NZ550078A - Electrical machines with composite poles - Google Patents

Abstract

An electric motor or generator in which the poles are separated from the remainder of the magnetic structure is disclosed. The motor has a stator (103) carrying pole pieces and their coacting coils. The stator is surrounded on one side by field creating permanent magnets adjacent one face of the poles, and on the other by a flux return path element positioned adjacent the other face of the poles. The stator coils are preferably bobbin mounted.

Description

Patents Form # 5 *10054167417* NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION AFTER PROVISIONAL # : 550078 DATED : 25 September 2006 TITLE : Electrical Machines with Composite Poles We, WELLINGTON DRIVE TECHNOLOGIES LIMITED Address: 13 William Pickering Drive, North Harbour, Auckland, New Zealand, 0632 Nationality: A New Zealand company do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: IPONZ 202057NZ_Cap_20070904_104SJXDT.doc FEE CODE 1050 SEP 2007 550078 ELECTRICAL MACHINES WITH COMPOSITE POLES Technical Field The invention generally relates to electrodynamic machines in which the poles are separated from the remainder of the magnetic structure.

More particularly the invention relates to an electrodynamic machine in which the pole windings and the pole face which is contiguous the relatively moving part of the machine are created separated from the magnetic material which acts as the return path for the magnetic flux.

Background Art Electrodynamic machines such as motors and generators typically consist of a stator and a rotor, one of which carries pole pieces associated with coils which, in the case of a motor, are energised by a current while the other either has permanent magnets or electromagnets to create a flux against which the coils act. Normally there are many pole pieces with their associated coils and the number of connections to these encourage the placement of this part of the machine as the stator, while the magnetic field creation portion is the rotor.

The stator requires a flux path to return the magnetic flux from the pole pieces via the magnetic flux creation path to the rear of the pole pieces. This is normally done with a path through an adjacent pole or poles or through the support structure to the magnetic structure supporting the pole pieces at the rear. Such a magnetic structure is complex to assemble and expensive to manufacture as the coils for the pole pieces normally need to be shaped to fit the poles and the backing magnetic structure. US patent specification 7067944 shows a typical example of such a construction in which the stator structure is injection moulded to the baseplate. 202057NZ_CompSpsc.doc Received at IPOhjg 26 ^Bpj^r^bgr 2Q0$T All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process.

Summary of the Invention In one exemplification the invention consists in an electrodynamic machine having a unitary annular first structure comprising multiple magnetically isolated pole pieces arranged around an axis, each pole piece having a first face and a second face and at least one pole coil located on each pole piece between the planes of the first and second faces, a second structure rotatably mounted on the first structure axis and comprising a magnetic flux creation device for each pole piece wherein there exists a magnetic flux conducting path via the second structure from a first face of each pole piece via at least one magnetic flux creation device to the second face of the pole piece.

Preferably the machine is an axial flux machine and the pole pieces are radially arranged around the axis. 202057NZ_CompSpec.doc Received at IPONZ 26 September 2008 Preferably the machine is a radial flux machine and the pole pieces are axially arranged around the axis.

Preferably the pole pieces are trapped between a common base plate and a common top plate.

Preferably each pole piece carries a groove at each end to facilitate the trapping.

Preferably the groove is arcuate and coacts with a corresponding projection on the base plate or top plate.

Preferably the machine is a drum machine.

Preferably each pole coil is wound on a bobbin.

Preferably the bobbins, coils and pole pieces are unitised as a first structure by embedding in a substrate.

Preferably the substrate is created by injection moulding.

Preferably the second structure has an annular band of magnetic structure located adjacent the first faces of the poles.

Preferably the band forms part of the sccond structure.

Preferably the band is inside the first structure and the magnetic flux creation devices are permanent magnets and are outside the first structure.

Preferably the band and magnets are mounted to the same magnetic material Preferably the first structure is stationary and the second structure rotates.

Preferably the magnetic flux creation devices are permanent magnets.

Alternatively the invention relates to a method of constructing a radial flux electrodynamic machine having a unitary annular stator structure comprising providing a plurality of isolated pole pieces, mounting pole coils to the pole pieces and assembling the pole pieces and coils to form an annular stator with each pole piece magnetically isolated from other pole pieces and each pole axis radially 202057NZ_CompSpec.doc Received at IPONZ 26 September 2008 oriented, embedding the pole pieces and coils iri a substrate to thereby unitise the stator, assembling magnetic field creating elements and a pole piece backing element in a rotor with at least one magnetic flux path between the magnetic field creating elements and the pole piece backing element and assembling the stator and rotor.

Preferably the pole coils are wound on bobbins and the bobbins are placed on pole pieces.

Preferably the pole pieces and bobbins are retained in place on a base plate prior to embedding the pole pieces and coils.

Alternatively the invention relates to a method of constructing an annular flux electrodynamic machine having a unitary annular stator structure comprising providing a plurality of isolated pole pieces, mounting pole coils to the pole pieces and assembling the pole pieces and coils to form an annular stator with each pole piece magnetically isolated from other pole pieces and each pole axis axially oriented, embedding the pole pieces and coils in a substrate to thereby unitise the stator, assembling magnetic field creating elements and a pole piece backing element in a rotor with at least one magnetic flux path between the magnetic field creating elements and the pole piece backing element and assembling the stator and rotor.

These and other features of as well as advantages which characterise the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.

Brief Description of the Drawings Figure 1 is a sectioned perspective view of a motor according to the invention.

Figure 2 is a cross section of the rotor of Figure 1.

Figure 3 is a cross section of the stator of Figure 1.

Figure 4 is a cross section on line 4-4 of the stator of Figure 3.

Figure 5 is an exploded view of the stator of Figure 1. 202057NZ_CompSpec.doc 550078 Figure 6 is an exploded view of a winding and pole piece of Figure 5.

Figure 7 is a sectioned view of a radial flux motor according to the invention.

Description of the Invention Referring now to Figure 1 a motor according to one exemplification of the invention is shown in cross section and consists of an outer casing 101, a rotor 102 and a stator 102.

As best seen in Figure 2 the rotor 102 consists of an axle 201 journalled in bearings 202, 203. A cup 204 of magnetic material such as iron or soft steel carries magnets 205 and a back iron 206. The magnets face alternately north and south pole inwards. Magnetic flux is conducted through the rotor body 204 from the magnets to the back iron 206, which may be of laminated form.

Co-operating with rotor 102 is stator 103 shown in Figure 3, with a cross section in Figure 4 and detail in Figure 5. A base plate 301 which locates on bearing 203 receives an assemblage of magnetically isolated pole pieces such as 302 carrying coils wound on bobbins 303. This assemblage is encapsulated in a suitable potting material 304 and is fixed to the base plate typically by through bolts.

A suitable potting material may be any non-conductive material with a modulus of expansion approximating that of the bobbins and pole pieces and adhering to them, and a strength and modulus of elasticity sufficient to maintain the part placement while reducing the likelihood of brittle fracture. Most electronic component epoxy or poiyurethane potting compounds are suitable and thermoplastics may also be used in low temperature applications.

The pole pieces may be assemblies of laminated steel but preferably they are moulded pieces of magnetic powder and may be fired ferritic components or pressure moulded adhesive magnetic powder of the required qualities. Each pole piece is isolated magnetically from the other pole pieces, that is, there are no magnetic members bridging between the pole pieces within the stator. This reduces the amount of 202057NZ_CompSpec.doc 550078 magnetic material required to form the stator, reducing the cost and weight of the stator assembly.

Figure 5 shows base 301with a recess to receive the pole pieces 302 when fitted with windings 303. As best seen in Figure 6 the windings consist of a bobbin 601 which receives a winding 602. The winding and bobbin may be tapered at one side to allow the windings to be as close together as possible. A groove 603 at each end of a pole piece co-acts with a projection 503 on the base and a similar projection on end cap 502 to prevent movement of the pole pieces. Cap 502 is retained by bolts 501. The assemblage of pole pieces and windings may be potted into an integral assembly prior to assembling it to the base, or it may be potted once assembled to the base, thus rendering the stator an integral assembly.

In operation rotor 102 is journalled in casing 101 and the base of stator 103, and the case and base secured together so that the permanent magnets 205 and back iron 206 rotate around the stator. The clearance between back iron 206 and the stator inner surface is preferably as small as is consistent with tolerances, load and temperature. Because the backiron moves in synchronism with the magnetic poles there is a reduction in eddy currents in the backiron, providing an increase in efficiency.

Figure 7 and 8 show respectively a sectioned side view and a sectioned perspective view of an axial flux version of a motor in which a motor casing 701 has a stator 702 secured to it by screws at 703. The stator 702 is an injection moulded assembly having embedded within it coils 704 which may be wound within bobbins 705 and which are mounted around pole pieces 706. The coils 704, which may be sectorial in plan, may be wound on bobbins for ease of manufacture, although coils wound directly upon the pole pieces 706 and injection moulded into a whole are an alternative construction.

Case 701 may be moulded as either a zinc based die casting or as injection moulded fibre reinforced plastic, since no magnetic material is required in the case. A central axle 707 journals, on bearings 714, a rotor structure 708, this including two planar discs 709 and 710. Disc 710 is attached to the remainder of the rotor 708 by screw in holes 711. Affixed to disc 709 is a back iron continuous annular strip 712. Similarly affixed to the upper disc 710 is a magnet ring 713, with a magnet formed for each 202057NZ_CoinpSpec.doc 550078 pole 706. Alternatively the magnets may be sectorial magnets secured to a back iron such as that at 712. The back iron 712 and magnet ring 713 act to provide a flux return path through the pole pieces, and hence the rotor may also be of injection moulded fibre reinforced plastics, albeit the top disc 710 must be secured to the bottom disc 709 after assembly.

The bobbins are intentionally simple both to wind and place, providing advantages in the construction of the motor while simultaneously achieving an efficiency comparable with current deformed winding technology. In addition the construction provides a very compact motor form containing only components which are simple to manufacture.

While permanent magnet pole flux generators are described the technology is equally applicable to electromagnetic flux generators.

The machine in the drum form may be constructed with either the back iron inside the coils or the back iron outside the coils.

It is to be understood that even though numerous characteristics and advantages of the various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functioning of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail so long as the functioning of the invention is not adversely affected. For example the particular elements of the machine may vary dependent on the particular application for which it is used without variation in the spirit and scope of the present invention.

In addition, although the preferred embodiments described herein are directed to a six pole permanent magnet motor, it will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems such as generators or motors with a differing number of poles, without departing from the scope and spirit of the present invention. 202057NZ__CompSpec.doc 550078 Industrial Applicability The construction of the invention is used in the construction of motors and generators which are employed it electrical industry. The present invention is therefore industrially applicable. 2G2057NZ_CompSpec.doc Received at IPONZ 26 September 2008 _5£$Q78

Claims (20)

Claims

1. An electrodynamic machine having a unitaiy annular first structure comprising multiple magnetically isolated pole pieces arranged around an axis, each pole piece having a first face and a second face and at least one pole coil located on each pole piece between the planes of the first and second faces, a second structure rotatably mounted on the first structure axis and comprising a magnetic flux creation device for each pole piece wherein there exists a magnetic flux conducting path via the second structure from a first face of each pole piece via at least one magnetic flux creation device to the second face of the pole piece.

2. An electrodynamic machine as claimed in claim 1 wherein the machine is an axial flux machinc and the pole pieces are radially arranged around the axis.

3. An electrodynamic machine as claimed in claim 1 wherein the machine is a radial flux machine and the pole pieces are axially arranged around the axis.

4. A radial flux electrodynamic machine as claimed in claim 3 wherein the pole pieces are trapped between a common base plate and a common top plate.

5. A radial flux electrodynamic machine as claimed in claim 4 wherein each pole piece carries a groove at each end to facilitate the trapping.

6. A radial flux electrodynamic machine as claimed in claim 5 wherein the groove is arcuate and coacts with a corresponding projection on the base plate or top plate.

7. An electrodynamic machine as claimed in claim 3 wherein the machine is a drum machine.

8. An electrodynamic machine as claimed in claim 1 wherein each pole coil is wound on a bobbin.

9. An electrodynamic machine as claimed in claim 8 wherein the bobbins, coils and pole pieces are unitised as a first structure by embedding in a substrate. 202057NZ_CompSpec.doc Received at IPONZ 26 September 2008 5qopZ8

10. An electrodynamic machine as claimed in claim 9 wherein the substrate is created by injection moulding.

11. An electrodynamic machine as claimed in claim 1 wherein the second structure has an annular band of magnetic structure located adjacent the first faces of the poles.

12. An elcctrodynamic machine as claimed in claim 11 wherein the annular band forms part of the second structure.

13. An electrodynamic machine as claimed in claim 12 wherein the band is inside the first structure and the magnetic flux creation devices are permanent magnets and are outside the first structure.

14. An electrodynamic machine as claimed in claim 13 wherein the annular band and magnets are mounted to the same magnetic material.

15. An electrodynamic machine as claimed in claim 1 wherein the first structure is stationary and the second structure rotates.

16. An electrodynamic machine as claimed in claim 1 wherein the magnetic flux creation devices are permanent magnets.

17. A method of constructing a radial flux electrodynamic machine having a unitary annular stator structure comprising providing a plurality of isolated pole pieces, mounting pole coils to the pole pieces and assembling the pole pieces and coils to form an annular stator with each pole piece magnetically isolated from other pole pieces and each pole axis radially oriented, embedding the pole pieces and coils in a substrate to thereby unitise the stator, assembling magnetic field creating elements and a pole piece backing element in a rotor with at least one magnetic flux path between the magnetic field creating elements and the pole piece backing element and assembling the stator and rotor.

18. A method of constructing a radial flux electrodynamic machine as claimed in claim 17 comprising winding the pole coils on bobbins and placing the bobbins on pole pieces. 202057NZ_CompSpec.doc Received at IPONZ 26 September 2008 -5$gpz8

19. A method of constructing a radial flux electrodynamic machine as claimed in claim 17 comprising retaining the pole pieces and bobbins in place on a base plate prior to embedding the pole pieces and coils,

20. A method of constructing an annular flux electrodynamic machine having a unitary annular stator structure comprising providing a plurality of isolated pole pieces, mounting pole coils to the pole pieces and assembling the pole pieces and coils to form an annular stator with each pole piece magnetically isolated from other pole pieces and each pole axis axially oriented , embedding the pole pieces and coils in a substrate to thereby unitise the stator, assembling magnetic field creating elements and a pole piece backing element in a rotor with at least one magnetic flux path between the magnetic field creating elements and the pole piece backing element and assembling the stator and rotor. Pipers Attorneys for Wellington Drive Technologies Limited 202057NZ_CompSpec.doc