WO2007040483A1

WO2007040483A1 - Multipolar machines - improvements

Info

Publication number: WO2007040483A1
Application number: PCT/US2005/034066
Authority: WO
Inventors: Doris Wilsdorf
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-09-23
Filing date: 2005-09-23
Publication date: 2007-04-12
Anticipated expiration: 2008-03-23

Abstract

A rotor for multipolar machine is made layers of wires (2(1) and 2(2)). The wires are compacted twisted wire bundles (154) in order to reduce cogging and gradients of the magnetic flux density.

Description

Title: Multipolar Machines - Improvements

Inventor: Wilsdorf, Doris Background and Abstract

CROSS-REFERENCE TO RELATED APPLICATIONS

Related U.S. Patent Applications are:

"Multipolar Machines," Doris Kuhlmann-Wilsdorf, International Patent Application PCT/US03/21298 filed 8 July 2003

"MP-A and MP-T Machines, Multipolar Machines for Alternating and Three-Phase Currents," Patent Application PCT/US05/30186 filed 24 August 2005

"Multipolar-Plus Machines — Multipolar Machines with Reduced Numbers of Brushes," Patent Application PCT/US05/23245 filed 29 June 2005

FIELD AND AIM OF THE INVENTION

The present invention pertains to the family of "multipolar" (MP) machines, i.e. electric motors and generators, described in the patent applications© "Multipolar Machines", (ii) "MP-A and MP-T Machines, Multipolar Machines for Alternating and Three-Phase Currents" and (iii) "Multipolar-Plus Machines - Multipolar Machines with Reduced Numbers of Brushes" by D. Kuhlmann- Wilsdorf. Specifically, the present invention concerns three improvements in the manufacture and use of MP machines, as may be applicable from case to case. These concern 1. the construction of rotor bodies, 2. the construction of rotor end- pieces where in the case of MP-Plus machines electrical brushes are replaced by "flags" and 3. the magnet morphology in magnet tubes. The aim in the first two cases is simplification and/or cost reduction in manufacturing, together with potential mechanical strengthening of rotors; the aim in the third case is reduction gradients of magnetic flux density in the zones in which the current flows and that translates into increased power density of machines and/or reduced "cogging".

It may be noted here that the width of any one "zone" is not precisely defined. Below, the "zone width" is labeled L_n, and is primarily identified with the circumferential width of the radially oriented permanent magnet poles in a Hallbach arrangement as projected on the rotor mid-line, and is secondarily identified with the width of the correlated electrical brushes that pick up the current in a zone. However, the magnet arrangement may not be of Hallbach type, and/or the brush width may not equal the magnet pole width. In fact, with Hallbach arrangements, brush widths may advantageously be made narrower than the circumferential width of the correlated magnet pole pair as projected on the rotor mid-line, so as to raise the "effective" value of B, i.e. the average radial magnetic flux density to which the machine current is exposed while passing through the zones.

It follows that equations derived for machine torques and power are approximations. This is unavoidable because the position dependence of the radial magnetic flux density, i.e. B(x) if x denotes the circumferential distance from any selected point in the rotor wall, is a continuous function whose magnitude typically peaks close to the radial symmetry planes between opposing magnet poles and vanishes at the radial symmetry planes at which the magnet polarity switches sign. Resides, a machine current will mildly displace opposing magnet poles from strict radial correlations, which radial misalignment will rarely if ever exceed two degrees of arc and is therefore disregarded below.

Hence a "zone" designates a strip of rotor wall about the maximum of B(x), of a width generally and conveniently assumed to be one half of the spacing between (nearly) radial planes at which the radial component of B changes sign, and the value of B in cited equations represents the average magnetic flux density through which the current passes.

I. GENERAL DESCRIPTION OF THE INVENTION

Improvement of Making Rotor Bodies by Means of Twisted Wire Bundles

Rotors of MP machines of all types must be "current channeling" as well as be essentially free of eddy currents. To this end they require axially extended insulation barriers whose properties largely overlap but not coincide for the two purposes. Specifically, for the great majority of MP machines, as an upper limit, eddy current barriers need to be about

1/16" or more narrowly spaced in the circumferential direction. For rotor bodies made of parallel strips of metal, this means that rods or wires of 1/16" or smaller diameter need to be assembled. However, the cost of assembling and gluing together very slender, initially straight rods or wires rises more steeply than in proportion with the number of rods or wires per rotor. According to the present invention, therefore, a cheaper method that at the same time will result in mechanically stronger rotors is the assembly and gluing together of preformed twisted wire bundles in lieu of individual rods or wires.

Improvement in Making rotor Ends by Means of "Flag Modules" In MP-Plus machines, one or both ends of a rotor need to be fitted with "flags" that replace sliding electrical brushes by leading the current from the end of any one rod or wire to an equivalent rod or wire at the same rotor end but one zone periodicity distance away. The use of twisted wire bundles for the construction of rotor bodies in accordance with the previous point will be helpful in reducing the number of individual flags and thus will help in reducing rotor construction costs. Even more helpful will be the use of "flag modules" in accordance with the present invention, wherein a multiplicity of "flags" is pre-formed into modules that are conductively joined to the ends of rotor bodies, in lieu of individual flags.

Attaining More Uniform Magnetic Fields Through Novel Magnet Arrangements hi the preceding patent applications no restrictions were placed on the nature or arrangement of the magnetic field sources that establish a magnetic flux density B in a multiplicity of axially extended zones in the wall of a rotor. These could be permanent magnets, electromagnets and/or superconducting magnets. The most frequently assumed were Hallbach arrangements, composed of axially extended strips of permanent magnets with alternating radial and tangential directions of magnetization, and these alternating in sense of direction, i.e. radially in and out and tangentially clockwise and anticlockwise. Additional, novel types of permanent magnet arrangements were proposed in a previous patent application. hi accordance with the present invention a further class of permanent magnet arrangement is proposed, namely of only radial direction of magnetization with alternating sense of orientation. The major objective herein is the reduction of gradients, in the circumferential direction, of the magnetic flux density in the zones. This is for the reason that currents inevitably tend to crowd into the regions of smallest possible B which not only reduces machine efficiency but also gives rise to "cogging". Both of these undesirable effects are reduced through reducing circumferential gradients of B in zones. The optimal choices between the various possible magnet morphologies in accordance with the present invention to best fulfill the two indicated objectives may depend on specifics of individual machines and on detailed analyses of the resulting magnetic flux densities in the zones relative to weight and cost of the magnets.

II. BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Figure 1 is a perspective partial view of the end of a rotor body made of twisted wire bundles affixed to which is part of a "flag module." Figure 2 clarifies the origin and magnitude of cogging for different cases.

III. DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, the present invention will now be described.

Rotors Made of Wire Bundles (Figure 1)

The upper right of Figure 1 shows the end of a rotor body composed of two layers, 2(1) and 2(2), that are mutually electrically insulated via insulation layer 4, as for an MP-Plus machine. Instead of being composed of individual wires or rods, layers 2(1) and 2(2) are composed of bundles of, preferably twisted, wires (154) that are bonded together with electrically insulating layers 57. The cross sectional shape of the wire bundles is optional. In a preferred embodiment, the wires will be mutually insulated by means of thin layers that may soften on heating. After bundling and optional twisting by say, one to four revolutions per rotor length, the bundles may be compacted into the desired shape, e.g. by rolling, while warm, and will harden into the compacted shape on cooling. According to the present invention, in preferred embodiments, the insulation of the individual wires will be applied as a commercially available very thin enamel, and bonding layers 57 between wire bundles 154 will be made of several times thicker, but still less than one millimeter thick, commercially available glass insulation. According to a US manufacturer, the enamel can sustain up to 900 V per single layer and the glass insulation up to 360V, thus permitting up to, say, 2,500 V potential difference between neighboring twisted wire bundles. For the electrical separation between adjoining layers, e.g. 2(1) and 2(2), in the rotor of very large machines, extra insulation thickness may be needed. For this reason, insulation layer 157 at rotor midline 4 between rotors 2(1) and 2(2) in conductive layer 155 may have to be made extra thick, as is suggested in Figure 1.

The objective of twisting the bundles is to prevent the current to crowd into areas of lowest B in their respective zone. Namely, in the twisted form, all wires in a bundle will sample the same values of B so that a conductor, such as 155 in Figure 1, conductively connected across a cut of a bundle that intersects all wires in it, will receive current of essentially uniform current density across the whole bundle. Insulating "seams" (156) in Iayerl55 will then permit selective current conduction from any one bundle.

"Flag Modules" in Lieu of Individual Flags.

As already indicated, in MP-Plus machines, electrical brushes sliding on slip rings and aligned with their respective zones, are replaced by "flags" which are mutually insulated conductors that connect any one rod, wire or wire bundle, with a corresponding rod, wire or wire bundle exactly one periodicity distance displaced, - and in fact in a neighboring rotor layer. Thus in Figure 1, flags will be needed that conductively connect any one wire bundle 154 in rotor layer 2(1) to a wire bundle in rotor layer 2(2) that is displaced by (nearly exactly) one zone periodicity distance, i.e. from, say, zone N in layer 2(1) to zone (N+l) in layer 2(2).

The morphology of the "flags" is illustrated at lower left in Figure 1. Herein the flags

(20) are mutually insulated foils or strips of metal that conduct current between an upper conductive layer (201), that on its outside will commonly also serve as a slip ring (34), to a lower layer 202, both of which are electrically sub-divided to propagate the pattern of the insulation layers 57 between the wire bundles, but displaced by one zone periodicity distance between top and bottom layer.

As seen in Figure 1, the current flows into the top layer strips (201) from the adjacent wire bundles, namely through conductive layer 155 that is subdivided into the corresponding sections by means of insulation strips 156 and 157, as already indicated. Insulation strip 153 further insulates layers 201 and 202 from each other. Thus each flag 20 conducts currents between bundles of the two rotor layers, i.e. 2(1) and 2(2), but one periodicity distance displaced, as intended. The morphology of the flags in Figure 1 may be regarded as a refinement of the "flags between tabs" construction of Figure 11 in the patent application "Multipolar-Plus Machines - Multipolar Machines with Reduced Numbers of Brushes," Patent Application PCT/US05/23245 filed 29 June 2005, or alternatively as a variant of "inserts in groove" as in Figure 9B of that application, wherein in Figure 1 the equivalent of the groove with inserts has been conductively butt-joined to the rotor body (i.e. the rotor part that rotates in the gap between magnet tubes 5 and 6, not shown in this figure) that is constructed from said twisted and compacted wire bundles

The electrically conductive butt joint between rotor body 2 and what has been dubbed the "module" of flags 20, i.e. subdivided layer 155, would, in an MP-Plus machine, be located just outside of the magnet tubes that are not shown in Figure 1. By virtue of the insulation layers between the wires, e.g. of enamel as already indicated, the bundles will inhibit eddy currents, but no such precautions against eddy currents are needed outside of the tubes where the magnetic flux density is minimal. To restate the geometry, conductive layer 155 between rotor and flag modules 20 will conduct the current from the bundles to solid layers 201 and 202 on the inner and outer surface of the flag modules that are divided into mutually insulated strips that are coordinated with the bundles. Layers 201 and 202 play the role of the layer of rods thinned down to ~T/3 on either side of the groove in Figure 9B of the application "Multipolar-Plus Machines - Multipolar Machines with Reduced Numbers of Brushes."

Insulating layer 203 is sized so as not to obstruct the current passage from wire bundles to layers 201 and 202, but to prevent short-circuiting between flags 20 and wire bundles 154. Thus insulating layer 203 plays the role of the insulated bottom of groove 41 in Figure 9B of the earlier application. The actual flags in the flag module are mutually insulated pieces or strips of metal sheet, conductively joined to layers 201 and 202, and shaped to span the circumferential distance between neighboring zones, as in the earlier Figures 9, 10 and 11.

According to the present invention, construction of a rotor on the pattern of Figure 1, i.e. including compacted twisted bundles of mutually electrically insulated wires in lieu of individual rods or wires, is favored because it will eliminate a considerable amount of otherwise requisite handwork and thus cost. Specifically, compacted twisted wire bundles may be assembled in the same manner as rods but, by being generally thicker and much stiffer, will be more easily handled, besides requiring fewer insulating joints between them. Next, flag "modules," to be butt-joined to rotor 2 as in Figure 1, may be made in arbitrary chosen circumferential lengths, and flags 20 in them will be rather thicker, and thus be fewer per unit circumferential length, than in Figures 9B, 1OB and 11 of application "Multipolar-Plus Machines . . . ." Also there will be no need to drill holes as in the "flags on poles" method or to solder or conductively glue individual tabs as in the "flags on tabs" method of the previous patent application on MP-Plus machines.

The one step that in the construction of Figure 1 will require particular care, besides making sure that the offset between the ends of flags is exactly the same as the distance between neighboring zones, is the conductive joining of layer 155 to the rotor end with the exposed wire bundle cross sections, such that the insulation between bundles 154 and the conductive areas between insulation strips 156 and 157 closely match. In order to simplify this task, is it proposed to moderately widen insulating strips 156 and 157 beyond what would be require for electrical insulation.

Optimum Size of Twisted Wire Bundles or Number of Flags per Zone

An important consideration in accordance with the present invention is the number of flags per zone. This is limited in two ways. Firstly by electric noise producing "cogging," as already indicated above and further discussed below in connection with Figure 2. This will require six or more flags per zone periodicity interval depending on magnet arrangement. A critical point herein is the fact that the electrical impedance among mutually insulated similar conductors, e.g. compacted wire-bundles, decreases with the average value of B across their width. Therefore, among bundles 154 that at any one moment are in electrical contact with a single brush (that may be physically positioned any number of zones away), those at the edges of zones and protruding beyond these will offer the smallest electrical resistance, will therefore conduct far more than their geometrically expected share of the current, and thus depress the machine value of B below the average across the zone, assuming that all flags are accurately aligned with the zones.

It will require a detailed analysis to determine the best compromise between saving construction cost through increasing the average bundle width and correspondingly decreasing the number of flags, and the resulting decrease of machine power, as further discussed below. Fortunately, with lazily twisted fiber bundles, i.e. at least one whole turn per rotor body length and typically no more than, say, four complete turns, this effect is much smaller than it would be for widened tabs (153) in Figure 11 of the previous application ("Multipolar-Plus Machines - Multipolar Machines with Reduced Numbers of Brushes") This is so because every wire in a lazily twisted wire bundle will sample all B values over the width of the bundle and current cannot crowd into one or the other side of those bundles, as already indicated above. Thereby the effective flux density for each bundle will nearly average the value of B over its width, while wide tabs will individually crowd the current into regions of lowered B.

An interesting facet of this problem is the possible increase of machine efficiency through decreased brush width. For example, for a fiber bundle width of L_m/3, as in Figure 1, with a brush of the same width as the zone, i.e. L₀₁, he outermost fiber bundles to conduct current and therefore able to partly bypass the highest values of B, will extend up to 2/3 towards the midline of the gap with the correspondingly lowered average B value, whereas with a brush of only L_m/3 width, none of the current-carrying bundles will ever extent beyond the zone edges and the machine will exhibit the actual average value of B in the zones. It may even prove advantageous to increase the bundle width to LJ2 and decrease the brush width to ¹LJl. However, given a limiting brush current density, narrower brushes require wider slip rings which are another important consideration to weigh.

As shown in Figure 1, one (and typically the outer) surface of the flag module will serve as slip ring 34 and commonly its axial extent will be determined by the current carrying capability of the brushes.

Novel Magnet Arrangement for Improving Machine Costs and Reducing "Cogging"

As already emphasized above, a critical issue in MP machine construction costs, especially of large machines, is the uncomfortably close spacing of axially oriented current insulation barriers needed for current channeling as well as eddy current barriers. Indeed, a strong motivation for the use of twisted wire bundles as in the above sections is reduced machine construction cost. The degree to which this approach may be exploited is limited by the fact that increasing spacing of current insulation barriers causes increasingly strong "cogging" and thus degrades the highly desired feature of homopolar machines to be electronically very quiet. Perhaps more importantly yet, wide spaces between current insulation barriers increase the effective width of the zones as the possible machine current paths extend farther from the symmetry plane of maximum magnetic flux density, thereby lowering the average B-value. This undesirable effect is aggravated well beyond simple geometry because lowered B-values translate into steeply decreasing impedance so that currents will divert into paths of low flux density, thereby reducing machine efficiency.

According to the present invention, one of two important means for decreasing the number of axially oriented current barriers without those twin problems is the use of twisted wire bundles instead of rods, for providing the needed eddy current barriers as in Figure 1 already discussed. The second is a novel magnet arrangement that provides a much flatter maximum of B(x), with x-the local circumferential coordinate, than do Hallbach arrangements. By using both approaches together, according to the present invention, the goal of as few as three insulation barriers per brush may be achieved at minimum "cogging" and minimum loss of machine efficiency, even while present best knowledge suggests that the cost of magnet material may also be reduced.

Figure 2 clarifies the effects of insulating barrier spacing for two different types of magnet arrangements, namely (i) a Hallbach array (Figure 2A and C) and (n) in Figure 2B, a novel magnet arrangement for which no detailed modeling is as yet available. Also considered are two different spacings between the current-channeling insulation layers in the rotor, i.e. bundle widths in terms of Figure 1.

The magnet arrangements are shown in the vertical center of Figure 2, including magnets with indicated direction of magnetization by means of arrows pointing from South to North. Also shown are mechanical magnet support (129) in the case of Hallbach arrangements in Figures 2 A and 2C, and flux return material (131) that at the same time serves as mechanical support in the case of a the novel magnet arrangement in Figure 2B. Mechanical support 129 may be made of any suitable material, whether a metal or non-metal such as a plastic. Flux return material 131 should be a "soft" ferromagnetic material such as FeSi alloy. The approximate magnitude and distribution of the magnetic flux density in the rotor mid-line for the three cases is shown in the diagrams at top, and the geometry of the rotor body (2) and slip ring (34) with brush (27) including insulating bonding layers (57) for the three cases is shown at bottom.

In agreement with various finite element models, Figures 2A and 2C show that a typical Hallbach arrangement yields a roughly sinusoidal B(x) distribution, if x denotes the circumferential axis direction which is the direction in which the brush moves relative to the rotor. By contrast, as seen, the novel arrangement of Figure 2B yields a substantially flattened B(x) distribution. Further, it is assumed that the rotor is made such that there are n_x flags per zone and thus n_x/2 flags per brush width, L_m. For the particular example of Figure 2A, n_x = 6, i.e. three flags per brush, the minimum acceptable number already cited above. Accordingly, the number of conductors, e.g. twisted compacted wire bundles as in Figure 1 that are in electrical contact with an electrical brush (i.e. mediated by an arbitrary number of flags, so that the brush may be physically an arbitrary number of zones distant) is intermittently as low as n_x/2 = 3, but generally the brush contacts four bundles, two of which are fully underneath the brush footprint and two that protrude beyond the brush at its two sides, for a total protruding width of one bundle. Similarly, for n_x = 10 in Figure 2C, i.e. ten bundles per zone, the number previously cited as acceptable, the brush always fully contacts four bundles, whereas two bundles, one on each side, protrude by varying amounts, again for a total of one protruding bundle width.

In the top diagrams of Figure 2, the extreme positions of the left-most insulating bonding layers 57, e.g. the momentarily edges of the left-most current-conducting bundle, are indicated by vertical arrows. Herein, x_u shows the leading bundle boundary position as it just begins to protrude beyond the trailing edge of the brush, and X_L shows the position of the trailing insulation layer (57) as the bundle just loses contact with the brush. These positions are significant because, assuming the example of the rotor construction from compacted bundles and flag modules as in Figure 1, the wires in each twisted wire bundle (154) will sample the B values over its whole width and the brush will make electrical contact with all wires in the bundle at once. The effective B-value of the bundle will therefore change between the values according to the mid-point positions between those limits, i.e. from B₁₁ to B_L indicated by the circles on the curves, while the bundle protrusion beyond the brush increases from zero to a full bundle width on losing contact. When the bundle is just one half under the brush footprint, the effective B-value will be B_ave • Meanwhile on the opposite brush side, i.e. three bundles width ahead to the right, another bundle enters the footprint of the brush and undergoes very closely the opposite change. The average change of B for all momentarily current conducting bundles together, and thus the force per unit of current, will thus be minor.

However, and as already stated above, the impedance of a bundle (or tab) steeply decreases with decreasing B. As a result, a disproportionately large fraction of the machine current passes through the one or two bundles with the lowest B-value and thus the current will cyclically shift to and fro, always favoring the bundle or tab with the widest protrusion beyond the brush footprint. And this effect of constantly concentrating the current in the bundle with the lowest average B-value will significantly degrade the machine efficiency. In sum, then, on account of the described equal but opposite current cycling in the two bundles on opposite brush edges, "cogging" in terms of cyclic brush current variation (and thus machine current variation) in the case of Hallbach arrangements with n_x = 6 as in Figure 2A, is moderate. More significant will be a to and fro cyclic of current flow distribution between leading and trailing brush edges. And most importantly, the machine efficiency will be significantly degraded because machine power is proportional to B², again assuming that flags are accurately aligned with zones. Misalignments between flags and zones with somewhat "wash out" the discussed effect but will tend to further degrade machine power and is therefore to be avoided.

Figure 2C shows the same analysis but for n_x = 10. As seen, now the difference between B_u and B_L is greatly decreased, in fact roughly in proportion with the two n_x-values, i.e. by the factor of -6/10. In accordance with the above explanation, the major effect of increasing numbers of bundles per brush is thus some decrease of "cogging," which is modest in any event, but more importantly, for fixed machine current, an increase of machine voltage and thus of machine power. According to the rather crude analysis of Figures 2A and 2C, then, with Hallbach arrangements, the machine power could be roughly halved if there are only six bundles per zone as in Figure 2 A but may be relatively increased by, say, 50% by increasing n_x from three to five. Another result that also can be seen from considering Figures 2A and 2C, is that machine power may be considerably improved through cutting down on the width of the brush. Namely, the protruding bundles maximally extend by one bundle width from the brush edges, and thus, at maximum as well as on average, to lower B-values for wider than for narrower brushes. In the cases of Figures 2A and 2C, for example, halving the brush width would raise the effective magnetic flux density of the outermost bundles almost to the indicated value of B_ave and above.

The same analysis for the assumed magnetic flux density distribution of Figure 2B, again for n_x = 6, i.e. for the same values of x_u and X_L, yields very much smaller variations of effective B-values, namely the B₀ and B_L indicated in Figure 2B, amounting only to about 10% variation from B_ave for the edge bundles. A magnetic flux density distribution as in Figure 2B, and even more so a still flatter one, thus permits the use of n_x as low as 3 without current cogging and at a minor penalty in terms of machine power. In fact, with still further flattened B(x) profiles, the brush width could be increased beyond L_n, which would lead to a possible increase of machine current, thus of machine power and a reduction of machine loss, hi this connection it may be noted that a close agreement between B inferred from machine performance and modeled via finite element analysis for prototype II, with Hallbach arrangement, was achieved with n_x = 8 but with brush width cut down to almost Vi L_m. In summary: 1) Machine construction cost may be significantly reduced by increasing bundle width, i.e. by decreasing n_x. However, with Hallbach arrangements, decreased n_x values significantly decrease machine power unless brush width is decreased. Yet decreasing brush width increases Joule loss and thereby decreases machine efficiency and raises cooling needs. Therefore, with Hallbach magnet arrangements, both measures against cogging, i.e. decreasing bundle width and decreasing brush width, have significant drawbacks, as demonstrated by means of Figures 2A and 2C. By contrast, shaping the B(x) distribution to comprise a broad, flat maximum, if not perhaps a shallow relative minimum at the center, will achieve high machine power even with wide brushes, as demonstrated in Figure 2B.

Preliminary calculations suggest that the desired shape of B(x) as in Figure 2B may be achieved, in fact with better effective B-values and less magnet mass than Hallbach arrangements, by the use of magnets of alternating radial magnetic polarity (i.e. eliminating magnets with tangentially oriented polarity as in Hallbach arrangements), that are flat in radial direction and extended in circumferential direction by a few gap widths between the opposing poles, as suggested in Figure 2B and perhaps even more extended. From case to case, the optimal shape of magnets of the type in Figure 2B that will produce suitably small B(x) gradients in the mid-half of zones, so as to keep cogging at a low level, and do so at minimum magnet mass, will still have to be determined through, say, finite element analysis. However, shape details are expected to be less important than the circumferential magnet length, 2L_1n, in Figure 2B, relative to average radial magnet thickness, H_m, and both in relation to the average gap width between opposing poles, LQ. hi fact smooth cylindrical shell shapes, i.e. constant H_m over the whole circumferential magnet length, may be satisfactory, and this perhaps without gaps between neighboring magnets. According to the present invention, then, any combination of 2L_m/L_<3>1.25 and Hm/Lo >0.1 maybe suitable for the purpose of achieving acceptable B(x) in terms of Figure 2B. However, at otherwise same machine parameters but increasing values of 2L_nZLo and H_m/Lo machine voltage will decrease and cost will rise, respectively. Practically speaking, this may provide the limits of 2L_nZLo ^< 20 and H_m/Lo< 5. Thus, according to the present invention, 0.1LQ ≤H_m <5L_G and 1.25LQ ≤2Lm <20LQ are preferred dimensions for magnetic field sources in the form of permanent magnets and gap widths between opposing poles in machines of the MP family.

Other upper limits, namely tied to machine dimensions, would be πD/2L_m >4, i.e.

2L_m<πD/4 and H_m≤D/4. More typical values would be 2WL_G = 1.5, 2, 3, 4 or 5 but with possible values ranging up to 10, 15 or 20, as already indicated, and any values in-between. Similarly, typical expected values for H_m/L_G would include 0.2, 0.4, 0.7 and 1.0 and any values in-between, with possible values ranging up from H_m/Lo =1 to 2,and up to 5 as already stated, and all values in-between.

In summary, then, according to the present invention, superior MP machine performance may be achieved by the use of magnets of alternating, predominantly radial sense of magnetization, with few if any, say, less than 10% of circumferential space occupancy, of magnets with tangential orientation of magnetization, and the indicated range of dimensions.

LIST OF REFERENCES

The following references and foregoing related applications are incorporated herein by reference as if fully set forth herein:

"Multipolar Machines," Doris Kuhlmann-Wilsdorf, International Patent Application PCT/US03/21298 filed 8 July 2003;

"MP-A and MP-T Machines, Multipolar Machines for Alternating and Three-Phase Currents," Patent Application PCT/US05/30186 filed 24 August 2005;

"Multipolar-Plus Machines - Multipolar Machines with Reduced Numbers of Brushes," Patent Application PCT/US05/23245 filed 29 June 2005.

Claims

WHAT IS CLAIMED AS NEW AND DESIRED TO BE SECURED BY LETTERS PATENT OF THE UNITED STATES IS:

1. An electrical machine capable of operating as an electric motor, an electric generator, and/or an electric transformer, comprising: multiple magnetic field sources surrounding a rotor set of N_T > 1 layers at the outside and inside; said magnetic field sources establishing a magnetic flux density B in a multiplicity of axially extended zones in said rotor wall; and said magnetic flux density B alternating in radial orientation between neighboring zones; and said rotor wall constructed from compacted twisted wire bundles.

2. An electrical machine capable of operating as an electric motor, an electric generator, and/or an electric transformer, comprising: multiple magnetic field sources surrounding a rotor set of N_T ≥ 1 layers at the outside and inside; said magnetic field sources establishing a magnetic flux density B in a multiplicity of axially extended zones in said rotor wall; and said magnetic flux density B alternating in radial orientation between neighboring zones; and said magnetic field sources shaped to reduce gradients of said magnetic flux density in the middle half of zones by means of predominantly radial sense of magnetization, with less than 10% of circumferential space occupancy of magnets with tangential orientation of magnetization..

3. An electrical machine capable of operating as an electric motor, an electric generator, and/or an electric transformer, comprising: multiple magnetic field sources surrounding a rotor set of N_T ≥ 1 layers at the outside and inside; said magnetic field sources establishing a magnetic flux density B in a multiplicity of axially extended zones in said rotor wall; and said magnetic flux density B alternating in radial orientation between neighboring zones; and said rotor wall comprising a multiplicity of permanent internal connections conductively connecting correlated positions in neighboring zones of neighboring rotors; and which permanent internal connections are arranged into at least one flag module.

4. A homopolar machine according to claims 1, 2 or 3 wherein a plurality of said magnetic field sources are configured into at least one of an outer and an inner magnet tube.

5. A homopolar machine according to claim 2 wherein said magnetic field sources have alternating radial magnetic polarity and have a ratio of radial thickness H_m to gap width between poles L_G between the limits of 0.1 < H_Π/L_G ≤ 5.

6. A homopolar machine according to claim 2 wherein said magnetic field sources have alternating radial magnetic polarity and have a ratio of circumferential length 2L_m to gap width between poles LQ between the limits of 1.25 <2LΠ,/L_G ≤20