Abstract:
A plurality of embodiments of rotating electrical machines having improved arrangements for securing plate type permanent magnets to a cylindrical surface of one component of the machine in facing relation to another relatively rotatable component thereof with a small gap therebetween. The magnets are secured by embedding them in a bonding material surrounding the peripheral edges of the magnets and at least a portion of the sides thereof facing the gap and leaving an area of said sides directly exposed to the gap to maintain good electrical properties and machine performance without necessitating an increase in the gap.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to a rotary electric apparatus and more particularly to animproved construction for firmly securing the permanent magnets while maintaining good electrical performance.  
           [0002]    Normally these rotary electric apparatus, 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 tips of a plurality of pole teeth around which electrical coils are wound. If the apparatus 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 apparatus 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 desired intervals.  
           [0004]    Japanese Published Application 2002-27690 shows a type of 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.  
           [0005]    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.  
           [0006]    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.  
           [0007]    Japanese Published Application 2000-166141A shows a SPM type of structure. 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. The gap length between the permanent magnet surfaces and the stator is different on opposite sides of the recess so as to reduce torque ripple by producing induction voltage including high harmonic content.  
           [0008]    There are, however problems dealing with the attachment of the magnets in connection with the SPM type of structure. These may be best understood by reference to the examples of prior art structures commonly employed as shown in FIGS. 1 and 2,  3  and  4 .  
           [0009]    Referring first to the prior art example of FIGS. 1 and 2, these figures show a rotor construction of a permanent magnet motor of the SPM type of constructionin which the rotor which carries the magnets is located inside the stator. As seen in these figures, a rotor indicated generally ask comprises a plural number of permanent magnet pieces  12  glued with adhesive in respective slots  13  formed in the cylindrical outer surface  14  of a rotor core  15 . The outside magnetic pole surface  12   a  of each permanent magnet piece  12  is rounded in a cylindrical shape to face a stator (not shown) that encircles the rotor  11 .  
           [0010]    The rotor  11  is journalled for rotation about an axis by two bearings  16  and  17  at two axially spaced positions along a rotor shaft  18 . This rotor  11  represents a typical conventional magnet holding construction in which the adhesively secured permanent magnet pieces  12  are retained from coming off the rotor core  15  under the influence of centrifugal force by encasing the entire outside cylindrical surface of the rotor  11  including the permanent magnet pieces  12  with molding resin  19 .  
           [0011]    The disadvantage of the construction in which the rotor  11  is entirely wrapped around with the molding resin  19  the gap between the rotor and specifically the magnet surfaces  12   a  and the stator is reduced by the thickness of the molding resin layer  19 . Thus to avoid mechanical interference, the gap must be increased by at least the thickness of the resin  19 . As a result, the magnetic interaction between the rotor and stator is weakened, which leads to a decreased output torque in the case of a motor or decreased electrical output in the case of a generator.  
           [0012]    Referring now to the prior art construction shown in FIG. 3, this shows another conventional DC motor of an inner rotor construction. In this example, a rotor indicated generally at  21  is comprised of a laminated rotor core having a plurality of magnetic pole portions  22  around which coil windings(not shown) are place. These windings extend into slots  23  formed between the pole teeth  22 . The pole teeth have outermost surfaces of an arcuate shape  24 . The rotor  21  is journalled on a motor shaft (not shown) that passes through a shaft hole  25  bored in the center of the core of the rotor  21 .  
           [0013]    A stator indicated generally at  26  is placed outside the rotor  21  with an annular gap  27 formed therebetween. A plurality of permanent magnets  28  are placed at equal circumferential intervals in the annular gap  27  on a cylindrical inner surface  29  of the stator  26 . These magnets  28  are of a curved shape to conform to the inside cylindrical surface  29  of the stator  26  and oppose the arcuate outermost surfaces  24  of the respective magnetic pole portions  22  of the rotor  21 . Small gaps are formed therebetween for clearance reasons.  
           [0014]    The curved magnets  28  are secured to the stator  26  only by means of an adhesive to adhesively bond the inside surface  28   a  of the magnets  28  and to the inside cylindrical surface  29  of the stator  26 . Therefore, the DC motor of the conventional inner motor constitution does not employ the technique of securing the magnets  28  encasing it with a molding resin agent and reliance is placed solely on the adhesive to prevent separation.  
           [0015]    [0015]FIG. 4 shows another prior art construction, similar to that of FIG. 3, and in this case comprises, for example, a generator of a conventional outer rotor constitution commonly used in motorcycles. This conventional generator comprises a stator indicated generally at  31  located radially inside a rotor, indicated generally at  32 . AS with the construction of FIG. 3, coils (not shown) are wound around poles of the stator  31 . When driven these coils generate the electricity output.  
           [0016]    The rotor  32  is provided with four permanent magnets  33  of a arcuate shape that are secured to an inside cylindrical surface  34  of the rotor  32  at equal circumferential intervals.  
           [0017]    Each of the four, arcuate shaped permanent magnets  33  is magnetized with three poles of alternation polarity to act as if three permanent magnets were placed in tight contact with each other.  
           [0018]    This generator of the outer rotor constitution is to produces an alternate current output from the coils of the stator  31  as the rotor  32  is rotated by external power and is used as a power for motorcycles to light up lamps and the like. However, this generator of the conventional outer rotor constitution only employs the method of adhesive securing the arcuate shaped permanent magnets  33  to the inside cylindrical surface  34  of the rotor  32  and involves no technical concept of cast-wrapping and mold-securing the permanent magnets  33  using the molding resin agent. Thus these prior art constructions raise the risk of the permanent magnets becoming detached in operation.  
           [0019]    It is therefore a principal object of the invention to provide a rotating electrical machine that is extremely efficient, but also has a very secure arrangement for affixing the permanent magnet so that the risk of detachment is substantially eliminated.  
         SUMMARY OF INVENTION  
         [0020]    This invention is adapted to be embodied in a rotating electrical machine having a component having a cylindrical surface adapted to face a gap defined by a cooperating cylindrical surface of formed by poles wound with electrical coils. A plurality of plate type permanent magnets are spaced around the cylindrical surface. A bonding agent surrounds the peripheral edges of the magnets and at least a portion of the sides thereof facing the gap and leaving an area of said sides directly exposed to the gap. The bonding agent is affixed to the cylindrical surface. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0021]    [0021]FIG. 1 is a side elevational view, with a portion broken away, of rotor of a rotating electrical machine of a first prior art type.  
         [0022]    [0022]FIG. 2 is a cross sectional view taken along the line  2 - 2  of FIG. 1.  
         [0023]    [0023]FIG. 3 is a cross sectional view taken perpendicular to the rotational axis of a rotating electrical machine of a second prior art type.  
         [0024]    [0024]FIG. 4 is a cross sectional view taken perpendicular to the rotational axis of a rotating electrical machine of a third prior art type.  
         [0025]    [0025]FIG. 5 is a side elevational view, with a portion broken away, in part similar to FIG. 1 but showing the rotor of a rotating electrical machine of a first embodiment of the invention.  
         [0026]    [0026]FIG. 6 is a cross sectional view taken along the line  6 - 6  of FIG. 5.  
         [0027]    [0027]FIG. 7 is a graphical view showing the electromotive force of the machine of FIGS. 5 and 6 in relation to the electrical angle.  
         [0028]    [0028]FIG. 8 is an enlarged, partial cross sectional taken along an axial plane of a rotating electrical machine of a second embodiment of the invention.  
         [0029]    [0029]FIG. 9 is an cross sectional taken along an axial plane of a rotating electrical machine of a third embodiment of the invention.  
         [0030]    [0030]FIG. 10 is an cross sectional taken along an axial plane, in part similar to FIG. 9, of a rotating electrical machine of a third embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0031]    Referring now in detail to the drawings and initially to the embodiment of FIGS. 5 and 6, a portion of a rotating electrical machine of the inner rotor type, with the rotor placed inside the stator is shown although from the following description it will be apparent to those skilled in the art that the invention is not so limited.  
         [0032]    The rotary electric apparatus of this embodiment is comprised of a rotor, indicated generally by the reference numeral  51 . The rotor  51  includes a rotor core  52  made of a magnetic material. The rotor core  52  has a splined opening  52   a  for non-rotatably coupling it to the splines  53  of a rotor shaft  54 .  
         [0033]    The rotor  51  is journalled relative to a stator (not shown) by means of antifriction bearings  55  and  56  provided on both ends of the rotor shaft  54 .  
         [0034]    An annular sensor magnet  57  having circumferentially spaced magnetic poles of alternate polarity is attached to the side face of rotor core  52  facing the front bearing  55 . The sensor magnet  57  makes it possible to measure the rotational angle of the rotor  51 through cooperation with a magnetic sensor element such as a Hall effect element (not shown) carried by the associated stator (not shown).  
         [0035]    A plurality of plate type permanent magnets  58  are secured by adhesion of an adhesive or the like at even or uneven intervals into slots formed in an outside cylindrical surface  59  of the rotor core  52  of the rotor  51 . These permanent magnets  58  are securely held in place by molding preferably by a thermosetting molding resin  61  in a manner to be described shortly.  
         [0036]    The permanent magnets  58  are made by cutting a magnetic material into pieces having a flat rectangular shape of the desired dimension. The radially inner and outer rectangular flat surfaces of the cut pieces are suitably magnetized to be N pole and S pole surfaces  58 N and  58 S. According to the magnetizing method generally practiced, one of the rectangular surfaces of the rectangular metallic material for each magnet is secured into a shallow groove  59  formed in the outside cylindrical surface of the rotor core  52  with an adhesive, and magnetized to be a permanent magnet by subjecting to a strong magnetic field. The polarity of the poles is alternated circumferentially around the core  52 .  
         [0037]    After gluing and positioning the permanent magnets  58  to the rotor core  52  as described above, they are placed into a molding die (not shown). The inside surface of the molding die has the shape of a cylinder that is tangent to the circumferential ends  58   a  and  58   b  of the magnets  58  as positioned on the rotor core  52 . Then, the molding resin  61  for partially covering and securely holding the permanent magnets  58  is poured into the molding die and permitted to set.  
         [0038]    With the above arrangement, a gap is formed between the central part of the flat magnetic pole surface  58 N or  58 S of the respective permanent magnets  58  and the inside surface of the molding die. Therefore, the molding resin  61  fills the gap and also surrounds the outside cylindrical surface  59  between the magnets  58  and both end areas of the rotor core  52  where the permanent magnets  58  are not glued so as to finish molding the permanent magnets  58  into a unit with the core  52 .  
         [0039]    Referring now to FIG. 6, it will be seen that the both circumferential width ends  58   a  and  58   b  of each magnetic piece  58  are not covered with the molding resin  61  but exposed. Only the central area of each flat magnetic pole surface  58 N or  58 S is covered with the molding resin  61 .  
         [0040]    As a result, the rotor  51  can rotatably supported without any mechanical interference with the stator even if no measure is taken to increase the amount of gap for magnetic interaction between the rotor  51  and the inside cylindrical surface of the stator in consideration of the covering layer of the molding resin  61 . Equally as important, since the magnets  58  are only partially covered with the molding resin  61 , the electrical efficiency is only slightly reduced. This is advantageous in terms of the performance of the rotary electric apparatus used as a motor or generator because there is no significant reduction in output torque in the case of a motor or generated output in the case of a generator while increasing the strength of holding the permanent magnets  58 .  
         [0041]    [0041]FIG. 7 is a graphical view showing the back electromotive force measured by rotating the rotor  51  of a motor constructed in accordance with the embodiment of FIGS. 5 and 6. The back electromotive force shows a very smooth sine curve. This confirms that the output torque characteristic will be smooth with cogging or torque pulsation sufficiently reduced.  
         [0042]    While the above embodiment is described about a rotary electric apparatus of the SPM type of the inner rotor constitution as an example in which the rotor  51  is placed inside the stator, the technical concept of this invention can also be applied to the SPM type of the outer rotor constitution in which the rotor is placed outside of the stator. Such an embodiment is shown in FIG. 8 and will now be described in detail by reference to that figure.  
         [0043]    [0043]FIG. 8 is a partial sectional view of the constitution of an embodiment of an outer rotor, SPM type of rotary electric apparatus. A rotor, indicated generally at  71  is formed to as an annular member. Flat plate-like permanent magnets  73  that are substantially the same as the permanent magnets  12  of the previous embodiment are placed in circumferential positions at equal intervals on a cylindrical inside surface  72  of the annular flywheel member  71 .  
         [0044]    The magnets  73  have their radially inner faces  74  facing a stator, indicated generally at  75 . The stator  75  is made by laminating a large number of stator cores of a magnetic material to form equally spaced, radially extending pole teeth  76  each of the pole teeth  76  is wound with a respective coil  77 . The wound coils  77  extend through slots  78  formed between the pole teeth  76 . The rotor  71  and specifically faces  73   b  of the permanent magnets  73  are spaced from the tips of the pole teeth  76  of the stator  75  by a gap  79 .  
         [0045]    Each of the permanent magnets  73  has radially spaced outer and inner flat magnetic pole surfaces  73   a  and  73   b,  respectively. Each outer magnetic pole surface  73   a  is secured in a respective shallow slot  81  formed in the inner cylindrical surface  72  of the flywheel member  71  by suitable means such as by an adhesive.  
         [0046]    The radially inner magnetic pole surface  73   b  of each permanent magnet  73  is covered with a molding resin  82 . The resin  82  is cylindrical in shape with its inner circumferential area tangent to the faces  73   b.  Thus unlike the previous embodiment, a central area between the circumferential end portions  81   c  and  81   d  is exposed while these end portions  81   c  and  81   d  are covered.  
         [0047]    The covering layer of the molding resin  82  is formed by pouring and solidifying the molding resin  82  into a molding die formed along an envelope cylinder centered on the center of the stator  75  extending to cover the both width end portions  81   a  and  81   b  of each of the permanent magnets  73 . The envelope cylinder is defined to be a cylinder tangent to the inside central area of each permanent magnet  73 . Therefore, when the magnetic pieces  73  are covered with the molding resin  82 , the central area is exposed out of the molding resin layer to face directly the stator  75 .  
         [0048]    Since the resin covering layer  82 , like the previous embodiment, covers only a portion of the face  73   b  of each permanent magnet  73 , (the end portions in this embodiment as opposed to the central portion as in the embodiment of FIGS. 5 and 6) mechanical interference of the rotor  71  with the stator  75  as the rotor  71  rotates can be avoided without increasing the gap relative to the stator  75 . As a result, it is possible to firmly secure each permanent magnet  73  for producing a magnetic field for the rotor  71  without impairing the magnetic performance of the associated rotary electric apparatus be it either a motor or a generator.  
         [0049]    In each embodiment already described, the permanent magnets have all been of the same circumferential width and spacing. The invention, however, is not so limited, as will be apparent from the following description of the embodiment of FIG. 9.  
         [0050]    [0050]FIG. 9 shows a rotary electric apparatus as still another embodiment of the invention, constituted as an inner rotor type of DC motor like the DC motor of the conventional inner rotor constitution shown in FIG. 3. The DC motor of this embodiment comprises a rotor, indicated generally at  91  and a stator indicated generally at  92 .  
         [0051]    The rotor  91  is made up of laminated magnetic steel plates having a core portion  93  from which pole teeth  94  radially extend. Coil windings (not shown) encircle the pole teeth  94  and extend into slots  95  formed between the magnetic pole teeth  94 . The rotor  91  is supported for rotation by a rotor shaft (not shown) that is nonrotatably fixed in a center hole  96  of the core portion  93 .  
         [0052]    The stator  92  comprises an annular housing  97 . A plural number of flat plate-like permanent magnets  98  are placed and secured in groups of three, in this embodiment, to an inside cylindrical surface  99  of the annular housing  97 . These groups of magnets  98  are positioned in specified plural (four in the drawing) circumferentially spaced positions.  
         [0053]    The permanent magnets  98  are each magnetized to have radially spaced poles of opposite circumferentially spaced polarity. Preferably each of the groups of three magnets  98  are arranged to be of the same magnetic pole sequence. Of the flat plate-like permanent magnets  98 , as shown, the two that are diametrically opposite each other are positioned to be in the same phase in the circumferential direction with the magnetic pole teeth  94  of the rotor  91 . Other permanent magnets  98  in two adjacent places are displaced in the circumferential direction with the magnetic pole teeth  94  of the rotor  91 , so that attracting and repelling forces are produced between the permanent magnets  98  of the stator  92  and the magnetic pole teeth  94  of the rotor  91  as the coils (not shown) are energized, to cause rotation of the rotor  91 .  
         [0054]    As with the preceding embodiments, the permanent magnets  98  are first affixed to the stator surface  99  by adhesive bonding, as previously described. Here, the flat plate-like permanent magnets  98 , three for each of the four positions, have their radially outer flat faces firmly fixed to the inside cylindrical surface  99  of the housing  97  of the stator  92 . Then a molding resin  101  of thermosetting property such as unsaturated polyesters deposited in the manner previously described in a cylindrical pattern tangent to the magnetic pole face  98   a  that faces the magnetic pole teeth  94  of the rotor  91 . This results, as with the embodiment of FIG. 8 only the width central area of the flat magnetic pole surface  98   a  being exposed. However the circumferential end areas on both sides of the central area are covered as the molding resin  101  solidifies.  
         [0055]    The above construction in which the central area of the magnetic pole surfaces  98   a  is left uncovered with the molding resin  101  makes it possible to eliminate the presence of molding resin layer in the gap through which the flat plate-like permanent magnets  98  face the magnetic pole teeth  94  of the rotor  91 . Therefore, the amount of gap between the rotor  91  and the stator  92  can be maintained as small as possible and the motor output can be prevented from lowering due to the amount of the gap.  
         [0056]    The molding resin  101  also fills spaces, four are shown as present in the circumferential direction, between two adjacent groups of the flat plate-like permanent magnets  98 , with each group made up of three permanent magnets  98 . Therefore, the molding resin portion  101   a  shown with hatching extends in the circumferential direction and solidifies. The molding resin  101  also fills the tiny space present in the circumferential direction between adjacent flat plate-like permanent magnets  98  of each group and solidifies. This contributes together with the molding resin portion  101   a  to firmly securing the permanent magnets  98  and reliably prevents the flat plate-like permanent magnets  98  from separating and coming off while the motor is in operation.  
         [0057]    [0057]FIG. 10 is a sectional view of still another embodiment of the invention, an example of a construction similar to the generator of the outer rotor type described before in reference to FIG. 8, arranged to prevent generated output from decreasing due to increase in the amount of gap between the rotor and stator while fixing the flat plate-like permanent magnets of the invention by means of molding resin.  
         [0058]    As seen in FIG. 10, a rotor, indicated generally at  121 , is comprised of an annular flywheel  122 . A plurality of flat plate-like permanent magnets  123 , made as previously described, are placed in a plurality of positions in slots  124  formed on the inside cylindrical surface of the flywheel  122 , with the flat plate surfaces  123   a  forming poles on one radial side of the permanent magnets  123  facing a like number of magnetic pole teeth  125  of an inner stator, indicated generally at  126 . The opposite poles  123   b  of the magnets  123  are adhesively fixed in the slots  124 , as previously described.  
         [0059]    As with the previous embodiments, the pole teeth  125  are wound with electric coils. In this case, since the number of the flat plate-like permanent magnets  123  is the same as the number of the magnetic pole teeth  125  provided on the stator  126 , as the flat plate-like permanent magnets  123  rotate they will face the next magnetic pole tooth  125  of the stator  126  every time the rotor  121  rotates by an angle of 360 degrees divided by the number of pole teeth  125  and magnets  123 .  
         [0060]    As with the previously described embodiments, the flat plate-like permanent magnets  123  in are magnetized so that polarities of N and S change alternately for one magnet to another in the circumferential direction. In other words, if the surface of one permanent magnet  123  facing the magnetic pole portion  125  of the stator is magnetized to be an N pole radially with respect to the center of the generator and the opposite surface is magnetized to be an S pole, the permanent magnet  123  next in the circumferential direction is magnetized so that the surface facing the magnetic pole portion  125  of the stator is radially an S pole while the opposite surface is an N pole. This arrangement makes it possible to generate electricity from the coils wound around the magnetic pole teeth  125  of the stator as the rotor  121  rotates outside the stator  126 .  
         [0061]    The flat plate-like permanent magnets  123  are firmly fixed to the inside cylindrical surface  52  of the flywheel  122  of the rotor  121  as a thermosetting molding resin  127  such as unsaturated polyester solidifies. The resin  127  covers the both width end areas of the flat plate surface  123   a  and also the gap between adjacent permanent magnets  123 , while leaving the central area of the flat plate surface  123  uncovered In the above arrangement, like the embodiment described before in reference to FIG. 9, the central area of the flat plate surfaces  123  of the permanent magnets  123  facing the magnetic pole portion  125  of the stator  126  are not covered with the molding resin  127  while only the both side areas are covered with the molding resin  127 . Therefore, it is not necessary to increase the amount of gap between the rotor  121  and the stator  126  according to forming the layer of the molding resin  127 . As a result, the permanent magnets  123  are firmly fixed without decrease in the generator output, and the risk of the flat plate-like permanent magnets  123  separating and coming off due to rotating operation of the rotor  121  can be reliably avoided.  
         [0062]    Thus from the foregoing description it should be readily apparent that the described embodiments make it possible to firmly fix the permanent magnets to either the rotor or stator by covering the permanent magnets with the molding resin while leaving a substantial part of the flat magnetic pole surfaces uncovered. This also makes it possible to maintain a small gap between the rotor and stator without increasing the gap by the thickness of a covering layer of the molding resin. As a result, permanent magnet pieces for producing magnetic field can be firmly fixed without sacrificing output torque or generated electromotive force when the invention is applied to the rotary electric apparatus, whether the motor or generator. This leads to the effects of improving the functional reliability and extending the service life of the rotary electric apparatus, and further makes it possible to arrange that the rotor and stator face each other through a small gap while sufficiently preventing the permanent magnet pieces for separating. 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.