Abstract:
An inner rotor ( 5 ) provided with a plurality of magnetic poles is disposed on an inner side of a ring-shaped stator ( 3 ) of a motor/generator ( 1 ). The outer rotor ( 7 ) provided with a number of magnetic poles is disposed on an outer side of the stator ( 3 ). The number of magnetic poles of the outer rotor ( 7 ) differs from the number of magnetic poles of the inner rotor ( 5 ). The stator ( 3 ) is provided with coils ( 16 ) simultaneously generating a magnetic field synchronized with the rotation of the inner rotor ( 5 ) and a magnetic field synchronized with the rotation of the outer rotor ( 7 ). The stator ( 3 ) is provided with a plurality of cores ( 3 A) partitioned on a circumferential periphery and composed of a magnetic material to allow coils ( 16 ) to be wound thereon. Connectors ( 19 ) are provided connecting a part of one core ( 3 A) to a part of an adjacent core ( 3 A). One magnetic resistance is created on an inner peripheral section of cores ( 3 A) located between the inner rotor ( 5 ) and the coils ( 16 ) and a second magnetic resistance is created on an outer peripheral section of the cores ( 3 A) located between the outer rotor ( 7 ) and the coils ( 16 ). The ratio of these magnetic resistances may arbitrary be set by the arrangement of connectors ( 19 ).

Description:
FIELD OF THE INVENTION 
     This invention relates to a motor/generator which has two rotors and a single stator. 
     BACKGROUND OF THE INVENTION 
     Tokkai-Hei-11-275856 published by the Japanese Patent Office in 1999 discloses a synchronous motor/generator having two rotors and a single stator. Tokkai-Hei-11-275856 is a pre-examination publication of the Japanese patent application Tokugan-Hei-10-77449, the base of U.S. Pat. No. 6,049,152 that was issued after the priority date of this patent application. 
     A synchronous motor/generator disposes respective rotors superimposed co-axially in a radial direction on the outer and inner sides of a stator. Although the number of magnetic poles of the two rotors differs, the stator generates rotating magnetic fields by using one type of coil. The rotating magnetic fields consist of a rotating magnetic field which synchronizes the rotation of the inner rotor and a rotating magnetic field which synchronizes the rotation of the outer rotor. The inner and outer rotors are independently driven by applying a composite current to the single type of coil. The composite current comprises an alternating current generating the rotating magnetic field for the inner rotor and the alternating current generating the rotating magnetic field for the outer rotor. The stator comprises plate members laminated in an axial direction and is provided with a plurality of cores extending in a radial direction to allow wire to be wound thereon. When the motor/generator is assembled, the plate members are laminated and wire is wound onto each core. 
     SUMMARY OF THE INVENTION 
     In this motor/generator, leakage of magnetic flux which drives the inner rotor is defined by the magnetic resistance (hereafter termed “inner magnetic resistance”) between inner peripheral sections of cores situated between the inner rotor and the coil. 
     The leakage of magnetic flux which drives the outer rotor is defined by the magnetic resistance (hereafter termed “outer magnetic resistance”) between outer peripheral sections of cores situated between the outer rotor and the coil. 
     Characteristics of the motion of the motor/generator vary on the basis of the ratio of the inner magnetic resistance and the outer magnetic resistance (hereafter termed “magnetic resistance ratio”). For example, a power density, the power ratio of the inner rotor and the outer rotor or the ratio of the power source load factors of the inner rotor and the outer rotor varies on the basis of the magnetic resistance ratio. As a result, a desired magnetic resistance ratio differs depending on the required characteristics of the motor/generator. 
     However, in order to alter the magnetic resistance ratio, the design of the stator must be modified, so altering the magnetic resistance ratio during the manufacturing process of the motor/generator is difficult. 
     It is therefore an object of this invention to enable the magnetic resistance ratio of the stator to be set in an arbitrary manner during the manufacturing process of the motor/generator. 
     In order to achieve the above object, this invention provides a motor/generator comprising an inner rotor having a plurality of magnetic poles, an outer rotor having a plurality of magnetic poles which differs from the number of magnetic poles of the inner rotor, and a ring-shaped stator disposed between the inner rotor and the outer rotor. The stator is provided with a plurality of coils which simultaneously generate a magnetic field synchronized with the rotation of the inner rotor and a magnetic field synchronized with the rotation of the outer rotor. The stator is also provided with a plurality of cores on which the coils are wound. The cores are arranged in a circumferential direction and composed of a magnetic material. The cores have a connector magnetically connecting a part of a single core to a part of an adjacent core so as to set a magnetic resistance in a circumferential direction of an inner peripheral section of the cores located between the inner rotor and the coils and a magnetic resistance in a circumferential direction of an outer peripheral section of the cores located between the outer rotor and the coils. 
     The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a motor/generator according to this invention. 
     FIG. 2 is a partial cross sectional view of a stator according to this invention. 
     FIGS. 3A and 3B is a front view of a first plate unit and a second plate unit constituting the stator of the motor/generator. 
     FIG. 4 is a diagram showing a relation between the magnetic resistance ratio and various characteristics of the motor/generator. 
     FIG. 5 is a front view of the second plate unit according to a second embodiment of this invention. 
     FIG. 6 is a front view of a plate unit according to a third embodiment of this invention. 
     FIG. 7 is a front view of a plate unit according to a third embodiment of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 of the drawings, a motor/generator  1  according to this invention is provided with a stator  3 , an inner rotor  5  facing an inner periphery of the stator  3  and an outer rotor  7  facing an outer periphery of the stator  3 . 
     The inner rotor  5  is provided with a rotation shaft  6  and the outer rotor  7  is provided with a rotation shaft  8  which is positioned co-axially with the rotation shaft  6 . 
     The inner rotor  5 , the outer rotor  7  and the stator  3  are disposed co-axially and superimposed in a radial direction. The inner rotor  5  and the outer rotor  7  are supported to rotate freely on a case  4  by respective rotation shafts  6  and  8  and the stator  3  is fixed to the case  4 . 
     The inner rotor  5  is formed by a permanent magnet, half the circumference of which forms an S pole and the other half of the circumference of which forms an N pole. The outer rotor  7  is formed by a permanent magnet having twice the number of magnetic poles as the inner rotor  5 . That is to say, the S poles and N poles alternate every 90 degrees. 
     With the above ratio of magnetic poles, the magnet of the inner rotor  5  does not apply a magnetic force on the outer rotor  7  in a direction of rotation and the magnet of the outer rotor  7  does not apply a magnetic force on the inner rotor  5  in a direction of rotation. 
     Referring now to FIG. 2, the stator  3  comprises a plurality of cores  3 A and coils  16  wound onto the cores  3 A. 
     The cores  3 A comprises tooth members  11  as shown in FIG.  3 A and tooth members  11 A as shown in FIG. 3B which are laminated with a fixed layer ratio in the direction along the rotation shaft  6 . The tooth members  11  and  11 A are formed from ferro-silicon plate of a 0.5 mm thickness which creates an insulating layer on their surfaces. 
     Referring to FIG. 3A, the tooth member  11  is disposed radially with a fixed interval  13  being maintained between the outer peripheral end of adjacent tooth members  11 . Referring to FIG. 3B, the tooth member  11 A is disposed radially in the same manner with a fixed gap  13  being maintained between the outer peripheral end of adjacent tooth members  11 A. 
     Notches are pre-formed on the tooth member  11  to create a bolt hole  17  and a slot  15 . The coil  16  wound onto the core  3 A is accommodated in this slot  15 . Notches are formed in the same manner on the tooth member  11 A. 
     The tooth members  11  and  11 A differ in the following respects. 
     As shown in FIG. 3B, the inner peripheral section of the tooth member  11 A which is positioned between the slot  15  and the inner rotor  5  makes contact with the inner peripheral section of an adjacent tooth member  11 A at a part  19 . Thus the magnetic resistance of the inner peripheral sections of adjacent tooth members  11 A is equal to zero. 
     In the following description, this contacting part is named as a connector  19 . In contrast, the inner peripheral section forms a gap with respect to the adjacent tooth member  11  as shown in FIG.  3 A. Thus the connector  19  is not disposed between the inner peripheral sections of adjacent tooth members  11  and the magnetic resistance of the inner peripheral sections of the tooth member  11  is much larger than that of the inner peripheral sections of the tooth members  11 A. 
     The tooth members  11  and  11 A are assembled in the following manner. 
     As shown in FIG. 3A, the first plate unit  10 A has twenty four tooth members  11  aligned in a ring shape on the same flat surface. As shown in FIG. 3B, the second plate unit  10 B has twenty four tooth members  11 A aligned in a ring shape on the same flat surface. 
     Each core  3 A is a lamination of the tooth members  11 ,  11 A positioned at the same rotational angle as a result of laminating first plate units  10 A and second plate units  10 B at a fixed layer ratio and securing with each other by bolts inserted into the bolt holes. 
     The bolts inserted into the bolt holes  17  are formed of a non-magnetic material such as stainless steel or the like. 
     Connectors  19  are scattered in the direction along the rotation shaft  6  in the cores  3 A at the locations of the second plate units  10 B. 
     In the following description, the inner magnetic resistance of the adjacent cores  3 A is designated as Rin, while the outer magnetic resistance thereof is designated as Rout. The inner magnetic resistance is a resistance between the inner peripheral sections of the cores  3 A. The outer magnetic resistance is a resistance between the outer peripheral sections of the cores  3 A. 
     The inner peripheral sections of the cores  3 A form a leakage magnetic circuit for the driving magnetic flux of the inner rotor  5 . The leakage of driving magnetic flux for the inner rotor  5  decreases as the inner magnetic resistance Rin increases. 
     The outer peripheral sections of the cores  3 A form a leakage magnetic circuit for the driving magnetic flux of the outer rotor  7 . The leakage of driving magnetic flux for the outer rotor  7  decreases as the outer magnetic resistance Rout increases. 
     The relationship of the leakage of magnetic flux of the inner magnetic resistance Rin and outer magnetic resistance Rout is relative. For example, when the inner magnetic resistance Rin is small, the leakage of driving magnetic flux passing through the inner peripheral sections of cores  3 A increases while the leakage of driving magnetic flux passing through the outer peripheral sections of cores  3 A decreases. 
     The connectors  19  are provided on sections facing the inner rotor  5  which has fewer magnetic poles than the outer rotor  7 , for the following reason. 
     The number of boundaries of N pole and S pole fields increases as the number of rotating magnetic poles increases and thus the possibilities for leakage of magnetic flux in the stator increases. Thus the magnetic resistance between the tooth members must be greatly increased as the number of rotating poles increases or, in other words, as the number of magnetic poles of the rotors increases. 
     The inner rotor  5  has two magnetic poles and the outer rotor  7  has four magnetic poles. Thus it is preferred that the outer magnetic resistance Rout should be greater than the inner magnetic resistance Rin. 
     The connectors  19  are provided on the inner peripheral sections of the core  3 A in order to realize the above relationship. 
     By selectively applying the layer number ratio of first plate units  10 A and second plate units  10 B in an assembling process of the cores  3 A, the ratio Rin/Rout of the inner magnetic resistance Rin and the outer magnetic resistance Rout of cores  3 A can be set in an arbitrary manner. 
     After the cores  3 A are assembled, the coils  16  are formed by winding wire onto each core  3 A. It is possible to cool the stator  3  by passing a cooling medium such as hydrogen gas, air or the like through the gap  13 . 
     Returning now to FIG. 1, an electric current is supplied from the inverter  23  to the coils  16  of the stator  3 . The inverter  23  comprises a fixed number of transistors and an equal number of diodes. A pulse width modulation signal is output from a control unit  29  to each gate of the inverter  23 , that is to say, to the base of the transistor. The inverter  23  outputs a composite alternating current to the coils  16  of the stator  3  in response to the PWM signal. 
     In order to control the composite alternating current, signals are input to the control unit  29  from a rotation position sensor  25  detecting the rotational position of the inner rotor  5  and a rotation position sensor  27  detecting the rotational position of the outer rotor  7 . Inner torque command values indicating a target torque of the inner rotor  5  and outer torque command values indicating a target torque of the outer rotor  7  are also input to the control unit  29 . 
     The torque command value is a positive value when the rotor functions as a motor and a negative value when the rotor is driven as a generator. The control unit  29  calculates a current required to generate the rotating magnetic field to realize the inner torque command value based on the detected rotational position of the inner rotor  5  and the inner torque command value. 
     In the same manner, the current required to generate the rotating magnetic field to realize the outer torque command value is calculated based on the rotational position of the outer rotor  7  and the outer torque command value. 
     By outputting PWM signals to the inverter  23 , the control unit  21  controls the inverter  23  so that the inverter  23  provides the coils  16  with a composite current of the above two types of the currents. This principle is disclosed in the above-mentioned Tokkai-Hei-11-275856. 
     Referring to FIG. 4, the various characteristics of the motor/generator  1  are determined by the magnetic resistance ratio Rin/Rout of the cores  3 A. 
     In the figure, the curved line A shows torque acting on the inner rotor  5  (hereafter termed “inner torque”). The curved line B shows torque acting on the outer rotor  7  (hereafter termed “outer torque”). The curved line C shows power of the inner rotor  7  (hereafter termed “inner power”). The curved line D shows the sum of the inner power and power of the outer rotor  7  (hereafter termed “outer power”). The curved line E shows the power source load factor. 
     The outer power is obtained by subtracting the inner power from the sum of the power. The power source load factor is the ratio of the absolute value of the power supplied by the battery  21  and the absolute value of the sum of the inner power and outer power. 
     The point S shows the point of maximum power density and represents the maximum value of the sum of the power. The total output of the motor/generator is a maximum at the maximum point of power density. The point S is obtained when the magnetic resistance ratio Rin/Rout has a value of approximately 0.03. 
     The point T shows the power equivalence point where the inner power and the outer power are equal. When one rotor  5  or  7  is driven as a generator and the other rotor  5  or  7  is driven as a motor with the generated electrical energy, it is possible to use the electrical energy most efficiently at this point. The point T is obtained when the magnetic resistance ratio Rin/Rout has a value of approximately 0.38. 
     The point U shows the minimum point for power source load factor which is the point at which the efficiency of the inverter  23  becomes the maximum and calorific value of the inverter  23  is minimized. The point U is obtained when the magnetic resistance ratio Rin/Rout has a value of approximately 0.54. 
     Thus the magnetic resistance ratio Rin/Rout desired for the core  3 A and the corresponding layer number ratio of the first plate units  10 A and the second plate units  10 B are determined based on the required motion characteristics of the motor/generator, and the plurality of cores  3 A are assembled by laminating the plate units  10 A,  10 B under the determined layer number ratio. 
     In the above manner, it is possible to vary the magnetic resistance ratio Rin/Rout during the manufacturing process in an arbitrary manner in response to the required motion characteristics without varying the design of the stator  3 . 
     The layer number ratio of the first plate unit  10 A and the second plate unit  10 B are determined in the following manner. 
     The magnetic resistance ratio of the first plate unit  10 A, the magnetic resistance ratio of the second plate unit  10 B and the desired magnetic resistance ratio of the core  3 A are designated by α, β, γ respectively. The total number of layers of the plate units  10 A and  10 B is taken to be N, and the number of layers of the first plate unit  10 A is taken to be X. 
     The core  3 A creates an extremely large magnetic resistance in an axial direction due to the formation of an insulating layer on the surface of the tooth member  11 ,  11 A. The magnitude of the magnetic resistance is approximately proportional to the number of layers. The following relationship is established on the basis of the above arrangement.        γ   =       α   ·     X   N       +     β   ·       1   -   X     N                                
     where, α&gt;β, and 
     X=1,2, . . . ,N. 
     When it is desired to set the magnetic resistance ratio of the core  3 A to γ, the layer ratio Y/N of the first plate units  10 A may be set to a value satisfying the above formula. The values of the magnetic resistance ratio α of the first plate unit  10 A and the value of the magnetic resistance ratio β of the second plate unit  10 B may be appropriately varied by varying structure of the plate units  10 A and  10 B, that is to say, the number, dimensions and shape of the tooth members  11 ,  11 A. 
     The lower limit P 1  of the settable range of the magnetic resistance ratio γ of the core  3 A is the magnetic resistance ratio Rin/Rout of the core  3 A when the layer number ratio of the first plate unit  10 A is 0% and the layer number ratio of the second plate unit  10 B is 100%. The upper limit P 2  is the magnetic resistance ratio Rin/Rout of the core  3 A when the layer number ratio of the first plate unit  10 A is 100% and the layer number ratio of the second plate unit  10 B is 0%. In FIG. 3 a  and  3   b , the magnetic resistance ratio α of the first plate unit  10 A is set to 0.6 and the magnetic resistance ratio β of the second plate unit  10 B is set to a value which is close to 0. 
     Thus it is possible to facilitate the variation of the characteristics of the motion of the motor/generator under the same basic design by assembling two types of plate units  10 A and  10 B with a layer number ratio calculated as above. 
     A second embodiment of this invention will now be described with reference to FIG.  5 . 
     This embodiment differs from the first embodiment with reference to the structure of the second plate unit  10 B. In other respects, the second embodiment is the same as the first embodiment. 
     The second plate unit  10 B is formed from a ferro-silicon plate formed as a single plate  31 . 
     The second plate unit  10 B is provided with a plurality of tooth members  31 A extending in a radial direction. A gap  13  is formed between the outer ends of adjacent tooth members  31 A. On the other hand, the inner peripheral sections of the tooth members  31 A are contiguous in a circumferential direction. 
     Thus the magnetic resistance in a circumferential direction between the inner peripheral sections of the tooth members is extremely small. The first plate unit is exactly the same as the first plate unit  10 A as described in the first embodiment. 
     The second embodiment allows the inner magnetic resistance Rin to be further reduced below that of the second plate unit  10 B in the first embodiment. 
     A third embodiment of this invention will be described below with reference to FIG.  6  and FIG.  7 . 
     In this embodiment, the core  3 A is formed by laminating a single type of plate unit  40  in place of the two types of plate units  10 A and  10 B used in the first and second embodiments. 
     Referring to FIG. 6, the plate unit  40  is divided into two sections  41 ,  43 , each of which corresponds to 180 degrees of the plate unit  40 . 
     The section  41  is formed from the tooth members  11  of the first embodiment. The section  43  is formed from the tooth members  11 A of the first embodiment. 
     The plate unit  40  shown in FIG. 7 is divided into a 315-degree section  41  formed of the tooth members  11  and a 45-degree section  43  formed of the tooth members  11 A. 
     In either case, the tooth members  11 B disposed on the border of the sections  41  and  43  form halves equal to the shape of the tooth members  11 . The remaining halves have a shape equal to the tooth members  11 A. 
     As shown above, the magnetic resistance ratio Rin/Rout when the core  3 A is formed by the lamination of the plate units  40  can be arbitrarily set by varying the angle ratio of the sections  41  and  43 . In this embodiment, connectors  19  are only provided only at a specific angular range in the circumferential direction of the plate unit  40 . 
     In this embodiment, the tooth members  11  and  11 A are combined. However it is possible to combine a single plate unit by assembling the tooth members  11  with the second plate unit  10 B of the second embodiment. 
     When the plate units  40  are laminated to form the core  3 A, it is preferred to shift the position of the section  43  in a rotational direction at each layer so as to create an even distribution of sections  43 . In this manner, it is possible to ensure an even heat distribution in the stator  3  and to improve cooling. 
     The contents of Tokugan Hei 11-306030, with a filing date of Oct. 27, 1999 in Japan, are hereby incorporated by reference. 
     Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. 
     For example, it is possible to combine the plate unit  40  of the third embodiment with the two types of plate unit  10 A and  10 B in the first and second embodiments. 
     The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows: