US3437885A - Electromagnet - Google Patents

Description

April 8, 1969 F, -w. Kussv ET L 3,437,885

' y 4ELECTRONIACNET Filed July 25, 1966 Sheet /I of 2 F. w. KUssY ET AL April 8, 19.69

ELECTROMAGNET sheet Z @f2 Filed yJuly 25. 196e United States Patent O 3,437,885 ELECTROMAGNET Frank W. Kussy, Birmingham, and Bernard Di Marco, Lincoln Park, Mich., assignors to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed July 25, 1966, Ser. No. 567,538 Int. Cl. H01h 47/32, 51/22 U.S. Cl. 317-150 13 Claims ABSTRACT F THE DISCLOSURE Copending application Ser. No. 568,249, led July 27, 1966, entitled, Industrial Control Relay, with B. Di Marco et al. as inventors and assigned to the assignee of the instant invention, discloses an electromagnetic contactor of a type often referred to as an industrial control relay. Brieily, an electromagnetic contactor is a multi-pole switch having biasing means urging ythe switch arms to a lirst position and an electromagnet which when energized acts against the biasing means to operate the switch arms to a second position. For the most part, prior art electromagnetic contacto'rs are so constructed that the operating coil must be continuously energized to maintain the switch means in the second position.

This often leads to undesirable conditions. In particular, by momentary loss of control power, the magnet coil will be deenergized and the switch means will not be maintained in its second position. Further, continuous currents how through the magnet operating coil requiring excessively large winding size to prevent overheating.

In order to overcome these disadvantages, for some applications the prior art has provided mechanical latches and permanent magnet latches to maintain the switch arms in the second position against the force of biasing means urging the switch arms to the iirst position. The instant invention is concerned with the permanent magnet type latch for electromagnetic contactors.

In particular, the device of the instant invention includes a novel insert molded assembly consisting of a conventional magnet armature, a permanent magnet and a retainer, all imbedded in a molded plast-ic member.

High strength permanent magnets of convenient shapes are readily constructed of ceramic material. However, such material is extremely brittle and has failed to stand up when used with electromagnets that are operated lfrequently. The device of the instant invention is able to utilize a ceramic permanent magnet by forming it as a relatively flat plate-like member sandwiched between two relatively strong members constructed of relatively high permeability steel. The relationship between the retainer and armature is such that when the armature is remote from the yoke short gaps between the retainer and armature act as short circuit paths for the permanent magnet ux to shunt such flux away from the main gaps between the armature and yoke. One of these steel members is the conventional electromagnet armature while the other of these Isteel members is designated as the retainer and is interposed between the permanent magnet and stationary yoke of the electromagnet. By imbedding all three members, armature, permanent magnet and retainer, in a molded plastic body, preferably constructed of nylon, a unitary assembly is formed which `is highly resistant to ICC shock. This construction permits utilization of a high strength ceramic permanent magnet.

The instant invention also includes a number of novel control circuits for closing the electromagnet and releasing the permanent magnet latch.

Accordingly, a primary object of the instant invention is to provide a novel construction for an electromagnet device having a permanent magnet latch.

Another object is to provide an electromagnet of this Vtype having a unitary assembly including a ceramic permanent magnet and a movable magnet armature both imbedded in a molded plastic body.

Still another object is to provide an electromagnet of this type having a permanent magnet sandwiched between a steel retainer and the movable armature of the magnetic frame.

A further object is to provide novel control circuitry of minimal cost for an electromagnet having a permanent magnet latch.

These objects as well as other objects of the instant invention will 'become readily apparent after reading the following description of the accompanying drawings in which:

FIGURE l is an exploded perspective showing the main assemblies of an electromagnet constructed in accordance with the teachings of the instant invention.

FIGURE 2 is a side elevation of the movable armature assembly of FIGURE l.

FIGURE 3 is a bottom View of the movable armature assembly looking in the direction of arrows 3-3 in FIG- URE 2.

FIGURE 4 is an exploded perspective showing the armature, permanent magnet and retainer of the armature assembly.

FIGURE 5 is an electrical schematic illustrating a novel control circuit for the electromagnet of FIGURE 1.

FIGURES 6 through 8 are electrical schematics illustrating three additional control circuits for an electromagnet having a permanent magnet latch.

As seen in FIGURE 1, electromagnet 10 constructed in accordance with the teachings of the instant invention includes a stack of E-shaped laminations constituting stationary yoke 11, coil assembly 12 having aperture 12a to receive the center leg 11e of yoke 11, and armature assembly 13 biased away from yoke 11 by return spring 14 (see FIGURE 5) and mounted for movement toward yoke 11 with the free ends of armature legs 15a, 15b engaging the free ends of the outer yoke arms 11a, 11b, respectively.

As seen by particular reference to FIGURE 5, coil assembly 12 includes ON coil 21, OFF coil 22 and semiconductor diode 17 paralleled by surge protective device 18. Coils 21, 22 are multi-turned windings each having an end thereof connected to one electrode of diode 17 by conductor 19 internal of coil assembly 12. The other electrode of diode 17 is connected to terminal 20 extending externally of coil assembly 12 for connection to one terminal L-1 of an AC control power source (not shown). The other ends of coils 21, 22, are connected to insulation covered conductors 21a, 22a, respectively, which extend externally of coil assembly 12. Elements 17, 18, 21, 22 are encapsulated in a suitable plastic material forming body 23 thereby providing coil assembly 12 as a unit which is highly resistant to mechanical shock and other harmful environmental conditions such as high humidity. The connection of leads 21a, 2lb to additional circuit elements will be hereinafter explained.

As best seen by reference to FIGURES 2, 3 and 4, armature assembly 13 consists of armature 31, permanent magnet 32 and retainer 33 all imbedded in plastic body 34. Armature 31 and retainer 33 are each preferably constructed of cold rolled steel which is mechanically strong and of reasonably high magnetic permeability. Permanent magnet 32 is constructed of ceramic material, preferably Indox 5, and body 34 is molded of a relatively tough plastic material, preferably nylon.

Permanent magnet 32 is a rectangular plate-like element magnetized transverse to the plane thereof and is sandwichtd between armature 31 and retainer 33. Armature 31 is a generally U-Shaped member having relatively short legs a, 15b connected by a web section having its central part 31a offset away from permanent magnet 32 to provide a partial boundary for passage 34a. extending through body 34. As explained in detail in the aforesaid copending application Ser. No. 568,249 a passage corresponding to through passage 34a is provided to receive a securing means (not shown) which mechanically connects armature assembly 13 for operating switches such as coil clearing switches 28, 29. This same securing means also provides a mechanical connection between armature assembly 13 and return spring 14.

Retainer 33 includes rectangular plate-like portion 41 having two upturned ears 42, 42 along each of the longer edges thereof. L-shaped offsets 43, 44 are formed along the respective short edges of section 41 with the legs of offsets 43, 44 that extend directly from section 41 extending in the same directions as ears 42. The other legs 43a, 44a extend in opposite directions away from section 41 in a plane generally parallel to section 41, for a reason which will hereinafter be explained.

As best seen in FIGURES 2 and 3, permanent magnet f 32 is adjacent to the upper surface of retainer section 41 being positioned by ears 42 and L-shaped offsets 43, 44. The upper surface of magnet 32 is adjacent to the lower surface of the web of armature 31 and is equally spaced from armature legs 15a., 15b by protrusions 31b, 31b formed in the web of armature 31.

As best seen in FIGURE 2, the free ends of retainer legs 43a, 44a are in close proximity to armature legs 15a, 15b, respectively, so that when armature assembly 13 is in its released position remote from yoke 11 there is essentially no flux from permanent magnet 32 extending external of body 34. As will hereinafter become apparent, this lack of leakage flux facilitates rapid operation of armature assembly 13 to its released position from its latched position wherein armature 31 is in engagement with yoke 11. With armature legs 15a, 15b in engagement with yoke arms 11a, 11b, the gaps betwetn legs 43a, 44a and legs 15a., 15b are relatively long and under these conditions essentially all of the flux of permanent magnet 32 oWs through yoke 11.

Now referring to FIGURE 5. Switches 28, 29 are normally closed and normally opened, respectively. Switch 28 is interposed between lead 21a and one of the stationary contacts of ON control switch 51 whose stationary contact is connected to terminal L-2 of the AC control voltage source. Switch 29 is interposed between lead 2lb and one of the stationary contacts of OFF control switch 52 whose other stationary contact is connected to terminal L-2.

Operation of the device of FIGURES 1 through 5 proceeds as follows. Starting with armature assembly 13 in its released position remote from yoke 11, having been moved there by return spring 14, ON control 51 is closed to complete an energizing circuit for ON coil 21 extending from terminal L-l, through diode 17 acting as a half-wave rectifier, ON coil 21, switch 23 and control 51 to L-2. With this energizing circuit completed current flows through ON coil 21 in a direction generating flux in the magnetic frame 11, 31 of sufficient magnitude to operate armature assembly 13 against the force of return spring 14 toward yoke 11 to latched position. In moving to its latched position, armature assembly 13 opens switch 28, closes switch 29 and in addition operates additional switch units (not shown).

When ON coil 21 is `de-energized by opening ON control 51, armature assembly 13 remains in latched position in that the linx from permanent magnet 32 is of sufficient strength to maintain armature 31 in engagement with yoke 11.

Closing of OFF control 52 at this time completes an energizing circuit for OFF coil 22 from terminal L-1, through half-wave rectifier diode 17, OFF coil 22, the now closed switch 29, OFF control switch 52 to terminal L-2. Current flowing in OFF coil 22 generates flux in yoke 11 opposing the fiux of permanent magnet 32 with the net fiux being of insufficient strength to maintain armature assembly 13 latched against the force of return spring 14. Thus, return spring 14 operates armature assembly 13 to its released position shown in FIGURE 5 and in so doing opens switch 29 and closes switch 28 so that upon subsequent operation of ON control 51 the energizing circuit for ON coil 21 may be completed.

It is noted that in FIGURE 5 the arrows for the respective coils are not to indicate current flow but rather indicate that the fiuxes generated by coils 21, 22 are in opposite directions through magnetic frame .11, 31 when their respective energizing circuits are completed.

In the embodiment of FIGURE 5 a half-wave rectifier consisting of a single semiconductor diode 17 is utilized for energization of the electromagnet operating coils 21, 22, while in the embodiment of FIGURE 6, the electromagnet operating coils 21, 22 are energized through bridge rectifier 56 having line terminals 57, 58 and load terminals 61, 62. Opposite terminals of AC source 59 are connected to line terminals 57, 58. The energizing circuit for ON coil 21 extends from load terminal 61, through ON concontrol 51, ON coil 21 and switch 28 to the other load terminal 62. The energizing circuit for OFF coil 22 extends from load terminal 61 through OFF control 52, OFF coil 22 and normally open switch 29 to terminal 62.

As in the embodiment of FIGURE 5, when the energizing circuit for ON coil 21 is completed through the closing ol ON control S1, DC current flows through ON coil 21 generating flux which aids in the flux of permanent magnet 32. Also as in the embodiment of FIGURE 5, when the energizing circuit of FIGURE 6 for OFF coil 22 is completed by the closing of OFF control 52 at a time when switch 29 is closed, DC current flows through OFF coil 22 in a direction to generate magnetic flux which opposes the flux of permanent magnet 32 so that the permanent magnet flux is ineffective to maintain armature assembly 13 in latched position. i

The embodiments of FIGURES 7 and 8 are modifications of the embodiments of FIGURES 5 and 6, respectively, eliminating coil clearing switch 29 for the OFF coil. More particularly, in the half-wave rectifier energizing circuit of FIGURE 7 the energizing circuit for ON coil 21a extends from terminal L-l through diode 17, ON control 51, normally closed coil clearing contact 28, ON coil 21a and OFF `coil 22a to terminal L-2. Coils 21a, 22a are connected in magnetic opposition so that ON coil 21a must be considerably larger than OFF coil 22a. OFF control 52 is connected in shorting position across the series combination of ON control 51, switch 28 and ON coil 21a so that OFF coil 22a can be of the same size as OFF coil 22 of FIGURES 5 and 6.

In view of the explanation of FIGURES 5, 6 and 7 it is deemed that the circuitry of FIGURE 8 is self-explanatory and no further description thereof is contained herein. y

In the embodiments of FIGURES 7 and 8 coil clearing contact 28 may be eliminated if ON coil 21a is constructed for continuous duty so that it will not be damaged in the event that ON control 51 is depressed for a long period of time.

Thus, it is seen that the instant invention provides a novel construction for an electromagnet having a permanent magnet latch and also provides novel circuitry for operation of the electromagnet.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art.

We claim:

1. An electromagnetic device including a magnetic frame having a first and a second section, coil means mounted in magnetic coupling relation to said frame whereby a flow of electric current in said coil means generates magnetic flux in said frame, an assembly including said first section, biasing means urging said assembly and said second section away yfrom each other, to a released position, said assembly also including a permanent magnet fixed in relation to said first section and of sufficient holding power to maintain said assembly and said Second section adjacent to each other in a latched position when said coil means is deenergized, a first and second energizing circuit for said coil means, said first circuit when energized causing current flow in said coil means in a direction generating a first magnetic flux aiding a second magnetic flux of said permanent magnet with the resultant of said first and said second fluxes being of sufiicient strength t-o overcome said biasing means and operate said assembly and said second section to said latched position; said second circuit when energized causing current fiow in` said coil means in a direction generating a third magnetic flux opposing said second flux with the resultant of said second and said third fluxes causing said assembly and said second section to be released from each other ena-bling them to be operated by said biasing means to said released position, said assembly including a mounting member formed by molding around said first section and said permanent magnet.

2. A device as set forth in claim 1 in which said assembly includes a retainer means for said magnet, said mounting member also formed by molding around said retainer means, said magnet sandwiched between said retainer means and said first section, said retainer means interposed between said magnet and'said second section.

3. A device as set forth in claim 2 in which said magnet is magnetized generally parallel to the direction of relative movement tbetween said assembly and said second section when operating between said latched and said released positions.

4. A device as set forth in claim 3 in which said magnet is constructed of ceramic material and said first section and said retainer means are each constructed of a metal having ferro-magnetic properties.

5. A device as set forth in claim 4 in which said second section is generally E-shaped having arms extending toward said assembly and said first section is generally U-shaped having legs extending toward said second section with the free ends of said llegs confronting the free ends of the outer ones of said arms, said arms and said legs extending generally parallel to the direction of magnetization for said magnet.

6. A device as set forth in claim 5 in which the first section and said retainer means are free from engagement with each other, said retainer means having extending portions in close proximity with said legs to form relatively narrow gaps which act as short circuit paths for said second fiux when said assembly and said second section are in said released position.

7. A device as set forth in claim I6 in which the gaps are located at points intermediate the ends of each of said legs.

8. A device as set forth in claim 7 in which the magnet is a plate-like member which is magnetized perpendicular to the plane thereof.

9. An electromagnetic device including a magnetic frame having a first and a second section, coil means mounted in magnetic coupling relation to said frame whereby a flow of electric current in said coil means generates magnetic flux in said frame, an assembly including said first section, biasing means urging said assembly and said second section away from each other, to a released position, said assembly also including a permanent magnet fixed in relation to said first section and of sufficient holding power to maintain said assembly and said second section adjacent to each other in a latch position when said coil means is deenergized, a first and second energizing circuit for said coil means, said first circuit when energized causing current flow in said coil means in a direction generating a first magnetic flux aiding a second magnetic flux of said permanent magnet with the resultant of said first and said second fluxes being of sufiicient strength to overcome said biasing means and operate said assembly and said second section to said latched position; said second circuit when energized causing current flow in said coil means in a direction generating a third magnetic ux opposing said second ux with the resultant of said second and said third fluxes causing said assembly and said .second` section to be released from each other enabling them to Ibe operated by said biasing means to said released position, a rectifier means common to said first and said second circuits, first and second normally open control switches in said first and second circuits, respectively, a first switch means in said first circuit, said first switch means connected to said magnetic frame for operation upon relative motion between said sections Iand lbeing connected in electrical series with said rectifier means, with said assembly and said second section in said released position said first switch means being closed to permit energization of said first circuit, with said assembly and said second section in said latched position said first switch means being open to prevent energization of said first circuit.

10. A device as set forth in claim 9 in which there is a second switch means in said second circuit in series with said rectifier means, said second switch means connected to said mag-netic frame for operation upon relative motion between said sections, with said assembly and said second section in said latched position said second switch means being closed to permit energization of said second circuit, with said assembly and said second section in said released position said second switch means being open to prevent energization of said second circuit.

11. A device as set forth in claim 9 in which the rectifier means is a single semi-conductor diode element, said circuits constructed so that current flows in different portions of said winding means when a different one of said -circuits is energized.

12. A device as set -forth in claim 9 in which the entire coil means has current flowing therethrough when said first circuit is energized and only a portion of said coil means has current flowing therethrough when said second circuit is energized, the remaining portion of coil means and said first control switch 'connected in series combination, said second control switch in parallel with said series combination.

13. A device as set forth in claim 12 in which the rectifier means is a single semi-conductor diode element.

References Cited UNITED STATES PATENTS 2,427,719 9/ 1947 Exner 317-150 2,452,034 10/1948 Campbell 317-150 X 3,029,369 4/1962 Lang et al. 317-150 3,202,244 8/1965 Vogelsong et al. 335-281 X 3,204,059 8/1965 Saaty 335-179 X JOHN F. COUCH, Primary Examiner. J. D. TRAMMELL, Assistant Examiner.

U.S. C1. X.R.

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