US2393211A - Eddy-current electric apparatus - Google Patents

Description

EDDY-CURRENT ELEGIR fC APPARATUS Filed DEC. lO', 1943 39 Z v2:3 z 39 25 ifi/25 J P 5 3 I -J /8 Z9 /8/ 7.38V 20 0 g? 778 [25 fa 22 35 352/ 0 3 4] u f gl Z( s J 9] m &'\ x 35 9 5/ f z 7 /3 M 1 49 f /3 6 f I m 7 67 /z 7l 3 7;] I 57 Q /l 65 63 T J g 3 V f FIG 5 /s 9 a al /5 I7 /3 ,5 5g 4749 45 ,7

/z 6R 71%/ M2! 6V 74 3 fl l1 57 Jan. 15,401946:Y 4 Y "i M. WINTHER- EDDYCURRENT ELECTRC APPARATUS Filed Dec, y10, 1943 3 sheets-sheet 2 Patented Jan. l5, 1946 Mmm 'r'.mnsnea Waukegan, n1., assignmto Martin P. Winther, Waukegan, Ill., trustee anneau 1o, 1943, sensi No. 513,801

iz clama. (c1. 17a-zw This invention relates to eddy-current electric apparatus, and more speciflcallylto eddy-current couplings, clutches, brakes, dynamometers and the like. 1 Y,

AAmong the several objects of the invention may be noted th'e provision of an electric eddy-current slip coupling, clutch, brake, dynamometer or the like having a more constant flux gap over a wide temperature range; the provision of a clutch of the class described having a low manufacturing cost because the use of pilot bearings may be avoided in view of said improved vgap condition; the provision of a clutch of the class described which, by eliminating said pilot bearings, also eliminates the usual critical lubricating requirements encountered therewith; and the provision of a clutch oi' this class which may be made with and which retains a vibration tolerance which is less than that which could be maintained with said pilot bearings. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elemental-features of construction, and arrangements of yparts which will be exemplified 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 several of various possible embodiments of th'e invention,

Fig. 1 is a longitudinal section of one form of the invention;

Fig. 2 is a right-end elevation of Fig. 1;

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

Fig. 4 is a fragmentary left-end view of Fig. 1;

Fig. 5 is a fragmentary longitudinal section corresponding to the lower regions of Fig. 1 but showing an alternative form of the invention;

and,

ligJ is a view similar to Fig. 5 and showing anotbsr'slternative form.

Similar reference characters indicate correspending parte throughout the several views `of the drawings.

- Thstarmulipolutchandliipeouplingasused air gap, under cold starting conditions, was made as small as possible without actually having mechanical interference. Becoming warm under operating condition, the outer rotary member, which usually was the eddy-current member, would expand away from the rotating field member or spider, thus considerably increasing the air gap. As the torque ratings had to be established under maximum gap conditions, that is, under maximum operating temperatures, such ratings were based on the characteristics prevailing when the air gap was at a maximum, which, in itself, was satisfactory enough.

- However, as the coupling cooled to normal room temperature, the air gap would again shrink to the minimum value, and when the coupling was Aagainstarted for a succeeding cycle of operation,

it would, for a time, operate with a small air gap.

Then, if perchance, an operator would fully excite the field under such conditions of minimum air gap, the eccentric or oil-center forcev generated between the magnetic surfaces would be tremendous, even with only slight variation in the air gap due to misalignment or looseness in the bear- Off-center pull varies approximately with the inverse square of the air gap. Thus 1/M-inch air gap will have four times the olf-center pull of a als-inch air gap.

The above made necessary a pilot bearing directly between the driving and driven members.

One of the remedies was found to be obtained through the use of a copper lining inside of the eddy-current drum of the order of a 11g-inch in thickness. This separated the magnetic members sufliciently to reduce the off-center pull to a value that did not become dangerous to the operation of the machine when starting. While this was a substantial improvement, the manufacturing costs of the liner was relatively high. The present invention eliminates both the need for the liner and the pilot bearing and maintains a close air gap when needed, and automatically prevents formation of too small a gap under starting conditions when not needed, thus minimizing said eccentric loading condition.

In order that the objection to a pilot bearing `may be fully understood, it may be explained that the methodof lubricating anti-friction bearings of this class is by means of grease. It is not very often possible to use oil, unless speciaiprecau- Ations are taken and these precautions are also costly. Where grease is used, which is by far in most of the cases, centrifugal force will cause the grease to form a circular sheet clinging to the outer surface of the bearing member, which in the case of a pilot bearing rotates. If the grease content of the bearing is exactly right, the thickness of this layer in the bearing will be such as to feed a small volume of the grease to 4the bearing constantly. If, however, the grease content is too low, the layer will be so thin that no grease will enter the bearing. If, on the other hand, the grease content is too high, it will form a layer with a considerably smaller inside diameter than the inside diameter of the .ball bearing outer race. The result is that a copious flow of grease to the bearing is constantly had with a resultant extreme agitation of the grease with accompanying generation of heat. This heat soon destroys the grease, volatilizing the lighter ends and before long the bearing is destroyed. Thus it will be seen how critical lubrication of pilot bearings is and how desirable it is to eliminate it, or take other suitable precautions.

There are other mechanical reasons for avoiding the use of a pilot bearing. For example, the normal tolerances of the eccentricity in such bearings are not close enough to make the coupling always operate smoothly. Machines of this type are balanced to a vibration tolerance of one mil, or .001 inch. The normal eccentric tolerance of a ball bearing is from one and onehalf to three times one mil. Thus a clutch may be balanced with the bearing running out as low as one mil and be perfectly smooth until but not after this bearing wears down. Also, a newly installed bearing may run out three mils. Furthermore, if a newly fitted bearing has a run-'out 180 from that of the original bearing, the machine will be very badly out of balance. The difficulty is accentuated in pilot bearings because these have rotating inner and outer races which must fit tightly in the housing and on the, shaft without physical play between the housing and the outer race of the bearing. Thus the eccentricity of the outer race and the inner race are both elements in producing eccentric rotation of the two members, which would not be a condition met with when using a bearing with a stationary outer race in a stationary housing. In the latter Vcase only the eccentricity of the inner race becomes a factor in the trueness of rotation of the unit. According to the construction herein described only bearings having stationary outer races are used.

Referring now more particularly to Fig. 1, there is shown at numeral l a stationary case made in two cup- shaped halves 3 and 5 which are substantially enough identical so that they may be cast from a single main pattern. Then, by slight differences in auxiliary loose pattern pieces, or in machining as, for example, as the tongue-andgrooved joint 1, they may be adapted to one another or other parts. Parts 3 and 5 are thus organized at 1 by means of bolts 9 to form a complete hollow frame.

Each frame member 3 and 5 has similar legs II and also a series of axially located ports I3 for air inlet purposes, and a series of radial ports I5 for air outlet purposes. Suitable annular screens I1 cover the ports I3 and a cylindric screen I9 covers the outlet ports I5. The ports I3 are within annular rings I2 and I4 connected by arms I6. Connected to the inner rings I4 by means of webs 95 are cylindric bearing sleeves shown at 2I. These carry the outer stationary races 23 of ball bearings 25. One set of bearings 25 (the righthand set in Fig. l) support a rotary drive shaft 21 and the other set of bearings 25 (lefthand set) support a rotary driven shaft 23.

The shafts 21 and 23 are flanged at their ends as indicated at 3| and 33 respectively. The shafts 21 and 29, including the flanges 3i and 33 respectively, are preferably made identical. Their end portions are broken away in Fig, l, but it is to be understood that these are identical stubs to which the desired driving and driven members are keyed. The inner races I3 of the bearings 25, as well as other appurtenances, are held in position by suitable spacing sleeves 20 clamped by nuts 22. The identicalness of shafts 21 and 23, along with the substantial identity between the frame members 3 and l5 is very desirable from a manufacturing viewpoint.

Suitable inner lubricant-retaining, stationary labyrinths 31 are bolted to the inner ends of the cylinders 2|. These cooperate with rotary labyrinth members 33 on the rotary shafts respectively. At the outer stub ends 35 suitable oil retainers 39 are used. The labyrinth members 31 are held in place by means of studs such as exemplified at numeral 4I. The labyrinth members 31 are the ends of spaced cylindric sleeve members 43 surrounding the cylinders 2l, being spaced' by webs 42 and bolted at the outer ends as indicated at 44. Thus air may flow in between rings Il and sleeves 43 on the one hand and the respective cylinders 2| on the other hand.

On the flange 3| of the driving shaft 21 is bolted a magnetic field member 45 recessed at 41 to provide for an annularly wound field coil 49 located between two peripheral rows of tapered, flux concentrating teeth 5I. These teeth 5I concentrate the torio flux field generated around the annular coil 49 when the latter is electrically energized. They are also extended and tapered endwise to act as air fans. Exciting currentl is circulated through the coil 43 through suitable slip rings 53 and brushes 55 (see Figs. l and 2). Wiring between the slip rings and the coil is not shown, the necessary character of which is obvious.

The armature of the coupling comprises a rotary composite ring indicated generally at numeral 51. This armature is made up in either two or more pieces. depending upon the speed at which it is to .be rotated. For nominal, or slow speed operation such as 1200 R. P. M., the three piece form illustrated in Fig. 1 is suitable. In all forms there is used a main cone-shaped supporting member 59 having openings 93, which is bolted to the flange 33 of the driven shaft 28. In the case of the Fig. l, the remainder of the composite ring 51 is made in two identical cast steel halves 6I, welded at the center as exemplined at 63 and elsewhere if necessary, the assembly of the two being welded to the ring 53 as at G5. The reason for having two halves 6I is to meet foundry conditions; otherwise steel castings constituted by rings 6I may be made up in one piece as indicated at 60 in Fig. 5.

The shapes of the confining rings 6I (Fig. l). and their integral counter-part 60 (Fig. 5), are of substantial importance to the inventionf They comprise continuous inner rings 81 having smooth cylindric eddy-current surfaces next to the ends of the teeth 5I of the field member 45. Each ring 61 is initially cast in a continuous form, being connected to its respective outer ring 6I or 60, as the case may be, by forty-eight (according to the present example) fins 1| approximately one-half inch thick. The fins 1I at their axial ends are extended and tapered as shown at 13 to act as air fans.

After the` eddy-current e been made up by welding parts 59 and 6| (Fig. 1) or parts 59 and 60 (Fig. 5), and has been roughmachined, the spaced inner eddy-current rings 61 are sawed completely through, for example, at twelve placesin each ring as indicated at 15, the saw being of approximately 315 inch gauge. Thus each circular eddy-current ring adjacent to the teeth consists of twelve segments 68 indicated in Fig. 3. These are supported by the fins 1| and are held in circular positions by the respective outer solid ring portion 6|.

It will be seen that when the field coil 49 is energized its toric iiux field, which is indicated by dotted lines at the bottom of Fig. 1 interlinks the field member 45 (including its fluxconcentrating teeth 5|), and the members 6| (including the fins 1| and segments 68). Upon rotation of the driving shaft 21, shaft 29 will be driven with some slip by reasonof the magnetic reaction set up due to eddy-current generation primarily in the segments 68. Most of the eddycurrent generation is in the segments 68 of the` such generation takes place quite close to the point where lines of magnetic flux enter an eddy-current member. The segmental rings 61 may therefore be referred to as eddy-current heating rings.

When the clutch is operated, the segments 68 will become much hotter than the outer ring portion 6|, because of the temperature drop through the fins 1| brought about by air circulation between rings 6| and 61. There may be as much as 100 F. to 125 F. difference in mean temperature between the outer portions 6l and the inner ring segments 68.` However, since the temperature of the outer ring members 6| will determine 'the normal diameter of the clutch. increase in this diameter is small. In other words, the spaced segments 68 are more or less held in xed radial positions by reason of the fact that their supporting fins 1| are anchored on the outside to relatively cool metal in the rings 6|. Stated otherwise, the hottest ring portions of the armature have been both structurally isolated and slitted so as to allow peripheral expansion to take place in the slots 15 without commensurate radial expansion. A continuous steel ring will increase in diameter approximately rs of 1% for every 150 F. rise in temperature. By cutting up the rings 61 into the segments 69 by slits 15 any increase in diameter of the inside of the segments is only a fraction as much as if the inner eddy-current surface were continuous. Thus the flux gap is more nearly constant, at whatever value is set for it.

- The above remarks all apply to the construction shown in Fig. 5 wherein it is to be understood that the rings 61 are also cut up into segments as above described. The only difference is that the two welded outer rings 6| of Fig. l are in Fig. 5, cast into (a single outer ring 60.

In Fig. 6 is shown a modification of the ininvention for high-speed operation, say 1300 R.

rings 61 because P. M. or so. In this case, like numerals designate like parts as in Fig. 1. A rolled or forged steel band ring 11 is shrunk to the outside of the cast steel rings 6I, and welded thereto as indcated at 62. It is to be understood that this banded structure can be made also to apply to the Fig. 5 structure by suitable modification. The band provides a structure which will, with drum 51 as a. whole has y more safety, withstand the added centrifugal forces due to increased speed.

Tapers 13 of the webs 1I act as air'paddles which centrifugally induce a. flow of air through the inlets I3 and to the outlets I5. Some flow of air is also induced by and between the teeth 5I to flow up around and in between the segmental rings 61- and around the cooling webs 1|. The outwardly flared shapes of the passages 14 between the rings 6| and blowing action. Thus not only is cooling of ring 61 accomplished, but a large temperature gradient is maintained-between the outerA continuous rings 6| and the segmental rings 61. n Also, the supporting member 59 of the composite armature 51 has the openings 93 therein for accommodating flow of air. Another feature to be noted in this connection is that the sleeves 43 are spaced from the cylinders 2| and openings are provided at so that air may be drawn in axially between said sleeve 43 and said cylinders 2| for bearing cooling purposes. Fins 91 on the inside of the inner cone formed by the supporting member 59 of the armature 51 help to induce a radial flow of air from the center out.

Fig. l shows an auxiliary which .may be used if desired. This is an induction brake 19 composed of a magnetic ring 8| having inwardly directed radial teeth 83. An annular coil 65 is carried between the rows of teeth 63 and when energized sends a torio flux eld through the member 8|, including the teeth, and inte-rlinking the outer rin-gs 6I of the driven rotary member. This induction brake will fit any standard unit and is designed to be used in the kind of service requiring frequent starting and stopping, but very `little speed reduction for constant operation.

The brake of course operates to decelerate the output shaft, since it is effective upon lthe driven drum 51. y

In Fig. 4 is shown an end view of an auxiliary generator unit 81, the internal operating portions of which are not shown with the exception of a rotor unit 89 and a stator unit 9|. This item is used in connection with associated control apparatus and forms no part of the present invention but is shown for completeness of the device as it exists.

It is clear that the principles of the invention may be carried the outer member with teeth 5| extending inward and the armature member inside with the rings of pads 68 extending outward. In this event the segmental eddy-current members would be outside of their cooler supporting rings and attached thereto by fins. The same advantages would accrue, namely, that the cool continuous ring would maintain a mean armature diameter which is more constant than if the eddy-current surfaces per se were continuous.

It will also be understood that under the principles of the invention the shaft 29 may be the driver and shaft 21 the. driven member, making the armature 51 the driver and the field member the driven member. Also, coil 49 may be mounted in member 51, instead of in 49.

In view of the above.it will be seen that the eddy-current armature of this machine consists of interrupted rings forming separate segments or pads in which the eddy currents are generated and in which the majority of Athe heating occurs. The other continuous ring or rings, as the case may be, provide the entire support for the interrupted rings by means of connecting cooling between the inner interrupted fins. The cooling 61 Afacilitate centrifugal out by making the field member rings and the outer continuous rings is suiiicient to obtain a substantial working temperature difference or gradient between the interrupted eddy-current rings and the outer supporting rings.

'Ihe fact that the coaxial cylindric extensions 2i reach farther inward into the bodies 3 and 5 than outward therefrom provides long steady bearings without occupying much space outside of the device. At the same time, no pilot bearing is required because of the reduction of oiI- center pull during starting.

It is preferable that the rings 61 forming the segments 68 be of low carbon steel because this is best for eddy-current production. Of course all of the material in the rings B1 and 6| should be magnetic and likewise the material of the field member 45.

While the slip coupling herein is shown between two rotating members, it may be between two members one of which is held stationary, as in the case of an eddy-current dynamometer or a brake and the claims are intended to cover such application of the invention.

In view of 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. In eddy-current electric apparatus, an inner field-concentrating member having outwardly directed iiux concentrating teeth, an outer armature, said member and armature being relatively rotary, means providing a iiux iield interlinking the iield member and said armature, the armature comprising an outer continuous ring, at least one inner discontinuous ring closely adiacent to the periphery of the field member and spaced radial cooling and supporting members joining the outer continuous ring and the inner discontinuous ring, the discontinuous ring carrying most of the eddy currents and heating while the relatively cool continuous ring maintains the discontinuous ring at a substantially constant iiux gap distance with respect to the field-concentrating member.

2. In eddy-current electric apparatus, an inner rotary ileld member, at least two peripheral rows of nuit-concentrating teeth thereon, an annular coil in a plane between said rows, a cooperating armature, said armature and field member being relatively rotary, the armature comprising inner segmental eddy-current rings respectively adjacent to said rows of teeth on the field member, a continuous outer supporting ring forming part of said armature and supporting said segmental rings, spaced supporting and heat dissipating webs connecting between said continuous supporting ring and the segmental rings, the planes of said webs being substantially axial, and the axial sectionbetween the outer and inner armature rings flaring outward from points between the rows of eld member teeth, said coil generating a toric flux iield interlinking said rows of teeth, said segmental rings, the webs and the outer supporting ring.

3. In eddy-current electric apparatus, an inner rotary field member comprising an annular coil, outwardly directed radial rows of teeth on opposite sides of said coil, a relatively rotary armature outside of said ileld member and comprising en outer continuous coniining ring means oppositev said coil, inner discontinuous eddy-current heating rings respectively closely adiacent and opposite to said rows of teeth on the field member, spaced tins joining said continuous outer ring means with the discontinuous inner rings o! the armature, and a peripheral strengthening band around said outer ring means and attached thereto.

4. In eddy-current field member an annular field coil, radial teeth on the field member and in the held of said coil, a relatively rotary armature and comprising an outer continuous conning ring, an inner discontinuous eddy-current heating ring closely sdjacent and opposite to said teeth on the eld member and spaced supports joining said continuous outer ring with the discontinuous ring, said continuous outer ring being joined to a rotary supporting member located at one axial end of the field member, separate rotary shafts respectively carrying the iield member and the armature, and a frame surrounding said rotary members and separate bearings independently supporting the shafts in the frame.

5. In eddy-current electric apparatus, an inner rotary field member, an annular field coil, outwardly directed radial rows of teeth in planes on opposite sides of said coil, a relatively rotary armature outside of said eld member and comprising an outer continuous confining ring opposite said coil, inner discontinuous eddy-current heating rings closely adjacent and opposite respectively to said rows of teeth on the field member, and spaced ilns joining said continuous outer ring with the discontinuous ring, said continuous outer ring being formed in two parts joined in a median plane, the assembly of said two parts being joined to a third supporting member, and an outer band around said outer ring.

6. In eddy-current electric apparatus, an inner rotary held member, an annular tleld coil, outwardly directed radial teeth on said coil and in the eld of said coil, a relatively rotary armature outside of said eld member and comprising an outer continuous coniining ring, an inner discontinuous eddy-current heating ring adiacent and opposite tn said teeth on the ileld member, spaced webs joining said continuous outer ring with the discontinuous ring, and axial extensions from said webs adapted to induce a ow of air around the discontinuous inner ring and past the continuous outer ring.

7. In eddy-current electric apparatus, an inner rotary ileld member, an annular neld coil, outwardly directed radial rows of teeth on opposite sides of said coil and in the field o! said coil, a relatively rotary armature outside of said field member and comprising an outer continuous conlining ring opposite said coil, inner discontinuous eddy-currentI heating rings respectively closely adjacent and opposite to said teeth on the field member, spaced groups of webs joining said continuous outer ring with the discontinuous rings, and opposite axial extensions from the respective groups of webs adapted to induce separate flows of air through said teeth around the discontinuous inner rings and past the continuous outer ring.

8. In an electric clutch, a drive shaft, a driven shaft, a rotary field member on one of the shafts, a rotary armature on the other shaft, a housing comprising two joined cup-shaped bodies, spaced coaxial inward extensions forming parts of said bodies and extending farther inward than outelectric apparatus, e rotary Y 4 shaft, a rotary field member on one of the shafts,

a rotary armature on the other shaft, a housing comprising two cup-shaped bodies Joined at a median line, spaced coaxial cylindric extensions forming parts of said bodies, flanges on said shafts located between said coaxial extensions, said rotary members being attached to said flanges between said extensions, independent bearing means for said shafts respectively in said extensions, sleeves spaced from said extensions and reaching from a region adjacent to the spacing between said extensions to points of attachment with the cup-shaped members, radial openings in said cup-shaped members, axial openings therein communicating both outside and inside of said sleeves and adapted to direct air to inside points in the housing, and said sleeves supporting labyrinth means for retaining lubricant within said bearings.

l0. In eddy-current electric apparatur, an inner rotary field member, an annular field coil, outwardly directed radial teeth on said field member and in the field of said coil, a relatively rotary armature outside of said fleld member and comprising an outer continuousvconflnlng ring. an

inner discontinuous eddy-current heating ring adjacent and opposite to said teeth on the field member, spaced webs joining said continuous outer ring with the discontinuous ring, axial extensions from said webs adapted to induce a flow of air around the discontinuous inner ring and past the continuous outer ring, and axial extensions from said radial teeth cooperating to produce said flow of air.

l1. In eddy-current electric a `ferraille, an eddy-current member, a field .n miser having spaced flux-concentrating means re toward the eddy-current member, said in ibers being relatively rot-aryY means providing ay .iiux fiele interlinking said members, said eddy-current member comprising a confining ring substantially spaced from the field member, spaced eddy-current segments forming a sectional ring close to the points of flux concentration from said field member, and spaced supporting connections between said confining ring and said eddy-current segments, whereby the confining ring may be maintained substantially cooler than the segments and whereby at various higher segment temperatures caused by eddy currents therein the flux gap between the segments and the adjacent flux-concentrating portions of the field member tends to be maintained substantially constant.

12. In eddy-current electric apparatus, a magnetic eddy-current member; a magnetic field member having axial flux-concentrating teeth directed toward the eddy-current member, said members being relatively rotary, a circular field coil generating a toric flux field interlinking said members and carried by one of them, said eddycurrent member comprising a continuous magnetic ring portion substantially spaced from the field member, spaced eddy-current magnetic pads forming a sectional ring close to the points of flux concentration in said field member, and spaced magnetic supporting connections between said solid ring and said eddy-current pads, said pads, connections and continuous ring accommodating substantially all of said flux field, circulation of a cooling medium being accommodated between the Kpads and the ring to maintain the ring cooler than the pads, whereby a substantiaily constant flux gap tends to be maintained between the pads and the toothed portions of the field member regardless of temperature variations in said pads.

MARTIN P. WINTHER.

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