Abstract:
A rotary electric machine is composed of an armature core, an armature winding, a rotor core disposed opposite said armature core, a rotary magnetic-flux source for supplying first magnetic flux to the rotor core, a frame for supporting the armature core and the rotor core and a stationary magnetic flux source, fixed to the frame, for supplying second magnetic flux to the rotor core in a direction to supplement the first magnetic flux.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority from the following Japanese Patent Applications: 2002-77774, filed Mar. 20, 2002 and 2002-117775 filed Apr. 19, 2002, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a compact and powerful rotary electric machine to be used for a passenger car, an airplane and an electric power tool. 
     2. Description of the Related Art 
     A typical rotary electric machine to be used for a vehicle is an alternator that has a Lundell type rotary magnetic core. The Lundell type rotary magnetic core is composed of a boss portion, a pair of disk portions disposed at opposite ends of the boss portion and a plurality of claw poles extending from the disk portions in the axial direction of the core to alternately interleave with each other. A cylindrical field coil is wound around the boss portion to supply magnetic flux to parallel magnetic circuits that respectively include the claw poles. Therefore, comparatively large magnetomotive force can be applied to the claw poles, so that the alternator can generate comparatively high power. 
     However, the thickness of the claw poles have to be limited in order to limit the outside diameter of the alternator. This limitation may cause DC magnetic saturation, which limits an amount of effective magnetic flux and output power of the alternator. 
     In order to increase the effective magnetic flux, it has been proposed that a permanent magnet is inserted between adjacent claw poles. However, the space for accommodating the permanent magnets is limited and cooling performance of the alternator may get worse because the permanent magnets close air passages. 
     SUMMARY OF THE INVENTION 
     Therefore, a main object of the invention is to provide a more compact and powerful rotary electric machine. 
     According to a feature of the invention, a rotary electric machine includes an armature core and an armature winding mounted in the armature core, a rotor having a rotor core, a rotary magnetic-flux source fixed to the rotor core, a frame and a stationary magnetic flux source fixed to the frame. The stationary magnetic flux is supplied to the rotor core in a direction to supplement the first magnetic flux. Therefore, effective magnetic flux supplied to the armature core can be increased without increasing the size of the rotor. Because the stationary magnetic source can be disposed in a dead space of the front frame, the frame does not increase the size. The second magnetic flux source may include a yoke for magnetically connecting the armature core and the rotor core and a stationary field coil for providing dc magnetomotive force in a direction opposite the polarity of the rotor core. The rotary or stationary magnetic flux source may be composed of a permanent magnet. In such a case, the other includes a field coil. The field current supplied to the field coil is controlled to change magnetic flux supplied to the armature core. 
     Another object of the invention is to provide an electric rotary machine whose rotor has a reduced moment of inertia in order to rotate as soon as it is started. 
     According to another feature of the invention, a rotary electric machine includes a stator core, a three-phase armature winding and a field coil, an inductor rotor disposed opposite the stator core via a first air gap and a magnetic circuit means for connecting the rotor, the stator core via a second air gap. The inductor rotor is composed of a plurality of magnetically conductive portions and magnetically non-conductive portions that are alternately disposed in the circumferential direction thereof between the first air gap and the second air gap. 
     Because the inductor does not include a cylindrical field coil or claw poles, the moment of inertia thereof is very small as compared to the rotor having a Lundell type pole cores. When the motor-generator is operated as a motor, the inductor can rotates in a very short time after armature current is supplied by the inverter because of the small moment of inertia of the inductor. 
     The inductor rotor may include a plurality of permanent magnets having the same polarity disposed in the circumferential direction thereof at two magnetic pole-pitches. The field coil may be disposed inside the inductor rotor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings: 
     FIG. 1 is a schematic cross-sectional diagram of a main portion of an ac generator for a vehicle according to the first embodiment of the invention; 
     FIG. 2 is a graph showing two magnetic flux waves generated in the ac generator; 
     FIG. 3 is a graph showing a power characteristic of the ac generator; 
     FIG. 4 is a schematic cross-sectional diagram of a main portion of an ac generator for a vehicle according to the second embodiment of the invention; 
     FIG. 5 is a schematic cross-sectional diagram of a main portion of an ac generator for a vehicle according to the second embodiment; 
     FIG. 6 is a schematic cross-sectional diagram of a main portion of an ac generator for a vehicle according to the third embodiment of the invention; 
     FIG. 7 is a schematic cross-sectional diagram of a main portion of an ac generator for a vehicle according to the third embodiment of the invention; 
     FIG. 8 is a cross-sectional side view of an ac generator according to the fourth embodiment of the invention; 
     FIG. 9 is a cross-sectional plan view of the ac generator according to the fourth embodiment; 
     FIG. 10 is a circuit diagram of the ac generator according to the fourth embodiment; 
     FIG. 11 is a cross-sectional side view of a motor generator according to the fifth embodiment of the invention; 
     FIG. 12 is a cross-sectional plan view of a main portion of the motor generator according to the fifth embodiment; 
     FIG. 13 is a circuit diagram of the motor generator according to the fifth embodiment; and 
     FIG. 14 is a cross-sectional side view of an ac generator for a vehicle according to the sixth embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An ac generator for a vehicle according to the first embodiment of the invention will be described with reference to FIGS. 1-3. 
     The ac generator  1  is composed of an armature  2 , a rotor  3 , a cylindrical stationary field coil  4 , a front frame  5 , a rear frame  6 , a front bearing  8 , and a rear bearing  9  etc. 
     The armature  2  is composed of an armature core  21 , a three-phase armature winding  23  that is mounted in a plurality of slots formed in the armature core  21 . The armature winding  23  has output lead wires connected to a three-phase full-wave rectifier unit (not shown), which provides DC output power. 
     The rotor  3  is composed of a cylindrical rotary field coil  31 , a pair of Lundell type magnetic pole cores  32  each of which has six claw poles extending to enclose the rotary field coil  31  and a rotary shaft  33 . Field current is supplied to the rotary field coil  31  via a pair of brushes and a pair of slip rings (which arc not shown but well known). 
     The front frame  5  and the rear frame  6  accommodate the armature  2  and the rotor  3  so that the rotor  3  and the rotary shaft  33  can rotate inside the armature  2  and so that the peripheral surfaces of the claw poles can face the inside surface of the armature core  21  through a first air gap. The front frame  5  is made of soft iron and has a stationary magnetic pole  51  at a portion that faces an axial end of one of the pole cores  32  through a second air gap. Thus, the front frame  5  functions as a magnetic yoke that magnetically connects the armature core  21  and the pole cores  32 . On the other hand, the rear frame  6  is made of aluminum or other non-magnetic material. 
     The stationary field coil  4  is disposed inside the front frame  5  and fixed to a radially outer surface of the stationary magnetic pole  51 . The stationary field coil  4  supplies magnetic flux to the armature  2  through a magnetic circuit in parallel with a magnetic circuit of the rotary field coil  31 . When field current is supplied to the rotary field coil  31 , the pole core  32  on the side of front frame  5  is polarized to be magnetic N-pole, and the pole core  32  on the other side is polarized to be S-pole. Accordingly, alternating magnetic flux A is supplied to the armature core  21  when the rotor rotates. When field current is supplied to the stationary field coil  4 , the stationary pole  51  is polarized to be N-pole. Accordingly, one way magnetic flux B is supplied from the stationary magnetic pole  51  to the armature core  21  as long as the field current is supplied to the stationary field coil  4 . When field current is supplied to both the rotary field coil  31  and the stationary field coils  4 , the armature core  21  is supplied with magnetic flux A and magnetic flux B, as shown in FIG.  2 . In other words, the magnetic flux supplied from the claw poles of the magnetic pole core  32  on the side of the front frame  5  is larger than the magnetic flux from the claw poles on the other side. 
     Therefore, effective magnetic flux supplied to the armature winding  23  is increased by the stationary field coil  4  and the stationary magnetic pole  51 , which can be disposed in a dead space of the front frame. As a result, the output power can be increased by approximately 30%, as shown in FIG. 3, without increasing the size of the generator. 
     In the above embodiment, the stationary field coil  4  can be disposed inside the rear frame instead of the front frame, or another stationary field coil can be added to the rear frame  6 . In this case, the rear frame  6  is preferably made of soft iron. 
     An ac generator  1 A according to the second embodiment of the invention will be described with reference to FIGS. 4-5. 
     The rotary field coil  31  of the ac generator  1  according to the first embodiment is replaced by a disk-shaped permanent magnet  131 . Therefore, the ac generator  1 A is composed of an armature  2 , a rotor  3 A, a first stationary field coil  4 A, a second stationary coil  4 B, a front frame  5 A, a rear frame  5 A, and yokes  71 ,  72 ,  73 ,  74 . 
     The armature  2 , which is the same in structure as the ac generator according to the first embodiment, has an armature core  21  and an armature winding  23 . The rotor  3 A has a pair of magnetic pole cores  132  each of which has six claw poles enclosing the disk-shaped permanent magnet  131  and a rotary shaft  133 . The front frame  5 A and the rear frame  6 A are made of aluminum and accommodate the armature  2  and the rotor  3 A therein in the same manner as the first embodiment. 
     The yoke  71  is an L-shaped member made of soft iron having one side fixed to the inner surface of the front frame  5 A and the other side extending in the axial direction of the frame  5 A. The yoke  72  is fixed to the yoke  71  so as to hold the first stationary field coil  4 A together with the yoke  71 . The yoke  72  is disposed opposite the pole core  132  on the side of the front frame  5 A so as to function as a stationary pole core that is polarized to have the same magnetic pole as this pole core  132 . 
     The yoke  73  is an L-shaped member made of soft iron having one side fixed to the inner surface of the rear frame  5 B and the other side extending in the axial direction. The yoke  74  is fixed to the yoke  73  so as to hold the second stationary field coil  4 B together with the yoke  73 . The yoke  74  is disposed opposite the pole core  132  on the side of the rear frame  6 A so as to function as a stationary pole core that is polarized to have the same magnetic pole as this pole core  132 . 
     A magnetic circuit through which the magnetic flux of the first stationary field coil  4 A flows is formed in parallel with a magnetic circuit through which the magnetic flux of the permanent magnet flows. As shown in FIG. 4, the pole core  132  on the side of the front frame  5 A is polarized by the permanent magnet  131  to be N-pole, and the yoke  72  is polarized to be N-pole when the first stationary field coil  4 A is supplied with field current. On the other hand, the pole core  132  on the side of the rear frame  6 A is polarized by the permanent magnet  131  to be S-pole, and the yoke  74  is polarized to be S-pole when the second stationary field coil  4 B is supplied with field current. Thus, the effective magnetic flux supplied to the armature winding  23  can be increased. 
     When no field current is supplied to the first and second stationary field coils  4 A,  4 B, the flux of the permanent magnet  131  flows through the pole core  132  on the side of the front frame, the yoke  72 , the yoke  71 , the armature core  21 , the yoke  73 , the yoke  74  and the pole core  132  on the side of the rear frame. Therefore, no magnetic flux cross the armature winding. As a result, no power is generated when no current is supplied to the stationary coils although the ac generator has a permanent magnet. 
     On the other hand the output power can be easily controlled by changing the field current supplied to the stationary field coils  4 A,  4 B. In this embodiment, the front and rear frames can be made of soft iron so that the yokes can be integrated therewith. 
     An ac generator  1 B according to the third embodiment of the invention will be described with reference to FIGS. 6 and 7. 
     As shown in FIG. 6, the ac generator for a vehicle is composed of an armature  2 , a rotor  3 B, a front frame  5 B, a rear frame  6 B, a first stationary permanent magnet  81  and a second stationary permanent magnet  82 . The armature  2 , which is basically the same as the armature of the ac generator according to the first embodiment, is composed of an armature core  21  and an armature winding  23 . Tile rotor  3 B has permanent magnets  34  between adjacent claw poles in addition to the components of the rotor  3  of the ac generator according to the first embodiment. The front frame  5 B and the rear frame  6 B are made of soft iron so as to function as a magnetic yoke and accommodate the armature  2  and the rotor  3 B in the same manner as the previously described ac generators. 
     The first stationary permanent magnet  81  is disposed at a portion of the inside wall of the front frame  5 B opposite the front surface of the pole core  32  that is disposed on the front end of the rotor  3 B. The permanent magnet  81  is magnetized so that rear surface of the permanent magnet  81  has the same polarity as the front surface of the said pole core  32 . The second stationary permanent magnet  82  is disposed at a portion of the inside wall of the rear frame  6 B opposite the rear surface of the pole core  32  that is disposed on the rear end of the rotor  3 B. The permanent magnet  82  is magnetized so that front surface of the permanent magnet  82  has the same polarity as the rear surface of the said pole core  32 . 
     Thus, the magnetic flux of the permanent magnets  81 ,  82  can be added to the magnetic flux of the rotary field coil  31  so that the output power of the ac generator can be increased. 
     When no field current is supplied to the rotary field coil  31 , the composite magnetic flux of the permanent magnets  81 ,  82  flows from the permanent magnet  81  through the pole core  32  on the side of the front frame, the pole core  32  on the side of the rear frame, the permanent magnet  82 , the rear frame  6 B and the front frame  5 B to the permanent magnet  81 . In addition, the magnetic flux of the permanent magnet  34  flows through the pole core on the side of the front frame  32 , the pole core on the side of the front frame  32  to the permanent magnet  34 . Therefore, no magnetic flux cross the armature winding. As a result, no power is generated when no current is supplied to the stationary coils although the ac generator has a permanent magnet. 
     In this embodiment, the front and rear frame can be made of non-magnetic material if the portions of the magnetic circuit of the frames are replaced by yokes as shown in FIG.  4 . 
     An ac generator for a vehicle according to the fourth embodiment of the invention will be described hereafter with reference to FIGS. 8-10. 
     The ac generator includes a front frame  5  made of cast iron, a three-phase armature winding  23 , a cylindrical stator core  21  in which the stator winding  23  is mounted, a cylindrical inductor  3 C made of laminated iron sheets disposed inside the stator core  21 , a non-magnetic retainer plate  35 , a rotary shaft  33 , a rear frame  6  made of non-magnetic material, a front bearing  8 , a rear bearing  9 , a cylindrical field coil  4  and a plurality of permanent magnets  34 . The non-magnetic retainer plate  35  is disposed at an end of the inductor  3 C to fix the inductor  3 C and the rotary shaft  33  together. The front frame  5  and the rear frame  6  are coupled together to hold the stator core  21 . The inductor  3 C and the shaft  33  are rotatably supported by the front and rear bearings  8 ,  9 . The front frame  5  has a cylindrical core portion that axially projects into the inside of the inductor  3 C. The cylindrical core portion has an inner bore through which the rotary shaft  33  extends so as to freely rotate. The cylindrical core portion also has an end portion having a smaller outside diameter around which the inductor  3 C is disposed and a base portion having a larger outside diameter around which the field coil  4  is wound. 
     The stator core  21  has six teeth around which the armature winding  23  is wound, as shown in FIG.  9 . The armature winding  23  has three output ends that are connected to a rectifier unit  11  to provide de output power at an output terminal  12 , as shown in FIG. 10. A field-current control unit  13  is connected to the field coil  4 . 
     The inductor  3 C is composed of a outer ring, an inner ring and a plurality of honeycomb shaped slots between the outer and inner rings. Two rings are magnetically connected by a pair of diametrically formed thick spoke members. The outer ring is so thin that no magnetic circuit can be formed thereby. The inner ring forms a portion of a magnetic circuit. The permanent magnets  34  are disposed at two pole-pitches in the circumferential direction of the inductor  3 C. Thus, the inductor  3 C has magnetically conductive portions and magnetically non-conductive portions. 
     The rotary shaft  33  carries a pulley, which is rotated by an engine via a belt. 
     When the rotary shaft  33  is driven by an engine via a pulley, the inductor  3 C is rotated by the shaft  33  via the retainer plate  35 . When field current is supplied to the field coil  4  by the field current control unit  13 , the field coil  4  generates magnetic flux flowing from the field coil  4  through the front frame  5 , the stator core  21 , the inductor  3 C to the cylindrical core portion of the front frame  5 . When the inductor  3 C rotates, magnetic flux flowing through the inductor  3 C changes because of the magnetically conductive portions and the magnetically non-conductive portions of the inductor  3 C. Accordingly, ac voltage is induced in the armature winding  23 . Because the permanent magnets  34  are disposed at two pole pitches and magnetized to have a polarity opposite the direction of the magnetomotive force of the stator core  21 , the amplitude of change in the magnetic flux that crosses the armature winding is increased by the permanent magnets. The ac voltage is converted into de voltage by the rectifier unit  11 . 
     Thus, the outside diameter of the inductor  3 C can be made very small as compared by a rotor having a Lundell type pole cores because the inductor  3 C does not include a cylindrical field coil or claw poles. Because the inductor  3 C is made of laminated iron sheets that have hollow slots, the moment of inertia thereof is very small as compared to the rotor having a Lundell type pole cores. 
     For example, the moment of inertia is compared between a rotor that has a Lundell type pole cores of an ac generator whose rated power is 100 A and an inductor of an ac generator according to the invention whose rated power is approximately the same. The rotor, which has a Lundell type pole cores, has about 28 kg-cm 2 , while the inductor has about 7 kg-m 2 . Thus, the moment of inertia of the inductor  3 C is about one fourth of that of the rotor having a Lundell type pole cores. 
     A motor generator according to the fifth embodiment of the invention is described with reference to FIGS. 11-13. 
     The motor generator includes a cylindrical stator core  21  in which a stator winding  23  is mounted, a cylindrical inductor  3 C made of laminated iron sheets disposed inside the stator core  21 , a non-magnetic retainer plate  35 , a cylindrical field coil  4  and a plurality of permanent magnets  34 , a frame  5 , a yoke  71  and a rotary shaft  33 . The non-magnetic retainer plate  35  is disposed at an end of the inductor  3 C to fix the inductor  3 C and the rotary shaft  24  together. The frame  5  and the yoke  22  hold the stator core  21 . The stator core  21  has a plurality of teeth around which the armature winding  23  is wound. The armature winding  23  has three output ends that are connected to an inverter unit  17 . The armature winding  23  and the field coil  4  are connected in series so that starting torque can be increased. A field-current control unit  13  is connected to the field coil  4 . 
     The inductor  3 C is composed of an outer ring, an inner ring and a plurality of rectangular slots between the outer and inner rings. Two rings are magnetically connected by a plurality of spoke members  36 . The outer ring is so thin that no magnetic circuit can be formed thereby. The inner ring has a thickness of about ⅙ of the distance between the outer ring and the inner ring and forms a portion of a magnetic circuit. The permanent magnets  34  are disposed at two pole-pitches in the circumferential direction of the inductor  3 C. Thus, the inductor  3 C has magnetically conductive portions and magnetically non-conductive portions. The rotary shaft  24  is connected to an engine  20  directly. 
     When the rotary shaft  24  is driven by an engine, the inductor  3 C is rotated by the shaft  24  via the retainer plate  35 . When field current is supplied to the field coil  4  by the field current control unit  13 , the field coil  4  generates magnetic flux flowing from the field coil  4  through the yoke  22 , the stator core  21 , the inductor  3 C to the field coil  4 . When the inductor  3 C rotates, magnetic flux flowing through the inductor  3 C changes because of the magnetically conductive portions and the magnetically non-conductive portions of the inductor  3 C. Accordingly, ac voltage is induced in the armature winding  23 . Because the permanent magnets  34  are disposed at two pole pitches and magnetized to have a polarity opposite the direction of the magnetomotive force of the stator core  21 , the amplitude of change in the magnetic flux that crosses the armature winding is increased by the permanent magnets  34 . The ac voltage is converted into dc voltage by the inverter unit  17 . Because the inductor  3 C does not include a cylindrical field coil or claw poles, the moment of inertia thereof is very small as compared to the rotor having a Lundell type pole cores. When the motor-generator is operated as a motor, the inductor can rotates in a very short time when armature current is supplied by the inverter  17  because of the small moment of inertia of the inductor  3 C and series connection of the armature winding  23  and the field coil  4 . 
     An ac generator for a vehicle according to the sixth embodiment of the invention will be described hereafter with reference to FIG.  14 . 
     The ac generator includes a cylindrical front field coil  4   a , a cylindrical rear field coil  4   b , a front frame  5  made of magnetic material, a rear frame  6  made of magnetic material, a front bearing  8 , a rear bearing  9 , a cylindrical stator core  21  in which a stator winding  23  is mounted, a cylindrical inductor  3 C made of laminated iron sheets disposed inside the stator core  21 , a non-magnetic retainer plate  35 , a rotary shaft  33 , and a plurality of permanent magnets  34  circumferentially disposed inside the inductor  3 C. The non-magnetic retainer plate  35  is disposed at the axial middle of the inductor  3 C to fix the inductor  3 C and the rotary shaft  33  together. The front frame  5  and the rear frame  6  jointly hold the stator core  21 . The inductor  3 C and the shaft  33  are rotatably supported by the front and rear bearings  8 ,  9 . The front frame  5  and the rear frame  6  respectively have a cylindrical core portion that axially projects into the inside of the inductor  3 C. Each of the cylindrical core portions has an inner bore through which the rotary shaft  33  extends so as to freely rotate and an end portion having a smaller outside diameter and a base portion having a larger outside diameter. The inductor  3 C is disposed around the end portions of the front and rear frames  1 ,  7 , and the retainer plate  35  is disposed between the two end portions. The field coil  4   a  or  10   b  are respectively disposed around the base portions. 
     Other portions are substantially the same as those of the ac generator according to the fourth embodiment. 
     Thus, the outside diameter of the inductor  3 C can be made very small as compared by a rotor having a Lundell type pole cores, so that the moment of inertia thereof can be made very small. 
     In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.