US1590025A - Induction motor - Google Patents

Description

June 22 1926.

C. l. HALL INDUCTION MOTOR Filed June 20 1924 r r mf n t Z A s ,w H 6 2 5,0 flu w P! A Patented June 22,1926.

CHESTER I. BALL, FORT WAYNE, INDIANA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, CORPORATION OF NEW YORK.

mnucrron' MOTOR.

Application filed June 20, 1924. Serial No. 721,322.

My invention relates to improvements in electric motors of the induction disc type.

One object of my invention is to provide an induction disc motor of improved mechanical construction. Another object is to increase the torque and speed of this type of motor, and another object is to decrease the magnetic hum incident to this type of motor.

Although the novel features of my invention a e generally applicable to induction disc motors, the motor is particularly applicable for driving phonographs and the invention will be explained as for such use.

In carrying my invention into effect, I make the magnetic circuit of the motor from a light skeleton casting which constitutes the framework for'the motor. The shifting magnetic flux is produced by a plurality of shading coils per. pole so arranged as to obtain an unusually large distortion of the flux which cuts the disc. This distortion is further increased and the useless flux which ordinarily cuts the disc is decreased to a minimum by means of a novel magnetic shunt which diverts a portion of the flux away from the disc after it has passed through the shading coils. The result is that the flux that cuts the disc is very efiiciently used in producing torque and has an unusually small component perpendicular to the disc which decrease" the tendency of the disc to hum due to the magnetic pulsations therethrough.

The features of my invention which are believed to be novel andpatentable will be pointed out in the claims appended hereto. or a betterunderstanding of my invention reference is made in the following description to the accompanying drawings in which Fig. 1 shows a plan view of the lower portion of the motor, the upper section of the magnetic framework being removed and a portion of the disc being cut away to better expose the parts; Fig.2 represents a cross section of the motor taken on line 2-2 of Fig. 1; and Fig. 3 illustrates by way of comparison. the difference between a, shaded pole having a single shaded coil ,and one having a plurality of shading coils arranged according to my invention.

Referring now to Figs. 1 and 2, .in'the present embodiment I have represented the motor as being designed to drive anordinary disc type phonograph. The framework and magnetic circuit of the motor comprise two annular castings 10 and 11 arranged to fit together like the base and cover of a cylindrical box. The base portion has three integral pole pieces 12 rising from the skeleton floor and symmetrically arranged 'at the same distance from the center thereof. In the center of the floor is a step bearing 13 which supports the vertical shaft 14. The shaft 14 carries a worm wheel 15 for driving an adjustable speed governor 16 which is suit-ably supported in bearing lugs 17 and 18 integral with the casting 10. The shaft 14 also carries "the induction disc armature 19 and passes through a guide bearing 20 in the center of the upper casting 11.

The contacting surfaces of the castin 10 and 11 are machined and flanged as illustrated at 21 so as to fit together accurately and the two sections are held together by three screws, one of which is shown at 22. Lugs 23 are provided on the inner'wall of the casting 10 to receive these screws. Thev I upper casting has three integral pole pieces 24 depending from its lower side in alinement with the pole pieces 12 rising from the base and the disc 19, which is preferably made of copper, is arranged to rotate in the narrow air gaps thus formed.

The pole pieces 12 are preferably made hollow as illustrated so as to decrease the weight of the motor. The three pole pieces 12 are provided with energizing coils 25 and these three coils may either be connected in series or in parallel across the line. Preferably the three coils will be connected so as to simultaneously produce fluxes in the same direction. This connection and symmetrical arrangement of the pole pieces is in accord ance with the invention described and claimed in my copending application Serial No. 639,895, filed May 18, 1923, entitled Electric drive for phonographs. This arrangement is such that the forces which are perpendicular to the disc and which are produced by the currents set up in the disc reacting against the magnetic fields therequally balanced with respect through are e to the center line of the shaft 14, Consequently, there can be no resultant force which tends to tip the disc first in one direction and then in another direction. As more fully explained in my prior application, this arrangement substantially eliminates noise and vibration if the disc is made sufiieiently thick to resist bending by the forces in question.

B my present invention I have materially reduced the forces which are perpen dicular to the disc and at the same time increased the driving torque. Consequently,

1 it is not so essential that the disc be made V solid tops of the pole pieces 12.v The slots in which the shading coils are contained divide the pole face into four sections, A, B, C, and D, section A being unshadcd. section B being shaded by one coil, sgction C shaded by two coils, and section D by all three coils. Since each shading coil displaces the flux whichit encircles, it will be seen that the flux in section B lags behind the unshaded flux in section A; that in section C lags behind that in section B and that in section D lags behind that in section C, thus producing a progressive phase displacement of motor, and therefore its efiiciency, for two reasons; first, the torque is increased over the single shading coil construct-ion because of the fact that the individual poles corresponding to A, B, C, and D are brought closer together giving a shorter effective dis tance between poles for torque reactions; and second, the speed is increased because the total pole displacement is increased;

therefore the shifting field actually travels a greater distance during each cycle. This reasoning may be made clear by referring to the diagram in Fig. 3. In this figure 12 and 12 represent two poles, the first having a single shaded section B and the second three shaded sections B,C, and D. It will be clearly seen that the pole displacements PP, in the single shaded pole is much less than in the multiple shaded pole. From this point of view, it will be seen that during one cycle the flux shifts a greater distance int-he multiple shaded pole and therefore causes a higher speed of rotation of the disc.

Considering the diagram from the point of view of standstill torque, it is seen that the poles must react on poles in the disc through a distance proportional PP, in i2".

' If the shaded part P, be split up into smaller units placed close together as B, G, and D in pole 12 while the pole area and total shaded.

- coil sections are maintained constant, the

torque will be increased since the total flux 'view of disc vibrations.

will remain constant while theindividual poles will be closer together. Due to the fact that the attraction varies inversely as the square of the distance, the increased spacing between P and P, in pole 12 is more than compensated for by the much shorter spacing between the intermediate poles cor responding to A, B, C, and D.

The provision of a plurality of displaced individual shading coils as above described constitutes an important improvement in this type of motor. I have further improved the motor by the provision of a magnetic shunt 28. It will be seen from an inspection of Figs. land. 2 that the solid portions of the pole pieces extend slightly above the shading coils so as magnetic shunt 28 secured between the trailingpole tip and the side wall of the casting 10. This shunt is made of soft iron and is preferably keyed into the part D of the pole piece and secured to the frame 10 by means of a screw 29 threaded into a lug 30 in the wall 10. This shunt thus connects the part D of the pole piece above the shading coils with the lower casting forming a parallel path for a portion of the main coil flux which does not cut the copper disc 19. All of the flux which traverses this shunt circuit is effective in creating currents in all three shading coils which in turn causes a greater phase displacement of the flux cutting the- Without the shunt, the currents in the shading coils must be induced by flux which cuts the disc and While the resultant shading coil-effect will be greater than with a single shading coil, it will be less than with the shunt for two reasons; first, the shunt increases the total useful flux because it decreases the resultant-reluctance of the flux circuit which is now partially across the air gap cutting the disc and partially through the shunt treading all the shading coils; and second, while the flux cutting the disc is not greatly reduced, it is progressively lagged to a greater extent than before because of the increased current in all the shading coils. The resultant direction of the force acting upon the disc due to the reaction between the flux cutting the disc and the currents set up by this flux is now more nearly parallel to the disc and increases the rotative torque and efliciency of the motor and decreases the component of force perpendicular to the disc which is not effective in producing torque and which is detrimental from the point of It may be stated that the resultant effect of this arrangement is to shunt a large proportion of the detrimental component of the flux from the disc which is not efiective in producing torque at the same time increasing the torque creative the flux which cuts the disc is more efiective to cooperate \vitha small in creating torque than with the usual shading coil arrangement, the amount of flux nece'ssary to cut the disc may be decreased proportionall which, in turn, has the beneficial result in ecreasing the tendency of the disc to vibrate and hum. To obtain the best results, the character of the shunt 28 should be properly proportioned to the remainder of the design in any particular case. For

through which said armature is arranged example, if'the air gap through which the disc rotates is increased, the reluctance of the shunt should be increased, for instance, by decreasing its cross section or its permeability.

'In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof; but I desire to have it understood that the apparatus shown and described is only illustrative and that the invention may be carried out by other means.

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

1. An induction motor having a rotatably mounted armature of conducting material, a magnetic member having an air ap to rotate, an energizing winding for said magnetic member, and a plurality of individual shading coils on said member adjacent said air gap for producing a progressive shifting of the flux in the air gap.

2. An induction motor having a rotatably mounted armature of conducting material, a magnetic member having cooperating pole faces on opposite sides of said armature for one of said producing an alternating flux therethrough, 40

an energizing winding for said magnetic member, and a plurality of individual shading coils arranged one within the other on pole faces for producing a pro-.'

gressive shi armature.

3. An induction motor having a rotatably mounted disc armature, a magnetic member provided with an air gap through which said armature is arranged to rotate, an energizing winding on said magnetic member for producing an alternating flux through said air gag transversely of said disc armature, a s a ing coil on said magnetic member adjacent the air and means for diverting a portion 0 t e flux threading only said shading coil away from the air ting of the flux throughsaid up. y g 4. An induction motor having a rotatably mounted armature of conducting material, a mag'petic member provided with an air gap t rough which said armature is arran (1 to rotate, an energizing winding for sai magnetic member for producing an alternating flux. through the air gap, a plurality of shading coils on said ma etic member'adjacent the air gap for prmfiibing a progressive shifting of the flux in the air gap' and a magnet shunt for diverting a portion of the flux threading all of said shading coils away from the air gap.

5. An induction motor having a rotatabl mounted armature of conducting material: a magnetic member having cooperating ole faces on opposite sides of said armature or producing an alternatin flux therethrough, an energizing win 'ng for said magnetic member, a plurality of shading coils on one of said pole faces arranged one within the other and enclosing different areas of said Pole faces for producing a progressive shi ting of the flux through said armature and a magnetic shunt for diverting flux from the area of said pole face in closed by all of said shading coils so that it does not ass through said armature.

6. An indhction motor provided with a short circuited armature and a single base field member having an ener 'zing po e adjacent said armature for pro ucing an alternating field therethrough, the pole face thereof being progressively shaded from one side to the other in the direction of rotation and means for shunting flux from the most heavily shaded portion of said pole face away from said armature.

7. An electric motor of the induction disc type comprising a magnetic circuit formed by a air of skeleton castings fitted together like t e base and cover of a cylindrical box, the castings having symmetrically arranged internal pole pieces integral with said castings and extending towards each other from the base and cover ture, the upper and ower pole pieces being separated and aligned to form air ga s, an energizing coil for each pair of align pole pieces, means for shifting the fluxes of said pole pieces within the air gaps, a vertical shaft rotatably mounted in the center of said structure, and a disc of conducting material on saidshaft extending into said air CHESTER I. HALL;

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