Abstract:
A three-phase magneto generator that provides a greater and more uniform output for a given driving force and at a lower temperature to provide a more compact generator. This is accomplished by having no more than two armature teeth are in registry with a single magnetic segment during the relative rotation.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a three-phase magneto generator and more particularly to such a device that provides a greater and more uniform output for a given driving force and at a lower temperature to provide a more compact generator. 
     Conventional magneto generators have a rotor carrying permanent magnets that is driven by a prime mover such as an internal combustion engine to induce voltages in stator coils as the rotating magnetic fields pass the stator coils. The number of magnetic poles of the permanent magnets disposed in the rotating (circumferential) direction of the rotor is 2n where “n” is a positive integer. This is because the same number of N-poles and S-poles must be located at equal intervals in the circumferential direction. In the case of a three-phase generator, the number of teeth or armature cores P of the stator core is 3m with “m” being a positive integer. 
     Conventionally, n=m. That is, when the number of magnetic poles M of the rotor is arranged as 2n, the number of teeth P of the stator core is set to 3m=3n. For example, when n=6, the number of magnetic poles M is set to 12, the number of teeth or armature cores P is 18. When n=8, those numbers are defined as M=16, and P=24. 
     This conventional relationship is shown in FIGS. 1 and 2 that show respectively, a partial cross sectioned front view a diametrical cross section a magneto generator, with n=m =6, or M=12 and P=18. A rotor, shown generally at  21 , comprises a boss portion  22  is driven for example by being secured to a crankshaft (not shown) of an internal combustion engine or other suitable prime mover. The rotor  21  further comprises a generally cup-shaped cup portion  23  secured to a flange of the boss portion  22 . A plurality of annular permanent magnets  24  are suitably secured to the inside circumferential surface of the cup portion  23 . The permanent magnets  24  are magnetized to have 2n poles of opposite polarities in the circumferential direction. This conventional example is arranged as n=6, and so number of magnetic poles M is 2n=12. 
     A stator  25  cooperates with the rotor  21 . The stator  25  is comprised of a stator core formed by laminating thin steel plates having teeth or armatures  26  on which coils  27  are wound. The number of teeth  26  of the stator  25  is 18. In this case, m=6 because 3×m=18. The coils  27  have U-, V-, and W-phases. The coil of each phase is wound on every three teeth  26  in succession. In this case, the every three teeth or armature on which the coils  27  of the same phase are wound oppose the same polarity of the magnet  24  at the same electrical angle. In order to arrange that the teeth of the same phase oppose the same polarity of the magnet  24  at the same electrical angle as described, it is necessary that either n=m or at least n is an integer multiple of m. 
     With the conventional generator as described above, since electricity is generated in the state of that the m (six) teeth  26  wound on the coils  27  having same place are opposed to the m (six) permanent magnets in the same phase, harmonics induced at the respective m (six) teeth are superimposed in the same phase, and distortion in the output waveform is intensified. This distortion is graphically illustrated in FIG.  3 . The three phase wiring diagram for the machine and voltage outputs V 1  and V 2  are shown in FIG.  4 . 
     Because of this distortion the torque required for driving the rotor  21  increases for a given output to be produced. This problem has been exacerbated in recent years because the performance of permanent magnets has been significantly improved. For example, the neodymium-iron-boron magnet having a high maximum magnetic energy product has come to be known. When such a high performance magnet is used, variation in the driving torque for the rotor also increases. 
     With the increase in the driving torque, when the rotor is driven with an internal combustion engine, cyclic variation in the load on the engine also increases. This in particular necessitates increase the of the driving power or output of the engine. This is shown in the broken line curves of FIG.  5 . In the case the generator is driven with the engine, this means that the size of the engine increases. Moreover, since the coils of respective phases are connected in series at the same electrical angle, generated voltage is increased, but the output voltage waveform is not smooth and includes many harmonics, resulting in a low generation efficiency as also shown in this figure. 
     This further results in problems of self-heat generation of the generator as seen in the broken line curve of FIG.  6 . Thus the amount of generated electricity cannot be increased without increasing the size of the generator. 
     Moreover, the output voltage waveforms in respective phases are heavily disturbed and include many sharp spike-shaped waveforms with high peak voltages as seen in FIG.  3 . This has necessitated a capacitor for smoothing the output voltage which, in turn, has resulted in the use of a large size and high cost capacitor. Such problems become particularly acute when the neodymium-iron-boron magnet is used. 
     It is therefore an object of this invention to provide a three-phase magnetic generator that makes it possible to reduce the size and power of the driving prime mover by reducing the driving torque while at the same time improving the generation efficiency by smoothing the output voltage waveform. 
     It is a further object of the invention to reduce the size of coils or to produce a high output by making the coils compact by reducing the amount of self-generated electricity and also to reduce the size and cost of the smoothing capacitor by reducing the peak voltage or totally eliminating the need for such capacitors. 
     SUMMARY OF THE INVENTION 
     This invention is adapted to be embodied in a generator that is comprised of relatively rotatably first and second components. The first component has affixed to it in circumferentially spaced array, a plurality of segmented cylindrical, permanent magnets. The second member has a plurality of armature teeth around which coils are wound so that an electrical current will be induced in the coil windings upon relative rotation between the two members. The configuration is such that no more than two armature teeth are in registry with a single magnetic segment during the relative rotation. 
     In accordance with another feature of the invention, the configuration is such that the voltages induced at the armature teeth is the same phase voltage and of the same phase around the circumference of the machine. 
     In accordance with a still further feature of the invention, this is achieved by having the number of magnetic poles being equal to 2n and the number of armature teeth is equal to 3m where n and m are positive integers and that 2n divided by m is not an integer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a conventional generator arrangement. 
     FIG. 2 is a diametric cross sectional view of the conventional generator shown in FIG.  1 . 
     FIG. 3 shows phase voltage waveform of the conventional generator. and one constructed in accordance with a first embodiment of the invention. 
     FIG. 4 is a schematic circuit diagram showing the voltage value measurement points used in FIG.  3 . 
     FIG. 5 is a graphical view comparing efficiency, driving power and electrical output verses speed in a prior art machine, in broken lines, and for a machine practicing the invention, shows output waveform distortion. 
     FIG. 6 is a graphical view showing thermal characteristics in a prior art machine, in broken lines, and for a machine practicing the invention, in solid lines. phase voltage waveform. 
     FIG. 7 is a diametric cross sectional view, in part similar to FIG. 1, and shows a generator constructed in accordance with a first embodiment in driving relation to an internal combustion engine shown in part. 
     FIG. 8 is a front view of the embodiment shown in FIG.  7 . 
     FIG. 9 is a graphical view in part similar to FIG. 3 but shows the phase voltage waveform of the embodiment of FIGS. 7 and 8. 
     FIG. 10 is a front view, in part similar to FIG.  8  and shows a second embodiment of the invention. 
     FIG. 11 is a graphical view showing the phase voltage waveform of a conventional arrangement. 
     FIG. 12 is a graphical view showing the phase voltage waveform of a generator constructed in accordance with the invention. 
     FIG. 13 is a graphical view showing the inter-phase voltage waveform of a conventional arrangement. 
     FIG. 14 is a graphical view showing the inter-phase voltage waveform of a generator constructed in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to the embodiment of FIGS. 7 and 8, the output shaft of a prime mover such as an internal combustion engine  31 , namely a crankshaft  32  is supported with a right-left split crankcase  33 . A bearing  34 , together with another bearing (not shown), supports the crankshaft  32  for rotation within the crankcase  33 . The crankshaft  32  is formed by joining paired right and left crank webs  35  and  36  together by a crank pin  37 . The big end of a connecting rod  38  is supported through a needle bearing  39  on the crank pin  37 . The small end of the connecting rod  38  is pivotally connected to a piston (not shown) for reciprocation within a cylinder  41  of the engine  31 . 
     Part of the crankshaft  32  projects through a wall of the crankcase  33  to drive a three-phase magnetic generator  42  is mounted thereon and constructed in accordance with this first embodiment. The generator  42  comprises a stator  25  (using the same reference numerals as applied to the prior art construction previously described). This is done because the components are the same except for their size and number. The stator  25  is secured by bolts  43  to a stator holder  44  fixed to a front wall of the crankcase  33 . That is, four bolts  43  are inserted into four bolt holes  45  (FIG. 8) bored in a stator core. 
     The boss portion  22  of the rotor  21  is fit over a tapered surface of the crankshaft  32  and held against rotation by a key  46 . A nut  47  is threaded onto a threaded end  48  of the crankshaft  32 . A fan  49  is secured to the rotor  21  and covered with a cowling  51 . The fan  49  sends cooling air around the cylinder  41  for forced air cooling of the engine  31 . 
     In this embodiment, 8 permanent magnets  24  of neodymium-iron-boron having 16 (=2n) poles are used. The stator core has 15 (3m=15) teeth or armatures  26  and associated windings  27 . Therefore, n=8, and m=5. In this case, the angle between magnets  24  or the pitch angle θ 1  is 2π/2n (radian)=22.5°. The angle between teeth  25  or the pitch angle θ 2  is 2π/3m (radian)=24°. Coils or windings  27  of the same phase are wound on successive m (=5) teeth  26 . Here, since adjacent teeth  26  are located opposite the magnets  24  of alternately different polarities, the five coils  27  are wound alternately in opposite directions, so that the polarities of voltages induced in respective coils  27  are the same each other. No more than two teeth or armatures  26  are ever associated with any one of the magnets  24 . 
     Progressing circumferentially along five teeth  26 , the fifth tooth  26  is displaced from the respective magnet  24  by a phase of Δθx (m−1)=Δθ×4=6°. In order that the angle 6° remains within the range of the magnet  24 , it is arranged that the displacement angle is smaller than a half of the pitch angle θ 1  of the magnet  24 , Δθ×4&lt;θ 1 /2. As a result, the voltage induced in the coil  27  can be increased sufficiently. Thus the smooth output waveform output shown in FIG. 9 also results. 
     FIG. 10 is a front view of another embodiment of the generator. In this figure, parts that are the same as those in the embodiment of FIGS. 7 and 8 are provided with the same reference numerals and their descriptions will not be repeated. 
     This embodiment employs a neodymium-iron-boron magnet  24  with 16 (=2n) poles, and 18 (=3m) teeth or armatures  26 . Therefore, n=8 and m=6. In this case, the angle between magnets  24  for the pitch angle θ 1  is 2π/2n (radian)=22.5°. The angle between teeth or the pitch angle θ 2  is 2π/3m (radian)=20°. Since the number of teeth  26  is the multiple of two, the coils  27  of the same phase (U-phase in FIG. 10) are divided into two sets. That is, each set consists of three (=m/2) coils  27  wound on successive three teeth  26  and located symmetrically with respect to the center. 
     Here, since adjacent teeth  26  face the magnets  24  of different polarities, the coils  27  are wound alternately in opposite directions, so that the voltages induced in respective coils  27  do not have opposite directions from one to another. In this embodiment, the displacement angle of three (=m/2) teeth  26  relative to three magnets  24 , or the phase difference ⊖ is Δθx (m/2−1)=Δθ·2. Therefore ⊖=Δθ·2&lt;θ 1 /2. 
     As has been noted, FIGS. 9 and 3 show respectively the distortion of the output voltage waveform obtained with an embodiment of the invention in comparison with that obtained with a conventional arrangement. Here, the embodiment of the invention is the one shown in FIGS. 7 and 8 with 16 poles and 15 teeth, and the conventional arrangement is the one shown in FIGS. 1 and 2 with 12 poles and 18 teeth. FIG. 9 shows phase voltage V 1  and inter-phase voltage V 2  obtained according to the invention, and FIG. 3 shows phase voltage V 1  and inter-phase voltage V 2  obtained according to the conventional arrangement. As seen from FIG. 3, the output voltage waveforms V 1  and V 2  of the conventional arrangement include not only large distortion but also many sharp spike-shaped waveforms and many harmonic components. On the other hand, as seen from FIG. 9, the output voltage waveforms V 1  and V 2  of the invention are smooth and include less distortion and harmonic components. 
     FIGS. 11 and 12 show the phase voltage waveforms obtained by computer simulation analysis. FIG. 12 shows the result obtained with an embodiment of the invention (with 16 poles and 18 teeth) similar to that shown in FIG.  10 . FIG. 11 shows the result obtained with a conventional arrangement (with 12 poles and 18 teeth). From these figures, it should be apparent that this invention can reduce distortion in the resultant waveform by reducing the amplitudes of the basic (primary) wave, third order wave, and fifth order wave. 
     FIGS. 13 and 14 show the inter-phase voltage waveforms obtained by computer simulation analysis. FIG. 13 shows the result obtained from the phase voltage shown in FIG.  11 . FIG. 14 shows the result obtained from the phase voltage shown in FIG.  12 . 
     FIG. 5 shows comparison between an embodiment of the invention (with 16 poles and 18 teeth, indicated as New in the figure) and a conventional arrangement (with 12 poles and 18 teeth, indicated as Conventional in the figure) for driving power, electric output, and efficiency. As seen from the figure, the driving power decreases and the efficiency improves about 10% over the entire range of revolution. 
     FIG. 6 shows thermal characteristics. In the figure, differential temperature ΔT (° C.) between the stator coil and the stator holder  44  for securing the stator is plotted against the revolution (rpm). As seen from the figure, this invention reduces the coil temperature, by a large margin in comparison with the conventional arrangement, about 40% over the entire revolution range. As a result, room is provided to reduce the size of the stator and rotor by making the stator coil more compact, or from the viewpoint of the generator size, it is possible to provide more power with the same size of the generator. 
     It should be understood that the foregoing describes only preferred embodiments of the invention and that various changes are possible without varying from the spirit and scope of the invention as set forth in the appended claims. For example, while the above described embodiments use a neodymium-ron-boron magnet for the permanent magnet  24 , this invention also includes arrangement using other permanent magnets such as those using rare-earth and ferrite. Moreover, while the above embodiments are of the outer rotor type with the rotor rotating outside the stator, the invention also includes a inner rotor type in which a rotor rotates radially inside an annular stator.