GB2131629A - A rotor for an external rotor machine - Google Patents

Abstract

The invention relates to a rotor for an inverted (in-out) electric machine of the type having a stationary shaft, which allows the manufacturing costs to be lowered and the rotor efficiency improved, comprising a toroidal element 15 and two covers 19. The toroidal element comprises core laminations and shorting rings 16 cast thereon, as well as surfaces 28 intended to adhere against the covers. The covers comprise each a hub 23 wherewith a bearing 24 is made rigid which rotates therewith, and surfaces 31 mating with the surfaces of the toroidal element. The invention further concerns a method of manufacturing said rotor, and an inverted electric rotary machine incorporating it. <IMAGE>

Description

SPECIFICATION An improved rotor for an inverted (in-out) electric machine, method for the manufacture thereof, and an electric machine incorporating the rotor This invention relates to an improved rotor for an inverted electric machine, to a method forthe manufacturethereof, and to a machine incorporating it.

Known areso-called "inverted" or "in-out" electric rotary machines, wherein the stationary part or stator is located within the gap which separates it from the rotary part or rotor, which is located on the outside thereof.

The family of such machines being considered herein is that known because, and characterized by that, its bearings contained within the hubs of the covers (or shields) delimiting the machine axially form a single piece construction with the rotor and rotate rigidlytherewith,whereasthe shaft around which the rotor and shields and bearings rotate is stationary, rigid with the stator, and perfectly centered to the outer cylindrical surface ofthe stator.

To the ends of the shaft, orto only one ofthem, connections are made to supportthe machines ofthis known family, and from an axial bore in the shaft emergethe cables which feed the currentto the inside ofthe winding.

Known are the difficulties which have been always encountered in developing machines inthisfamily, namely: -the (rotary) bearings occupy the space wherein the heads of the (stationary) winding should extend; -the heat released by the inside stator is difficult to dissipate; - machining the rotor bearing seats to be truly concentricwith the cylindrical inner surface of the rotor and stator outer surface is difficult; -closing or assembling the various rotary parts poses centering problems and is time-consuming, owing to the connection means used heretofore.

Such prior problems are solved by this invention, in the various aspects thereof. According to one of its aspects, it provides a rotorfor an inverted (in-out) rotary electric machine of the type having a stationary shaft, characterized in that it comprises a toroidal element and two covers, the toroidal element including the core laminations and shorting rings cast thereon, as well as adhesion surfacesforthe covers, and the covers including each a hubwherewith a bearing is made rigid which rotates along therewith, and adhesion surfaces mating with said surfaces of thetoroidal element; the assemblyfurthercomprising elements adapted for adhering togetherthe toroidal element and covers.

According to a preferred embodiment, the invention contemplates that such elements for adhering togetherthetoroidal element and covers comprise deformable lugs incorporated to thetoroidal element and deformed into seats formed in the covers.

According to a modified embodiment, the invention contemplates that adhesion between the surfaces of the toroidal element and covers be achieved by depositing a cement overthe surfaces priortotheir being broughttogether.

In another modified embodiment, the invention arrangesforthe adhesion between said surfaces to be achieved through a means allowing the rotorto be disassembled, i.e. screws, self-tapping or otherwise, or other conventional means clamping the covers ontothetoroidal element.

Preferably, the toroidal element is provided with fins for centrifugal ventilation and/orthe covers are apertured to admit ventilation air. The fin ends may constitute the surfaces of adhesion to the covers, but preferablythesurfacesofthetoroidal element and covers mating with each other are defined and configured to increase their mutual adhesion. In general, the cast material ofthe toroidal element is aluminium oralloythereof.

In a preferred embodiment ofthe invention, the bearing carrier hubs are arranged axially on the outside ofthe area occupied by the winding heads, so as to allow the wires which come out of one stator grooveandenteranothertofollowtheshortest route represented by the chord, thus reducing the wire used in the head, and accordingly its size, the length ofthe turns, weight ofthe wire used, its resistance, and improving the electric efficiency ofthe machine.

In yet another preferred embodiment, dissipation of the heat generated inthewindingsisfacilitated by conveying axially to their heads cool air picked up from the outside environment by means of plural small radial fins set atan angle similarly to a fan blades and being formed in the shields or covers.

According to a further modified embodiment of the inventian, such fins direct air from one face of the statorto the otherthrough thetoroidal slit of the gap and that portion of the grooves where the wire is wound which is not completely filled thereby, thus providing forthewinding to be ventilated exactlywhere it generates heat.

The method of this invention for manufacturing a rotor intended for a rotary in-out electric machine of the type having a stationary shaft, comprises the steps of: providing a toroidal element by assembling the rotor core laminations and casting into the grooves thereof a conductive metal (generally aluminium) to form the two shorting rings and surfaces adapted for adhesion onto the covers, as well as deformable lugs; providing two covers including each a hub accommodating a bearing and surfaces mating with said surfaces ofthetoroidal element, as well as seats adapted to receive said deformable lugs therein; sliding the rotoroverthe electric machine statorwhile holding it spaced concentrically apart therefrom, preferably by means of shims or probes; bringing the coverstoward the toroidal element while sliding the bearings thereon overthe machine shaft, to juxtapose said cover surfaces to those ofthe toroidal element and insert said lugs of said elements into respective seats in said covers; deforming said deformable lugs such as to interengage thetoroidal element and The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy.

covers and make the assem bly stiffer. Th e deformable lugs may replaced as regards theirfastening function byotherconventional means, such as screws or adhesives, withoutjeopardizing the method nonobviousness.

In orderforthe machine two be regarded as "closed" the invention provides a limitation to the inlet apertures of the cited fins and to the number ofthe air outlet channels atthe peripheries of the shorting rings sloping toward the shields, which channels prevent, owing to their configuration, pin-like bodies with a diameter of 1 mm and/or ball-like ones with a diameter of3 mm from entering and contacting stationary parts, i.e. foreign to the rotor.

Particularly interesting, in the rotor of this invention, arethemeans providedforsecuringtogethertheparts which make up the rotor, while keeping the inner surface ofthe toroidal element truly concentrical with the shaft axis, and equidistant throughout from the outer surface ofthe stator.

To better explain the novelty character of such means, itwill be appropriate to recall herein that, at the present state ofthe art, it is not difficult to punch the circular rings from a ferrous sheet, which comprise the rotor, such that both the interior and exterior are perfectly centered. Nor is it difficultto cast, over the core laminations thus punched and packed, shorting rings across the two flat faces, which are conventionally interconnected by the cast material which flows to fill the grooves in the core laminations. No difficulties are to be expected of casting to shape such rings as desired, forming ventilation fins or other figures thereon, the whole assembly to be properly centered with respect to the axis ofthe toroidal figure formed by the core laminations.Further, it is not difficultto punch outtheferrous sheet disks which make up the stator such thatthe exterior is centered true to the inside bore for keyed connection to the shaft.

A characteristic of this invention is that the toroid is first positioned around the stator previously slid over the shaft, while keeping it aparttherefrom by the width ofthe gap. This may be accomplished, as an example, by means of probes or shims located between the stator exterior and rotor interior, which probes or shims can be readily removed afterwards. Thereafter, this perfectly concentrical fitting ofthe toroid around the stator is made permanent by letting the covers adhere on the toroid and securing them through specially provided elements. Thus, the covers will have pre-assembled rolling or plain bearings made rigid therewith and slid over the shaft, so that they can turn perfectlytrueto its axis, and the toroid attached to them will turn true therewith.

The covers are caused to adhere on the toroid, according to this invention, by means of corresponding areas which can adhere on one another, and effected through deformable or upsettable lugs on the toroid which are deformed into seats formed in the covers orthrough other means as described hereinabove, after bringing the covers to face the toroid which is positioned truly concentrical with the stator. The rotor comprising the toroid and the two covers will thus be completed and turn true to center without requiring the provision of mating seats between the toroid and covers, and without involving any machining ofthe covers and toroid.

The invention features and advantages, and its embodiments, will be more clearly apparent from the description of some preferred examples, shown in the accompanying drawings, where: Figure 1 shows half in elevation and half in section a rotor according to the invention, as assembled and mounted on a wound stator; Figure 2 shows in section one half of the various elements, the other half being symmetrical, i.e. the inner stator rigid with the shaft, the two covers or shields complete with bearings and slid over the shaft ends,andthetoroid positioned around the statorand held spaced therefrom by means of probes, ready for assembling by riveting;; Figure 3 is a frag mentary view of the ring taken along the line Ill-Ill of Figure 2, showing one ofthe adhesion surfaces of the ring and the air outlet channels formed between the fins on the DC ring; Figure 4 is a fragmentary view ofthe covertaken along the line IV-IV of Figure 2, showing the air inlet aperturesthrough the cover and one ofthe adhesion surfaces; Figure 5 is a sectional viewtaken along the line V-V of Figure 4, showing the air inlet aperturesthrough the cover; Figure 6 is a diagramatical elevation view of one stator half, showing the saving in copper wire length and decrease in the volume of the heads ofthe stator winding to be achieved through the provision of a rotor constructed in accordance with the invention; and Figure 6Ashowsschematicallyone half of a stator with the heads arranged in a conventional way.

Figure 1 illustrates an inverted rotary electric machine ofthe in-outtype incorporating a rotor according to the invention. The bottom half of the figure shows the machine in elevation, whereas the top half shows it sectioned along a plane comprising the axis. Some parts of the machine are foreign to the invention and are shown to illustrate the influence of the invention thereon.

These arethe stator 11 with its winding, of which the heads 12' and 12"areshown; the shaft 13 extending through the stator center and mounted truly concentrical with its cylindrical outersurface and rigid therewith, which projects out of the two sides 13' and 13"; andthesupports 14' and 14"which connectthe shaft to the outside.

All the rest rotates and forms the rotor of this invention. Indicated at 15 are the core laminations of the rotor, in the grooves (not shown) whereof is cast a conductive metal (usuaily aluminium), which also forms the two shorting rings 16' and 16", electrically required. Preferably, but not necessarily, on at least one ofthe rings there may be formed, asshown in the drawing, centrifuging fins 17 which define channels therebetween through which air is centrifuged from the motor interiorto the exterior. The channels are bordered on their outerface by a shield 18which may be formed on the extension ofthe cover 19'.

According to a peculiarfeature ofthe invention, the channels have their axes inclined andlorconfigured labyrinth-like, such asto preventpin-like bodies such as 20 from entering the motor or reaching stationary parts thereof, such bodies being conveyed by said channels onlytowardwalls ofthe rotor.

The dimensions and configuration ofthe channels are such that a ball with a diameter of 3 mm cannot roll through them.

Otherextensions2l,shown here diagramatically in dash lines, may be formed in the cover 19"to connect to it any foreign elements to be driven, or they themselves may be extended to form fan blades.

Formed at the areas 22' and 22" of the covers 19' and 19" are cooling air inlets, the air being then centrifuged out by the fins 17 as explained hereinafter.

The hubs 23' and 23" enclose rolling or plain bearings 24' and 24", which are carried axially outside ofthearea occupied bythewinding heads 12' and 12".

The securing members,whichforsimplicityhave been represented inthe drawingswith upsetstuds 25' and 25", are formed with the same casting which producestheshorting rings. Indicated at26 isthe cablethatsupplies current to the machine.

Figure 2 shows the elements which make up the rotor of this invention, prior to their assembling.

Indicated at 19' and 19" are the covers, complete with the bearings 24' and 24" preassembled to the hubs 23' and 23" and with the seats 27' and 27" arranged to receive the studs 25' and 25", or other securing members. The numeral 15 designates the toroid, complete with the shorting rings 16' and 16", with the adhesion surfaces 28' and 28", and with the securing members 25' and 25".

Indicated at 11 is the stator, as pre-wound and attached to the shaft 13. The numeral 29 designates probes or a shim of any selected configuration, which function to create a temporary gap between the stator and rotor during the assembling step. It may be pulled out, e.g. through a slit 30 formed in one ofthe covers and shown in Figure 1.

The rotor manufacturing comprises the following steps. Firstly, the toroid 15 is slid over the stator 11 and held spaced concentrically apart therefrom by means ofshims 29 to be removed afterthe machine has been assembled. The two covers19' and and 19"arethen broughtclosetothetoroid by sliding their preassembled bearings 24' and 24" overthe shaft and aligning the seats 27' and 27" with the studs 25' and 25" on thetoroid; it is an important expedient here to provide for a sufficiently loose fit between the seats 27' and 27"and studs 25' and 25" to allowthefit between the shaft 13 and bearings 24' and 24"to take care ofthe centering ofthe covers on the shaft axis, and the outer surface of the stator 11, with the interposition of the removable elements 29, ofthe centering of the toroid 15 onto the shaft axis.

Suitable adhesion surfaces 31 ' and 31"formed on the covers arethusjuxtaposed and matched to the surfaces 28' and 28" ofthe toroid. They will the better adhere together since they are so configured as to present suitable rough areas or ridges and grooves.

Finally, the covers are secured together and to the toroid which will be centered true to the stator, by upsetting the studs 25' and 25" or other deformable members, or by the other securing means already described. As a last step, the shims 29 are removed.

Shown in Figures 3 and 4 are the surfaces specially formed on the rotor rings, and the corresponding surfaces formed on the covers,the adhesion whereof enhances the bond between the covers and toroid.

The surface 28' formed on the ring 16' and roughened through particularexpedients such as radial scoring orthe like, will align with the corresponding surface 31 'formed on the cover, which is also roughened by concentrical scoring criss-crossing the ring scoring lines, or by some other means.

The same will occur between the ring 16" and cover 19".

By upsetting the securing elements 25' which align with the seats 27', adhesion is created between the cover surfaces and the corresponding ones on the rings.

Figures 4 and 5 also show more clearlythe arrangement provided bythe invention to admit cooling air into the machinethrough the cover 19" or through both covers.

Formed in the discoid constituting the cover are closely spaced radial cuts 32 which create as many spokes which are bent to convert into as many inclined fins 33 having an angle of attack which, owing to the direction of rotation of the machine, will direct like a propeller external air axially toward the winding heads.

The numberofthe cuts will depend on the thickness ofthe cover discoid.

Between the fins, there is left an air passage 34 which should have a smallerwidth than 1 mm, in order to prevent pin-like bodies 20 having that diameter from entering and contacting the motor inside.

Figures 6 and 6A illustrate the path followed by the electric current lead in the form of an insulated wire forming the winding, on the two planes which delimit the statoraxially,that is on the winding heads.

Figure 6A illustrates the path in a conventional machine wherein a mostly insulating ring 35 leaves at the area around the shaft 13 a space 36 for accommo- dating the hub or rotary bearing, not carried axially on the outside as claimed by the invention, but placed therein traditionally, which space occupies most ofthe face or head ofthe stator 15.

Figure 6 shows instead the path in a machine incorporating the rotor of this invention. This includes, in fact, the hubs 23' and 23" of Figures 1 and 2, which enclosethe bearings24' and 24" as shifted axially more to the outside at areas which do not interfere with the areas where the winding heads extend.

Thus, the insulating ring 37 ofthe shaft 13 m-ay be held closely adherent on the shaft and the entire face ofthe stator left clear.

In the traditional Figure 6A, the bundle 38 ofthe wires coming out of one groove 39 follows of necessity a path along an arc of a circle 40 to enter the opposed groove 41.

Figure 6 illustrates the path followed, according to the invention, bythe bundle 42 emerging out ofthe groove 43 to reach into the opposed groove 44. It is appreciably rectilinear, much shorter than an arc of a circle.

Moreover, it is apparentfrom the figure that the invention leaves more room for the adjoining bundle, not shown, emerging from the groove 45 and required to reach into the groove 46. It shall have to lay beside the preceding bundle 42, on the same plane, whereas inthetraditional arrangement shown in the right-hand figure, a bundle extending out of the groove 47 and back into the groove 48 shall have to be laid on a successive underlying plane with respect two the bundle 38, to greatly increase the axial space require mentsofthewinding head.

The improvements illustrated hereinabove lead to a revolution in the construction of such rotors, which lowers their manufacturing costs and increases their efficiency.

In some particular cases, in order to meet individual application requirements, such asthatthe machine be fully sealed against dust penetration, orthatthe length between the hub ends be reduced, or that the rotor may be later disassembled and reassembled, some of the improvements described may be omitted without, however, departing from the invention scope.

Claims (25)

1. A rotorfor an inverted (in-out) rotary electric machine ofthe type having a stationary shaft, characterized in that it comprisesatoroidal element and two covers, the toroidal element including the core laminations and shorting rings castthereon and surfaces intended for adhering on the covers, and the covers including each a hub wherewith a bearing arrangedto rotatetherewith is made rigid, and surfaces mating with said surfaces ofthe toroidal element.

2. A rotor according to Claim 1, wherein the toroidal elementfurthercomprises lugsofa deformable material which are deformed to stiffen the toroidal element and covers assembly, the covers being formed with seats for receiving said lugs.

3. A rotor according to Claims 1 and 2, wherein the toroidal element lugs are an integral part of the casting thereof.

4. A rotor according to Claims 1 and 2,wherein the surfacesofthetoroidal element and covers mating with each other are configured to increase their mutual adhesion.

5. Arotoraccording to Claims land 2, wherein the toroidal element is provided with centrifugal ventilation fins and/orthe covers are apertured to admit the ventilation air.

6. A rotor according to Claims 1 and 2, wherein the material ofthe toroidal element casting is either aluminum of an alloy thereof.

7. A rotor according to Claims 1 and 2, wherein the toroidal element and covers are mutually held rigid in a concentric position with the rotation axis by the adhesion or friction ofthe surfaces purposely formed thereon.

8. A rotor according to Claim 4, wherein adhesion is achieved bydeforming orupsettingthe lugsformed onthetoroidal element.

9. A rotor according to Claim 1, wherein the adhesion between the toroidal element and covers is achieved through an adhesive.

10. A rotor according to Claim 1, wherein the adhesion between the toroidal element and covers is accomplished by screws, preferably but not critically ofthe self-tapping variety.

11. A rotor according to Claim 5, wherein apertures forthe admission of ventilating airformed in the disk-like element are configured as axial fans and pump airtowardthe interior against the heads ofthe winding existing on the stator.

12. A rotor according to Claim 5, wherein aperturesfor letting outtheventilation airformed in the toroidal element are configured labyrinth-like.

13. A rotor according to Claim 12,whereinthe labyrinth which prevents solid objects from entering the motor is achieved byforming with thefins cast on the shorting ring channels sloping outwards toward the symmetry plane ofthe core laminations perpendicularto the axis.

14. A rotor according to either Claim 11 or 12, wherein the apertures are restricted such as to prevent the entrance of pin-like bodies with a definite diameter and balls also having a definite diameter.

15. A rotor according to Claim 1, wherein the covers are characterized in that the bearings rotating therewith are positioned in a perpendicular plane to the axis, outboard of the area wherethe heads ofthe statorwinding extend.

16. A rotor according to Claim 15, which allows the bundles of wires coming out of one groove in the statorand entering the opposed grooveto layonthe head along the shortest route chord.

17. A rotor according to Claim 16, wherein the increased room leftforthe headsallowstwo ormore bundles to be laid side-by-side in the same plane, thus reducing the axial space requirements of said heads.

18. A rotor as herein described and illustrated.

19. A method of manufacturing a rotorforan inverted (in-out) rotary electric machine ofthe type having a stationary shaft, comprising the steps of: forming a toroidal element by providing the rotor core laminations and casting into the grooves thereof a conductive metal to form the two shorting rings, and surfaces intended for adhesion on the covers; providing two covers including each a hub wherewith a bearing is made rigid and surfaces mating with said surfaces ofthetoroidal element; sliding the rotor over the stator ofthe electric machine,the latter being already secured to the shaft and centered true to its axis, by holding it concentrically spaced aparttherefrom with shims or probes; bringing the covers close to thetoroidal element by sliding the bearings thereof overthe machine shaft, and juxtaposing said adhesion surfaces of the covers to those of the toroidal element; removing said shims or probes; and making the adhesion permanent.

20. AmethodaccordingtoClaim 19,whereinthe adhesion is made permanent by casting on at least one ofthe shorting rings deformable lugs and forming in the corresponding cover seats for accommodating said lugs; inserting said lugs into said seats while the covers are broughtcloseto the toroidal element; and deforming said lugs such thatthetoroidal element and cover are made rigid together and the assembly is stiffened.

21. A method according to Claim 20,whereinthe deformable lugs, priorto being deformed, fit loosely in the corresponding seats.

22. AmethodaccordingtoClaim 19,whereinthe adhesion is made permanent by means of an adhesive interposed between the adhesion surfaces of at least one ring and the corresponding cover.

23. A method according to Claim 19, wherein the adhesion is made permanent th rough a means allowing disassembly, such as the tightening of screws or bolts.

24. An inverted rotary electric machine incorporating a rotor according to Claim 1, substantially as described and illustrated.

25. An inverted rotary electric machine manufac tured with the method of Claim 19, and substantially as described and illustrated.