Patent Publication Number: US-2012032539-A1

Title: Permanent Magnet Rotating Machine

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese application serial No. 2010-178298, filed on Aug. 9, 2010, the content of which is hereby incorporated by reference into this application. 
     FIELD OF THE INVENTION 
     The present invention relates to a permanent magnet rotating machine and, more particularly, to a permanent magnet rotating machine suitable as a rotating machine having a medium or large capacity such as a wind turbine generator or a generator mounted on a vehicle. 
     BACKGROUND OF THE INVENTION 
     As rotating machines have been compact and highly efficient, permanent magnet rotating machines have been used in various fields in recent years. When permanent magnets are used, however, there is a problem in that not only electrical characteristics but also strength characteristics are restricted. 
     In particular, rotating machines with an output capacity in the several megawatt class, such as generators mounted in railroad vehicles and wind turbine generators, use large quantities of permanent magnets, so restrictions on strength characteristics become prominent. With railroad generators, which are connected directly to engines, vibration and shock caused by the engines and during running are applied to the generators, so high strength characteristics are demanded. With wind turbine generators, the service life of which is assumed to be about 20 years, so long-term durability is demanded. 
     To respond to this situation, conventional technologies for permanent magnet rotating machines that are compact, highly efficient, and highly reliable are disclosed in Patent Documents 1 to 3. 
     DOCUMENT OF PRIOR ART 
     Patent Document 1 
     
         
         Japanese Patent Laid-open No. 2005-86955 
       
    
     Patent Document 2 
     
         
         Japanese Patent Laid-open No. 2006-311730 
       
    
     Patent Document 3 
     
         
         Japanese Patent Laid-open No. 2009-153353 
       
    
     SUMMARY OF THE INVENTION 
     In Patent Document 1 above, to increase efficiency, gaps between the rotator and stator are increased near parts between magnetic poles, in comparison with a region near the center of the magnetic pole to prevent magnetic flux concentration and reduce harmonic components included in magnetomotive force waveforms. 
     When the gap between the rotor and stator is increased near parts between magnetic poles, however, the advantage of the salience structure of the rotating machine may be reduced and reluctance torque may also be reduced. The iron core (bridge on the internal diameter side) between two magnet insertion slots provided for one pole is under high stress due to centrifugal force. Therefore, stress exerted on the bridge may not be reduced just by providing a bridge between magnet insertion slots to divide the magnet insertion slots as described in a second embodiment in Patent Document 1, and thus an effect to reduce peak stress may be small. 
     In Patent Document 2, peak stress is reduced by preventing corners of a magnet embedded in a rotor iron core from being locally brought into contact with the rotor core. 
     Since the distance between an end of each magnet insertion slot on the external diameter side of the rotor and the outer circumference of the rotor is not constant, however, stress may concentrate at the shortest distance and thereby peak stress may be increased. Furthermore, the magnet insertion slot is shaped so that the corners of the magnet are not brought into contact, the cross sectional area of the iron core (bridge on the external diameter side) between the end of the magnet insertion slot on the external diameter side of the rotor and the outer circumference of the rotor is increased, so leakage magnetic fluxes, which cause a shorting between magnetic fluxes through the bridge on the external diameter side, may be increased and thereby the electrical characteristics may be worsened. 
     In Patent Document 3, leakage magnetic fluxes of magnets are reduced by restricting directions in which the magnets are magnetized. 
     When directions in which magnets are magnetized are restricted as in Patent Document 3, however, the magnets are not uniformly magnetized, as in a case in which flat plate magnets are magnetized. To achieve uniform magnetization, a specific mold is needed, resulting in a high cost. It can also be, considered that a magnet cannot be easily inserted into the magnet insertion slot provided in the rotor iron core. An end of each magnet insertion slot on the internal diameter side of the rotor is parallel to the center of the magnetic pole. This shape causes stress concentration on the corners of the magnet insertion slot on the internal diameter side of the rotor, so peak stress may be increased. 
     An object of the present invention is to provide a permanent magnet rotating machine that can reduce peak stress and leakage magnetic fluxes from magnets, can have superior electrical characteristics, and can reduce stress. 
     A permanent magnet rotating machine according to the present invention has a stator, in which armature windings are formed in a plurality of slots formed in a stator iron core, and also has a rotor, in which two magnet insertion slots are formed for each pole in a rotor iron core and one permanent magnet is embedded in each magnet insertion slot with polarity alternating for each pole; a wall at an end of the magnet insertion slot on an external diameter side of the rotor is formed so as to be parallel to the outer circumference of the rotor, and a wall at another end of the magnet insertion slot on an internal diameter side is formed in an arc shape. 
     More specifically, the permanent magnet rotating machine has a stator, in which armature windings are formed in a plurality of slots formed in a stator iron core, and also has a rotor, in which two magnet insertion slots are formed for each pole in an rotor iron core in a V shape when viewed from the outer circumference of the rotor and one permanent magnet is embedded in each magnet insertion slot with polarity alternating for each pole; a wall at an end of the magnet insertion slot on an external diameter side of the rotor is formed with three arcs having different curvatures, one of the three arcs being parallel to the outer circumference of the rotor, and a wall at another end of the magnet insertion slot on an internal diameter side is formed in an arc shape. 
     The structure described above enables the cross sectional area of the iron core of a bridge on the external diameter side to be reduced, so leakage magnetic fluxes of magnets can be reduced. Furthermore, the width of the bridge on the external diameter side becomes constant, so stress can be distributed, preventing stress concentration and reducing peak stress. On a bridge on the internal diameter side, stress is widely distributed over the entire bridge. Therefore, when the wall at the other end of the magnet insertion slot on the internal diameter side is formed in an arc shape, this stress concentration can be prevented and peak stress can be reduced. 
     The permanent magnet rotating machine according to the present invention can reduce leakage fluxes from magnets, peak stress and stress, and can also have superior electrical characteristics. 
     Other objects and features of the present invention will be clarified in the embodiments described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a lateral cross sectional view showing a first embodiment of a permanent magnet rotating machine according to the present invention. (First embodiment) 
         FIG. 2  is a cross sectional view taken along line A-A′ in  FIG. 1 . (First embodiment) 
         FIG. 3  is an enlarged view of one magnet insertion slot in the permanent magnet rotating machine shown in  FIG. 2 . (First embodiment) 
         FIGS. 4A to 4D  show rotor shapes to compare the shape of the magnet insertion slot in the permanent magnet rotating machine according to the present invention with other magnet insertion slots. (First embodiment) 
         FIG. 5  shows a rotor iron core for half of one pole to illustrate an effect of the present invention. (First Embodiment) 
         FIG. 6  is a characteristic graph that represents peak stress when a curvature, near the center of the magnetic pole, on the wall at an end on the external diameter side of the magnet insertion slot in the present invention is smaller than, equal to, and larger than a curvature near an part between magnetic poles. (First Embodiment) 
         FIG. 7  is a characteristic graph that represents peak stress when the width of the magnet insertion slot in the present invention is smaller than, equal to, and larger than the shortest distance between the magnet insertion slot and the inner circumference of the rotor. (First Embodiment) 
         FIG. 8  is a characteristic graph that represents peak stress and current when the shortest distance between the magnet insertion slot in the present invention and the center of the magnetic pole is smaller than, equal to, and larger than the shortest distance between the magnet insertion slot and the center of a quadrature axis. (First embodiment) 
         FIG. 9  is a characteristic graph that represents peak stress exerted to a bridge on the external diameter side and a bridge on the internal diameter side when the width of the magnet insertion slot in the present invention is changed. (First embodiment) 
         FIG. 10  is a characteristic graph that represents peak stress exerted to the bridge on the external diameter side and the bridge on the internal diameter side when the shortest distance between the magnet insertion slot and the inner circumference of the rotor is changed. (First embodiment) 
         FIG. 11  shows a second embodiment of the permanent magnet rotating machine according to the present invention, the figure being equivalent to  FIG. 2 . (Second Embodiment) 
         FIG. 12  is an enlarged view of a magnet insertion slot in the second embodiment. (Second embodiment) 
         FIG. 13  is an enlarged view of a variation of the magnet insertion slot shown in  FIG. 12 . (Second embodiment) 
         FIG. 14  shows a third embodiment of the permanent magnet rotating machine according to the present invention, the figure being equivalent to  FIG. 2 . (Third Embodiment) 
         FIG. 15  shows a fourth embodiment of the permanent magnet rotating machine according to the present invention, the figure being equivalent to  FIG. 2 . (Fourth Embodiment) 
         FIG. 16  is a cross sectional view, in the axial direction, of the permanent magnet rotating machine in the embodiments of the present invention. 
         FIG. 17  is a cross sectional view, in the axial direction, of the permanent magnet rotating machine having a cantilevered structure in the embodiments of the present invention. 
         FIG. 18  shows a fifth embodiment of the permanent magnet rotating machine according to the present invention, the figure being equivalent to  FIG. 2 . (Fifth Embodiment) 
         FIG. 19  shows a sixth embodiment of the permanent magnet rotating machine according to the present invention, the figure being equivalent to  FIG. 2 . (Sixth Embodiment) 
         FIG. 20  is a block diagram showing the structure of a hybrid drive vehicle system in which the permanent magnet rotating machine according to the present invention is used. (Seventh embodiment) 
         FIG. 21  is a block diagram showing the structure of a wind power generating system in which the permanent magnet rotating machine according to the present invention is used. (Eighth embodiment) 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the drawings. In the drawings, like elements are denoted by like reference numerals. 
     First Embodiment 
       FIG. 1  schematically shows the structure of a permanent magnet rotating machine with an output power of 1 to 3 MW that will be mounted in an electrical train as a railroad generator and will operate at a rotational speed of 500 min −1  to 2000 min −1 . 
     As shown in the drawing, a rotor  1 , in which permanent magnets are provided, is attached to a shaft  3 , and a stator  2  is oppositely disposed with a predetermined distance left between the rotor  1  and stator  2 . A coil  4  is embedded in the stator  2 . 
     As shown in  FIG. 2 , the rotor  1  includes a rotor iron core  5 , in which magnet insertion slots  6  are formed so that each two magnet insertion slots  6  with the same pole form a substantially V shape when viewed from the outer circumference of the rotor  1 . Specifically, the two magnet insertion slots  6  formed in one pole are formed in a substantially V shape in which the circumferential distance therebetween becomes larger as the two magnet insertion slots extend toward the outer circumference of the rotor  1 . A flat-plate magnet  7 , which is a permanent magnet, is embedded in each magnet insertion slot  6 . 
       FIG. 3  is an enlarged view of the magnet insertion slot  6 . 
     As shown in  FIG. 3 , both ends  8  of the magnet insertion slot  6 , in which the flat-plate magnet  7  is embedded, are void. In this embodiment, a wall  9  at an end on the external diameter side of the magnet insertion slot  6  is formed with three arcs R 1 , RC; and R 2 , which have different curvatures. The arc RC at the center of the wall  9  is parallel to an outer rotor circumference  10 . A wall  11  at another end on the internal diameter side of the magnet insertion slot  6  is formed in a semicircular shape. 
     Effects in the first embodiment will be described with reference to  FIGS. 4A to 4D  and Tables 1 and 2. 
       FIGS. 4A to 4D  compare rotor shapes. For the rotor in  FIG. 4A , the wall  9  at the end on the external, diameter side of the magnet insertion slot  6  and the wall  11  at the end on the internal diameter side are both semicircular. For the rotor in  FIG. 4B , the wall  9  at the end on the external diameter side of the magnet insertion slot  6  is semicircular, the wall  11  at the end on the internal diameter side is circular, and part of the wall  11  is parallel to the center of the magnetic pole. For the rotor in  FIG. 4C , the wall  9  at the end on the external diameter side of the magnet insertion slot  6  is formed with three arcs having different curvatures, the central arc being parallel to the outer rotor circumference  10 , and the wall  11  at the end on the internal diameter side of the magnet insertion slot  6  is semicircular (this shape is used in this embodiment). For the rotor in  FIG. 4D , the wall  9  at the end on the external diameter side of the magnet insertion slot  6  is formed with three arcs having different curvatures, the central arc being parallel to the outer rotor circumference  10 , the wall  11  at the end on the internal diameter side of the magnet insertion slot  6  is circular, and part of the wall  11  is parallel to the center of the magnetic pole. 
     Table 1 compares peak stress exerted to rotors having the shapes shown in  FIGS. 4A to 4D . The peak stress in Table 1 is represented in pu with the peak stress in  FIG. 4A  taken as 1.0. As is clear from Table 1, the shape in  FIG. 4C , which is used in this embodiment, can reduce the peak stress the most. This is because since the wall  9  at the end on the external diameter side of the magnet insertion slot  6  is formed with the three arcs, denoted R 1 , RC, and R 2 , having different curvatures and the arc RC at the center is parallel to the outer rotor circumference  10 , the width of the bridge on the external diameter side becomes constant and thereby the stress is dispersed, preventing stress concentration and reducing the peak stress. On the bridge on the internal diameter side, stress is widely distributed over the entire bridge. Therefore, when the end on the internal diameter side of the magnet insertion slot  6  is formed in a semicircular arc shape, the concentration of the stress can be prevented and the peak stress can be reduced. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Shape 
                 Peak stress 
               
               
                   
                   
               
             
            
               
                   
                 a 
                 1.00 
               
               
                   
                 b 
                 1.09 
               
               
                   
                 c (this embodiment) 
                 0.85 
               
               
                   
                 d 
                 0.95 
               
               
                   
                   
               
            
           
         
       
     
     Table 2 compares no-load inductive voltage (which is increased when the leakage magnetic flux is small) between shapes in  FIGS. 4A and 4C . The no-load inductive voltage in Table 2 is represented in pu with the no-load inductive voltage in  FIG. 4A  taken, as 1.0. As is clear from Table 2, since, as in this embodiment, the wall  9  at the end on the external diameter side of the magnet insertion slot  6  is formed with the three arcs R 1 , RC, and R 2  having different curvatures, the arc RC at the center being parallel to the outer rotor circumference  10 , and the wall  11  at the end on the internal diameter side of the magnet insertion slot  6  is shaped in a semicircular arc, the no-load inductive voltage is increased, indicating that the leakage magnetic flux is reduced. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Shape 
                 No-load inductive voltage 
               
               
                   
                   
               
             
            
               
                   
                 a 
                 1.00 
               
               
                   
                 c (this embodiment) 
                 1.03 
               
               
                   
                   
               
            
           
         
       
     
     Accordingly, when compared with the structure shown in  FIG. 4A , the structure in this embodiment can reduce leakage fluxes and peak stress; when compared with the structures shown in  FIGS. 4B and 4D , the structure in this embodiment can reduce peak stress. 
     This embodiment can be efficiently used under the conditions described below. 
       FIG. 5  shows a rotor iron core  12  for half of one pole. As shown in  FIG. 5 , the wall  9  at the end on the external diameter side of the magnet insertion slot  6  has a curvature denoted R 1  that is near the center of the magnetic pole and a curvature denoted R 2  near the part between magnetic poles. The width of the magnet insertion slot  6  is denoted W. The shortest distance between the magnet insertion slot  6  and the inner rotor circumference  13  is denoted T. The shortest distance between the magnet insertion slot  6  and the center of the magnetic pole is denoted M. The shortest distance between the magnet insertion slot  6  and the center of the quadrature axis is denoted L. 
     In graphs described below, the peak stress represented in pu takes a value of 1.0 when R 2  is equal to R 1 , W is equal to T, and L is equal to M. 
     First,  FIG. 6  shows peak stress when R 1  is smaller than, equal to, and larger than R 2 . It is found from  FIG. 6  that peak stress when R 2  is smaller than R 1  is higher than when R 1  is equal to R 2 . Accordingly, R 2  is preferably larger than or equal to R 1 . 
     Next,  FIG. 7  shows peak stress when W is smaller than, equal to, and larger than T.  FIG. 7  indicates that peak stress when T is smaller than W is higher than when T is equal to W. This is because when T is small, large stress is exerted to the bridge on the external diameter side. Accordingly, W is preferably smaller than or equal to T. 
     Next,  FIG. 8  shows peak stress and current when M is smaller than, equal to, and larger than L. Current values in the drawing are values measured under the same output condition. As the current value is reduced, copper loss is reduced, improving the efficiency and power factor, so it can be said that the electrical characteristics are superior.  FIG. 8  indicates that stress when L is larger than M is higher than when L is equal to M, but current under this condition is reduced. Since the electrical characteristics are improved by reducing M, there are a few cases in which L is smaller than M. Accordingly, to improve electrical characteristics, L is preferably larger than or equal to M. 
     Therefore, conditions to efficiently use this embodiment is that R 2  is larger than or equal to R 1 , W is smaller than or equal to T, and L is larger than or equal to M. 
     Appropriate values of W and T in  FIG. 5  will be described below. 
       FIG. 9  indicates stress exerted to a bridge  14  on the external diameter side and a bridge  15  on the internal diameter side when the value of W is changed. 
     The stress in  FIG. 9  is represented in pu and takes a value of 1.0 when peak stress on the bridge  14  is equal to peak stress on the bridge  15 . 
     It is found from  FIG. 9  that when W is increased, the stress on the bridge  14  on the external diameter side is reduced and the stress on the bridge  15  on the internal diameter side is increased. Specifically, since the stress on the bridge  14  on the external diameter side can be more dispersed as W becomes larger, the peak stress can be reduced. Since the magnets are enlarged, however, the centrifugal force is increased and the stress on the bridge  15  on the internal diameter side is increased. In this embodiment, the peak stress on the entire rotor can be minimized when W divided by the circumferential length of the rotor for one pole is about 11%. Accordingly, the value of W divided by the circumferential length of the rotor for one pole is preferably in the vicinity of 11%. 
       FIG. 10  indicates stress exerted to the bridge  14  on the external diameter side and to the bridge  15  on the internal diameter side when the value of T is changed. The stress in  FIG. 10  is represented in pu and takes a value of 1.0 when peak stress on the bridge  14  is equal to peak stress on the bridge  15 . 
     It is found from  FIG. 10  that when W is increased, the stress on the bridge  14  on the external diameter side is reduced and the stress on the bridge  15  on the internal diameter side is increased, these stresses become equal when T divided by the radius of the rotor is in the vicinity of 17%, and the stresses remain unchanged when 17% is exceeded. This is because when T is small, deformation is likely to occur due to the centrifugal force, so the stress on the bridge  14  on the external diameter side is increased. Conversely, when T is large, deformation does not easily occur. However, stress easily concentrates on the bridge  15  on the internal diameter side, which is less likely to be deformed, so the stress on the bridge  15  on the internal diameter side is increased. Accordingly, in this embodiment, the peak stress becomes small when T divided by the radius of the rotor is in the vicinity of 17%. 
     Although six poles are shown in the drawing, it will be appreciated that the use of any other number of poles can provide the same effect. The coils in this embodiment are embedded in the stator by distributed winding, but concentrated winding can also provide the same effect. 
     Second Embodiment 
       FIG. 11  shows the rotor of a six-pole permanent magnet rotating machine according to a second embodiment of the present invention. As shown in the drawing, the permanent magnet rotor includes a rotor iron core  16 , in which magnet insertion slots  17  are formed so that two magnet insertion slots  17  form a substantially V shape for each pole when viewed from the outer circumference of the rotor, and a flat-plate magnet  7  is embedded in each magnet insertion slot  17 . 
       FIG. 12  is an enlarged view of the magnet insertion slot  17 . In this embodiment, to form a step, the width W of an end  8  of the magnet insertion slot  17  is smaller than the width Wg of a magnet insertion portion. 
     In this embodiment, a range in which the flat-plate magnet  7  moves in the width direction is narrowed by the step. Accordingly, when the rotor rotates, movement of the flat-plate magnet  7  in the magnet insertion slot  17  can be suppressed, preventing the magnet from being damaged due to vibration and shock. When the flat-plate magnet  7  is inserted into the rotor iron core  16 , movement of the flat-plate magnet  7  in the magnet insertion slot  17  can also be suppressed, improving the productivity of the rotor. 
     Since W is smaller than Wg, however, an angular part C 1  is formed in the magnet insertion slot  17 , in correspondence to an angular part of the flat-plate magnet  7 . Stress exerted to the angular part C 1  is then increased. To solve this problem, an end wall  18  of the magnet insertion slot  17  on the internal diameter side may be formed by combining two arcs having different curvatures Ri 1  and Ri 2 . 
     Then, the stress exerted to the angular part C 1  can be distributed to the part having the curvature Ri 2 , so the stress to the angular part C 1  can be reduced, enabling the peak stress over the entire rotor to be reduced. To efficiently reduce stress, Ri 1  is preferably larger than Ri 2 . 
     Furthermore, a magnet insertion slot  20  may be used, which is hollowed out at a part  19 , as shown in  FIG. 13 , at which the angular part of the flat-plate magnet  7  of the rotor iron core is brought into contact, in such a way that the curvature of the hollowed-out part is larger than the curvature of the angular part of the flat-plate magnet  7 . 
     Since the angular part of the magnet insertion slot  20  has a larger curvature than the angular part of the flat-plate magnet  7 , the angular part of the magnet does not locally touch the rotor iron core and thereby the peak stress can be reduced. 
     The positional relationship between the magnet insertion slots  17  and  20  and the rotor iron core  16  and their sizes are the same as in the first embodiment. Although six poles are shown in the drawing, it will be appreciated that the use of any other number of poles can provide the same effect. 
     Third Embodiment 
     In addition to the structures in the first and second embodiments, permanent magnets  22  disposed in a rotor iron core  21  are divided in the width direction as shown in  FIG. 14 , in this embodiment. This enables the eddy current generated in each permanent magnet  22  to be reduced, and thereby the efficiency can be improved and the temperature in the permanent magnet rotating machine can be reduced. Even if the permanent magnet  22  is divided in the axial direction, the same effect can be obtained. 
     Fourth Embodiment 
     In addition to the structures in the first to third embodiments, as shown in  FIG. 15 , axial ducts  23  for draft cooling, through which cooling air passes in the axial direction of a rotor iron  24 , are provided on the internal diameter side of magnet insertion slots  6 . 
     In this structure, a duct space  27  is formed by duct pieces  26  provided among rotor iron cores  25  formed by laminating thin steel plates and among stator iron cores formed by laminating thin steel plates, as shown in  FIG. 16 , which shows the cross section of the permanent magnet rotating machines in the axial direction in the first to third embodiment. Cooling air from a fan  28  is expelled from the axial duct  23  used for draft cooling to a duct space  29  of the stator through the duct space  27 , and cooling can be carried out efficiently. 
     Even when the axial duct  23  for draft cooling and duct spaces  27  and  29  are provided, the effects described in the first to third embodiment can be expected. 
     Although, in this embodiment, two duct pieces  26  are disposed in each of the axial directions of the permanent magnet rotor and stator, any other number of duct pieces  26  may be disposed. Although the duct pieces  26  are disposed for both the rotor  1  and stator  2 , they may be disposed only for the stator  2 . 
     A permanent magnet rotating machine  31  having a cantilevered structure, in which a single bearing  30  supports the shaft  3  as shown in  FIG. 17 , may be used. 
     When the permanent magnet rotating machine  31  having a cantilevered structure is connected to an engine  32  through a coupling  33 , it is possible to prevent the rotor  1  from being brought into contact with the stator  2  even with the bearing  30  disposed on one side. Furthermore, the number of bearings can be reduced, so the cost and weight of the permanent magnet rotating machine  31  can be reduced. 
     Fifth Embodiment 
     In addition to the structures in the first to fourth embodiments, cooling ventilation paths  34  are provided between the poles of the rotor  1  as shown in  FIG. 18 , the ventilation path  34  extending in the axial direction of the rotor  1  from its outer circumference toward its inner circumference. 
     When the cooling ventilation paths  34  are formed as described above, a cooling area of the rotor  1  is expanded and thereby the temperature of the rotor  1  can be lowered. Cooling air can efficiently flow from the rotor  1  to the stator  2  due to fan action, enabling the temperature in the permanent magnet rotating machine to be leveled. Furthermore, since the harmonic components of fluxes entering the rotor  1  from a part between the poles, eddy currents generated in the magnets can be reduced, efficiency can be increased, and the temperature in the permanent magnet rotating machine can be reduced. 
     Sixth Embodiment 
     In addition to the structures in the first to fifth embodiments, a plurality of (four) shaft arms  35  are provided between the rotor iron core  5  and the shaft  3 , with a predetermined spacing therebetween in the circumferential direction, as shown in  FIG. 19 . 
     When the shaft arms  35  are disposed as described above, the outer diameter of the shaft  3  can be reduced while maintaining the same strength as when the shaft arms  35  are not provided. Therefore, the entire weight of the rotary electrical machine can be reduced. Although four shaft arms  35  are used in this embodiment, any other number of shaft arms  35  may be used. 
     Seventh Embodiment 
       FIG. 20  shows an example in which the permanent magnet rotating machine according to the present invention is applied to a hybrid drive vehicle system. 
     The permanent magnet rotating machine  36  described in the first to sixth embodiments is connected directly to an engine  37  and mounted in a power car vehicle. The permanent magnet rotating machine  36  is also connected to an electrical power system  38  through a power converter  39  to generate electrical power. A battery  41  is connected between the electrical power system  38  and power converter  39  through a battery chopper  40 . 
     The permanent magnet rotating machine according to the present invention  36  has improved electrical characteristics, so it is possible to reduce its weight and increase its efficiency in comparison with conventional rotational electrical machines, enabling the fuel efficiency of the entire vehicle system to be increased. It is also possible to operate the permanent magnet rotating machine  36  by using the engine  37  without mounting the battery chopper  40  and battery  41  and to supply power generated by the operation to the electrical power system  38  for an operation. 
     Eighth Embodiment 
       FIG. 21  shows&#39; an example in which the permanent magnet rotating machine according to the present invention is applied to a wind power generating system. 
     The permanent magnet rotating machine  42  described in the first to sixth embodiments is connected to a windmill  43  through a speed-up gear  44  and mounted in a nacelle  45 . The permanent magnet rotating machine  42  is also connected to an electrical power system  46  through a power converter  47  to generate electrical power. It is also possible to directly interconnect the windmill  43  and permanent magnet rotating machine  42 . 
     The permanent magnet rotating machine  42  has improved electrical characteristics, so it is possible to increase its efficiency in comparison with conventional rotational electrical machines, enabling the efficiency of the power generating system to be increased. Although, in the present invention, wind is used as the power source, a water mill, engine, and turbine can be adequately applied.