US2009188A - Alternating current magnet - Google Patents

Description

July 23, R N E 2,009,188

ALTERNAT ING CURRENT MAGNET Filed Oct. 14, 1933 FIG. FIG. 3.

INVENTOR A! ATTORNEY Patented July 23, 1935 PATENT OFFICE ALTERNATING CURRENT MAGNET Rufus A. Andrews, Mount Vernon, N. Y., assignor to Ward Leonard Electric Company, a corporation of New York Application October 14, 1933, Serial No. 693,594

8 Claims. (01. 175-338) This invention relates to alternating current magnets wherein a closed circuited path is provided for induced currents for the purpose of avoiding so called chattering or mechanical vibration of the movable part or parts.

The main objects of the improvement are to provide a form of construction and relationship of parts that will be of a simple character, require comparatively low manufacturing costs in material and labor, occupy small space, and ac-' complish its purpose eflectively and efficiently. Other objects and advantages will be understood from the following description and accompanying drawing.

When an electromagnet is excited by an alternating current, the attractiveforce on the armature varies from zero to a maximum, and returns to zero, twice during each cycle. Consequently, under the influence of any external force, such as a spring or gravity, the armature will alternately leave and return to the core with a frequency corresponding to that of the alternating current, resulting in vibration and considerable noise, or humming. .Thismay be largely overcome by some means for maintaining a flux continuously between the armature and core. It is common practice to use a shading coil or lag loop for this purpose. This loop embraces a portion of the core and has had the form of a single turn of copper, brass or similar-material, inserted in the endot the core. This low resistance closed circuited conductor has appreciable self-inductance which causes a phase difference between the flux passing to the armature by way of that portion of the cpre embraced by the lag loop and the flux passing to the armature directly through that portion of the core not so embraced. Consequently, there is no period when there is not a flux between the armature and the core. This results in an attractive force always being exerted between e armature and the core and reduction of vib tion andnoise.

A conventional practice has been to use a laminated or solid magnet core with a straight slot completely traversing the core face, adjacent to the armature, and of such size that one leg of the lag loop may be placed in it. The core face is thus divided into two sections, the centers of which are displaced relatively to each other and o to the axial center line of the core. The force of approximately equal to the center to center distance of the two sections. Unless the points of contact between the armature and the core are in a plane intersected by the line of action of both of the above forces of attraction, there will be resultant forces tending to rock or wabble the armature with a resultant noise of vibration. This rocking or wabbling effect may be reduced somewhat by careful-machining of the core and armature. In some cases two straight slots are cut across-the face of the core and two opposite sides of a rectangular shaped loop are placed in the two slots with the ends of the loop extending beyond the core. This gives a more symmetrical disposition of the fiux but requires careful and costly machine Work.

These prior forms of magnets are not eflicient or fully satisfactory in accomplishing their purpose. They are also objectional, not only on account of the refined machine work required, but also because the straight slot or slots for the loop have to be milled in a separate milling operation after the core is otherwise finished. Furthermore, the portion of the lag loop which extends beyond the core face prevents the magnet coil from being uniformly wound thereover and thus prevents the attainment of a compact form of structure and reduces the eificiency. Again, in some forms of magnets, it is desirable to insert a centrally located spring or a movable part and this cannot be done when the lag loop passes across or near the central axis of the core. By the present invention these various objections and disadvantages are overcome.

The accompanying drawing illustrates a preferred embodiment of my invention in a particularly advantageous form of electromagnet for a particular purpose. Fig. 1 is a vertical central section of a controlling magnet and associated parts; Fig. 2 is a cross-section of the movable element of the magnet on the line A-A of Fig. 1; Fig. 3 is a view similar to Fig. ,1 except that the ring loop is inserted in the face of the fixed core of the magnet, as distinguished from being inserted in the face of the movable element of the magnet; and Fig. 4 is a cross-section of the fixed core on the line BB of Fig. 3.

Referring to Fig. 1, the parts are embraced and supported by a U-shaped steel member I and riveted thereto are two spaced transverse steel members 2. At the bottom of the inverted U- shaped member I, is fastened a transverse plate 3 of insulating-material which carries the binding posts and supports the fixed switch contacts 4. These switch contacts are diametrically opposite each other. A dash pot 5, having a plunger 6, is supported in the upper part of the frame i and spaced from the top cross piece of the frame I. A check valve 5a is located in the end of the dash pot for permitting the plunger 6 to move down quickly when a downward force is exerted thereon. A stem or spindle i is secured at its upper end to the plunger 6. The spindle has an enlarged intermediate cylindrical portion I0 and at its lower end carries a cone 8 of metal which is insulated from the spindle by the insulating intermediate portion 9. The cone 8 is adapted to engage the contacts 4 when the spindle is raised to its upper position, as shown in Fig. 1. A cylindrical steel core ii, having a central opening, is riveted, or otherwise secured, to the lower transverse plate 2, the lower end of the core H extending within a central opening in the plate 2. A bridging cross plate i4 is riveted at its ends to the lower side of the lower cross plate 2 and has a central opening through which the spindle 1 passes. A spiral spring i2 encircles the spindle i and. extends between the enlarged portion ill of the spindle and the bridge plate It. This spring, by being supported at its lower end by the bridge plate tends to keep the spindle i and the dash pot 6 in their upper position and to keep the switch closed. The coil or winding M of the magnet is located between the two transverse plates 2 and is wound upon a tube E3 of insulating material extending between the central openings of the plates 2. The movable element of the magnet is in the form of a cylindrical steel plunger l5 having a small central opening through which the spindle 7 passes and a larger central opening at its lower end for the reception of the enlarged portion iii of the spindle. In the lower face of the plunger IS a circular concentric slot is cut for the reception of the lag ring I6. This lag ring is shown in the form of a short cylinder and is tightly forced into the slot so as to be firmly and permanently held therein. As shown in Fig. 2, a cylindrical concentric portion of the plunger I5 is embraced by the ring l6 and a cylindrical concentric portion of the plunger l5 envelops the outside of the ring l6. The ring is preferably made of copper but may be made of other conductive material.

When in the position shown in Fig. I, the cone 8 bridges the contacts 4 for the purpose of completing a circuit of some device which is to be controlled, the spring I! holding the parts in their upper position. When the magnet winding M is energized, the core I5 is magnetically drawn downwardly until it engages the fixed core II, the plunger 6 of the dashpot and the bridging contact 8 being moved downwardly by the core I 5 and causing the opening of the circuit to be controlled. As long as the winding M is excited, the parts will be held in their downward-position. When the winding M is de-energized, the spring I! will force the spindle and plunger 1 5 upwardly and cause the dashpot plunger to move against the compression of the air in the dashpot. After a certain time element, the bridging switch element 8 will engage the contacts 4. Thus when the magnet M is excited, the controlled switch will be opened quickly and held open until the magnet M is de-energized, when after a certain time interval, the switch controlled will again be closed.

In Figs. 3 and 4, the lag ring l6, instead of being" inserted in the face of the movable element i5, is embedded in the'upper face of the fixed element ii.

It will be appreciated from the foregoing, that by use of a circular lag ring located concentric with the axis of the core, any rocking or wabbling effect is avoided because the lagging flux and the fiux unaffected by the lag' ring are concentric and are uniformly distributed around the center and maintain an attractive force having the same center. Also, owing to the fact that the lag ring has no portions extending beyond the core, the magnet winding may be formed close to the core and thus be more emcient. Moreover, by placing the lag ring entirely within the contacting face of the core, the efilciency is increased because it is entirely surrounded on the inside and outside by the iron or steel and the leakage flux is reduced to a minimum.

This improved form of construction also permits the center of the core to be hollow for the reception of a spindle or counteracting spring, or other parts, without interfering with the location of the ring loop. In the particular application of this invention already described, it will be noted that an ample length of the spring i2 is provided so that within the range of movement of the plunger, the tension of the spring is not objectionably changed. It will also be noted that by reason of no projecting parts extending beyond the sides of the plunger or core, the air gap between the same and the cross plates 2 may be made very small which, of course, increases the efiiciency of the magnet. It will also be apparent that by making the lag ring concentric with the axis of the movable core, or :with the axis of the fixed core when placed therein, the machining of the cores may be accomplished in the least expensive manner, as the only machining necessary is to cut a circular slot in one end of the core at the time the core; is being turned in a lathe to its proper shape".-*Thus, by means of this invention, I am able to provide a magnet of a highly efficient type, compact in form, of low cost of manufacture and efiective in avoiding the ,noise of vibration of the movable element.

Although I have shown my improvement applied to a solenoid form of magnet, the invention may be embodied in other forms of magnets and have the ring loop embedded in the face of either the fixed or movable element of the magnet; and it will be understood that various applications and adaptations of the invention may be made without departing from the scope thereof.

I claim:

,1. The combination of a magnet winding, a movable cylindrical magnetic element within said winding, said element having a central recess in one end thereof, a spiral spring having one end seated in said recess for moving said element in one direction, and a closed conducting circular ring in the face of said end of said element and concentric with the axis of said element 2. The combination of a magnet winding, 9;

movable cylindrical magnetic element within said winding, 9. fixed cylindrical magnetic element within said winding, one of said elements having a central opening, a spindle passing through said and also having a central opening, a spindle passing within said openings, a spring encircling said spindle for moving said movable element in one direction, and a closed conducting circular ring in the face of one of the adjoining ends of'one of said elements and concentric with the axis thereof.

4. An electromagnet having a cylindrical form of winding and having a fixed magnetic element and a movable magnetic element, one of said elements being cylindrical and extending within said winding, a closed conducting circular ring in the face of the element extending within said winding, said ring being concentric with the axis of the magnet and enveloped by said winding.

5. An electromagnet having a winding and a fixed magnetic element and a movable magnetic element, and a closed conducting circular ring inserted in the face of one of said elements, said ring being continuously embraced on its outer side and on its inner side by portions of the element in which it is inserted.

6. An electromagnet having a winding and a fixed magnetic element and a movable magnetic element, a closed conducting circular ring inserted in the face of one of said elements and concentric with the axis of the magnet, said ring being continuously embraced on its outer side and on its inner side by portions of the element in which it is inserted.

'Z. An electromagnet having a winding and a fixed magnetic element and a movable magnetic element, one of said elements having a circular slot in its face concentric with the axis of said winding, and a closed conducting circular ring inserted in said slot and being continuously embraced on its outer side and on its inner side by the walls of said slot.

8. An electromagnet having a winding and a fixed magnetic element and a movable magnetic element, one of said elements having a circular slot in its face concentric with the axis of said winding, and a closed conducting circular ring inserted in said slot and being continuously embraced on its outer side and on its inner side by the walls of said slot and being also enveloped by said winding.

RUFUS A. ANDREWS.

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