US2731527A - Electromagnetic relays - Google Patents

Description

Jan. 17, 1956 G. E. MARSH 2,731,527

ELECTROMAGNETIC RELAYS Filed NOV. 4, 1952 3 Sheets-Sheet l FICLI.

FIC1.2.

ll H INVENTOR. G.E. MARSH HIS ATTORNEY Jan. 17, 1956 G. E. MARSH ELECTROMAGNETIC RELAYS 3 Sheets-Sheet 2 Filed Nov. 4, 1952 FIGS.

FIGAC.

FIG.4A. FIGA-B.

RELAY FULLY RELEASED FIC:.4D. FIGL4E.

INVENTOR.

GE. MARSH RELAY FULLY OPERATED HIS ATTORNEY Jan. 17, 1956 MARSH 2,731,527

ELECTROMAGNETIC RELAYS Filed NOV. 4, 1952 I5 Sheets-Sheet 3 FICLES.

ENERGIZ- ARMATURE ATION OF ../LOAD CURVE WINDTNGS 54 (f) N *J 2 wk 2 OQ/ 55 (D Q/Q// 8 O Q/ 0: 9E 50 O .0l0 .020 .030 .040 .050 ,oso

ARMATURE TRAVEL INCHES -C0NVENTI0NAL B. ANTI BOUNCE 2 HIT 0F ARMATURE Z l- LU z m .HITS FRONT I c: POLE PIECE m APMATURE 8 3 HITS FRONT T POLE PIECE TIME 1iv 1-Eiv 2'd1.

TME G.E.MARSH HIS AT TORNEN United States Patent fhce 2,731,527 I Patented darn. 1?, 1356 2,731,527 ELECTROMAGNETIC RELAYS Gareld E. Marsh, Rochester, N. Y., assignor to General Railway Signal CompanmRoclie'ster, N. Y. Application November 4, 1952, Serial No. 318,577 4-Ciaims. (Cl. 200-87) This invention relates to electromagnetic relays, and more particularly pertains to electrical contacts for such relays constructed to prevent armature bounce and also to prevent any transient opening of the contacts following their initial closing.

Generally speaking, there are at least three causes for contact bounce, i. e., transient contact openings, upon a contact closure near the end of an armature operating stroke. First, the movable contact'spring or finger attached to the armature may have such structural characteristics as to allow it to flutter or vibrate during the operating stroke of the armature, thereby causing such movable contact finger to make transient contact with its associated fixed contact one or more times before the final contact closure. Secondly, the relay armature acquires kinetic energy during its operating stroke which must be dissipated at the end of such stroke. If such kinetic energy is permitted to be reflected by the armature stops or pole pieces, the armature is caused to rebound before becoming stabilized in its new position. Such rebound may, of course, be transmitted to the movable contacts. Thirdly, the impact of the-movable contact finger against a fixed contact may result in a contact bounce.

With the above considerations in mind, it is proposed to provide in accordance with the "present invention a contact structure which eliminates all three of theabove mentioned causes for contact bounce by coordinating the contact operating load with the armature operatingforces, and also by providing a movable contact finger which is structurally rigid during armature operation.

Without making any attempt to define the exact nature of the invention, it'may beexplained that his proposed to provide a movable contact fingeror spring that is light in Weight but is supported 'on a rigid contact carrier attachedto the armature of the relay, with such contact spring having an initial trapped"p'ressi'1re to avoid any flutter or vibration during'the operating "stroke of the relay armature. It is also proposed to provide the movable contact finger or spring with a two step load characteristic to absorb the armature kinetic energy-and to make the contact load characteristics more nearly conform with the operating force characteristics.

Since the movable contact is light in weight and is held under trapped pressure, no contact bounce can take place upon its initial impact with'the'fiX'ed or stationary contact. During the primary deflectionof the movable contact spring after its initial impactwith the fixed or stationary contact, the increased load acts to decelerate the armature. But of course the working force acting on the armature is greater than the loadof the primary deflection so that the impact 'of the movable contact finger at the start of the secondary deflection does not create any bounce of the contact movement nordoe's it cause any hesitation in the armature movement. The load of the secondary deflection increases at a faster rate than the primary deflection which is efiective to 'decelerate the armature motion in readiness for its impact with its stops. In this way, the movable contact finger is maintained under constantly increasing pressure following its initial closure at the pickup point. This prevents contact bounce and also causes the contact load on the armature to more nearly parallel the net working force on the armature. In addition, the contact load is made to increase in such a way as to dissipate the kinetic energy in the armature and :prevent armature bounce when it strikes its stops, which bounce if it occurred, would be reflected as a vibration to the movable contacts.

Various other objects, purposes, and characteristic features of the present invention will be in part apparent and in part pointed out as the description of the invention progresses. In describing the invention in detail, reference will be made to the'accompanying drawings in which:

Fig. 1 is a top view, with certain parts removed, of the relay structure embodying the present invention;

Fig. 2 is a side sectional view of the relay structure taken on a line 2-2 of Fig. l

Fig. 2A is an isometric partial View of the movable contact structure of which a top View is shown in Fig. 1;

Fig. 3 is an isometric view of the electromagnetic structure of the relay, with'all other'parts of the relay removed;

Figs. 4A, 4B, 4C, 4D and 4E are detail top views of the contact structure of the present invention shown in different operating positions to illustrate the diiferent operating characteristics;

Fig. 5 is a graphical illustration of the operating force's involved in the relay;

Fig. 6A is a graph of the current rise in the windings of a conventional relay not'er'nploying the features of the-present invention; and

Fig. 6B is a graph of the current rise in the windings of a relay constructed in accordance with the present invention.

In connection with the drawings, it'should beunderstood that they have been made more with the purpose in mindof showing the general structural characteristics of a relay embodying the present invention than for the purpose of showing the details of such a'relay. For this reason, the drawings include sectional views, isometric views,'and the like, to more clearly show the characteristic forms contemplated asconstitutingthe elements of the present invention. it will, of course, be understood that various changes in position, she and shape may be made to the various elements constituting the structure embodying the'present invention without in any way departing from the basic principles involved in the proposed relay structure.

Relay structure As viewed in Figs. 1 and 2, it will be seen that "the relay structure includes a molded outer casing 55 of insulating material. This casing 5' is formed in two parts, an upper portion and a lower portion, as can be seen in Fig. 2. Mounted within this i'nsulating'casing 5 are two pole pieces 6 and 7 of U-shape. These pole pieces 6 and '7' are of suitable soft iron material and face each other as viewed in Fig. i with a suitable spacing to permit the movement of a pivoted armature The pole Zones 6 and 7 are fastened to the upper casing por n and have mounted beneath them two U-sha'pe'd permanent magnets 9 and iii. The ends of these permanent magnets 9 and 16 closely contact the pole pieces (a and 7, and for this reason are attracted thereto by reason of their residual permanent magnetism. in addition, springs 11 and 12 provide an upward force tending to hold the permanent magnets in their respective positions.

The armature is attacl'ied to a spindle which is pivotally supported by su t ble end supports and 14 attached to the upper casi 1 portion. Tne pivoted armature is surrounded by windings a. d 3%? res ectively formed on suitable insulating spools i7 and 2 These spools i7 and are held in position by g recesses for engaging the pole piecese and a'tta'chedto the outer casing 53; and these spools i7 and 1 8 have longitudinal central openings sufficiently large to surround the armature and permit its movement to its different positions limited by residual pins 33 of non-magnetic material.

Mounted on each pole piece 6 and 7 at one end are pole extensions 31 and 32, for opposite ends of the armature. Tl ese pole extensions 31 and 32 are for the purpose of magnetically biasing the armature 3 to ticular operated position as will be described in greater detail hereinafter; but for the time being, it will be noted that the armature S is shown in a mid-position in Fig. 1 rather than its normal biased position, so that the contact structure may be shown with contours normal y assumed when no contact pressures are involved.

The upper portion of the armature spindle is provided with extending arms attached to a molded member 29 upon which is attached the movable contact fingers. These movable contact fingers include a contact carrier which is formed of two metal strips 21 and 2?. These two strips 21 and 22 are riveted together at 25 and The inner ends of these strips forming the contact carrier are molded into the member 20, while the outer ends are so bent as to provide the contact carrier with a bifurcated portion.

The movable contact springs 23 and 24 are mounted on each side of the contact carrier and are held in position because their inner ends are attached to the contact carrier by the rivets 26. The outer ends of these contact springs 23 and 24 are bent to form hooks which extend around their respective bifurcated fingers of the contact carrier. This has been shown in Fig. 2A where one strip 21 and contact spring 23 has been illustrated in an isometric view. Each contact spring carries a contact point of suitable contact material such as contact silver, molybdenum, or the like. For example, contact spring 23 carries contact point 30; and contact spring 24 carries contact point 29. The inner ends of the contact springs 23 and 24 are bent outwardly to receive so-called pigtail connections extending to the stationary connectors forming a part of a plug coupled connection.

Suitable fixed contacts such as front and back contacts 27 and 28 are mounted on the outer casing 5 with contact points of contact material similar to the movable contacts. The fixed contact points are preferably rounded while the movable contact points are preferably flat for providing suitable contact wipe as the relay is operated. This operation will be discussed in greater detail hereinafter.

Electromagnetic structure With reference to the isometric View of Fig. 3, it can be seen that the ends of the pole pieces 6 and 7 are respectively made north and south poles by the permanent magnets 9 and 10. This is indicated by the letters N and S on the ends of the pole pieces 6 and 7. The pole piece extensions 31 and 32 of course assume the same polarity as their associated pole pieces 7 and 6. The armature 8, being pivoted so that its opposite ends fall in the air gaps between the respective north and south poles N and S, is normally attracted in a counterclockwise direction because the pole extensions 31 and 32 reduces the reluctance of the air gap for that position of the armature with respect to the reluctance of the air gaps for any other position. For this reason, the armature 8 is magnetically biased to the position shown in this isometric diagram.

The coils and 16 are shown diagrammatically merely as a winding about the armature in this Fig. 3. When the windings l5 and 16 are energized with such a polarity as to cause added flux to go from left to right through the armature 8, the armature is merely more firmly held in its normal biased position. On the other hand, when the windings 15 and 16 are energized with the opposite polarity, an electromagnetic force is produced which opposes the flux through the armature 8 from the permanent magnet, and in fact, produces a resultant flux from left to right. This causes the armature 8 to be actuated in a clockwise direction. This is because its right-hand end is made a north pole which repels the north of the pole piece 7 and is attracted to the south of the pole piece 6. The polarities, of course, are just the reverse with respect to the opposite end of the armature 8 under this condition. in this way, the armature 3 is normally biased magneticali y to a particular operated position; and may be electrically actuated to its opposite position by the energization of its windings. The extremes of armature movement are limited by the stops 33 (See Fig. l) which hit against the faces of the pole pieces 6 and 7.

[Movable Contact operation As previously mentioned, the armature and contacts of Fig. 1 are shown in mid-stroke positions, but the contacts and armature are normally biased to a released or reversed position by the magnetic characteristics of the relay structure as above described.

Under such normal conditions the contact carrier 21- 22 and its movable contact springs 23 and 2 assume positions as shown in Fig. 4A. The contact spring 24 is in its fully deflected position in which its outer end is braced against the outer end of the other movable contact spring 23 and the extreme end of the strip 21 of the contact carrier. For this reason, the contact spring 24 is depressed inwardly against its normal set toward the rivet 25 as can be seen from the illustration of Fig. 4A.

When the windings 15 and 16 are energized and the armature 8 begins an operating stroke, the contact carrier 21-22 moves in a clockwise direction and allows the contact spring 24 to pass through its primary deflected position and then come to a point where the contact carrier strip 22 picks up the outer hook of the movable contact spring 24 holding it under the original trapped pressure. In this condition, the armature operates the contact structure through mid-stroke in which no contact is made with either the front or the back point 27 or 28. This is illustrated in Fig. 4B.

Then the armature moves to a position where the movable contact point 30 just touches the front contact point 28. This is termed a picked up position, at which time no particular contact pressure is established. However any further armature movement causes the immediate application of the trapped pressure of the contact spring 23; While still further movement applies the pressure of the primary deflection. This has been illustrated in Fig. 4D. In other words, the movement of the armature after the contacts 30 and 28 initially touch each other immediately applies the trapped pressure and then builds the contact pressure to a higher value as the spring 23 is deflected from its normal set shown in Fig. 4C to its position shown in Fig. 4D. This deflection causes the outer end of the spring 23 to move through a distance indicated in Fig. 4B as 35, and this deflection has for convenience been termed the primary deflection.

As the armature moves still further, the secondary deflection takes place until the armature has completed its travel or operating stroke at which time the full secondary deflection is present as illustrated in Fig. 4E. In brief, the secondary deflection is the deformation of spring 23 while its outer end is resting against the spring 24 supported by the outer end of the contact carrier strip 22. This makes it so that the force required to cause such secondary deflection must rise much more rapidly for any given unit of armature travel.

It should also be noted that the spring 23 is in effect pivoted at 26 during the primary deflection which tends to draw the contact 30 inwardly to produce a wipe between points 28 and 30. But when the secondary deflection takes place, the tendency is to straighten the spring 23. This tends to move the contact point 30 outwardly over the same path which it has just followed along the surface of the back contact 28. A good electrical connection is thus established.

The forces acting on the relay armature for its ditferent positions have been illustrated in the graph of Fig. 5

as found in atypical relay:constructed-.in accordance with the :presentinvention. In otherwords, theseforces were measured for thegdifferent positions of the armature :and then plotted to .give a static .operation curve as distinguished from a dynamic operation curve.

Thepermanentmagnet foreach position of the armature exerts a .force on the:armature represented by the curve. 50. Since the pole piece extensions 31 and 32 render the magnetic circuit unsymmetrical, .a major portion of this curve 50 liesbeneaththe zero-line of the forcediagram. In other words, the forceof thepermanent magnet is applied in a counterclockwise.direction represented by the negative values in this diagram.

The contact load is represented by the curve 51. Actually the contact load. in thenormal position .of the relay armature is in opposition to .the..force produced by the permanent magnet and would normally be drawn as positive values above the zero line. But because it is desirable to compare the electromagnetic-forces acting on the armature with the contact load, itis convenient to represent the back contact load on thenegative side of the zero line and the front contact load on thepositive side of the zero line.

The magneticforces supplied by the energizationon the winding 15 and '16 with a proper polarity to cause operation of the armatureto its oppositeposition are, of course, in opposition to the permanent magnet force. Since it is desirable to know the net operating force on the arma: ture, the electromagnetic force produced by the energization of the winding is added to the magnetic force of the permanent magnet to give a working force curve '52, rather than showing the electromagnetic force of the windings merely as a curve of'positive values.

With this organization of the graph of Fig. 5, it can be readily seen that the force of the permanent magnet is greater than the force of the back contact load at the fully released position of the .relay armature to the extent of the difference in distances from the zero line. Similarly, it can be seen that thenet working force is greater than the front contact load during energization of the windings 15 and M to the extent of difierence in distances between-the curves '51 and '52from the zero line.

The amount of energy required to carry a relay armature from its back contact making'position to a point at which the movable contact'spring 23 causes the front point Sll-to make with the front contact 28 but insufficient to overcome the trapped pressure of spring 23 is known as the pickup current for the'relay in this case. For this reason the armature stalls 'in this'position. The electromagnetic force provided by such energization of the windlugs 15 and 16 has been added to thepermanent force to provide the pickup dotted line curve 53 which terminates at a point designated'PU point. This curve terminates at a positive value of force, which means that a corresponding contact pressure is developed. In effect such operation has overcome the operating losses of the relay and after moving the armature to this point, maintains this force on the front contact. Although this curve 53 is indicated as falling beneath the curve 51 as it approaches Zero, the armature carries through this point because of the kinetic energy stored therein so that the armature readily reaches the pickup point. Similarly, when the relay armature is in its fully operated position due to the working energization of the windings 15 and 16, it is conventional practice to decrease such value of energization to a point at which the relay armature will drop away or release and just close the back contacts 27 and 29. Such dropping away value of energization of the windings has been added to the permanent magnet force to give the curve 54. 'This curve terminates at a point where the'contacts just make and this is indicated on the graph of Fig. 5 as the DA point. Again it is to be understood that there is some contact pressure when the armature is stalled in this position because the armature has available that force shown on the graph, but insufllcient to overcome the trapped pressure; The electromagnetic forces-present when thewindings .15 iand.16 are. energized to a minimum value .of currentwhich may be allowed to flow and still obtain the full release of the relay armature is known as the minimumtull release current, and theelectromagnetic force of such current hasbeen added to the permanent magnet force to give the-minimum full release forcecurve 55.

Operational characteristics it is a well recognized fact that when a relay-is initially energized the armature builds up a velocity which .produces a counterelectrom'otive force in the relay windings so that-the current in the relay winding does not follow the normal buildup for a winding having that particular inductive characteristic. This hasbeen illustrated in Fig. 6A. The dotted line curve 60 represents the buildup of the current during the elapseoftirne after initial energization that would normally take place for the relay if the armature were'not allowed to move. Thecurve 61 represents the buildup of'the current 'when'the armature is allowed to move. It is notedthat the-curve 61 takes a dip, which is due to the hack electromotive force produced by the armature-movement. Thisback electromotive force is a maximum when the armature hits the front pole piece and this is because thevelocity of the armature is then a maximum. In fact, the armature is accelerating right up to a point of impact. .Since the back electromotive force is a'function of the velocity of the armature and thelength of the air gap, the slope of curve ol at its point of discontinuity, indicated by line AlA2 in Fig. 6A, is representative of the armature velocity at the point of impact.

Upon the first-impact of the relay armature there is sufficient kinetic energy to be reflected by the pole piece of.

the conventional relay that the armature bounces away from'the pole piece and in so doing the back electrometive force is reversed and the current begins to again build up toward a stable value; but, because the armature is againipulled toward the pole piece with a rising velocity a second back electromotive force is produced which causes another dip in the current rise. Apparently such second hit of the armature against the pole piece involves a minor amount of kinetic energy so that it does not again rebound to any substantial amount, and the current in the winding builds up to a stable value. This illustration of Fig. 6A is a graphic illustration of an actual relay operation as shownby an oscilloscope.

The rise of the operating current'of a relay constructed in accordance with the present invention is illustrated in Fig. 68, where the graphic illustration is taken from an oscilloscope connected to a typical relay. it will be seen that the dotted line curve 6% of Fig. 6B is the same as the corresponding curve 60 in Fig. 6A. This is because the rate of current rise is the same for correspondingly constructed relays if the armature is not allowed to operate. However, in this case the operating current curve 62 does not have the sharp discontinuities of the curve 61 of Fig. 6A.

This curve 62 indicates that the current rise is slower at first than indicated by the curve 61. This is because the characteristics of the contact load in the relay of the present invention is such as to allow more rapid acceleration of the relay armature. However, when the relay armature reaches that point at which the front contacts are picked up and a contact load is applied to the armature, deceleration'of the armature takes place to a sulficient extent that the actual velocity of the armature is reduced. This reduces the back electrornotive lforce built up in the relay windings so that the current rise, although reduced by the armature velocity, does not have a sharp discontinuity as shown in the curve 61. As above pointed out, the back electrcmotive force present in the windings the relay is a function of the armature velocity, so that the slope of the curve 62 at its depressed portion represents that the velocity of the armature at that point has been reduced substantially. Actually, the armature velocity is decelerated and reduced to such a value before it hits the front pole piece, that the effect on the current rise curve is to make it substantially horizontal at the point of impact as indicated by the line B1-B2 of Fig. 6B. Since the velocity of the armature is reduced before impact, the amount of kinetic energy still in the armature is considerably below that found in the conventional relay. This smaller amount of kinetic energy, even though reflected by the front pole piece upon the impact of the armature, is of a considerably smaller value than the then existing force or pull on the armature towards the pole-piece. Because of this fact, no rebound of the armature takes place; and this is indicated in Fig. 6B since the curve 62 directly rises toward a stable value without any secondary depressions.

Summary Although the above operation and discussion has been more particularly directed to the operation of the relay armature and its contacts from a deenergized or released position to an energized or operated position, it is to be understood that the operating characteristics are exactly the same upon the deenergization of the relay and the release of its armature and contacts. With reference to the graph of Fig. it will be noted that the contact load curve falls within the permanent magnet force curve 50 and the working current force curve 52. This contact load curve can obviously be moved, so to speak, within the limits of these two curves and still provide the features characteristic of the present invention.

For example, the cross over distance may be shortened by bringing the fixed contacts 27 and 28 closer together. The height of the initial rise of the contact load curve from the zero line may be lengthened or shortened depending upon the initial trapped pressure placed in the contact springs 23 and 24 by reason of the set. The length of the primary deflection line can be varied by adjustment of the distance 35 by separating or bringing closer together the fingers of the bifurcated contact carrier 21-42. The slope of the primary deflection and secondary deflection curves is, of course, dependent upon the degree of resiliency of the contact springs.

It should be noted that the primary deflection is inherently equal on the fronts and the backs because the distance 35 is the same for both. The length of the secondary deflection can be varied by changing the location of the front and back points 28 and 27 relative to the armature travel.

Although the contact structure has been shown as applied to a relay of the so-called polar biased type, it is to be understood that these contacts may also be applied to any type of relay either neutral or polar, alternating current or the like.

Having described an electromagnetic relay and contact structure as one specific embodiment of the present invention, it is desired to be understood that this form is selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be further understood that various modifications, adaptations, and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention.

What I claim is:

l. in an electromagnetic relay structure, an armature operable to either of two positions, a movable contact structure attached to said armature and operable between fixed front and back contacts comprising a rigid contact carrier attached to said armature at one end and bifurcated at the other end, two contact springs one on each side of said contact carrier, and both springs having their inner ends permanently attached to said contact carrier, but having their outer ends formed into hooks to engage their respective bifurcations of said contact carrier and both said springs being bent to provide predetermined trapped pressures against their respective bifurcations, and a contact point attached to each contact spring at a mid-point of its length such as to cooperate with a corresponding fixed contact point.

2. in an electromagnetic relay structure, an armature operable to either of two positions determined by stops, a movable contact structure attached to said armature and operable between fixed contacts corresponding to said two positions, said movable contact structure comprising a contact carrier attached to said armature at one end and bifurcated at the other end, two contact springs one on each side of said contact carrier and both said sprin s being connected at their inner ends to said contact carrier, but having their outer ends formed into hooks to engage their respective bifurcations of said contact carrier, each of said springs being given a predetermined set to give the outer ends of said springs a tendency to outward movement which is prevented by their hooked ends engaging the inner sides of their respective bifurcations, contact points attached to each contact spring at a midpoint of its length such as to cooperate with corresponding fixed contact points, whereby the movement of said armature to either extreme position causes the corresponding movable contact spring to contact its respective fixed contact and deflect such spring through one step until the outer hooked end of that spring touches the inner hooked spring to cause a secondary deflection for the remaining portion of the armature movement.

3. A contact structure for a relay having an electromagnetically operated armature comprising, a contact carrier attached to the armature at one end and having two spaced fingers at the other end, two contact springs one on each side of said contact carrier and both such springs being connected at their inner ends to said contact carrier but having their outer ends bent to engage their respective spaced fingers on the inside, said contact springs having a normal set to produce a tendency for outward movement which is opposed by said spaced fingers of said contact carrier, a contact point mounted on each of said springs between its outer and inner ends, and fixed con tacts adapted to cooperate with said contact points.

4-. In an electromagnetic relay, an armature cooperating with pole pieces and having stops for limiting its movement in its extreme positions, a movable contact structure mounted on said armature to be operable between front and back fixed contact points comprising a rigid contact carrier attached at one end to said armature, a contact spring having one end attached to said contact carrier and being formed with a predetermined tension tending to move said contact spring away from said contact carrier, said contact spring having a hooked projection to engage said rigid contact carrier to limit its movement away from said contact carrier with a predetermined degree of trapped pressure, and said rigid contact carrier at its said other end having means to allow said contact spring to be operated only a limited distance against its tension before its outer end is prevented from further movement and its tension away from said rigid contact carrier rapidly increases.

References Cited in the file of this patent UNITED STATES PATENTS

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