Abstract:
A rotary electrical machine device that reduces the distortion generated in the waveform of the electromotive force as much as possible while adopting inexpensive processes and assembling methods.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to a rotary electrical machine that provides a compact and simply constructed structure that reduces the harmonic components in the wave form existing between the permanent magnets and cooperating wound pole teeth on relative rotation.  
           [0002]    Normally these machines, which may comprise either motors or generators are comprised of cooperating relatively rotatable components comprised of a plurality of circumferentially spaced permanent magnets that cooperate with the tops of a plurality of pole teeth around which electrical coils are wound. If the machine is a motor, the coils are sequentially energized to effect rotation. If it is a generator it is driven and a voltage is generated in the coil windings. These type of machines may assume many forms.  
           [0003]    There conventional magnetic field type rotary electric devices adopt either an inner permanent magnet (IPM) structure in which permanent magnets for forming a magnetic field are buried in a stator yoke (core) or rotor yoke made from magnetic materials or the surface permanent magnet (SPM) structure in which the permanent magnets are disposed on the surface of the core at certain intervals.  
           [0004]    One form of IPM structure is shown in Japanese Published Application Hei 09-275645. This Published Patent Document discloses an IPM structure for a motor in which the stator is constructed with a core having plural magnet insertion holes within the inner peripheral surface of the core and into which magnet plates are inserted.  
           [0005]    Japanese Published Application 2002-27690 shows another IPM structure. In this construction, to facilitate flux distribution, a semi cylindrical bulge section is disposed on the outer edge of the core on the diameter line connecting the center line of the permanent magnet and the center of the rotor core.  
           [0006]    These IPM constructions have disadvantages because a part of the flux emitted from the permanent magnets to form the magnetic fields is shunted and flows through the inside of the core through the resulting gap between the core outer edge and the permanent magnet. It also causes flux leakage because it does not reach the rotor core or stator core, and therefore results in efficiency reduction that produces a drop in torque output if the machine is motor or a reduction of electromotive force if the machine is generator.  
           [0007]    With the SPM structures, the permanent magnets for forming a magnetic field are implanted on the surface of the rotor core and directly face the wound poles of the stator. Thus the permanent magnets can be positioned as close as possible to the magnetic pole of the coil. The flux flow of the permanent magnets acts on the windings through the very small gap. This permits the waveform of the electromotive force to approaches an approximately sinusoidal waveform. In this way that torque pulsation can be reduced. Therefore, there is a trend toward a greater use of the SPM type of structures.  
           [0008]    One typical SPM structure is shown in Published Japanese Application Hei 09-275648. In this arrangement, the stator containing the permanent magnets is disposed around the rotor having the wound pole teeth. The stator is provided with pairs of spaced magnet plates in V-shape with their edges abutted open toward the wound poles.  
           [0009]    Another SPM type of structure is shown in Japanese Published Application 2000-166141A. In this arrangement, the permanent magnets are carried by the rotor and are bonded in grooves formed on the outer peripheral surface of the cylindrical rotor at predetermined intervals. The permanent magnets have a semi cylindrical shape with a curved surface that faces the wound pole teeth of the stator.  
           [0010]    Although the SPM type of structures have the aforenoted advantage over the IPM structures, there is still room for improvement. Their shortcoming and particularly those of the last noted example may be best understood by reference to FIGS.  1 - 5 . Referring now initially to FIGS. 1 and 2, a rotary electric device of this type is identified generally at  21  and is comprised of an annular stator  22  that surrounds a rotor  23 . The stator  22  is constructed with thin laminated bodies of a magnetic material having a circular core  24  from which a plural pole teeth  25  extend radially inward inwardly. Slots  26  ( 18  slots in the shown example) are formed between the teeth  25 . Coil  27  are wound around each of the teeth  25  into the slots  26  on the sides of the teeth  25 .  
           [0011]    The rotor  23  is constructed similar to the stator  22  with thin plates of a laminated magnetic material  28  of a generally cylindrical configuration and forming a cylindrical outer peripheral surface  29 . A plurality of permanent magnets  31  (12 magnets in the exemplary drawing) are suitably fixed to the surface  29  at regular circumferential intervals. The rotor  23  is rotatably supported on a rotor shaft  32  that is suitably journalled, for example by roller bearings (not shown).  
           [0012]    A rotary electric device  21  having such SPM structure can function as a motor in which the rotor  23  is rotated by the effects with the flux on the rotor  23  when the magnetic field is formed by the current input to the coils  27  of the stator  22  is applied in a predetermined sequence for the flux flow of the magnetic fields formed by the permanent magnets  31  of the rotor  23 . Alternatively, the rotary electric device  21  having the SPM structure described can be constructed as a generator in which electromotive force can be taken from the coils  27  when the rotor  23  is rotated by an external mechanical torque.  
           [0013]    In such construction of a rotary electric device  21  having SPM structure, the waveform of the electromotive force approaches to an approximately sinusoidal waveform as described previously. However, when there are many harmonic components included in the electromotive force of the sinusoidal waveform and thus the distortion factor is high. These harmonic components can induce malfunctions of peripheral devices when the machine  21  functions as a generator. Also when the machine  21  functions as a motor problems are encountered such as torque pulsations caused by the harmonic components in case of a brushless motor.  
           [0014]    In order to prevent such problems, attempts are conventionally made such that windings  27  are selectively wound and the opposed surface  31   a  of the permanent magnet  31  facing the stator  22  is curved to form a semi cylindrical shape as shown in the partially enlarged view of FIG. 2 in an effort to control the flux flow to reduce the harmonic components. However, there are disadvantages to these approaches. For example when the distributive winding method is adopted, the winding end (coil end) protruding at both axial ends of the stator  22  is substantial and accordingly the axial dimension of the stator  22  increases to naturally enlarge the size of the rotary electric device. Therefore, there is a disadvantage that the device cannot satisfy the small sizing requirements when it is applied to various applications such as a power source motor and/or a generator.  
           [0015]    Also as shown in FIG. 2, the structure in which the permanent magnet  31  is shaped into the arc concentric with the rotor shaft  32  requires substantial labor for the initial processing of the permanent magnets and thus makes the resulting machine overly expensive. Furthermore, as will now be described, these attempts are not totally effective in improving the electrical performance.  
           [0016]    Referring now to FIG. 3, this shows a waveform chart in the rotary electric device  21  shown in FIG. 1 by detecting the waveform of the counter electromotive force generated during rotation in order to analyze the magnetic field analysis waveform in case that each of the permanent magnets  31  of the rotor  23  has an outward arc shape as shown in FIG. 2. This waveform includes the harmonic components in spite of the fact that the arc shape is given to the pole face of the permanent magnets  31 . Thus it is found from the fundamental sinusoidal waveform that the distortion nevertheless has occurred.  
           [0017]    The result of analysis separation of such magnetic field analysis waveform into each order after Fourier expansion is shown in a graph of FIG. 4, in which the vertical axis shows the component value of the electromotive force for each order and the horizontal axis shows the respective orders. As seen from the graph of FIG. 4 there are many harmonic components of 5th, 7th, 11th, and the like and that the harmonic components of the other orders are also generated.  
           [0018]    When the harmonic components of each order (2nd through 20th) are further enlarged, as shown in FIG. 5, harmonic components of electromotive force of almost all orders are generated. These harmonic components are found to be total harmonic distortion (T.H.D)=7.26% as a result of calculating the ratio to the fundamental electromotive force components. Therefore, this prior art attempted solution is not preferable because it may induce the aforementioned malfunctions of the peripheral devices as a result of the harmonic components and may cause the generation of the torque pulsation (torque ripple). T.H.D is a total of distortion in each order. In this example, it is a total of distortion from 1st order through n th order may be expressed as follows:  
             T.H.D={square root}{ 0.06(2nd order)} 2 +{0.02(3rd order)} 2   + . . . {n - th  order} 2 /{6.81(1st order)} 2  =7.26%  
           [0019]    Therefore it is a principal object of this invention to provide an improved, simplified, low cost rotary electrical machine.  
           [0020]    It is a further object of the invention to provide a rotary electrical machine in which the permanent magnets are mounted to the rotor in the SPM type rotary electric devices, but which has better performance than those previously employed.  
           [0021]    It is a yet further object of the invention to provide a rotary electrical machine device that can reduce the distortion generated in the waveform of the electromotive force as much as possible while adopting inexpensive processes and assembling methods.  
         SUMMARY OF INVENTION  
         [0022]    This invention is adapted to be embodied in a rotary electrical machine comprised of a pair of relatively rotatable components comprising an armature having a core from which a plurality of circumferentially spaced pole teeth extend in a radial direction. Coil windings are formed around the pole teeth. The other of the components comprises a permanent component having a plurality of circumferentially spaced permanent magnets mounted on the periphery thereof in confronting and closely spaced relation to the tip ends of the pole teeth to define a generally cylindrical gap therebetween. In accordance with the invention, at least one of the pole teeth and the permanent magnets having planar surfaces facing the gap. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0023]    [0023]FIG. 1 is a side elevational view of a prior art type of SPM machine.  
         [0024]    [0024]FIG. 2 is an enlarged view of the area encompassed by the circle  2  in FIG. 1.  
         [0025]    [0025]FIG. 3 is waveform chart showing the waveform of counter electromotive force as the efficiency of the conventional SPM type rotary electric device as shown in FIGS. 1 and 2.  
         [0026]    [0026]FIG. 4 is a graph showing analysis results of harmonic components included in the waveform illustrated in FIG. 3.  
         [0027]    [0027]FIG. 5 is a graph showing the enlarged harmonic components shown in FIG. 4.  
         [0028]    [0028]FIG. 6 is a side elevational view in part similar to FIG. 1, but shows a first embodiment of the invention.  
         [0029]    [0029]FIG. 7 a graph showing the low harmonic distortion efficiency of the rotary electric device shown in FIG. 6.  
         [0030]    [0030]FIG. 8 a tabular representation showing the low harmonic distortion efficiency of the rotary electric device shown in FIG. 6.  
         [0031]    [0031]FIG. 9 is a side elevational view, in part similar to FIG. 6, but shows another embodiment of the invention.  
         [0032]    [0032]FIG. 10 is a waveform chart of the electromotive force of the rotary electric device according to the embodiment shown in FIG. 9.  
         [0033]    [0033]FIG. 11 a graph showing the low harmonic distortion efficiency of the rotary electric device shown in FIG. 9.  
         [0034]    [0034]FIG. 12 a tabular representation showing the low harmonic distortion efficiency of the rotary electric device shown in FIG. 9.  
         [0035]    [0035]FIG. 13 is a cross sectional view showing the finished body structure of a rotary electric device according to yet another embodiment of the present invention.  
         [0036]    [0036]FIG. 14 is a view looking in the direction of the arrows  14 - 14  in FIG. 13. 
     
    
     DETAILED DESCRIPTION  
       [0037]    Referring now in detail to the drawings and first to the embodiment of FIGS.  6 - 8  and initially to FIG. 6, shows both yokes (cores) of the stator and the rotor removed from the rotary electric device according to an embodiment of the present invention. A stator, indicated generally at  51  of the rotary electric device has substantially the same structure as the conventional stator  21  shown in FIG. 1. That is it has a core  51  of a hollow cylindrical shape formed by laminating plural planar plates made of magnetic steel or other materials. Pole teeth (teeth)  53  extend radially inward from the core  52 . Slots  54  are formed between the adjacent pole teeth  53 .  
         [0038]    Coils  55  is wound around each pole tooth  53  and extend through the slots  54  on both sides of the teeth  53 . The radial inner end face of each of the pole teeth  53  is formed with a respective pole face  56 .  
         [0039]    A cooperating rotor, indicated generally at  57 , is formed as a cylindrical member with a laminated core  58  and has insertion holes to receive a shaft  59  at their centers. The core  58  is made of magnetic steel or other like materials. The core  57  has a generally cylindrical outer surface  61  that is formed with a plurality of circumferentially spaced narrow grooves of generally rectangular configuration forming flat surfaces  62 . Permanent magnets  63  are accommodated or seated in each of the grooves or flat surfaces  62  in manners to be described.  
         [0040]    The permanent magnets  63  in this example are formed as a planar member of a rectangular shape having the desired thickness. The wide outwardly facing side surface forms an external pole face  63   a . An internal pole face  63   b  is firmly bonded by, for example, an adhesive, and secured to the outer peripheral surface  61  of the rotor  57 . This is then fixed by a mold resin agent (not shown) as described later to prevent detachment from the outer peripheral surface  61  of the rotor  57 . Thus the entire structure is a laminated body of the rotor core  58 .  
         [0041]    In the illustrated embodiment, twelve (12) permanent magnets  63  are spaced and fixed in the circumferential direction at regular intervals (θ, 2θ, 3θ, . . . , nθ) and disposed to form a magnetic field in each magnet as well as 12 magnetic poles in all.  
         [0042]    Each of the permanent magnets  63  is processed and assembled for example in the following method. A number of planar pieces are cut and separated from a cube shaped permanent magnet metal block and corrected in terms of the dimension to form a planar member having two flat surfaces for forming the pole faces  63   a  and  63   b . Then, the planar member is bonded to the outer peripheral surface  61  of the rotor  57  and magnetized within a strong magnetic field to form the planar permanent magnet piece  63 .  
         [0043]    It is also possible to magnetize the permanent magnet piece  63  after the step of forming the planar member and then positioned, secured, and firmly bonded to the outer peripheral surface  61  of the rotor  57 . The permanent magnet piece  63  is disposed on the outer peripheral surface  61  of the rotor  57  by appropriate disposing method of permanent magnets.  
         [0044]    The rotor  57  is therefore constructed as an SPM type rotor having plural permanent magnets  63  for forming magnetic fields on the outer peripheral surface  61  and positioned in the radial direction opposite to the pole teeth faces  56  of the stator  51  through an annular gap  64  that is made as small as possible.  
         [0045]    Adopting the configuration having such planar permanent magnets  63  allows the annular gap  64  opposite to the stator  51  to be narrowed to the lowest limit within the characteristics of the SPM type rotor. This therefore, allows magnetic flux of the field formed by each piece of the permanent magnets  63  to act on the coils  55  of the stator  51  and keeps the efficiency of generating electromotive force or rotating torque as a rotary electric device at a high level.  
         [0046]    Furthermore, as described above, adopting the permanent magnet piece  63  as the planar magnet piece facilitates the manufacturing of the magnets and their assembly to the rotor  57 . This contributes to the reduction of the manufacturing cost and also results in the possibility of a substantial reduction in the ratio of harmonic power component to fundamental sinusoidal power.  
         [0047]    The total harmonic distortion (T.H.D) as a consequence of the measurement and analysis of counter electromotive force at the rotation as shown in FIGS. 7 and 8. FIG. 7 is a graph illustrating the ratio of respective harmonic components of 1st through 20th orders to the fundamental wave in spectral values, and harmonics in each order. Thease are shown within the frequency range of 100 Hz through approximately 2 kHz in the horizontal axis (X) and the ratio (dB) within the range of 0 through approximately 100 (dBVr) in the vertical axis (Y). FIG. 8 shows a tabular representation illustrating the result of FIG. 7. As the result, the total harmonic distortion (T.H.D) derived by addition and summation of the distortion factor (Dis: %) of the harmonics in each order is equal to 1.732% which is below 2%. Thus it is found that the T.H.D is significantly reduced as compared with the conventional distortion value of over 7%.  
         [0048]    When the total harmonic distortion (T.H.D) is reduced in this way, remarkable effects can be achieved and the torque pulsation can be substantially reduced and concerns about the induction of malfunction in peripheral devices can be eliminated. Also the reliability of the rotary electric device is improved.  
         [0049]    [0049]FIG. 9 shows an SPM type rotary electric device according to another embodiment of the present invention. The rotary electric device has substantially the same configuration and structure as the rotary electric device according to the embodiment shown in FIG. 6 and for that reason where the components thereof have substantially the same construction as that embodiment, they are identified by the same reference numerals and will not be described again in detail except where necessary for those skilled in the art to understand and practice this embodiment.  
         [0050]    The embodiment of FIG. 9 differs from that of FIG. 6 in that the planar permanent magnets  63  fixed on the cylindrical outer peripheral surface  61  of the rotor  57  are disposed in the circumferential direction of the rotor  57  at irregular intervals (θa, θb, θc, θd, θe, . . . ) rather than equal increments. Therefore, advantages in the processing of the planar permanent magnets  63  can be obtained exactly the same way as the aforementioned embodiment.  
         [0051]    On the other hand, by adopting the configuration such that the planar permanent magnets  63  for forming a field are disposed in the circumferential direction of the cylindrical outer peripheral surface  61  of the rotor  57  at irregular intervals, a significant decrease of cogging can accomplished particularly when the rotary electric device is used as a motor. Therefore, when measurement is made for the waveform of the electromotive force of the SPM type rotary electric device according to this embodiment, it is confirmed to exhibit the sinusoidal waveform with almost no distortion as shown in FIG. 10.  
         [0052]    Furthermore, when an analysis is conducted on the harmonic components of the sinusoidal waveform in the electromotive force, the results shown in FIGS. 10 and 11 are obtained. In other words, FIGS. 10 and 11 show the components of electromotive force in each order of 1st- through 20th-order harmonic component in spectral and tabular representations in the same manner as the graph and tabular representation of the spectral value shown in FIGS. 7 and 8 of the previous embodiment.  
         [0053]    The results in FIGS. 10 and 11 show that the total harmonic distortion is equal to 43.959 dBVr, even having distortion components in each order, and that the distortion (T.H.D) is further reduced to only 1.101% thus even below that of the previous embodiment. Therefore, it is found from the result that the harmonic component in the electromotive force of the SPM type rotary electric device according to the present embodiment is very small.  
         [0054]    The previous drawings of the preferred embodiments have only shown the rotor and stator. Next will be described by reference to FIGS. 13 and 14 how these constructions can be embodied in a complete electrical machine which may comprise either a motor or a generator. In these views where components have the same construction as already described they are described again only in so far as is necessary to permit those skilled in the art to practice the invention.  
         [0055]    The machine (motor or generator) is indicated generally by the reference numeral  71  is formed as a three-phase twelve-pole device integrated with the stator  51  and the rotor  57  and formed as a compact, integrated rotary electric device by way of molding each of the stator  51  and the rotor  57  with thermoplastic mold resin such as unsaturated polyester. The mold resin is injected into a molding die after the stator  51  is positioned in a respective molding die and hardened to form the housing body  72  of the machine  71 . At this time a bearing  73  for one end of the rotor shaft  59  is positioned in the mold body.  
         [0056]    After the housing body  72  is formed one end (the left side in FIG. 13) is open and the rotor  57  and its shaft  59  is inserted into the bearing  73  with the other end of the rotor shaft  59  protruding through this opening. Threaded fastener receivers  74  are molded into the body  72  around this opening at the time of molding.  
         [0057]    An encoder circuit board  75  is mounted to the end surface of the mold resin housing body  72  by using by well-known push nuts  76 . The circuit board  75  is provided with Hall effect devices (Hall IC)  77  and lead wire terminals  78 . These Hall effect devices  77  cooperate with sensor magnets, the polarity of which is noted in FIGS. 13 and 14, mounted on a side surface of the rotor  57  to detect the rotational speed or rotation angle of the rotor  57 . The sensor magnets are designed so that an annular magnetic material is magnetized such that the north and south poles are provided in the axial direction and alternately arranged in the circumferential direction. The magnetic field of the sensor magnets and the Hall effect devices  77  electromagnetically interact to constitute a rotary detector for detecting the rotational speed or rotation angle of the rotor  57 .  
         [0058]    A cover plate (not shown) carrying an external bearing  79  is then attached using fasteners and the receivers  74  to enclose the machine  71  with the one shaft end exposed for driving or driven relation.  
         [0059]    The coils  55  of the stator  51  are constructed such that the coil end is held with an insulator bobbin  81  made from an appropriate insulating material and the coil end of each phase is connected with a coil terminal  82  disposed in the end surface of the stator  51  to input from or output to the coil  55  of each phase through input or output terminal  83 .  
         [0060]    Such rotary electric device  71  can be used as a motor when input current is supplied to the input terminal  39   c  or as a generator when the rotor shaft  33  is mechanically driven from the outside and electromotive force is taken from the output terminal  39   c . Therefore, building in various external devices allows application to a power driving source or generator.  
         [0061]    Thus from the foregoing description it should be readily apparent that it is possible to build a very compact and efficient rotary electrical machine at a low cost. Of course those skilled in the art will readily understand that the foregoing description is of preferred embodiments and various changes and modifications may be made without deviating from the spirit and scope of the invention, as defined by the appended claims.