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Title:
ARMATURE FOR AN ELECTRIC MACHINE
Document Type and Number:
WIPO Patent Application WO/2018/163120
Kind Code:
A1
Abstract:
An armature (50) for an electric machine is provided having a plurality of brushes (52, 54, 56, 58) and a plurality of conductive segments (66) spaced about a rotation axis thereof. The segments (66) form a ring (62) and are electrically insulated from one another. The armature has more coils (68, 72) than brushes (52, 54, 56, 58) and each coil (68, 72) is electrically connected between a pair of complementary segments (70, 74). Each brush (52, 54, 56, 58) is configured to make simultaneous contact with a plurality of segments (66) such that at any angular rotation of the electric machine the number of segments (66) making contact with a brush (52, 54, 56, 58) is greater than the number of segments (66) not making contact with a brush (52, 54, 56, 58). The coils (68, 72) are configured to have a coil pitch such that its complementary segments (70, 74) are separated by a number of adjacent segments (66) that is greater than or equal to a maximum number of adjecent segments (66) in contact with a brush (52, 54, 56, 58) at any angular rotation of the electric machine.

Inventors:
IGNJATOVIC, Dragan (57 Versailles Village Life, Regent Street, 7655 Wellington, 7655, ZA)
Application Number:
IB2018/051556
Publication Date:
September 13, 2018
Filing Date:
March 09, 2018
Export Citation:
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Assignee:
IGNJATOVIC, Dragan (57 Versailles Village Life, Regent Street, 7655 Wellington, 7655, ZA)
International Classes:
H02K23/26; H01R39/18; H02K13/10; H02K23/36
Foreign References:
US4459503A1984-07-10
Attorney, Agent or Firm:
VON SEIDELS INTELLECTUAL PROPERTY ATTORNEYS (P O Box 440, Century City, 7446 Cape Town, 7446, ZA)
Download PDF:
Claims:
CLAIMS:

An armature for an electric machine including:

a plurality of brushes associated with the armature;

a plurality of electrically conductive segments circumferentially spaced about a rotation axis of the electric machine and forming a ring formation co-axial with the rotation axis, each segment being electrically insulated from its adjacent segments; and

a plurality of coils greater in number to that of the brushes, each coil electrically connected between a pair of complementary segments,

wherein each brush is configured to make simultaneous contact with a plurality of segments along an arcuate contact area of the ring formation such that at any angular rotation of the electric machine a combined total number of segments making contact with a brush is greater than a combined total number of segments not making contact with a brush, and

wherein each coil is configured to have a coil pitch such that its complementary pair of segments are separated by a number of adjacent segments that is greater than or equal to a maximum number of adjacent segments in contact with a brush at any angular rotation of the electric machine about its rotation axis.

An armature as claimed in claims 1 or 2 wherein the brushes are equidimensional arcuate segments circumferentially distributed about the rotation axis.

An armature as claimed in claim 2 wherein each brush is configured to make contact with the plurality of segments at a radially inner surface of the brush.

An armature as claimed in claim 3 wherein each brush is configured such that it makes contact in a sliding engagement with the segments at a radially outer surface of the ring formation.

An armature as claimed in any one of claims 1 or 2 wherein each brush is configured to make contact with the plurality of segments at an axial surface of the brush.

An armature as claimed in claim 5 wherein each brush is configured such that it makes contact in a sliding engagement with the segments at an axially outer surface of the ring formation.

7. An armature as claimed in claim 1 wherein the brushes are electrically conductive belts, each belt being configured to make contact with a plurality of segments at an arcuate belt contact area. 8 An armature as claimed in either claim 7 wherein each belt is configured such that its belt contact area makes contact with the segments at a radially outer surface of the ring formation.

9. An armature as claimed in claim 7 or 8 wherein the armature has a plurality of ring formations axially spaced along the rotation axis with an insulator interposed between adjacent ring formations such that the belts, in use, are electrically insulated from one another.

10. An armature as claimed in claim 9 wherein each segment of each ring formation is in electrical communication with a corresponding segment on each adjacent ring formation through an electric conductor.

1 1 . An armature as claimed in claim 10 wherein electrically corresponding segments on adjacent ring formations are angularly displaced from one another.

12. An armature as claimed in claim 7 or 8 wherein the ring formation includes a plurality of axially aligned and stacked segmented ring formations with electrical insulators interposed between adjacent ring formations, each ring formation having a contact sector, each segment of each ring formation being electrically connected to a segment on each other ring formation, the ring formations arranged such that the contact sector of the ring formations are substantially radially aligned.

13. An armature as claimed in any one of claims 1 to 12 wherein an outer periphery of the armature is a smooth, non-toothed armature surface that is at least partially non-magnetic or non-conductive, and wherein the coils are positioned on the smooth surface.

14. An armature as claimed in any one of claims 1 to 12 wherein an outer periphery of the armature has longitudinally extending slots that are circumferentially arranged about the outer periphery, and wherein the coils are held within the slots of the armature.

15. An armature as claimed in any one of claims 1 to 14 including a non-rotatable core.

16. An armature as claimed in claim 15 wherein the core is provided with additional field windings within the non-rotatable core.

17. An armature as claimed in either claim 15 or 16 wherein the core is provided with compensation coils within the non-rotatable core.

18. An armature as claimed in any one of claims 1 to 17 wherein each coil includes two substantially parallel coil sides, each coil having a plurality of conductor turns that are arranged such that the turns at or near an outer edge of one side of the coil are at or near an inner edge of the other side.

19. An armature as claimed in claim 18 wherein the two coil sides are angularly displaced by a predetermined angle relative to one another about a rotation axis of the armature. 20. An armature as claimed in claim 19 wherein the predetermined angle is substantially

360

— degrees where P is a total number of poles of the electrical machine.

Description:
ARMATURE FOR AN ELECTRIC MACHINE

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from South African provisional patent application number 2017/01745 filed on 10 March 2017, which is incorporated by reference herein.

FIELD OF THE INVENTION

The invention disclosed relates to rotary machines. More specifically it relates to electrical rotary machines such as electrical motors and generators. Even more specifically, it relates to armatures for such electric machines.

BACKGROUND TO THE INVENTION

Rotary electrical machines generally comprise two major components. The one major component is the stator and is the part of the machine that remains stationary during operation. The second major component is the rotor and is the part of the machine that rotates during operation. These two major components each comprise a number of different sub-components. Rotary electric machines may either be an electric motor or an electric generator. The term "electric machine" will therefore be used herein to refer to either motor or generator.

The power producing component of an electric machine is called the armature and can be on either the rotor or the stator of the electric machine.

Some DC electric machines have a mechanical rectifier called a commutator that generally comprises a cylindrical arrangement of electrically conductive segments. In a generator configuration the commutator converts the alternating current (AC) generated by the machine into DC for output therefrom. In a motor configuration the function of the commutator is to ensure that DC current provided as an input to the machine is transferred to the armature coils such as to produce a torque in a substantially constant rotational direction.

Conventional electric machines and specifically direct current (DC) electric machines have armatures that are generally wound according to either one of two methods. Depending on the manner in which the armature coils are connected to the segments of the commutator, the winding method will either be "lap winding" or "wave winding".

In a lap wound armature, for example a "simplex" lap wound armature, the two ends of any coil are connected to adjacent commutator segments. Furthermore, two successive coils each have an end sharing a common segment of the commutator to which they connected. Therefore, a second (finishing) end of a first coil is connected to the same commutator segment as a first (starting) end of a second coil succeeding the first coil. Successive coils also physically overlap one another from which the term "lap" winding originates. A number of parallel coil paths are provided through this winding method between brushes of the machine that are equal to the number of poles of the machine. Such a machine will generally have the same number of brushes as the number of poles of the machine.

In a wave wound armature a second (finishing) end of a first coil is connected to the same commutator segment as a first (starting) end of a second coil having the same polarity as that of the first coil. The ends of successive coils are therefore connected in series and wave winding is therefore also by some referred to as "series winding". Such a machine will generally require only two brushes. A typical lap winding diagram is shown in Figure 1 . This type of winding diagram is known as a "developed" winding diagram and is a two-dimensional schematic representation of the coils as if the armature had been cut in an axial plane and laid flat. In the coil section (1 ), the broken lines indicate the section of the particular coil that is overlapped by another coil. The numbering in the coil section (1 ) corresponds to respective individual inductors formed by the coils, each coil forming two inductors. The commutator section (2) shows the individual commutator segments and the numbering in the commutator section (2) is a sequential numbering of the successive segments of the commutator. The brush section (3) shows the individual brushes making contact with the commutator. Figure 2 shows a simplified schematic representation of the winding diagram of Figure 1 . In Figure 2 the coils of the coil section (1 ) are shown as they are connected end-to-end (in series) and the inductor numbers corresponding to each respective coil as shown in Figure 1 are also indicated. The segments in the commutator section (2) is therefore also not shown in sequential numbering, but rather as they are electrically connected with the coils. The brush section (3) indicates the segments with which the respective brushes make contact.

Similarly, Figures 3 and 4 respectively show a developed winding diagram of a typical wave winding diagram and a simplified schematic representation thereof, each also having a coil section (4), a commutator section (5) and a brush section (6) with numbering as explained for Figures 1 and 2.

In either configuration the brushes of the machine are arranged such that each brush makes contact with a successive commutator segment as the machine, and therefore the commutator, rotates. In a typical electrical machine the total number of segments making contact with a brush at any point of rotation is therefore substantially less than those not making contact with a brush at that particular point of rotation. This can also be seen in Figures 1 to 4. The applicant proposes a novel armature configuration and particularly with reference to the coils, commutator segments and brushes that at least to some extent offers improvement on conventional armature configurations.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided an armature for an electric machine including: a plurality of brushes associated with the armature;

a plurality of electrically conductive segments circumferentially spaced about a rotation axis of the electric machine and forming a ring formation co-axial with the rotation axis, each segment being electrically insulated from its adjacent segments;

a plurality of coils greater in number to that of the brushes, each coil electrically connected between a pair of complementary segments,

wherein each brush is configured to make simultaneous contact with a plurality of segments along an arcuate contact area of the ring formation such that at any angular rotation of the electric machine a combined total number of segments making contact with a brush is greater than a combined total number of segments not making contact with a brush, and

wherein each coil is configured to have a coil pitch such that its complementary pair of segments are separated by a number of adjacent segments that is greater than or equal to a maximum number of adjacent segments in contact with a brush at any angular rotation of the electric machine about its rotation axis.

In one embodiment the brushes are equidimensional arcuate segments circumferentially distributed about the rotation axis. Further features of the invention provide for each brush to be configured to make contact with a plurality of segments at a radially inner surface of the brush; and for each brush to be configured such that it makes contact in a sliding engagement with the segments at a radially outer surface of the ring formation.

Alternatively, further features of the invention provide for each brush to be configured to make contact with the plurality of segments at an axial surface of the brush; and for each brush to be configured such that it makes contact in a sliding engagement with the segments at an axially outer surface of the ring formation.

In another embodiment the brushes are electrically conductive belts, each belt being configured to make contact with a plurality of segments at an arcuate belt contact area; and for each belt to be configured such that its belt contact area makes contact with the segments at a radially outer surface of the ring formation.

Further features of the invention provide for the armature to have a plurality of ring formations axially spaced along the rotation axis with an insulator interposed between adjacent ring formations such that the belts, in use, are electrically insulated from one another; and for each segment of each ring formation to be in electrical communication with a corresponding segment on each adjacent ring formation through an electric conductor.

Further features of the invention provide for electrically corresponding segments on adjacent ring formations to be angularly displaced from one another; for each brush insulator to define an arcuate section of the ring formation that is not in contact with a brush; and for each brush contact area span to be configured so as to maximise a number of coils with which each brush makes simultaneous contact.

A further feature of the invention provides for each brush contact area span to be configured such that each coil is in electrical communication with more than one brush at any angular rotation of the electric machine about its rotation axis.

In a further embodiment the ring formation includes a plurality of axially aligned and stacked segmented ring formations with electrical insulators interposed between adjacent ring formations, each ring formation having a contact sector, each segment of each ring formation being electrically connected to a segment on each other ring formation, the ring formations arranged such that the contact sector of the ring formations are substantially radially aligned. Further features of the invention provide for an outer periphery of the armature to have a smooth, non-toothed armature surface that is at least partially non-magnetic or non-conductive; and for the coils to be positioned on the smooth surface, alternatively for an outer periphery of the armature to have longitudinally extending slots that are circumferentially arranged about the outer periphery; and for the coils to be held within the slots of the armature.

Further features of the invention provide for the armature to include a non-rotatable core; for the core to be provided with additional field windings within the non-rotatable core; and for the core to be provided with compensation coils within the non-rotatable core.

Further features of the invention provide for each coil to include two substantially parallel coil sides, each coil having a plurality of conductor turns that are arranged such that the turns at or near an outer edge of one side of the coil are at or near an inner edge of the other side; for each first and each second coil sides to be angularly displaced by a predetermined angle relative to one another about a rotation axis of the electric machine; and for the predetermined angle to be

360

substantially— degrees where P is a total number of poles of the electrical machine.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is prior art showing a developed winding diagram of an armature with a typical lap winding configuration;

Figure 2 is a schematic diagram of the developed winding diagram of Figure 1 ;

Figure 3 is prior art showing a developed winding diagram of an armature with a typical wave winding configuration;

Figure 4 is a schematic diagram of the armature of Figure 3;

Figure 5 is a developed winding diagram of a first embodiment of an armature in accordance with the invention having a full coil pitch and an even number of segments; is a schematic diagram of the armature of Figure 5; is a schematic representation of a second embodiment of an armature in accordance with the invention having an odd number of coils at a first angular position; is a schematic representation of the armature of Figure 7 at a second angular position; is a schematic representation of the armature of Figure 7 at a third angular position; is a developed winding diagram of the armature of Figure 7; is a schematic diagram of the windings of the armature of Figure 7; is a developed winding diagram of a third embodiment of an armature in accordance with the invention having an even number of segments; is a schematic representation of the armature of Figure 12; is a schematic representation of a fourth embodiment of an armature in accordance with the invention having an odd number of segments at a first angular position; is a schematic representation of the armature of Figure 14 at a second angular position; is a developed winding diagram of a fifth embodiment of an armature in accordance with the invention having an even number of segments and full pitch coils; is a schematic representation of the armature of Figure 16; is a developed winding diagram of a sixth embodiment of an armature in accordance with the invention having an even number of segments and long pitch coils; is a schematic representation of the armature of Figure 18; is a developed winding diagram of the armature of Figure 18 at a second armature position; is a schematic representation of the armature of Figure 18 at the second armature position; is a developed winding diagram of a seventh embodiment of an armature in accordance with the invention having an odd number of segments; is a schematic representation of the armature of Figure 22; is a developed winding diagram of an eighth embodiment of an armature in accordance with the invention having an even number of segments and long pitch coils; is a schematic representation of the armature of Figure 24; is a developed winding diagram of the armature of Figure 24 at a second armature position; is a schematic representation of the armature of Figure 24 at the second armature position; is a three-dimensional view of a ninth embodiment of an armature in accordance with the invention; is a front elevation of the armature of Figure 28; is a schematic representation of sections of a coil; is a cross-sectional view of an electrical machine which includes a tenth embodiment of an armature in accordance with the invention; is a cross-sectional view of the electrical machine of Figure 31 provided with compensation coils; Figure 33 is a schematic representation of an eleventh embodiment of an armature in accordance with the invention; Figure 34 is a three-dimensional view of a ring formation assembly for an armature in accordance with a twelfth embodiment of the invention; is a schematic representation of an armature in in use with the ring formation assembly of Figure 34; is a three-dimensional view of a ring formation assembly for an armature in accordance with a thirteenth embodiment of the invention; is a three-dimensional view of an electrical machine in use with an armature having the ring formation assembly of Figure 36;and is a schematic representation of an armature in accordance with a fourteenth embodiment of the invention in which the armature is provided by the stator of an electric machine.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

Exemplary embodiments of an armature for an electric machine are described below. The electric machine may be any rotary electric machine including direct current (DC) machines and alternating current (AC) machines where applicable. The electric machine may be operated in an electricity generating configuration, thus converting inputted rotational kinetic energy of the armature, in embodiments in which the armature is provided by the rotor of the electric machine, into outputted electrical energy, or in a motor configuration, thus converting inputted electrical energy into outputted rotational kinetic energy.

Embodiments of the armature described below, except where otherwise indicated, includes a number of components that in use rotate and that remain stationary. Some of these rotating and stationary components may be essential components of the present invention and the term armature should therefore herein be interpreted widely enough to include such components.

Any reference below to "an armature" or "the armature" should be understood to mean an/the armature of an embodiment in accordance with the present invention. The armature includes a plurality of brushes. The term brush is generally referred to as an electrically conductive component in a rotary electrical machine that is configured to make physical and electrical contact with parts of the machine to either inject current into the machine or to draw current therefrom. The term brush should therefore, except where otherwise indicated, be interpreted widely enough to include any conductive component that makes physical and electric contact with parts of the machine for the purpose of injecting or drawing current into or from the machine as the case may be. The term "brush" should therefore also be interpreted to include electrically conductive belts configured to make contact with a plurality of segments at an arcuate contact area between a belt and a ring formation.

Reference to "rotation of the electric", "angular displacement of the electric machine", "movement of the electric machine" or similar terminology should be interpreted as the rotation of the moving parts of the electric machine about its rotation axis relative to the stationary parts of the electric machine. Similarly, "angular position of the electric machine" and the like should be interpreted as a particular angular displacement of the electric machine's moving parts relative to its stationary parts, for example the particular position of the rotatable segments relative to stationary brushes. In embodiments in which the armature is provided by the rotor of the electric machine, "rotation of the armature", "angular displacement of the armature" and the like should therefore be interpreted to mean that of the rotor.

The armature further includes a plurality of coils. These coils are electrical coils formed by a predetermined number of turns of an insulated conductor with two electrically exposed coil ends, for example copper wire having an outer polymer based insulating coating. The coils of the armature are greater in number than that of the brushes. Each coil is electrically connected between a pair of complementary segments of the ring formation. This electrical connection may be formed by brazing, welding or soldering the electrically exposed ends of the coils to their respective complementary segments.

Reference to "complementary segments" should be understood as meaning those two segments that are electrically connected to a respective first and second end of a relevant coil. Reference to a particular segment's complementary segment should therefore be understood to be that segment connected to an opposite end of the coil to which the particular segment is connected.

Each of the brushes of the armature is configured to make simultaneous contact with a plurality of the segments of the ring formation. This contact refers to physical and electrical contact since the segments and brushes are all electrically conductive. Each brush makes contact with the segments of the ring formation along an arcuate contact area of the ring formation. At any angular rotation of the electric machine a combined total number of segments making contact with a brush is greater than a combined total number of segments not making contact with a brush.

Coil pitch is a term known in the art for referring to a predetermined distance between the two sides of an individual coil of an electrical machine. This may be expressed as a mechanical angle between the two ends of the coil about the axis of rotation. Therefore, for a particular coil pitch each coil will have a particular number of adjacent segments, connected to other coils, separating its complementary segments.

The coils of the armature are each configured to have a coil pitch such that the number of consecutive, adjacent segments separating each complementary pair of segments is greater than or equal to the maximum number of consecutive, adjacent segments in contact with a brush at any angular rotation of the electric machine.

The brushes may be equidimensional arcuate segments circumferentially distributed about the rotation axis, for example electrically conductive carbon/graphite brushes. Such brushes may be circumferentially spaced about the rotation axis of the electric machine.

Exemplary embodiments below may have a relatively small number of coils and segments in order to facilitate illustration of the features of the present invention. In practice an armature may comprise a substantially greater number of coils and segments depending on the performance requirements of a specific machine. Furthermore the number of brushes may also vary depending on the number of poles of an electric machine with which it is used, for example.

As the brushes are configured for a maximised contact area as described below, the brush dimensions accordingly need to be configured to achieve this maximised contact area. This may lead to the required brush dimensions becoming cumbersomely large to have one single continuous brush. Therefore, each of the brushes may comprise a number of smaller brushes that are electrically connected in parallel and that are configured to in concert achieve the desired maximised contact area, whether arranged immediately adjacent another in a common plane or staggered. Some brush embodiments may be generally arcuate in shape allowing for different configurations in terms of which of its outer surfaces are configured to make contact with the segments. Such configurations may include that the brushes and segments make contact with one another at their inner and outer circumferential surfaces respectively, the brushes therefore forming a larger ring around the segment ring formation. In an alternative configuration, the brushes and segments may make contact with one another at a common plane at their axial ends. Here the brushes therefore form a ring axially stacked against the segment ring formation. Figures 1 to 4 are figures showing prior art of an armature provided by a rotor. Figures 1 and 2 are a developed lap winding diagram and a simplified schematic diagram thereof, respectively. Figure 1 shows four brushes in the brush section (3), two positively polarised brushes and two negatively polarised brushes as indicated. At the armature's position illustrated in Figure 1 the positively polarised brushes are respectively making simultaneous contact with commutator segments 5 and 6, and 15 and 16. The negatively polarised brushes are respectively making simultaneous contact with commutator segments 10 and 1 1 , and 20 and 1 .

From the simplified schematic diagram in Figure 2, it can be seen that in this armature position the one positively polarised brush is shorting out the coil consisting of coil inductor numbers 9 and 20 that is connected between commutator segments numbers 5 and 6. Similarly, the second positively polarised brush is shorting out the coil consisting of coil inductor numbers 29 and 40 that is connected between commutator segments numbers 15 and 16. Furthermore, the one negatively polarised brush is shorting out the coil consisting of coil inductor numbers 19 and 30 that is connected between commutator segments numbers 10 and 1 1 . Similarly, the second negatively polarised brush is shorting out the coil consisting of coil inductor numbers 39 and 10 that is connected between commutator segments numbers 20 and 1 .

This may be undesirable for a number of reasons including that it may cause large electrical currents to flow in these short-circuited coils which may lead to undesirable heating of the coils and also in a loss of efficiency. Even if the coils that are short-circuited happen to be in a zone that is magnetically neutral when the machine is at rest at such time, the magnetically neutral zones may shift during operation of the machine due to the armature reaction. Therefore, these coils may have electrical current induced therein at the moment just before being shorted, thus leading to short-circuit currents when being shorted shortly thereafter.

Figures 3 and 4 are a developed wave winding diagram and a simplified schematic diagram thereof, respectively. Figure 3 shows two brushes (in solid lines) in the brush section (6), one positively polarised brush and one negatively polarised brush. At the armature's position illustrated in Figure 3 the positively polarised brush is making simultaneous contact with commutator segments 16 and 17. The negatively polarised brush is making simultaneous contact with commutator segments 1 1 and 12. From the simplified schematic diagram in Figure 4, it can be seen that in this armature position the positively polarised brush is shorting out the coil consisting of coil inductor numbers 29, 40, 9 and 20 that is connected between commutator segments numbers 1 1 and 12. The negatively polarised brush is shorting out the coil consisting of coil inductor numbers 23, 8, 19, and 30 that is connected between commutator segments numbers 16 and 17.

Figures 5 and 6 show a first embodiment of an armature in accordance with the invention. Figure 5 is a developed winding diagram having a coil section (7), a commutator section (8) and a brush section (9). In this embodiment, there are four brushes and 20 electrically conductive commutator segments, each segment being electrically insulated from its adjacent segments. The armature furthermore has 20 coils, each coil electrically connected between a pair of complementary segments. Each brush is configured to make simultaneous contact with a plurality of segments.

As shown in Figure 5, the total number of adjacent segments making contact with a brush is sixteen in the armature position shown and four segments are not making contact with a brush. However, when the armature is rotated slightly (in either direction) each brush will be making contact with five adjacent segments, five therefore being the maximum number of adjacent segments in contact with a brush at any armature position. In the latter position, the total number of segments making contact with a brush will therefore be twenty and those not making contact with a brush will be zero.

Each coil is furthermore configured to have a coil pitch such that its complementary pair of segments are separated by five adjacent segments and therefore by a number of adjacent segments that is equal to the maximum number of adjacent segments in contact with a brush at any armature position. For example, and as can be seen more clearly in Figure 6, the complementary segments for the coil shown in bold consisting of coil inductor numbers 21 and 32 is segments numbers 2 and 7. Segments 2 and 7 are therefore separated by five adjacent segments, starting from segment number 2 that being segment numbers 3, 4, 5, 6 and 7. It should be noted that as is shown in Figures 5 and 6 there is no coil that is short-circuited to the same brush or to one or more brushes of the same polarity.

Figures 7 to 9 show a schematic representation of a second exemplary embodiment of an armature for an electric machine. The armature (10) has two electrically conductive brushes (12, 14) that are arcuate in shape and that are evenly distributed at 180° about an axis of rotation (16) of the armature (10) and separated by two gaps (13, 15). The brushes (12, 14) are configured to remain stationary during operation of the machine and to have opposite electrical polarity. The armature (10) has a ring formation (18) co-axial with and rotatable about the axis of rotation (16). In this embodiment the rotation is counter-clockwise as indicated by the arrow (17). The ring formation (18) has fifteen electrically conductive segments (20) that are electrically insulated from another by means of an insulating material interposed between adjacent segments. The brushes (12, 14) are each configured to make simultaneous contact with a plurality of segments at an arcuate brush contact area (22, 24). The brush contact areas (22, 24) are defined at a radially inner surface of each respective brush (12, 14) and therefore at a radially outer surface of the ring formation (18). The armature (10) furthermore has fifteen electric coils (26) that are rotatable with the ring formation (18). Each coil (26) is connected between two complementary segments. Referring to the exemplary coil (27) shown in bold in Figure 7 and also specifically to the angular position of the ring formation in Figure 7, the coil (27) is configured such that a first terminating end thereof (28) is connected to a first segment (30) near the 9 o'clock position and a second terminating end thereof (32) is connected to a second segment (34) near the 3 o'clock position. Each segment (20) is therefore also connected to a terminating end of two different coils.

At this angular position, each of the brushes (12, 14) makes contact with seven segments. At any angular position of the armature (10) only one segment does not make contact with either brush (12, 14) as will be further explained below. At this angular position the segment not making contact with either brush is the segment (30) at the 9 o'clock position as it is positioned wholly within the gap (13). Therefore the total number of segments (20) electrically connected to either one of the brushes (12, 14) is greater than the number of segments that are not electrically connected to either of the brushes.

Figure 8 shows the armature of Figure 7 in which the armature (10) has rotated slightly further counter-clockwise than in Figure 7. In this angular position both the segments (30, 34) to which the exemplary coil (27) is connected is not making contact with any of the brushes (12, 14) as the one segment (30) wholly falls within the one gap (13) and the other segment (34) falls wholly within the second gap (15). When rotated even slightly further counter-clockwise as shown in Figure 9 the two complementary segments (30, 34) of the exemplary coil (27) have made contact with the two brushes (14, 12) respectively. Therefore at no angular position of the armature (10) do the complementary segments (30, 34) of the exemplary coil (27) make simultaneous contact with the same brush. This is therefore also the case with any of the other coils (20).

Each coil (26) is configured such that its complementary segment pair is separated by a predetermined number of adjacent segments that are equal to or greater than a maximum number of adjacent segments in contact with a brush at any angular rotation of the armature (10). As seen above the maximum number of adjacent segments in contact with any brush is seven in this embodiment. Furthermore, the number of segments separating the complementary segments (30, 34) of the exemplary coil (27) and thus every coil is eight segments when counted clockwise and seven segments when counted counter-clockwise. The number of separating segments is thus greater than or equal to seven. It therefore follows that the gaps (13, 15) span the area of three segments in total, thus one and a half segments per gap.

Figure 10 is a developed winding diagram of the armature of Figure 7. It should be noted that the numbering shown on the segments (1 - 15) as well as those next to the coil sections (1 - 30) is used to indicate the sequential parts of the segments and coil segments (inductors) respectively. They therefore do not correspond to like numbering in the reference numerals used in Figures 7 to 9. Figure 1 1 is a schematic diagram of the windings of the armature of Figure 7. From Figure 1 1 it can be seen that in the coils of the armature form three separate electric paths. Furthermore, the polarity of the brushes connected to the segments of each group are such that no coil is shorted to the same brush. Figure 12 is a developed winding diagram of a third embodiment of an armature in accordance with the invention. It is similar to the embodiment of Figures 7 to 1 1 , however in this embodiment the armature has an even number of segments. Figure 13 is a schematic representation of the armature of Figure 12.

Figures 14 and 15 show a schematic representation of a fourth exemplary embodiment of an armature for an electric machine. The armature (50) has four electrically conductive brushes (52, 54, 56, 58) that are arcuate in shape and that are evenly distributed at 90 ° about an axis of rotation (60) of the armature (50). The brushes (52, 54, 56, 58) have alternating opposite electrical polarities every 90° and are separated by a gap (53, 56, 57, 59) between adjacent brushes. The armature (50) therefore has two pairs of brushes with each pair having the same polarity. The brushes of each pair are therefore 180° displaced about the rotation axis (60).

In this embodiment the rotation is counter-clockwise as indicated by the arrow (64). The ring formation (62) has eleven electrically conductive segments (66) that are electrically insulated from one another by means of an insulating material interposed between adjacent segments. The armature (50) furthermore has eleven electric coils (68) that are rotatable with the ring formation (55), each coil being connected between two complementary segments. Similarly as was shown above for the previous embodiment it can be shown for this embodiment that at no angular position of the armature (50) do the complementary segments of any of the coils (68) simultaneously make contact with the same brush. However, since there is more than two brushes in this embodiment, it can furthermore be shown that at no angular position of the armature (50) do the complementary segments of any of the coils (68) simultaneously make contact with brushes of the same polarity.

It can also be shown that in this embodiment a maximum number of adjacent segments in contact with a brush at any angular rotation is three. Each coil (68) is configured to have a coil pitch such that its complementary pair of segments are separated by a number of adjacent segments that is greater than or equal to a maximum number of adjacent segments in contact with a brush at any angular rotation of the armature about its rotation axis. In the present embodiment, this maximum number is three. The coil pitch is therefore configured such that its complementary segment pair is separated by three adjacent segments and therefore equal to the maximum number of adjacent segments in contact with a brush.

Figure 15 shows the armature (50) having been rotated slightly counter-clockwise in comparison to Figure 14. From the angular rotation in Figure 14 to that of Figure 15 one of the complementary segments (70) of the exemplary coil (72) has progressed wholly into the gap (53) between two brushes (52, 56). During operation of the machine and at the moment just before this segment (70) disconnects from the brush (52), the coil (72) has an electric current flowing there through from the positively polarised brush (58) to the negatively polarised brush (52) through the connection of its complementary segments (70, 74) to the respective brushes (58, 52).

When the segment (70) disconnects from the brush (52) the current flowing through the coil (72) can continue to flow to the other negatively polarised brush (54) through another coil (76). The coil (72) therefore has an uninterrupted path of conduction for the current flowing through it even when one of its complementary segments (70, 74) is not making contact with any brush. This can be shown for any of the other coils (68) as well.

Figure 16 shows a schematic of a fifth embodiment of the invention. Figure 16 is a developed winding diagram. The armature (100) has a total of 20 windings (102) and 20 segments (104). An exemplary coil (105) is shown in bold in Figure 16. The armature (100) furthermore has four brushes (106, 108, 1 10, 1 12). Two of the brushes (108, 1 12) are configured to have a positive polarity in use and are connected in parallel and wired to a positive terminal (1 14). The remaining two brushes (106, 1 10) are configured to have a negative polarity in use and are also connected in parallel and wired to a negative terminal (1 16).

Angular displacement of the armature corresponds to a linear displacement of the segments (104) relative to the brushes (106, 108, 1 10, 1 12) in Figure 16. Similarly as for the previous embodiments it can be shown that at no angular position of the armature (100) do the complementary segments of any of the coils (68) simultaneously make contact with the same brush. It can also be shown that in this embodiment the maximum number of adjacent segments in contact with a brush at any angular rotation is five. Accordingly, each coil (102) is configured such that its complementary segment pair is separated by a five or more adjacent segments, five adjacent segments in the present embodiment. This configuration is therefore a full pitch configuration.

Figure 17 is a schematic representation of the armature of Figure 16.

Figure 18 is a developed winding diagram of a sixth embodiment of an armature in accordance with the invention. This embodiment is similar to that of Figure 16 and 17. However, in this embodiment the coils are configured to have a long pitch. Figure 19 is a schematic representation of the armature of Figure 18.

Figure 20 is a developed winding diagram of the armature of Figure 18 in a second armature position. In this armature position each of the brushes is in contact with a maximum number of segments, this maximum number being five. Therefore, in this armature position all the segments are connected to a brush. Figure 21 is a schematic representation of the armature corresponding to the armature position of Figure 20.

Figure 22 is a developed winding diagram of a seventh embodiment of an armature in accordance with the invention. In this embodiment the armature has an odd number of coils and segments. The maximum number of segments in contact with a brush in this embodiment is three. Therefore the coils are configured to have a coil pitch such that the complementary segments of each coil are separated by three segments.

Figure 23 is a schematic representation of the armature of Figure 22.

Figure 24 to 27 are representations of an eighth embodiment of an armature in accordance with the invention. In this embodiment, similar to that of Figures 20 and 21 , the armature has 20 segments and 20 coils with the coils configured in a long pitch configuration. However, this embodiment furthermore includes four auxiliary brushes (130) that are interposed between the positively and negatively polarised brushes. The auxiliary brushes (130) are not polarised but merely acts as an electrical contact to electrically connect adjacent segments at certain armature positions.

Furthermore, the maximum number of segments that are connected to a brush at any armature position is four. The coil pitch is configured such that the number of adjacent segments separating the complementary segments of each coil is six. In the armature position shown in Figures 24 and 25 the auxiliary brushes (130) are positioned such that it does not electrically connect any adjacent brushes. Figure 25 is a corresponding schematic representation of the armature when in the armature position of Figure 24.

In Figures 26 and 27 the armature position has progressed slightly such that the auxiliary brushes (130) electrically connects segment numbers 12 and 13; 17 and 18; 2 and 3; and 7 and 8 respectively. Figure 27 shows a schematic diagram of this configuration at the armature position of Figure 26.

Figure 28 shows a three-dimensional view of a ninth embodiment of an armature in accordance with the invention. In this exemplary embodiment, the armature is for a four-pole electrical machine.

The armature (150) has a smooth, non-toothed outer circumferential surface (152). It includes an aluminium alloy rear end cap (154) and front end cap (156) having substantially C-shaped cross- sections and an open-ended cylindrical shell (158) held between them. The shell (158) is manufactured from a non-conductive fibre-reinforced polymer such as Kevlar™ or fibreglass reinforced polymer. The armature (150) has 28 substantially identical coils having 17 turns each that are arranged about the outer circumference (152) as will be described in more detail below. Figure 28 shows only one such coil (160) for illustration purposes in order to show features that would otherwise be obscured by adjacent coils. The coil (160) is manufactured from a polymer insulated copper conductor with its two ends (162, 164) being electrically exposed to allow electrical connection thereof as will be described below. The coil (160) has a flattened, ribbon-like appearance with six coil sections (166, 168, 170, 172, 174, 176). In each section, the conductor strands run substantially parallel and immediately adjacent to one another. A first and a second coil section (166, 168) diverge from the exposed coil ends (162, 164) near an outer edge of the front end cap (156) at an obtuse angle. Where the first coil section (166) and second coil section (168) meet, the first section is folded over the second section at a first fold (178) to form the obtuse angle between them. The first fold (178) forms a substantially triangular area of overlap (182) between the first and second coil sections (166, 168). A dotted line is shown in the top-right enlarged view of Figure 28 to indicate this triangular area where the second coil section (168) extends below the first coil section (166).

At the respective ends of the first and second coil sections (166, 168) third and fourth (170, 172) coil sections extend at an obtuse angle relative to the first and second coil section (166, 168) respectively such that the third and fourth coil sections (170, 172) extend substantially parallel to one another toward the rear end cap (154).

From the respective ends of the third and fourth coil sections (170, 172) a fifth and a sixth coil section (174, 176) diverge toward one another to meet at a second fold (180) adjacent the outer edge of the rear end cap (154) where the fifth coil section (174) extends over the sixth coil section (176). The second fold (180) forms a substantially triangular area of overlap (184) between the fifth and sixth coil sections (174, 176). A dotted line is shown in the top-left enlarged view of Figure 28 to indicate this triangular area where the fifth coil section (174) extends over the sixth coil section (176).

This configuration of the coil (160) has the effect that the conductor turns near the outer edge of the third coil section (170) extend near the inner edge of the fourth coil section (172) and that the conductor turns near the outer edge of the fourth coil section (172) extend near the inner edge of the third coil section (170).

The armature includes a steel shaft (186) with a substantially circular cross-section. The shaft (186) is axially aligned with the armature's axis of rotation and extends from adjacent the outer edge of the front end cap (156) and away therefrom.

A segmented ring formation (188) is located about the shaft (186) substantially at the proximal end of the shaft (186). As more clearly shown on the bottom-left enlarged view of Figure 28, the segmented ring formation (188) includes a number of segments (190) equal to that of the number of coils, thus 28 in this exemplary embodiment. The segments (190) are substantially identical wedge-shaped copper shoes. The segments (190) extend radially from the axis of rotation and are angularly arranged about the axis of rotation with mica insulators interposed between adjacent segments (190) for electrical insulation from one another. Electrical connection between the coil ends (162, 164) and their corresponding segments (190) is facilitated through link conductors (198). These link conductors (198) are polymer insulated copper conductors the ends of which are soldered to a coil end and its corresponding segment respectively. The ends of the link conductors (198) proximate the coil ends (162, 164) are held captive in a non-conductive ring-like conductor spacer (200) that is co-axial with the axis of rotation and is fastened to the front end cap (156) by means of machine threaded screws.

An electrically conductive carbon-graphite brush (192) is provided for each pole of the machine, thus four brushes in total for this exemplary embodiment. Figure 28 shows only three brushes (192) with one brush hidden for illustration purposes so as to show features that would otherwise be obscured thereby. The brushes (192) are substantially identical cylindrical shell segments that are angularly spaced about the axis of rotation. Each brush (192) is provided with a conductor in electrical communication therewith and terminating in a crimped fork spade lug (194). Figure 29 shows a front elevation in which the armature is viewed from the shaft (186). From this perspective the arrangement of the coils (160), their respective link conductors (198) and segments (190) about the axis of rotation as well as that of the brushes are shown more clearly.

The exemplary coil (160) is configured to have a coil pitch such that its pair of complementary segments (204, 205) are separated by a number of adjacent segments (202) that is greater than or equal to the maximum number of adjacent segments in contact with a brush at any angular rotation of the armature about its rotation axis. A brush outline (192) is shown in broken lines to illustrate the orientation of a brush (192) and its arcuate contact area with the segments (190). At the angular position of the armature shown in Figure 29 the brush outline (206) shows that the brush (192) is momentarily in contact with six adjacent segments. However, should the armature be rotated slightly in either direction it would make contact with a total of seven adjacent segments. Therefore, the maximum number of adjacent segments in contact with the brush at any angular rotation (192) is seven.

Furthermore, the complementary segments (204, 205) of the exemplary coil are separated by seven adjacent segments indicated by the span (203) between the first and second complementary segments (204, 205) which includes the second complementary segment (205). The coil pitch in this embodiment therefore satisfies the criteria that the coil pitch is equal to or greater than a maximum number of adjacent segments in contact with the brush at any rotation of the armature. Figure 30 shows a schematic representation of a section of the exemplary coil (160) of Figure 28. Figure 30 illustrates the configuration of the coil described above having the effect that the conductor turns near the outer edge of the third coil section (170) extend near the inner edge of the fourth coil section (172) and that the conductor turns near the outer edge of the fourth coil section (172) extend near the inner edge of the third coil section (170). Therefore, the electrical potential induced in the conductor turns near the outer edge of the third coil section (170) will be the same as that of the conductors near the inner edge of the fourth coil section (172) and the potential induced in the conductor turns near the outer edge of the fourth coil section (172) will be the same as that of the turns at the inner edge of the third coil section (170). This is indicated by the exemplary positive and negative potentials indicated at the respective coil sections (180, 172).

Figure 31 is a cross-sectional view of an electrical machine (300) showing a stator (302) of the electrical machine (300) as well as a tenth embodiment of an armature (310) in accordance with the invention. The armature (310) has a plurality of longitudinally extending slots defined at an outer periphery thereof. As shown in the enlargement of Figure 31 , the conductor turns of each armature coil (310) are located within a slot (314) at the outer periphery (316) of the armature (310). A structural member (318) is provided that is in a sliding engagement with the slot (314) and partially envelopes the conductors of the coil (312). The electrical machine (300) has a stationary core. The armature (310) therefore rotates within a space defined between an outer periphery of the stationary core (320) and field pole shoes (322) circumferentially spaced about an inner periphery of the stator (302). In this embodiment additional field coils (324) are provided within the stationary core (320) opposite each stator field pole shoe (322) that are configured to provide an opposite polarity to that of its complementary stator field pole shoe (322). This configuration may result in a more desirable magnetic path of the field flux.

Figure 32 shows an electrical machine (350) similar to that of Figure 31 which furthermore includes compensation coils (352) within the stationary core (320).

Figure 33 is a schematic representation of an eleventh embodiment of an armature (400) in accordance with the present invention. In this embodiment the brushes are electrically conductive belts (404, 406). The armature (400) is configured for use with a two-pole electric machine and includes a ring formation (402) having fourteen electrically conductive segments (408). The armature (400) furthermore includes two electrically conductive belts (404, 406). A first belt (406) is shown in solid lines and is arranged to make contact with six segments from about the 10 o'clock position to the 2 o'clock position as shown. The second belt (408) is shown in broken lines and is also arranged to make contact with six segments from about the 8 o'clock position to the 4 o'clock position. Each segment (408) is electrically insulated from its adjacent segments by means of mica insulators interposed between adjacent segments.

The armature (410) has a plurality of coils greater in number to that of the belts (404, 408). One exemplary coil (414) has been shown for illustration purposes and it will be appreciated that all the coils of the armature (410) would have the same configuration as that of the exemplary coil (414). Each coil (414) is electrically connected between a pair of complementary segments (416, 418). Each belt (404, 406) is configured to make simultaneous contact with a plurality of segments along an arcuate contact area of the ring formation (402). The contact area zone associated with the first belt (404) is illustrated by the shaded section of segments (412) about which the first belt (404) spans to make electrical contact therewith. The contact area zone associated with each respective belt (404, 406) is configured such that at any angular rotation of the armature (400) a combined total number of segments making contact with a belt (404, 406) is greater than a combined total number of segments not making contact with a belt. The contact areas zones associated with the respective belts (404, 406) are 180° displaced about the rotation axis (410).

The coil (414) is configured to have a coil pitch such that the number of adjacent segments separating its complementary pair of segments (416, 418) is seven in this embodiment. This number is therefore greater than or equal to the maximum number of adjacent segments in contact with a belt (404, 406) at any angular rotation of the armature (400) about its rotation axis (410) being six in this embodiment.

The first belt (404) also spans about a first idler pulley (420) at an end of the belt opposite to that of its contact area (412). A pair of tensioner pulleys (422) are positioned substantially at the midway of the travel of the first belt (404) and are configured to urge the mid-sections of the belt outward such that the belt (404) only makes contact with the ring formation (402) at its predetermined contact area zone. The first idler pulley (420) is configured to facilitate electrical conduction between the first belt (404) and an axle (426) of the first idler pulley (420). The axle (426) of the idler pulley (420) remains stationary during operation and is electrically connected to a first wire conductor (428). The first wire conductor (428) is therefore in electrical communication with the segments with which the first belt (404) is in contact at its associated contact area zone (412). Similarly, but 180 ° displaced to that of the first belt (404), the second belt (406) spans about a second idler pulley (430) at an end of the belt opposite to that of its associated contact area zone. It also has a pair of tensioner pulleys (432) that are positioned substantially at its mid-way and are configured to urge the mid-sections of the belt outward such that the belt (406) only makes contact with the ring formation (402) at its the predetermined contact area zone. The idler pulley (430) is configured to facilitate electrical conduction between the second belt (406) and an axle (434) of the second idler pulley (430). The axle (434) of the idler pulley (430) also remains stationary during operation and is electrically connected to a second wire conductor (436). The second wire conductor (436) is therefore in electrical communication with the segments with which the second belt (406) is in contact at its associated contact area zone.

A ring formation assembly (600) for a twelfth embodiment of an armature is shown in Figure 34. The ring formation assembly (600) is configured for use with belt-type brushes similar to the embodiment of Figure 33. However, the ring formation assembly (600) comprises a first ring formation (610) and a second ring formation (612) that are substantially identical in structure and size. The first and second ring formations (610, 612) are co-axially stacked with an air gap between the formations to electrically insulate the ring formations from one another. Wire conductors (614) electrically connect each segment of the first ring formation (610) with a diametrically opposite segment on the second ring formation (612) or angularly displaced by 180° relative to it. An exemplary segment (616) is shown on the first ring formation (610) that is electrically connected through a wire conductor (617) to a diametrically opposite segment (618) on the second ring formation (612).

Figure 35 shows a schematic representation of an armature (700) in which the ring formation assembly of Figure 34 is used. The shaded segments on the first ring formation (610) are making contact with a first belt (702) spanning about a contact area thereof with the first ring formation (610) at the angular rotation of the ring formation assembly (700) shown in Figure 35. Each of these segments is electrically connected to diametrically opposite segments on the second ring formation (612). The armature (700) has a second belt (704) that makes contact with the second ring formation (612) at a contact area thereof. However, the shaded segments of the second ring formation (612) do not make contact with the second belt (704).

While the ring formations (610, 612), belts (702, 704) and pulleys are shown side-by-side in Figure 35, it should be noted that this is for illustration purposes only. Therefore in this embodiment, the belts (702, 704) span about ring formations (610, 612) that are co-axial. Furthermore the first belt (702) spans about a first idler pulley (712) and the second belt (704) spans about a second idler pulley (714), the two idler pulleys (712, 714) being co-axially positioned. It will be appreciated that the ring formation assembly (600) of Figures 34 and 35 is configured for a two-pole electrical machine. However, electrical machines with a greater number of poles can also be achieved. Figure 36 shows a partially cut-away three-dimensional view of a ring formation assembly for use with a thirteenth embodiment of an armature in accordance with the invention. In this exemplary embodiment, the ring formation assembly is configured for use with a four-pole electrical machine. Four co-axially stacked segmented ring formations (802, 804, 806, 808) are provided. Each ring formation (802, 804, 806, 808) is electrically insulated from its adjacent ring formations by means of mica insulators (810) interposed between adjacent ring formations.

A first ring formation (802) and a second ring formation (804) are angularly displaced by 180° relative to one another. A third ring formation (806) and a fourth ring formation are also angularly displaced by 180° relative to one another. However, the first and second ring segments (802, 804) are angularly displaced by 90° relative to the third and fourth ring segments (806, 808).

Wire conductors (812) electrically connect each segment of every ring formation (802, 804, 806, 808) with an electrically corresponding segment on every other ring formation. This angular configuration of each of the ring formations (802, 804, 806, 808) and the wiring of the electrically corresponding segments on each ring formation has the effect that in use the positively polarised segments of the first and second ring formations (802, 804) will be orientated at the same angular position and the negatively polarised segments of the third and fourth ring formations (806, 808) will also be at the same angular position. Furthermore, the positively polarised segments of the first and second ring formations (802, 804) will be orientated at the same angular position as that of the negatively polarised segments of the third and fourth ring formations (806, 808).

Therefore only two conductive belts will be required, a first belt spanning the positively polarised segments of the first and second ring formations (802, 804) and the second belt spanning the negatively polarised segments of the third and fourth ring formations (806, 808). It will be appreciated that the polarities may be reversed depending on the particular configuration of the electric machine.

Figure 37 shows a three-dimensional view of an electrical machine in use with an armature having the ring formation assembly of Figure 36. Two conductive belts (902, 904) are provided, the first belt (902) spanning the positively polarised segments of the first and second ring formations (802, 804) and the second belt (904) spanning the negatively polarised segments of the third and fourth ring formations (806, 808). It will again be appreciated that the polarities may be reversed depending on the particular configuration of the electric machine. Figure 38 shows an electric machine (1000) featuring a further, fourteenth embodiment of an armature (1001 ) illustrating that the armature (1001 ) may be provided by a stator. The electric machine (1000) includes an outer yoke (1002). The armature (1001 ) includes armature coils (1002) held in slots within the armature (1001 ). The magnetic field is provided by permanent magnets (1006) on the rotor assembly (1010), however it will be apparent to those skilled in the art that the field may be provided by electromagnets as well. The armature (1001 ) further includes a segmented ring formation (1008). In this embodiment, the brushes associated with the armature (1001 ) are also electrically conductive belts (1007) configured to make simultaneous contact with a plurality of segments along an arcuate contact area of the ring formation (1008). Whilst the belts (1007) are associated with the armature (1001 ) they are arranged to rotate with the rotor assembly (1010). An armature with a novel configuration is therefore provided. A number of different embodiments have been described above. However, those skilled in the art will appreciate that further embodiments are also possible that fall within the scope of the claimed invention.

Furthermore where specific materials are mentioned, such as copper and the like, it should be noted that these are for illustration purposes only and a number of other materials may be utilised in order to perform the same or similar function.

Throughout the specification unless the contents requires otherwise the word 'comprise' or variations such as 'comprises' or 'comprising' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.