US2546740A - Alternating-current electromagnet with armature - Google Patents

Description

March 27, 1951 L. J. GOLDBERG ALTERNATING Inven tor; Le om J Gold beT b @w m y H is Attorney.

Patented Mar. 27, 1951 UNITED STATES PATENT OFFICE ALTERNA'I-flNG-CURRENT ELEQIRO- MAGNET WITH ARMATURE Leon J. Goldberg, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July 26, 1949', Serial No. 106,917

1- Claim. 1

This invention relates to alternating current electromagnets, and more particularly to alternating current electrcmagnetsof the shaded pole type. The principal object of the invention is to provide an improved type of construction for such electromagnets.

Shading coils commonly are used in the pole faces of alternating current electromagnets to provide a shift in time phase of a portion of the magnetic flux in order to' produce a continuous pull for attracting and holding an armature. In order to provide such a shading coil, the magnetic path is split and one part of the magnetic path. is surrounded with a conducting loop. The presence of such a loop, because of the current which is induced in it, produces an additional component of magnetic flux in the core of the electromagnet which results in a time delay in the main flux in the portion of the magnetic circuit which the shading coil encircles, thuscaus= c ing the magnetic flux in this portion to pass through zero at a later point in the cycle than the flux in the other portion. When the pull due to the magnetic flux outside the loop is zero; there is a finite pull by the flux within the loop, and when thepulldue to the-magnetic flux within the loop is zero, there is a finite pull by the flux outside the loop; thus, a continuous magnetic pull is provided whereby chattering or vibration of the armature is minimized.

The magnetic cores of alternating current electromagnets are usually laminated to prevent ex' cessive eddy currents in the cores. I-Ier'etofore, in the construction of a magnetic core having a shading coil in a pole face thereon, it has been customary to provide a recess in the pole face perpendicular to the plane of the laminations. In this. recess. is located a portion of the conductive loop which. encircles a part of the magnetic path to form the shading coil. This construction is entirely satisfactory for holding an armature or other member once it has been attracted to the core; however, it has been found that such construction may cause the armature to stick, or not to retract immediately when ex citation is removed from the electromagnet, particularly if there is good magnetic contact between the core and the armature, this eifect being due to the remanent or residual flux caused by the shading coil within the coil and completing its loop around the embedded portion of the conductor which forms the loop.

It is an object of my invention to reducev the remanence caused by the shading. coil and thereby to prevent the. armature from sticking because of this remanence.

Inv carrying out my invention in one form, I provide an electromagnet having a U-sha'ped laminated core. An armature, which bridges the ends i? the core in the closed position, is operexcitation coil l3;

2. ated by the magnetic attraction of the electromagnet. The end surface on each leg ofthe core has a recess across it parallel tothe plane or the Iam-inations. A single loop shading coil, which encircles a portion of the magnetic path inthat leg of the core, is positioned in each such recess. In order to minimize the residual magnetic flux encircling the part of the shading coil embedded in the recess, during the time immediately following the tie-energizing of the electromagnet; a separator of non-magnetic material is provided between two of the laminations abutting on each such recess. This introduces into the path of the magnetic flux component aroundthe coriduster forming the shading coil, reluctance of sufficient magnitude to reduce the remanent value of this-flux sufficiently to prevent the armature from stickingdue to suchremanent but not sumcient to prevent flux around the shading coil during energizationof the electfo' magnet from reducing the chatter of the arma ture.

For a clearer and more complete-understanding of my invention, reference should be had to the accompanying drawing, Fig. I of which is aside view in elevation of one embodiment of the inven tion; Fig. 2 is a sectional view along theline 2"'-2 of Fig. 1; Fig. 3- is a partial end- View of the core of the device shown in Fig. 1 along the line 3*, with the excitation coil and shading coil removed; while Fig. 4'- is aperspec'tive- View of the core if Fig. l with the excitation coil removed but with theshading coils in position.

Referring to Fig. 1- of the drawing, atypical device embodying my invention is designated generall'y'by the numeral Ill. The device lfl' has' a U-shaped stationary core, or frame portion H and a movable armature I21 On one leg of core i l is positioned a multi-t'urnalternating current Together, core' I I and excite tion coil 3 comprise an electromagne't which at: tracts" armature I-Z when coi'l' I"? is energized, and thereafter holds the armature in' the closed posi-' tion illustrated in Fig. as long as the electro-* magnet remains energized; Armature I2 isbiased by springs M or other suitable means which-- pull= armature 2 away from core I i when" the electro' magnet is de-energized. The pullof theelect ro magnet is strong enough to overcome the pull of springs M whencoil l 3 is enei'g-izedz' Armature l2, as best seen in Fig. 2, is composed of a plurality of fiat laminations l5 of mag netic material, preferably steel, separatedby lay as It; of electrical insulating material in order to minimize eddy currents the armature duets alternating magnetic flux. Gore H is composed principally of similar flat lam-i-nations H oi mag: netic material separated bylayers I-B oi elee't'ri cal insulating material In" the: bi'ght; portion o'f core H is a separator, or spacer I9 of non-mag netic material. Spacer i9 is perpendicular to the plane of laminations I! and covers the entire cross sectional area of core II, completely separating the core into two laminated portions. Each upper horizontal surface of the legs of core II is provided with a slot or recess 20, one of which is clearly shown in Fig. 3. Each recess 20 extends entirely across the end surface, or pole face of the core leg in which it is located parallel to the laminations IT. The legs of frame I I may be termed polar projections inasmuch as these legs contain the magnetic poles of the electromagnet formed jointly by frame II and exciting coil 13; likewise, the end surfaces of the legs of frame I i may be called pole faces.

Each leg of core H is provided with a nonmagnetic separator 2! of suitable thickness which abuts on recess 20, thus providing a magnetic separation between the portions of each leg of the core which lie on opposite sides of the separator 2|. Positioned in recesses 20, as seen best in Fig. 4, are shading coils 22 which are composed of a single closed loop of electrically conductive material such as copper. Each coil 22 encircles a portion of the core leg adjacent the end, or pole face against which armature l2 abuts, thus providing an additional component of magnetic flux due to the current induced in the shading coil, which has the effect of retarding the portion of the main flux encircled by coil 22, thereby reducing the tendency of the armature to chatter.

, When coil I3 is energized, the restraining force of springs 14 is overcome and armature i2 is attracted and held in engagement with core ii, inthe position illustrated in Fig. 1. This forms a magnetic circuit around the loop formed by members I l and l 2 in which oscillating magnetic flux is present, the oscillations being at the frequency of the alternating current in coil l3. When coil I3 is deenergized, the flux in the loop formed by core II and armature l2 decays gradually in accordance with the hysteresis characteristic of the loop. If spacer l9 were not present in the bight portion of frame H, the hysteresis characteristic might, under some circumstances permit an amount of residual flux sufilcientto cause the armature l2 to stick closed against the pull of springs l4 even after the removal of coil excitation. Spacer 59 increases the reluctance of the loop formed by members H and I2 sufiiciently that the magnetic flux in this loop always decays to a low enough value when coil I3 is de-energized that the pull exerted this residual flux is insuificient to cause sticking of the armature.

Shading coils 22 also tend to cause armature l2 to stick when coil I3 is de-energized. The principal function of coils 22 is to produce a component of flux in a separate path in order to change the time phase of a portion of the main magnetic flux and thereby to prevent chatter or vibration of the armature. The effect of this addition flux component may be to cause sticking of the armature under some conditions, these conditions depending on where on the voltage wave the circuit is opened. In order substantially to counteract this effect, I provide nonmagnetic laminations or separators 2! which create relatively high reluctance paths for the components of magnetic flux surrounding the portions of coils 22 which are embedded in recesses 20. This is illustrated by the arrow 23, which is shown in Fig. 2 encircling the embedded portion of one coil 22, it being understood that the direction of the flux is reversed during half 4 of each cycle. Nonmagnetic separator 21 is substantially perpendicular to the path of the flux below coil 22, so that the reluctance of this path is increased. This causes the component of flux around coil 2'2 to decay to a lower value when the electromagnet is de-energized, thereby preventing sticking or delayed opening of the armature due to such flux.

The essential feature of my invention is the introduction of additional reluctance in the circuit of the component of magnetic flux resulting from the shading coil, in order to prevent the sticking of the armature because of the residual flux in this circuit. It will be understood, however, that the use of a nonmagnetic separator 2| is not the only manner in which sufficientreluctance may be introduced into this circuit. For example, the presence of layers It and I8 of insulating material between laminations l5 and I1, respectively, may provide sufficient reluctance, thus making separator 2| unnecessary. It will be noted from arrow 23 in Fig. 2 that the path of this component of magnetic flux is substantially normal to the layers It and 18 above and below conductor 22; therefore, one or more layers l6 and one or more layers is are always present in this path, even in the shortest possible path for this component of flux, providing recess 20 in wider than the thickness of laminations l5 and H. Consequently, if layers It and I8 are provided with sufficient reluctance, they alone may supply the reluctance that is required.

It will be noted in Figs. 1 and 4 that shading coils 22 in this typical apparatus embodying my invention are disposed on the two legs of core ll so that they are symmetrical with respect to a pull axis extending vertically through the geometrical center of the upper surface of armature l2. The eifect of this is to prevent unbalance of the force necessary to pull armature l2 away from core II when coil I3 is de-energized. The unbalancing effects of the two shading coils counteract each other, both laterally and longitudinally, when the electromagnet is constructed in the manner illustrated, causing the pull axis to remain substantially centralized with respect to the upper surface of armature l2.

While I have illustrated and described one preferred embodiment of my invention, together with one modification thereof, additional modifications will occur to those skilled in the art. Therefore, it should be understood that I intend to cover, by the appended claim, all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

An electromagnet device comprising a U -shaped frame of laminated magnetic material in which the laminations lie parallel to a plane coinciding with the center lines of the legs of said U, a first nonmagnetic separator in one leg of said U parallel to said laminations separating said leg into two laminated portions, said first separator being a predetermined distance from one side of said U-shaped frame, a second nonmagnetic separator in the other leg of said U parallel to said laminations separating said other leg into two laminated portions, said second separator being an equal distance from the other side of said frame, a first recess in the end surface of said one leg parallel to said laminations, said first separator abutting the bottom of said first recess, a first shading coil positioned in said first recess surrounding the portion of said one leg lying between said recess and said first side, a second recess in the end surface of said other leg parallel to said laminations, said second separator abutting the bottom of said second recess, a second shading coil positioned in said second recess 5 surrounding the portion of said other leg between said second recess and said second side, an exciting coil positioned on said frame, a symmetrical U-shaped laminated armature operatively positioned adjacent the end surfaces of 10 said legs, the end surfaces of the legs of said armature arranged to abut respectively said end surfaces of the legs of said frame when said exciting coil is energized, and means biasing said armature away from said frame.

LEON J. GOLDBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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