US3355629A

US3355629A - Electromagnetic switch with nonsnap-acting contacts

Info

Publication number: US3355629A
Application number: US464015A
Authority: US
Inventors: William W Schapira
Original assignee: Consolidated Electronics Industries Corp
Current assignee: Consolidated Electronics Industries Corp
Priority date: 1965-06-15
Filing date: 1965-06-15
Publication date: 1967-11-28
Anticipated expiration: 1984-11-28

Description

Nov. 28, 1967 w, $HAP|A 3,355,629

ELECTROMAGNETIC SWITCH WITH NON-SNAP-ACTING CONTACTS Filed June 15, 1965 v 4 Sheets-Shed 1 Nov. 28, 1967 w. w. SCHAPIRA 3,355,629

ELECTROMAGNETIC SWITCH WITH NON-SNAP-ACTING CONTACTS Filed June 15, 1965 4 Sheets-Sheet 2 50 I 3 '25 54 J00 y 30 1 51% 24108 173 Jaw/7 L 5i? 1* mmwbwm J04) Jfl i'Z/l L Nov. 28, 1967 w. w. SCHAPIRA 3,

ELECTROMAGNETIC SWITCH WITH NON-SNAP-ACTING CONTACTS Filed June 15, 1965 v 4 Sheets-Sheet 5 ARM/J rum GnP, INCHES NOV. 28, 1967 w, w, SCHAPIRA 3,355,629

ELECTROMAGNETIC SWITCH WITH NON-SNAP-ACTING CONTACTS Filed June 15, 1965 4 Sheets-Sheet 4 .134 70a, Jg

mp .128 529M United States Patent 3,355,629 ELECTROMAGNETIC SWITCH WITH NON- fiNAP-ACTIhlG C(DNTACTS William W. chapira, Skokie, 12L, assignor to Consolidated Electronics industries Corp, Skokie, 111., a corporation of Delaware Filed June 15, 1965, Ser. No. 464,015 2 Claims. (Cl. 317-11) ABSTRACT OF THE DISCLOSURE An electromagnetic switch in which a spring arrangement for the armature displays a gradually changing mechanical resistance to movement of the armature relative to the coil as the magnetic attractive force of the coil and the gap between the armature and the coil are varied. An energizing circuit is provided for gradually changing the energizing current to the coil so that the moveable contacts approach the fixed contacts in a slow and gradual manner.

This invention relates generally to the art of electrical switches and more particularly to electromagnetic switches or relays, for use with alternating current circuits, especially those circuits which are intended to carry relatively high current loads.

In conventional electromagnetic switches or relays, the contacts are opened and closed substantially instantaneously with a snap action. This fast making and breaking of contact is objectionable where relatively high alternating current loads are involved since severe arcing may result upon connecting or disconnecting the alternating current power. Severe arcing produces excessive erosion of the contact elements. Where the switching duty is severe, eroded contacts must be replaced frequently with the concomitant objectionable loss of working time and added expense.

A general object of the present invention is therefore to provide a new and improved electromagnetic switch arrangement.

Another object of the invention is to provide an electromagnetic switch arrangement that is characterized by a very low amount of arcing upon opening or closing of the contacts.

Still another object of the invention is to provide an electromagnetic switch arrangement having contacts which execute circuit-operating movements slowly whereby to minimize the problem of arcing and contact erosion.

Yet another object of the invention is to provide an electromagnetic switch arrangement wherein a plot of the mechanical resistance to armature movement versus the armature gap is free of regions of substantially constant mechanical resistance.

And yet another object of the invention is to provide an electromagnetic switch with cooperating circuit means for effecting a gradual increase and a gradual decrease in the energizing current.

These and other objects and features of the invention will become more apparent from a consideration of the following descriptions.

In accord with the invention, an electromagnetic switch is arranged to include a support, an electromagnetic coil affixed to the support, an armature swingably mounted to the support, a stationary contact, and a movable contact mounted on the armature for engaging and separating movements With respect to the stationary contact. The electromagnetic switch of the invention also includes a spring arrangement that is disposed to act between the support and the armature so as to provide a gradually 3,355fi29 Patented Nov. 28, lfifi? changing mechanical resistance to the movement of the armature relative to the electromagnetic coil and core as the gap between the armature and the core varies. This distinguishes from the conventional electromagnetic switch wherein the spring means used to bias the armature has a fiat or substantially constant spring rate. In compliance with another feature of the invention, an electromagnetic switch in compliance with the invention is arranged with an energizing circuit which is connected electrically to the electromagnetic coil and which is arranged to deliver a gradually changing current thereto for actuating the cooperating armature in a controlled manner.

The invention, both to its construction and mode of operation, will be better understood by reference to the following disclosure and drawings forming a part thereof, wherein:

FIG. 1 is a side elevational View of one embodiment of the invention, illustrated in the form of a double pole, single throw relay;

FIG. 2 is a front elevational view of the relay of FIG.

FIG. 3 is an exploded perspective view of the relay of FIGS. 1 and 2;

FIG. 4 is a rear elevational View of the armature of FIG. 3, the view being taken substantially along the line 44 of FIG. 3;

FIGS. 5, 6 and 7 are enlarged, fragmentary side elevational views of the relay of FIG. 1, showing three positions of the armature relative to the core and the corresponding positions of the fixed and movable contacts, FIG. 5 showing a fully open position of the contacts and a maximum armature gap, FIG. 7 showing a fully closed position of the contacts and an intermediate armature gap, and FIG. 6 showing an intermediate position of both the movable contacts and the armature;

FIGS. 8, 9 and 10 are plan views taken in cross-section along the lines 8-8, 9-9 and 1010 of FIGS. 5, 6 and 7 respectively;

FIG. 11 is a schematic diagram of a circuit used in operating the relay of FIGS. 1-10 in compliance with the principles of the present invention;

FIG. 12 is a graphic comparison of a conventionally arranged relay and the relay of FIGS. 1-10, showing in particular the attractive force exerted by the relay coil and the load encountered by the armature as the armature gap is varied;

FIG. 13 is a perspective view of a modified embodiment of the invention wherein the relay is arranged as a double pole, double throw switch;

FIG. 14 is a side elevational view of the relay of FIG. 13; and

FIG. 15 is a schematic diagram of a modified operating circuit for use in the invention.

Referring now in detail to the drawings, specifically to FIGS. 1 and 2, an electromagnetic switch or relay is designated generally by the reference numeral 20. The relay 29 comprises a base or support 22, an electromagnetic coil arrangement 24-, a magnetically attractable armature arrangement 26, stationary contacts 28, movable contacts 28, movable contacts 30, and a spring arrangement including a coil spring 32.

The support 22 includes an insulative platform 34 and an L-shaped metal bracket 36. Referring to FIG. 3, the platform 34 is pierced with Slots 38 for receiving the blades of the stationary contacts 28 and with slots 40 for receiving terminal blades 42, blades 42 providing electrical connection to the coil of the electromagnetic coil arrangement 24. The platform 34 also includes a channel or trough 44 which receives a foot 46 of the bracket 36.

A screw 48 or other suitable fastener is advantageously 3 employed in afiixing the bracket 36 to the platform 34 as by passing slidably through an aperture 50 in the floor of channel 44 to engage the foot 46 threadedly.

The bracket 36, in addition to the foot 46, includes an upright plate 52, a cantilevered plate 54 which is disposed parallel to the foot 46, and a stem portion or core 56 which is situated intermediate the foot 46 and the cantilevered plate 54 to act as the magnetic core of the electromagnetic coil arrangement 24. The attachment of the core 56 to the plate 52 is shown in FIG. 1. Cooperating with the core 56 in comprising the electromgnetic coil arrangement 24 is an annular coil 58 wound from a suitable length of conductive wire. The annular coil 58 is arranged so that its central aperture snugly receives the core 56. Various means of mounting the coil 58 to the core 56 may be employed; and one convenient method is illustrated in FIG. 3 where ears 60 are shown as having been struck out of the material of the core to confine the coil relative to the upright plate 52 of the bracket 36. Advantageously, an insulative spacer flange 62 is disposed between the coil 58 and the upright plate 52 to be fashioned with grooves or channels for passing terminal portions of the conductive wire used in winding the core to electrical connection with the blades 42.

The armature arrangement 26 is mounted on the support 22 for reversible movement relative thereto; and in the embodiment of FIGS. 1-10, the armature arrangement 26 is swingably mounted on the support. Specifically, the cantilevered plate 54 of bracket 3 is fabricated with abbreviated, projecting arms 64 which are spaced apart to receive a portion of the armature arrangement therebetween, reference being had in this regard to FIGS. 1, 3 and 4. cooperatively, the armature arrangement 26 includes a magnetically permeable plate 6, and this plate is fashioned with laterally opening notches 8 which re ceive the abbreviated arms 4, as is shown in FIG. 4, whereby to develop a pivot The magnetically permeable plate 66 serves other structural functions; and among these is its provision of a mounting situs for one end of the coil spring 32. For this latter purpose, the plate 66 is fashioned with an upstanding, T-shaped formation 70. A cooperating apendage 72 is struck up from the cantilevered plate 54 to provide an oposed mounting site for the opposite end of the coil spring. Thus is the coil spring 32 arranged to act between the support 22 and the armature arrangement 26.

The movable contacts 30 are mounted on the armature arrangement 26 for engaging and separating movements with respect to the stationary contacts 28. Specifically and with reference to FIG. 3, the armature arrangement 26 includes an insulative board '74 and a molded mounting block unit 76. Each of the contacts 30 is afiixed to the lower end of a spring leaf 80; and the spring leaves 80 are molded into the block unit 76. As will be described more fully herein after, the spring leaves 80 serve dual functions in mounting of the movable contacts 30 to the armature arrangement 26 and in developing mechanical resistance to certain movements of the armature arrangement relative to the electromagnetic core arrangement 24. Electrically, the contacts 30 are connected in series by means of a wire 84 that is soldered across the upper ends of the spring leaves 80 in the embodiment of FIGS. 1-4.

Because the relay 20 is arranged as a double pole, single throw switch, means must be provided for restraining the armature arrangement 26 against the tensile force of spring 32 when the coil arrangement 24 is de-energized. Therefore, the block unit 76 is also molded about a spring leaf 86 which is situated intermediate and parallel to the spring leaves 80 as is shown in FIGS. 2 and 3. Forming an abutment to be engaged by the leaf spring 86 is a stop blade 88, blade 88 being secured in a slot fashioned in the platform 34 in alignment with the path of movement which the spring leaf '86 experiences in conjunction with the movemetns of the armature arrangement 26. It is to be recognized that when the spring leaf 86 forcibly engages the blade 88 and when the contacts 30 are drawn into forcible engagement with the stationary contacts 28, the spring leaves 80 and 86 produce respective mechanical resistances to the swingable movement of the armature arrangement 26. While this mechanical resistance which is developed by the spring leaves 80 and 86 varies in magnitude with the displacement of the armature arrangement, the coil spring 32, in the size and design conventionally slected for use in relays of this type, presents a substantially constant mechanical resistance through out the range of movement of the armature arrangement. In compliance with the present invention, however, it has proved to be important that the spring means acting between the support 22 and the armature arrangement 26 develop a gradually changing mechanical resistance to the movements of the armature arrangement relative to the electromagnetic coil arrangement 24 as the gap between the armature arrangement and the core 56 of the coil arrangement varies. In order that the plot of the aggregate mechanical resistance of the several spring elements versus the armature gap be free of regions of substantially con stant mechanical resistance, an auxiliary spring has been provided in the relay 20. Specifically, this spring takes the form of the spring leaf 86.

A heel shim 90, shown in FIGS. 1 and 4, has been fastened to the permeable plate 66 utilizing rivets 82, and this leaf spring has been deflected to admit one end of a residual shim 94 beneath its lower end at the rivets 82. The

shims

90 and 94 prevent cocking of the armature element and could comprise a single shim if desired. These shims are specially arranged to be thicker than ordinary relay shims for purposes which will become more apparent hereinafter, being on the order of 0.010 inch thick as compared with conventional relay shims which take a thickness of 0.001 to 0.003 inch.

Shims

90 and 94 are fabricated from a non-magnetic material 'such as nickel silver in order to preserve an armature gap upon contact with the core 56.

The foregoing arrangement of the relay 20 precludes a snap action during circuit-operating movements of the movable contacts 30; and as will be described more fully hereinafter, the resultant gradual movements of the contacts 30 promote a long contact life substantially free of erosion due to arcing.

As has been pointed out hereinabove, conventional relays are arranged for opening and closing of the contacts with a snap action. It has also been pointed out hereinabove that these conventional relays are subject to severe erosion of the contacts as a result of arcing when relatively high alternating current loads are being switched. Arcing, as contrasted with sparking, is a comparatively low voltage, high current electrical discharge of substantial duration. Conventional relays are characterized by an opening or a closing of the contacts in. a time period on the order of 2-3 milliseconds whereas the nullto-null or half cycle period of customary alternating current has a duration of on the order of 8 milliseconds. Accordingly, the amount of arcing experienced at the contacts of a conventional relay depends on the particular point during the alternating current cycle when the opening or closing of the contacts is directed to take place. If it occurs at or near the peak amplitude of the current cycle, arcing can be extremely severe. If, on the other hand, opening or closing of the contacts is directed to take place at or near the null point, arcing can be mild or non-existent. In addition, since the opening or the closing of the contacts of a conventional relay occurs at less than one-half cycle of the current, substantially a direct current condition exists during the period of interest.

In accordance with the present invention, on the other hand, the time during which the contacts open or close is controlled to extend over two or more full cycles of current alternations. Thus, use is made of the naturally occurring transition through a zero current condition to' extinguish any arc actually drawn upon initial separation,

or upon closing, of the contacts and to prevent the elongation of any such are upon further separation of the contacts. Whereas in a conventional relay the contacts open or close in approximately 2-3 milliseconds, the contacts of the relay of the instant invention are arranged to open or close gradually during a period of 70-100 milliseconds for example.

Operation of the relay 20 so as to insure a slow and gradual opening and closing of the contacts, whereby to open or close in approximately 2-3 milliseconds, the conditions, will be better understood by consideration of the following descriptions given with reference to FIG. 11 wherein the relay 20 is embodied in an exemplary circuit 100. In the circuit 100, direct current power is supplied to the coil 58 from a battery 102, although suitably rectified alternating current power may be used in place of the battery 102 as is well known. A manual switch 104 and a load resistor 106 are advantageously disposed in series circuit with the battery 102. In compliance with the principles of the invention, a resistance-capacitance circuit 108 is arranged to contain the coil 5% in order to provide a slow build-up and a slow decay of the energy applied to the coil. Specifically, a resistor 110 is arranged in series with the coil 58, and a capacitor 112 is arranged in parallel circuit with the series connected coil 58 and resistor 110. In compliance with the previous descriptions, the operating circuit containing the fixed contacts 28 and the movable contacts 30 incorporates an alternating current source 114 and a high current load, such as is represented by the infrared-emitting, quart lamps 116 and 113.

When the relay 20 is operated by the circuit 100, closing of the manual'switch 104 applies a direct current voltage to the energizing circuit 108. Initially, the capacitor 112 acts as 'an electrical short across the series connected coil 58 and resistor 110, and no current flows through this latter circuit element. As current continues to flow through the capacitor 112, the capacitor gradually becomes charged, valving further current flow through the capacitor, and current gradually begins to flow through the series connected coil and resistor. correspondingly, the

attractive strength of the coil 58 begins to increase and act on the armature to initiate closing movement of the contacts 30, assuming an initially open condition thereof. As charging of the capacitor 112 continues, the flow of current through the relay coil 58 increases, concomitantly increasing the attractive force of the coil arrangement whereby to produce a corresponding movement of the armature and the movable contacts. Eventually, the movable contacts engage the stationary contacts to complete the operated circuit whereby to energize the lamps 116 and 118.

Displacement of the relay armature and the movable contacts from the open to the closed position is gradual and without any abrupt movement. Accordingly, if a short are is drawn at the contacts, passing of the alternating current through a null condition will extinguish this are, and the contacts may continue to open or close without any appreciable re-ignition of the arc.

It will also be recognized that, When the manual switch 104 is opened disconnecting the battery 102 from the energizing circuit 108, the charge built up in the capacitor 112 will produce a current flow through the series connected coil 58 and resistor 110 whereby gradually to diminish the attractive force exerted on the armature arrangement and thus slowly release the armature arrangement to the action of the return or biasing spring 32. A corresponding gradual opening of the contacts results.

In one specific embodiment of the circuit 100, the relay coil 58 has been arranged to have a resistance of 400 ohms, the resistor 110 a value of 800 ohms, the resistor 106 a value of 400 ohms, and the capacitor 112 a value of 100 microfarads. In addition, the combined wattages of lamps 116 and 118 has been selected to be 2300* watts so that when the alternating current source 114 has an output of 390 volts, approximately 6 amperes will flow through the operated circuit. When a conventional relay is caused to operate a circuit having a high current load, the contacts of the relay last not more than about 1,000 or 2,000 switching operations at the maximum. In contrast, a relay constructed in compliance with the invention and arranged as shown in FIG. 11 has operated a total of 600,000 switching cycles before failure of the contacts has occurred. In both relays in this comparison, general purpose contacts having a nominal diameter of inch and a rating of 5 amperes were employed.

The reason for the exceptional life of the contacts in the relay of the invention will be more clearly understood by reference to FIG. 12 and the following descriptions. In FIG. 12, a family of curves indicated by the reference letter P have been drawn showing the attractive force exerted by a given relay coil, measured at the axis of the core, as a function of the armature gap, also measured at the axis of the core. It is to be observed that the closed condition of the armature is represented at the left-hand portion of the graph where a zero gap is indicated. The individual curves P represent individual ampere-turn levels in the relay coil, starting with 25 ampere-turns and increasing in steps of 25 ampere-turns to an extreme limit of 300 ampere-turns. It will also be observed that each of the curves P has a characteristic shape representative of the fact that the attractive force exerted on the armature by the relay coil is relatively low when the armature gap is large and, as the armature gap is reduced, the attractive force increases rapidly and attains a rather high value for comparatively small armature gaps.

in compliance with the features of the present invention, energizing current is applied to the relay coil in a slow and gradual manner; .and even in the case of a conventional relay that is circuitwise arranged for rapid energization. of the coil, there is a progressive increase in the attractive force of the coil as the current is applied thereto, despite the fact that the time period for this latter application of current may be radically shorter than that involved in the relay of the invention. In FIG. 12, a curve indicated by the reference letters KLM sets forth the mechanical resistance or load encountered by the armature at various armature gap measurements as a result of the composite spring forces extant in the relay construction. Curve KLM shows the characteristics of a relay of the type shown in FIGS. 1-4, i.e. a double pole, single throw electromagnetic switch constructed in compliance with the invention and arranged with normally open contacts, For comparison, the curve indicated by the reference letters ABCDEFG illustrates the corresponding mechanical resistance or load encountered by the armature of a conventionally constructed double pole, double throw electromagnetic switch. The completely closed positions of the two relays are shown by the ends of the respective curves at points M and G, a residual shim 0.010 inch thick being employed for the relay of the invention and a residual shim 0.002 inch thick being em- 'ployed for the conventional relay. Similarly, completely open positions are represented by the opposite ends of the curves indicated respectively by the reference letters K and A, showing a maximum armature gap of 0.033 inch for the relay of the invention and a maximum armature gap of 0.0258 inch for the conventional relay.

A third curve shown in broken line and indicated by the reference letters H and I represents the mechanical resistance or load encountered by the armature of the conventional relay if the only force acting upon it was the coil spring corresponding to the coil spring 32 in the relay of FIGS. 1-4. It will be noted that the curve HI possesses only a very slight slope, rising very gradually from right to left in FIG. 12. This slope indicates that, in the construction and arrangement under consideration, the coil spring has a substantially constant spring rate. Due to the construction of the hinge section of the relay armature, thearmature cannot be displaced from the relay coil a suflicient distance to permit the coil spring to relax completely. Therefore, the armature is always sub jected to the tensile forces stored in the coil spring. Moreover, the amount of elongation of the coil spring which is normally experienced during opening and closing movements of the armature is so slight that the force exerted by the coil spring on the armature is substantially constant.

Turning to a detailed consideration of the conventional relay in conjunction with a consideration of curve ABCDEFG, when sufiicient current is passed through the relay coil to produce an ampere-turn level of 75, the attractive force at an armature gap of 0.0258 inch approximates 17 grams; and since the curve ABCDEFG is beneath the 75 ampere-turn curve at this point, the attractive force exerted by the coil obviously exceeds the corresponding mechanical resistance which is encountered by the armature. The armature therefore begins to close and move as far as point B on the curve where the attractive force and the mechanical resistance are balanced. In order to close the armature further, additional current is passed through the coil to increase its attractive force on the armature. At each point along the curve ABCDEFG from A up to but short of point B, the attractive force of the relay coil is balanced by a mechanical resistance encountered by the armature due to the various springs in the structure, friction and other mechanical forces. In addition, at points along the curve from point A to a. position just short of point E, the normally closed contacts of the relay remain closed, those movements of the armature which have occurred produce, not a separation of the contacts, but a reduction in the contact pressure.

However, when sufiicient current is passed through the relay coil to generate approximately 135 ampere-turns, point B is reached along the curve ABCDEFG; and here, the contact pressure is substantially zero. When the contact pressure reaches this zero level, the force of the coil spring is substantially the sole controlling resistive force acting to oppose movement of the armature. Accordingly, the portion EF of curve ABCDEFG is substantially coincident with the load curve HI. Therefore, as soon as the ampere-turn level in the relay coil exceeds 135 ampere-turns, the attractive force exerted on the armature becomes greater than the mechanical resistance encountered by the armature. This is apparent from the almost horizontal position of the curve between points E and F. As a consequence of this condition, the armature begins to move toward its closed position and it is important to realize that this movement continues until the closed position is reached, indicated at point G, without any further increase in the number of ampere-turns developed in the relay coil. The abrupt movement fthe armature along that portion of the curve from point B to point F radically reduces the armature gap so that the attractive force represented by 135 ampere-turns in the relay coil is more than sufiicient to produce a complete closing of the contacts. This is the snap action which is normally experienced in conventional relays-The steepness of the curve from point F to point G represents the mechanical resistance to further closing of the armature after the contacts have closed, principally the resistance to deformation of the spring leaves carrying the movable contacts as these contacts engage the stationary contacts and the armature continues to move.

The opposite pattern of behavior exists upon reverse operation of the relay coil, i.e., upon de-energizing the coil to open the contacts. Upon opening of the contacts, the snap action occurs between points G and A.

Considering a relay of the invention as characterized by curve KLM, it will be apparent that this latter curve incorporates no substantially horizontal portion and hence has no region where the mechanical resistance to armature movement is substantially constant over some appreciable range of armature gap values. In other words, the relay of the invention as characterized in curve KLM provides a gradually changing mechanical resistance to the movement of the armature relative to the core of the relay coil as the gap between the armature and the core varies. More specifically, that portion of the curve between points K and L represents the movement of the armature, in response to increasing the number of ampereturns in the coil, from the completely open position of the contacts to the point where the contacts actually close. It will be apparent that, for this portion of the curve, each increase in the ampere-turn level results in a corresponding movement of the armature. Accordingly, the gradual energization of the coil as achieved by the circuit 108, as has been described hereinabove, produces a gradually and slowly closing of the contacts. Reverse operation of the relay coil produces a similar gradual opening of the contacts. Arching of the contacts is thus educed substantially because any are drawn is extinguis'hed, while still of abbreviated dimension, by virtue of the passage of the alternating current in the operated circuit through a null or Zero current condition. Even in the portion of the curve from point L to point M, that is, that portion of the curve which corresponds to the movement of the armature while the contacts are closed, the level of ampere-turns in the relay coil must be increased in order to obtai neach increment of reduction of the armature gap, at least for those portions of the curve which are significant.

An inspection of curve KLM and the graph of FIG. 12 also will reveal that the use of the

thick shims

90 and 94 serves to locate the curve KLM more to the right of the ordinate of the graph where the family of curves P is generally less vertical and where the curve KLM therefore needs to be less vertical in order to cut curves P of successively greater value as the armature gap decreases.

As will be apparent from the foregoing descriptions, various other relay structures having characteristics similar to those represented by the curve KLM may be constructed to possess the same advantages. For example, in the embodiment of FIGS. l-4, an auxiliary spring 86 has been arranged in cooperation with the coil spring 32 and the spring leaves to develop a relay having the characteristics exhibited in the curve KLM. However, a single coil spring without an auxiliary leaf spring may be arranged to provide the desired characteristics. In one specific embodiment of the invention, a coil spring has been used which produced a spring rate of 390 grams per inch as measured along its own axis with corrections for the leverage factors resulting from the spacing of the armature hinge axis from the core axis and the spacing of the axis of the coil spring from the hinge axis. Such a coil spring has been employed in conjunction with an auxiliary leaf spring such as the leaf spring 86. A unit without an auxiliary leaf spring may be made when the coil spring has an equivalent spring rate of approximately 8,560 grams.

Various positions of the armature arrangement 26 relative to the core 56 are shown in FIGS. 5-10. FIGS. 5 and 8 illustrate the position of the parts associated with point K of curve KLM in FIG. 12. FIGS. 6 and 9 show the armature disposed at an intermediate gap position and the movable contacts 30 adjacent but not engaging the stationary contacts 28, FIGS. 6 and 9 thus representing a position between points K and L in curve KLM. Finally, FIGS. 7 and 10 illustrate the position of the parts at point L in the curve KLM, i.e. the condition wherein the movable contacts have engaged the fixed contacts but wherein the armature has not yet engaged the core 56.

While a particular embodiment of the invention has been thus far shown and described, it should be understood, of course, that the invention is not limited thereto since many modifications may be made. Therefore and in order to enhance the understanding of the invention, certain modified embodiments are illustrated in FIGS. 13 and 14 and in FIG. 15. Since many of the elements found in the embodiments of FIGS. 13l5 are similar to those shown in the embodiment of FIGS. 1-11, like numerals have been used to designate like parts with the suffix letter a being employed to distinguish those elements associated with the embodiment of FIGS. 13 and 14 and with the sutfix letter 12 being utilized to discriminate those elements associated with the embodiment of FIG. 15.

The embodiment of FIGS. 13 and 14 is characterized by arrangement of the relay as a double pole, double throw switch. structurally, a medial spring leaf such as the spring leaf 86 and its cooperating, generally forwardly disposed stop blade have been eliminated in relay 20a. The function of these eliminated members has been taken over by the provision of a pair of generally rearwardly disposed stop blades 120. Cooperatively, a pair of spring leaves 122 is secured in the block unit 76a intermediate the leaves 80a. Furthermore, an interconnecting conductor such as the conductor 84 is eliminated from the relay 20a; and in its place, individual lead wires 124 are connected to the spring leaves 80a and to terminal blades 126 which are mounted in the platform 34a.

In accordance with the features of the embodiment of FIGS. 13, and 14, the spring leaves 122 are arranged to taken substantially the same length, width and thickness as the spring leaves 80a and to be fabricated from the same material. Thus, the spring leaves 122 have substantially the same characteristics as the spring leaves 80a. In addition, the spring leaves 80a carry contacts 30a on the opposite sides of their free ends; and normally, a set of contacts 30a engages the stop blades 128 which are disposed generally forwardly of the stop blades 28a. The spring leaves 122 are intended to develop a gradually increasing resistance to closing of the armature gap, starting at approximately the instant that the contacts 30:: initiate separation from the stop blades 128. Thus, the spring leaves 122 introduce mechanical resistance at about the instant that spring leaves 80a no longer introduce mechanical resistance. The resultant characteristic of relay 20a is shown graphically in FIG. 12 by the curve NOQR.

Considering this curve in detail, the point N represents the open position of the armature, and point R represents the closed position of the armature, a residual shim 0.010 inch thick having been employed to position the curve NOQR generally toward the right hand portions of the pull curves P. Point represents the position at which the closed contacts begin to open, and point Q represents the position in which the open contacts begin to close. It should be noted that the curve from N to Q- is substantially straight, and this is due to the facts that the spring leaves 122 and the spring leaves 80a are substantially equal and opposite in their behavior and that each set of spring leaves is arranged to be active While the other set is inactive mechanically. For this latter purpose, the stop blades 120 are positioned slightly forwardly of the stop blades 28a, as is shown in FIG. 14. Alternatively or conjunctively, the spring leaves 122 may be positioned slightly rearwardly of the spring leaves 80a in block unit 76a or have their cantilevered ends bent slightly rearwardly to insure proper contact with the stop blade 120. A single spring leaf of double thickness [may be employed to replace the two spring leaves 122; however it is more convenient to mold four spring leaves of equal thickness in manufacturing the block unit 7611 and the spring leaves incorporated therewith.

The embodiment of FIG. should be considered with reference to the embodiment of FIG. 11, both embodiments delineating circuits in which a relay of the invention may be advantageously connected. The circuit 1011b of FIG. 15 is similar to the circuit of FIG. 11 in that the relay incorporated therein is a double pole, single throw relay. However, the circuit 10012 is characterized by the elimination of the resistance-capacitance network of circuit 100 and its replacement by a thermistor which is connected circuitwise in series with the coil 58b of the relay 2%. As is well known, thermistors have a characteristic, negative temperature coefiicient. Hence, their electrical resistance decreases as their temperature increases and vice versa. Accordingly, thermistor 130 is capable of delivering a gradually increasing current to the coil of the relay after the switch 104]) has been closed. Nonetheless, the thermistor 130 only provides gradually increasing current to the relay coil but not gradually de creasing current since it has no energy storing capabilities.

The specific examples herein shown and described are to be considered as being primarily illustrative. Various changes beyond those described will, no doubt, occur to those skilled in the art; and such changes are to be understood as forming a part of this invention insofar as they fall within the spirit and scope of the appended claims.

The invention is claimed as follows:

1. In an electromagnetic switch arrangement, the combination comprising: support means; electromagnetic coil means fixed to said support :means; magnetically attractable armature means connected to said support means for reversible movements relative thereto; a sationary contact mounted on said support means in fixed position; a movable contact mounted on said armature means for engaging and separating movements with respect to said stationary contact; spring means acting between said support means and said armature means to provide a gradually changing mechanical resistance to the movement of said armature means relative to said electromagnetic coil means as the magnetic attractive force of said coil means and the gap between said armature means and said coil means are varied, the plot of the mechanical resistance of said spring means versus the armature gap being free of regions of substantially constant mechanical resistance; and energizing circuit means connected electrically to said coil means and arranged to deliver a gradually changing current thereto on energization thereof.

2. An electromagnetic switch, according to claim 1 wherein said circuit means includes a junction, a capacitor in circuit between said junction and one terminal of said coil means, and a resistor in circuit between said junction and the other terminal of said coil means whereby to arrange said coil means and said resistor in series circuit with each other and in parallel circuit with said capacitor and whereby said coil means experiences gradually changing current conditions on both energization and d'e-energization.

References Cited UNITED STATES PATENTS 2,471,181 5/1949 Wilson 335-128 3,115,56-1 12/1963 Lewis et al. 335-128 3,230,329 1/1966 Richert et al 335-128 X 3,233,150 2 /1966 Maynard 3l741 X FOREIGN PATENTS 1,245,235 9/1960 France 335128 MILTON O. HIRSHFIELD, Primary Examiner. R. V. LUPO, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,355,629 November 28, 1967 William W. Schapira It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, lines 61 and 62, strike out "movable contacts 28"; column 3, line 29, for "bracket 3" read bracket 36 line 34, for "plate 6" read plate 66 line 35, for "notches 8 read notches 68 5 same column 3, line 36, for "arms 4"'read arms 64 column 5, lines 10 and 11, for "open or close in approximately 2-3 milliseconds, the conditions," read eliminate severe arcing even under high current load conditions, line 30, for "quart" read quartz column 6, line 3, after "having", insert such column 8, line 16, for "Arching" read Arcing column 9, line 24, for "taken" read take Signed and sealed this 31st day of December 1968.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

1. IN AN ELECTROMAGNETIC SWITCH ARRANGEMENT, THE COMBINATION COMPRISIN: SUPPORT MEANS; ELECTROMAGNETIC COIL MEANS FIXED TO SAID SUPPORT MEANS; MAGNETICALLY ATTRACTABLE ARMATURE MEANS CONNECTED TO SAID SUPPORT MEANS FOR REVERSIBLE MOVEMENTS RELATIVE THERETO; A STATIONARY MOUNTED ON SAID SUPPORT MEANS IN FIXED POSITION; A MOVABLE CONTACT MOUNTED ON SAID ARMATURE MEANS FOR ENGGING AND SEPARATING MOVEMENTS WIHT RESPECT OT SAID STATIONARY CONTACT; SPRING MEANS ACTING BETWEEN SAID SUPPORT MEANS AND SAID ARMATURE MEANS TO PROVIDE A GRADUALLY CHANGING MECHANICAL RESISTANCE TO THE MOVEMENT OF SAID ARMATURE MEANS RELATIVE TO SAID ELECTROMAGNETIC COIL MEANS AS THE MAGNETIC ATTRACTIVE FORCE OF SAID COIL MEANS AND THE GAP BETEEEN SAID ARMATURE MEANS AND SAID COIL MEANS ARE VARIED, THE PLOT OF THE MECHANICAL RESISTANCE OF SAID SPRING MEANS VERSUS THE ARMATURE GAP BEING FREE OF REGIONS OF SUBSTANTIALLY CONSTANT MECHANICAL RESISTANCE; AND ENERGIZING CIRCUIT MEANS CONNECTED ELECTRICALLY TO SAID COIL MEANS AND ARRANGED TO DELIVER A GRADUALLY CHANGING CURRENT THERETO ON ENERGIZATION THEREOF.