Abstract:
An electric motor or generator consists of a stator carrying pole pieces and their coacting coils, the stator being surrounded on one side by the 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:
TECHNICAL FIELD 
       [0001]    The invention generally relates to electrodynamic machines in which the poles are separated from the remainder of the magnetic structure. 
         [0002]    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 
       [0003]    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. 
         [0004]    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. U.S. Pat. No. 7,067,944 shows a typical example of such a construction in which the stator structure is injection moulded to the baseplate. 
         [0005]    The present invention provides a solution to this and other problems which offers advantages over the prior art or which will at least provide the public with a useful choice. 
         [0006]    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. 
         [0007]    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 
       [0008]    In one exemplification the invention consists in an electrodynamic machine having a unitary annular first structure comprising multiple magnetically isolated pale 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 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. 
         [0009]    Preferably the machine is an axial flux machine and the pole pieces are radially arranged around the axis. 
         [0010]    Preferably the machine is a radial flux machine and the pole pieces are axially arranged around the axis. 
         [0011]    Preferably the pole pieces are trapped between a common base plate and a common top plate. 
         [0012]    Preferably each pole piece carries a groove at each end to facilitate the trapping. 
         [0013]    Preferably the groove is arcuate and coacts with a corresponding projection on the base plate or top plate. 
         [0014]    Preferably the machine is a drum machine. 
         [0015]    Preferably each pole coil is wound on a bobbin. 
         [0016]    Preferably the bobbins, coils and pole pieces are unitised as a first structure by embedding in a substrate. 
         [0017]    Preferably the substrate is created by injection moulding. 
         [0018]    Preferably the second structure has a band of magnetic structure located adjacent the outer faces of the poles. 
         [0019]    Preferably the band forms part of the second structure. 
         [0020]    Preferably the band is inside the first structure and the permanent magnets are outside the first structure. 
         [0021]    Preferably the band and magnets are mounted to the same magnetic material 
         [0022]    Preferably the first structure is stationary and the second structure rotates. 
         [0023]    Preferably the magnetic flux creation devices are permanent magnets. 
         [0024]    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 pole pieces, mounting pole coils to the pole pieces and assembling the pole pieces and coils to form an annular stator with 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. 
         [0025]    Preferably the pole coils are wound on bobbins and the bobbins are placed on pole pieces. 
         [0026]    Preferably the pole pieces and bobbins are retained in place on a base plate prior to embedding the pole pieces and coils. 
         [0027]    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 pole pieces, mounting pole coils to the pole pieces and assembling the pole pieces and coils to form an annular stator with 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. 
         [0028]    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 
         [0029]      FIG. 1  is a sectioned perspective view of a motor according to the invention. 
           [0030]      FIG. 2  is a cross section of the rotor of  FIG. 1 . 
           [0031]      FIG. 3  is a cross section of the stator of  FIG. 1   
           [0032]      FIG. 4  is a cross section on line  4 - 4  of the stator of  FIG. 3   
           [0033]      FIG. 5  is an exploded view of the stator of  FIG. 1   
           [0034]      FIG. 6  is an exploded view of a winding and pole piece of  FIG. 5 . 
           [0035]      FIG. 7  is a sectioned view of a radial flux motor according to the invention. 
           [0036]      FIG. 8  is a sectioned perspective view of an axial flux motor according to the invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0037]    Referring now to  FIG. 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 . 
         [0038]    As best seen in  FIG. 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. 
         [0039]    Co-operating with rotor  102  is stator  103  shown in  FIG. 3 , with a cross section in  FIG. 4  and detail in  FIG. 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. 
         [0040]    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 polyurethane potting compounds are suitable and thermoplastics may also be used in low temperature applications. 
         [0041]    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 magnetic material required to form the stator, reducing the cost and weight of the stator assembly. 
         [0042]      FIG. 5  shows base  301  with a recess to receive the pole pieces  302  when fitted with windings  303 . As best seen in  FIG. 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. 
         [0043]    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. 
         [0044]      FIG. 7  and  FIG. 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. 
         [0045]    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 . Affixes 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 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. 
         [0046]    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. 
         [0047]    While permanent magnet pole flux generators are described the technology is equally applicable to electromagnetic flux generators. 
         [0048]    The machine in the drum form may be constructed with either the back iron inside the coils or the back iron outside the coils 
         [0049]    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. 
         [0050]    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. 
       INDUSTRIAL APPLICABILITY 
       [0051]    The invention is used in the construction of motors and generators which are employed it electrical industry. The present invention is therefore industrially applicable.