US2798916A - Electrical relay - Google Patents

Description

July 1 57 H. Y. FISHER 2,798,916

ELECTRICAL RELAY Filed Sept. 3, 1953 2 Sheets-Sheet l MW .Hamfm 2775/74 2" July 9, 1957 H. Y. FISHER ELECTRICAL RELAY 2 Sheets$heet 2 Filed Sept. 3, 1953 will 2. F/i/W ELECTRECAL RELAY Hardin Y. Fisher, Hillside, 111., assignor, by mesne assignrnents, to Controls Company of America, Schiller Park, 11]., a corporation of Delaware Application September 3, 1953, Serial No. 378,373

4 Claims. (Ci. 20%87) This invention relates to electrical relays and refers more particularly to a relay of the type which responds to small variations in power and which has a coil mounted upon a U-shaped frame, between the legs thereof, and an armature extending across the open end of the frame and fulcrumed on ledges on one leg of the frame for swinging motion toward and from a pole piece located between the extremities of the frame legs.

Relays of the type here under consideration are designed to open and close a power circuit in response to relatively small changes in the value of current in a control circuit in which the coil of the relay is connected. For example, such a relay may be required to close when its coil is energized by about 0.1 watt and to open when the power drops to about .01 watt. In order to achieve this responsiveness to small changes in current value (as distinguished from energization and complete de-energization of the coil), together with the necessary snap action of the contacts, it is essential to regulate very precisely both the air gap between the armature and the pole piece of the coil and the pressure with which the fixed and movable contacts are engaged in the attracted position of the armature.

Heretofore it has been considered impossible to attain such accurate establishment of the air gap by means of ordinary production methods. The reason for this will be apparent in the light of the fact that a tolerance of about .00075 inch must be maintained in the air gap in the case of a relaywhich will be responsive to the power values mentioned.

Where the attracted position of the armature was defined by the engagement of the underside of its free end against the end of the frame leg opposite that upon which the armature was fulcrumed, the frame surface which faced the underside of the armature had to be painstakingly finished with respect to the fulcrum points and the pole face to obtain the desired air gap and, moreover, had to be perfectly straight and parallel with the ledges upon which the armature was fulcrumed. In addition, the armature had to be absolutely flat and untwisted; otherwise the armature would assume a virtually unpredictable attracted position, depending upon the extent to which it tilted laterally in seating upon the frame stop in response to the magnetic attractive forces upon the armature.

A simpler expedient, therefore, for regulating the size of the air gap in such relays was the use of a non-magnetic set screw threaded into the armature for engagement with the pole piece in the fully attracted position of the armature. However, adjustment of this set screw to regulate the air gap unavoidably resulted in a varia tion of contact pressure.

Ordinarily the armature carries at least one movable contact which is cooperable with afixed contact on the leg of the frame opposite that on which the armature, is fulcrurned. One of the two contacts is resiliently mo d; fo xamp e, th m va le con t y be Q "ice 7 2,798,916 Fatentecl July 9, 1957 mounted on the end of a spring arm carried by the armature. The fixed contact is so mounted that the movable contact engages it before the armature attains its fully attracted position, so that the spring arm is required to flex in the final stages of such motion of the armature, and the two contacts will therefore be held together under a pressure determined by the amount of fiexure of the spring arm. Thus, for example, if the air gap was increased by turning the set screw downwardly, contact pressure was decreased. Moreover, because contact pressure was determined in part by the position of the end of the spring arm when the same was unflexed, any slight initial curvature of the spring arm imparted thereto during the manufacturing and assembling operations resulted in a further and unpredictable variation in con tact pressure.

With the problems of precise control of air gap dimension and contact pressure in mind, it is an object of the present invention to provide an electromagnetic relay of the character described which is so constructed that a very simple and expeditious adjusting step in the final assembly of the relay will enable simultaneous but independent establishment of the precise air gap desired and the exact contact pressure required, regardless of variations in the dimensional accuracy of the relay components such as are normally encountered in mass production, and regardless of whether one or two sets of contacts are provided.

Another object of this invention resides in the pro-. vision of an electromagnetic relay of the character de scribed which is not dependent upon adjustment of a set screw for the establishment of the required air gap dis tance, but wherein both the air gap dimension and the contact pressure may be independently but very accurately established by the simple tightening of two securement screws during final assembly of the relay.

Another object of this invention resides in the provision of a stop for the armature comprising, in effect, an extension of one leg of the relay frame which is so mounted thereon as to be adjustable in opposite directions normal to the plane of the pole face to enable said stop to be moved against the underside of the armature when the latter is held precisely spaced the desired distance from the pole face, as by a shim, and to enable the stop to be readily secured to the frame leg in the position of the stop thus established to fix the desired air gap. The adjustability of the armature stop, of course, also enables the size of the air gap to be changed at will to suit almost any other pullain and drop-out values.

In this connection it is a-further object of the invention to prov de ,a relay wherein engagement between the armature and its stop is confined to a pair of spaced apart localized points. Such localized engagement of the armature with its stop may be effected by coining either the stop or the armature, or both, and it will be appreciated that this expedient eliminates the necessity for flattening the armature to overcome any warpage thereof occur ring as the result of punching or shearing the armature. More over, since the area of contact between the armature and its stop affects the drop-out characteristics of a relay of the type here under consideration, the expedient of limiting such engagement to only a pair of localized points enables the area of engagement to be held as near- 1y constant as possible so as to achieve the greatest consistency of operating characteristics with a given air gap between the armature and the pole piece.

With the above and other objects in view, which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate one complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

Figure l is a side elevational view of an electromag- Z Figure 5 is a partial vertical sectional view of the relay shown in Figure 4.

Referring now more particularly to the accompanying drawings, in which like numerals designate like parts throughout the several views, the numeral 5 designates generally an electromagnetic relay embodying the principles of this invention and having a coil or winding 6 mounted between the legs of a magnetically permeable, substantially U-shaped frame 7, with the axis of the coil extending parallel to the legs of the frame. The frame is preferably formed from flat strip material, as is a mounting base 8 to which the frame is secured. A pole piece 9 between the extremities of the frame. legs comprises the enlarged head of a rod-like magnetically permeable core member which extends downwardly through the coil. The head overlies the upper end of the coil, while the core has a reduced lower end portion extending through aligned holes in the closed end of the frame and the base and peened over, as at 10, to secure the coil to the frame and also to secure the mounting base 8 to the bottom of the relay structure.

A flat armature 11, stamped or otherwise formed from permeable strip material, is fiatwise fulcrumed at one end portion on a pair of ledges 12 on the rear leg 13 of the frame, with the armature spanning the open end of the frame and swingable toward and from the pole piece 9. Lateral and endwise displacement of the armature olf of the frame is precluded by a pair of tongues 14 comprising integral upward extensions of the rear frame leg, at the sides thereof, which extend through loosely fitting slots 15 in the armature opening to the side edges of the latter near the rear thereof. Upward displacement of the armature is precluded by a flat, thin finger 16 which is secured to the rear face of the rear frame leg, intermediate the side edges thereof, and which projects upwardly through a medial slot 18 in the armature between and slightly to the rear of the slots 15 therein. At its top the finger 16 terminates in an arrow-like head 19 which is wider than the slot 18. The slot 18 in the armature opens forwardly to an aperture 21 which is in line with the slots 15 and which is wide enough to clear the arrow-shaped head on the finger. Thus when the armature is placed on the ledges 12 beneath the top surface of the rear frame leg and between the tongues 14, and with the finger extending straight up, the arrowhead 19 readily passes through the aperture 21, and the finger may then be bent rearwardly to carry its reduced upper end portion beneath the arrowhead into the slot 18 to a position where the downwardly facing shoulders on the arrowhead will block upward displacement of the armature.

The rear end portion of the armature provides an anchor 22 for the upper end of a coiled tension spring 23. The lower end of the spring is anchored to the lower end portion of the finger 16, which is bent rearwardly substant-ially at right angles to the plane of the leg 13, as at 24. The spring, of course, tends to rock the armature on the fulcrum provided by the ledges 12, in a direction away from its attracted position.

Movable contacts 25 are carried on the ends of elongated spring arms 26 and cooperate with fixed contacts 27 mounted on the front leg 28 of the frame in a manner described hereinafter. The spring arms are, in turn, secured to a strip of insulative material 29 fastened to the armature just ahead of its fulcrum as by means of rivets, and the arms are disposed at the opposite side edges of the armature, preferably spaced outwardly therefrom. On an insulative terminal strip 30 secured to the outer face of the rear frame leg 13 are mounted power circuit terminals 32 which are connectable with a circuit to be controlled by the relay and which are electrically connected with the spring arms by short lengths of soft, flexible wire 33. The rivets 34 which secure the insulative terminal strip 30 to the rear frame leg may also fasten the finger 16 thereto.

Each of the fixed contacts 27 is mounted on the top of a conductive post 35 which is secured, as by means of rivets 36, to an insulative mounting member 37. The conductive posts are inverted L-shaped strips having their stem portions extending upwardly parallel to one another and spaced apart a distance corresponding to the distance between the spring arms 26, and a fixed contact is secured on the rearwardly extending base portion 38 of each post. The insulative mounting member 37 has a pair of vertically elongated slots 39 through which-screws 40 pass somewhat loosely to be received in threaded holes 41 in the front frame leg 28. The screws secure the mounting member to the outer side of the front frame leg and at the same time enable the mounting member to be readily adjusted up and down as well as tilted edgewise to thus effect accurate adjustment of the contact pressure, as will appear presently. A stop 43, comprising an inverted L-shaped strip of metal, with the base 44 of the L extending rearwardly over the front portion of the armature, is also secured to the mounting member 37, between the conductive posts, and defines the fully retracted position of the armature wherein the upper surface of the armature engages the stop.

In the relay of this invention the front frame leg terminates a substantial distance below the upper end of the coil, and the fully attracted position of the armature is defined by a stop comprising the top surface of a permeable extension 45 of the front frame leg 28 which provides for adjustment of the air gap. The extension 45 has the shape of an inverted L, with its flange 46 providing the armature stop beneath the front portion of the armature. The stem 47 of the extension is provided withvertical slots 48 that align laterally with the slots 39 in the insulative mounting member 37. The same screws 40 which secure the insulative mounting member to the front frame leg also extend somewhat loosely through the slots 48 in the extension 47 to secure it in place on the front frame leg. It will be seen that as the permeable extension 47 is adjusted up and down on the frame the position of its flange 46 will determine the size of the air gap between the armature and the pole piece.

In order to decrease the area in which the armature and its. stop are in contact with one another when the armature is in its fully attracted position, the two are caused to engage only at two relatively small areas adjacent to their side edges by reason of the fact that the flange 46 of the permeable extension has a pair of laterally spaced, relatively small bumps or protrusions 49 coined upwardly therefrom while the armature has downwardly coined flats 51 on its marginal side edge portions in positions to engage the protrusions on the extension. It should be understood, however, that it is not essential to coin both the armature and its stop in order to assure the desired limited contact therebetween. Equally good results are obtained, for instance, when only the flange 46 comprising the armature stop is coined to provide it with the two'npwardly projecting bumps or protrusions 49, which have sufficient height to overcome any warpage in the armature that may have resulted from stamping or shearing the same from sheet stock. 0n the other assi tahand, if the top surface of the armature stop is relatively straight and flat, only the armature may be coined to provide it with the downwardly projecting flats 51 on its marginal side edge portions. relay of the type herein concerned, the area of contact between the armature and its stop has a relatively great effect upon the drop-out characteristics of the relay. Hence, if contact is confined to two small laterally spaced locations along the underside of the armature, these areas can be made as close to constant as possible to achieve the greatest consistency of operating characteristics with relays having a given air gap between their armatures and pole pieces.

When the relay of this invention is assembled, the two screws 40 are very loosely inserted into the front frame leg so that both the insulative mounting member 37 and the extension 45 are held in place thereon in such a manner as to be freely slidable up and down, and edgewise tiltable, independently of one another. The air gap and contact pressure may thenbe readily established by the very simple operation illustrated in Figure 4. A shim 53, preferably of magnetically permeable metal and having a thickness exactly equal to the desired air gap is inserted between the pole piece 9 and the underside of the armature; and with the relay mounted upside down, i. e., armature lowermost, the coil is energized so that the armature will assume the desired fully attracted position seated against the shim. With the coil so energized the extension 45 will of its own weight slide downwardly to bring both of its protrusions 49 into engagement with the underside of the armature, and since the permeable shim has a thickness equal to the size of the desired air gap, and the armature is therefore occupying its desired fully attracted position, the armature stop will likewise assume exactly the position required to maintain that air gap. Moreover, any tendency of the armature to rock or tilt laterally upon its fulcrum in the course of its swinging motion in response to energization of the coil will be fully compensated by reason of the fact that the stop will assume a position to accommodate such rocking or tilting motion. It is for this reason that it is preferable to retain the armature in its attracted position by energizing the coil, so as to cause the armature to seat itself in the same position that it will assume when the relay is placed in service, rather than holding it in its attracted position by the application of externally applied force thereto.

With the coil energized, the mounting member carrying the fixed contacts is biased downwardly, i. e., toward the armature, with a force equal to the desired contact pressure. This may be readily accomplished by han ing weights 54 on the mounting member, the total weight of the mounting member and said weights being equal to the desired contact pressure. To facilitate this operation holes 55 are provided near the lower ends of the conductive posts 35, in which the weights may be hooked and which also serve as terminals for power circuit conductors when the relay is installed in service. With the mounting member so weighted the fixed contacts will, of course, engage the movable contacts under a pressure which will flex the spring arms carrying the movable contacts to exactly the position they are required to have in the fully attracted position of the armature in order to provide the desired contact pressure. It is then necessary only to tighten the two screws 40 in order to complete the assembly, securing the permeable extension 45 with the armature stop thereon and the contact mounting member 37 in exactly their required positions. After the screws 40 are tightened, varnish or the like is applied to their extremities to prevent them from loosening during use of the relay.

From the foregoing description, taken together with the accompanying drawings, it will be apparent that this invention provides an electromagnetic relay of the type which is capable of responding to relatively small changes In an extremely sensitive in power and which is so constructed that both the air gap and contact pressure may be very precisely determined by high-speed production methods despite inevitable inaccuracies in dimensions of the components within normal mass production tolerances.

What I claim as my invention is:

1. In a relay of the type having a coil mounted in a U-shaped frame with a pole piece between the legs of the frame and with the coil axis substantially parallel to the legs of the frame, an armature extending across the open end of the frame, hingedly connected at one end to one leg of the frame to swing toward the pole piece to an attracted position, and a movable contact carried by the armature cooperable with a fixed contact mounted on the frame, said contacts being engageable in the attracted position of the armature and one of said contacts being resiliently mounted, means for precisely adjusting the spacing between the armature and the pole piece in the attracted position of the armature and for precisely adjusting the pressure with which said contacts are engaged in the attracted position of the armature, said means comprising: a screw threaded into the other leg of the frame with its axis transverse to that of the coil; an extension on said other leg of the frame having a surface facing the underside of the armature and with which the armature is engageable to define the attracted position of the armature, said extension having a slot therein through which said screw passes, so that said extension may be freely slid along said leg, in directions parallel to the coil axis, to enable precise establishment of the air gap between the armature and said pole piece, said extension being retainable in any position to which it is thus moved by tightening the screw; and a member upon which said fixed contact is mounted, said member having a slot therein through which said screw passes so that said member may be freely slid along said other leg of the frame (independently of said extension) in directions parallel to the coil axis when the screw is loose to permit said member to be moved to a position at which the desired contact pressure will obtain by holding the armature in its position at which the desired air gap obtains and biasing the member toward the movable contact with a force equal to the desired contact pressure, said member being retainable in the position to which it is thus biased by tightening the screw.

2. In a relay of the type having a coil mounted in a U-shaped frame with a pole piece between the legs of the frame and with the coil axis substantially parallel to the legs of the frame, an armature extending across the open end of the frame, hingedly connected at one end to one leg of the frame to swing toward the pole piece to an attracted position, and a movable contact carried by the armature cooperable with a fixed contact mounted on the frame, said contacts being engageable in the attracted position of the armature and one of said contacts being resiliently mounted, means for precisely adjusting the spacing between the armature and the pole piece in the attracted position of the armature and for precisely adjusting the pressure with which said contacts are engaged in the attracted position of the armature, said means comprising: an extension for the other leg of the frame having a surface against which the armature is engageable in its attracted position; means for adjustably mounting said extension on the frame adjacent to said other leg of the frame and with said surface facing the underside of the armature to be engaged thereby, said mounting means enabling sliding adjustment of said extension in directions parallel to the coil axis to enable precise establishment of the air gap between the armature and said pole piece; a member upon which said fixed contact is mounted; means mounting said member on the frame and permitting said member to be freely slidable in directions parallel to the coil axis so that saio member may be moved to a position at which the desired the open end of the frame, hingedly connected at one end to one leg of the frame to swing toward the pole piece to an attracted position, and a movable contact carried by the armature cooperable with a fixed contact mounted on the frame, said contacts being engageable in the attracted position of the armature and one of said contacts being resiliently mounted, means for precisely adjusting the spacing between the armature and the pole piece in the attracted position of the armature, said means comprising: an extension member adjustably mounted on the other leg of the frame and having a-surface facing the underside of the armature and engageable by the armature when the armature is in its fully attracted position, said extension member being movable in directions parallel to the coil axis; and means for securing said extension member in any of its positions of adjustment so that the position of its said surface may be adjusted in directions parallel to the coil axis and retained in a position in which it will precisely establish the desired air gap between the armature in its attracted position and said pole piece.

4; The relay of claim 3, wherein the rigid armature is engageable with said surface on the extension, when the armature is in its attracted position, at two spaced apart points, to preclude lateral rocking of the armature when it is in said position and thereby assure maintenance of a uniform air gap and also to insure consistent operating characteristics for the relay.

References Cited in the file of this patent UNITED STATES PATENTS 7 281,249 DInfreville July 17,1883 1,785,887 Chryst Dec. 23, 1930 2,545,835 Wilson et a1. Mar. 20, 1 951 FOREIGN PATENTS I 464,336 Great Britain Apr. 15, 1937 581,459 Germany July 27, 1933

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