GB2475095A

GB2475095A - Armature arrangement in permanent magnet electrical machines

Info

Publication number: GB2475095A
Application number: GB0919495A
Authority: GB
Inventors: Frank Heinrich Moeller
Original assignee: Nexxtdrive Ltd
Current assignee: Nexxtdrive Ltd
Priority date: 2009-11-06
Filing date: 2009-11-06
Publication date: 2011-05-11
Also published as: WO2011055124A1; GB0919495D0

Abstract

An electrical machine having a magnetic field provided by a plurality of permanent magnets 10 mounted on a field yoke 1 to form a rotor. A series of cores 6 are provided with coils 8 thereon to form wound poles of a stator of the electrical machine. The rotor forms a channel within which poles of the stator are accommodated. Unwound cores 15 are formed with apertures to receive bolts 16 so as to secure the armature to the carrier. Wedges 12 are provided between adjacent ones of the wound poles with the wedges 12 being bolted to a body of the stator. The arrangement is such that the coils 8 and the cores 6 on which they are mounted are secured relative to one another and also to the wedges 12, and hence to the remainder of the stator. The machine may be linear or rotary and the arrangement reversed to provide a permanent magnet rotor and a wound stator, the armature being supplied via a commutator (Fig7).

Description

ELECTRICAL MACHINES

The present invention relates to electrical machines.

Electrical machines have always been of great technical and commercial interest and have been continually improved over many years.

US Patent 6,459,179 (Lynch) is one example of a relatively modern proposal for an axial flux electrical machine in which a commutated, wound rotor is formed from a large number of conductive sections, outer ends of which are interconnected by members having vanes arranged to direct cooling fluid over the ends of the conductive sections.

1 0 US Patent 6,812, 615 (Ettridge) discloses a radial flux motor using H-shaped coils, having a pole piece at each end of a wound iron core. The pole pieces are used for fixing the poles to an armature carrier.

Despite many improvements over the years, there remains a continuing demand for electrical machines that are smaller, lighter, more powerful and, in general, more efficient.

Preferred embodiments of the present invention aim to provide electrical machines that respond to these demands.

At the present time, control circuits for electrical machines are at an advanced state. For example, circuits for generating travelling fields in polyphase synchronous machines are well known. Circuits for controlling power and speed of machines in response to loads and demands are well known. As the present invention is not particularly concerned with such control circuits per se, they are not described here in any detail. The skilled reader has a wealth of information available from the general state of the art.

Rather, preferred embodiments of the present invention are more concerned with the physical arrangement of windings and associated parts in an electrical machine.

According to one aspect of the present invention, there is provided an electrical machine having a field source and an armature, wherein: the field source provides magnetic poles that are of opposite polarity and are physically opposite one another with an air gap therebetween; the armature comprises a plurality of wound poles, each comprising a winding carried on a respective iron core to leave the core with two exposed faces that face respectively in opposite directions; and the wound poles of the armature are positioned with the two exposed faces of each core between opposite poles of the field source, with an air gap between each of the exposed faces and the opposing pole of the field source.

In the context of this specification, "armature" means a wound part of an electrical machine that interacts with a magnetic field created by a field source of the machine. The armature may be either a stator or a rotor.

An "exposed face" of a core is a face that is not covered by a winding.

2 0 Preferably, the armature is supported by supporting elements disposed between adjacent ones of said wound poles.

Preferably, said supporting elements comprise elements that are physically separate from said iron cores.

Preferably, said supporting elements comprise unwound iron cores disposed between said wound poles.

Preferably, said supporting elements are provided on a carrier.

Preferably, at least some of said supporting elements are secured to said carrier by securing elements that pass through said supporting elements and engage said carrier.

At least some of said supporting elements may be formed integrally with said carrier.

Preferably, said supporting elements are in the form of wedges.

Said supporting elements may comprise a non-ferrous thermally conductive material.

Preferably, the core of each said wound pole is of substantially constant cross-sectional area along its length.

Preferably, the core of each said wound pole and the respective said exposed faces have a substantially constant cross-sectional shape.

Preferably, the winding of each said wound pole extends for substantially the full length of its respective iron core.

Preferably, the winding of each said wound pole comprises copper alloy or aluminium alloy strip material.

Preferably, the winding of each said wound pole comprises a side by side pair of coils wound in mutually opposite senses such that current flows in the same direction in each coil, with connection lugs outside of each coil.

Preferably, the iron cores of the wound poles comprise thin electrical steel lamination sheet or strip material, which has been roll formed in the direction of the flux, to achieve a directionally oriented or anisotropic grain structure.

Preferably, the field source comprises Halbach magnet arrays.

An electrical machine according to any of the preceding aspects of the 1 0 invention may comprise a rotary machine or a linear machine.

An electrical machine according to the preceding aspects of the invention may comprise a motor or a generator.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 a is a developed view in longitudinal sectional of a single layer rotary motor with coil-less inter poles; Figures lb and 1 c are sectional views on the lines B-B and A-A respectively of Figure la, in the case of a single armature carrier; Figures 1 d and 1 e are sectional views corresponding to Figures lb and lc respectively, but in the case of a double armature carrier; Figures 2a to 2e are views similar to those of Figures la to le respectively, but for a double layer machine with non-ferrous support pieces instead of coil-less inter poles; Figure 3a is an isometric view of a single layer radial flux machine, from one side; Figure 3b is an isometric view of the single layer radial flux machine of Figure 3a, from the other side; Figure 4a is an isometric view of a double layer radial flux machine, from one side; Figure 4b is an isometric view of the double layer radial flux machine of Figure 4a, from the other side; Figures 5a and 5b are sectional views corresponding to Figures 2c and 2b respectively, but in the case of a machine with only outer permanent magnets on a rotor; Figures 6a and 6b are sectional views similar to Figures 2c and 2b respectively, but in the case of a high speed axial flux machine; Figures 7a and 7b are sectional views similar to Figures 6b and 6a respectively, but in the case of a brushed axial flux machine; Figures 8a to 8e show various different iron cores, each in elevation and 2 0 section; Figure 9a is an isometric view of a core with flat strip coils for a radial flux machine; Figure 9b is a longitudinal sectional view of the core and coils of Figure 9a; Figure 9c is a cross-sectional view of an inward coil of Figures 9a and 9b; and Figure 9d is a cross-sectional view of an outward coil of Figures 9a and 9b.

In the figures, like references denote like or corresponding parts.

Figures 1 a to 1 e show a permanent magnet polyphase synchronous electric motor in which a wound armature 4 is located between opposing poles of a permanent magnet array 10 mounted on legs or annuli 5 of a field yoke 1, with field infifis or iron lands 2 between the magnets 10. The field yoke 1 is typically in the form of a steel channel, with poles of the armature 4 within it.

The wound armature 4 comprises a series of wound poles, which are formed on iron cores 6 that alternate evenly with a series of unwound iron cores 15. The unwound cores 15 are formed with apertures 14 through which bolts 16 pass to secure the cores 15 to an armature carrier 17. Each wound pole carries a coil 8 that surrounds four faces of the core 6, leaving two exposed end faces 6a, 2 0 6b that face respectively in opposite directions, with air gaps between the exposed end faces and opposite poles of the field magnet array 10. Each coil 8 has terminals 20 that connect with control circuitry on a printed circuit board (PCB) 18, or a phase connection plate or ring.

In Figures lb and lc, there is a single, outer armature carrier (non-iron) 17, to which the unwound iron cores 15 are secured.

In the variation of Figures 1 d and 1 e, there is a second, inner armature carrier (non-iron) 12, to which the unwound iron cores 15 are also secured.

It will be appreciated that a motor as illustrated in Figures 1 a to 1 e may afford an efficient construction that utilises a relatively low amount of iron and therefore has relatively low iron losses. Using the unwound cores 15 to secure the armature 4 is particularly efficient.

Figures 2a to 2e correspond generally to Figures la to le, but show a double layer machine in which all available iron cores are wound with coils 8, leaving no unwound cores 15 as in Figures 1 a to 1 e. Instead of unwound cores 15, the machine of Figures 2a to 2e has non-iron support plates 12 disposed between adjacent coils 8. Like the unwound cores 15 of Figures la to le, the support plates 12 are formed with holes 14 through which bolts 16 pass to secure the armature to the outer armature carrier 17 -and inner armature carrier 11, if provided.

The skilled reader wifi appreciate that, although Figures 1 a and 2a are developed views of a rotary motor, they could equally well represent linear machines, the various sectional views AA and BB corresponding.

2 0 Figures 3a and 3b are isometric views of a rotary machine having a configuration similar to that illustrated in Figures la to le. Thus, pairs of coils 8 on respective cores alternate with unwound cores 15 (which may be referred to as coil less inter poles). A non-iron support wedge or plate 12 is inserted between the coils 8 of each pair. The wound armature comprising the coils 8, unwound cores and other components form a stator that cooperates with a rotor comprising the permanent magnet array 10 on field yoke or channel 1.

Bolts passing through the unwound cores 15 and support wedges or plates 12 secure the armature to the armature carrier 17.

The machine shown in isometric views in Figures 4a and 4b is generally similar to that of Figures 3a and 3b, but is a double layer machine in which all available iron cores are wound with coils 8, leaving no unwound cores 15 as in Figures 3a and 3b. In Figures 4a and 4b, a non-iron support wedge or plate 12 is inserted between each adjacent pair of coils 8. Bolts passing through the support wedges or plates 12 secure the armature to the armature carrier 17.

As may be seen in Figures 3a and 4a, each coil 8 is formed as a strip winding, with the terminals of the strip windings all facing the same way, for ready connection to respective PCBs or other terminal components.

Figures 5a and Sb show a variation of Figures 2b and 2c respectively, in which permanent magnets 10 are provided only on an outer ring or annulus S of the field yoke, the inner magnet poles being provided by the inner ring or annulus S of the field yoke. Such an arrangement may avoid use of a bandage as often used to hold magnet strips glued to the outer surface of a radial flux machine. This may have not such a high torque capacity, but could physically be 2 0 taken to much higher speeds, because the magnets on the inside of the outer ring are held in position by a centrifugal force that increases with rotor speed.

Figures 6a and 6b show a variation of Figures lb and 1 c respectively, in which the various components have the same references as before, but are arranged in an axial flux rather than a radial flux configuration. Permanent magnets 10 are mounted on annuli of a field yoke having a connecting web or cross-member 3, such that wound cores 6 and unwound cores 15 are disposed alternately in the air gap between opposing magnets 10. The magnets 10 are mounted within recesses 7 to restrain the magnets when subjected to centrifugal forces. Bolts 16 pass through the unwound cores 15 to secure the armature to the armature carrier 17.

As seen in Figures 6a and 6b, the connecting web or cross-member 3 of the field yoke, which may comprise a circular soft steel channel, is radially inside the rotor and its annuli or discs carrying the magnets 10 are arranged outwards, to result in the smallest possible inertia of the rotor. With the magnets partly 1 0 recessed into the annuli or discs by means of the recesses 7 to locate them firmly, and the armature inserted between the magnets 10, this arrangement may be very suitable for very high rotational speeds.

Such high speed motors could also use relatively thick magnet segments made of Ferrite material which would result in extremely cost effective, but stifi high performance motors, if one compares for instance the future availability and cost of Neodymium magnets against Ferrite magnets.

Figures 7a and 7b show another machine which, like that of Figures 6a and 6b, is an axial flux machine. However, in Figures 7a and 7b, the positions of the field source and the armature are reversed. That is, the field source including 2 0 magnets 10 is the stator and, within that, the armature is the rotor. Thus, a shaft 24 rotates in bearings 22 located within a bearing housing and cover 21, which is provided with a shaft seal 23. A brush assembly 25 and commutator 26 afford electrical connections, with conductors 27 extending between commutator 26 and coil terminals 20. Bolts 16 pass through the unwound cores 15 to secure the armature to the armature carrier 17, which is mounted on the shaft 24.

-10 -As seen in Figures 7a and 7b, the connecting web or cross-member 3 of the field yoke, which may comprise a circular soft steel channel, is radially outside the rotor and its annuli or discs carrying the magnets 10 are arranged inwardly. The rotating armature is placed inside the stator with the coil connections 27 terminating in the commutator 26, which should be on the smallest possible diameter.

Figures 8a to 8e show various examples of core configurations, in elevation and section.

Figure 8a shows a main core 6 of a radial flux machine that carries a coil 8 -as shown in Figures 3a, 3b, 4a, 4b, for example. Figure 8b shows an intermediate core 15 that remains unwound, for use in such a radia' flux machine. Providing laminations of different shapes for the wound and unwound cores may afford a maximum fill factor, resulting in additional strength and stability of the armature. The wedge shape of the intermediate core 15 is particularly effective for retaining the wound cores 6 in position.

Figure 8c shows a mixed composition round pole for an axial flux machine. This comprises iron laminations 6 surrounding a ferrite core 28.

Figure 8d shows a main core 6 of an axial flux machine that carries a coil 8. Figure 8e shows an intermediate core 15 that remains unwound, for use in an axial flux machine.

Figure 9a is an isometric view of a main core 6 as shown in Figure 8a, wound with two flat strip coils 8 -as shown in Figures 3a, 3b, 4a, 4b, for example. The sectional view of Figure 9b shows the two adjacent coils 8 with cross connection 9, coil terminals 20 and PCB 18. Reference 19 ifiustrates a -11 -common grain orientation of steel laminations of the core 6. As may be seen in Figures 9c and 9d, the two coils 8 are wound in opposite senses, from their innermost to outermost turns. The cross-connection 9 preferably introduces a twist in the strip of the coils. It wifi be appreciated that, although the two coils 8 are wound physically in opposite directions, they make up a composite coil assembly in which current always flows in the same direction. For example, if current flows in a clockwise direction in the coil as seen in Fig 9d, from outermost to innermost turn, the current passes through the cross connection 9 and continues to flow clockwise in the coil as seen in Fig 9c from innermost to outermost turn and terminal 20.

The various examples of construction of electric motors as ifiustrated in the accompanying drawings and described above afford compactness, efficiency, wide range of application and ease of manufacture. An arrangement in which opposite ends of the wound poles are disposed in an air gap between opposing field magnets can provide motors with a high torque capacity and good efficiencies over a large speed range.

The above embodiments of the invention employ individual non-headed iron cores, which over substantially their full length (at least 8O%, 9O% or 95% of their length) are surrounded or flanked by wire or strip windings. The cores 2 0 are modest in number and of significant bulk as compared to cores disclosed in US 6,459,179 (Lynch), for example, to make them suitable for individual connection to a 3-phase supply, so that brushless and radial flux designs are both feasible.

Embodiments of the invention afford the possibility to intersperse a coil core array with non-ferrous plates or wedges, which can positively support the -12 -armature, particularly if they extend into or are fixed to a supporting ring carrier, which is preferably of non-ferrous but thermally conductive material.

For a brushless design, the armature wifi generally be the stator, in which case a non-ferrous supporting ring can then be directly joined to the casing of the motor. The rotor can be made of soft electrical steel, which can be machined to any shape, but can also run at much higher speeds before disintegrating due to centrifugal forces.

For a single layer polyphase permanent magnet synchronous motor (PPSM), wound cores 6 alternate with unwound cores 15. The latter have windings flanking the core on two sides only, leaving the end faces free to be mounted to a supporting ring of non-ferrous material, which could be in aluminium. However, eddy currents in an electrically conductive material could still cause some power losses. Therefore, the supporting ring could comprise a plastic compound material -e.g. a plastics filled with aluminium particles -to get good thermal conductivity and to take away heat generated in the coils.

On double layer machines, there are generally no unwound cores and space is left between the wound cores, to be filled with plates or wedges which may be of non-ferrous material as above, which then has to have good thermal conductivity but also requires some structural strength, as the plates or wedges need to be extended into the supporting ring, so that the whole of the armature is carried not just by the windings, but also by the wedges or plates.

Wedges are ideal for radial flux and axial flux rotating machines, if they are combined with flat winding strip around the cores, because these can be wound without leaving any air space and pushing in the wedges when assembling in a mandrel wifi firmly locate the whole of the armature. Such an -13 -assembly will not have to rely on potting to keep its shape and the air gaps can be made as small as is desirable for high torque operation.

Advantages of embodiments of the invention will now be described for a fixed armature radial flux motor having permanent field magnets mounted on the inside of an outer ring and on the outside of an inner ring of a soft steel rotor. A double layer machine may provide lower speed but higher torque capacity.

1. Double-ended cores (pole pieces) with magnets directly across the air gap can provide a very high torque of the motor for a given 1 0 stack length.

2. The active iron of the compact disjointed individual cores minimises the iron that sees any flux variation and therefore reduces iron losses. Shorter stack length and grain-oriented laminations can be utilised, allowing very high flux densities and very high constant power speed ranges to be reached by the motor, without much loss of efficiency at the lowest and highest rated speeds.

3. Further reduction of iron losses in the armature is achieved, because the individual cores (pole pieces) do not connect directly with a flux backing ring and carrier and do not rely on any armature backing iron to carry their flux to an opposite pole. The total iron losses will therefore be substantially lower than that of conventional machines.

-14 - 4. The motors can be very short and because the iron can be kept to a minimum their weight and bulk will be substantially lower than that of conventional motors.

5. The cores (pole pieces) can be mounted on a relatively large diameter, for good torque capacity throughout the speed range and because of the high circumferential speed difference between stator and rotor at the air gap interfaces, extreme powers can be reached at the rated speed.

6. Flat winding strip coils terminating on the outside of the coils ensure easy connection to appropriately phased PCBs.

7. Furthermore, flat winding strip coils ensure that a maximum winding fill factor is reached, so that low cost aluminium windings can be considered.

8. The flat strips can be wound so they stay in close contact with the iron cores, allowing heat conducting non-ferrous wedges or plates to be inserted between the coils, which can firmly locate each of the individual poles (cores) within the armature, so that the whole armature becomes a stable structure without having to rely on potting for stability.

9. Locating coil terminals on the outside, by using a pair of coils wound in opposite directions, makes for very compact, easy to make coil assemblies.

-15 - 10. Non-ferrous heat conducting wedges or plates can be extended into a non-ferrous armature support ring for additional stability and heat conductivity.

11. Iron core lamination pieces may be all the same, being generally rectangular, and can easily be assembled and potted into segmented cores matching the inside and outside radius of the rotor with the radius of the permanent magnet field arrays.

12. Additional to the normal flux return path through the soft steel channel legs (rings or discs/annuli), for double layer machines the yoke of the channel also can serve as a flux conductor and the total soft steel content can be minimised, taking both flux return paths into account.

13. The individual parts of the armature, the cores, coils, PCB and non-ferrous support parts can all be manufactured separately on dedicated production lines and then assembled on a dedicated assembly plant, ensuring low-cost production at low and high production levels.

14. If Halbach field magnet arrays are utilised opposite both ends of the armature poles (cores) across the air gaps, instead of flat 2 0 magnet strip soft steel backed type, the field component can be made from a lighter non-magnetic material, which would not have any of the iron field losses conventionally experienced.

Various features of embodiments of the invention may be as follows.

-16 -Iron cores of wound poles may be substantially bulky rectangular, trapezoidal, semicircular or segmented bodies, surrounded or flanked by electric windings that may typically comprise aluminium or copper or alloys thereof.

For brushed machines, supporting wedges or plates may extend into fan blades.

Permanent field magnets may be replaced by electrically energized coil cores, which in the case of a brushed machine are static, but in the case of a brushless machine require slip rings to be connected and energised. Alternatively the rotating field energy can also come from batteries carried within the rotor, or the excitation energy may be electromagnetically induced.

For axial flux brushless machines, the rotor may be made from "soft" electrical steel.

A soft electrical steel field component (rotor of brushless machine) may be made from steel laminations or sintered iron or resin coated iron particles to reduce high frequency flux losses in this component.

For brushless electronically commutated types of machine, magnet arrays may be generally equispaced and have sufficient distance between them to allow protruding steel lands of similar height to the magnets between them, allowing some electronic field weakening to be applied.

2 0 Armature iron cores may be made from thin electrical stee' lamination sheet or strip material, which has been roll formed in the direction of the flux, to achieve a directionally oriented or anisotropic grain structure which can pass a higher flux and results in lower energy losses, than isotropic material.

-17 -For high motor efficiencies, Halbach magnet arrays may be utilised instead of flat unidirectional field magnets, eliminating the need to circulate the field flux in the field component (rotor of brushless machine) so this can be constructed from a lighter non-ferrous material, eliminating any field iron losses and allowing design for maximum strength to contain the Halbach arrays at high rotor speeds.

Although the above embodiments of the invention are described mostly as brushless motors, it will be appreciated that embodiments of the invention may apply to electrical machines more generally, including brushed or 1 0 commutated machines, as in the example of Figure 7, and generators as well as motors.

In this specification, the verb "comprise" has its normal dictionary meaning, to denote non-exclusive inclusion. That is, use of the word "comprise" (or any of its derivatives) to include one feature or more, does not exclude the possibility of also including further features.

The reader's attention is directed to all and any priority documents identified in connection with this application and to all and any papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with 2 0 this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except -18 -combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel 1 0 combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

-19 -CLAIMS1. An electrical machine having a field source and an armature, wherein: a. the field source provides magnetic poles that are of opposite polarity and are physically opposite one another with an air gap therebetween; b. the armature comprises a plurality of wound poles, each comprising a winding carried on a respective iron core to leave the core with two exposed faces that face respectively in opposite directions; and c. the wound poles of the armature are positioned with the two exposed faces of each core between opposite poles of the field source, with an air gap between each of the exposed faces and the opposing pole of the field source.
2. An electrical machine according to claim 1, wherein the armature is supported by supporting elements disposed between adjacent ones of said
3. An electrical machine according to claim 2, wherein said supporting elements comprise elements that are physically separate from said iron cores.
4. An electrical machine according to claim 2 or 3, wherein said supporting elements comprise unwound iron cores disposed between said wound poles.
5. An electrical machine according to claim 2, 3 or 4, wherein said 2 0 supporting elements are provided on a carrier.
6. An electrical machine according to claim 5, wherein at least some of said supporting elements are secured to said carrier by securing elements that pass through said supporting elements and engage said carrier.-20 -
7. An electrical machine according to claim 5, wherein at least some of said supporting elements are formed integrally with said carrier.
8. An electrical machine according to any of claims 2 to 7, wherein said supporting elements are in the form of wedges.
9. An electrical machine according to any of claims 2 to 8, wherein said supporting elements comprise a non-ferrous thermally conductive material.
10. An electrical machine according to any of the preceding claims, wherein the core of each said wound pole is of substantially constant cross-sectional area along its length.1 0
11. An electrical machine according to any of the preceding claims, wherein the winding of each said wound pole extends for substantially the full length of its respective iron core.
12. An electrical machine according to any of the preceding claims, wherein the winding of each said wound pole comprises copper alloy or aluminium alloy strip material.
13. An electrical machine according to any of the preceding claims, wherein the winding of each said wound pole comprises a side by side pair of coils wound in mutually opposite senses such that current flows in the same direction in each coil, with connection lugs outside of each coil.2 0
14. An electrical machine according to any of the preceding claims, wherein the iron cores of the wound poles comprise thin electrical steel lamination sheet or strip material, which has been roll formed in the direction of the flux, to achieve a directionally oriented or anisotropic grain structure.-21 -
15. An electrical machine according to any of the preceding claims, whereinthe field source comprises Halbach magnet arrays.
16. An electrical machine according to any of the preceding claims, being a rotary machine.
17. An electrical machine according to any of claims 1 to 15, being a linear machine.
18. An electrical machine according to any of the preceding claims, being a motor.
19. An electrical machine according to any of claims 1 to 17, being a 1 0 generator.
20. An electrical machine substantially as hereinbefore described with reference to any of the accompanying drawings.