, a coil spring biasing said member to one extreme position, said member being moved from the one extreme position to the other extreme position in response to magnetic ux of a predetermined level supplied to the core structure; the force exerted by the coil spring on said member being substantially uniform throughout the range of movement of the member, the force exerted by the dat spring on said member increasing as said member is moved from the intermediate position toward either of its extreme positions; both of said springs coacting to move said member from the other extreme position toward the one extreme position when the magnetic iiux level of the core structure falls below the magnetic flux level at which the member was moved from the one eX- treme position to the other extreme position, and means for varying the bias of each of said springs to vary the magnetic flux level at which said member is moved from its one extreme position to its other extreme position and to vary the ratio of the magnetic iiux level at which said member is moved from its other extreme position to the magnetic flux level at which the member is moved to its other extreme position.

10. An electrical relay comprising a nonmagnetic frame member, magnetizable core members secured in said frame, a rotor pivotally mounted in said frame including a magnetizable armature for oscillation between two extreme positions, a pair of oppositely extending at springs secured in said rotor, means for confining the free ends of said flat springs to bias said rotor to a position intermediate the two eXtreme positions, and a coil spring secured at one end in said rotor and at the other end with said frame to bias said rotor to one extreme position against the bias of said iiat springs, said rotor being moved to the other extreme position by said armature in response to magnetic flux of a predetermined level supplied to said core members, said flat springs and said coil spring coacting to move said rotor from the other extreme position when the magnetic flux level in said core members falls below the magnetic ux level at which said armature was moved to the other extreme position.

l1. An electrical relay comprising a nonmagnetic frame member, magnetizable core members secured in said frame, a rotor pivotally mounted in said frame including a magnetizable armature for oscillation between two extreme positions, a pair of oppositely extending flat springs secured in said rotor, an adjustment screw conned in said frame member and having oppositely threaded ends, two confining members threaded on the ends of said screw and conning the ends of said iiat springs, the turning of said adjustment screw moving said conning members toward and away from each other to vary the effective lengths of said flat springs, said flat springs biasing said rotor to a position intermediate the two extreme positions, and a coil spring secured at one end in said rotor and at the other end to said frame to bias said rotor to one extreme position against the bias of said dat springs, said rotor being moved to the other extreme position by said armature in response to 1 magnetic ux of a predetermined level supplied to said core members, said at springs and said coil spring coacting to move said rotor from the other extreme position when the magnetic iiux level in said core members falls below the magnetic flux level at which said armature was moved to the other extreme position.

l2. An electrical relay comprising a nonmagnetic frame member, magnetizable core members secured in said frame, a rotor pivotally mounted in said frame including a magnetizable armature for oscillation between two extreme positions, a pair of oppositely extending flat springs secured in said rotor, an adjustment screw coniined in said frame member and having oppositely threaded ends, two conning members threaded on the ends of said screw and confining the ends of said iiat springs, the turning of said adjustment screw moving said confining members toward and away from each other to vary the effective lengths of said at springs, said flat springs biasing said rotor to a position intermediate the two extreme positions, a coil spring secured at one end to said rotor; an arm pivoted to said frame member, the end of said arm being secured to the other end of said coil spring, a second adjustment screw threaded in said frame for abutting the end of said arm, the turning of said second adjustment screw varying the tension ci said coil spring, said coil spring biasing said rotor to one extreme position against the bias of said flat springs, said rotor being oscillated to the other extreme position by said armature in response to magnetic ilux of a predetermined level supplied to said core members, the tension of said coil spring determining the magnetic flux level at which said armature is moved to the other extreme position; said flat springs and said coil spring coacting to move said rotor from the other extreme position when the magnetic flux level falls below the magnetic ux level at which said armature was moved to the other extreme position; the variation of the effective lengths of the flat springs varying the ratio of the magnetic flux level at which the rotor is moved from the other extreme position to the magnetic ilux level at which the rotor is moved to the other extreme position.

13. An electrical relay operable in response to current flowing in a bus bar comprising a nonmagnetic frame member, magnetizable core members secured in said frame and adapted to be positioned in the magnetic eld established by the current flowing in said bus bar, a rotor of insulation material pivotally mounted in said frame including a magnetizable armature for oscillation between two extreme positions, a pair of oppositely extending fiat springs secured in said rotor, means for conning the free ends of said fiat springs, said fiat springs biasing said rotor to a position intermediate the two extreme positions, a coil spring secured at one end to said rotor and at the other end with said frame member to bias said rotor to one eXtreme position against the bias of said at springs; said rotor being moved to the other extreme position by said armature in response to magnetic flux threading said armature and core members of a predetermined magnitude determined by the value of the current traversing the bus bar, said iiat springs and said coil spring coacting to move said rotor from the other eXtreme position when the value of the current through the bus bar falls below the value of the bus bar current at which the rotor is moved to the other eXtreme position, means for varying the bias of said coil spring to vary the value of the current at which said rotor is moved to the other eXtreme position, and means for moving said confining means on the ends of said flat springs toward and away from each other to vary the effective lengths of the flat springs to vary the ratio of the value of the current at which the rotor is moved from the other extreme position to the value of the current at which the rotor is moved to the other extreme position.

14. ln combination, a member pivoted for osciliation between two extreme positions; two oppositely extending flat springs, each secured at one end to said member; a coniined adjustment screw coextensive with the at springs and oppositely threaded at each end, and a confining member threaded on each end of said screw and confining the free end of a flat spring, the turning of said screw moving said conning members toward and away from each other to vary the effective lengths of said at springs, said flat springs biasing said member to a position intermediate the two extreme positions.

15. In combination, a member pivoted for oscillation between two extreme positions; two oppositely extending at springs, each secured at one end to said member; a coniined adjustment screw coextensive with the iiat springs and oppositely threaded at each end, a coniining member threaded on each end of said screw and confining the free end of a flat spring, the turning of said screw moving said conning members toward and away from each other to vary the effective lengths of said fiat springs, said nat springs biasing said member to a position intermediate the two extreme positions, a coil spring secured at one end to said member, an arm pivoted at one end and having its free end secured to the free end of said coil spring, a second adjustment screw abutting the free end of said arm to vary the tension of said coil spring, said coil spring biasing said member to one extreme position, and means for applying a force to said member to move said member from the one extreme position to the other extreme position, said coil spring and said nat springs moving said member from the other extreme position when the magnitude of the force required to move said member to its other extreme position is decreased.

15. In an electrical relay operable in response to current flowing in a bus bar having two spaced openings therein, the combination comprising a base plate of insulation material, a nonmagnetic frame member secured to said base plate, two magnetizable core members secured in said frame member and passing through said base plate, a rotor assembly pivotally mounted in said frame member including a magnetizable armature for oscillation between two extreme positions; said core members being adapted to extend through the bus bar openings when said base plate abuts the bus bar, a magnetizable backstrapfor the ends of said core members extendingI through the bus bar openings, a cover of insulation material accommodating said backstrap, means for clamping said cover and said base plate to said bus bar, and resilient means interposed between said cover and said backstrap to bias said backstrap against the extending ends of said core members.

17. An electrical relay operable in response to current owing in a bus bar having two slots cut into the opposite edges thereof, comprising a base plate of insulation material, a nonmagnetic frame secured to said base plate, two magnetizable core members secured in said frame member and extending through said base plate, a rotor of insulation material pivotally mounted in said frame including a magnetizable armature for oscillation between two extreme positions, a pair of oppositely extending flat springs secured in said rotor, means for connning the free ends of said flat springs, said flat springs biasing said rotor to a position intermediate the twoextreme positions, a coil spring secured at one end to said rotor and at the other end with said frame member to bias said rotor to one extreme position against the bias of said fiat springs; said core members being adapted to extend through the bus bar slots when the base plate abuts the bus bar, a magnetizable backstrap for the ends of said core members extending through the bus bar slots, a cover of insulation material accommodating said backstrap, means for clamping said base plate and said cover to said bus bar, and resilient means interposed between said cover and said bus bar to bias said backstrap against the extending ends of said core members; said rotor being moved to the other extreme position by said armature in response to magnetic flux threading said armature backstrap and core members of a predetermined magnitude determined by the value of the current traversing the bus bar, said nat springs and said coil spring coacting to move said rotor from the other extreme position when 14 the value of the current through the bus bar falls below the value of the bus bar current at which the rotor was moved to the other extreme position.

18. An electrical relay operable in response to current iowing in a bus bar having two slots cut into the opposite edges thereof, comprising a base plate of insulation material, a nonmagnetic frame secured to said base plate, two magnetizable core members secured in said frame member and extending through said base plate, a rotor of insulation material pivotally mounted in said frame including a magnetizable armature for oscillation between two extreme positions, a pair of oppositely extending flat springs secured in said rotor, means for conning the free ends of said flat springs, said flat springs biasing said rotor to a position intermediate the two extreme positions, a coil spring secured at one end to said rotor and at the other end with said frame member to bias said rotor to one extreme position against the bias of said flat springs; said core members being adapted to extend through the bus bar slots when the base plate abuts the bus bar, a magnetizable backstrap for the ends of said core members extending through the bus bar slots, a cover of insulation material accommodating said backstrap, means for clamping said base plate and said cover to said bus bar, resilient means interposed between said cover and said bus bar to bias said backstrap against the extending ends of said core members; said rotor being moved to the other extreme position by said armature in response to magnetic flux threading said armature, backstrap and core members of a predetermined magnitude determined by the value of the current traversing the bus bar, said fiat springs and said coil spring coacting to move said rotor from the other extreme position when the value of the current through the bus bar falls below the value of the bus bar current at which the rotor is moved t0 the other extreme position, means for varying the bias of said coil spring to vary the value of the current at which said rotor is moved to the other extreme position, and means for moving said confining means on the ends of said at springs toward and away from each other to vary the eiective lengths of the flat springs to vary the ratio of the value of the current at which the rotor is moved from the other extreme position to the value of the current at which the rotor is moved to the other extreme position.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 786,696 Vreeland Apr. 4, 1905 940,319 Hoyt 1 Nov. 16, 1909 2,140,604 Snavely Dec. 20, 1938 2,256,653 Snavely Sept. 23, 1941 2,283,270 Laurenson May 19, 1942 2,294,484 Snavely Sept. l, 1942 2,334,514 Snavely Nov. 16, 1943 2,428,784 Cole Oct. 14, 1947 2,584,749 Snavely Feb. 5, 1952