US2294484A - Electrical relay - Google Patents

Description

Sept. 1, 1942. c. s. sNAvELY ET AL 2,294,484

ELECTRICAL RELAY Filed May 17, 1941 Insulazz'on Figi.

Patented Sept. ll, 1942 UNITED STATES PATENT OFFICE ELECTRICAL RELAY pplication May 17, 1941, Serial No. 393,952

(Cl. Zell-93) 2 Claims.

Our invention relates to electrical relays, and particularly to polar relays which are magnetically biased to enable them to be operated as neutral relays for certain applications.

Relays embodying our invention are particularly suitable for, although in no way limited to, use in brake control systems for high speed trains, such for example, as the system which is disclosed in an application for Letters Patent of the United States, Serial No. 342,941, filed by Andrew J. Sorensen, on June 28, 1940, for Brake control means, which application is assigned to the Westinghouse Air Brake Company.

In systems of the type referred to the relays are connected to an axle driven generator, the voltage output of which varies with the speed of the train, and the relays are intended to accurately respond to changes in the voltage oi the generator to effect the application or release of the brakes.

To enable the relays to satisfactorily perform their intended functions, it is desirable that the relays should meet the following requirements:

(a) Their operating values must be low to permit the use of small inexpensive generators. Large generators cannot be used because of the limited space available for the generators, and the cost of the generators must be inexpensive to enable them to compete with mechanical governors.

(b) The relays must be immune to changes in operating values caused by vibration, since they are subjected to severe vibration due to the high train speeds.

(c) The relays must be capable of maintaining their initial operating values over long periods of time.

(d) The relays must not change their operating values in response to changes in temperature or humidity.

(e) The operating values of the relays must remain fixed regardless of whether the relays have previously been fully energized or only energized to some lesser Value, that is to say, the effects of hysteresis must be eliminated.

(f) The operating values of different relays must be held between rather narrow limits in order to permit adjustment in the units.

One object of our invention is to provide a relay of the type described which will meet the above outlined requirements.

Other objects and characteristic features of our invention will become apparent as the description proceeds.

Relays embodying our invention are an improvement upon the relay described and claimed in an application for Letters Patent of the United States, Serial No. 365,039, led by Robert M. Laurenson, on November 9, 1940, for Electrical relay.

According to our invention, an armature comprising part of a suitable pivoted dynamically balanced rocker has its opposite ends disposed between and cooperating with pole faces formed by the confronting ends of two U-shaped magnetiaable yokes which are constantly supplied with iiux, preferably by a permanent magnet. The armature is surrounded by an energizing winding, and is provided with core pins of unequal lengths so arranged that the armature is free to swing closer to one set of pole faces than the other. The rocker carries two exible contact fingers formed on the opposite ends of a strip of metal which is moulded at its central portion into the rocker. Each finger is provided with a single low resistance contact button which, in the energized position of the armature, engages a similar button secured to a fixed contact member mounted in a suitable frame which pivotally supports the rocker. The two contacts thus formed are connected in multiple to provide the same protection as is obtained with the multiple button type of Contact usually employed in relays of this type, and the gauge of each linger is reduced to provide the same contact pressure per button as is obtained with multiple button contacts. The rocker is also provided with two load springs which cooperate with stops mounted on the frame to form the proper load curve to give the desired operating characteristics. The springs and contact iingers are so adjusted that when the armature moves from its released or`normal position to its attracted or picked-up position, the springs will move out oi engagement with the associated stops before the contacts close, but that the rotor will be biased by the iingers to such a position that when the relay winding is deenergized the combined forces due to the ngers and the permanent magnet bias will always cause the armature to move toward the one set of pole pieces.

We shall describe one form of relay embodying our invention, and shall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. l is a front elevational View showing one form of relay embodying our invention, the front and rear cover plates of the relay being removed to better illustrate the construction of the operating parts. Fig. 2 is a sectional view taken substantially on the line II-II of Fig. l. Fig. 3 is a View showing graphically the operating characteristics of the relay embodying our invention.

Similar reference characters refer to similar parts in all three views.

Referring to the drawing, the relay in the form here shown comprises a rectangular frame I of insulating material that can be readily moulded,

such, for example, as a phenol condensationA product, which frame supports all of the operating parts of the relay. Mounted on one side of the frame I are two U-shaped yokes 2 and 3 of Inagnetizable material. These yokes are disposed with their upper and lower legs in spaced parallel confronting relation to provide pole faces 2a, 3a, 2b and 3b, and are constantly magnetized by a pair of permanentI magnets only one of which 4 is visible in the drawing. Y A

The relay also comprisesV an armature 5 o f magnetizable material such as silicon steel moulded into an insulating rocker 6 adjacent the rear end thereof. The rocker E is pivotally mounted on front and rear pivots I and 8 secured respectively to front and rear pivot supports 9 and I0, which pivot supports, in turn, are secured to the frame I in the manner described and claimed in an application for Letters Patent of the United States, Serial No. 317,577, filed by Clarence S. Snai/ely, on February 6, 1940, for Electrical relays now Patent No. 2,256,652, issued September 23, 1941.` The upper and lower ends of the armature 5 extend between and cooperate with the pole faces 2a 3a., 2b 3b of the yokes 2 and 3 in such manner that the armature is free to swing between a normal extreme position in which a core pin 5a secured to the upper end of the armature engages the pole face 2a, and a core pin 5b secured to the lower end of the armature engages the pole face 3b, and a reverse extreme position in which a core pin 5c secured to the upper end of the armature opposite the core pin 5a engages the pole face 3a, and a core pin 5d secured to the lower end of the armature opposite the core pin 5b engages the pole face 2b, For a reason which will appear hereinafter, the core pins 5a and 5b are made shorter than the core pins 5c and 5d, whereby the armature 5 `is free to swing closer to the pole faces 2a and 3b than to the pole faces 2b and 3a; l

The operating winding ofthe relay comprises two coils I I and I-2 which surround the upper and lower` ends of the armature with sufficient clearance to permit the necessary rocking movement thereof, The coil II is connected by Ymeans of leadsI ia and IIb to coil connectors fI3a and I5a moulded into the opposite sides of the frame I, and the coil I2 is similarly connected by means of 'leads I2a. and I2b to coil connectors Ida and I3b which-are likewise moulded into the opposite sides of the frame I. v

The insulating lrocker B is provided at its forward end with two diametrically opposite flexible contact fingers I5 and I 6 formed on the opposite ends of a single strip of metal which is moulded intermediate its ends into the rocker. The contact Yfingers I5 and I6 vcooperate respectively with xed front contact members I5aI and [6a which are moulded into the opposite sides of the frame I. The fixed front contact members are each provided at their inner ends with a portion which i is bent at an angle to the main part of the contact member in such manner that when the armature 5 is midway between the two extreme positions determined by the core pins 5a, 5b, '5c and 5d, the bent portion of each contact member will `extend parallel to the associated fing-er, and each bent portion is provided with a single contact button 2li which cooperates 'with a similar contact button 2I provided on the associated flexible contact finger to form 'a low resistance contact. External electrical connection'with both exible contact fingers is 'made by means of a single v'flexible fiat spring connector member 23 whichis Asecured at one end to the vfinger I5 by means 'of the associated contact button 2 I, and at the other end to a circuit connector 24 moulded into the frame I above the coil connector I3a. The spring connector member 23 is made relatively tlnn to reduce to a minimum its mass and the force required to iiex it, and it is bent into a gradual curve to keep down stresses and lengthen its life. The contacts formed by the flexible contact fingers and associated fixed Contact inembers are so adjusted that the buttons 2l carried by the fingers i5 and I6 will just move into engagement with the buttons 20 carried by the fixed contact members IEaI and ISU. when the armature has moved a short distance past its mid stroke position in a clockwise direction as Viewed in Fig. 1, and it follows that movement of the armature to its attracted position willY cause iiexure of the fingers I5 and I to thereby provide contact compression.

The insulating rocker 6 is also provided with two diametrically opposite load springs v25 and 26 which are moulded into the rocker at the sameend of the rocker as the flexible Contact fingers, and which springs cooperate adjacent their free ends with stops formed on the inner ends of the coil connectors I5a and Ida, respectively. These load springs are so adjusted that theyV will engage the associated stops when the armature occupies any position between its normal or release position in which it is shown in the drawings and a position just a little beyond its mid stroke position in a counterclockwise direction, as viewed in Fig. 1. The force exerted by the springs Vmay be varied by bending the stops to change the associated lengths of the springs, and these load springs provide a means for decreasing the energy required to cause the armature to move to its attracted position as will appear more fully hereinafter. These springs also provide a means to compensate for uncontrollable variations in manufacture as will also appear hereinafter.

With the relay constructed in the -ma'nner described, t will be apparent that when the armature occupies its magnetic center, that is to say, when it is midway between the pole pieces, no torque will be exerted on it, and hence on the rocker, due to the permanent magnet 'ux,but that, when the armature is rotated iri either direction from this position, if the winding I I-I'Z is then deenergized, fa torque will be exerted on the armature by the permanent magnet flux, which torque will urge the rocker toward the nearest pair of pole pieces. It will also be apparent that since the core pins 5a and Y5b of the one set are shorter than the core'pins 5c and E'dof the other set, when lthe armature is in its mid stroke position as determined rby the vcore pins, it will be displaced in a counterclockwise direction, as viewed in Fig. l from its magnetic center, with the result that in this position of the rocker the permanent magnet fiux traversing the armature will exert a lforce on the armature which urges it to its normal or released position in which it is shown in Fig. l. According to my invention, the parts fareso proportioned that when the ii/indir'i'gl II-I2 is energized to the point where the armaturestarts to 'move to its attracted position, 'it will move vall of the way to this position without further increase in current, vand that, when the energiza'tion of the winding II--I2 is subsequently lowered lto the point where the armature starts to move toward itsreleased position, it will move all of the 'way to this latter position due to 'the' combined vforbe exerted on it by the contact springs I5 arid'l and the permanent magnet bias, Without any further decrease of current. That is to say, the parts are so proportioned that the permanent magnet curve has a greater slope than the mechanical load curve, and that the spread between the magnetic and mechanical centers is such that the permanent magnet curve and the mechanical load curve never cross. This is illustrated graphically in Fig. 3.

Referring to Fig. 3, the abscissa represents the displacement of the armature, while the ordinates represent the forces applied to the armature. The horizontal line OR represents the effective distance between the normal and reverse pole faces, the line OP the lengths of the normal core pins a and 5b, the line QR the lengths of the reverse core pins 5c and 5cl, and the line PQ the stroke of the armature. Curve HJK represents the force acting on the armature due to the permanent magnets alone when the relay is picking up, while the curve EFG represents the force acting on the armature due to the permanent magnets alone when the armature is releasing. The difference between these two curves represents the forces due to friction on the pivots and residual magnetism. The portion AB of the curve ABNCD represents the force acting on the armature due to the load springs and 26, the portion BC the force due to the spring connector. 23, and the portion BD the force due to the contact ngers I5 and I5. It should be noted that the curve ABNCD is plotted upside down with respect to the curves EFG and HJK from the way in which the forces react in the relay. That is, the distance QK represents the permanent magnet force acting in a clockwise direction, as viewed in Fig. 1, when the armature is moving toward its attracted position, While the distance QD represents the contact spring force acting in a counterclockwise direction. This is done to more clearly show the exact relation in magnitude between the two forces. It will be seen from an inspection of the permanent magnet curves EFG and HJ'K that the magnetic center of the armature lies at point M which is midway between the normal and reverse pole faces, and that the slope of these curves is steeper than the slopes of the curves ABNCD. The mechanical center of the curve ABNCD lies at the point N which is to the left of the point M a suflicient amount so that the curves EFG and HJK never cross the curve ABNCD. The offset between the points M and N is due to the fact that the core pins 5a and 5b are shorter than the core pins 5c and 5d.

With this proportioning of the parts, when current of the proper polarity to attract the armature is applied to the winding II-I2, the permanent magnet pull curve HJK is in effect shifted vertically, and when the current reaches the pick-up value, the curve HJK is shifted to the position represented by the dotted line AKI. It will be noted that due to the fact that the permanent magnet pull curve has a greater slope than the mechanical load curve, all points of the line AKI are disposed above the curve ABNCD, and it follows that when the current supplied to the winding II-I2 increases to its pick-up value, the armature will move all of the way to its attracted position Without further increase in current. In fact, the current supplied to the winding II--I2 could actually decrease a certain amount after the armature has started to move toward its attracted position, and the armature would continue to move al1 the way to its attracted position. In a similar manner, if the current be decreased after the armature has been moved to its attracted position until the point (not shown) which corresponds to the Vertical point to which the point G is moved when the armature picks up coincides with the point D, the armature will move all of the way to its released position Without a further decrease in current. This is represented by the line DE. I-Iere again the armature will continue its movement even if the current increases a certain amount after the armature starts to move. The armature cross section is made small enough so that the permanent magnet ux saturates it, so that regardless of how high the current in the Winding II-i2 may go, there is little more residual added to the armature over that produced by the permanent magnet flux. This insures that variations will not occur in the release value of the relay.

In manufacturing a relay of the type described, after the relay has been assembled and the contacts adjusted, the relay is baked to stabilize the contact adjustment. The permanent magnets are then placed on the relay and their charge varied until the permanent magnet pull curves HJK and EFG shown in Fig. 3 are produced. In this adjustment two things are sought. First, the release value of the relay must be between an upper and a lower limit. This is governed by the distance QG in Fig. 3, which distance may be varied by Varying the charge of the permanent magnet. Second, the slope of the curve-EFG must be greater than the slope of the curve ABNCD to cause the relay to have the toggle action described hereinbefore. The slope of the curve EFG can also be varied by varying the strength of the permanent magnet so that in the event there are enough variables in production and the same charge on the permanent magnet does not produce both snap action and the proper release values, some form of adjustment in addition to varying the charge of the magnets must be used to further control either the release level or else the snap action. By bending the member 2d shown in Fig. 1, the whole spring curve ABNCD may be either shifted up or down slightly, so that the release elevation may be altered slightly by this means, which together with the permanent magnet adjustment already mentioned permits both the toggle or snap action and the release level to be accurately controlled. The pick-up level and the snap action on attraction of the armature are then nxed by adjusting the load spring stops to control the point in the motion of the armature at which the load springs engage the stops. This controls the distances AB and HA in Fig. 3, since the strength of the permanent magnet has already been xed. In order to change the slope of the line AB so that it is atter than the curve HJK at its lower end, the stops may be adjusted so as to engage the load springs 25 and 26 at a greater or lesser distance from the pivotal axis of the rocker. This is done by bending the coil connectors Ida and I 5a close to the inner sides of the frame I so that the inner ends of the stops move in an arc tangent to the load springs. However, if large adjustments need be made to correct the slope of line AB, or if the load springs are out of adjustment, corrections for the point of contact with respect to the armature travel may be made by bending the stops at the points Where they join the coil connectors at an angle. Finally, to insure permanence of calibration, the permanent magnets are soldered in place. ToV permit this to be done readily, both the yokes and permanent magnets are tinned before the assembly to the relay.

As was pointed out hereinbefore, relays embodying our invention are intended primarily for use as speed control relays in speed control systems in which the relays are energized from an axle driven generator the voltage output of which increases or decreases according as the speed of the vehicle increases or decreases, and in which each relay is intended to pick up when the generator voltage increases to a predetermined voltage corresponding to a particular car speed and to release when the generator voltage decreases to a somewhat lower voltage corresponding to a lower car speed. It is essential to the proper operation of the system that each relay should pick up only at the desired predetermined pickup voltage and should release only at the desired predetermined release voltage. YTo accomplish this result it is necessary that the relay should lbe immune to the effects of vibration and also to the effects of hysteresis.

Since relays embodying our invention have a rotor which is substantially dynamically balanced, they are unaifected by vibration. For the rocker yto be perfectly dynamically balanced, a flexible spring connector similar to the connector 23 should be attached to the finger i6. However, the connector 23 is extremely light in weight 'compared Ato the other parts secured to or carried by the rocker, so that the complete rocker is suiciently well balanced for all practical purposes.

The necessary immunity to hysteresis is obtained by providing the snap or toggle action described hereinbefore upon picking up or release of the relay and in providing suiiicient permanent magnet iiux to saturate the relay armature when the relay is deenergized. This eliminates the variable eiects on the relay armature caused by the fact that the relay operates both in picking up and in releasing from variable current levels which tend 'to cause variable residual ux in the magnetic parts.

1'n relays of the type described as they have heretofore generally been manufactured, each contact Vlinger has been provided Vwith two contact buttons disposed on bifurcations provided on the ends of the fingers, whereby if Vdirt accumulates under one button, the Vother button will still make contact to prevent circuit failure. With the relay constructed in accordance with our invention, the two contact fingers i5 and I6 are connected in multiple in actual practice, thereby providing the same protection vin the circuits as is obtained with multiple buttons. Since each finger is provided with only one button, the same contact pressure per button can be produced with a thinner gauge spring and the gauge Yof the springs has been reduced to produce the same force per button as is provided in multiple button contacts. The reduction in gauge of the ysprings enables the relay to be operated at 'alower energy level than has heretofore been possible.

Althoughwe have herein shown and described only one form of electrical relay embodying vour invention, it is understood that Various changes and modifications `maybe made therein Within 'the scopeof the appended claims without depart- :ing from the spirit 'and scope of our invention.

Having thus described our invention, what We claim is:

1. A polar relay comprising an armature, a rocker supporting said armature intermediate its ends, a pair of magnetizable yokes having confronting pole faces between which the opposite ends of the armature are disposed, means for limiting the movement of said armature within the air gaps between a normal position and an attracted position, the armature .being separated from the adjacent pole faces by a larger air gap when it occupies its attracted position than when it occupies its normal position, an energizing winding associated with said armature, load springs carried by said rocker and biasing said armature away from its normal position, contact lingers carried by said rocker and biasing said armature away from its attracted position, and a permanent magnet connecting said yokes and magnetized to exert a force on said armature according to a predetermined magnetic pull curve, said load springs and said contact fingers being adjusted to exert a force on said armature according to a load curve which has a lesser slope than said magnetic pull curve and which never crosses said magnetic pull curve, whereby said armature is caused to move from either extreme position to the other with a snap action and is cause-d to always return to its normal position when the relay is deenergized or is energized below a predetermined level.

2. A polar relay comprising an armature, a rocker supporting said armature intermediate its ends, a pair of magnetizable yokes having confronting pole faces between which the opposite ends of the armature are disposed, means for limiting the movement of said armature within the air gaps between a normal position and an attracted position, the armature being separated from the adjacent pole faces by a larger air gap when it occupies its attracted position than when it occupies its normal position, an energizing winding associated with said armature, a pair of diametrically opposite load springs carried by said rocker and cooperating with stops to bias said armature away from its normal position,

iametrically opposite contact ngers carried by said rocker and engaging fixed contact members to close contacts when said armature is moved to its attracted position, and a permanent magnet connecting said yokes and eiiective together with the contact ngers to exert on said armature a torque which when said winding is deenergized or is energized below a predetermined level moves said armature to its normal position, said magnet being magnetized to an extent necessary to produce a predetermined magnet pull curve, and the stops which cooperate with the load springs being adjusted to change the length of the load springs and the point in the armature stroke at which the stops engage the load springs until a mechanical load curve is produced which has a lesser slope than the magnetic pull curve and the spread between the magnetic and mechanical centers is such that the two curves never cross, whereby when said armature starts to move from either extreme position to the other it'will do so with a snap action Without further change in the level of the energy supplied to said winding.

CLARENCE S. SNAVELY. DAVID P. FITZSIMMONS.

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