US3740650A

US3740650A - Electromagnetic switch

Info

Publication number: US3740650A
Application number: US00134997A
Authority: US
Inventors: A Grenier; R Suter; L Cooper
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1971-04-19
Filing date: 1971-04-19
Publication date: 1973-06-19
Anticipated expiration: 1990-06-19

Abstract

In an electromagnetic switch assembly having a solenoid and a movable armature attractable to the solenoid by a first electromagnetic force, improved control of armature movement is achieved including maintaining the armature away from the solenoid until a predetermined current condition exists and then causing the armature to move with improved rapid motion, that is with snap action, by applying a second force in the form of a magnetic bias to the armature in a direction opposing or negating a portion of the first force maintaining the armature away from the solenoid until the predetermined current condition comes into existence at which point the ratio of the first force to the second force changes to reverse the direction of the resultant force to allow the armature to move to the solenoid with the first force increasing as the second force is decreasing with armature movement. A second embodiment uses the first and second forces to avoid nuisance tripping upon momentary overloads by utilizing the position of a movable core within the solenoid. In a first position, the second force, tending to maintain the armature away from the solenoid, is significantly higher than the first force even upon an overload while in a second position the first force, tending to attract the armature to the solenoid, is significantly higher than the second force.

Description

United States Patent 1 1 Grenier et al.

11 3,740,650 1 June 19,1973

[ ELECTROMAGNETIC SWITCH [75] Inventors: Aime J. Grenier, North Attleboro;

Richard E. Suter, Norton; Lawrence E. Cooper, Attleboro, all of Mass.

[73] Assignee: Texas Instruments Incorporated,

' Dallas, Tex

1221 Filed; Apr. 19, 1971 21 A .N6.;134,997-

[52] US. Cl. 335/239, 335/242 Primary ExaminerGeorge Harris At t0rneyI-Iarold Levine, Edward J. Connors, John A. I-Iaug, James P. McAndrews and Gerald B. Epstein 514 76/1 MiM/VASN Qfis IIIIIIIIIIIIII [57] ABSTRACT In an electromagnetic switch assembly hav-ing a solenoid and a movable armature attractable to the solenoid by a first electromagnetic force, improved control of armature movement is achieved including maintaining the armature away from the solenoid until a predetermined current condition exists and then causing the armature to move with improved rapid motion, that is with snap action, by applying a second force in the form of a magnetic bias to the armature in a direction opposing or negating a portion of the first force maintaining the armature away from the solenoid until the predetermined current condition comes into existence at which point the ratio of the first force to the second force changes to reverse the direction of the resultant force to allow the armature to move to the solenoid with the first force increasing as the second force is decreasing with armature movement.

significantly higher than the second force.

8 Claims, 4 Drawing Figures v I [lire/26ers:

by Aim J. Grem'er Ric/20rd E. Safer Lawrence E. Cooper may PATENTED Jul 1 sun-112mg n u 1w nu n n tal GE WJMW I i M ARL W ELECTROMAGNETIC SWITCH This invention relates to electromagnetic switches, and with regard to certain more specific features to flux path defining means for controlling the movement of an armature of a device for opening or closing a circuit.

Among the several objects of this invention may be noted the provision of means to improve the characteristic of armature movement to obtain improved rapid or snap action movement of the armature toward the solenoid of the device to effect concomitant opening or closing of a circuit. Another object of the invention is the provision of an electromagnetic switch which is insensitive to overloads of short durations. Yet another object is the provision of suchapparatus which is reliable yet relatively inexpensive, apparatus which is readily calibrated, has few moving parts to maximize longevity and apparatus which can be used with essentially any electromagnetic device having a movable armature. Another object of this invention is the provision of a new and improved magnetic circuit breaker assembly for the protection of electrical circuits and components against sustained overloads and short circuits especially one in which the flux generated is efficiently used both to actuate the circuit breaker and to obviate nuisance tripping. Other objects and features will be in part apparent and in part pointed out hereinafter. I

The invention accordingly comprises the elements and combinations of elements, steps and sequence of steps, features of construction and manipulation, and arrangements of parts, all of which will be exemplified in the structures and methods hereinafter described, and the scope of the'application of which will be indicated in the appended claims.

In the accompanying drawings in which several of the various embodiments of the invention are illustrated:

FIG. 1 is an elevational view, partly in cross section and partly schematic-of'one of the various possible embodiments of the'invention;

I picted in FIG. 2 and showing forcesacting upon it.

Corresponding reference characters indicate corresponding parts throughout the two views of the drawings.

Dimensions of certain of the parts as shown in the drawings may have beenmodified or exaggerated for the purposes of clarity of illustration.

Conventionally an electromagnetic switch has an armature movable toward and away from a solenoid to actuate some type of switch mechanism. Spring means is normally used to bias the armature into a first position removed from the armature when there is either no current or insufficient current in the solenoid to attract the armature to the second position contiguous to the solenoid. This spring may be adjusted, for example, to maintain the armature in the first position even with a certain current, or predetermined level, passing through the solenoid thus offsetting the electromagnetic force on the armature caused by the passage of current through the solenoid. When the current exceeds the predetermined level the electromagnetic force on the armature exceeds the spring force and thus the armature begins to move toward the solenoid against the bias of the spring. This bias of the spring, however, still acts on the armature and militates against its movement toward the solenoid thereby tending to slow its movement. It is possible to offset this characteristic to some extent by employing a spring having a decreasing rate, that is, a spring which exerts decreasing bias or force on the armature as it moves toward the solenoid. However, this does not completely solve the problem since it is desirable to provide vibration insensitivity for the device. In order to avoid the situation of having a sudden force applied to the armature in a direction tending to move the armature toward the solenoid, which might happen if the device were suddenly jarred, and not having sufficient bias left in the spring to overcome this jarring force along with any existing electromagnetic force a reasonably large safety factor must be factored into the spring, thus resulting in slower motion of the armature upon an overload. The present invention results in improved snap acting characteristics of the armature by applying a second force to the armature which biases the armature away from the solenoid at the same time the usual first electromagnetic force is applied to the armature biasing the armature toward the solenoid. The second force can be adjusted so that the spring need not be employed. That is, the second force can be made greater than the first keeping the armature away from the solenoid until a certain current level is achieved in the solenoid at which point the resultant of the forces is reversed with the first force becoming greater than the second and the armature is then attracted to the solenoid. As the armature moves toward the solenoid, the second force on the armature rapidly decreases while the first force concomitantly rapidly increases. In some instances it may be desirable to use a relatively small spring bias just to maintain the armature away from the solenoid when in the deactuated condition. Inthis case, as well as in the case of not employing a spring, the second force is sufficient to prevent movement of the armature toward the solenoid upon vibrations.

As seen in FIG. 1, a device 10 comprises flux producing means in the form of a solenoid 12 preferably wound on a nonmagnetic bobbin 14. A solid core 16 of magnetic material such as steel is telescopically received within the solenoid and is provided with a pole piece 18 on one end and is attached at the other end thereof to a magnetic path defining frame member generally indicated as 20. Frame 20 is formed into a first magnetic path P, comprising pole piece 18, core 16, bottom portion 22 contiguous with an end of the solenoid, upstanding member 24, air gap B, armature 26 contiguous to member 24, air gap C and back to pole piece 18. Frame 20 is also formed into a second magnetic path P comprising pole piece 18, core 16, a generally U-shaped portion of frame 20 comprising a leg or bottom portion 22, bight portion 28 and top leg 30, gap D, distal armature portion 32, air gap C, and back to pole piece 18. Means 34 for altering the reluctance of magnetic path P is shown schematically in bight portion 28. This may take the form of a constricted section of bight portion 28, a switch changing an air gap, forming all or a portion of the frame 22 lying within P of material which magnetically saturates before P or any other conventional means for altering the reluctance of a member. The total reluctance of path I: may be calibrated or adjusted by placing a layer 36 of nonmagnetic material on distal portion 32 of the armature and also by forming dimple 38 in top member 30. Provision of layer 36 also avoids the possibility of armature 26 sticking to top leg 30 and provides more consistent operation over the life of the breaker by reducing the effect of wear-in or small foreign particles collecting at the contact point. The radius of dimple 38 not only affects the reluctance of path P but also affects the magnitude of F obtained for a given flux level in path P by affecting the flux patterns and distribution in gap D between the dimple and the top of armature 26. Dimple 38 further provides more consistent operation since the area of contact of a flat surface mating with a rounded surface is more predictable than two mating flat surfaces. It should be noted that it may be desirable in some instances to round off the top surface of pole 18 for the same reason.

It will be seen that the U-shaped portion of frame 20 encompasses solenoid 12 and distal armature portion 32. Armature 26 is pivotably mounted at 40 and movable from a first position in contact with top leg 30, shown in FIG. 1 in solid lines, to a second position in contact with pole piece .18, shown in dashed lines, and vice versa. Movement of armature 26 actuates a switch mechanism shown schematically at 42 through any convenient linkage arrangement as suggested by dashed line 44. Armature 26 is normally biased into the position shown in solid lines in the nonactuated condition either through the linkage mechanism 44 or by a separate spring, for instance a spring located at pivot 40. This bias is preferably'just enough to cause the armature to move toward top member 30.

Operation of device is explained as follows. When electric current flows through solenoid 12 an electromagnetic field is established with flux concentrated in pathsP, and P The reluctances of the paths can be adjusted so that the force F see FIG. 1a, occasioned by normalcurrent flow applied to armature 26 through path P, tending to attract the armature toward pole piece 18 less the bias of a spring, if one is employed, is less than the force F FIG. 1a, applied to armature 26 through path P tending to attract the armature toward top member 30 so that the armature, remains in the solid line position. As the current increases in the solenoid, the flux in path P increases proportionately. The increase of flux in path P however, is limited by means 34, for instance by saturation of a portion of leg 28, so that upon sufficient increase in current flow through solenoid 12 force F 1 becomes larger than force F and thus the armature 26 is attracted to pole piece 18. As soon as armature 26 begins to move the reluctance of gap D markedly increases while the reluctance of gap C decreases reversing the resultant of forces, F sharply increasing while opposing force F, is sharply decreasing resulting in snap-acting motion of armature 26. This positive, fast motion of the armature permits a more precise and accurate calibration of the device, that is, of actuating switch mechanism 42 at the same time of making available a high force for transmission through linkage 44.

Another problem which is commonly associated with electromagnetic switches, particularly when they are used as circuit breakers, is that of nuisance tripping of the device. This refers to interruption of a circuit upon occurrence of a high overload of duration sufficiently short that it is not detrimental to the particular load being protected. An example of a common type of momentary overload is the occurrence of high amplitude transients of relatively short duration occasioned by the switching on an electric power supply. It is desirable in such instances to provide some means to prevent tripping of such a circuit breaker until the overload exists for some predetermined interval of time related to the specific amount of overload. A typical electromagnetic circuit breaker is provided with a time delay mechanism such as a dashpot mechanism in which a core moves through a fluid-filled dashpot chamber. The desired time delay is obtained by retarding movement of the core through the fluid chamber. When the core approaches the pole piece the flux density is increased sufficiently to attract the armature and cause it to pivot toward the pole piece thus tripping the breaker. However, this type of time delay mechanism may not prevent tripping due to the high amplitude transients mentioned above which occur when a power supply is switched on, even through the inrush lasts for a period of time less than that required for movement of the core to the pole piece. The magnitude of this type of overload is sufficiently large to-substantially instantaneously attract the armature of the circuit breakers operating mechanism thereby tripping the breaker and frustrating the function of the time delay.

Various attempts have been made to prevent this type of nuisance tripping including the provision of shunt paths in which a portion of the flux developed by the solenoid is shunted away from the armature. Such schemes however are inherently inefficient since a significant portion of the flux produced is shunted away from the armature and is in effect, wasted and results in a device which is less sensitive to sustain overloads and has less force available for desired tripping. Further, such devices frequently require additional moving parts for the shunt mechanism adding to the expense of the apparatus and introducing maintenance and reliability problems. i

The embodiment of the present invention depicted in FIG. 2 eliminates the nuisance tripping problem yet obviates the disadvantage of the prior art. In this embodiment flux producing means in the form of solenoid 12, similar to that shown in FIG. 1, is wound about bobbin 14; however, instead of the solid core used in FIG. 1 a dashpot mechanism comprising a thin-walled elongate tube preferably of brass or other suitable nonmagnetic material, closed at its upper end by a cover or cap 18 secured to the tube, is telescopically received within solenoid 12. Cover 18 is magnetizable and constitutes a pole piece of a circuit breaker, relay or the like. The lower end of the tube 102 is closed by any conventional stopper means or formed integrally with the side walls as indicated in the Figure, as by drawing. An elongate armature core 104 located in tube 100 is shorter than the tube and movable axially therein. Core 104 is made of iron, steel or other suitable magnetizable material.

A hydraulic fluid or other suitable fluid maybe inserted and fill substantially the portion of tube 100 not occupied by core 104. The fluid is forced from one end of the tube to the other around the periphery of the core when core 104 is moved in the tube. Passage around the periphery constitutes a restriction which limits the rate of fluid flow from one end of tube 100 to the other end thereof, thereby retarding the rate of movement of the core 104 and providing a desired time delay for sustained overloads. It will be understood that a fluid passage can be provided by other means, such as by grooves or other shape formations in the inner surface of tube 100 or in the outer surface of core 104 or by a passage through the core.

The bottom end of tube 100 projects from the solenoid and the core is biased against closed end 102 (the position shown in the drawings) by a return coil spring (preferably nonmagnetic) which reacts from the inner surface of cover 18 against the upper end of core 104. Spring 106 iskept axially aligned in tube 100 by stub 108 on core 104.

Passage of current through solenoid l2 creates a magnetic field in ad around the solenoid and within tube 100 which attracts core 104 toward the upper portion of tube 100 and into a central portion of the solenoid. When the core 104v reaches a central portion of the solenoid, the reluctance of the magnetic circuit is reduced due to the presence of the magnetizable core and there is a resulting increase in the strength of the magnetic field initially created by passing current through the solenoid. This increase in the magnetic field attracts armature 26 and .is used to operate a v free portion 32adapted to move toward and away from pole piece 18.

A' second bracket 120 of magnetizable material is generally U-shaped and encompasses frame 1 10, armature 26 and solenoid 12. Frame 120 has a first leg 122 located on the side of the armature portion 32 removed from thesolenoid and is preferably provided with a dimple 38 as in the FIG. '1 embodiment. Shim 36 is also shown on the face of armature portion 32 which comes into engagement with dimple 38. A second leg 124 is spacedfrom the bottom'of the solenoid and interposed supporting member 112 by a cylindrical spacer 126 of nonmagnetic material. Leg 124 is provided with aperture 128 which receives the bottom portion of tube 100. In order to minimize the reluctance between leg 124 and core. 104 a sleeve 130 of magnetic material may beplaced about tube 100 in contact with leg 124.

Magnetic path P comprises pole piece 18, gap E, core104, gap F between the core and leg 112, frame 110, gap H, armature 26 and gap I back to pole piece 18. Another magnetic path comprises a pole piece 18, gap E, core 104, gap .1 between core and leg 124 when the-core is located at the bottom of the tube as shown or gap J from the bottom of the core 104 and leg 124 when in the raised or actuated position (indicated by dashed line 132 bracket 120, gap-K including shim occurs (magnitude and duration of the overload being inversely proportional). As explained above when the core moves to a central position in the solenoid, the electromagnetic force on the armature F see FIG. 2a, tending to attract it to the pole piece becomes strong enough to cause the armature to pivot to the dashed line position. This in turn causes the circuit breaker 42 to trip or break the circuit through linkage 44. However upon momentary overloads, that is overloads which last for a period of time less than that required for the core 104 to move upwardly, the flux in path P, is concentrated due to the low reluctance between the core and leg 124 when the core is in the position shown and is greater than the flux path P Thus a force F,, FIG. 2a, is applied to armature portion 32 attracting it to dimple 38 and away from pole piece 18. This results in a ratio of forces acting upon the armature such that on momentary overloads a resultant force attracts the armature to the full line position shown. The higher the overload,-when the relationships of the components are optimized, the greater this resultant force keeping the armature away from the pole piece (i.e. F F, F However, when the core moves into the solenoid (the bottom surface of the core indicated by dashed line 1 32) the resultant force is reversed. A large reluctance (gap J) is added to magnetic path P, largely eliminating force Fnand force F due to the lower reluctance of diminished gap E with the core in the upper position has increased. The resultant force on the armature por tion 32 (F F;, F, with F, negligible) attracts the armature toward the pole piece 18 and causes it to pivot to the dashed line position. The sudden change in the ratio of forces results in a sudden snap acting type movement of the armature. This movement is enhanced since nearly all of the flux produced by the current in the solenoid is used to attract the armature to the pole piece, yet no moving parts are added to the device to increasethe cost or decrease longevity and reliability.

Thus it will be seen that by providing flux path P, momentary overloads actually increase the force maintaining the armature away from the solenoid thereby completely obviating nuisance tripping. Further, this is accomplished with no additional moving parts and in such a way that the flux generated in the solenoid is efficiently utilized. That is, all the working flux passes through the armature to either maintain it away from the solenoid or to cause it to move toward the solenoid to cause tripping of the breaker.

As many changes could be made in the above constructions without departure from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

We claim:

1. An electromagnetic switch comprising a solenoid having first and second ends,

a pivotably mounted armature having an end adapted to move toward and away from the first end of the solenoid,

first flux path means including a member of low magnetic reluctance having a first end contiguous with the second end of the solenoid, the member having a second end contiguous with the armature,

second flux path means including a generally U- shaped element of low magnetic reluctance, the U- shaped element having first and second legs joined by a bight portion, the first and second legs having distal end portions, the distal end portions of the first and second legs mounted adjacent respective first and second ends of the solenoid, a portion of the armature being intermediate the first end of the solenoid and the distal end portion of the first leg and the first end of the first flux path member being intermediate the second end of the solenoid and the distal end portion of the second leg and time delay means to prevent actuation of the switch upon a sustainedoverload until passage of a predetermined time interval, the time delay including a hollow elongate tubularelement of nonmagnetic material having two ends telescopically received within the solenoid and extending outwardly from the second end of the solenoid and an elongate core of magnetic material shorter than the tubular element slidablyv received within the tubular element and adapted to slide from one end of the tubular element to the other end thereof.

2. A switch according to claim 1 in which hydraulic fluid is placed in the tubular element to retard movement of the core, and a spring is placed in the tubular element to bias the core toward an end thereof.

3. A switch according to claim 1 in which the first end of the first flux path member and the distal end portion of the second leg are separated by a nonmagnetic spacer, the position of the core in the tubular element affecting the magnetic reluctance between the second end of the solenoid and the distal portion of the second leg, when the core is at one end of the tubular element a relatively large reluctance exists between the second end of the solenoid and the distal portion of the second leg while a relatively small reluctance exists when the core is at the other end of the tubular element.

4. A switch according to claim l in which a shim of high reluctance material is located on the distal end portion of the first leg and is adapted to be engaged by a portion of the armature.

5. A switch according to claim 1 further including a switch mechanism which is actuated upon sufficient movement of the armature.

6. A switch according to claim 1 in which an aperture is defined in the first end of the first flux path member and an aperture is defined in the second leg of U- shaped element, the cylindrical element being received in the two apertures.

7. A switch according to claim 6 in which a bushing of low reluctance material is received about the periphery of an end of the cylindricalelement and is in contact with the secondleg of the U-shaped member.

8. An electromagnetic switch comprising flux producing means including a solenoid having first and second ends,

second flux path means including a generally U- shaped element of low magnetic reluctance, the U- shaped element having first and second legs joined by. a bight portion, the distal end portions of the first and second legs encompassing the solenoid and the said end of the armature adapted to move toward and away from the solenoid, and time delay means to prevent actuation of the switch upona sustained overload until passage of a predetermined time interval, the time delay means including a movable core of low magnetic reluctance and means for slidingly mounting the core within the solenoid, the core movable into and out of the second flux path.

Claims

1. An electromagnetic switch comprising a solenoid having first and second ends, a pivotably mounted armature having an end adapted to move toward and away from the first end of the solenoid, first flux path means including a member of low magnetic reluctance having a first end contiguous with the second end of the solenoid, the member having a second end contiguous with the armature, second flux path means including a generally U-shaped element of low magnetic reluctance, the U-shaped element having first and second legs joined by a bight portion, the first and second legs having distal end portions, the distal end portions of the first and second legs mounted adjacent respective first and second ends of the solenoid, a portion of the armature being intermediate the first end of the solenoid and the distal end portion of the first leg and the first end of the first flux path member being intermediate the second end of the solenoid and the distal end portion of the second leg and time delay means to prevent actuation of the switch upon a sustained overload until passage of a predetermined time interval, the time delay including a hollow elongate tubular element of nonmagnetic material having two ends telescopically received within the solenoid and extending outwardly from the second end of the solenoid and an elongate core of magnetic material shorter than the tubular element slidably received within the tubular element and adapted to slide from one end of the tubular element to the other end thereof.

4. A switch according to claim 1 in which a shim of high reluctance material is located on the distal end portion of the first leg and is adapted to be engaged by a portion of the armature.

6. A switch according to claim 1 in which an aperture is defined in the first end of the first flux path member and an aperture is defined in the second leg of U-shaped element, the cylindrical element being received in the two apertures.

7. A switch according to claim 6 in which a bushing of low reluctance material is received about the periphery of an end of the cylindrical element and is in contact with the second leg of the U-shaped member.

8. An electromagnetic switch comprising flux producing means including a solenoid having first and second ends, a pivotably mounted armature having an end adapted to move toward and away from the first end of the solenoid, first flux path means including a member of low magnetic reluctance having a first end contiguous with the second end of the solenoid, the member having a second end contiguous with the armature, second flux path means including a generally U-shaped element of low magnetic reluctance, the U-shaped element having first and second legs joined by a bight portion, the distal end portions of the first and second legs encompassing the solenoid and the said end of the armature adapted to move toward and away from the solenoid, and time delay means to prevent actuation of the switch upon a sustained overload until passage of a predetermined time interval, the time delay means including a movable core of low magnetic reluctance and means for slidingly mounting the core within the solenoid, the core movable into and out of the second flux path.