US2596649A - Eddy current disk mechanism - Google Patents

Description

y 1952 w. BUTLER EDDY CURRENT DISK MECHANISM Filed April 5, 1946 M M. 7 3 s r I w u. n m e m 2 r n e 0 mg a mm k. t m 9 W b W Patented May 13, 1952 UNITED EDDY CURRENT DISK MECHANISM William Lawrence Butler, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 5, 1946, Serial No. 659,717

1 Claim. 1

My invention relates to eddy current disc mechanism, more particularly to direction responsive eddy current disc clutch mechanism, and has for its object a simple and reliable direction responsive clutch for use especially in the operation of electric switches.

The clutch disclosed herein i particularly useful with the electric switch mechanism disclosed in my copending application Serial No. 216,216, which is a division of the present application and is assigned to the assignee of the present application, however, this clutch is not limited in its adaptability to such a switch mechanism.

In carrying out my invention in one form I provide a shaft having rigidly mounted thereon an eddy current disc made of electrically conducting material. Also mounted rotatably on the shaft on opposite sides of the disc are two supporting disc members on which are mounted around their peripheries a plurality of small permanent magnets having their pole faces adjacent the disc. Also, the magnets are arranged in axially opposed pairs with unlike poles axially opposite each other. Rotation of the shaft and disc between the poles of the magnets produces eddy currents in the disc whereby a magnet torque is applied to the disc supporting structure for the magnets. The supporting structure is mounted for limited angular movement in each direction and is provided with an operating arm which may be arranged to actuate a single pole, double throw switch.

For a more complete understanding of my invention reference should be had to the accompanying drawing, Fig. 1 of which is a side elevation view with the enclosing casing in section showing a switch mechanism embodying my invention; Fig. 2 is an end view of Fig. 1 with the cover removed; Fig. 3 isa sectional view taken along line 33 of Fig. 1 looking in the direction of the arrows, Fig. 4 is a sectional view taken along the line 4-4 of Fig. 1 looking in the direction'of the arrows, while Fig. 5 is a sectional view of the eddy current disc.

Referring to the drawing, in one form of my invention I provide a metal enclosure r casing comprising a cylindrical portion I to the right hand end of which is integrally joined a rectangular portion 2. Mounted in the cylindrical portion I is a shaft 3 having its lefthand end as seen in Fig. 1 projecting from the casing for connection through a suitable coupling to a source of rotational energy such as the shaft of an electric motor to be controlled. The shaft 3 is mounted in a ball bearing 4 mounted in the lefthand end wall of the enclosure portion I, and a ball bearing which is mounted on a supporting 2 plate 6 secured by suitable screws 1 to the lefthand wall of the enclosure portion 2. Preferably, as shown, the shaft is supported by the bearings 4 and 5 with its axis of rotation coaxial with the center line of the enclosure I.

The shaft 3 drive an eddy current disc 8, which is rigidly secured to the shaft, between axially disposed permanent magnets carried by a supporting structure 9 rotatably mounted on the shaft. As shown, this supporting structure for the permanent magnets consists of supporting discs I0 and II mounted on central bearings I2 and I3 secured to the shaft 3. At their peripheries the two discs I0 and II are rigidly connected together by axially extending straps I4, I5, and I6 which extend across the periphery of the disc 8 in spaced relation therewith. It will be understood that the two discs I0 and II and the connecting members I4, I5 and I6 are made of a suitable non-magnetic and preferably light material such as aluminum.

As shown in Fig. 3, five small bipolar permanent magnets I! to 2 I, inclusive, are mounted on the disc I0 on the side adjacent the eddy current disc 8 and with the two poles of each magnet in closely spaced relation with the eddy current disc. The magnets are conveniently secured in place each by a screw 22 extending centrally through it and into a tapped hole in the disc I0. Preferably as shown, the magnets are equally spaced apart around the periphery of the disc II] with unlike poles of adjacent magnets adjacent each other. An identical set of five magnets, only three of which are shown and indicated by reference numerals 23, 24 and 25, are mounted on .the disc II in the same equally spaced relation with each other and with each magnet directly opposite axially a magnet on the disc I0. As shown, the magnet 24 is directly opposite the magnet I9 thereby to form a pair of axially oppositely disposed magnets. Moreover, the magnets of each oppositely disposed pair are arranged with their north poles, axially opposite their south poles, as indicated by the letters N and S on the magnets I9 and 24. This relative pole positional arrangement of the magnets provides for the maximum generation of eddy currents and the maximum torque.

As the disk 8 is rotated in the magnet field produced by the permanent magnets eddy currents are set up in the disc whereby a torque is produced tending to rotate the magnet supporting structure 9 in the same direction as the disc 8 is being driven. This rotation of the structure 9 is limited to a small angle by means of an operating member 26 made of electrically insulating material having one end secured to the disc H and extending parallel with the shaft 3 through a rotation limiting aperture 21 in the supporting plate 6. At its opposite end the member 26 is provided with a slot 28 through which extends the end of a flexible switch arm 29 the other end of which is secured to a bracket 30 mounted on a supporting block 3| made of a molded electrically insulating material. A switch contact 32 on the movable end of the arm 29 cooperates with stationary contacts 33 and 34 on opposite sides of the switch arm so as to engage one or the other of the stationary contacts in dependence upon the direction of the rotation of the magnet supporting structure 9. It will be observed that the switch arm and two stationary contacts form a single pole double throw switch.

The magnet supporting structure 9 and the switch arm are biased to an intermediate position with the switch arm midway between the two stationary contacts by means of two helical springs 35 and 36, as shown in Fig. 4, on the side of said support 3| opposite the switch arm. The springs are secured each at one end respectively to spring tension adjusting members 31 and 38 which are in turn secured by screws 39 and 4D to the insulating support 3|. The opposite ends of the springs are secured respectively to arms 4| and 42 mounted on pivots 43 and 44 secured to the molded support 3|. As shown in Fig. 4, the arms 4| and 42 are biased by the springs against a projection 45 extending between them and formed integrally with the support 3|. Extending between the righthand ends of these arms as seen in Fig. 4 is the operating member 26 whereby the springs bias the operating member, the magnet supporting structure and the switch arm in their intermediate positions shown. The right ends of the arms 4| and 42, as seen in Fig. 4, move between the walls Ma and 42a of the recess in the support 3| into which the ends extend.

In order that the lefthand ends of the arms as seen in Fig. 4 may overlap, the arm 42 is somewhat lower than the other arm so that its left end is free to move under the lefthand end of the other arm. A protuberance 45 is provided on the lower side of the arm 4| which rubs on the arm 42 thereby providing a minimum of friction between them. A similar protuberance, not shown, is provided on the upper side of the arm 42 which engages the lower side of the arm 4|.

For the purpose of latching the movable parts in their intermediate position shown when the driving motor is deenergized, a pivoted latch 41 is provided having its lower end as seen in Fig. 4 bent toward the right and extending between the arms 4| and 42 whereby pivotal movement of the arms is prevented. When the motor is energized the latch 47 is moved about its pivot 48 in a clockwise direction by a magnet 49 mounted on a bracket 50 which in turn is mounted on the support 3|, the pivot 48 being mounted on the bracket. The coil of the magnet has its terminals connected to connectors 52 and 53 on the front side of the support 3| as seen in Fig. 2.

To facilitate adjustment of the force applied by the spring 35, a cam 54 is provided having an aperture through which extends the screw 39. This cam engages a projection 55 on the member 31 which has a slot (not shown) for the screw 39. After loosening the screw 39, the member 31 may be moved about a pivot 56 at its lower end to adjust the tension of the spring 35, after which the cam is turned to a position to contact the member 31 and the screw 39 is then tightened. A similar adjustment is provided for the member 38 and spring 36. The pivot 56 is conveniently formed by extruding a hole in the lower end of the member 31 whereby a circular flange (not shown) is provided on its lower side, which flange seats in an aperture in the support 3|. It will be understood that adjustment of the springs adjusts the device for opening of the switch at a predetermined low speed of the shaft 3 whereby the driving motor is deenergized and coasts to a standstill.

The support 3| is secured to the plate 6 by means of screws 51 and 58 and by removing these screws the support with all of the parts mounted on it may be removed. In a similar manner the plate 6 may then be removed by removing the screws 1 after which the shaft 3 and the support structure 9 can be removed. A cover 59 is provided for the enclosure portion 2. The device may be mounted on a suitable support by means of screws or bolts passing through the apertures 60 .to 63 inclusive.

Electric conductors for connectin the coil 5|, the two stationary contacts, and the contact arm 29 in their control circuits are led in through an aperture 84 in the rectangular enclosure portion 2. The electric connections for connecting the switch for the control of a three-phase motor may be as shown in Fig. 3 of U. S. Patent No. 2,141,278 issued to Joseph W. Owens on December 27, 1938 for switch mechanism. In addition, the terminals of the coil 5| are connected directly across two terminals of the motor so that the coil is energized and the latch 41 moved to release the arms 4| and 42 only when the motor is energized. The latch is provided for the purpose of preventing the closure of the switch inad vertently when the shaft of the driving motor is turned manually, which is sometimes done for the purpose of adjusting the apparatus driven by the motor while the motor is deenergized. It will be understood that closure of the switch by movement of the contact arm 29 into engagement with either one of the stationary contacts effects the closure of one or the other of the starting contactors and energization of the motor.

The permanent magnets mounted on the supporting structure 5 preferably are made of a material having a high coercive force and high resistance to change in magnetic properties. One such material is an alloy of 12 percent aluminum, 25 percent nickel and 5 percent copper, the balance being mainly iron, such as described and claimed in Patent 1,947,274, issued on February 13, 1934, to William E. Ruder and Patent 2,027,997, issued on January 1, 1936, to Tokushichi Mishima.

As shown in Fig. 5, for the purpose of increasing the torque I provide tubular flanges 65 and 66 on opposite sides of the eddy current disc 8 and concentric with the axis of rotation of the disc. These flanges are each inside of its series of magnets, two of which, such as I8 and 23, are indicated in dotted lines. The flanges serve the purpose of providing a conducting path for eddy curcents of increased cross section, and therefore, decreased resistance, whereby the flow of eddy currents and hence torque is increased. In a typical device I found that these flanges on the disc increased the torque applied to the magnet supporting structure from ten to twenty percent.

A similar pair of flanges on the outer periphery of the disc outside of the magnets would serve to give a still greater increase in torque but, for manufacturing reasons, I prefer not to use such flanges on the periphery of the disc. Instead, I

mount the permanent magnets in such positions that they are inside the periphery of the disc, as shown clearly in Fig. 3, i. e., they are spaced from the periphery. The metal of the disc outside of the magnets serves to some extent to provide a path of decreased resistance for eddy currents whereby the torque is increased.

It will be noted that the disc 8 is of substantial thickness which also is for the purpose of providing a low resistance path for the fiow of eddy currents. In a typical device the disc was onequarter inch thick, while the distance between the two poles of each magnet, i. e., the width of the air gap between the two poles was also onequarter inch. The disc is preferably made of good copper having a conductivity ninety-five percent of the conductivity of pure silver. It will be understood that the thickness of the disc for maximum torque is a compromise between the air gaps between the poles of each magnet and between the poles of oppositely disposed magnets. If the thickness of the disc is decreased, oppositely disposed magnets will be closer together and, therefore, give more magnetic flux through the disc but, on the other hand, the decreased thickness of the disc gives increased resistance to the flow of eddy current. On the other hand, if the disc, and therefore the air gap between oppositely disposed magnets, is too great, the magnetic flux will tend to pass between the two poles of each magnet without passing through the disc, with resulting decrease in torque.

It will be noted that, because of the spacing between the magnets and the disc, the distance between the poles of oppositely disposed magnets is somewhat greater than the width of the slot between the two poles of each magnet, although the distance between oppositely disposed poles is very considerably less than the distance from center to center of the pole faces of each magnet.

The efiicient distribution of the magnetic field for the generation of eddy current is further increased by spacing the magnets apart, as seen in Fig. 3, at such distances that the effective distance between the adjacent poles of separate magnets is substantially the same a the distance between the two poles of a single magnet.

As shown in Fig. 5, I have provided a series of holes 61 in the web of the disc joining the flanges 65 and 66 with the hub 68. Preferably, six equally spaced holes are provided in this web. These holes serve the purpose of reducing the cross section of the disc thereby to reduce the loss by conduction of heat from the outer portion of the disc in which eddy currents are generated, whereby that portion is heated more quickly to a stable operating temperature providing the ultimate operating torque for which the switching device is calibrated. This rapid heating of the dis-c is desirable to prevent non-uniform operation in the event that the motor is plugged before the disc is heated to its calibrated temperature. In such case the contacts would open later because of the increased torque at the lower disc temperature with undesirable control of the motor. It will be understood that the copper disc has a positive temperature coefficient of resistance with higher resistance and decreased torque at the higher temperatures.

I have also found that increased torque is provided by arranging each magnet as seen in Fig. 3 with the centers of both of its poles lying on a circle whose center is the axis of rotation of the disc, 1. e. equidistant from the shaft. This arrangement gives the greatest possible torque 6 about the axis of rotation. At high speeds the torque is limited by the leakage of flux directly between the two poles of each magnet.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made and I therefore contemplate by the appended claim to cover any 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 eddy current disc mechanism comprising a shaft mounted for continuous rotation, a flatly disposed eddy current disc secured to said shaft for rotation therewith, a movably mounted supporting member arranged for limited rotation about the rotational aXis of said shaft, a plurality of bi-polar permanent magnets mounted on said supporting member in equally spaced relation with each other on each side of said disc, said magnets being constructed each with its poles spaced apart a distance substantially equal to the thickness of said disc, the centers of both poles of the magnets on one side of said eddy current disc coinciding approximately with a circle having its center on said axis and the centers of both poles of the magnets on the other side of said eddy current disc coinciding approximately with a circle of the same diameter as said first circle and also having its center on said axis, the magnets on each side of said disc having unlike poles adjacent each other and the distance between adjacent poles of separate magnets being substantially the same as the distance between the two poles of a single magnet, and the magnets adjacent opposite surfaces of said disc being arranged with unlike poles directly opposite each other on opposite sides of said disc in a direction parallel with said axis.

WILLIAM LAWRENCE BUTLER.

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

UNITED STATES PATENTS Number Name Date 446,488 Waring Feb. 17, 1891 568,046 Spratt Sept. 22, 1896 653,424 Lunt July 10, 1900 847,597 Onsum et al Mar. 19, 1907 908,707 Steckel Jan. 5, 1909 912,504 Steckel et a1 Feb. 16, 1909 1,058,885 Meyer Apr. 15, 1913 1,222,720 Bijur Apr. 17, 1917 1,756,671 Alden Apr. 29, 1930 1,960,915 Morse May 29, 1934 2,125,055 Taliaferro July 26, 1938 2,141,278 Owens Dec. 27, 1938 2,206,696 Hall July 2, 1940 2,209,368 Whittaker July 30, 1940 2,263,264 Duwe Nov. 18, 1941 2,293,748 Johnson Aug. 25, 1942 2,298,521 Uehling Oct. 13, 1942 2,300,773 Cornwell Nov. 3, 1942 2,361,239 Ransom Oct. 24, 1944 2,443,623 Koenig, Jr June 22, 1948 2,465,932 Romine Mar. 29, 1949 2,470,928 Halter May 24, 1949 FOREIGN PATENTS Number Country Date 28,845 Great Britain of 1910 107,144 Great Britain Apr. 23, 1939

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