AU2004298828B2

AU2004298828B2 - Hybrid construction electric machine

Info

Publication number: AU2004298828B2
Application number: AU2004298828A
Authority: AU
Inventors: Donald Alfred Atkinson
Original assignee: Intelligent Electric Motor Solutions Pty Ltd
Current assignee: Intelligent Electric Motor Solutions Pty Ltd
Priority date: 2003-12-18
Filing date: 2004-12-16
Publication date: 2009-08-13
Anticipated expiration: 2024-12-16
Also published as: AU2004298828A1

Description

WO 2005/060073 PCT/AU2004/001766 1 TITLE HYBRID CONSTRUCTION ELECTRIC MACHINE TECHNICAL FIELD 5 This invention relates to electric machines and in particular to brushless electric machines with salient pole stators. BACKGROUND ART Electrical machines be these motors, generators or transformers currently 10 conventionally use coils of electrically conductive wire wound around a magnetically inducible core to create or be affected by magnetic fields. In order to reduce eddy current losses in a core, it is also conventional to laminate the core using a plurality of separate plates or laminations which are laid against one another with the alignment of each lamination being determined 15 by the overall structure of the electric machine and where any magnetic fields induced therein are required to be directed. This required structure however which is to say wound coils and laminated cores currently determine the current conventional electric motor construction requirements. I have discovered that there can be an alternative construction which I have 20 found can provide alternative options for electric machine designers which does in at least some cases provide advantages over the current machines designed according to current techniques. Other objects and advantages of the present invention will become apparent from the following description taken in connection with the accompanying 25 drawings wherein by way of illustration and example an embodiment of the present invention is disclosed.

2 Laminations are used to provide an anisotropic core. Electrical steel, from which the laminations are traditionally made, has low electrical resistance. It cannot be 5 employed in an isotropic form. An alternative solution to the problem of eddy currents is the use of "bonded iron" or soft magnetic composite to form the core. This material is known by the trade name of "Somaloy", "FM-CM" or "Permedyn". This material has magnetic properties suitable for use as a coil core, combined with high electrical 10 resistance. It allows an isotropic core (3D) to be constructed which does not suffer from the problem of excessive eddy currents. However, in many electric machines, the stator serves more than electrical and magnetic purposes. It also provides the mechanical frame of the machine. The mechanical properties of bonded iron (strength TRS in the range 40-1OOMpa) 15 are inferior to those of electrical steel. Somaloy or Permedyn has 10% the impact strength of electrical steel. A typical 56 frame motor has a radial load of 41 kgs. A Somaloy frame motor has a maximum radial load capacity of 1 Okgs. Further, mechanical fabrication of solid stators with complex internal profiles as may be required for optimum positioning of windings within the stator is 20 expensive. On the other hand, components from dies can have intricate shapes with smooth curvatures and excellent surface finishes. Laminations can be cheaply pressed out in a great variety of shapes. DISCLOSURE OF THE INVENTION 25 Accordingly we have discovered that both types of core material can indeed be used jointly and this provides significant advantages both electrically and mechanically. By having some of the structure being of laminate construction and some that is suitable for being a core but is of non laminar construction allows for complex shapes and efficiencies to be achieved that have not been 30 previously thought to be possible. Amended Sheet

IPEA/AU

3 In one form of this invention although this may not be the only or indeed the broadest form of this there is proposed an electric machine which includes at 5 least one magnetically inducible structure, said structure comprising at least two magnetically inducible portions, at least one said portion being of laminar construction and at least another said portion being non-laminar in construction. In the alternative there is provided an electric motor or generator having a stator and a rotor, characterised in that in at least the stator has at least one coil and 10 a core that is magnetically inducible from said coil where the core has at least two parts where one of the parts is of laminar construction and provides a rugged support and a further part is of non laminar construction. In preference, the laminar portion is arranged to be in a location where its more rugged mechanical strength is effective to protect the other less rugged non 15 laminar portion. In preference the non-laminar portion is positioned so that it is protected by laminar materials of more rugged construction. In preference, the magnetically inducible structure is a stator of an electric machine. 20 A significant advantage of a hybrid stator with both laminated and non laminated portions is that it combines the mechanical properties of a laminated stator with the ease of construction of a solid stator. In preference the laminar portion is a frame of a stator of an electric machine typically a motor or generator. 25 In preference, the non-laminar portion is a pole piece of a stator of an electric machine. Amended Sheet

IPEA/AU

xeceiveu Uv 3/1 The non-laminar portion has low eddy current losses and hysteresis losses less than laminated at medium motor frequencies. 5 In preference, a frame or back-iron of the machine is constructed from electrical steel. In preference, pole pieces of the machine are constructed from bonded iron. Electrical steel has low electrical resistance and thus is conventionally in a laminated construction when used as a magnetic core in order to reduce eddy 10 currents. Bonded iron has high electrical resistance and can be used as a solid piece as a magnetic core. The low electrical resistance aids to balance the reluctance between pole pieces. Amended Sheet mT A / ATT PCT/AU2004/001766 Received 3 April 2006 In preference, each lamination of the frame is pressed in such a shape that, when assembled into the frame, the internal profile of the frame is non-circular in such a way as to maximise the amount of space available for a stator coil. 5 In preference the electric machine is an electrical motor. In preference in the alternative the electric machine is an electrical generator. In preference in the alternative the electric machine is an electrical transformer. The invention in a further form may be said to reside in a method of constructing an electric machine which includes the steps where approximately annular 10 laminations are pressed from magnetically inducible, mechanically strong material, said laminations are assembled into a frame, and pole pieces made from a magnetically-inducible material of high electrical resistance are attached to said frame. 15 For a better understanding of this invention it will now be described with reference to a preferred embodiment which shall be described herein with the assistance of the drawings wherein; BRIEF DESCRIPTION OF THE DRAWINGS 20 Figure 1 is a perspective view of an electrical machine constructed according to a preferred embodiment of the present invention; and Figure 2 is plan view of the electrical machine of figure 1; and Figure 3 is a cross-section of the electrical machine of figure 2; and Figure 4 is a plan view of a lamination of the stator of the electrical machine of 25 Figure 1; and Figure 5 is a plan view of a 12 pole salient pole machine embodiment of the invention. Amended Sheet WO 2005/060073 PCT/AU2004/001766 5 BEST MODE FOR CARRYING OUT THE INVENTION Now referring to the illustrations and in particular Figure which is a perspective view of an embodiment of the present invention. Illustrated is a brushless DC 5 electric motor. There is a rotor 1 which has permanent magnetic pole pieces 5. The stator 2 consists of an outer approximately cylindrical frame 3 and a series of salient pole pieces 4. In the illustrated embodiment there are six pole pieces on the stator and four on the rotor. This 6-4 arrangement is common in the field, but many other combinations are possible. Coil windings, which will surround 10 each stator pole piece, have been omitted from the drawing for clarity but are included in the embodiment. The stator 2 is constructed of a stack of laminations 32, one of which is illustrated in Figure 4. These laminations are made of electrical steel, which has excellent magnetic and mechanical properties and very low electrical 15 resistance. The laminated structure is required to avoid excessive eddy currents in the frame. Mechanically, the frame is very robust, so that the stator requires no other support or protection. The pole pieces are made of a soft magnetic composite material, in this embodiment, this being bonded iron, which has is sold in Australia under the 20 trade name "somaloy". This material has appropriate magnetic properties to provide a core of the stator coils. It has a high electrical resistance, so it does not require lamination in order to avoid excessive eddy currents within the pole pieces. The mechanical properties of somaloy are relatively poor. The pole pieces 25 would shatter if struck forcefully. However, in use they are protected by the stator frame. Referring to Figure 2, which is a cross-section of the machine of Figure 1, it is clear that the stator frame 3 supports pole pieces 4. These are held into the lamination stack which makes up the frame by a wire 11 which is force fit into a 30 hole formed by matching semicircular grooves on the pole piece 4 and the WO 2005/060073 PCT/AU2004/001766 6 stator frame 3. It will be understood that any other suitable fixing method, for example dovetails, fixing screws, semi-enclosed slots or adhesive means could be employed to hold the pole pieces in place. It can be seen that the inner profile of the lamination stack frame includes a 5 section 8 which is perpendicular to the axis 9 of the adjacent stator coil. This allows for a larger coil in closer contact with the stator than would be the case if the frame were made as a simple annular cylinder with a perfectly circular inner profile. Such an inner profile would be the only one possible if the frame were machined from a solid piece of isotropic material. 10 The flat step 8 can be clearly seen in Figure 4, which shows a plan view of a single lamination of the frame. The sections 8 serve, along with the sides of the stator pole pieces 4, serve to define a space 7 for the stator coils (not shown). The faces 6 of the stator pole pieces 4 are shaped in order to reduce the air gap 15 10 between the rotor and the stator. Referring to Figure 3, which is a cross-section A-A of the machine of Figure 2, it can be seen that the stator pole pieces are composed of individual elements 20 which are joined to form the stator pole piece 4. Looking at Figure 4, which is a plan view of a single lamination of the stator 20 frame, it can be seen that the shape of the inner profile of the lamination is relatively complex. This is easily manufactured since the laminations are produced by stamping. The laminations are then stacked to form the stator frame. This allows the stator frame to have a much more complex inner profile than could be achieved by machining a solid block. 25 There is a recess 31 with a notch 30 which, when the laminations are stacked, form a slot with a semi-circular groove into which the stator pole pieces fit. The groove matches with a groove on the stator pole pieces to form the hole which receives wire 11 to hold the stator pole piece in place.

PCT/AU2004/001766 7 Received 3 April 2006 Figure 5 is a plan view of a 12 pole salient pole motor made in accordance with the current inveniton. There is a stator frame 52 which is constructed from laminated electrical steel. This surrounds 12 salient pole pieces 53 which are of 5 bonded iron construction. These form a self supporting ring but are attached to the laminated stator frame by a slot and cleat arrangement 56. There is a central rotor 55 within the ring of salient pole pieces. Coils which are not shown for clarity are around the web 54 of the salient pole 10 pieces 53. The purpose of this description is to describe the invention and not to limit this. Amended Sheet TDV A / A TT

Claims

1. An electric machine, said electric machine including: a substantially cylindrical stator frame constructed of a stack of electrical steel laminations; 5 a series of individual stator magnetisable pole members made of a soft magnetic composite material fixably supported within said stator frame; a rotor having permanent magnetic pole pieces; and wherein each individual stator magnetisable pole member has coil windings about said stator magnetisable stator pole member, pre-wound before 10 being fixably supported in said stator frame, wherein the or each stator magnetisable pole member has an inner peripheral rim and an outer circumferential rim separated by a longitudinal column to which said coil is pre-wound thereabout said column before each stator pole member is fixably supported within said stator frame, 15 wherein the longitudinal column is of length so that the wounded coil need not extend out over and above the inner and outer rims thereby providing for a more compact stator frame.

2. The electric machine of claim 1 wherein the stator frame provides an inner substantially circular ring for fixable support for said stator magnetisable 20 pole member thereabout, such that the outer circumferential rim of the stator magnetisable pole member and an inner face of the circular ring of the stator frame engage in a tongue and groove fit. 9

3. The electric machine of claim 2 wherein the circumferential rim includes a tongue longitudinally configured substantially down its length and the inner face of the circular ring of the stator frame includes a series of grooves about said ring inner face, so that individual stator magnetisable pole member maybe 5 position in a substantially annular arrangement about circular ring.

4. The electric machine of claim 2 wherein the inner circular ring of the stator frame provides for a flat section or spacing between individual stator magnetisable pole members such that each individual stator magnetisable pole member is perpendicular to the axis of an adjacent individual stator 10 magnetisable pole member to allow for a larger coil or winding of coil in closer contact with the stator than would be the case if the frame were made as a single annular cylinder with a perfectly circular inner profile.

5. The electric machine of claim 1 wherein the inner peripheral rim and the outer circumferential rim of each stator pole member supported within said 15 stator frame is such to reduce the air gap between the rotor and the stator.

6. The electric motor of any one of the preceding claims wherein there are six magnetisable pole pieces on the stator and four permanent pole pieces on the rotor.

7. The electric machine of any one of the preceding claims wherein the soft 20 composite material is bonded iron.

8. The electric machine of any one of the preceding claims wherein each lamination of the frame is of such a shape that, when assembled into the frame, the internal profile of the frame is non-circular in such a way as to maximise the amount of space available for coil pre-wound about each of the stator pole 25 member.

9. An electric machine as in any one of the preceding claims wherein the electric machine is an electrical motor. 10

10. An electric machine as in any one of the preceding claims wherein the electric machine is an electrical generator.

11. An electric machine as in any one of the preceding claims wherein the electric machine is an electrical transformer.