US3365598A - Eddy-current apparatus including a magnetizable metal facing - Google Patents

Description

Jan. 23, 1968 R JAESCHKE 3,365,598

EDDY-CURRENT APPARATUS INCLUDING A MAGbLETIZABLE METAL FACING Filed Aug. 31, 1964 2 Sheets-Sheet l FIGI.

3,365,598 EDDY-CURRENT APPARATUS INCLUDING A MAGNETIZABLE METAL FACENG Ralph L. .llaeschlre, Kenosha, Win, assignor to Eaton Yale & Towne Ina, a corporation of Ohio Filed Aug. 31, 1964, Ser. No. 393,147 3 (Ilaims. (Cl. 310105) ABSTRAT OF THE DISCLOSURE Eddy-current apparatus comprising coaxial relatively rotary polarizing field and ferro-magnetic inductor members separated by a distance determining a circular magnetic gap. The inductor at the gap is faced with a magnetic material. This magnetic material has wear resistance and corrosion resistance greater than that of iron. Its electrical resistance is less than that of iron. The preferred magnetic material for the layer having these properties is nickel. In general, the nickel or other appropriate material should also have an electrical resistance at 20 C. in the range of approximately to 8 micro ohm centimeters (with 6.8 preferred). The thickness is in the range of approximately .005 to .030 inch, with .010 inch preferred for a machine having a running gap in the range of approximately & to A2 inch.

Among the several objects of the invention may be noted the provision of eddy-current apparatus of the class described, the eddy-current inductor of which is improved at the face of its magnetic gap so as to obtain superior torque-transmitting functions over a wide range of slip speeds and which will have the subsidiary advantage of being corrosion-resistant. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the constructions hereinafter described, and the scope of which will be indicated in the following claims.

In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated,

FIG. 1 is an axial section of an eddy-current coupling embodying the invention;

FIG. 2 is an enlarged fragmentary cross section taken on line 22 of FIG. 1; and

FIG. 3 is a chart illustrating certain torque-slip-speed functional relationships.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawmgs.

The invention is an improvement upon apparatus such as shown, for example, in my United States patent 2,971,- 105.

Various facings have been proposed for the surfaces at the magnetic gaps of electrical machines for providing resistance against corrosion by coolants employed in their magnetic gaps, or for providing wear resistance in those of such machines which, without the use of eddy currents, employed magnetic particles in the gaps. The selection of facings to meet these requirements has not resulted in improvements in the torque vs. slip-speed functions of such machines and in many cases has resulted in interior functions in that regard. According to the present invention, useful primarily in eddy-current machines, an inductor facing on the eddy-current inductor is employed which greatly improves the stated functions, while at the same time providing protection against corrosion.

Referring now more particularly to FIG. 1, there is shown (for purposes of illustration) an eddy-current slip 3,365,538 Patented .ian. 223, i968 coupling of known type to which the invention has been applied. This comprises a casing 1 formed by abutted pole rings 3 and 5 which support an annular field coil 7 and end bells 9 and 11. The end bells 9 and 11 respectively contain bearings 13 and 15, surrounding coaxial driven and driving shafts 17 and 19, respectively. Keyed to the driven shaft 17 is a magnetizable (iron or steel) polar field rotor 21 carrying peripherally disposed and axially extending pole-forming teeth 23. The ends of these teeth or poles face the inner surface of a two-piece ferromagnetic (iron or steel) drum 25 across a running gap 27. This running gap 27 is made as small as possible consistent with maintaining safe clearance. A gap of from to /8 inch is typical. The drum 25 is internally cylindrical. The two sections of the drum 25 are joined by a welded ring 2 (preferably nonmagnetic) in which are suitable radial openings. The outside cylindrical portions of the drum 25 face continuous internal cylindrical surfaces 29 and 31 of the pole rings 3 and 5 across small gaps 33 and 35, respectively. The inside portions of the drum 25 are, according to the invention, faced as shown at A with a material to be particularized below.

When the coil 7 is magnetized by applying current thereto through suitable wiring (not shown), a toroidal magnetic flux field passes through the members 3, 5, 25, 23 and in doing so crosses the gaps 2'7, 33 and 35. The peripheral distribution of flux in the gaps 33 and 35 is homogeneous so that no coupling torque is transmitted across gaps 33 and 35. In the gap 27 the flux is bunched or concentrated at intervals by the pole-forming teeth 23. Therefore, upon relative rotation of the pole member 21 and the drum 25, the sweeping action of flux-"leld concentrations will induce eddy currents in the drum 25. Induction of these currents is strongest near the inner surface of the drum. The eddy currents produce a reactive magnetic field with the fields from the poles 23, to effect a driving slip coupling therebetween.

The drum 25 is supported at one end upon a spider 37 carried upon bearings 39 in the end bell 9. The other end of the drum 25 is supported upon a disc 41 attached to a flange 43 of the drive shaft 19. Shafts 17 and 19 are maintained in alignment by means of a pilot bearing 45. Coolant such as water is introduced through an inlet 4. Part of the coolant progresses as shown by the lower line of curved darts L through the drum 25, then passing along the poles 23. It then escapes through ports 6 into a space 8 from whence it passes to an outlet 10.

Another part of the coolant, as illustrated by the upper line of darts U, passes around the drum 25 through the magnetic gap 35 to the space 8 and then out through said outlet 10. Shaft seals and lubricating means such as shown, or the like, are provided for various bearings but require no detailed discussion, being of known type and function. A control generator 12, belt-driven from the shaft 17 as shown, is employed in connection with the electrical circuit for exciting the coil 7. This serves as a speed control by controlling the intensity of the toroidal field around the coil. Such controls are conventional and further description will not be required.

The invention relates to the character of the inner face of the drum 25 which defines the outer part of the gap 27 opposite the ends of the poles 23. In the past, such facings have been variously constructed. For example, the sur face was sometimes left bare, thus presenting an iron or steel face, with the result in operation such as shown by the curve B in FIG. 3. Curve B displays torque which rises with increased slip and then continues more or less horizontally. While it is a satisfactory type of curve as to shape, it is amenable to improvement by use of known copper facing on the inside of the drum, with the result such as shown by the curve C on FIG. 3, formed by short and long dashes. This has increased the torque transmitted at lower slip speeds but has decreased them at higher slip speeds, as indicated. The reason for this is that copper, being nonmagnetic, in effect increased the magnetic gap with the concomitant requirement of a higher magnetomotive force required to drive the magnetic field across the gap. At higher slip speeds, this higher magnetomotive force was rapidly offset with the drooping results shown by the right end of curve C. Copper, although resistant to corrosion (as compared to iron), is soft and therefore not as effective as iron to inhibit abrasion by any foreign particles that might be in the coolant.

Difiiculties were sometimes encountered in plating copper directly to iron or steel, and it was former practice to underlay the copper facing with a nickel flashing or the like to form a better bond between the copper and the iron. This resulted in a torque vs. slip-speed curve such as shown by curve K, which fairly closely follows the curve C. Thus this copper-nickel arrangement does not significantly change the drooping characteristics of the torque curve. This is apparently for the reason that it does not reduce the effects of the nonmagnetic inner face of copper in increasing the magnetic gap.

I have discovered that if nickel is employed as the facing A, great improvement is effected in the torque vs. slipspeed curve as shown by curve N on FIG. 3. This closely follows the improved features of curves C and K in the lower slip range but does not fall off in the higher slip range. Thus curve N is substantially horizontal over a wide range of slip speeds in which the curves C and K droop. It is also higher than curve B throughout the entire slip range.

The use of nickel for the inner facing of the inductor drum 25 is shown at A. I have found that an appropriate range of thickness of the facing A is approximately .005 inch through .030 inch. The thickness employed on a machine such as shown in FIG. 1 and which supplied the data for FIG. 3 was .010 inch for the nickel.

Reasons for the improvement are apparently as follows, although I do not wish to be bound by any theory of operation, the improved results being independent of the same. Nickel is magnetic. Therefore, its use as a facing on the inductor drum does not increase the magnetic gap beyond that of the so-called air gap between the ends of the teeth 23 and the inner face of the drum 25. The meaning of the term air gap is a gap sufficient to permit free running and may be in fact filled with a liquid coolant. The use of any nonmagnetic material at A has the deleterious effect of increasing the magnetic gap beyond that of the air gap. The magnetic gap is measured by the distance across which the flux field must extend without encountering magnetizable material. Thus (FIG. 2) if the facing A were nonmagnetic, the magnetic gap would be as indicated at 47. This is greater than the air gap indicated at 49. With the facing A composed of nickel, the magnetic and air gaps are the same, namely, as shown at 49.

In view of the above, it is apparent that the magnetic nickel facing reduces (relative to the use of nonmagnetic facing material) the magnetomotive force required to drive a given field from the poles 23 into the inductor 25. Therefore, according to curve N the torque transmission is greater than for curve B at all slip speeds. Moreover, curve N is level at high slip speeds. The reason for this (at least partly) is that nickel has electrical resistance which is lower than that of the iron of drum 25, although higher than that of any copper facing that might be used, as heretofore. Thus the eddy currents induce flow in lower resistance paths in the facing A than in iron and thus more eddy currents are available at higher slip speeds to produce torque. It is to be noted in this connection that most of the eddy currents in an inductor fiow quite close to the surface being swept by the concentrated magnetic fields. Thus the fact that the resistance of the nickel is lower than that of the iron is quite important to prevent droop of the curve N. I may be questioned why copper would not be better in this regard because it is a better conductor; but the difliculty with copper is that it is not magnetic and its effect of increasing the magnetic gap offsets whatever gains are obtained by its use as a lower resistance eddycurrent conductor on the inductor drum.

It will thus be seen that an important feature of the invention is the use of a facing such as A, all or a large por tion of which is magnetic rather than nonmagnetic. Nickel is such a material and it is of course to be understood that any other material having similar properties could be used. I have found that some tolerances in the resistance range for the facing A may be had, provided it is lower than that of iron, even though it may be higher than that of copper. The following table shows for two different temperatures comparative figures for resistances of iron, copper and nickel, these being measured in micro ohm centimeters. Although the metals upon which the table is based are pure, it will be understood that in actual practice inclusions of impurities or alloying materials would result in somewhat different resistances. Thus steel might have a somewhat higher resistance than pure iron. It will also be understood that the resistances of copper and nickel might also vary somewhat in practice, depending upon the amount of impurities or those additions therein. It is contemplated, however, that the relative resistances would be related as shown.

I have determined that a range of resistances desirable for the facing A would be on the order of from 5 to 8 micro ohm centimeters at 20 C. With the preferred nickel facing, the specific resistance is about 6.8 micro ohm centimeters. It Will be recalled that the desired thickness of the facing material is in the range of approximately .005 inch to .030 inch with .010 inch preferred.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Eddy-current apparatus comprising relatively movable ferromagnetic inductor and peripherally polarized field pole members having a running gap therebetween, means for producing a magnetic field extending through said members and across said gap, a facing on said inductor member forming one side of said gap, said facing consisting of nickel to establish a magnetic gap equal to that of the running gap.

2. Eddy-current apparatus comprising relatively rotary ferromagnetic inductor drum and peripherally polarized field pole members having a running gap therebetween, a field coil positioned to produce a magnetic field extending through said members and across said gap, a facing on said inductor drum member forming one side of said gap, said facing consisting of a iayer of a magnetizable metal which has an electrical resistance in the range of approximately 5 to 8 micro ohm centimeters at 20 C. and the thickness of which is in the range of approximately .()05 to .030 inch.

3. Eddy-current apparatus comprising relatively rotary ferromagnetic inductor drum and peripherally polarized 5 6 field pole members having a running gap therebetween References Cited in the range of approximately to /8 inch, 21 field coil UNITED STATES PATENTS positioned to produce a magnetic field extending through 2,447,130 8/1948 Matulaivtis et a1 said members and across said gap, a facing on said 2,971,105 2/1961 Jaeschke 310 105 inductor drum member forming one side of said gap, said 5 3,223 91 12 19 5 Sh f k et 1 31() 168 facing consisting of a single layer of nickel the thickness of which is in the range of approximately .005 to .030 ROBERT SCHAEFER: P r Exammerinch. H. O. JONES, Assistant Examiner.

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