WO2018029552A1

WO2018029552A1 - An electric generator having a central magnetic shaft

Info

Publication number: WO2018029552A1
Application number: PCT/IB2017/054321
Authority: WO
Inventors: Kabu Walter MAKGERU; Anthony BASS
Original assignee: The Trustees For The Time Being Of The Kmn Fulfilment Trust
Priority date: 2016-08-12
Filing date: 2017-07-18
Publication date: 2018-02-15
Also published as: AR109329A1

Abstract

An electric generator (100) has a stator and a rotor, and the stator comprises a central shaft (102) and has at least one axially-offset coil (104) at an axial end (referred to as the coiled portion 106)) of the central shaft (102) such that a major central portion (108) of the central shaft (102) is not surrounded by the coil (104), the coil (104) being configured to magnetise the central shaft (102) such that the central shaft (102) has axially spaced apart unlike magnetic poles (S, N), with one pole (S, N) being provided at the coiled portion (106) and the other pole (N, S) being provided at the major central portion (108). The rotor comprises a magnetising layer (112) arranged co-axially around a first generating layer (110) and radially aligned with the major central portion (108), the magnetising layer (112) having radially spaced apart unlike magnetic poles (S, N) with an inner magnetic pole (N, S) having an unlike polarity to that of the aligned major central portion (108).

Description

An electric generator having a central magnetic shaft

FIELD OF INVENTION

This invention relates to electric machines and specifically to electric generators. It relates more specifically to a generator having a central magnetic shaft.

BACKGROUND OF INVENTION

In a conventional electric generator design, an innermost central part of the generator is the rotor, which is the rotating member of the Generator. This rotating part is the source of a magnetic field (that is, a magnetising member or magnetising layer) that generates EMF (electromagnetic field) for the generator. This rotor-generated magnetic field intersects or "cuts" conductors in windings which are part of the stator and generates an electric current. The Applicant is aware of generator designs that have multiple rotor layers and/or multiple stator layers.

In most conventional designs of which the Applicant is aware, the magnetic field source is the rotor whilst the stator is always stationary and a conductor for generators. In other designs, the stator is not a source of the magnetic field. The Applicant notes that it is desirable to increase the magnetic flux density to increase the electric power generation capability of the generator.

In W02012/018467, there is disclosed a dual armature machine with flux linkage. The main focus of this design is the flux linkage between the armature and the field source. In this design, the field source is a source of magnetic flux and the armature is not a field source.

In Patent US20040195931 , the electromagnet provides the rotational force to the permanent magnet of the rotor and this provides the driving force for the rotation of the machine.

The Applicant desires a generator in which the stator assists in shaping and strengthening the magnetic field but nonetheless is a generating layer rather than a magnetising layer.

SUMMARY OF INVENTION

Accordingly, the invention provides an electric generator having a stator and a rotor, wherein: the stator comprises a central shaft and has at least one axially-offset coil at an axial end (referred to as the coiled portion) of the central shaft such that a major central portion of the central shaft is not surrounded by the coil, the coil being configured to magnetise the central shaft such that the central shaft has axially spaced apart unlike magnetic poles, with one pole being provided at the coiled portion and the other pole being provided at the major central portion; the stator comprises a generating layer comprising windings provided concentrically around the central shaft, fixed relative to the central shaft, and radially aligned with the major central portion of the central shaft; and the rotor comprises a magnetising layer arranged co-axially around the first generating layer and radially aligned with the major central portion, the magnetising layer having radially spaced apart unlike magnetic poles with an inner magnetic pole having an unlike polarity to that of the aligned major central portion of the central shaft. The major central portion may be considered the active or magnetising part of the central shaft, even though the central shaft is generally a generating layer.

The central shaft may be hollow or solid.

The central shaft may have a single coil at a single end thereof. In such case, the central shaft may have two magnetic poles, one at the coiled portion and one at the major central portion. The major central and coiled portions may be N-S or S-N (where, throughout this specification, N stands for north pole and S for south pole).

The central shaft may have a pair of coils, one at each end thereof. In such case, the central shaft may have three magnetic poles, one at each coil portion and one at the major central portion. The three magnetic poles may alternate, e.g., N-S-N or S-N-S.

The central shaft may project axially outwardly past the generating layer. More specifically, the coiled portion may project outwardly past the generating layer while the major central portion may be surrounded or enveloped by the generating layer. If there are two coils, then both ends of the central shaft may project axially outwardly past the generating layer.

The major central portion may be larger or longer than the coiled portion, may be 1 -5 times larger or longer, and may be 2-3 times larger or longer.

The generating layer may be a first generating layer and the generator may comprise plural generating layers. The generating layers may all comprise the stator. The generating layers may be fixed relative to each other and to the central shaft. The generating layers may be fixed relative to a support structure or housing of the generator. There may be plural magnetising layers. The magnetising layers and generating layer or layers may be arranged alternatingly. The magnetising layers may all comprise the rotor. The magnetising layers may be fixed relative to each other. Instead, the magnetising layers may be counter-rotating. The magnetising layers may have alternating polarity.

There may be N magnetising layers and N generating layers, where N is 1 or more.

There may be N magnetising layers and N+ 1 generating layers, where N may be 1 or more, e.g., 2. The outermost layer may be a generating layer. The outermost layer may be stationary. The generator may include a cylindrical metallic sleeve that envelops an outermost layer. The metallic sleeve and the outermost layer may rest on, or be fixed to, a frame of the generator. The metallic sleeve may serve to provide a magnetic return path and to shape the magnetic field.

By way of development, where there are three or more magnetising layers (i.e., N > 3), alternating magnetising layers may be rotary, forming part of the rotor, while the remaining magnetising layers may be stationary, forming part of the stator. One set of the magnetising layers (e.g., the stationary magnetising layers) may be electronically switched as the rotor rotates in order to maintain the alternating polarity arrangement.

The (or each) magnetising layer may be provided by permanent magnets or by electromagnets. If the magnetising layer is provided by electromagnets, then these electromagnets may be electronically switchable to switch or reverse their polarity.

A purpose of the configuration of the generator in accordance with the invention may be to:

^■ Increase the magnetic flux between magnetic layers thereby increasing the efficiency of the generator; ^■ Straightening the magnetic field between the magnetising layers by linkage for a perpendicular intersection or cut by conductors (in windings) in the generating layer(s);

^■ Decrease the centrifugal loading, due to the innermost part (that is, the central shaft) attracting all layers to the centre by flux linkage

^■ Reduce a distance between the poles, and thereby increasing the efficiency of the generator.

A formula (1 ) is shown below, derived from Lorentz and Faraday's laws of induced EMF in a conductor. This formula forms the basis for calculating output voltage in a conventional generator.

EMF = vlBsin(6), (1 ) where v is the relative velocity between the conductor and the magnetic field, / is the length of the conductor exposed to the magnetic field, B is the magnetic field density, and

Θ is the angle between the conductor and the magnetic field vector.

The generator of the present invention aims to increase the EMF by increasing the magnetic field density (B) and improving the angle of intersection by the conductor through the magnetic field to an angle of 90 degrees.

The electric generator may be configured for DC (Direct Current) power generation.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be further described, by way of example, with reference to the accompanying diagrammatic drawings. In the drawings:

FIG. 1 shows a schematic axial-sectional view of a first embodiment of a generator in accordance with the invention;

FIG. 2 shows a schematic axial-sectional view of the generator of FIG. 1 with two coils;

FIG. 3 shows a schematic axial-sectional view of a second embodiment of a generator in accordance with the invention;

FIG. 4 shows a schematic axial-sectional view of the generator of FIG. 3 with one coil and a sleeve; and

FIG. 5 shows a schematic axial-sectional view of the generator of FIG. 3 with a sleeve.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT

The following description of the invention is provided as an enabling teaching of the invention. Those skilled in the relevant art will recognise that many changes can be made to the embodiment described, while still attaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits of the present invention can be attained by selecting some of the features of the present invention without utilising other features. Accordingly, those skilled in the art will recognise that modifications and adaptations to the present invention are possible and can even be desirable in certain circumstances, and are a part of the present invention. Thus, the following description is provided as illustrative of the principles of the present invention and not a limitation thereof.

FIG. 1 illustrates a first embodiment of a generator 100 in accordance with the invention. In all of the FIGS, thicknesses of the various layers and gaps between the layers may not be to scale but they may be exaggerated or scaled for clarity of illustration. The generator 100 is an electric generator for generating output electricity from a mechanical rotational input. The generator 100 has a central shaft 102 which forms a basis of a stator of the generator 100. The central shaft 102 is cylindrical and elongate. The central shaft 102 has an axially-offset coil 104 wound around one end thereof. The presence of the coil 104 serves to divide the central shaft 102 into two portions: a coiled portion 106 and a major central portion 108. The major central portion 108 is about three times longer than the coiled portion 106.

The coil 104 is energised in use and serves as an electromagnet to magnetise the central shaft 102. Accordingly, when the coil 104 is energised, the central shaft 102 develops two magnetic poles which are axially spaced apart. In this example, the coiled portion 104 has an N polarity and the major central portion 108 has an S polarity.

Generating windings 1 10 are provided around the major central portion 108 of the central shaft 102. These generating windings 1 10 essentially constitute a generating layer 120. The windings 1 10 may be in close proximity to, even abutting, the central shaft 102.

A rotor includes a magnetising layer 122 is provided around the generating layer 120 in order to create a magnetic flux (generally indicated by numeral 124) extending through the generating layer 120. The magnetising layer 122 is provided by electromagnets. Magnetic poles in a pair provided by the magnetising layer 122 are radially spaced and arranged such that an opposite pole (N) of the magnetising layer 122 is aligned with the pole (S) major central portion 108. The magnetic flux 124 extends straight between the magnetising layer 122 and the major central portion 108 of the central shaft 102 so that the windings 1 10 of the generating layer 120 intersect the magnetic field 124 perpendicularly at at least two points in a full revolution.

FIG. 2 illustrates a slight variation of the generator 100. In this variation, the central shaft 102.1 is longer and includes two coils 104, 104.1 , one at each end of the central shaft 1 02. The principle is the same as that of FIG. 1 but the magnetic flux 124 generated due to the magnetisation of the central shaft 1 02 may be stronger, at the expense of slightly increased complexity. The axially spaced polarities of the central shaft 1 02.1 are N-S-N.

FIG. 3 illustrates a second embodiment of a generator 200 in accordance with the invention. The generator 200 includes a central shaft 202 similar to that of FIG. 2, i.e., having two coils 204, 204.1 , one at each end, but with polarities opposite to that of FIG. 2, i.e., being S-N-S. Corresponding reference numerals in the FIGS refer to corresponding parts in the generators 1 00, 200.

A notable difference in this embodiment of the generator 200 compared to those of FIGS 1 -2 is that the generator 200 has plural generating and magnetising layers 220- 228. In this example, there are Λ/+1 generating layers 220, 224, 228 and N magnetising layers 222, 226, where N=2. The major central portion 208 of the central shaft 202 and the magnetising layers 222, 226 have radially alternating magnetic poles which, in this example, are arranged as N-S-N-S-N and therefore provide a relatively radially straight magnetic field or flux 234 extending outwardly from (or inwardly to, as the case may be) the central shaft 202.

Like with the previous generator 1 00, this generator 200 has the magnetising layers 222, 226 configured to rotate, thus forming part of a rotor structure of the generator 200. Although not illustrated, the magnetising layers 222, 226 are coupled to a rotational input to the generator 200. As the magnetising layers 222, 226 rotate relative to the generating layers 220, 224, 228, the radially outwardly directed magnetic flux 234 rotates, like spokes of a wheel, and intersects windings 210 of the generating layers 220, 224, 228 at right angles, thereby inducing a voltage in the windings 21 0.

FIG. 4 shows a slight variation of the generator 200. In addition to having an offset coil 204 on only one side of the central shaft 202, a metallic sleeve 250 is provided which is fast with a support frame (not illustrated) of the generator 200. An outermost generating layer 252 is mounted to an inside of the sleeve 250 and to at least one end of the central shaft 202. This serves to isolate and enhance the magnetic flux 234 therein. By connecting one end of the central shaft 202 an outermost surface of the outer generating layer 252, a magnetic return path will be provided. FIG. 5 illustrate an embodiment of the generator 200 with two coils 204, 204.1 and a metallic sleeve 250.

The Applicant believes that the advantages of the generator 100, 200 as exemplified are numerous but not always readily apparent. Unlike a conventional generator, the innermost part of the present generator 100, 200 is essentially a stationary electromagnet. This improves the efficiency of the generator by enhancing or amplifying strength/density of the magnetic flux 124, 234.

Although not illustrated, electronic control could be used to change the poles of the magnetic layer(s) 122, 222, 226 including the coil 104, 104.1 of the central shaft 102, 202. The magnetising layers 222, 226 could be configured to rotate in the same direction or can be rotated in opposite direction as the poles on each layer 222, 226 have the same polarity. The magnetising layers 222, 226 could also be rotated in opposite direction at the same speed or a different speed.

Due to the fact that the central core 102, 202, which is now participates actively in the generation of the magnetic flux 124, 234, is situated coaxially within the inner magnetising layer 122, 222, it halves the distance between magnetic field sources. According to Coulombs law, the force on the charges is indirectly proportional to a square of the distance between the charges, and therefore, according to Coulombs law, this action (positioning of magnetic field sources) increases the force on the charges in proportion to the decrease of the distance and therefore increases the overall efficiency of the generator 100, 200.

Claims

1. An electric generator having a stator and a rotor, wherein: the stator comprises a central shaft and has at least one axially-offset coil at an axial end (referred to as the coiled portion) of the central shaft such that a major central portion of the central shaft is not surrounded by the coil, the coil being configured to magnetise the central shaft such that the central shaft has axially spaced apart unlike magnetic poles, with one pole being provided at the coiled portion and the other pole being provided at the major central portion; the stator comprises a generating layer comprising windings provided concentrically around the central shaft, fixed relative to the central shaft, and radially aligned with the major central portion of the central shaft; and the rotor comprises a magnetising layer arranged co-axially around the first generating layer and radially aligned with the major central portion, the magnetising layer having radially spaced apart unlike magnetic poles with an inner magnetic pole having an unlike polarity to that of the aligned major central portion of the central shaft.

2. The electric generator as claimed in claim 1 , in which the central shaft has a single coil at a single end thereof.

3. The electric generator as claimed in claim 1 , in which the central shaft has a pair of coils, one at each end thereof.

4. The electric generator as claimed in any one of claims 1 -3, in which: the central shaft projects axially outwardly past the generating layer and, accordingly, the coiled portion projects outwardly past the generating layer; and the major central portion is surrounded or enveloped by the generating layer.

5. The electric generator as claimed in any one of claims 1 -4, in which the major central portion is larger or longer than the coiled portion.

6. The electric generator as claimed in any one of claims 1 -5, in which: the generating layer is a first generating layer; and the electric generator comprises plural generating layers.

7. The electric generator as claimed in claim 6, in which the stator comprises the plural generating layers.

8. The electric generator as claimed in claim 7, in which the generating layers are fixed relative to a support structure or housing of the electric generator.

9. The electric generator as claimed in any one of claims 6-8, in which there are N magnetising layers and N+1 generating layers, where N is 1 or more.

10. The electric generator as claimed in any one of claims 6-9, in which an outermost layer is a generating layer.

11. The electric generator as claimed in claim 10, in which the generator includes a cylindrical metallic sleeve that envelops the outermost layer.

12. The electric generator as claimed in any one of claims 6-1 1 , in which there are plural magnetising layers.

13. The electric generator as claimed in claim 12, in which the rotor comprises the plural magnetising layers.

14. The electric generator as claimed in any one of claims 12-13, in which the magnetising layers are fixed relative to each other.

15. The electric generator as claimed in any one of claims 12-13, in which the magnetising layers are configured to be counter-rotating.

16. The electric generator as claimed in any one of claims 12-15, in which the magnetising layers have alternating polarity.

17. The electric generator as claimed in claim 16, in which: there are three or more magnetising layers ; and alternating magnetising layers are rotary, forming part of the rotor, while remaining magnetising layers are stationary, forming part of the stator.

18. The electric generator as claimed in claim 17, in which either the rotary or the stationary magnetising layers are electronically switchable as the rotor rotates in order to maintain the alternating polarity during rotation.

19. The electric generator as claimed in any one of claims 1 -18, in which magnetising layer is provided by permanent magnets or by electromagnets.

20. The electric generator as claimed in any one of claims 1 -19, which is configured for DC (Direct Current) power generation.