Patent Publication Number: US-2013234553-A1

Title: Magnetic modulation motor and electric transmission

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims the benefit of priority from earlier Japanese Patent Application Nos. 2012-053227 filed Mar. 9, 2012, 2012-176329 filed Aug. 8, 2012, and 2012-200426 filed Sep. 12, 2012, the descriptions of which are incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a magnetic modulation motor and an electric transmission suitable for use in a power device for hybrid vehicles which are driven by a mechanical power of an internal combustion and an electric power of a battery. 
     2. Description of the Related Art 
     As related art of a power transmission device for hybrid automobiles, there is a commonly used device which transmits power via a motor and a CVT (continuously variable transmission) between an output shaft of an internal combustion and an input shaft of a gear that switches between speed reduction and back-and-forth motion. Recently, new technologies combining these functions are proposed. 
     For example, there is known a motor with hybrid functions that includes an armature corresponding to a stator, a magnet rotor fixed to a first rotary shaft, and a magnetic induction rotor fixed to a second rotary shaft. Based on a principle of magnetic modulation, this motor smoothly converts speed between the first rotary shaft and the second rotary shaft, or adds an electric power to the second rotary shaft and outputs it. For example, JP-A-2010-017032 discloses a technique for achieving the hybrid functions as describe above. 
     The motor based on the principle of magnetic modulation (hereinafter referred to as “magnetic modulation motor”) has been evolved from the study of magnetic gears by Professor Kais Atallah, the university of Sheffield of the United Kingdom, et al. This motor has a basic structure including an outer rotor, an inner rotor, and a plurality of soft magnetic materials for magnetic induction poles. The outer rotor comprises a plurality of permanent magnets with m pole pairs. The inner rotor comprises a plurality of permanent magnets with n pole pairs. The number of the soft magnetic materials is determined by the sum or difference of m and n. The soft magnetic materials are used as the magnetic induction poles, which are arranged between the outer and inner rotors in such a way as to modulate magnetic field acting between both rotors through their permanent magnets. 
     A motor using an outer rotor as an armature of winding type follows the same principle of the magnetic modulation as described above. 
     The structure disclosed in JP-A-2010-017032 as described above includes an armature, a magnet rotor, and a magnetic induction rotor. The armature comprises a plurality of multi-phase windings with m pole pairs (m=8 in this case). The magnet rotor comprises a plurality of permanent magnets with n of pole pairs (n=8 in this case). The magnetic induction rotor is provided with k soft magnetic materials which are used as the magnetic induction poles and are circumferentially arranged between the armature and the magnet rotor (k=16 in this case). This structure is designed for the magnetic modulation motor of k=m+n (m=n=8 and k=16 in this case). 
     However, the magnetic modulation motor as described above has the following issues. 
     In JP-A-2010-017032, the magnetic induction poles of the magnetic induction rotor need to be made of discrete soft magnetic materials due to functional requirements. In the structure of the magnetic modulation motor, the magnetic induction rotor is located between the armature and the magnet rotor in a rotatable manner. Due to this structure, magnetic flux passes through a part of the magnetic induction rotor. If a metallic member is present around the magnetic induction pole, it acts as a shorting coil and then short-circuit current flows. This prevents the magnetic flux from passing through the part of the magnetic induction rotor and leads to generation of large loss. This is why the magnetic induction rotor has a difficulty in casting soft magnetic material by a method such as aluminum die casting commonly used in well-known motors. Thus, the magnetic induction rotor has a difficulty in ensuring mechanical rigidity and in being fixed to the rotary shaft, which causes a fundamental issue that proof stress is low. 
     A design of magnet fixation can be comparatively easily realized by the case where the magnetic induction rotor is arranged at the most inner diameter side at which the magnetic modulation motor is likely to be fixed to the rotary shaft. This is because a design of strong structure can be adopted. For example, it is possible to adopt such a structure design that a plurality of magnets are embedded in laminated iron cores and are connected by bridges without need for considering leakage of magnetic flux between the magnetic poles. This is because the magnet rotor is not as sensitive as the magnetic modulation motor and is a source of field magnetomotive force which provides magnetic flux using strong rare-earth magnets. 
     However, in the case where the magnetic induction rotor is arranged at the most inner diameter side, there is a problem that preferable magnetic modulation is not established. 
     In order to solve the problem, in the case where the magnet rotor is arranged between the armature and the magnetic induction rotor, the presence or absence of magnetic modulation action and problems are examined by the present inventors, and then, the following findings and solutions are obtained. 
     In the case where the magnet rotor is arranged between the armature and the magnetic modulation motor, a preferable magnetic modulation cannot be obtained and motor characteristics are greatly reduced. This cause is described below. 
     The magnet itself is a source of magnetomotive force, i.e., a source of magnetic flux, and has a low permeability as similar to that of air. Then, even if the magnetic induction poles modulate magnetic flux of the magnet depending on the number of poles, the magnet stands in a path of the modulated magnetic flux going toward the armature or returning from it, and is an obstacle in the path of the modulated magnetic flux. Therefore, the permanent magnet with strong magnetomotive force blocks the modulated magnetic flux over a widely-covered range, thereby disturbing the modulated magnetic flux. 
     On the other hand, in related art, as a transmission for hybrid vehicles, there is known a power conversion technique that combines two motors: (i) a magnetic modulation motor having two rotors and one stator; and (ii) a magnet motor having one rotor and one stator, which are well known. By such motors, high-speed low-torque power of an engine is converted into low-speed high-torque power, and then the converted power is transferred to an axle side. 
     As described above, the magnetic modulation rotor is derived from a combination of the principle of magnetic modulation and a magnetic gear transmitting power in non-contact manner, as described above. This basic structure includes: (i) an outer rotor with a plurality of permanent magnets having m pole pairs; (ii) an inner rotor with a plurality of permanent magnets having n pole pairs; and (iii) a magnetic modulation element located between the outer rotor and the inner rotor. The magnetic modulation element is made of m±n soft magnetic material segments, and magnetically modulates magnetic field acting between the outer and inner rotors through their magnets. 
     For example, JP-B2-4505524 discloses a case of a first rotary machine corresponding to the magnetic modulation motor. The first rotary machine includes: (i) a stator of winding type that is configured by the outer rotor of the magnetic modulation motor; and (ii) first and second rotors that are located in a relatively rotatable manner with respect to the stator. For example, an input shaft of the second rotor is directly coupled to a crank shaft of an engine, and an output shaft of the first rotor is coupled to driven unit (axel side) via a gear mechanism or the like. 
     The first rotor includes a plurality of magnetic poles located in such a way as to face an armature of the stator. The magnetic poles are circumferentially arranged at intervals, and the adjacent two magnetic poles differ in polarity from each other. 
     The second rotor includes a plurality of soft magnetic materials located between the armature of the stator and the magnetic poles of the first rotor. The soft magnetic materials are circumferentially arranged at intervals. 
     In addition to the first rotary machine, JP-B2-4505524 also discloses a second rotary machine which is a well-known magnet motor. In this disclosure, the following cases are described. 
     (1) In the first case, the first and second rotary machines are axially arranged on an output shaft. 
     (2) In the second case, the first rotary machine is arranged at the radially outer side of the second rotary machine. In this case, the first and second rotary machines are radially arranged. This can downsize an axial size of the power device, thereby making it possible to increase its design freedom. 
     (3) In the third case, the first and second rotary machines are separately arranged (mounted). For example, the first rotary machine is used as a power source for front-wheel drive, and the second rotary machine is used as a power source for rear-wheel drive. 
     As describe above, JP-B2-4505524 discloses a technique of the power device that generates drive power and converts speed by combining the first rotary machine corresponding to the magnetic modulation motor and the second rotary machine which is a well-known magnet motor. 
     In the first rotary machine disclosed in JP-B2-4505524, a relationship of (i) a velocity (speed) of rotating magnetic field, (ii) a rotational velocity of the first rotary machine, and (iii) a rotational velocity of the second rotary machine can be expressed by collinear diagram used in explanation of operation of a well-known mechanical planetary gear motor. In other words, this first rotary machine can be operated in the same manner as the mechanical planetary gear motor. 
     The mechanical planetary gear motor transmits power through gears meshing with each other. This requires oil lubrication, thereby resulting in low transmission efficiency. Compared to this, in the magnetic modulation motor such as the first rotary machine described above, the stator and the rotor operate in a non-contact manner. Therefore, the magnetic modulation motor is expected to be an advantageous technique capable of using a substitute for the mechanical planetary gear motor. 
     In order for the above-expected technique to be embodied, design and realization of an electric transmission using a combination of a magnetic modulation motor and a magnet motor were also examined by the present inventors, and then, the following findings and solutions were obtained. 
     In the configuration disclosed in JP-B2-4505524, a body of the first and second rotary machines is likely to be large, and then, it is difficult to realize two rotors as above-described in the second case in which the first and second rotary machines are radially arranged. As a result of analyzing this cause, it is found that the technique disclosed in JP-B2-4505524 has the following issues. 
     The configuration of the first rotary machine makes it difficult to downsize the first and second rotary machines (especially, the first rotary machine corresponding to the magnetic modulation motor). In the magnetic modulation motor in related art, the magnetic modulation element is located between the armature and the field element. In the case of the first rotary machine disclosed in JP-B2-4505524, the second rotor (configuring the magnetic modulation element) is located between the stator (configuring the armature) and the first rotor (configuring the field element). 
     In this configuration, the magnetic modulation element is positioned in a path of magnetic flux going and returning between the armature and the field element. This causes eddy current in the magnetic modulation element. This also causes a current path in a metallic support structure that supports the magnetic modulation element. Thus, the eddy current circulates in a loop formed in the current path. Therefore, this makes it difficult to: (i) support, by a metallic member, a plurality of soft magnetic materials forming the magnetic modulation element, or (ii) support the magnetic modulation element by a support member to which the plurality of soft magnetic materials are directly connected by welding or fastening. 
     As this regard, an insulator such as resin is considered for a use of a support structure of the magnetic modulation element. However, the support structure uses resin or the like having a strength lower than metallic member, thereby being unable to resist high speed high vibration of an engine. In other words, the support structure of the magnetic modulation element is required to be large, in order to be able to resist high speed high vibration of the engine by using low strength resin or the like. 
     Therefore, the magnetic modulation element for causing operation of magnetic modulation is required to magnetically separate the plurality of soft magnetic materials from one another and to reliably support each of the soft magnetic materials. On the other hand, as described above, the magnetic modulation element is positioned in the path of magnetic flux going and returning between the armature and the field element, thereby causing generation of eddy current. This generation of eddy current makes it difficult to support the magnetic modulation element by using a metallic member. 
     In addition, in the configuration disclosed in JP-B2-4505524, two inverters called as PDU (power drive unit) are required, and then, it is also difficult to realize two rotors as above-described in the second case in which the first and second rotary machines are radially arranged. 
     In this regard, in JP-B2-4505524, the first rotary machine generates electric power and transmits the generated power to the second rotary machine in such a way as to regenerate power on its output shaft. In such a mode, two inverters are used for transmitting electric power with different frequency between the first and second rotary machines. 
     To deal with these issues described above, the magnetic modulation motor may be designed in such a way that the magnetic modulation element is not located between the armature and the field element, but is located outside them. However, this case has the following issues. 
     The rotary machine based on the principle of magnetic modulation is a non-synchronous machine. In such a non-synchronous machine, the armature and the field element, which differ from each other in the number of poles, are arranged adjacent to each other, thereby increasing magnetic interference between them so as to magnetically disturb each other. This makes it impossible for the magnetic modulation element to cause operation of magnetic modulation. This is why a rotary machine, in which the magnetic modulation element is located outside the armature and the field element, has not been proposed and put into practical use. Such a configuration of the rotary machine is excluded from the disclosures of JP-B2-4505524. 
     SUMMARY 
     The present disclosure provides a magnetic modulation motor including a magnet rotor arranged between an armature and a magnetic induction rotor, which is able to improve a strength and proof stress of the magnetic induction rotor. 
     The present disclosure also provides an electric transmission configured by a first rotary machine using a magnetic modulation motor and a second rotary machine using a magnet motor, which is able to be downsized. 
     The present disclosure further provides an electric transmission configured by a first rotary machine using a magnetic modulation motor and a second rotary machine using an induction motor, in which the second rotary machine is able to be electrically driven by generated power of the first rotary machine, and which is able to be downsized. 
     According to first exemplary aspect of the present disclosure, there is provided a magnetic modulation motor, including: an armature provided with a multi-phase winding having m pole pairs, m being an integer of one or more; a magnetic induction rotor including k magnetic paths, k being an integer of one or more; and a magnet rotor in which 2n permanent magnets forming a polarity region of n pole pairs are separately and annularly placed, n being a sum or difference of m and k, 2n being twice n. 
     The armature, the magnet rotor, and the magnetic induction rotor are arranged in the order from a radially outer side to a radially inner side of the magnetic modulation motor. 
     In the magnetic induction rotor, each of the magnetic paths has both ends, each projecting toward a magnetic flux entry and exit located at an outer diameter face of the magnetic induction rotor, each of the magnetic paths forming a magnetic flux path between the magnetic flux entry and exit. 
     The magnet rotor includes a magnetic flux penetration region which is magnetically penetrated by magnetic flux between each circumferentially adjacent two permanent magnets. 
     In the magnetic modulation motor according to the first exemplary aspect, the magnetic induction rotor is located at the most inner diameter side, and the magnet rotor being a source of magnetomotive force is located between the magnetic induction rotor and the armature. Even for this arrangement, since the magnetic flux penetration region is provided in the magnet rotor, the modulated flux of the magnetic induction rotor is not disturbed even if facing the source of magnetomotive force in arrangement of the permanent magnets in the magnet rotor. Then, its penetrated component passes through the magnetic flux penetration region, and therefore, magnetic modulation action works with the armature. 
     Thus, even if the magnet rotor is present between the armature and the magnetic induction rotor, magnetic modulation action works well. Such a motor can be realized. Therefore, this motor can work as a modulation motor, though the magnetic induction rotor being a modulation element is located externally to the armature and the magnet rotor. In addition, the magnetic modulation rotor is located at the most inner diameter side, thereby being able to improve a strength and proof stress of the magnetic induction rotor. 
     According to second exemplary aspect of the present disclosure, there is provided an electric transmission, including: a first rotary machine including a first rotary shaft supported by a device frame via a first bearing in a rotatable manner; and a second rotary machine including a second rotary shaft supported by the device frame via a second bearing. 
     The first rotary machine includes: a first armature, a first field element, and a magnetic modulation element. 
     The first armature is fixed to the device frame, and has three-phase windings of m pole pairs, where m is an integer of one or more. 
     The first field element includes a plurality of permanent magnets. The permanent magnets is circumferentially arranged relative to the first armature via a gap in a rotatable manner. The permanent magnets form a plurality of magnetic poles of n pole pairs, where n is an integer of one or more. Each circumferentially adjacent two permanent magnets circumferentially adjacent two permanent magnets are magnetized so as to differ in polarity from each other. A soft magnetic material is located around the circumference of an opposite surface facing the first armature so as to cover an armature side surface of the permanent magnets and a space between each circumferentially adjacent two permanent magnets. 
     The magnetic modulation element includes m+n magnetic paths. The m+n magnetic paths are located relative to the first field element via a gap in a rotatable manner. The m+n magnetic paths form passes of magnetic flux. The m+n magnetic paths are magnetically separated from one another and being arranged. 
     The first field element is located between the first armature and the magnetic modulation element. The first field element and the magnetic modulation element configures two rotors, one of which being coupled to the first rotary shaft and being configured to rotate integrally with the first rotary shaft. 
     The second rotary machine includes: a second armature fixed to the device frame, the second armature having a three-phase winding; a second field element located with the second armature via a gap in a rotatable manner, the second field element circumferentially forming a plurality of magnetic poles, and the circumferentially adjacent two magnetic poles differing in polarity from each other. 
     The second field element is connected to the second rotary shaft via a connecting member, and is configured to rotate integrally with the second rotary shaft. In the first and second rotary machines, the second field element and the other of the first field element and the magnetic modulation element are mechanically connected to each other via the connecting member. 
     In the first rotary machine used in the electric transmission according to the second exemplary aspect, the first field element is located between the first armature and the magnetic modulation element. This is different from the magnetic modulation motor in related art in which the magnetic modulation element is located between the armature and the field element. 
     In addition, in the first field element, the soft magnetic material is located around the circumference of an opposite surface facing the first armature so as to cover an armature side surface of the permanent magnets and to also cover a space between the circumferentially adjacent two permanent magnets. Thus, magnetic field generated by the first armature of m pole pairs can be transmitted to the magnetic modulation element having m+n magnetic paths. As a result, the magnetic field of m+n−m=n pole pairs, generated by the magnetic modulation element, synchronizes in frequency with the first field element of n pole pairs. Then, torque is produced. 
     Therefore, even if the first field element is located between the first armature and the magnetic modulation element (this arrangement cannot be easily derived from related art), magnetic modulation action can effectively work. 
     In the first rotary machine, the magnetic modulation element is not located between the first armature and the first field element, but can be located at the opposite side of the first armature with respect to the first field element. Thus, magnetic flux passing though the magnetic paths of the magnetic modulation element forms a flow that passes though the magnetic paths and U-turns. This causes no generation of large loop eddy current, even if a metallic member is embedded between the m+n magnetic paths. In other words, the magnetic modulation element can be reliably and easily supported. This makes it possible to increase rotation speed of the first rotary machine and to downsize the first rotary machine. 
     Further, in the first and second rotary machine, one of two rotors (i.e., the first field element and magnetic modulation element) of the first rotary machine and the second field element of the second rotary machine are mechanically coupled to each other. This can provide the electric transmission with one compact body. 
     According to third exemplary aspect of the present disclosure, there is provided an electric transmission, including: a first rotary machine including a first rotary shaft supported by a device frame via a first bearing in a rotatable manner; and a second rotary machine including a second rotary shaft supported by the device frame via a second bearing. 
     The first rotary machine includes a first armature, a field element, and a magnetic modulation element. 
     The first armature including a first armature core fixed to the device frame, and first three-phase windings of m pole pairs that is wound around the first armature core, where m is an integer of one or more. 
     The field element includes a plurality of permanent magnets. The permanent magnets are circumferentially arranged relative to the first armature via a gap in a rotatable manner. The permanent magnets form a plurality of magnetic poles of n pole pairs, where n is an integer of one or more. Each circumferentially adjacent two permanent magnets are magnetized so as to differ in polarity from each other. A soft magnetic material are located around the circumference of an opposite surface facing the first armature so as to cover an armature side surface of the permanent magnets and a space between each circumferentially adjacent two permanent magnets. 
     The magnetic modulation element includes m+n magnetic paths. The m+n magnetic paths are located relative to the field element via a gap in a rotatable manner. The m+n magnetic paths form passes of magnetic flux. The m+n magnetic paths being magnetically separated from one another. 
     The field element is located between the first armature and the magnetic modulation element. The field element and the magnetic modulation element configures two rotors, one of which being configured to rotate integrally with the first rotary shaft via a first rotor disc. 
     The second rotary machine includes: a second armature including a second armature core fixed to the device frame and second three-phase windings that is wound around the second armature core; a squirrel-cage rotor located relative to the second armature via a gap in a rotatable manner. The squirrel-cage rotor is configured to rotate integrally with the second rotary shaft via a second rotor disc. 
     In the first and second rotary machines, the squirrel-cage rotor and the other of the field element and the magnetic modulation element are mechanically connected to each other. The first three-phase windings and the second three-phase windings are connected to each other in such a manner that their phase sequence is a negative sequence. 
     The electric transmission according to the third exemplary aspect includes the first and second rotary machines. The first rotary machine is configured by a magnetic modulation motor. The second rotary machine is configured by an induction motor. The armature of the first rotary machine is provided with the first three-phase windings. The armature of the second rotary machine is provided with the second three-phase windings. The first three-phase windings and the second three-phase windings are connected to each other in such a manner that their phase sequence is a negative sequence. 
     Then, for example, the engine is rotated at high speed and the axle is rotated at low speed, i.e., the first rotary machine generates electric power while the first three-phase windings generate a rotating magnetic field of the reverse direction of the rotational direction of the engine. By current due to this generated power, a rotating magnetic field of the positive direction is generated in the second three-phase windings of the second rotary machine. This rotating magnetic field induces magnetic field generated in the squirrel-cage rotor of the second rotary machine. Thus, the squirrel-cage rotor rotates in the positive direction with a slip. 
     As a result, the second rotary machine can be electrically driven by using the generated power of the first rotary machine, without a dedicated inverter. 
     Further, in the first rotary machine, the field element is located between the first armature and the magnetic modulation element. This is different from the magnetic modulation motor in related art in which the magnetic modulation element is located between the armature and the field element. 
     In addition, in the field element, the soft magnetic material is located around the circumference of an opposite surface facing the first armature so as to cover an armature side surface of the permanent magnets and a space between each circumferentially adjacent two permanent magnets. Thus, magnetic field generated by the first armature of m pole pairs can be transmitted to the magnetic modulation element having m+n magnetic paths. As a result, magnetic field of m+n−m=n pole pairs, generated by the magnetic modulation element, synchronizes in frequency with the field element of n pole pairs. Then, torque action works. 
     Therefore, even if the field element is located between the first armature and the magnetic modulation element (this arrangement cannot be easily derived from related art), magnetic modulation action can effectively work. 
     In the first rotary machine, the magnetic modulation element is not located between the first armature and the field element, but can be located at the opposite side of the first armature with respect to the field element. Thus, magnetic flux passing though the magnetic paths of the magnetic modulation element forms a flow that passes though the magnetic paths and U-turns. This causes no generation of large loop eddy current, even if metallic member is embedded between the m+n magnetic paths. In other words, the magnetic modulation element can be reliably and easily supported. This makes it possible to increase rotation speed of the first rotary machine and to downsize the first rotary machine. 
     Further, in the first and second rotary machine, one of two rotors (i.e., the field element and magnetic modulation element) of the first rotary machine and the squirrel-cage rotor of the second rotary machine are mechanically coupled to each other. This can provide the electric transmission with one compact body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is an elevation view showing a radial half part of a magnetic modulation motor according to a first exemplary embodiment as viewed from its axial direction; 
         FIG. 2  is a schematic diagram showing an overall configuration of the magnetic modulation motor of  FIG. 1 ; 
         FIG. 3  is a partial elevation view showing a part of the magnetic modulation motor of  FIG. 1  as viewed from its axial direction; 
         FIG. 4  is a connection diagram showing an armature winding which is connected to an inverter in the magnetic modulation motor of  FIG. 1 ; 
         FIG. 5A  is a configuration diagram showing an analysis model for a motor in related art; 
         FIG. 5B  is an a analysis diagram showing a simulation result in a magnetic field analysis for the analysis model of  FIG. 5A ; 
         FIG. 6A  is a configuration diagram showing an analysis model for the magnetic modulation motor according to the first exemplary embodiment; 
         FIG. 6B  is an a analysis diagram showing a simulation result in a magnetic field analysis for the analysis model of  FIG. 6A ; 
         FIG. 7A  is a configuration diagram showing an analysis model A; 
         FIG. 7B  is an a analysis diagram showing a simulation result in a magnetic field analysis for the analysis model A of  FIG. 7A ; 
         FIG. 8A  is a configuration diagram showing an analysis model B; 
         FIG. 8B  is an a analysis diagram showing a simulation result in a magnetic field analysis for the analysis model B of  FIG. 8A ; 
         FIG. 9A  is a configuration diagram showing an analysis model C; 
         FIG. 9B  is an a analysis diagram showing a simulation result in a magnetic field analysis for the analysis model C of  FIG. 9A ; 
         FIG. 10A  is a configuration diagram showing an analysis model D; 
         FIG. 10B  is an a analysis diagram showing a simulation result in a magnetic field analysis for the analysis model D of  FIG. 10A ; 
         FIG. 11  is an elevation view showing a radial half part of a magnetic modulation motor according to a second exemplary embodiment as viewed from its axial direction; 
         FIG. 12A  is a configuration diagram showing an analysis model for the magnetic modulation motor according to the second exemplary embodiment; 
         FIG. 12B  is an a analysis diagram showing a simulation result in a magnetic field analysis for the analysis model of  FIG. 12A ; 
         FIG. 13  is an elevation view showing a radial half part of a magnetic modulation motor according to a third exemplary embodiment as viewed from its axial direction; 
         FIG. 14A  is a configuration diagram showing an analysis model for the magnetic modulation motor according to the third exemplary embodiment; 
         FIG. 14B  is an a analysis diagram showing a simulation result in a magnetic field analysis for the analysis model of  FIG. 14A ; 
         FIG. 15A  is a partial cross-sectional view showing a configuration of a magnetic modulation motor according to a fourth exemplary embodiment; 
         FIG. 15B  is a circumferential development diagram showing a mounted state of a short-circuit coil in the magnetic modulation motor of  FIG. 15A ; 
         FIG. 16A  is a partial cross-sectional view showing a configuration of a magnetic modulation motor according to a fifth exemplary embodiment; 
         FIG. 16B  is a circumferential development diagram showing a mounted state in which a copper plate is fixed by a bolt in the magnetic modulation motor of  FIG. 16A ; 
         FIG. 17  is a longitudinal cross-sectional view showing an electrical transmission according to a sixth exemplary embodiment; 
         FIG. 18  is partial transverse cross-sectional view showing a first rotary armature, a first field element, and magnetic modulation element configuring a first rotary machine of the electrical transmission of  FIG. 17 ; 
         FIG. 19  is partial transverse showing a second armature and a second field element configuring a second rotary machine of the electrical transmission of  FIG. 17 ; 
         FIG. 20  is a schematic diagram showing an overall configuration of a hybrid vehicle provided with the electrical transmission of  FIG. 17 ; 
         FIG. 21A  is an explanatory diagram showing an engine start mode in the vehicle of  FIG. 17 ; 
         FIG. 21B  is a motion diagram of the first rotary machine in the mode of  FIG. 21A ; 
         FIG. 22A  is an explanatory diagram showing an engine acceleration and axle activation mode in the vehicle of  FIG. 17 ; 
         FIG. 22B  is a motion diagram of the first rotary machine in the mode of  FIG. 22A ; 
         FIG. 23A  is an explanatory diagram showing an EV (electric vehicle) drive mode in the vehicle of  FIG. 17 ; 
         FIG. 23B  is a motion diagram of the first rotary machine in the mode of  FIG. 23A ; 
         FIG. 24A  is an explanatory diagram showing a vehicle regenerative braking mode in the vehicle of  FIG. 17 ; 
         FIG. 24B  is a motion diagram of the first rotary machine in the mode of  FIG. 24A ; 
         FIG. 25  is a longitudinal cross-sectional view showing an electrical transmission according to a seventh exemplary embodiment; 
         FIG. 26  is a longitudinal cross-sectional view showing an electrical transmission according to an eighth exemplary embodiment; 
         FIG. 27  is a diagram showing a overall configuration of the electrical transmission of  FIG. 26 ; 
         FIG. 28  is a transverse cross-sectional view showing a structure of a first rotary machine of the electrical transmission of  FIG. 26 ; 
         FIG. 29  is a transverse cross-sectional view showing a structure of a second rotary machine of the electrical transmission of  FIG. 26 ; 
         FIG. 30  is a cross-sectional view taken along the line V-V of a squirrel-cage rotor in the second rotary machine of  FIG. 29 ; 
         FIG. 31  is a schematic diagram showing an overall configuration of a hybrid vehicle provided with the electrical transmission of  FIG. 26 ; 
         FIG. 32A  is an explanatory diagram showing an engine start mode in the vehicle of  FIG. 31 ; 
         FIG. 32B  is a motion diagram of the first rotary machine in the mode of  FIG. 32A ; 
         FIG. 33A  is an explanatory diagram showing an engine acceleration and axle activation mode in the vehicle of  FIG. 31 ; 
         FIG. 33B  is a motion diagram of the first rotary machine in the mode of  FIG. 33A ; 
         FIG. 34A  is an explanatory diagram showing an EV (electric vehicle) drive mode in the vehicle of  FIG. 31 ; 
         FIG. 34B  is a motion diagram of the first rotary machine in the mode of  FIG. 34A ; 
         FIG. 35A  is an explanatory diagram showing a vehicle regenerative braking mode in the vehicle of  FIG. 31 ; 
         FIG. 35B  is a motion diagram of the first rotary machine in the mode of  FIG. 35A ; and 
         FIG. 36  is a longitudinal cross-sectional view showing an electrical transmission according to a ninth exemplary embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, referring to the drawing, exemplary embodiments according to the present invention will be described in detail. 
     First Exemplary Embodiment 
       FIGS. 1 to 4  show a magnetic modulation motor (hereinafter referred to as “motor”)  1  according to a first exemplary embodiment of the present invention, which is mounted between an engine and a transmission in a hybrid vehicle. 
     First, a configuration of the motor  1  is described. As shown in  FIG. 2 , the motor  1  includes a motor frame  2 , an armature  3 , a first rotary shaft  4 , a magnetic induction rotor  5 , a second rotary shaft  6 , and a magnet rotor  7 . The armature  3 , the magnet rotor  7 , and the magnetic induction rotor  5  are arranged in the order from the radially outer side to the radially inner side (center side) of the motor  1 . The armature  3  is fixed to the motor frame  2 . The first rotary shaft  4  is coupled with an output shaft of an engine E 1 , and is supported by the motor frame  2  in a rotatable manner via a bearing (not shown). The magnetic induction rotor  5  rotates integrally along with the first rotary shaft  4 . The second rotary shaft  6  is coupled with an driven shaft of a transmission M 1 , and is supported by the motor frame  2  in a rotatable manner via bearings (not shown). The magnet rotor  7  rotates integrally along with the second rotary shaft  6 . 
     (Description of Armature  3 ) 
     The armature  3  is configured by an armature iron core  30  and an armature winding  31 . The armature iron core  30  is configured by laminating a plurality of electromagnetic steel plates. The armature winding  31  is wound around the armature iron core  30 . 
     As shown in  FIG. 1 , the armature iron core  30  has a radially inner periphery on which a plurality of slots (e.g., 72 slots in the first exemplary embodiment) are formed circumferentially at regular pitches. 
     The armature winding  31  is configured by three-phase (X-phase, Y-phase, and Z-phase) windings with m pole pairs (m=6 in the first exemplary embodiment). The three-phase windings are connected in a star configuration in which one end thereof are connected to one common neutral point O and the other end are connected to an inverter  8 . The inverter  8  is a well-known power converter for converting direct current (DC) power into alternating current (AC) power, and is connected to a battery B 1  which is a main power supply mounted in a vehicle. This inverter  8  is driven in a controlled manner by an inverter ECU (electronic control unit) that communicates signals with a vehicle control ECU (not shown). 
     (Description of Magnetic Induction Rotor  5 ) 
     As shown in  FIG. 1 , the magnetic induction rotor  5  is configured by: (i) 16 segments (segment poles)  9  that form magnetic paths; and (ii) a rotor hub  10  that supports the 16 segments  9 . In the present embodiment, the number of magnetic paths (formed by the segments) is given by k=16. 
     Each of the 16 segments  9  is configured by laminating a plurality of electromagnetic steel plates which are formed into an approximate V-shape by punching. The segments  9  are circumferentially arranged at predetermined intervals. Hereinafter, two sides of the segment  9  which are opened into a V-shape are referred to “two segment arm sections  9   a ”. A base (root) side of the two segment arm sections  9   a  is referred to “segment base section  9   b ”. A concave portion (e.g., a recess or hollow portion) formed between the two segment arm sections  9   a  is referred to “segment concave portion  9   c”.    
     The segments  9  as described above are arranged in such a manner that the two segment arm sections  9   a  are open into a V-shape radially outward, i.e., the segment base section  9   b  faces radially inward. In the present embodiment, an anchor section  9   d  which has a dovetail-shape is formed in the bottom face of the segment base section  9   b.    
     The rotor hub  10  is made of high-strength aluminum material (for example, duralumin) which is a non-magnetic and a good electric conductor, and is produced by die-casting in which the 16 segments  9  are integrally cast. Therefore, high-strength aluminum material is filled between two circumferentially adjacent segments  16  up to a position of its outer diameter face. In other words, two circumferentially adjacent segments  16  are magnetically separated from each other by high-strength aluminum material forming the rotor hub  10 . Here, the segment concave portion  9   c  is not filled with aluminum material. The anchor section  9   d , provided in the segment base section  9   b , is buried in the rotor hub  10 . Thus, each of the segments  9  is tightly fixed to the rotor hub  10 . This prevents the segments  9  from being detached from the rotor hub  10 . 
     In the rotor hub  10 , a central hole  10   a  is formed in a radial inner periphery thereof. The first rotary shaft  4  is fitted into the central hole  10   a  of the rotor hub  10  by press fitting or the like, and then, the rotor hub  10  is fixed to the first rotary shaft  4 . 
     In each of the 16 segments  9 , an apical face of the respective segment arm sections  9   a  projects toward a “rotor outer diameter face”, and forms an entry and exit of magnetic flux. Here, the “rotor outer diameter face” is an outer diameter face of the magnetic induction rotor  5  which faces the magnet rotor  7  via a gap between the magnetic induction rotor  5  and the magnet rotor  7 , and corresponds to an outer diameter face of aluminum material filled between the circumferentially adjacent two segments  9 . Hereinafter, the apical face of the respective segment arm sections  9   a  projecting toward the rotor outer diameter face is referred to as a “magnetic flux entry and exit  9   e”.    
     Each of the segments  9  is arranged at an angular range of a center angle θ 1 =22.5 degrees which is obtained by dividing 360 degrees of full circumference of the magnetic induction rotor  5  by 19 which is the number of segments  9 . The magnetic flux entry and exit  9   e  of the segment arm section  9   a  projects toward the rotor outer diameter face at an angular range of a center angle θ 2 =4.5 degrees which is approximately ⅕ of the center angle θ 1 =22.5 degrees. 
     (Description of Magnet Rotor  7 ) 
     As shown in  FIG. 1 , the magnet rotor  7  is configured by 20 permanent magnets made of rare-earth permanent magnets (e.g., neodymium magnets)  11  and soft magnetic materials  12 ,  13  which support the 20 permanent magnets  11 . In the present embodiment, the number of poles (made of permanent magnets) is 2n=20, and the number of pole pairs (made of permanent magnets) is n=10. 
     As shown in  FIG. 3 , the permanent magnets  11  have a pole arc angle α=12.5 degrees which, in the present embodiment, is defined by a center angle which is formed by: (i) a rotation center of the magnet rotor  7 ; and (ii) both circumferential ends of an inner diameter face of the permanent magnets  11  that faces the outer diameter face of the magnetic induction rotor  5  via the gap between the magnetic induction rotor  5  and the magnet rotor  7 . 
     The permanent magnets  11  are circumferentially spaced at predetermined intervals and are annularly arranged. Each of permanent magnets  11  are radially magnetized. Each circumferentially adjacent two permanent magnets  11  are arranged in such a manner that they are different in polarity from each other, i.e., alternate between N and S poles. 
     As shown in  FIG. 1 , the soft magnetic material  12 , which is ring-shaped, is located at a full circumference of the magnet rotor  7  in such a way as to cover an outer periphery (radially outside surface) of the 20 permanent magnets  11 . Hereinafter, the soft magnetic material  12  is referred to as “ring-like soft magnetic material  12 ”. 
     As shown in  FIG. 1 , the soft magnetic material  13  is located between the circumferential adjacent two permanent magnets  11  (magnetic poles) in such a way as to form a magnetic flux penetration region. Hereinafter, the soft magnetic material  13  is referred to as “interpolar soft magnetic material  13 ”. 
     In other words, at the inner diameter side of the ring-like soft magnetic material  12 , the 20 interpolar soft magnetic materials  13  are circumferentially arranged at regular intervals. The permanent magnets  11  are placed in an opening portion which is formed between the circumferential adjacent two interpolar soft magnetic materials  13 . 
     The ring-like soft magnetic material  12  and the interpolar soft magnetic materials  13  is formed by, for example, laminating electromagnetic steel plates, but may be integrally or separately formed. 
     As shown in  FIG. 3 , the following relationship is satisfied: 
         W 1 ≦W 2 
     where W 1  denotes a circumferential width of the magnetic flux entry and exit  9   e  projecting toward the outer diameter face of the magnetic induction rotor  5 , and W 2  denotes a circumferential distance between each circumferentially adjacent two permanent magnets  11 , i.e., a circumferential width of the inner diameter face of the interpolar soft magnetic materials  13 . 
     In other words, a center angle θ 3 =5.5 degrees with respect to the circumferential width W 2  of the inner diameter face of the interpolar soft magnetic materials  13  is larger than a center angle θ 2 =4.5 degrees with respect to the circumferential width W 1  of the magnetic flux entry and exit  9   e.    
     As shown in  FIG. 3 , a maximum depth of the segment concave portion  9   c  formed in the segments  9 , i.e., a depth D from the outer diameter face to the bottom face of the segment concave portion  9   c  is set to a size equal to or larger than the circumferential width W 2  of the inner diameter face of the interpolar soft magnetic materials  13 . 
     Next, operation of the motor  1  is described. 
     In the magnet rotor  7 , the permanent magnets  11  are arranged in such a way as to alternate between N and S poles. Thus, this magnet rotor  7  provides the magnetic induction rotor  5  with a change of magnetomotive force having a frequency of 10ωn which is obtained as the product of (i) n=10 that is the number of pole pairs of the magnet rotor  7  and (ii) an angular velocity con of the magnet rotor  7 . 
     In the magnetic induction rotor  5 , the 16 segments  9  forming magnetic paths are formed into an approximate V-shape, and the apical face of the respective two segment arm sections  9   a , as the magnetic flux entry and exit  9   e , projects toward the outer diameter face of the magnetic induction rotor  5 . This can produce a change of magnetic path having a frequency of 16ωk where ωk is an angular velocity of the magnetic induction rotor  5 . Thus, the change of magnetomotive force of 10ωn is modulated as the change of magnetic path of frequency 16ωk. 
     Magnetic flux, which is transmitted from one permanent magnet  11 , passes through one segment  9  from its one of the two magnetic flux entry and exit  9  which is an entry side. Subsequently, when the other of the two magnetic flux entry and exit  9 , which is an exit side, faces another permanent magnet  11  having a reverse polarity with respect to one permanent magnet  11 , the magnetic flux passes through another permanent magnet  11  from the other of the two magnetic flux entry and exit  9 , which is the exit side, and then, propagates to the armature  3 . On the other hand, when the other of the two magnetic flux entry and exit  9 , which is the exit side, faces the interpolar soft magnetic material  13 , the magnetic flux passes through the interpolar soft magnetic material  13  forming the magnetic flux penetration region, and then, propagates to the armature  3 . 
     If all of the magnet rotor  7  facing the outer diameter side of the magnetic induction rotor  5  is covered by the permanent magnets  11 , a component of the magnetic induction rotor  5  does not fully propagate to the armature  3 . In the present embodiment, the interpolar soft magnetic material  13  is arranged between each circumferentially adjacent two permanent magnets  11  in such a way as to form the magnetic flux penetration region therebetween, thereby providing good magnetic modulation. 
     Here, a frequency of a magnetic change which propagates to the armature  3  is expressed as the sum and difference of 10ωn (change of magnetomotive force) and 16ωk (change of magnetic path) due to modulation action. Provided that ωm denotes an angular velocity of rotating magnetic field produced in the armature winding  31  (three-phase windings) with pole pairs of m=6, action of the inverter  8  is controlled so as to satisfy the following formula (1) with respect to ωm, and then, the armature winding  31  is energized. 
       6 ωm=| 10 ωm± 16 ωk|   (1)
 
     Thus, the magnetic induction rotor  5 , the magnet rotor  7 , and the armature  3  can interact with one another for energy conversion. Due to this, they can function aas a magnetic modulation motor. 
     In the motor  1  as described above, the magnetic induction rotor  5  can be arranged at the most inner diameter side, not between the armature  3  and the magnet rotor  7 . Thus, the 16 segments  9  forming the magnetic path can be integrally cast in high-strength aluminum material (for example, duralumin). This can achieve a rotary structure with high rigidity. 
     In addition, the magnetic induction rotor  5  is arranged at the most inner diameter side. This enables the magnetic induction rotor  5  to be easily fixed to the first rotary shaft  4 . Therefore, in the magnetic induction rotor  5 , the 16 segments  9  are supported by the rotor hub  10  in which the central hole  10   a  is formed. The first rotary shaft  4  can be fitted in this central hole  10   a  by press fit or the like. Thus, the magnetic induction rotor  5  can be tightly and easily fixed to the first rotary shaft  4 . 
     Further, in the magnetic induction rotor  5 , high-strength aluminum material with high electric conductivity is filled between the circumferential adjacent two segments  9 . Thus, in dynamic magnetic field, an effect of reducing magnetic leakage (leakage flux) in this portion can be caused. As a result, magnetic modulation is orderly performed between the magnet rotor  7  and the magnetic induction rotor  5 . This can further improve performance of the motor  1 . 
     As described above, according to the first exemplary embodiment, a strength of centrifugal force resistance can improved, and the motor  1  can be downsized and upgraded. Such advantageous effects can be obtained. In addition, modulation action of a magnetic circuit can be well performed. This can further improve performance of the motor  1 . 
     In the motor  1  described in the first exemplary embodiment, the circumferential width W 1  of the magnetic flux entry and exit  9   e  of the respective segments  9  is set to be equal to or less than the circumferential width W 2  of the inner diameter face of the interpolar soft magnetic materials  13  (W 1 ≦W 2 ). 
     Here, if W 1  is larger than W 2  (W 1 &gt;W 2 ), magnetic fields of the adjacent two permanent magnets  11  are short-circuited near the magnetic flux entry and exit  9   e . Thus, magnetic flux does not effectively pass through the segments  9 . This can cause significant leakage flux near the magnetic flux entry and exit  9   e . Thus, magnetic force of the respective permanent magnets  11  may be weakened. 
     On the other hand, if the relationship (W 1 ≦W 2 ) as described above is satisfied, magnetic fields of the adjacent two permanent magnets  11  are not short-circuited near the magnetic flux entry and exit  9   e . Therefore, magnetic force of the respective permanent magnets  11  cannot be weakened, which can provide good magnetic modulation for the segments  9 . 
     Further, in the motor  1  described in the first exemplary embodiment, the depth D from the outer diameter face to the bottom face of the segment concave portion  9   c  is set to a size equal to or larger than the circumferential width W 2  of the inner diameter face of the interpolar soft magnetic materials  13  (D≧W 2 ) (see  FIG. 3 ). This operation and effect are described below. 
     In each circumferentially adjacent two permanent magnets  11 , their width and size are set so as to reduce interpolar leakage as described above. Here, in a part of the magnetic induction rotor  5  other than the segments  9 , i.e., the segment concave portion  9   c  that is required to avoid occurrence of magnetic leakage, its depth D is set to a size equal to or larger than the circumferential width W 2  of the inner diameter face of the interpolar soft magnetic materials  13 . This can reduce magnetic leakage to an acceptable level. Such an effect can be obtained in the present embodiment. 
     Next, based on simulation results in magnetic field analysis, effects of the motor  1  are described compared to a motor in related art (hereinafter referred to as a “comparative motor”) in which the magnetic induction rotor  5  is arranged between the armature  3  and the magnet rotor  7 . 
       FIG. 5A  is a configuration diagram showing an analysis model for the comparative motor, and  FIG. 5B  is an a analysis diagram showing a simulation result in magnetic field analysis for this analysis model of  FIG. 5A .  FIG. 6A  is a configuration diagram showing an analysis model for the motor  1  according to the first exemplary embodiment, and  FIG. 6B  is an a analysis diagram showing a simulation result of a magnetic field analysis for this analysis model of  FIG. 6A . 
     Here, the analysis model of the motor  1  is different from that of the comparative motor in arrangement of the magnetic induction rotor  5  and the magnet rotor  7 . Both analysis models are the same outer diameter and axial length of the armature  3 . For example, the outer diameter (□2) of the armature  3  is set to 54 mm (□2-54 mm) and the axial length of the armature  3  is set to 50 mm. In the magnetic induction rotor  5  of the comparative motor, a plurality of magnetic induction poles  50  are circumferentially arranged at regular intervals, and a space is formed between each two circumferential adjacent magnetic induction poles  50 , which is not filled with aluminum material. 
     In the motor  1  and the comparative motor, under the condition that the magnet rotor  7  is static, the armature winding  31  is energized with three-phase alternating current (AC) of 170 A (effective value) to generate a rotary magnetic field, which rotates the magnetic induction rotor  5  at 750 rpm to generate torque. The generated torque is compared as follows. 
     The results show that the generated torque of the comparative motor is 152 Nm and the generated torque of the motor  1  is 183 Nm which is larger than that of the comparative motor. 
     Compared to simulation results in magnetic field analysis, as shown in  FIG. 5B  and  FIG. 6B , similar magnetic modulation is performed in the comparative motor (see  FIG. 5B ) and the motor  1  (see  FIG. 6B ). There, even if a configuration of the motor  1  in which the magnet rotor  7  is arranged between the armature  3  and the magnetic induction rotor  5 , the flow of magnetic flux is not blocked by the magnet rotor  7 , and then magnetic flux passes through the interpolar soft magnetic materials  13  provided in the magnet rotor  7 , which propagates from the magnetic induction rotor  5  to the armature  3 . This prevents the generated torque from decreasing. 
     As described above, the magnetic induction rotor  5  is provided with the magnetic flux penetration region (interpolar soft magnetic materials  13 ) between the adjacent two permanent magnets  11  in such a way that all of the magnetic induction rotor  5  is not covered by the permanent magnets  11  arranged between the magnetic induction rotor  5  and the armature  3  when magnetic flux is transferred therebetween. Thus, in the motor  1 , magnetic modulation action works, even if the magnet rotor  7  and the magnetic induction rotor  5  are reversely arranged. This can provide performance equivalent to or larger than that of the comparative motor in which the magnetic induction rotor  5  is arranged between the armature  3  and the magnet rotor  7 . 
     In the configuration of the motor  1  according to the present exemplary embodiment, as described above, the magnetic induction rotor  5  is arranged at the most inner diameter side. This can improve mechanical rigidity of the magnetic induction rotor  5  and can improve centrifugal force resistance. 
     In the comparative motor in which the magnetic induction rotor  5  is arranged between the armature  3  and the magnet rotor  7 , the obtained centrifugal force resistance is up to approximately 7000 rpm. In contrast, in the motor  1  described in the first exemplary embodiment, the obtained centrifugal force resistance is up to approximately 15000 rpm more than twice that of the comparative motor. Thus, the motor  1  can be downsized and upgraded more than twice compared to the comparative motor, which is able to produce advantageous effects compared to the comparative motor. 
     Next, a simulation of magnetic field analysis is performed by using four analysis models A, B, C and D with different configurations of the magnet rotor  7 . 
       FIG. 7A  shows the analysis model A with a configuration of the magnet rotor  7  including the ring-like soft magnetic material  12  and the interpolar soft magnetic materials  13  as described in the first exemplary embodiment. 
       FIG. 8A  shows the analysis model B with a configuration of the magnet rotor  7  in which the interpolar soft magnetic materials  13  are omitted and the outer periphery of the permanent magnets  11  is covered by the ring-like soft magnetic material  12 . 
       FIG. 9A  shows the analysis model C with a configuration of the magnet rotor  7  in which both of the ring-like soft magnetic material  12  and the interpolar soft magnetic materials  13  are omitted. 
       FIG. 10A  shows the analysis model D with a configuration of the magnet rotor  7  in which both of the ring-like soft magnetic material  12  and the interpolar soft magnetic materials  13  are not used and there is no magnetic flux penetration portion, i.e., the permanent magnets  11  are circumferentially and tightly arranged with no space. 
       FIGS. 7B ,  8 B,  9 B, and  10 B are magnetic figures showing analysis results of the analysis models A, B, C, and D. In this analysis, the magnetic induction rotor  5  used in the respective analysis models A, B, C, and D has a configuration with only segments  9 , and high-strength aluminum material described in the first exemplary embodiment is not filled. The reason is to expressly examine the effect of existence or non-existence of a space or magnetic material around magnets and effects of being covered by magnets. 
     In the four analysis models A, B, C, and D, the generated torques are compared. As a result, the analysis model A using the ring-like soft magnetic material  12  and the interpolar soft magnetic materials  13  has the best result of the generated torque which is 147 Nm. The generated torque is decreased in order of: (i) the analysis model B using only the ring-like soft magnetic material  12 ; (ii) the analysis model C forming the magnetic flux penetration region without using the soft magnetic material; and (iii) the analysis model D. As is clear from these results, the generated torque of the respective analysis models A, B, and C including the magnet rotor  7  provided with the magnetic flux penetration region are higher than that of the analysis D including the magnet rotor  7  in which the magnetic flux penetration region is not provided. 
     Next, the second to fifth exemplary embodiments are described below. 
     In these embodiments, an arrangement of the armature  3 , the magnet rotor  7 , and the magnetic induction rotor  5  is the same as the first exemplary embodiment, i.e., the magnetic induction rotor  7  is arranged at the most inner diameter side. In the components identical with or similar to those in the first exemplary embodiment are given the same reference numerals for the sake of omitting unnecessary explanation. 
     Second Exemplary Embodiment 
     Referring to  FIGS. 11 ,  12 A and  12 B, the second exemplary embodiment is described. In this embodiment, as shown in  FIG. 11 , a concave portion (recess or hollow portion)  13   a  is formed in the respective interpolar soft magnetic materials  13  of the magnetic induction rotor  5  described in the first exemplary embodiment. 
     As shown in  FIG. 11 , the concave portion  13   a  is formed in a surface of the respective interpolar soft magnetic materials  13  facing the magnetic induction rotor  5 , i.e., an inner diameter face of the interpolar soft magnetic material  13  facing an outer diameter face of the magnetic induction rotor  5  via the gap between the magnet rotor  7  and the magnetic induction rotor  5 . The concave portion  13   a  has a depth of approximately ⅔ of a thickness (i.e., a radial size) of the magnet rotor  7  and is formed into a taper shape in which an circumferential opening width is gradually widened from the deepest portion toward the inner diameter face of the magnet rotor  7 . 
     The magnetic induction rotor  5  is configured by casting the 16 segments  9  in high-strength aluminum material as is the case in the first exemplary embodiment. In the second exemplary embodiment, the segment concave portion  9   c  is also filled with high-strength aluminum material  15 . As shown in  FIG. 11 , this aluminum material  15  is retained (held) in the segment concave portion  9   c  by a retaining section (e.g., catch, locking, or holding section)  9   f  that is configured to project from a side surface of the segment arm section  9   a.    
     Next, a magnetic field analysis of the motor  1  according to the second exemplary embodiment is also performed under the same condition as the first exemplary embodiment.  FIG. 12A  shows a model configuration diagram of an analysis model of the motor  1  according to the present embodiment, and  FIG. 12B  shows a simulation result of the magnetic field analysis for this analysis model. 
     The results show that the generated torque of the motor  1  is 166 Nm which is equivalent to or larger than that of the comparative motor shown in  FIGS. 5A and 5B  which is 152 Nm described in the first exemplary embodiment. 
     According to the present embodiment, the concave portion is formed in the inner diameter face of the respective interpolar soft magnetic materials  13 , which is able to expect an effect of reducing leakage flux between surfaces of the adjacent two permanent magnets  11 . 
     If the interpolar soft magnetic material  13 , which is located between each circumferentially adjacent two permanent magnets  11 , has a surface that is formed so as to be the same as magnetic pole surfaces of the adjacent two permanent magnets  11 , leakage flux increases via the interpolar soft magnetic material  13 . In contrast, the concave portion is formed in the inner diameter face of the respective interpolar soft magnetic materials  13 , which is able to narrow and lengthen a path from which magnetic flux is leaked. This can prevent magnetic flux from being leaked, thereby providing good magnetic induction for the segments  9 . 
     Third Exemplary Embodiment 
     Referring to  FIGS. 13 ,  14 A and  14 B, the third exemplary embodiment is described. In the present embodiment, the magnetic induction rotor  5  is formed into a gear shape. 
     As shown in  FIG. 13 , the magnetic induction rotor  5  is configured by laminating a plurality of electromagnetic steel plates which are cut out in the form of a gear shape, and includes k tooth-shaped portions  5   a  which radially project toward the outside, where k is the number of tooth-shaped portions  5   a . The k tooth-shaped portions  5   a  are circumferentially arranged at regular intervals, which form an entry and exit of magnetic flux for the magnetic path. 
     Next, a magnetic field analysis of the motor  1  according to the third exemplary embodiment is also performed under the same condition as the first exemplary embodiment.  FIG. 14A  shows a model configuration diagram of an analysis model of the motor  1  according to the present embodiment, and  FIG. 14B  shows a simulation result of the magnetic field analysis for this analysis model. As shown in  FIG. 14A , in the analysis model of the motor  1 , aluminum material  14  is filled between the circumferential adjacent two tooth-shaped portions  5   a.    
     The results show that the generated torque of the motor  1  is 137 Nm which is lower than that of the comparative motor, but there is no remarkable difference between the motor  1  and the comparative motor. In this case, the magnetic induction rotor  5  is formed into a gear shape, which allows this rotor  5  itself to also act as a rotor hub. In other words, the k tooth-shaped portions  5   a  are integrally formed of the same material as the rotor hub, which provides a strong structure with respect to centrifugal force and enables the magnetic induction rotor  5  to be very firmly fixed to the first rotary shaft  4 . In addition, the motor  1  has high durability with respect to rotation vibration of the engine E 1  or the like. Compared to the magnetic induction rotor  5  described in the first exemplary, the motor  1  has a potential for downsizing and lightening in view of high resistance to high speed use. 
     Fourth Exemplary Embodiment 
     Referring to  FIGS. 15A and 15B , the fourth exemplary embodiment is described. In the present embodiment, as shown in  FIGS. 15A and 15B , with respect to the magnetic induction rotor  5  which is formed into a gear shape described in the third exemplary embodiment, a shorting coil  16  is provided between the circumferential adjacent two tooth-shaped portions  5   a.    
     Here, in the motor  1  described in the first exemplary embodiment, high-strength aluminum material which forms the rotor hub  10  is filled between the circumferential adjacent two segments  9  (see  FIG. 1 ). This can reduce magnetic leakage between the two segments  9 . 
     As is the case with this, in the motor  1  of the present embodiment, the shorting coil  16  is located between the circumferential adjacent two tooth-shaped portions  5   a , as shown in  FIGS. 15A and 15B . This can also reduce dynamic magnetic leakage between the two tooth-shaped portions  5   a , thereby being able to improve magnetic modulation action. 
     Fifth Exemplary Embodiment 
     Referring to  FIGS. 16A and 16B , the fifth exemplary embodiment is described. In the present embodiment, with respect to the magnetic induction rotor  5  formed in a gear shape described in the third exemplary embodiment, a copper plate  17  is provided between the circumferential adjacent two tooth-shaped portions  5   a , as shown in  FIGS. 16A and 16B . The copper plate  17  is fixed to the magnetic induction rotor  5  by a bolt  18  made of non-magnetic material. 
     As is the case with the fourth exemplary embodiment, a configuration of the fifth exemplary embodiment can also reduce dynamic magnetic leakage between the two tooth-shaped portions  5   a , thereby being able to improve magnetic modulation action. In addition, the copper plate  17  can be easily mounted to the magnetic induction rotor  5 , because it can be fixed by the bolt  18 . 
     (Modifications) 
     In the magnetic induction rotor  5  described in the first exemplary embodiment, the segment concave portion  9   c  is not filled with aluminum material, i.e., a space is formed in the segment concave portion  9   c . However, in this motor  1 , the segment concave portion  9   c  may be filled with aluminum material, as is the case with the second exemplary embodiment. In the case where the segment concave portion  9   c  is filled with aluminum material, in an axial end surface of the magnetic induction rotor  5 , two aluminum materials, where one is aluminum material forming the rotor hub  10  and the other is aluminum material with which the segment concave portion  9   c  is filled, are configured so as not to cross the segments  9  and to magnetically connect with each other. 
     The magnetic induction rotor  5  described in the first exemplary embodiment is configured by a die-casting product which are integrally produced by casting the 16 segments  9  in high-strength aluminum material (e.g., duralumin), but need not be produced by die-casting. For example, this magnetic induction rotor  5  may be configured by annularly connecting the k segments  9  by use of a connecting member such as a stainless steel material (k is the number of segments  9 ). Alternatively, the magnetic induction rotor  5  may be configured by directly fixing the k segments  9  to the first rotary shaft  4  formed of a high-strength non-magnetic stainless steel material by welding or the like. 
     Next, the sixth to ninth exemplary embodiments are described below. 
     In these embodiments, the magnetic modulation motor as described above is applied to an electric transmission mounted in vehicles such as hybrid vehicles. 
     Sixth Exemplary Embodiment 
     Referring to  FIGS. 17 to 20 ,  21 A,  21 B,  22 A,  22 B,  23 A,  23 B,  24 A and  24 B, the sixth exemplary embodiment is described. In the present embodiment, an electric transmission using the magnetic modulation motor described above is applied to a hybrid vehicle. 
     As shown in  FIG. 17 , an electric transmission  101  according to the present embodiment includes: a first rotary machine M 11  having a first rotary shaft  102 ; a second rotary machine M 12  having a second rotary shaft  103 ; a front frame  104  mainly covering an outer periphery of the first rotary machine M 11 ; and a rear frame  105  mainly covering an outer periphery of the second rotary machine M 21 . 
     The first rotary shaft  102  is rotatably supported by the front frame  104  via an one-way clutch  106  also functioning as a bearing. This first rotary shaft  102  has an axial end portion which projects from the front frame  104  toward an axial outside (left side in  FIG. 17 ). As shown in  FIG. 20 , this axial end portion is directly or indirectly connected to a crank shaft (not shown) of an engine E 11 . 
     The one-way clutch  106  is configured by, for example, a well-known roller type clutch and has a function for allowing the first rotary shaft  102  to rotate in only positive rotational direction of the engine E 11  and for preventing it from rotating in the reverse rotational direction thereof. 
     The second rotary shaft  103  is arranged in such a manner that its shaft center is coincident with a shaft center of the first rotary shaft  102 , and is rotatably supported by the rear frame  105  via two bearings  107 . This second rotary shaft  103  has an a axial end portion which projects from the rear frame  105  toward an axial outside (right side in  FIG. 17 ). As shown in  FIG. 20 , this axial end portion is directly or indirectly connected to a propeller shaft  108 . This propeller shaft  108  is connected to a final stage reducer  111  with a differential mechanism for transferring a turning force (torque) to an axle  100  of a driving wheel  109 . 
     In the front frame  104  and the first rotary shaft  102 , a rotation angle sensor  112  is mounted. This rotation angle sensor  112  is configured by, for example, a resolver, and detects a rotation angle position of the first rotary shaft  102 . In the rear frame  105  and the second rotary shaft  103 , a rotation angle sensor  113  is mounted. This rotation angle sensor  113  is configured by, for example, a resolver, detects a rotation angle position of the second rotary shaft  103 . 
     As shown in  FIG. 17 , the first rotary machine M 11  includes: (i) an armature (hereinafter referred to as “first armature  114 ”) which is fixed to the front frame  104 ; (ii) a field element (hereinafter referred to as “a first field element  115 ”) which is rotatably arranged at an inner periphery side of this first armature  114  via a gap; and (iii) a magnetic modulation element  116  which is rotatably arranged at an inner periphery side of this first field element  115  via a gap. The first field element  115  is connected to the first rotary shaft  102  via a first rotor disc  117 . 
     The first rotor disc  117  is made of a non-magnetic metal material (for example, aluminum material) and includes a cylindrical boss section  117   a  at its radial central portion. The cylindrical boss section  117   a  is fixed to an outer periphery of the first rotary shaft  102  by, for example, a serration fitting or a key coupling, and then, integrally rotates together with the first rotary shaft  102 . 
     As shown in  FIG. 17 , the second rotary machine M 12  includes: (i) an armature (hereinafter referred to as “second armature  118 ”) which is fixed to the rear frame  105 ; and (ii) a field element (hereinafter referred to as “second field element  119 ”) which is rotatably arranged relative to this second armature  118  via a gap. The second field element  119  is connected to the second rotary shaft  103  via a second rotor disc  120 . 
     As is the case with the first rotor disc  117 , the second rotor disc  120  is made of a non-magnetic metal material (for example, aluminum) and includes a cylindrical boss section  120   a  at its radial central portion. The cylindrical boss section  120   a  is fixed to an outer periphery of the second rotary shaft  103  by, for example, a serration fitting or a key coupling, and then, integrally rotates together with the second rotary shaft  103 . 
     Next, referring to  FIG. 18 , a configuration of the first rotary machine M 11  is described in detail.  FIG. 18  is partial transverse cross-sectional view of the first rotary machine M 11 , which is perpendicular to a shaft center direction of the first rotary machine M 11 . In the  FIG. 18 , hatching showing the cross-section is omitted. 
     The configuration of the first rotary machine M 11  is based on the magnetic modulation motor as described in the first to fifth exemplary embodiments, for example, the second exemplary embodiment as shown in  FIG. 11 . 
     (Description of First Armature  114 ) 
     The first armature  114  includes an annular armature core  121  and an armature winding  122  (see  FIGS. 17 and 20 ). In the armature core  121 , a plurality of slots  121   s  (72 slots in the sixth exemplary embodiment) are circumferentially formed at regular pitches. The armature winding  122  is wound around the armature core  121  through the slots  121   s.    
     The armature core  121  is configured by laminating a plurality of annular core sheets in which the slots  121   s  are formed by punching an electromagnetic steel plate. 
     The armature winding  122  is configured by a star connection of three-phase windings with m=6 pole pairs, and is connected to a well-known inverter  124  (see  FIGS. 17 and 20 ) via three-phase harnesses  123 . 
     (Description of First Field Element  115 ) 
     The first field element  115  includes: 20 permanent magnets  125  (for example, neodymium magnets) forming poles with n=10 pole pairs; and a soft magnetic material  126  holding the 20 permanent magnets  125 . 
     The 20 permanent magnets  125  are circumferentially arranged at regular intervals and are radially magnetized. Each circumferentially adjacent two poles (permanent magnets  125 ) are magnetized in such a way as to differ from each other in polarity. 
     The soft magnetic material  126  includes a plurality of interpolar soft magnetic materials  126   a  and a ring-like soft magnetic material  126   b . Each of the interpolar soft magnetic materials  126   a  is located between each circumferentially adjacent two permanent magnets  125 . The ring-like soft magnetic material  126   b  covers a first armature side surface of the permanent magnets  125 , and is arranged in all circumferential surface of the first field element  115  facing the first armature  114 . 
     The interpolar soft magnetic materials  126   a  and the ring-like soft magnetic material  126   b  are configured by laminating a plurality of soft magnetic material sheets which are formed into both shapes by punching press of an electromagnetic steel plate. The interpolar soft magnetic materials  126   a  and the ring-like soft magnetic material  126   b  are integrally provided in the present embodiment, but may be separately provided. 
     In each of the interpolar soft magnetic materials  126   a , a concave portion (recess)  126   c  is formed at an inner diameter side facing the magnetic modulation element  116 . The concave portion  126   c  has a depth of approximately ⅔ of a width between an inner diameter face and an outer diameter face (i.e., a size in a radial direction) of the first field element  115  and is formed into a taper shape in which an circumferential opening width is gradually widened from the deepest portion toward the inner diameter face of the first field element  115 . 
     (Description of Magnetic Modulation Element  116 ) 
     The magnetic modulation element  116  includes: 16 (m+n) segment magnetic poles (segments)  127  forming a path of magnetic flux; and a rotor hub  128  holding the 16 segment poles  127 . As shown in  FIG. 17 , this magnetic modulation element  116  is supported by the second rotor disc  120  in such a manner that an outer periphery of a cylindrical support  120   b  integrated with the second rotor disc  120  is fitted in a circular hole  128   a  which opens an inner periphery of the rotor hub  128 . Thus, the magnetic modulation element  116  is connected to the second rotary shaft  103  via the second rotor disc  120 , and then, integrally rotates together with the second rotary shaft  103 . 
     The segment poles  127  are configured by laminating a plurality of segment parts which are formed into an approximate V-shape (see a shape shown in  FIG. 18 ) by punching an electromagnetic steel plate. 
     Hereinafter, two sides of the segment magnetic pole  127  which are opened into a V-shape are referred to “two segment arm sections  127   a ”. A base (root) side of the two segment arm sections  127   a  is referred to “segment base section  127   b ”. A recess (concave portion) formed between the two segment arm sections  127   a  is referred to “segment concave portion  127   c”.    
     The 16 segment poles  127  are annularly arranged in a circumferential direction of the magnetic modulation element  116  at regular intervals. In such an arrangement of the segments  127 , the two segment arm sections  127   a  are open into a V-shape radially outward, i.e., the segment base section  127   b  faces radially inside. In the present embodiment, a dovetail-shaped anchor section  127   d  is formed in the bottom face of the segment base section  127   b . In the side surface of the respective segment arm sections  127   a , a pair of locking parts  127   e  are provided in such a way as to project toward the segment concave portion  127   c.    
     The rotor hub  128  is made of high-strength aluminum material (for example, duralumin) which is a non-magnetic and good electric conductor, and is produced by die-casting in which the 16 segment poles  127  are integrally cast. Thus, the anchor section  127   d , provided in the segment base section  127   b , is buried in aluminum material, and then, each of the segment poles  127  is tightly fixed to the rotor hub  128 . In addition, the segment concave portion  127   c  is filled with the same aluminum material which is locked by the pair of locking parts  127   e  projecting from the side surface of the respective segment arm sections  127   a . This prevents aluminum material from being detached from the segment concave portion  127   c.    
     The 16 segment poles  127 , held by the rotor hub  128 , are magnetically separated from one another by aluminum material filled between the circumferentially adjacent two segment poles  127 . Each of the 16 segment poles  127  is not fully filled in aluminum material. There, an apical face of the respective segment arm sections  127   a  exposes on the outer diameter face of the rotor hub  128 , thereby forming an entry and exit of magnetic flux (magnetic flux entry and exit). 
     Next, referring to  FIG. 19 , a configuration of the second rotary machine M 12  is described in detail.  FIG. 19  is partial transverse cross-sectional view of the second rotary machine M 12 , which is perpendicular to a shaft center direction of the second rotary machine M 12 . In the  FIG. 19 , hatching showing the cross-section is omitted. 
     (Description of Second Armature  118 ) 
     The second armature  118  includes: (i) an outer armature  118 A located at the side of an outer periphery of the second field element  119 ; and (ii) an inner armature  118 B located at the side of an inner periphery of the second field element  119 . Both armatures  118 A and  118 B are integrally formed. 
     The outer and inner armatures  118 A and  118 B are configured by an armature core  129  (made of: (i) an outer armature core  129   a  of the outer armature  118 A; and (ii) an inner armature core  129   b  of the inner armature  118 B) and an armature winding  130  (see  FIG. 17 ). In the armature core  129 , a plurality of outer and inner slots  129   s   1  and  129   s   2  (e.g., 96 outer and inner slots in the present embodiment) are circumferentially formed at regular pitches. The armature winding  130  is wound around the armature core  129  though the outer and inner slots  129   s   1  and  129   s   2 . 
     The armature core  129  is configured by laminating a plurality of annular core sheets in which the outer and inner slots  129   s   1  and  129   s   2  are formed by a punching press of an electromagnetic steel plate. As shown in  FIG. 17 , the outer and inner armature cores  129   a  and  129   b  are linked in the form of an approximately U-shaped cross section and integrally configured. 
     The armature winding  130  is configured by: (i) an outer armature winding  130   a  wound around the outer armature  118 A; and (ii) an inner armature winding  130   b  wound around the inner armature  118 B. Each of the outer and inner armature windings  130   a  and  130   b  is configured by a star connection of three-phase windings which are wounded in the form of a distributed winding with a predetermined winding pitch satisfying the following conditions: (i) the number of slots per pole per phase is q=2; and (ii) the number of poles is 16 (i.e., the number of pole pairs is 8). 
     The outer and inner armature windings  130   a  and  130   b  are connected in series to each other every phase winding of the three-phase windings, and are connected to an inverter  132  (see  FIGS. 17 and 20 ) via three-phase harnesses  131 . 
     The outer and inner armature windings  130   a  and  130   b  produce a winding magnetomotive force in such a manner that their poles, which are radially facing each other via the second field element  119 , have the same polarity in the same circumferential position. 
     (Description of Second Field Element  119 ) 
     The second field element  119  includes: (i) a plurality of segment magnetic poles  133  (16 segment magnetic poles  133  in the present embodiment) which are circumferentially arranged at regular intervals; and (ii) a plurality of permanent magnets (hereinafter referred to as “interpolar magnets  134 ”) which are located between the circumferential adjacent two segment magnetic poles  133 . In the inner and outer surfaces of the respective segment magnetic poles  133 , a magnetic field concave portion is formed as described below. 
     The 16 segment magnetic poles  133  are configured by laminating a plurality of annular segment sheets which are formed by punching an electromagnetic steel plate. For example, each of the 16 segment magnetic poles  133  are fastened to one another in a laminated direction by a fasting pin  135  made of soft magnetic material. 
     In the 16 segment magnetic poles  133 , the circumferential adjacent two segment magnetic poles  133  are annularly and contiguously connected by an outer interpolar bridge  136  and an inner interpolar bridge  137 . Specifically, in the circumferential adjacent two segment magnetic poles  133 , the most outer diameter face and the most inner diameter face are annularly and contiguously connected. 
     Hereinafter, one of the circumferential adjacent two segment magnetic poles  133  is referred to as a “first segment magnetic pole  133   a ”, and the other is referred to as a “second segment magnetic pole  133   b ”. In the first and second segment magnetic poles  133   a  and  133   b , their opposed faces circumferentially facing each other are referred to as “interpolar opposed faces  138 ”. Between the outer and inner interpolar bridges  136  and  137 , an interpolar space is formed so as to open between the interpolar opposed faces  138  of the first and second segment magnetic poles  133   a.    
     The interpolar magnets  134  are inserted in the interpolar space described above, and are magnetized in a circumferential direction indicated by arrows of  FIG. 19 . Specifically, the circumferential adjacent first and second segment magnetic poles  133   a  and  133   b  are magnetized in such a manner that their magnetic poles, which circumferentially face each other, differ from each other in polarity. 
     The interpolar magnets  134  are formed into such a shape that a radial width at the contact side of the second segment magnetic pole  133   b  is smaller than a radial width at the contact side of the first segment magnetic pole  133   a , i.e., a so called arrowhead shape. Due to this, between the interpolar magnet  134  and the outer interpolar bridge  136  and between the interpolar magnet  134  and the inner interpolar bridges  137 , a cavity portion  139  is formed at a rear side with respect to a rotational direction (counterclockwise direction indicated by arrows of  FIG. 19 ) of the second field element  119 . 
     In the circumferential central portion of the respective segment magnetic poles  133 , an outer and inner magnetic field concave portions are formed at their radial outer and inner peripheries. 
     The outer magnetic field concave portion are formed by: (i) an outer slit  140  which is formed in the segment magnetic pole  133 ; and (ii) a permanent magnet (hereinafter referred to as an “outer pole center magnet  141 ”) which is inserted in the outer slit  140 . The outer slit  140  is formed so as to be close to the most outer diameter side of the segment magnetic pole  133 . The outer diameter side of the outer slit  140  is closed by an outer pole center bridge  142 . The outer pole center magnet  141  is inserted in the outer slit  140 , and is magnetized in a radial direction indicated by arrows in  FIG. 19 . Specifically, the circumferential adjacent outer pole center magnets  141  are magnetized in such a way as to differ from each other in polarity. 
     The inner magnetic field concave portion are formed by: (i) an inner slit  143  which is formed in the segment magnetic pole  133 ; and (ii) a permanent magnet (hereinafter referred to as an “inner pole center magnet  144 ”) which is inserted in the inner slit  143 . The inner slit  143  is formed in such a way as to be close to the most inner diameter side of the segment magnetic pole  133 . The inner diameter side of the inner slit  143  is closed by an inner pole center bridge  145 . The inner pole center magnet  144  is inserted in the inner slit  143 , and is magnetized in a radial direction indicated by arrows of  FIG. 19 . Specifically, the circumferential adjacent inner pole center magnets  144  are magnetized in such a way as to differ from each other in polarity. The outer and inner pole center magnets  141  and  144  are magnetized in such a manner that their magnetic poles, which radially face each other, have the same polarity. 
     Next, referring to  FIG. 17 , features related to an overall configuration of the electric transmission  101  are described below. In the following explanation, a left side of an axial direction (left-right direction shown in  FIG. 17 ) is referred to as a “front side”, and a right side of the axial direction is referred to as a “rear side”. 
     In the first and second rotary machines M 11  and M 12 , the magnetic modulation element  116  of the first rotary machine M 11  and the second field element  119  of the second rotary machine M 12  are mechanically coupled to each other via the second rotor disc  120 . The magnetic modulation element  116  and the second field element  119  are configured so as to integrally rotate with the second rotary shaft  103 . 
     The first and second rotary shafts  102  and  103  are located in such a manner that an opposite central position between first and second rotary shafts  102  and  103  axially facing each other via a gap is displaced to the front side. In other words, the opposite central position between the first and second rotary shafts  102  and  103  is shifted toward the front side from an axially intermediate position (hereinafter referred to as an “axially central position”) between the first and second rotary machines M 11  and M 12 . In the case of  FIG. 17 , a front side end surface of the second rotary shaft  102  extends beyond the axially central position, and then reaches up to the inner periphery side of the first rotary machine M 11 . 
     Thus, the second rotor disc  120  can allow the cylindrical boss section  120   a , which is fitted in the second rotary shaft  103 , to be located at a position (axially central position) between the first and second rotary machines M 11  and M 12 . 
     In addition, (i) the first field element  115  of the first rotary machine M 11  and (ii) two rotors (the magnetic modulation element  116  and the second field element  119 ) connected to each other via the second rotor disc  120 , are supported in a relatively rotatable manner via a bearing  146  which is located at approximately axially intermediate position (axially central position) between both two rotors. Specifically, the first field element  115  is provided with an annular inner support section  147  at the axial rear side (right side of  FIG. 17 ). The second rotor disc  120  is integrally provided with an annular outer support section  148 . The inner and outer support sections  147  and  148  are located so as to axially wrap. The bearing  146  described above is located between the inner and outer support sections  147  and  148 . Though this bearing  146 , the first field element  115  of the first rotary machine M 11  and the two rotors (the magnetic modulation element  116  and the second field element  119 ) connected to each other are supported in a relatively rotatable manner. 
     In the present embodiment, the first field element  115  may be provided with the outer support section  148 , and the second rotor disc  120  may be provided with the inner support section  147 . 
     The two bearings  107 , which support the second rotary shaft  103  with respect to the rear frame  105 , are spaced at a predetermined distance. Hereinafter, one of the two bearings  107  which is located at the front side (left side of  FIG. 17 ) is referred to as a “first rear bearing  107   a ”, and the other which is located at the rear side (right side of  FIG. 17 ) is referred to as a “second rear bearing  107   b ”. The first rear bearing  107   a  is located in such a way as to be close to the axially central position at the inner diameter side away from the bearing  146  described above. Specifically, the first rear bearing  107   a  is located adjacent to the rear side of the cylindrical boss section  117   a  of the second rotor disc  120  in which the second rotary shaft is fitted. 
     The front and rear frames  104  and  105  are combined by an axial spigot-joint of their opening portions. Inside the front and rear frames  104  and  105 , the first and second rotary machines M 11  and M 12  are integrally contained. Outside (anti-front side) the rear frame  105 , a mounting space capable of mounting the inverters  124  and  132  described above is ensured. 
     The inverter  124  is mounted in the mounting space described above, and is connected to the armature winding  122  of the first armature  114  via the three-phase harnesses  123 . The inverter  132  is mounted in the mounting space described above, and is connected to the armature winding  130  of the second armature  118  via the three-phase harnesses  131 . 
     The front frame  104  is provided with a harness protector  104   a  that protects the three-phase harnesses  123  which are externally extracted from the front frame  104 . The rear frame  105  is provided with a harness protector  105   a  that protects the three-phase harnesses  131  which are externally extracted from the rear frame  105 . 
     In the final end (right end of  FIG. 17 ) of the rear frame  105 , a rear cover  149  is assembled. The rear cover  149  covers a rear side end surface of the inverters  124  and  132  mounted in the mounting space described above, and closes the opening side of this mounting space. 
     As shown in  FIG. 20 , the inverters  124  and  132  have DC (direct current) terminals which are connected to a vehicle battery  150  which is a DC power supply, and are activated upon reception of control signals from a powertrain integrated ECU (electronic control unit)  151 . 
     As shown in  FIG. 20 , the powertrain integrated ECU  151  receives information, for example, (a) a vehicle state signal including a steering angle signal, an acceleration position signal, a brake signal, a shift position signal, (b) an engine state signal for informing engine state such as start and stop of the engine E 11 , and (c) a detected signal of the respective rotation angle sensors  112  and  113 . And then, based on these information, the ECU  151  controls operation of the respective invertors  124  and  132 . 
     Next, referring to  FIGS. 21A ,  21 B,  22 A,  22 B,  23 A,  23 B,  24 A and  24 B, operation of the electric transmission  101  is described. 
     a) Engine Start Mode 
     In an engine start mode, the engine E 11  is started. This operation is described with reference to  FIGS. 21A and 21B . 
     First, the first field element  114 , which is connected to the first rotary shaft  102 , is static, i.e., the engine E 11  is stopped. Under this condition, as shown in  FIG. 21A , a rotating magnetic field directed to an opposite direction of a rotational direction of the engine E 11  is generated in the armature winding  122  of the first armature  114 . Then, the magnetic modulation element  116  of the first rotary machine M 11  tries to rotate in the opposite direction (the same direction as the rotating magnetic field). At this time, when the operation of the inverter  132  is controlled so as to short-circuit the armature winding  130  of the second armature  118 , the second field element  119  of the second rotary machine M 12  is braked. This restricts a reverse rotation of the magnetic modulation element  116  connected to this the second field element  119  (see a sign “x” shown in  FIGS. 22A and 22B ). Along with this, a torque directed to a positive rotational direction as shown in arrows of  FIG. 22B , i.e., the rotational direction of the engine E 11  is generated in the first field element  115  of the first rotary machine M 11 , and then, the engine E 11  is started. In this way, the second rotary machine M 12  also assists the engine E  11  to start. 
     b) Engine Acceleration and Axle Activation Mode 
     In an engine acceleration and axle activation mode, the engine E 11  is accelerated to activate an axle side, thereby starting and accelerating the vehicle. This operation is described with reference to  FIGS. 22A and 22B . 
     In this operation, as an engine speed is increased, a rotational velocity of the first field element  115  is increased. Subsequently, the magnetic modulation element  116 , which is connected to the second rotary shaft  103  located at the axle side, receives reaction force due to vehicle inertial resistance or the like. Thus, the rotating magnetic field of the first armature  114  is directed to a reverse rotation, as shown in  FIG. 22A . In this state, the first armature  114  generates electric power to provide its reaction force. Then, the magnetic modulation element  116  receives rotational torque due to the reaction force of power generation and the drive force of the engine E 11 , and increases the rotational velocity, as shown in  FIG. 22A . In addition, the AC power generated by the first rotary machine M 11  is transferred to the inverter  132  for driving the second rotary machine M 12 . Thus, the second rotary machine M 12  receives the AC power supplied from the inverter  132 , and electrically drives the second field element  119 . 
     In this way, the second rotary shaft  103  receives the power generation reaction force and the engine drive force via the magnetic modulation element  116 , and also receives the electric drive force via the second field element  119  by using the power generated by the first rotary machine M 11  to drive the second rotary machine M 12  thorough the inverter  132 . There, the second rotary shaft  103  is driven by three types of torque. In the engine acceleration and axle activation mode, the second rotary machine M 12  can regenerate drive force of the propeller shaft  108  from the power generated by the first rotary machine M  11 , as shown in  FIG. 22A . This can achieve a function of the electric transmission that efficiently performs torque and velocity conversion that converts the engine power to the drive force of the propeller shaft  108 , without using the power of the vehicle battery  150 . 
     When the engine speed reaches a predetermined high engine speed, the magnetic modulation element  116  cannot be started by the power generation reaction force. In this case, it is possible to increase a rotation of the magnetic modulation element  116 , i.e., a rotation of the second rotary shaft  103  by energizing the first armature  114  to generate torque (electric drive power). This consumes the power from the battery  150  and results in a vehicle driving method similar to an EV (electric vehicle). 
     c) EV Drive Mode 
     In an EV drive mode, the engine E 11  is stopped, and the vehicle is driven by only the motor. This operation is described with reference to  FIGS. 23A and 23B . 
     The first rotary machine M 11  is accelerated by supplying the first armature  114  with electric power while receiving a rotational resistance of the magnetic modulation element  116  which is connected to the second rotary shaft  103  located at the axle side. Then, a torque, which tries to reversely rotate, acts on the first field element  115  connected to the first rotary machine  102 . At this time, as shown in  FIGS. 23A and 23B , the one-way clutch  106  prevents the first field element  115  from reversely rotating, and then, its magnetic torque reaction force is produced in the magnetic modulation element  116 . There, an axle drive torque is produced. 
     In this way, due to the presence of the one-way clutch  106  that prevents the reverse rotation of the first rotary shaft  102 , the first rotary machine M 11  can also electrically operate as well as the second rotary machine M 12 , as shown in  FIG. 23B . This can downsize the first rotary machine M 11  as well as the second rotary machine M 12 . 
     d) Vehicle Regenerative Control Mode 
     In a vehicle regenerative control mode, the running vehicle is decelerated and a regenerative braking is produced. This operation is described with reference to  FIGS. 24A and 24B . 
     In this mode, in order to efficiently charge the vehicle battery  150  with braking energy as much as possible, the operation of the inverter  124  is stopped and the energization of the first armature  114  is turned off (as shown in a sign “X” of  FIGS. 24A and 24B ). Then, as shown in  FIG. 24B , a rotation of the axle causes a rotation of the magnetic modulation element  116 , but the magnetic connection with the first magnetic element  115  is discontinued, thereby preventing the braking energy from being given to a rotation or the engine E 11 . Thus, when the regenerative braking works, the first rotary machine M 11  can function as a power cutoff clutch. As a result, the vehicle battery  150  can be efficiently charged with regenerative braking energy, as shown in  FIG. 24B . 
     (Effects of Sixth Exemplary Embodiment) 
     According to the first rotary machine M 11  of the sixth exemplary embodiment, the magnetic modulation element  116  is not located between the first armature  114  and the first field element  115 , and can be located at the opposite side (the most inner diameter side of the first rotary machine M 11  in the present embodiment) of the first armature  114  with respect to the first field element  115 . Thus, magnetic flux passing though the magnetic modulation element  116  forms a flow that U-turns around the segment poles  127  formed into the approximate V-shape, without interlinkage with the rotor hub  128  holding the segment poles  127 . This causes no generation of large loop eddy current, even if the 16 segment poles  127  are casted in high-strength aluminum material. In other words, the 16 segment poles  127  can be reliably and easily supported and fixed by the high-strength aluminum material. This makes it possible to improve mechanical rigidity of the magnetic modulation element  116 , which can improve vibration resistance and centrifugal force resistance of the magnetic modulation element  116 . This enables the magnetic modulation element  116  to be tailored to high rotation and high torque specification. 
     In the two rotors (the first field element  115  and the magnetic modulation element  116 ) of the first rotary machine M 11  and the second field element  119  which is the rotor of the second rotary machine M 12 , two rotor (the magnetic modulation element  116  and the second field element  119 ), which are connected to each other, and the first field element  115  are supported in a relatively rotatable manner via the bearing  146  which is inserted between (i) the inner support section  147  located at the axial rear side of the first field element  115  and (ii) the outer support section  148  provided in the second rotor disc  120 . The second rotor disc  120  extends toward the inner diameter side from the bearing  146 , and is fixed in such a manner that the cylindrical boss section  117   a , which is located at its radially central portion, is fitted in the outer periphery of the second rotary shaft  103 . 
     The second rotary shaft  103  is rotatably supported by the rear frame  107  via the two bearings  107  (the first rear bearing  107   a  and the second rear bearing  107   b ) axially spaced at a predetermined axial distance. Specifically, the first rear bearing  107   a  is located adjacent to the rear side of the cylindrical boss section  117   a  of the second rotor disc  120  in which the second rotary shaft  103  is fitted. This can improve rigidity of the magnetic modulation element  116  and the second field element  119 , thereby being able to provide a durable structure. 
     The first field element  115  of the rotary machine M 11  has (i) an axial front side which is connected to the first rotary shaft  102  via the first rotor disc  117 , and (ii) an axial rear which is supported by the second rotor disc  120  via the bearing  146  described above. Therefore, both axial ends of the first field element  115  are supported. Such a structure of the first field element  115  are referred to as a “both ends supported structure”. This structure can improve also vibration resistance of the first field element  115 . 
     Thus, it is possible to improve accuracy of the shaft center of the electric transmission  101  in which the first and second rotary machines M 11  and M 12  are integrally provided, and to improve durability thereof, thereby being able to respond to high speed. 
     Further, a body of the first and second rotary machines M 11  and M 12  used for the electric transmission  101  of the sixth exemplary embodiment is determined by a condition that can supply an output necessary for the EV drive mode in which the engine E 11  does not operate and the vehicle is driven by only the vehicle battery  150 . In this EV drive mode, the second rotary machine M 12  produces electric torque. At this time, in the first rotary machine M 11 , the reverse rotation of the first rotary shaft  102  is restricted by the one-way clutch  106  and the first armature  114  is energized. This can make it possible to electrically drive the magnetic modulation element  116  which is connected to the second field element  119  via the rotor that is not connected to the first rotary shaft  102 , i.e., the second rotor disc  120 . In this way, necessary integrated torque can be produced in cooperation with the two rotors (the first and second rotary machines M 11  and M 12 ). This makes it possible to downsize the first and second rotary machines M 11  and M 12 , thereby being able to provide a compact electric transmission  101 . 
     In the electric transmission  101  according to the sixth exemplary embodiment, the front and rear frames  104  and  105  are combined by an axial spigot-joint of their opening portions. Inside these frames  104  and  105 , the first and second rotary machines M 11  and M 12  are integrally contained. This structure makes it possible to reduce the number of components and to shorten the three-phase harnesses  123  and  131 , compared to a structure in which the first and second rotary machines M 11  and M 12  are separately contained in separate frames. This can further promote downsizing of the entire electric transmission. 
     In the rear frame  105 , a mounting space capable of mounting the two inverters  124  and  132  is ensured. Therefore, these inverters  124  and  132  need not to be located outside the electric transmission  101 , and then, can be integrally mounted in the mounting space ensured in the rear frame  105 . In the case where these inverters  124  and  132  are located outside the electric transmission  101 , many harnesses are needed to connect the first and second rotary machine M 11 , M 12  and these inverters  124  and  132  located outside. In the present embodiment, such many harnesses can be shortened and reduced. In this case, only DC (direct current) lines is needed as power harnesses. As a result, effects of wiring reduction are expected, and there is no need to design the surrounding area of connectors in order to extract harnesses from the first and second rotary machine M 11  and M 12 , thereby being able to contribute downsizing and simplification of the electric transmission  101 . 
     Seventh Exemplary Embodiment 
     Referring to  FIG. 25 , the seventh exemplary embodiment is described. In the present embodiment, the components identical with or similar to those in the sixth exemplary embodiment are given the same reference numerals for the sake of omitting unnecessary explanation. 
     As shown in  FIG. 25 , in the electric transmission  101  of the present embodiment, the magnetic modulation element  116  of the first rotary machine M 11  is coupled to the first rotary shaft  102  via the first rotor disc  117 . The first field element  115  and the second field element  119  of the second rotary machine M 12  are mechanically coupled to each other via the second rotor disc  120 . 
     The first field element  115  is supported at the axial front side (left side of  FIG. 25 ) through a bearing  152  in a rotatable manner with respect to the front frame  104 . 
     According to a relationship of the number of poles based on the principle of magnetic modulation, the number of pole pairs of the first field element  115  is smaller than the number of segment poles  127  of the magnetic modulation element  116 . In the case of the sixth exemplary embodiment, the number of pole pairs of the first field element  115  is n=10, and the number of segment poles  127  of the magnetic modulation element  116  is 16. 
     In the case of the present embodiment, a rotating speed of the first field element  115  is higher than the engine speed, compared to the case of sixth exemplary embodiment in which the first field element  115  is coupled to the first rotary shaft  102 . Therefore, the first and second field elements  115  and  119  coupled to each other via the second rotor disc  120  rotate at a speed higher than the engine speed. This enables the second rotary machine M 12  to be tailored to high speed and to be downsized. In addition, due to a relationship that a rotating speed of the propeller shaft  108  is higher than a rotating speed of the engine E 11 , the engine speed can be reduced during high speed driving using engine power, thereby resulting in fuel saving. 
     (Modifications) 
     In the sixth and seventh exemplary embodiments, the second rotary machine M 12  is configured by: (i) the outer armature  118 A in which the second armature  118  is located at the outer periphery of the second field element  119 ; and (ii) the inner armature  118 B located at the inner periphery of the second field element  119 . This structure is a so called motor structure with a double face gap (two face gap) that forms a gap at the respective inner and outer peripheries of the second field element  119 . In the exemplary embodiments described above, this motor structure with two-face gap is applied. In modifications of the embodiments described above, so called a motor structure with a triple face gap (three face gap) may be applied to the present disclosure. In this motor structure, another gap is further formed with the second armature  118 , at the axial rear side of the second field element  119 . 
     In another modifications, an ordinary used motor structure with a single face gap (one face gap) may be also applied to the present disclosure. In this motor structure, a redundant space can be formed inside of the second rotary machine M 12 . In this case, bearings and resolvers can be located in the redundant space. Due to such an effective use of space, a mounting space for the inverter can be largely ensured. 
     In the second armature  118  of the sixth exemplary embodiment, the outer and inner armatures  118 A and  118 B are integrally configured. Specifically, the armature core  129   a  of the outer armature  118 A and the armature core  129   b  of the inner armature  118 B are linked in the form of an approximately U-shaped cross section and integrally configured. Alternately, the armature cores  129   a  and  129   b  may be separately provided. In this case, the following features are the same as the sixth exemplary embodiment. The outer armature winding  130   a  wound around the outer armature  118 A the inner armature winding  130   b  wound around the inner armature  118 B are connected in series to each other every phase winding of the three-phase windings. The outer and inner armature windings  130   a  and  130   b  produce a winding magnetomotive force in such a manner that their poles, which are radially facing each other, have the same polarity in the same circumferential position. 
     In the sixth exemplary embodiment, the magnetic modulation element  116  is configured by a die-cast product which is integrally produced by casting the 16 segment poles  127  in high-strength aluminum material. However, there is no need to produce the magnetic modulation element  116  by die-casting. For example, the magnetic modulation element  116  may be formed by annularly connecting the 16 segment poles  127  by use of a connecting member, for example, non-magnetic mechanical structural member such as stainless steel. 
     In the configuration of the seventh exemplary embodiment, the magnetic modulation element  116  may be configured by: (i) forming the first rotary shaft  102  by use of high-strength non-magnetic stainless steel; and (ii) directly fixing the 16 segment poles  127  to the first rotary shaft  102  by welding or the like. 
     Eighth Exemplary Embodiment 
     Referring to  FIGS. 26 to 31 ,  32 A,  32 B,  33 A,  33 B,  34 A,  34 B,  35 A and  35 B, the eighth exemplary embodiment is described. In the present embodiment, an electric transmission using the magnetic modulation motor described above is applied to a hybrid vehicle. 
     As shown in  FIG. 26 , an electric transmission  201  according to the present embodiment includes: a first rotary machine M 21  having a first rotary shaft  202 ; a second rotary machine M 22  having a second rotary shaft  203 ; a front frame  204  mainly covering an outer periphery of the first rotary machine M 21 ; and a rear frame  205  mainly covering an outer periphery of the second rotary machine M 22 . 
     The first rotary shaft  202  is rotatably supported by the front frame  204  via an one-way clutch  206  also functioning as a first bearing. This first rotary shaft  202  has an axial end portion which projects from the front frame  204  toward an axial outside (left side in  FIG. 26 ). As shown in  FIG. 31 , this axial end portion is directly or indirectly connected to a crank shaft (not shown) of an engine E 21 . 
     The one-way clutch  206  is configured by, for example, a well-known roller type clutch and has a function for allowing the first rotary shaft  202  to rotate in only a positive rotational direction of the engine E 21  and for preventing it from rotating in the reverse rotational direction thereof. 
     In the first rotary shaft  202 , a rotation angle sensor  207  is mounted. This rotation angle sensor  207  is configured by, for example, a resolver, and detects a rotation angle position of the first rotary shaft  202 . 
     The second rotary shaft  203  is arranged in such a manner that its shaft center is coincident with a shaft center of the first rotary shaft  202 , and is rotatably supported by the rear frame  205  via two bearings (second bearing)  208 . This second rotary shaft  203  has an a axial end portion which projects from the rear frame  205  toward an axial outside (right side in  FIG. 26 ). As shown in  FIG. 31 , this axial end portion is directly or indirectly connected to a propeller shaft  209 . This propeller shaft  209  is connected to a final stage reducer  212  with a differential mechanism for transferring a turning force (torque) to an axle  211  of a driving wheel  210 . 
     As shown in  FIG. 26 , the first rotary machine M 21  includes: (i) an armature (hereinafter referred to as “first armature  213 ”) which is fixed to the front frame  204 ; (ii) a field element  214  which is rotatably arranged at an inner periphery side of this first armature  213  via a gap; and (iii) a magnetic modulation element  215  which is rotatably arranged at an inner periphery side of this first field element  214  via a gap. The first field element  214  is connected to the first rotary shaft  202  via a first rotor disc  216 . 
     The first rotor disc  216  is made of a non-magnetic metal material (for example, aluminum material) and includes a cylindrical boss section  216   a  at its radial central portion. The cylindrical boss section  216   a  is fixed to an outer periphery of the first rotary shaft  202  by, for example, a serration fitting or a key coupling, and then, integrally rotates together with the first rotary shaft  202 . 
     As shown in  FIG. 26 , the second rotary machine M 22  is configured by an induction motor that includes: (i) an armature (hereinafter referred to as “second armature  217 ”) which is fixed to the rear frame  205 ; and (ii) a squirrel-cage rotor (hereinafter referred to as “second rotor  119 ”) which is rotatably arranged relative to this second armature  118  via a gap. The second rotor  119  is connected to the second rotary shaft  203  via a second rotor disc  219 . 
     As is the case with the first rotor disc  216 , the second rotor disc  216  is made of a non-magnetic metal material (for example, aluminum material) and includes a cylindrical boss section  219   a  at its radial central portion. The cylindrical boss section  219   a  is fixed to an outer periphery of the second rotary shaft  203  by, for example, a serration fitting or a key coupling, and then, integrally rotates together with the second rotary shaft  203 . 
     Next, referring to  FIGS. 26 to 28 , a configuration of the first rotary machine M 21  is described in detail.  FIG. 28  is a partial transverse cross-sectional view of the first rotary machine M 21 , which is perpendicular to a shaft center direction of the first rotary machine M 21 . In  FIG. 28 , hatching showing the cross-section is omitted. 
     The configuration of the first rotary machine M 21  is based on the magnetic modulation motor as described in the first to fifth exemplary embodiments, for example, the second exemplary embodiment as shown in  FIG. 11 . 
     (Description of First Armature) 
     The first armature  213  includes an annular armature core  220  and an armature winding  220  with m=6 pole pairs (see  FIG. 28 ). In the armature core  220 , a plurality of slots  220   a  (72 slots in the eighth exemplary embodiment) are circumferentially formed at regular pitches. The armature winding  220  is wound around the armature core  220  through the slots  220   a.    
     The armature core  220  is configured by laminating a plurality of annular core sheets in which the slots  220   a  are formed by punching an electromagnetic steel plate. 
     As shown in  FIG. 27 , the armature winding  221  is configured by a star connection of three-phase windings (hereinafter referred to as “first three-phase windings X1, Y1, Z1”) in which a phase of each is set at 120° apart from each other. 
     (Description of Field Element  214 ) 
     As shown in  FIG. 27 , the field element  214  includes: 20 permanent magnets  222  (for example, neodymium magnets) forming poles with n=10 pole pairs; and a soft magnetic material  223  holding the 20 permanent magnets  222 . 
     The 20 permanent magnets  222  are circumferentially arranged at regular intervals and are radially magnetized. The circumferential adjacent two poles (permanent magnets  125 ) are magnetized in such a way as to differ from each other in polarity. 
     The soft magnetic material  223  includes a plurality of interpolar soft magnetic materials  223   a  and a ring-like soft magnetic material  223   b . Each of the interpolar soft magnetic materials  223   a  is located between each circumferentially adjacent two permanent magnets  222 . The ring-like soft magnetic material  223   b  covers a first armature side surface of the permanent magnets  213 , and is arranged completely around the circumferential surface of the field element  214  facing the first armature  213 . 
     The interpolar soft magnetic materials  223   a  and the ring-like soft magnetic material  223   b  are configured by laminating a plurality of soft magnetic material sheets which are formed into both shapes by punching press of an electromagnetic steel plate. The interpolar soft magnetic materials  223   a  and the ring-like soft magnetic material  223   b  are integrally provided in the present embodiment, but may be separately provided. 
     In each of the interpolar soft magnetic materials  223   a , a concave portion (recess)  223   c  is formed at an inner diameter side facing the magnetic modulation element  215 . The concave portion  223   c  has a depth of approximately ⅔ of a width between an inner diameter face and an outer diameter face (i.e., a radial size) of the field element  214  and is formed into a taper shape in which an circumferential opening width is gradually widened from the deepest portion toward the inner diameter face of the field element  214 . 
     (Description of Magnetic Modulation Element  215 ) 
     The magnetic modulation element  215  includes: 16 (m+n) segment poles (segments)  224  forming a path of magnetic flux; and a rotor hub (metal member)  225  holding the 16 segment poles  224 . As shown in  FIG. 26 , this magnetic modulation element  215  is supported by the second rotor disc  219  in such a manner that an outer periphery of a cylindrical support  219   b  integrated with the second rotor disc  219  is fitted in a circular hole  225   a  (see  FIG. 28 ) which is located at an inner periphery of the rotor hub  225 . Thus, the magnetic modulation element  215  is connected to the second rotary shaft  203  via the second rotor disc  219 , and then, integrally rotates together with the second rotary shaft  203 . 
     The segment poles  224  are configured by laminating a plurality of segment parts formed into an approximate V-shape (see a shape shown in  FIG. 28 ) by punching an electromagnetic steel plate. 
     Hereinafter, two sides of the segment magnetic pole  224  which are opened into a V-shape are referred to as “two segment arm sections  224   a ”. A base (root) side of the two segment arm sections  127   a  is referred to as “segment base section  224   b ”. A recess (concave portion) formed between the two segment arm sections  224   a  is referred to as “segment concave portion  224   c”.    
     The 16 segment poles  224  are annularly arranged in a circumferential direction of the magnetic modulation element  215  at regular intervals. In such an arrangement of the segment poles  224 , the two segment arm sections  224   a  are open into a V-shape radially outward, i.e., the segment base section  224   b  faces radially inside. In the present embodiment, a dovetail-shaped anchor section  224   d  is formed in the bottom face of the segment base section  224   b . In the side surface of the respective segment arm sections  224   a , a pair of locking parts  224   e  are provided in such a way as to project toward the segment concave portion  224   c.    
     The rotor hub  225  is made of high-strength aluminum material (for example, duralumin) which is a non-magnetic and good electric conductor, and is produced by die-casting in which the 16 segment poles  224  are integrally cast. Thus, the anchor section  224   d , provided in the segment base section  224   b , is buried in aluminum material, and then, each of the segment poles  224  is tightly fixed to the rotor hub  225 . In addition, the segment concave portion  224   c  is filled with the same aluminum material which is locked by the pair of locking parts  224   e  projecting from the side surface of the respective segment arm sections  224   a . This prevents aluminum material from being detached from the segment concave portion  224   c.    
     The 16 segment poles  224 , held by the rotor hub  225 , are magnetically separated from one another by aluminum material filled between the circumferentially adjacent two segment poles  224 . Each of the 16 segment poles  224  is not fully filled in aluminum material. Therefore, an apical face of the respective segment arm sections  224   a  exposes on the outer diameter face of the rotor hub  225 , thereby forming an entry and exit of magnetic flux (magnetic flux entry and exit). 
     Next, referring to  FIGS. 26 ,  27 ,  29  and  30 , a configuration of the second rotary machine M 22  is described in detail.  FIG. 29  is partial transverse cross-sectional view of the second rotary machine M 22 , which is perpendicular to a shaft center direction of the second rotary machine M 22 . In the  FIG. 29 , hatching showing the cross-section is omitted. 
     (Description of Second Armature  217 ) 
     As shown in  FIG. 29 , the second armature  217  includes an outer armature core  226 , an inner armature core  227 , and an armature winding  228  (see  FIG. 26 ) The outer armature core  226  is located at the side of the outer periphery of the second rotor  218 . The inner armature core  227  is located at the side of the inner periphery of the second rotor  218 . The armature winding  228  is wound the outer and inner armature cores  226  and  227  through a plurality of outer and inner slots  226   a  and  227   a  (e.g., 96 outer and inner slots in the present embodiment) which are circumferentially formed in the outer and inner armature cores  226  and  227  at regular pitches. The number of the outer slots  226   a  is the same as that of the inner slots  227   a  (in the present embodiment, 96 outer slots  226   a  are formed in the outer and inner armature cores  226 , and  96  inner slots  227   a  are formed in the inner armature cores  227 ). 
     The outer and inner armature cores  226  and  227  are configured by laminating a plurality of annular core sheets in which the outer and inner slots  226   a  and  227   a  are formed by a punching press of an electromagnetic steel plate. The outer and inner armature core  226   a  and  227   a  are mechanically connected to each other at the axial rear side (right side of  FIG. 26 ). 
     As shown in  FIG. 27 , the armature winding  228  includes three-phase windings (hereinafter referred to as “second three-phase windings X2, Y2, Z2”) in which a phase of each is set at 120° apart from each other. The second three-phase windings X2, Y2, Z2 are wound around the outer and inner armature cores  226  and  227  in the form of a distributed winding with a predetermined winding pitch satisfying the following conditions: (i) the number of slots per pole per phase is q=2; and (ii) the number of poles is 16 (i.e., the number of pole pairs is 8). 
     The second three-phase windings X2, Y2, Z2 are connected to the first three-phase windings X1, Y1, Z1 configuring the armature winding  221  of the first armature  213  in such a manner that their phase sequence is a negative sequence. 
     Here, (i) three-phase connection points, at which the first and second three-phase windings X1, Y1, Z1 and X2, Y2, Z2 are connected to each other, are referred to as “three-phase connection points x0, y0, z0”, (ii) three-phase terminals opposite to the three-phase connection points x0, y0, z0 of the first three-phase windings X1, Y1, Z1 are referred to as “first three-phase terminals”, and (iii) three-phase terminals opposite to the three-phase connection points x0, y0, z0 of the second three-phase windings X2, Y2, Z2 are referred to as “second three-phase terminals”. The three-phase connection points x0, y0, z0 are connected to an inverter  230  via a three-phase harness  229 . This inverter  230  has DC (direct current) terminals  230   a ,  230   b  that are connected to a vehicle battery  231  which is a DC power supply. 
     The first three-phase windings X1, Y1, Z1 are connected in the form of a star connection in which the first three-phase terminals form its neutral point O. In the second three-phase windings X2, Y2, Z2, the second three-phase terminals are connected to a well-known three-phase full-wave rectifier (hereinafter referred to as a “rectifier  233 ”) via a three-phase harness  232 . 
     The rectifier  233  has positive and negative terminals  233   a ,  233   b  that are connected to a short circuit  234  which is provided with a semiconductor switch  235  (for example, a transistor). 
     As shown in  FIG. 31 , operation of the inverter  230  and on/off (close/open) operation of the semiconductor switch  235  are controlled by a powertrain integrated ECU (electronic control unit)  236  which is mounted in the vehicle. 
     The ECU  236  receives information, for example, (a) a vehicle state signal including a steering angle signal, an acceleration position signal, a brake signal, a shift position signal, (b) an engine state signal for informing engine state such as start and stop of the engine E 21 , and (c) a detected signal of the respective rotation angle sensors  207 . And then, based on these information, the ECU  151  controls operation of the inverter  230  and on/off (close/open) operation of the semiconductor switch  235 . 
     (Description of Second Rotor  218 ) 
     The second rotor  218  is configured by an annular rotor core  237  and a squirrel-cage conductor which is assembled in this rotor core  237 . 
     As shown in  FIG. 29 , the rotor core  237  is configured by laminating a plurality of annular core sheets formed by a punching press of an electromagnetic steel plate. In the rotor core  237 , the outer and inner slots  237   a  and  237   b  are circumferentially formed at the radial outer and inner peripheries the rotor core  237  at regular pitches. The number of the outer and inner slots  237   a  is the same as that of the inner slots  237   b.    
     As shown in  FIG. 30 , the squirrel-cage conductor is configured by a plurality of rotor bars  238  and an end ring  239 . The rotor bars  238  are inserted in the outer and inner slots  237   a  and  237   b  formed in the rotor core  237 . The end ring  239  short-circuits both ends of the respective rotor bars  238 . The rotor bars  238  and the end ring  239  are produced by, for example, aluminum die-casting, in such a way as to be configured by aluminum material which is conductive material. 
     Next, referring to  FIG. 26 , features related to an overrall configuration of the electric transmission  201  are described below. In the following explanation, a left side of an axial direction (left-right direction shown in  FIG. 26 ) is referred to as a “front side”, and a right side of the axial direction is referred to as a “rear side”. 
     In the first and second rotary machines M 21  and M 22 , the magnetic modulation element  215  of the first rotary machine M 21  and the second rotor  218  of the second rotary machine M 22  are mechanically coupled to each other via the second rotor disc  210 . The magnetic modulation element  215  and the second rotor  218  are configured so as to integrally rotate with the second rotary shaft  203 . 
     The first and second rotary shafts  202  and  203  are located in such a manner that an opposite central position between both rotary shafts  202  and  203  axially facing each other via a gap is displaced to the front side. In other words, the opposite central position between the first and second rotary shafts  202  and  203  is shifted toward the front side from an axially intermediate position (hereinafter referred to as an “axially central position”) between the first and second rotary machines M 21  and M 22 . In the case of  FIG. 26 , a front side end surface of the second rotary shaft  102  extends beyond the axially central position, and then reaches up to the inner periphery side of the first rotary machine M 21 . 
     Thus, the second rotor disc  219  can allow the cylindrical boss section  219   a , which is fitted in the second rotary shaft  203 , to be located at a position (axially central) between the first and second rotary machines M 21  and M 22 . 
     In addition, (i) the field element  214  of the first rotary machine M 21  and (ii) two rotors (the magnetic modulation element  215  and the second rotor  218 ) connected to each other via the second rotor disc  219 , are supported in a relatively rotatable manner via a bearing  240  which is located at approximately axially intermediate position (axially central position) between both two rotors. Specifically, the field element  214  is provided with an outer support section  241  on a rear side end surface of the field element  214 . The second rotor disc  219  is provided with an inner support section  219  which radially facing the outer support section  241 . The field element  214  and two rotors (the magnetic modulation element  215  and the second rotor  218 ) are supported in a relatively rotatable manner via the bearing  240  located between the outer and inner support sections  241  and  242 . 
     In the present embodiment, the inner support section  242  may be located on the rear side end surface of the field element  214 , and the outer support section  242  may be located in the second rotor disc  219 . 
     The two bearings  208 , which support the second rotary shaft  203  with respect to the rear frame  205 , are spaced at a predetermined distance. Hereinafter, one of the two bearings  208  which is located at the front side (left side of  FIG. 26 ) is referred to as a “first rear bearing  208   a ”, and the other which is located at the rear side (right side of  FIG. 26 ) is referred to as a “second rear bearing  208   b ”. The first rear bearing  208   a  is located close to the axially central position. Specifically, the first rear bearing  208   a  is located close to the rear side of the cylindrical boss section  219   a  of the second rotor disc  219 . 
     The front and rear frames  204  and  205  are combined by an axial spigot-joint of their opening portions. Inside the front and rear frames  204  and  205 , the first and second rotary machines M 21  and M 22  are integrally contained. 
     The rear frame  205  is integrally provided with an cylindrical frame  243  at the radial inner periphery side of the rear side end surface. In the cylindrical frame  243 , a cylindrical bearing section is axially extended. The cylindrical bearing section supports the outer periphery of the second rear bearing  208   b . Radially outside the cylindrical frame  243 , a mounting space capable of mounting the inverter  230  and the rectifier  233  described above is ensured. 
     Outside the rear frame  205  (right end of  FIG. 26 ), a rear cover  244  is assembled. The rear cover  244  covers a the inverter  230  and the rectifier  233  mounted in the mounting space described above. 
     The front and rear frames  204  and  205  are integrally provided with harness protectors  204   a  and  205   a  that protect (i) a three-phase harness  229  connected to the inverter  230  and (ii) a three-phase harness  232  connected to the rectifier  233 . 
     Next, referring to  FIGS. 32A ,  32 B,  33 A,  33 B,  34 A,  34 B,  35 A and  35 B, operation of the electric transmission  201  is described.  FIGS. 32A ,  33 A,  34 A and  35 A show diagrams for explaining operations corresponding to several drive modes required for hybrid vehicles, and  FIGS. 32B ,  33 B,  34 B and  35 B show motion diagrams of the first rotary machine M 21 . Each of the motion diagrams represents a relationship between (i) the field element  214  and the magnetic modulation element  215  which are two rotors of the first rotary machine M 21 ; and (ii) mechanical angular velocity of rotating magnetic field produced by the armature winding  221  of the first armature  213 . 
     Hereinafter, a positive rotational direction of the engine E 21  is referred to as a “positive direction”, and an opposite direction of the positive rotational direction of the engine E 21  is referred to as a “reverse direction”. 
     a) Engine Start Mode 
     In an engine start mode, the engine E 21  is started. This operation is described with reference to  FIGS. 32A and 32B . 
     First, the field element  214 , which is connected to the first rotary shaft  202 , is static, i.e., the engine E 21  is stopped. Under this condition, operation of the inverter  230  is controlled by the ECU  236  in such a manner that a rotating magnetic field directed to an opposite direction of a rotational direction of the engine E 21  is generated in the armature winding  221  (the first three-phase windings X1, Y1, Z1) of the first armature  213 , as shown in left-pointing arrows of  FIG. 32B . Then, the magnetic modulation element  215  tries to rotate in the opposite direction (the same direction as the rotating magnetic field produced by the first armature  213 ), as shown in arrows of  FIG. 32A . 
     On the other hand, in the armature windings  221  and  228  of the first and second armatures  213  and  217 , the first three-phase windings X1, Y1, Z1 and the second three-phase windings X2, Y2, Z2 are connected to each other in such a manner that their phase sequence is a negative sequence. Then, when the semiconductor switch  235 , which is inserted between the positive and negative terminals  233   a ,  233   b  of the rectifier  233 , is turned on, as shown in  FIG. 32A , a rotating magnetic field produced by the armature winding  228  (the second three-phase windings X2, Y2, Z2) rotates in the positive direction (corresponding to a direction indicated by arrows of  FIG. 32A ). 
     In this way, as shown in right-pointing allows of  FIG. 32B , the second rotor  218  tries to rotate in such a way as to follow the rotating magnetic field produced by the armature winding  228  with a slip. This leads to an action to restrict a reverse rotation of the magnetic modulation element  215  connected to this the second rotor  215 . As its reaction, a torque of a positive direction is generated in the field element  214 . Thus, as shown in  FIG. 32A , the crank shaft of the engine E 21  connected to the first rotary shaft  202  rotates in the positive direction (corresponding to a direction indicated by arrows of  FIG. 32A ), thereby starting the engine E 11 . In this engine start mode, the second rotary machine M 22  also assists a start of the engine E 21 . 
     b) Engine Acceleration and Axle Activation Mode 
     In an engine acceleration and axle activation mode, the engine E 21  is accelerated to activate an axle side, thereby starting and accelerating the vehicle. This operation is described with reference to  FIGS. 33A and 33B . 
     In this operation, as an engine speed is increased, a rotational velocity of the field element  214  is increased. Subsequently, the magnetic modulation element  215 , which is connected to the second rotary shaft  203  located at the axle side, receives reaction force due to vehicle inertial resistance or the like, as shown in left-pointing arrows of  FIG. 33B . Thus, the rotating magnetic field of the first armature  213  is directed to a reverse rotation. In this state, the first armature  213  generates electric power to provide its reaction force. Then, the magnetic modulation element  215  receives rotational torque due to the reaction force of power generation and the drive force of the engine E 21 , and increases the rotational velocity, as shown in right-pointing arrows of  FIG. 33B . 
     The power generation of the first armature  213  is performed as follows. 
     As shown in  FIG. 33A , under the condition that the inverter  230  is turned off, the semiconductor switch  235 , which is inserted between the positive and negative terminals  233   a ,  233   b  of the rectifier  233 , is turned on. Then, when voltage is induced in the first three-phase windings X1, Y1, Z1, current flows in the second three-phase windings X2, Y2, Z2, which is connected to the first three-phase windings X1, Y1, Z1 in such a manner that their phase sequence is a negative sequence, thereby exciting the second three-phase windings X2, Y2, Z2 in the positive direction (corresponding to a direction indicated by arrows of  FIG. 33A ). 
     When the engine speed reaches a predetermined engine speed, the second rotor  218  overcomes the running resistance to provide rotational drive force, and starts to rotate with a slip with respect to a velocity of the rotating magnetic field generated by the second three-phase windings X2, Y2, Z2. At this time, as shown in  FIG. 33A , the magnetic modulation element  215  receives rotational torque in the positive direction (corresponding to a direction indicated by arrows of  FIG. 33A ) due to the reaction force of power generation of the reverse direction which is received by the field element  214  from the first armature  213 . Then, the magnetic modulation element  215  assists a rotation of the second rotary shaft  203  as well as the second rotor  218 . 
     c) EV Drive Mode 
     In an EV drive mode, the engine E 21  is stopped, and the vehicle is driven by only a motor. This operation is described with reference to  FIGS. 34A and 34B . 
     The first rotary machine M 21  is accelerated by supplying the first armature  213  with the electric power while receiving a rotational resistance of the magnetic modulation element  215  which is connected to the second rotary shaft  203 . Then, a torque, which tries to rotate in the reverse direction, acts on the field element  214  connected to the first rotary machine  202 . At this time, as shown in right-pointing triangular marks of  FIG. 34B , the one-way clutch  206  prevents the field element  214  from reversely rotating, and then, its magnetic torque reaction force acts on the magnetic modulation element  215 . Therefore, a drive torque, which rotates the second rotary shaft  203  connected to the axle side in the positive direction (corresponding to a direction indicated by arrows of  FIG. 34B ), is generated. In this way, due to the presence of the one-way clutch  206  that prevents the reverse rotation of the first rotary shaft  202 , the first rotary machine M 21  can also electrically operate as well as the second rotary machine M 22 . This can downsize the first rotary machine M 21  as well as the second rotary machine M 22 . 
     In the EV drive mode, the semiconductor switch  235  is turned off, such that the second three-phase windings X2, Y2, Z2 does not operate, and the vehicle is driven by only the first rotary machine M 21 . 
     d) Vehicle Regenerative Control Mode 
     In a vehicle regenerative control mode, the running vehicle is decelerated and a regenerative braking is produced. This operation is described with reference to  FIGS. 35A and 35B . 
     In this mode, it is necessary to stop a rotation of the field element  214  of the first rotary machine M 21  in order to efficiently charge the vehicle battery  231  with braking energy as much as possible. For such a measure, there are two methods. 
     As shown in  FIG. 35A , the first method is a method for: generating electric power at the second three-phase windings X2, Y2, Z2 by use of the regenerative braking, while controlling an output frequency of the inverter  230  with respect to the first armature  213  in such a manner that a rotation of the field element  214  is zero. At this time, if the semiconductor switch  235  is turned on, a rotating magnetic field of the reverse direction is generated in the second three-phase windings X2, Y2, Z2. Therefore, the semiconductor switch  235  is turned off, so as to make the second rotary machine M 22  ineffective. 
     The second method is a method for: (i) controlling the inverter  230  in such a manner that: (a) a rotating magnetic field produced by the first three-phase windings X1, Y1, Z1 is in the reverse direction with respect to the first rotary machine M 21 ; and (b) a rotating magnetic field produced by the second three-phase windings X2, Y2, Z2 is in the reverse direction with respect to the second rotary machine M 22 ; and (ii) generating electric power at the second rotary machine M 22  by use of the regenerative braking. In this case, the rotating magnetic field in the reverse direction is generated in the first armature  213 . Due to this, a phase control is performed by selecting a phase angle in such a way that a torque does not act on the field element  214  and the magnetic modulation element  215 . This enables the field element  214  to rotate freely, thereby preventing braking energy from being lost due to engine braking or the like. Thus, during the regenerative braking, the first rotary machine M 21  can function as a power cutoff clutch. As a result, the vehicle battery  231  can be efficiently charged with braking energy. 
     (Effects of Eighth Exemplary Embodiment) 
     According to the eighth exemplary embodiment, (i) the first three-phase windings X1, Y1, Z1 are wound around the armature core  220  of the first rotary machine M 21 , the second three-phase windings X2, Y2, Z2 are wound around the outer and inner armature cores  226 ,  227  of the second rotary machine M 22 , and (iii) the first three-phase windings X1, Y1, Z1 and the second three-phase windings X2, Y2, Z2 are connected to each other in such a manner that their phase sequence is a negative sequence. Then, for example, the engine E 21  is rotated at high speed and the axle is rotated at low speed, i.e., the first rotary machine M 21  generates electric power while the first three-phase windings X1, Y1, Z1 generate a rotating magnetic field of the reverse direction to the rotational direction of the engine E 21 . By current due to this generated power, a rotating magnetic field of the positive direction is generated in the second three-phase windings X2, Y2, Z2 of the second rotary machine M 22 . This rotating magnetic field induces magnetic field generated in the second rotor  218  of the second rotary machine M 22  which is the squirrel-cage rotor. Thus, the second rotor  218  rotates in the positive direction with a slip. 
     As a result, the second rotary machine M 22  can be electrically driven by using the generated power of the first rotary machine M 21  without a dedicated inverter, which can correspond to several drive modes required for hybrid vehicles even if one inverter  230  described in the eighth exemplary embodiment is available. 
     According to the first rotary machine M 21  of the eighth exemplary embodiment, the magnetic modulation element  215  is not located between the first armature  213  and the field element  214 , and can be located at the opposite side (the most inner diameter side of the first rotary machine M 21  in the present embodiment) of the first armature  213  with respect to the field element  214 . Thus, magnetic flux passing though the magnetic modulation element  215  forms a flow that U-turns around the segment poles  224  formed into the approximate V-shape, without interlinkage with the rotor hub  225  holding the segment poles  224 . This causes no generation of large loop eddy current, even if the 16 segment poles  224  are cast in high-strength aluminum material. In other words, the 16 segment poles  224  can be reliably and easily supported and fixed by the high-strength aluminum material. This makes it possible to improve mechanical rigidity of the magnetic modulation element  215 , which can improve vibration resistance and centrifugal force resistance of the magnetic modulation element  215 . This enables the magnetic modulation element  215  to be tailored to high rotation and high torque specification. 
     In the two rotors (the field element  214  and the magnetic modulation element  215 ) of the first rotary machine M 21  and the second rotor  218  of the second rotary machine M 22 , two rotor (the magnetic modulation element  215  and the second rotor  218 ), which are connected to each other, and the field element  214  of the first rotary machine M 21  are supported in a relatively rotatable manner via the bearing  240  which is inserted between: (i) the outer support section  241  located at the axial rear side of the field element  214 ; and (ii) the inner support section  242  provided in the second rotor disc  219 . In the second rotor disc  219 , the cylindrical boss section  219   a  is located at the radial central portion that extends toward the inner diameter side from the inner support section  242  supporting the bearing  240  with the outer support section  241 . The second rotor disc  219  is fixed by fitting the cylindrical boss section  219   a  in the outer periphery of the second rotary shaft  203 . 
     The second rotary shaft  203  is rotatably supported by the rear frame  205  via the two bearings  208  (the first rear bearing  208   a  and the second rear bearing  208   b ) axially spaced at a predetermined axial distance. Specifically, the first rear bearing  208   a  is located adjacent to the rear side of the cylindrical boss section  219   a  of the second rotor disc  210  in which the second rotary shaft  203  is fitted. This can improve rigidity of the magnetic modulation element  215  and the second rotor  218 , thereby being able to provide a durable structure. 
     The field element  214  of the rotary machine M 21  has (i) an axial front side which is connected to the first rotary shaft  202  via the first rotor disc  216 , and (ii) an axial rear which is supported by the second rotor disc  219  via the bearing  240  described above. Therefore, both axial ends of the field element  214  are supported. Such a structure of the field element  214  is referred to as a “both ends supported structure”. This structure can improve also vibration resistance of the field element  214 . 
     Thus, it is possible to improve accuracy of the shaft center of the electric transmission  201  in which the first and second rotary machines M 21  and M 22  are integrally provided, and to improve durability thereof, thereby being able to be used at high speed. 
     Further, a body of the first and second rotary machines M 21  and M 22  used for the electric transmission  201  of the eighth exemplary embodiment is determined by a condition that can supply an output necessary for the EV drive mode in which the engine E 21  does not operate and the vehicle is driven by only the vehicle battery  231 . In this EV drive mode, the second rotary machine M 22  produces electric torque. At this time, in the first rotary machine M 21 , the reverse rotation of the first rotary shaft  202  is restricted by the one-way clutch  206  and the first armature  213  is energized. This can make it possible to electrically drive the magnetic modulation element  215  which is connected to the second rotor  218  via the rotor that is not connected to the first rotary shaft  202 , i.e., the second rotor disc  219 . In this way, necessary integrated torque can be produced in cooperation with the two rotors (the first and second rotary machines M 11  and M 12 ). This makes it possible to downsize the first and second rotary machines M 21  and M 22 , thereby being able to provide a compact electric transmission  201 . 
     In the electric transmission  201  according to the eighth exemplary embodiment, the front and rear frames  204  and  205  are combined by an axial spigot-joint of their opening portions. Inside these frames  204  and  205 , the first and second rotary machines M 21  and M 22  are integrally contained. This structure makes it possible to reduce the number of components and to shorten the three-phase harnesses  229  and  232 , compared to a structure in which the first and second rotary machines M 21  and M 22  are separately contained in separate frames. This can further promote downsizing of the entire electric transmission. 
     Outside the rear frame  205 , a mounting space capable of mounting the inverter  230  and the rectifier  233  is ensured. Therefore, the inverter  230  and the rectifier  233  need not to be located outside the electric transmission  201 , and then, can be integrally mounted in the mounting space ensured outside the rear frame  205 . In the case where the inverter  230  and the rectifier  233  are located outside the electric transmission  201 , the three phase harnesses  229  and  232  are needed to connect the first and second rotary machine M 21 , M 22  and the inverter  230  and the rectifier  230  located outside. In the present embodiment, the three-phase harnesses  229  and  232  can be shortened and reduced. In this case, only DC (direct current) lines is needed as power harnesses. As a result, effects of wiring reduction are expected, and there is no need to design the surrounding area of connectors in order to extract the three-phase harnesses  229  and  232  from the first and second rotary machine M 21  and M 22 , thereby being able to contribute downsizing and simplification of the electric transmission  201 . 
     Ninth Exemplary Embodiment 
     Referring to  FIG. 36 , the ninth exemplary embodiment is described. In the present embodiment, the components identical with or similar to those in the eighth exemplary embodiment are given the same reference numerals for the sake of omitting unnecessary explanation. The following explanation focuses on differences with the eighth exemplary embodiment. 
     As shown in  FIG. 36 , in the electric transmission  201  of the present embodiment, the magnetic modulation element  215  of the first rotary machine M 21  is coupled to the first rotary shaft  202  via the first rotor disc  216 . The field element  214  and the second rotor  218  of the second rotary machine M 22  are mechanically coupled to each other via the second rotor disc  219 . The field element  214  is supported at the axial front side (left side of  FIG. 36 ) via a bearing (fourth bearing)  245  in a rotatable manner with respect to the front frame  204 . 
     The second rotor  218  is a squirrel-cage rotor. The first three-phase windings X1, Y1, Z1 of the first armature  213  and the second three-phase windings X2, Y2, Z2 of the second armature  217  are connected to each other in such a manner that their phase sequence is a negative sequence. This configuration is the same as the eighth exemplary embodiment. 
     According to a relationship of the number of poles based on the principle of magnetic modulation, the number of pole pairs of the field element  214  is smaller than the number of segment poles  224  of the magnetic modulation element  215 . In the case of the eighth exemplary embodiment, the number of pole pairs of the field element  214  is n=10, and the number of segment poles  224  of the magnetic modulation element  215  is 16. 
     In the case of the present embodiment, a rotating speed of the field element  214  is higher than the engine speed, compared to the case of eighth exemplary embodiment in which the field element  214  is coupled to the first rotary shaft  202 . Therefore, the two rotors (the field element  214  and the second rotor  218 ) coupled to each other via the second rotor disc  219  rotate at a speed higher than the engine speed. This enables the second rotary machine M 22  to be tailored to high speed and to be downsized. In addition, due to a relationship that a rotating speed of the propeller shaft  209  is higher than a rotating speed of the engine E 21 , the engine speed can be reduced during high speed driving using engine power, thereby resulting in fuel saving. 
     In the second rotary machine M 22  of the eighth and ninth exemplary embodiments, the armature core of the second armature  217  is configured by: (i) the outer armature core  226  located at the outer periphery of the second rotor element  218 ; and (ii) the inner armature core  227  located at the inner periphery of the second rotor element  218 . This structure is so called a motor structure with a double face gap (two face gap) that forms a gap at the respective inner and outer peripheries of the second rotor element  218 . In the exemplary embodiments described above, this motor structure with two-face gap is applied. In modifications of the embodiments described above, so called a motor structure with a triple face gap (three face gap) may be applied to the present disclosure. In this motor structure, another gap is further formed with the second armature  217 , at the axial rear side of the second rotor  218 . 
     In another modifications, an ordinary used motor structure with a single face gap (one face gap) may be also applied to the present disclosure. In this motor structure, a redundant space can be formed inside of the second rotary machine M 22 . In this case, the bearing  208  or the like can be located in the redundant space. Due to such an effective use of space, a mounting space for the inverter  230  and the rectifier  233  can be ensured. 
     (Modifications) 
     In the second armature  218  of the eighth exemplary embodiment, the outer and inner armatures cores  226  and  227  are linked in the form of an approximately U-shaped cross section and integrally configured. Alternately, the outer and inner armature cores  226  and  227  may be separately provided without being connected to each other. 
     In the eighth exemplary embodiment, the magnetic modulation element  215  is configured by a die-cast product which is integrally produced by casting the 16 segment poles  127  in high-strength aluminum material. However, there is no need to produce the magnetic modulation element  215  by die-casting. For example, the magnetic modulation element  215  may be formed by annularly connecting the 16 segment poles  224  by use of a connecting member, for example, non-magnetic mechanical structural member such as stainless steel. 
     In the configuration of the ninth exemplary embodiment, the magnetic modulation element  215  may be configured by: (i) forming the first rotary shaft  202  by use of high-strength non-magnetic stainless steel; and (ii) directly fixing the 16 segment poles  224  to the first rotary shaft  202  by welding or the like. 
     The present invention may be embodied in several other forms without departing from the spirit thereof. The exemplary embodiments and modifications described so far are therefore intended to be only illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them. All changes that fall within the metes and bounds of the claims, or equivalents of such metes and bounds, are therefore intended to be embraced by the claims.