US2414583A - Polarized electromagnet - Google Patents

Description

Jan. 21, 1947. u 5R 2,414,583

POLARIZED ELECTROMAGNET Filed June 26, 1944 3nventor L2 ,0 I I K)?- I 2 p Gttomeg Patented Jan. 21, 1947 POLARIZED ELECTROMAGNET George E. Duffy, Sr., Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

Application June 26, 1944, Serial No. 542,203

7 Claims. (Cl. 175-339) This invention relates in general to electromagnetic relays, and more particularly pertains to relays. of the two-position polarized type which have their armatures biased to on position and which are actuated to the other position only in response to the energization of their coils with current of a particular polarity.

The relay of the present invention is to be considered in the nature of an improvement over the relay disclosed in the application of O. S. Field, Ser. No. 588,748, filed April 17, 1945, which is a division of his prior application Ser. No. 361,060, filed October 14, 1940, now Patent No, 2,376,534, granted May 22, 1945; and no claim is made herein to any subject matter disclosed in said applications.

In relays of this type it is desirable to employ polarizing permanent magnets which have a high coercive force, so that the energization of such relays with current of a polarity which produces a magnetomotive force in opposition to the residual induction of the permanent magnets will not have any material effect in reducing such residual induction of the permanent magnets. Permanent magnets of this type generally do not have as high a residual induction per unit of cross-sectional area as those having a lesser coercive force, and for this reason it is necessary to organize the relay structure so as to provide permanent magnets with a relatively large crosssectional area, and yet adapt such relay organization to the structure required to give the desired operating characteristics. This purpose has been accomplished by the organization of the present invention.

Another structural characteristic of the relay of this invention is that the permanent magnets are provided with keepers which are effective to reduce the demagnetizing efiects during the time the relay is not in use.

A further object of the present invention is to provide structure so that the core member of the relay which is normally arranged to shunt the permanent magnets and act as a keeper, cannot be removed without the removal of the permanent magnets, and thus avoid the possibility of the false operation of the relay armature by the flux of the permanent magnets with the core member removed. 1

A further object of the present invention is to so organize the relay structure that to effectively actuate the armature by reverse energization of the relay requires such a high operating potential, that such operation due to reverse energization will never occur even upon accidental en- 5.5 ably supported by bearing 6. The armature A.

2 ergization of the relay by a relatively high potential.

It sometimes happens that relays which are associated with line circuits, will receive high potentials from lightning strokes even though the usual lightning protective features are employed, and such lightning strokes may in some cases cause the demagnetization of the permanent magnets either partially or completely. In View of such a contingency, it is proposed in accordance with the present invention to make provision such that the relay will not respond to its usual energization in the event of the complete demagnetization of its permanent magnets.

Various other objects, purposes and characteristic features of the present invention will be in part apparent and in part pointed out as the de-'- scription of the invention progresses.

In describing the invention in detail, reference will be made to the accompanying drawing in which:

Fig. 1 represents a fragmentary perspective view of the essential elements of a relay constructed in accordance with the present invention; and

Fig. 2 is a sectional view taken on line 2--'2 of Fig. 1 looking in the direction of the arrows to show the manner in which the core members are joined with the permanent magnet structure of the relay.

The drawing has been made more for the purpose of showing the necessary structural characteristics of a relay embodying the present invention rather than showing the details of design of a completerelay. For this reason the drawing has been made fragmentary in nature eliminating the housing portions, terminal blocks, and the like, and reducing the showing of detail contact structures, coils and'the like to a minimum, it being believed that a disclosure and explanation of the essential structural characteristics will be sufiicient for an understanding-of the principles of the invention so that they may be readily adapted to any particular relay designed for specific purposes, such as railway signalling relays, telephone type relays, or the like.

Referring to Fig. 1, it will be seen that the relay comprises a U-shaped core member C having its opposite legs connected to elongated pole pieces PI and P2 respectively, which pole pieces have pole shoes or faces with which a pivoted armature A is associated. The armature A is pivoted by suitable trunnions 5, or other type bearings, suitalso carries movable contact, arms I which cooperate with front and back contacts 8 and 9.

At opposite sides of the core member are keepers KI and K2 which are attached to the core member C and the elongated pole pieces Pl and P2 respectively as indicated in Fig. 2. More specifically, the keeper K2 contacts against a flattened portion of the left-hand leg of the core member C and these two members have holes through which a bolt B2 freely passes so that it can enter the threaded portion of the pole P e P2. The pole piece P2 also has a flattened portion which bears against the opposite side of the left-hand leg of core member C and these three members make close mechanical contact due to the pressure exerted by the tightening of the-stud bolt B2.

Between the keepers Kl and K2 in back and in front'of the core member C are two permanent magnets PMi and PME which have their respective leakage strips LI and L2 located on the in side of the permanent magnets towards the core member. These leakage strips and permanent magnets tightly fit between the keepers KI and K2 so as to form smooth and complete contact at the joints when the bolts Bl and'BZ are tightened. The leakage strip LI and permanent magnet PM] are held in place by bracket members it and H which fit over the ends of the keepers KI and K2 respectively with suitable overlapping portions to engage and support the leakage strip and permanent magnet. 'In a similar way, bracket members t2 and 13 are provided to support the leakagestrip L2 and permanent magnet PM2 in their proper positions. These bracket members '10, 1|, :2 and 1:3 are fastened to their respective keepers by suitable machine screws.

The core member C with its windings WI and W2 and associated permanent magnets are of course in the open, while the armature and its associated contacts, bearings, and the like, are suitably enclosed in a housing constructed of suitable insulating material, which has been merely indicated at M. course unessential to an understanding of the present invention, although quite necessary in the actual construction of a relay for practical fuses.

The armature A is ordinarily provided with a released air gap of the required dimensions to i give the desired pick up value with regard to the drop away value of the relay, and the armature A is prevented from making contact with the pole ,faces, when picked up, by suitable residual pins of non-magnetic material. These have not been shown in detail but it should be understood that they are present and the minimum air gap is properly selected in accordance with the values involved, and may in some cases be in the order of ten thousandths of an inch.

:The core member C, the pole pieces PI and P2, armature A, and the keepers KI and K2 are formed of some suitable magnet material of relatively low reluctance, such ,for example, as the commonly used silicon steel. Likewise, the leakage strips LI and L2 are also formed of a suitable .ferrous material of relatively low reluctance, although it is not .essential that the reluctance of these leakage strips be as low as the reluctance of the core structure. The permanent magnets PM! and PMZ may be of any suitable permanent magnet steel having the desired characteristics, and as one example it may be mentioned that the material known under the trade-name of Black Streak Alnico has been found to be very Such details are of suitable, although it should be understood that any suitable material may be employed.

With reference to the drawing, it should be noted that the permanent magnets PM] and PMZ are poled in the same direction such as with the north poles N to the left against the keeper 2. Thus, the lines of induction produced by the residual magnetism in the permanent magnets passes through three paths in multiple. The first and best magnetic path is from the permanent magnets through keepers KI and K2 and core member C. The leakage strips LI and L2 are also direct multiple with this path, and in fact are in contact with the permanent magnets 7 along the side as well as in contact with the keepers Kl and K2. Thus, the leakage strips will be considered as providing the second path. In this connection, it may be noted that the term keeper has been applied to the members Ki and K2 for convenience in applying the nomenclature, but these members are not keepers in the true sense of each individually providing a complete path for the lines .of induction from its permanent magnet, but act as connecting links with the core member C so that they are a part of an actual closed path through the core member for the lines of induction from both the permanent magnets. The third path for the lines of induction from the permanent magnets is through the pole pieces and the armature, but ince this path includes a substantial air gap, the lines of induction which pass'through it, and which comprise lines of force, are relatively small in number compared to the lines of induction passing through the first path including the core member C, or passing through the second path including the core members LI and L2.

'As is of course well understood, the permanent magnets PMl and PMZare magnetized by means of an electromagnet capable of producing a very large number of lines of induction so as to completely magnetize the permanent magnet material, Then, the residual magnetism of the permanent magnets is reduced to the desired degree, which process provides the magnet with the maximum amount of coercive force for the amount of remenance in the 'magnet. The amount of remenance, or residual induction of the magnet in accordance with the present invention should be suiiicient to produce lines of induction in the core member C to a density relatively near to the knee of the magnetization curve of the core member C. In order to do this,

it is desirable to have the cross-sectional area of the combined permanent magnets several times the cross-sectional area of the core member C, and one relationship which has been found practical with a particular degree of magnetization is where the combined cross-sectional area of the permanent magnets is about five times as great as the cross-sectional area of the core member C. r

The lines of force which normally pass through the air gap between the pole faces and the cooperating armature A should be ineffective to pick up the armature or to hold it up should it become picked up. Stating this in another way, the biasing force on the armature A should be sufliciently great to overcomegany lines of force passing through the air gap with the coils or windings of the relay deenergized. In this particular embodiment of the invention, the biasing force is gravity, which of course depends upon the weight of the armature A, but it is to be understood that mechanical means, such as springs or the like, may be provided to give .the proper bias if desired.

The leakage strips LI and L2 are preferably arranged on the inside of the permanent magnets towards the core member C. In other words, regardless of the particular form of the invention, it is preferable that these leakage strips form a closed magnetic circuit with respect to the core member C with the permanent magnets on the outer side of such closed magnetic circuit. Such an organization provides that the leakage strips give the greatest protection, against the operation of the relay when it is energized in the reverse direction. For example, if the permanent magnets were arranged to be between the legs of the core, as is possible with some designs of relay, then the leakage strips should preferably be placed above the permanent magnets, that is, between the permanent magnets and the coils on the U-shaped core member 0. Although such relative location of the leakage strips is desirable for maximum efficiency, it is to be understood that other locations can be employed and still practice the principles of the present invention.

The leakage strips are preferably formed to have a combined cross-sectional area within reasonable variations on either side of the cross-sectional area of the core member. In other words, substantially the same normal operation of the relay occurs if the leakage strips have a crosssectional area slightly above the cross-sectional area of the core, but the combined cross-sectional area of the core and leakage strips should be but a fractional portion of the combined cross-sectional area of the permanent magnets. way, it is possible to maintain the desired degree of saturation in the core structure from the lines of induction produced by the residual magnetism in the permanent magnets.

Operation Although there may be several possible theories of operation of such a relay, and although the actual positions and densities of the lines of flux in the relay are difiicult to ascertain so as to substantiate any particular theory of operation of the relay, it is thought desirable to point out certain results obtained by a relay constructed in accordance with the present invention, and then point out one possible theory of operation, which may be employed in applying the principles of the present invention so as to obtain desired results even though the relay structure itself may take different forms.

It is of course obvious that if the permanent magnets and leakage strips are removed from the relay, that such relay will then act as a regular neutral relay having pick up and drop away current values as well as the so-called working current value where the armature is against the residual pins and the contact pressures are properly established. It has been found that to add the permanent magnets to such a relay without the leakage strips will cause the pick up, drop away and working current values to be substantially reduced when the relay is energized in the normal direction such as by movement of the switch arm SW to a lower position; but upon movement of the switch arm SW to an upper position and thereby energizing the windings of the relay in the reverse direction, it is found that the relay will not pick up upon the normal degree of energization such as that used if the relay were employed as a neutral relay above mentioned. The amount ofenergy required to be applied in the In this reverse direction with the permanent magnets inserted, is several times the normal working current; and thus a biased polar relay is provided, which responds to the application of only a particular polarity of energization.

However, should the permanent magnets with such an organization having no leakage strips become demagnetized, as previously mentioned, the relay would then act substantially as a neu tral relay and the reverse working current values would be substantially the same as the normal working current values.

On the other hand, it has been found that, by the use of the leakage strips as proposed by the present invention, the normal working current of the relay is not materially changed over the normal working current of the relay having no leakage strips; while the current required to operate the relay upon reverse energization is many times greater than the current required for reverse operation where no leakage strips are em- ,ployed. Also, with such an organization having leakage strips as shown in the present disclosure, the magnets may be completely demagnetized and under such circumstances the relay will not operate its armature upon either normal or reverse energization with current values substantially the same or even greater than those used under the normal operation of the relay.

Thus, it is seen that the provision of the leakage strips to complete a leakage path for magnetic flux upon reverse energization of the relay and upon energization of the relay in either direction when the permanent magnets are demagnetized, provides protective features which are obviously new and useful. It might be noted here that the reluctance of the permanent magnets is so high that even when such magnets are completely demagnetized, practically none of the lines of induction produced by the energization of the windings is shunted by these permanent magnet pieces.

In brief, the leakage strips provided in accordance with the present invention in connection with permanent magnets as disclosed, in total effect appear to provide shunt paths for magnetic lines of induction under conditions where it is desirable to prevent operation of the relay, while on the other hand such leakage strips appear to have no substantial undesirable effects upon the normal operation of the relay.

As one possible theory of operation, it is considered that the energization of the windings with the switch SW in the lower position for normal energization produces a flux in the core member in opposition to the flux produced therein by the permanent magnets. This opposition causes additional flux to pass through the air gap and armature so that the lines of force are suificient to pick the armature up. The additional lines of induction in the leakage strips, although increased to some extent, are not increased to any great extent due to the fact that the lines of induction already there by reason of the permanent magnets are at a density already at the knee of the magnetization curve, so that the lines of induction produced by the energization of the coils is very effective to cause lines of force to pass through the air gap. It is also thought that since the lines of induction produced by the energization of the windings in the normal direction are in opposition to the lines of induction produced therein by the permanent magnets, a cancellation effect occurs so that the resulting density of lines .of induction in the coremember during normal energization of the relay is maintained at a value below the knee of the magnetization curve. Thus, the provision of the usual number of ampere turns will cause operation of the relay.

Perhaps it should be noted here that the switch SW in a lower position provides for the normal energization of the relay at a proper value to efiect the picking up of the armature; while the operation of the switch SW to an upper position provides that the relay is energized in the reverse direction but since it is at the same degree of energization as for normal operation, the armature does not respond. In order for the armature to be picked up in response to the energization of the relay windings in the reverse direction, it is necessary to produce lines of induction in the armature air gap which is suflicient to oppose those lines of induction normally present due to the permanent magnet plus a sufiicient number of lines of force to cause the armature to be attracted. Since the degree of reverse energization of the relay windings with switch SW in an upper position, is incapable of producing such a number of lines or induction in the armature air gap, the armature does not respond.

In order to produce lines of induction in the armature air gap to an extent that the armature will pick up, it is necessary to energize the relay in a reverse direction to an extent that will supply the added lines of induction which pass through the leakage strips as well as the required lines of induction to efiect the response of the armature as above mentioned. When the winding is energized to this extent, the core member C has lines of induction at a density Well above the lmee of its magnetization curve. With the core member C at such a high density, it is apparent that the number of ampere turns required to produce the lines of induction passing through the leakage strips is much greater in proportion to the number of ampere turns that are required to supply the lines of induction for the leakage strips under normal operation where the core member is being operated at densities of flux below the knee of the magnetization curve. Thus, the leakage strips provide the desired effect on the operation of the relay, since they have substantially no effect under normal operation of the relay when the flux densities are below the knee of the magnetization curve of the core member, and since they become very effective upon the reverse energization of the relay when the flux densities are well above the knee of the magnetization curve of the core member.

In the above discussion, the degree of energization in a reverse direction required to efiect the picking up of the armature is an abnormal condition which has been discussed to merely bring out the degree of protection provided by the present invention against the response of the relay armature upon accidental energization in such reverse direction. a

As above mentioned, this theory of operation is merely to be taken as one possible explanation which when considered in View of the structural characteristics of the relay organization as above described will be found useful in adapting the necessity causes the permanent magnets PM! and PMZ to also be removed. Thus, it is impossible to replace windings on the relay without at the same time removing the permanent magnets. This insures that should the relay contacts be left connected in control circuits at the time that an efiort was made to change the windings, no erroneous or undesired picking up of the relay can occur due to the magnetism of the permanent magnets with the shunting core member C removed. This arrangement provides a high degree of safety, especially where the relay organization is employed in connection with safety control circuits, such as in connection with railway signalling circuits.

Having thus described a polarized relay structure of the biased to one position type, as one specific embodiment of the present invention, it is desired to be understood that this form is selected-to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be further understood that Various modifications, adaptations, and alterations may be applied to the specific iorrn shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention except as limited by the appended claims.

What I claim is:

1. In a relay structure, a U-shaped electromagnetic core, a pivoted armature associated with the ends of said core and normally biased away from said core to a retracted position, a leakage member connected across the legs of said core to make a closed magnetic circuit through said core, a permanent magnet connected across the legs of said core in multiple with said leakage member for normally causing a relatively high density of magnetic flux in said core and said leakage member, windings on said core effective when energized with a current of one polarity to cause the induction of magnetic flux to oppose the lines of induction from said per manent magnet for causing the attraction of said armature toward said core, but eiiective when energized with current of the opposite polarity to produce lines of induction adding to the lines of induction from said permanent magnet in such a way as to fail to actuate the armature from its retracted position, whereby said leakage member is relatively inefiective on the normal operation of said relay because of relatively low flux densities in said core but is highly effective to prevent the actuation of said armature upon the energization of said windings with said other polarity because of the relatively high flux densities in said core.

2. In a relay structure, an electromagnetic core member with an associated pivoted armature and having an energizing winding mounted on said core, a permanent magnet anda leakage member connected magnetically in 'multiple across said core to be in multiple with that portion of said core having the energizing winding mounted thereon, said permanent magnet causing lines of magneticinduction. in said core and leakage members to a densityrelatively near to. the saturation point of said members, said armature being actuated to an operated position when said winding is energized with one polarity of energization but remaining in its retracted position when said winding is energized with the opposite polarity of energization even if such opposite polarity of energization is several times the current value of the normal energization.

- -3. In a relay structure of the type described,

an electromagnetic core member having a pivoted cooperating armature, a shunt member connected across the electromagnetic core member, means for normally producing magnetic lines of induction in said core and said shunt member relatively'near the saturation point of said members, and an energizing winding on said core member energizable with current in either direction to thereby induce a magnetic flux in said core opposing said normal magnetic flux in said core member to cause the actuation of said armature but acting when energized with the opposite polarity to produce a magnetic flux which is additive with said normal magnetic flux in said core member to oppose the normal magnetic iiux in said armature to thereby allow said armature to remain in its retracted position.

4. In a relay structure of the type described, an electromagnetic core having extending pole pieces, a permanent magnet and a leakage strip all magnetically connected in multiple between said extending pole pieces, a pivoted armature associated with said pole pieces in a manner to assume attracted or unattracted positions and normally biased away from said pole pieces by a torque suflicient to overcome the leakage flux from said permanent magnet with the armature in either an attracted or unattracted position, and windings on said core for producing a magnetic flux in said core in either direction depending upon the polarity of energization of said windings to thereby cause the attraction of said armature under one condition of energization but to allow said armature to remain in its biased position under another condition of energization, said leakage strip being a more efiective shunt for the flux in said core under said another condition of energization than under said one condition of energization.

5. In a, relay structure, a pair of pole pieces and a cooperating pivoted armature normally biased away from said pole pieces, an electromagnetic core connected across said pole pieces, a leakage strip connected across said pole pieces, a permanent magnet connected across said pole pieces to complete a closed magnetic circuit for the flux of said permanent magnet to pass through said core and said leakage strip in multiple with said armature including an air gap, and a winding on said core efiective when energized with current of one polarity to produce flux opposing the flux of said permanent magnet but aiding the flux of said permanent magnet in said air'gap and armature to thereby cause the flow of flux to effect the actuation of said armature toward said pole pieces, but eiTective when energized with current of the opposite polarity to produce flux that is in the same direction as the flux of said permanent magnet but opposing the flux of said permanent magnet in said air gap and armature and thereby allows said armature to remain in its biased position, whereby said leakage strip acts as a shunt to prevent actuation of said armature in the event said permanent magnet becomes demagnetized.

6. In a relay structure, an electromagnetic core, a permanent magnet mechanically connected to said core to complete a closed magnetic circuit through said core for the flux of said magnet,

an armature associated with said core and normally having a portion of the flux from said permanent magnet passing through an air gap between said armature and the core, said armature bein biased away from said core with sufiicicnt torque to overcome the normal magnetic flux from said permanent magnet irrespective of the attracted or retracted position of the armature, windings on said core effective when energized with a normal value current of one particular pclarity to produce a magnetic flux in the air gap additive with the normal magnetic flux therin from said permanent magnet to thereby cause the actuation of said armature to an attracted position, a leakage strip having a cross-section area relatively small in comparison to the cross section area of said permanent magnet, said leakage strip bein located adjacent to and parallel with said permanent magnet and magnetically connected across said core and acting as a relatively poor magnetic shunt when said windings are energized by said normal value current of said one polarity, but acting as a relatively good magnetic shunt when said windings are energized with the opposite polarity at a relatively high value to thereby prevent the attraction of said armature during such energization of said windings.

F. In a relay structure, a U-shaped electromagnetic core, a pivoted armature associated with the end of said core with an intervening air gap and movable to attracted and retracted positions but normally biased away from said core to said retracted position, a permanent magnet of relatively high reluctance connected across the legs of said core to make a closed magnetic circuit through said core for a portion of the flux of said permanent magnet and to make a magnetic circuit for another portion of the flux of said permanent magnet through said air gap aid said armature, such magnetic flux through said armature being insufiicient to overcome said normal bias, windings on said core effective when energized with a normal current of one polarity to increase the magnetic flux in said air gap for causing the attraction of said armature toward said core, but effective when energized with a normal current of the opposite polarity to produce a magnetic flux in said air gap opposing the magnetic flux emanating from said permanent magnet whereby said armature is actuated to an attracted position by a. normal current of said one polarity but cannot be actuated to an attracted position by a normal current of the opposite polarity, and a leakage strip of relatively low reluctance connected across the legs of said core adjacent said permanent magnet of relatively high reluctance to thereby act as a relatively ineffective magnetic shunt during the normal energization of said windings with said one polarity but to act as a relatively good magnetic shunt during an abnormal energization of said windings of the opposite polarity, whereby said relay is protected from undesired response to said armature upon accidental abnormal energization of its windings with current of said opposite polarity.

GEORGE E. DUFFY, SR.

Images