US2922088A - Electromagnetic device - Google Patents

Description

Jan. 19, 1960 J. F. DRIES ELECTROMAGNETIC DEVICE Filed June 7. 1957 INVENTOR. Jerome [fir/e5 ATTORNEY 2,922,088 ELECTROMAGNETIC DEVICE Jerome F. Dries, Hales Corners, Wis., ass'iguor to Cutler- Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application June 7, 1957, Serial No. 664,377 4 Claims. (Cl. 317-165) This invention relates to electromagnetic devices and particularly to electromagnetic devices which may be employed as an actuator for a control means.

Devices of this type generallyhave a low value of pull in the armature open position and a very steep rise in pull just prior to armature sealed position. A low value of pull in the open armature position is undesirable from a standpoint of low voltage pickup, and a high sealed pull is undesirable for a quick release from sealed These objects are attained by an electromagnetic device which includes a magnet frame having a core, an energizing coil mounted on the core, a convex surface on the 'frame spaced from the core and an armature mounted on-the frame for rolling movement on the convex surface toward the core when the coil is energized.- Biasing means are provided which acts on the armature to move the armature away from the core when the coil is deenergized. The convex surface is related to the core and armature so that contact between the armature and convex surface moves nearer the core and away from the biasing means acting on the armature as the armature moves toward the core. The length of the moment arm with which the magnetic force acts on the, armature decreases and the length of the moment arm with which the biasing means acts on the armature increases as the armature moves toward the core, thereby reducing the ratio of energy available to move the armature at or near sealed position to that available to move the armature at open or unsealed position for an electromagnetic device of given capacit The rolling contact between the armature and frame provides a closed magnetic path between the two parts. An increased pull results.

Means including a pair of non-magnetic links pivotally connected between the frame and armature are provided for supporting the armature on the frame and to allow the armature to roll freely on the convex surface toward and away from the core. There is little or no load carried by the links thereby minimizing friction between the moving parts.

Other objects and advantages will be pointed out in, or be apparent from the specification and claims, as will obvious modifications of the one embodiment shown in the drawings, in which:

Fig. 1 is a view in side elevation of an electromagnet embodying the present invention showing the armature in sealed position;

United States Patent Fig. 2 is a top plan view of the electromagnet shown in Fig. l;

Fig. 3 is a rear elevation view of the electromagnet shown in Fig. 1;

Fig. 4 is a view similar to Fig. 1 but with the links removed and the armature in a position intermediate that between open and sealed positions; and

Fig. 5 is a view similar to Fig. 4 but with the armature in unsealed or completely open position.

Referring now to the drawings in detail, the electromagnet includes a U-shaped magnet frame 10 preferably of magnetic ingot iron having a base portion 12 and upstanding legs 14. A cylindrical core 16 preferably of magnetic ingot iron with windings or coil 18 is mounted on base 12 between legs 14 by a screw 20 extending through a countersunk opening in base 12 and threaded into the lower end of the core.

An armature 22 of a suitable magnetic material such as Armco metal is mounted for rolling movement toward and away from core, 16 on convex surfaces 24 formed on the upper edges of arms 14 of the :frame. The armature is supported in position on the convex surfaces by a pin 36 fastened by silver soldering or other suitable means to the rear edge of the armature and extending beyond the sides thereof. Pin 26 is pivotally connected to the frame by links 28 of non-magnetic material and pins 30 fixedly secured in openings in the upper portions of legs 14 and extending outwardly therefrom. Links 28 are mounted between pin 26 and pins 30 by openings at either end of the links through which the ends of the pins extend. Cotter keys 32 are fitted in the ends of the pins to hold the links in assembled position.

The load of the moving armature is carried by the convex surfaces on the frame so there is little or no load carried by the links thereby eliminating much of the friction normally present in devices having an armature pivoted in a fixed bearing. Links 28 are made from non-magnetic material to eliminate magnetic attraction between the links and the pins and frame to thereby further reduce friction between the moving parts.

The curvature of convex surfaces 24 is such as to eliminate or reduce to a negligible factor any sliding between the armature and frame as the armature rolls on the convex surfaces under the guiding influence of pivotally mounted links 28. The curvature may be constructed by well known principles used in the design of gears. In the embodiment shown in the drawings, the constructed curvature approaches very closely the arc of a circle so for facilitating manufacture of the frame the curve is made as an arc of a circle havinga radius R.

The armature is biased for movement away from core 16 by coil spring 34 connected between pin 26 (at cut-out portion 35 inv armature 22) and lug 36 on horizontal extension 38 of the base portion 12 of the frame. An inverted L-shaped stop member 40 rigidly mounted on frame 10 by off-set bracket 42 fastened to legs 14, limits the movement of armature 22 away from core 16 (Fig. 5) under the bias of spring 34.

Fig. 5 shows the electromagnet in the open or unsealed position with armature 22 engaged by the stop 40. In this position the armature contacts convex surface 24 (for purposes of this explanation reference is made to only one convex surface on one leg of the frame) at point '(axis) P. In the open or deenergized position the spring 34 acting on the armature produces a moment about point P equal to the force component F times the distance y. This moment is sufficient to lift the armature from a horizontal position to that shown in Fig. 5. Upon energization of the coil, a magnetic force is produced by the coil which acts on the armature. The component F of such force times the distance x less to the rollingmovementof the armature on such surface.- The electromagnet exerts a pull on the armature represented by the, component F jtimes distance x less the component F times the distance y, (although the springcomponent F increases slightly as the armature moves towards the core it is considered constant for purposes of this explanation. Component F is greater than component F because the armature is closer to the core. Howeven'the distance x is less than the distance and the distance 5 is greater than the distance 3/. Therefore, .the increased force acting on the armature is compensated either wholly or partially by the decreased moment arm x; andthe increased moment arm y Fig. 1 shows the armature-inclosed or sealed position with the point: of contact moved. up to point (axis) B In this position the-force F acts on the armature at a distance x from the point P The work or energy available to movethe armature in this position is equal to F times x less F times y Here again the force F v isgreater than forces F and F (Fig. 4 or 5), but the moment arm x has been further reduced and the moment arm y has been further increased to reduce or neutralize the effect of the increased magnetic force (F exerted on the armature as it moves toward the core. I

From the above description it is clear that as the armaturemoves from open to closed position the distaricefrom the axis of rolling contact and the force acting on the'armature is gradually reduced and the distance between the-spring force and the axis of rolling contact is correspondingly increased. This reduced moment arm of the magnetic force and increased moment arm of the spring forcetends to level out the steep rise in energy or work available to move the armature as it moves toward the coil. Thus, the pull or energy available to move the armature from open position is increased over that of conventional constructions providing improved operation from the standpoint of low voltage pickup. Similarly, the relatively low value of pull at the sealed position reduces the elfect of residual magnetism and increases the effective force of the return spring to provide a quickreleaseof the armature from thesealed position Y 1 r arrangement also provides the desirable feature of eliminating the air gap at the pivoted joint between the armature and frame generally present in conventional'constructions. The rolling armature is in con tinuouscontact with the frame and thereby maintains aclosed magneticpath for the magnetic lines of force to thereby increase the magneticpull between the core and armature. V

Although but one embodiment ofthe present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

I claim: 7 V

1. In an electromagnetic device, a: magnet frame having a core, an energizing coil mounted on said core, a

convex surface on said'frame' spaced from said core, anarmature mounted on said frame for rolling movement on said convex surface toward said core when said coil is energized, biasing means acting on said armature to move said armature away from said core when said coil is deenergized, said convex surface being related to said core and biasing means so that the contact between said armature and said convex surface moves nearer said core and away from said biasing means acting on said armature as said armature moves toward said core, and means for supporting said armature on said frame topermitjsaid armature to roll freely on said convex surface toward and away from said core, said means including no other contact between said armature and said frame except said contact between said armature and said convexsurface which moves nearer said core andaway from said biasing means acting on said armature as said armature moves toward said core. 7

2. An electromagnetic deviee according to claim 1 in which said supporting means includes a pair of links pivotally connected between said armature and said frame; 3.fAn electromagnetic device according to claim 2 in which said links are'of non-magnetic material and are pivotally connected to said armature by means of a pin fastened along one-edge of said armature.

4. In an electromagnetic device, a magnet frame having a core, an energizing coil mounted on said core; an

I armature mounted for swinging movement toward said core when said coil isenergized, biasing means acting a on said armature for moving said armature away from said core whensaid coil is deenergized, means for reducing the length of the moment arm with which the magnetic force acts on said armature and for increasing the length of the moment arm with which the biasing force actson saidarmature as said armature moves toward saidcore, and means'including a pair of links pivotallyconnected between said armature and said frame for supporting said armature'on said frame to' permit said armature to swing freely toward said core ,when said coil is energ zed. i I

a References Cited in the file of this patent UNITED STATES PATENTS, I

1,714,336 Yaxley May'21', 19 29 2,120,178. Hausrath June 7, 1938 i i FOREIGN PATENTS I l 695,555 Germany Aug; 28, 1940' 822,407

Germany Nov. 26,1951

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