US2428104A

US2428104A - Eddy-current apparatus

Info

Publication number: US2428104A
Application number: US540202A
Authority: US
Inventors: Winther Anthony
Original assignee: Individual
Current assignee: Individual
Priority date: 1944-06-14
Filing date: 1944-06-14
Publication date: 1947-09-30
Anticipated expiration: 1964-09-30
Also published as: FR925341A; BE464392A; GB607083A

Description

Sept. 30, 1947. A. wlNTHr-:R

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vEDDY-CURRENT APPARATUS Filed June 14, 1944 8 Sheets-Sheet '7 Sept. 30, 1947.

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W A. N* m Hm f W N/ /M/ A/ f J) i 4 w ///V/// m M m W I m Mlm w .M m 40| 0 Patented seat. 3o, 1947 EDDY-CURRENT APPARATUS Anthony Winther, Kenosha, Wis., assignor to Martin P. Winther, Waukegan, lil., as trustee Application June 14, 1944, Serial No. 540,202

12 Claims. (Cl. 172-284) This invention relates to eddy-current apparatus, and with regard to certain more specific features, to infinitely variable torque transmissions y of the eddy-current slip clutch type.

Among the several objects of the invention may be noted the provision of an iniinitely variable eddy-current transmission having a low-inertia driven member which may be rapidly accelerated and decelerated for driving devices such as for example, textile knitting machines, automotive vehicles and the like; the provision of apparatus oi the class described which may be excited far above normal rating and caused proportionally to produce increased torque above normal torque rating much higher than that obtainable heretofore; the provision ofv apparatus of the class described which operates with a relatively large reliable magnetic gap; and the provision of apparatus oi this class which is substantiallyqsmall-l er in size than apparatus of the general class proposed heretofore. Other objects will be in part obvious 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 exemplied in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims. In the accompanying drawings, in which are illustrated two of various possible embodiments of the invention,

Fig. l is a longitudinal section of one form of the apparatus;

Fig. 2 is a vertical section taken on line 2--2 of Fig. 1;

Fig. 3 is a vertical section taken on line 3--3 of Fig. 1;

Fig. 4 is a vertical section taken on line 4-4 of Fig. l;

Fig. 5 is a longitudinal section similar to Fig. ,-1 but showing another form of the invention;

Fig. 6 is a vertical section taken on line ,Q -S of Fis. 5;

Fig. 7 is a vertical section taken on line 1-1 of Fig. 5:

Fig. 8 is a vertical section taken on line ii--B of Fig. 5; i

Fig. 9 is a detailed section of a supporting spider used inthe Fig. 5 construction;

Fig. 10 is 9, right elevation of the supporting spider of Fig. 9; and

Figs. 11 and 12 are graphs showing certain torque-speed relationships.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Eddy-current slip clutches have heretofore been constructed with relatively moving (sometimes called slipping) driving and I,driven members composedof magnetic materials, one of which was sometimes provided with a thin copper or like facing in conductive relation thereto. field winding was used which generated a ilux iield interlinking these members.,n One of the members carried flux-concentrating poles and the other received concentrated flux from these poles and constituted an armature. The copper, when used, was generally on, and in conductive rela-` tion to, the magnetic armature. The relative motion (slip) between the members produced movements of concentrations of ux in the armature. These produced eddy currents in the armature which in turn produced mechanically reactive flux, through which torque was transmitted between the driving and driven members. The copper or other highly conductive, non-magnetic facings were used on the armature, in direct conductive contact therewith, and were for improving the production of eddyA currents and increased the desired reactive torque.

The same principles were employed in dynamometer constructions, which diier from slip clutches only in that the driven member has only a limited rotary motion and has for its purpose the transmission of torque to a stationary element with conversion of mechanical energy into heat, rather than transmission of mechanical energy. This point is here mentioned because it should be understood that the principles set forth in the present application may also be applied to dynamometer constructions, simply by making the driven member herein as a rocking stator.

These former constructions had driven meinbers of relatively high inertia and while satisfactory for certain services were not entirely the best for others, such as for example textile knitting machines, automotive drives, etc. For such applications they should have light driven members and should be small in size. In addition they should, besides transmitting their rated torque at low slip. also be able to transmit very high torque. for short periods at high slip. This is in order to produce any high acceleration desired. The present invention in addition to allowing for transmission of rated torque at rated output speeds with maximum efilciency, also permits f transmission of exceedingly high torque at low output speeds at less than maximum efiiciency but supplying the acceleration in many cases required.

Referring now more particularly to Figs. 1, 2,

3 and 4, numeral I indicates a'motor frame from non-magnetic, highly conductive material may be used for the drum. It is supported upon a magnetic rim I1 of a spider or driven transmis- `sion member I9. The legs of the spider are formed with webs 29 which act as fan blades. Several fastening means 2I in a single ring are used for bolting the copper drum I5 to the rim I1. This provides a single axial anchor for the drum I5, thus allowing it freely to expand and contract axially. In order further to hold the drum I5 to the rim I1, it is banded by means of helically wound wire 23 fastened at opposite ends to the rim I1, as indicated at 25. This wire prevents buckling without unduly interfering with axial expansion.

A hollow hub 21 of the spider I9 is bolted to a flange 29, the latter being welded to a driven shaft 3 I. The shaft 3| constitutes the power takeoi of the machine and it is between this shaft 3I and the drive shaft 3 that-a variable, torqueconverting slip coupling ls desired.

The shaft 3| is carried upon spaced

bearings

33 and 34 carried in an inner sleeve 32 of a housing be.l 35. A spacing sleeve 31 and collar 39- space the inner races of these bearings on the shaft 3|. An oil channel 4I in the bell 35, including a lubricant fitting 43, serves todeliver lubricant to the bearing 33. Labyrinth means 45 prevents this oil from running from the bearing into the rotary parts of the machine. Beyond the bearing 34 is an encasement 41 attached to the bell 35 which carries a shaft seal 49. Between the shaft seal 49 and the bearings 34 is a generator unit 5I, the rotor 53 of which is driven by the shaft 3| and the stator 55 of which is carried within the extension 41. This generator supplies the `*control current for certain field members to be described.

The bell 35 is attached by means of bolts 59 to a main frame 51. Radial openings 8i covered by means of a circular screen 63 allow inlet of air into one end of the machine. It will be noted from Fig. 3 that arms 55 are left between the openings. Inwardly tapered teeth 61 extend from a ring 69 which is welded to the. frame 51 as indicated at 1 I. The ends of these teeth clear the wire winding'23 of the copper drum I5.

Mounted in the frame 51, next to the

toothed ring

61, 59 is a stationary annular eld coil 13. n the other side of this field coil is a second stationary toothed ring 15 having inwardly extending teeth 11. The ends of these teeth also clear the copper drum I including the wire winding 23. Notches 19 are located adjacent to an inlet opening 8| through which wires are introduced, but are not shown. The wires serve the field coil 13 and another field coil to be mentioned.

At numeral 83 is shown a second stationary annular field coil supported in the frame 51 in the plane of the central portion of the teeth 1. Spacers 85 are shown as adjacent to the coil 83 and next to these are spaced, opposite, circular, radially laminar pole rings 81 and 89. The laminated characters of these rings inhibit the formation therein of any substantial eddy currents, but being of magnetic iron, they will transmit a magnetic field. The pole piece 89 is adjacent to the toothed ring 15 and the pole piece I1 has next to it a spacer ring 9| which holds in place a defiector ring 93 for controlling air cir- .culation.

The frame 51 is attached `to the motor frame I by means of bolts 95. It carries openings 91 covered by a screen 99 for the outlet of circulated air. 'I'he pole rings 81 include axial openings therethrough forA said air circulation. Their inner peripheries are spaced from the drum I5 byv means of air gaps.

Operation is as follows, assuming that the annular eld coils 13 and 83 are suitably energized from the generator unit 5I, or elsewhere. This energization causes toric iiux fields around said coils such as indicated by the dotted lines F--I and F-2 at the top in Fig. 1.

As to the coil 83, the toric iiux field F-I passes through the casing 51 (which is magnetic), the circular, laminar pole rings 81 and 89, twice through the non-magnetic but conductive copper drum i5 and through the teeth 1 of the drum 5. The spaced and tapered character of these teeth concentrates this toric flux field in concentrations at spaced intervals peripherally around the copper drum I5.

Thus if the shaft 3 be driven by the. motor I, the rotor 5 revolves the teeth 1 and causes progression of these ux concentrations through the copper drum I5. The concentrated effect of this field is to some extent dissipated upon entering the laminar pole rings 81 and 89, but not altogether. However, since the pole rings 81 and 89 are laminated radially, very few eddy currents are generated in them due to these partially dissipated moving flux concentrations. The drum I5 is made of copper in order to provide a higher conductivity than even solid iron, so that the passage of the flux concentration emanating from the teeth 1 will generate high eddycurrents in the drum. These induce reactive flux, which, with the flux emanating from the teeth 1, causes the drum I5 to be driven with some lag, depending upon the intensity of the flux field. Thus the amount of rotary slip is determined by the degree of energization of the field coil 83, which of course governs the flux density, upon which slip depends.

The thickness of the copper drum I5 may, for example, be from .0625 inch up to 1% of an inch or so. The sum of the air gaps on either side of the drum section may be of the same order. As a specific example, a copper drum thickness of .16 inch may be used with an inside air gap' between the drum I5 and the teeth 1 of .08 inch and an outside gap between the drum I5 and the laminated pole rings 81 and 89 o'f .08 inch. This` makes a total flux gap between the ends of the teeth 1 and the laminated pole rings 81 and 88 of .32 inch. Heretofore it was permissible to use air gaps of the order of only .025 inch because it was necessary to prevent dissipation of the flux emanating from the polar teeth before reaching the eddy-current surfaces. This made a construction with small gap tolerances which were difficult to maintain under high temperatures at heavy loads and high slip.

By means of the present invention, flux concentrations emanating from the teeth1 pass on through the low resistance, eddy-current structure of the copper drum I5, and pass on into the substantially non-eddy-current inner surfaces of the pole rings 81 and 89. These concentrations in passing through the merely conductive and non-magnetic drum I5 do not dissipate as much as they-would if the drum I5 were backed up by, and in direct conductive contact with, an ordinary iron inductor, as heretofore was the case with copper facings on iron inductors. In addition, the

polar rings

81 and 89 herein are substantially not inductors at all but simply close the magnetic circuit. The result is that currents are efficiently obtainable in the conductive Adrum I5 and consequently high reactive driving the ends of teeth 1 nearer to and including saturation for delivery of additional much higher torque from spider 5 to drum I5 under conditions of higher slip, as for example during acceleryation.

The

teeth

51 and 11 are fixed to the frame and I the flux field F--Z from coil 13 is therefore sta- Itionary. But it is concentrated at intervals by these teeth. This field passes through the magnetic drum I1, traversing also the wire and air gap. By energizing the coil 13, the toric flux field thus interlinking the drum I5 may be caused to exert a braking reaction on the driven elements attached to the drum I5. Thus the driven shaft 3I may be rapidly decelerated when required.

Some heating necessarily occurs 'in the drum I5 due to the eddy currents therein and this is disposed of by air circulation through the device. Air enters through the grill 83 and openings 8|. Some of it passes outside of the drum I5 within the teeth 61, coil 13, teeth 11, ring 89, coil 83, ring 81, thence under the baille 93 and out of the openings 91.

Another current of air passes around the righthand end of the copper drum I5 and passes through it, traversing the openings in spider I9 and the spaces between teeth 1 through the fan `blades II to be projected through the outlets 91.

Although air cooling is shown, by proper provisions therefor, the device can be either oil or water cooled if conditions warrant it.

In view of the above it will be clear that an important feature of the invention is the use per se of the independently movable copper-drum armature, which, so far as are concerned the torque transmitting elements of the machine, is not attached to any magnetic ilux circuit-forming means. The magnetic flux circuit-forming means for completing the magnetic circuit on the side of the drum I5 opposite the teeth 1 is composed only by the spaced, non-eddy-currentformi-ng inner polar surfaces of the rings 81 and 85.

It is to be understood that, although as shown, the fiux-concentrating teeth such, as 1 on the driving member may be internal with respect to the copper drum I5, these may be external and tapered radially inward with the associated fixed coil 83 on the inside of the drum along with the laminated

polar rings

81 and 89. This would simply be an inversion without change of essential principle.

`It is also clear that the copper drum could be made the driving element of the combination,

since it is only the relative movement between the drum and the flux-concentrating teeth that is necessary to obtain the reactive flux field for driving.

An important point to be noted is that the teeth 1 taper toward the non-magnetic, eddycurrent drum I5. This taper allows the ends of the teeth to operate at flux saturation under suitable excitation above normal of the field coil 83. On the other hand, the copper Inductor drum and the'fiux gaps associated with it are -of thicknesses which allow transmission of normal torque at low slip speeds at flux densities at the ends of the teeth which are substantially below saturation; and to transmit greater torques at flux densitiesfrom the teeth which are closer to or at saturation and obtainable by increased excitation of the coil I5.

Additional structural advantage accrues by making the

coils

13 and 83 stationary and mounting them on the frame 51.

'I'he Fig. il graph makes clear important results of the invention. In the ordinary application of a variable-speed transmission it is ncessary to have a low slip under conditions of normal torque transmission, so that for full speed conditions the device is able to transmit this normal torque with maximum eiiiciency. Thus if a minimum slip of 3 per cent is desired under full speed conditions, the normal excitation must be enough to produce this result. Heretofore this normal excitation was so close to flux saturation of the flux circuit that the maximum torque above normal available by added excitation could only be increased 2% times or so. In other words, the gain in torque due to momentary over-excitation was relatively small since saturation had been substantially reached under normal torquetransmitting conditions.

Fig. 11 shows curves A to F which are torquespeed curves at various excitations of the field coil 83 in apparatus of this class employing a 5 H. P. motor I. The horizontal dotted line G indicates normal torque required at minimum slip.

This is obtained, in the case of curve B, by means of excitation of 4 amperes at 14 volts. The coil 83 for furnishing the magneto-motive force is normally rated at 10 amperes at 35 volts, as indicated on curve F. 'I'his curve has a peak at about lbs. it. torque which corresponds to well over 600 per cent of normal torque obtained without over-excitation of the field coil.

Fig. 12 is a torque-speed graph under conditions of over-excitation which may be tolerated for short intervals. A normal torque line of 15 lbs. ft. is shown at G. The curves J to N show what torques are available at various speeds under various conditions of tolerable over-excitation. For example, the curve N shows 25 amperes of excitation, which is 21/2 times normal (compare curve F of Fig. 11). This curve N also shows a peak at 340 lbs. ft. torque, or, about 221/2 times the torque required to make the unit a commercial item at 1800 R. P. M. maximum speed. Stated otherwise, Fig. 1l shows that normal torque may be obtained at high output speeds (little slip) at very nominal excitation, meaning that a smaller machine than heretofore meets given normal torque conditions; and Fig. 12 shows that with very nominal over-excitation which may be carried for short times enormous torque gains may be expected. While the highest ofthese occur at output speeds which are lower, corresponding to increased slip values and lower efliciency, nevertheless these can be tolerated for short periods under accelerating conditions. For example, in a motor car, temporary high excitation could be tolerated during the high-torque acceleration period and then under normal running conditions the normal torque would be attained at low excitation and high eiliciencies.

Both Figs. l1 and 12 exhibit data taken from a unit designed for H. P. at 1800 R, P. M. with a normal torque of lbs. ft. Thus it is clear that the unit is capable of producing the enormous excess torque shown in Fig. 12 (necessarily at the higher slip). With the older type of machine it would have required a 116 H. P. unit at 1800 R. P. M. to produce the 340 lbs. ft. of torque shown in Fig. 12 at 800 R. P. M output which corresponds to a slip-condition of the order of 1000 R. P. M. It must be remembered in this connection that there is some slip even at the normal torque speed rating. 'For example, to obtain 1800 R. P. M. about 50 R. P. M. of slip is required since a device of this nature has no torque at synchronous speeds of the driving and driven elements.

In Figs. 5-10 is shown another form of the invention in which numeral |0| indicates the motor, |03 is the driving shaft, |05 the driving spider and |01 the flux-concentrating teeth thereon. In this case the support |08 for the fan blades is staked to the left end of the spider |05, as indicated at ||3. The air outlets are shown at |81.

The spider |51 is shown in detail in Fig. 9. It comprises extensions |06 threaded for receiving said bolt fastenings |04. Webs |08 spacedly surround a central cylinder ||0. These webs |08 at their ends have welded thereto a flange ||2. Bolts ||4 are used for bolting this iiange ||2 to a main frame member |5|. `Studs ||6 hold this main frame member to a ring ||8 which in turn is bolted to the motor frame |0| (see bolts |20). Between the bell |35 and the frame |5| is mounted a screen |63 which provides for an air inlet. The air may iiow between the webs |08.

The central cylinder I |0 on the fixed spider |51 carries a stationary magnetic sleeve |22 having spaced rows of radial tapered teeth |24 between which is wound a brake energizing coil |26. These teeth |24, as indicated in Fig. 8, are opposite the webs |08 so that toric flux field concentrations may be obtained from the coil |26. The teeth |24 concentrate this flux field at intervals, considered peripherally. This constitutes the braking field.

The copper drum is shown at ||5 mounted on a series of pins |26 held by keys |28 in radial openings` |30 in arms |50 of a supporting spider |32 (see also Fig. 7). This provides the desired central axial anchorage permitting free lateral and axial expansion of the copper. One end of this drum I5 extends between the rows of teeth |24 and the webs |08, thus forming an eddy-current inductor for braking action. It Will be understood that the webs |08 and member |22, including teeth |24, are 'all magnetic parts to support the magnetic circuit. The magnetic iield crosses through the copper drum ||5 and the air gaps on each side of it. The copper drum Ill is extended in the opposite direction along the outside of the teeth |01 and is terminated by l stiii'ening flange |34.

Carried outside of this end of the drum ||l are laminated magnetic pole rings |81 and |03. The former are carried by said ring ||0 and the latter by the case |5|. Both are stationary and between them in frame 5| is held an annular coil |83 which supplies the toric flux iield. This field passes around the coil and through the members |5|. Ill, |81, |88, teeth |01 (all of which are magnetic), and also twice through the intermediate copper drum ||5 and the air gaps on each side of it.

Operation of this form of the invention is similar to the one first described. The toric flux field F-3, generated by coil |83, is concentrated by the teeth |01 at peripheral intervals and traverses the gaps between these teeth and the rings |81 and |88, respectively. In doing so it traverses the copper drum ||5 and engenders eddy currents therein of a high order, at excitation below that needed to saturate the ends of the teeth |01. Then by only a nominal and usable increase in excitation of the coil |83, the flux field may :be increased, up to saturation o! the teeth |01 with consequent enormous increase in the torque that may be transmitted at increased slip.

Braking action occurs when desired by energizing the coil |26 which energizes the stationary concentrated flux field F-4. This engenders eddy currents in the rotary drum and by iiux re action tends to decelerate it, as required.

Air circulation is maintained by the fan which draws air in through the grill |63 and pest the flanges |08 and outside of the drum. This part of the air passes through the laminar ring |83, coil |83, openings |88 in the ring |81 and thence out of the openings |81. Another portion of this air may travel through the drum ||5 past the teeth |24, outside of the coil |28, through the spider |32 and along the teeth |01, and then through the fan blades and out through the openings |91.

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

As many 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.

I claim:

1. Torque transmission apparatus comprising an annular field coil producing a torio flux field, a pair of magnetic pole rings radially laminated, a driving member, a driven member, flux-concentrating magnetic pole means on one of said members reaching from one of said rings to the other but spaced therefrom and completing while concentrating the magnetic circuit therebetween, and a non-magnetic eddy-current conductive means on the other member and extending through thespaces between the said rings and said pole members.

2. Torque transmission apparatus comprising an annular field coil producing a toric flux field, magnetic pole-forming rings on Opposite sides of said field coil, means whereby induction of eddy currents is substantially inhibited in the rings, a driving member, a driven member, said members being relatively rotary, one oi said members carrying magnetic flux-concentrating teeth extending axially through the coil and from one ring to the other but spaced from both rings, the other member carrying a non-magnetic eddycurrent inductor extending spacedly between said rings and the teeth.

3. Torque transmission apparatus comprising an annular eld coil producing a toric flux held, annular and radially laminated magnetic poleforming rings on opposite sides of said field coil 'wherein induction of eddy currents is substana laminated magnetic pole ring located on each side of said coil and carrying the magnetic field, a rotary driven member carrying a thin nonmagnetic, eddy-current drum of high conductivity and extending through said rings and spaced therefrom by small gaps. a rotary driving .member carrying magnetic axially-directed nuxconcentrating teeth, the ends of 'which are spaced from the inside of the drum and which extend axially from the plane of one of said rings to the plane of the other.

5. Torque transmission apparatus comprising a driving member. a driven member, a conductive drum fastened to one of said members and polar teeth on the other member, axially spaced and stationary radially laminated rings forming axially spaced gaps with respect to said conductive member on one side thereon, said polar teeth being located on the other side of said conductive member and forming a gap with respect thereto, said teeth extending axially between the planes of said rings, and a coil between said rings exciting a toric iiux field interlinking the teeth with the rings through the conducting members through said air gaps, the sum o1' the thickness of said drum and of the two gaps on each side oi' it being of the order oi' one-half inch or less.

6. Torque transmission apparatus comprising driving and driven transmission members, axially spaced stationary magnetic rings which are radially laminated to suppress eddy currents, magnetic teeth on one of said transmission members and extending axially from the plane of one ring to the plane of the other and being in radially spaced relation thereto, a highly conductive non-magnetic drum attached to the other transmission member and forming gaps with respect to the rings and the teeth, and an annular coil between said rings forming a toric iiux field interlinking the rings with the teeth through said conductive drum and through said gaps.

7. Torque transmission apparatus comprising a driving transmission member, a driven transmission member, a stationary magnetic frame, stationary magnetic axially spaced rings in said frame, said rings being radially laminated to suppress eddy currents therein, an annular iield coil carried in said frame and located between said rings, a conductive non-magnetic drum attached to one of said transmission members and extending through said rings and eld coil and being in spaced relation thereto to form gaps,

flux-concentrating teeth peripherally arranged on the other transmission member and extending axially from the plane of one of said rings to the plane of the other but within said drum and forming an air gap with respect to the drum, and means for energizing said coil to excite a toric flux field interlinking the frame and rings with said teeth through spaced portions of said drum and through the gaps.

8. Torque transmission apparatus comprising a driving transmission member, a driven transmission member, a stationary magnetic frame, stationary magnetic axially spaced rings in said frame, each ring being radially laminated to suppress eddy currents therein, an annular eld coil in said frame and between said rings, a conductive drum on one of the transmission members and extending through said rings and held coil and in spaced relation thereto forming gaps with respect to the rings. linx-concentrating teeth peripherally arranged on the other transmission member and respectively extending axially from one of said rings to the other but within said drum and forming a gap with respect to the drum, and means for energizing said coil to excite a torio ux i'leld interlinking the frame, said rings, said teeth and passing through axially spaced portions of said drum.

9. Torque transmission apparatus comprising a driving transmission member, a driven transmission member, a stationary magnetic frame, stationary magnetic axially spaced rings in said frame, each ring being radially laminated to suppress eddy currents therein, an annular field coil in said frame and between said rings, a conductive drum attached to one transmission member and extending through said rings and field coil and in spaced relation thereto forming gaps with respect to the rings, flux-concentrating teeth peripherallyarranged on the other transmission member and respectively extending axially from one of said rings to the other but within said drum and forming gaps with respect to the drum, and means for energizing said coil to excite a toric flux eld interlinking the frame, said rings, said teeth and passing through axially spaced portions of said drum, air circulating lmeans connected to the driving member, means for admitting air to both sides of the drum whereby air may be drawn both through the drum along said teeth and along the-outside of the drum through said openings in the rings.

10. Torque transmission apparatus comprising an annular field coil producing a toric iiux eld, a peripherally smooth magnetic pole-forming ring adjacent to said field coil, means whereby induction of eddy currents is substantially inhibited in said ring, a driving member, a driven member, said members being relatively rotary, one of said members carrying flux-concentrating teeth extending in a direction from a location adjacent to the coil to a location adjacent to said ring but spaced from both, the other member carrying a homogeneous nonmagnetic eddy-current inductor extending spacedly between said ring and the teeth. 4

11. Torque transmission apparatus comprising an annular ileld coil producing a toric flux eld, a peripherally smooth magnetic pole-forming ring at one end of said fieldv coil and coaxial therewith, means whereby induction of eddy currents is substantially inhibited in said ring, a driving member, a driven member, said members being relatively rotary and coaxial with the coil and ring, one of said members peripherally carrying flux-concentrating teeth extending axially from a radial location in the plane of the coil to a radial location in the plane of the pole-forming ring but radially spaced from both, the other member carrying a homogeneous nonmagnetic eddy-current inductor extending spacedly between said ring and the teeth and also being coaxial with the coil and the ring.

12. Torque transmission apparatus comprising an annular ileld coil producing a toric ux eld, magnetic pole-forming rings on opposite sides of said field coil, means whereby induction of eddy currents is substantially inhibited in the rings, a driving member, a driven member, said members being relatively rotary, one of said members carrying magnetic nunc-concentrating teeth extending across the coil from one ring to the other but spaced from both rings, the other member carrying a nonmagnetic eddy current inductor extending spacedly between said rings and the teeth.

ANTHONY WINTHER.

REFERENCES CITED The following references are of record in the 5 file of this patent:

UNITED STATES PATENTS