Patent Publication Number: US-2022216779-A1

Title: Superconducting induction rotating machine, and superconducting drive force generating system using said superconducting induction rotating machine

Description:
FIELD OF THE INVENTION 
     The present invention relates to an induction rotating machine and a superconducting driving force generation system using the same. 
     BACKGROUND OF THE INVENTION 
     In recent years, in the process of development of newly emerging high-temperature oxide superconductors (yttrium-based (Y-based), bismuth-based (B-based) ones), which transition to a superconducting state in the vicinity of the liquid nitrogen temperature (77K), various research and development efforts using these superconductors have been put forth in the field of electric motors among others, aiming for size reduction, weight reduction and higher efficiency. 
     In superconductor applications in electric motors, ones using a superconducting rotor and a normal conducting stator, and ones using a superconducting rotor and a superconducting stator have been contemplated, but in AC electric motors, alternating currents need to be applied to armature coils, which lead to a problem of alternating current losses generated in the superconductor employed for the armature coils, and a problem of coil shapes becoming complex, hence, the current main stream is to develop electric motors applying a superconductor for a rotor, of which the following prior art documents are known as published research and development case examples. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         [Patent Document 1] Japanese Translation of PCT International Application Publication No. H8-505515 
         [Patent Document 2] Japanese Translation of PCT International Application Re-Publication No. 2009-116219 
         [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2013-240147 
       
    
     Non-Patent Document 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     Of the above, an electric motor of Patent Document 1 has a rotor constructed with a laminated body of a high-temperature superconductor and a torque shield made of a normal conducting material, wherein upon activation at a room temperature, a rotating machine is activated in an induction mode by applying an alternating magnetic field (rotating magnetic field) generated by energizing armature coils (primary winding) arranged in a stator to thereby induce a torque generated by an interaction between an electric current induced in the torque shield and the alternating magnetic field, wherein once the rotor activates and reaches a predetermined rotation speed, the rotor is rotated synchronously by cooling the superconductor to its superconducting state at its critical temperature or lower, and causing the superconductor to use its magnetic flux to capture the alternating magnetic field. 
     This superconducting induction rotating machine may be operated without externally supplying the electric power to the rotor to enable simplification of this machine&#39;s structure. 
     However, upon the activation of rotating machine, transition from the induction mode to a synchronous operation requires determining the critical temperature of the superconductor and cooling the superconductor to the critical temperature or lower, which temperature control process takes a relatively long time, possibly reducing this electric motor&#39;s operational responsiveness. For this reason, in rotating machines used for applications where the machines are frequently and repeatedly activated and stopped as in electric vehicles, for example, significant joule heat (copper loss) is considered to occur in the torque shield, making it difficult to maintain the superconductor at or below the critical temperature, causing the decline of the rotating machine efficiency due to the increase of the copper loss itself. 
     Whereas, Patent Document 2 proposes an electric motor for addressing the inherent problem in Patent Document 1. A superconducting induction rotating machine of Patent Document 2 provides a structure which houses a combination of a rotor core of a squirrel-cage induction rotating machine, normal conducting squirrel-cage winding of rotor bars made of normal conducting wires with end rings connected with both ends of the rotor bars, respectively, and superconducting squirrel-cage winding of rotor bars made of superconducting conducting wires connected with end rings, wherein this combination is housed in slots formed in the circumferential surface of the rotor core. 
     In the normal conducting state, this electric motor may be activated and operated mainly by the torque generated by the interaction between the electric current induced in the normal conducting squirrel-cage winding and the rotating magnetic field generated by energizing the armature coils arranged in a stator, whereas, in the superconducting state, this electric motor may be operated independent of the superconductor critical temperature by the superconducting squirrel-cage winding which captures the magnetic flux of the rotating magnetic field applied by the armature coils of the stator to thereby achieve the synchronous operation. 
     However, even the electric motor of Patent Document 2 has the following challenges in its practical applications. That is, since the electric motor of Patent Document 2 is configured with the rotor core having the squirrel-cage rotor configured with both the normal conducting squirrel-cage winding and the superconducting squirrel-cage winding, when activating the rotating machine at a room temperature equal to or above the critical temperature of the superconducting squirrel-cage winding, large joule heat or copper loss occurs due to the induced electric current in the normal conducting squirrel-cage winding as in the torque shield of the superconducting rotating machine of Patent Document 1. Also, for the superconducting squirrel-cage winding, its winding structure becomes complex due to the required electric connections between both ends of the rotor bars and the end rings of the structure. Further, the electric connections between the rotor bars and the end rings are generally achieved by soldering, but their bonding strength is often problematic, leading to difficulties in ensuring high reliability in terms of centrifugal load bearing capacity and long-term use. Moreover, since the electric motor of Patent Document 2 employs a configuration to accommodate both the normal conducting squirrel-cage winding and the superconducting squirrel-cage winding in the slots in the heavy rotor core, it is difficult to reduce the weight and the size of this superconducting rotating machine. 
     Patent Document 3 discloses a novel superconducting rotating machine, which requires no supply of external electric power to a superconductor incorporated in a rotor, wherein the rotor is not provided with a torque shield of Patent Document 1, any normal conducting metal body as a joule heating source, such as normal conducting squirrel-cage winding of Patent Document 2, or a heavy rotor core, and wherein the superconducting rotating machine is configured to take advantage of superconducting characteristics of the superconductor with ingenuity such that the size and weight reduction of the superconducting rotating machine as well as its high-efficiency rotation performance may be achieved. In other words, the superconducting rotating machine of Patent Document 3 is equipped with an armature coil provided on the stator side, and a superconducting rotor having a plate-like superconductor, and the superconducting rotating machine is configured to cause the superconducting rotor to generate a rotating force based on an electromagnetic force produced by an interaction between a shielding current induced in the plate-like superconductor due to a magnetic field that the armature coil applies to the superconductor, and the magnetic field. However, while the superconducting rotor having the plate-like superconductor contributes to reducing the rotor size and weight, it was difficult to improve the torque for imparting the rotational force to the superconducting rotor. 
     Means for Solving the Problem 
     Considering the above challenges, the purpose of the present invention is to provide a superconducting induction rotating machine which is more compact, and capable of operating with less electric power and generating a driving force very efficiently. 
     Also, another object of the invention is to provide a superconducting induction rotating machine which has a simple structure, and is widely applicable as a propulsion generation system. 
     In other words, according to a principal aspect of the present invention, the following invention is provided. 
     (1) A superconducting induction rotating machine, comprising: 
     a stator having a plurality of superconducting armature coils arranged along circumferential direction of the stator, and 
     a rotor rotatably disposed around a central axis line, and opposing the stator across a predetermined gap, 
     wherein the rotor is configured of a complex consisting of a cylindrical electrically conductive material layer disposed on a side opposing the stator, and a magnetic material layer disposed on a side opposite from the electrically conductive material layer&#39;s side opposing the stator, and 
     wherein the superconducting induction rotating machine rotationally drives the rotor by generating a rotational torque in the rotor with a rotating magnetic field created by the armature coils while the superconducting armature coils disposed on the stator being cooled to a superconducting state. 
     (2) The superconducting induction rotating machine of (1), wherein 
     a propulsion generation body for generating propulsion is secured on an inner circumferential surface or an outer circumferential surface of the rotor, and the rotor is rotationally driven to, in turn, drive the propulsion generation body to thereby generate propulsion. 
     (3) The superconducting induction rotating machine of (2), wherein 
     the propulsion generation body are propeller blades secured on the inner circumferential surface or the outer circumferential surface of the rotor, which is on the side opposite from the side opposing the stator. 
     (4) The superconducting induction rotating machine of (2), wherein 
     the propulsion generation body is a propeller blade secured on the inner circumferential surface, which is on the side opposite from the side opposing the stator, or the outer circumferential surface of the rotor. 
     (5) The superconducting induction rotating machine of (2), wherein 
     the propulsion generation body is a tread body for transmitting a driving force from the rotating machine by friction with an object, and the tread body is secured on the inner circumferential surface or the outer circumferential surface of the rotor, which is on the side opposite from the side opposing the stator. 
     (6) The superconducting induction rotating machine of (1), wherein 
     the stator comprises a stator main body retaining a plurality of superconducting armature coils, and 
     the stator main body maintains its mechanical strength in low temperature, and is formed of an electrically non-conductive material. 
     (7) The superconducting induction rotating machine of (1), wherein 
     the rotor is an outer rotor of the rotating machine, and 
     the electrically conductive material layer is provided on the inner diameter side of the stator, and the magnetic material layer is provided on the outer diameter side of the stator. 
     (8) The superconducting induction rotating machine of (1), wherein 
     the rotor is an inner rotor of the rotating machine, and 
     the electrically conductive material layer is provided on the outer diameter side of the stator, and the magnetic material layer is provided on the inner diameter side of the stator. 
     (9) The superconducting induction rotating machine of (1), wherein 
     the rotor is provided with radiation fins. 
     (10) The superconducting induction rotating machine of (1), wherein 
     the rotor is defined by embedding strip-shaped superconducting wires in the electrically conductive material layer, and securing short-circuit rings on both ends of the rotor in a direction of its central axis line. 
     (11) The superconducting induction rotating machine of (10), wherein 
     both ends of the superconducting wires are curved. 
     (12) The superconducting induction rotating machine of (10), wherein 
     grooves are formed in the electrically conductive material layer for embedding the superconducting wires in. 
     (13) The superconducting induction rotating machine of (1), wherein 
     the rotor is defined by arranging the superconducting wires on a surface of the electrically conductive material layer in a circumferential direction and a direction intersecting the circumferential direction, respectively, at predetermined intervals. 
     (14) The superconducting induction rotating machine of (1), wherein 
     liquid feed propeller blades are secured in the inner diameter section of the rotor, and a fluid flowing through the inner diameter section is pump-driven along an axis line of the rotor. 
     (15) A fluid drive system having the stator and the rotor of the superconducting rotating machine of (14), wherein the stator is attached in the mid-section of a fluid flow pipe with a circular cross section with the stator&#39;s central axis positioned concentrically with the fluid flow pipe, and the stator is disposed so that it is exposed inside the fluid flow pipe to thereby pump-drive a fluid flowing through the fluid flow pipe.
 
(16) The fluid drive system of (15), wherein
 
     the pump-driven fluid is a refrigerant, and 
     the superconducting armature coils are cooled with the refrigerant. 
     (17) The fluid drive system of (16), wherein 
     the superconducting induction rotating machines are provided at predetermined intervals along the fluid flow pipe. 
     (18) A superconducting driving force generation system, comprising the superconducting induction rotating machine of (1), a superconducting electric generator for supplying electricity to the rotating machine, and a superconducting cable for connecting the electric generator and the rotating machine.
 
(19) The superconducting driving force generation system of (18), further comprising:
 
     a common freezing system for cooling the superconducting induction rotating machine, the superconducting electric generator and the superconducting cable. 
     (20) The superconducting driving force generation system of (18), further comprising: 
     a gas turbine engine for driving the superconducting electric generator, 
     wherein the gas turbine engine uses a LNG having a refrigerant function or a gas made of a liquid hydrogen treated by a freezing system. 
     (21) An aircraft to which the superconducting driving force generation system of (12) is applied, wherein 
     the superconducting induction rotating machine is installed in parallel on an upper surface of main wings of the aircraft. 
     Effect of the Invention 
     According to a configuration of the present invention, rotor may be configured with a thin and light-weight cylindrical body, and a superconducting induction rotating machine with high efficiency and high output may be provided. 
     Also, according to the present invention, a rotor may be configured with a simple cylindrical body having no windings and the like, and the entire structure may have reduced size and weight to provide a rotating machine which is inexpensive as well as highly durable and reliable. 
     Further, propulsion generation body or bodies such as fins, propellers, tires or the like may be directly attached, for example, on an inner surface or an outer surface of the cylindrical body to thereby provide a propulsion generation system with a simple structure and a reduced driving force transmission loss. 
     Note that features and marked effects of the present invention other than those described above will become apparent to those skilled in the art upon referring to the following embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a superconducting driving force generation system according to an embodiment of the present invention; 
         FIG. 2  is a schematic structural view showing an outer rotor-type superconducting induction motor according to the embodiment; 
         FIG. 3  is a schematic structural view showing an inner rotor-type superconducting induction motor according to the embodiment; 
         FIG. 4  is a top view showing a stator according to the embodiment; 
         FIG. 5  is a perspective view showing the stator according to the embodiment; 
         FIG. 6  are a top view and a front view, respectively, showing a superconducting armature coil according to the embodiment; 
         FIG. 7A , B are a side view and a front view, respectively, showing a part of a superconducting coiling wire according to the embodiment; 
         FIG. 8  is a perspective view showing a rotor according to the embodiment; 
         FIG. 9  is a perspective view showing the rotor according to the embodiment; 
         FIG. 10  is a perspective view showing the stator and the rotor combined according to the embodiment; 
         FIG. 11A, 11B  are a top view and a perspective view, respectively, showing a stator according to another embodiment; 
         FIG. 12  is a perspective view showing a rotor according to yet another embodiment; 
         FIG. 13  is a perspective view showing assembly of the rotor of  FIG. 12 ; 
         FIG. 14  is a perspective view showing assembly of the rotor of  FIG. 12 ; 
         FIG. 15  is a schematic view showing a rotor according to another embodiment of the present invention; 
         FIG. 16A , B are schematic views showing a liquid feed system according to another embodiment of the present invention; and 
         FIG. 17  is a schematic view showing a tire system according to still another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A best mode of the present invention will be described below with reference to accompanying drawings. 
     (Fully Superconducting Propulsion Generation System) 
       FIG. 1  is a schematic view showing a structural concept of a fully superconducting system  2 , which includes a superconducting induction motor  1  according to the present embodiment. 
     This system  2  has a basically high-efficient gas turbine engine  3 , a superconducting electric generator  4 , a superconducting inverter/superconducting cable  5  and the superconducting induction motor  1 . This system  2  uses LNG or liquid hydrogen, having a refrigerant function, as a fuel for the gas turbine engine  3 , and liquid nitrogen as a refrigerant for cooling a superconductor. Also, the system  2  is configured to be capable of suppressing overall electric power consumption by processing the above fuel and refrigerant with a common freezing machine  6 . 
     In addition, this fully superconducting system  2  connects the electric generator  4 , the superconducting inverter/cable  5  and the superconducting induction motor  1  without exposing them to a room temperature to thereby integrate a common refrigerant flow channel for cooling them. Thus, the system  2  is configured so that it may further decrease a refrigerant load to allow reduction of the electric power consumption. 
     It is contemplated that this fully superconducting system  2  is implemented in an aircraft (indicated with “A” in the figure), for example. 
     Currently, aircrafts have one to two jet engines mounted on each of their wings, but when the superconducting propulsion system is used, for example, four superconducting induction motors are disposed such that they are distributed at regular intervals in a lengthwise direction of the wings on top of the aircraft, as shown in  FIG. 1 . 
     Current jet engines have output of 5 kW/kg, this fully superconducting system may theoretically achieve 20 kW/kg output. Thus, if this system is mounted on an aircraft, it may take off using less than half of the power current aircrafts use. 
     Note that, when the system is applied to an aircraft, the number of motors and their respective outputs may be selected as needed. Also, when applied to an aircraft, the system may be configured such that each motor may be independently controlled for steering in up, down, left and right directions. 
     (Outer Rotor-Type Superconducting Induction Motor) 
       FIG. 2  shows a conceptual diagram of a demonstration system  10  of an outer rotor-type motor  1 ′ as a superconducting induction motor  1  used for the fully superconducting system  2 . This demonstration system  10  is configured to validate if enough output may be obtained from the superconducting induction motor  1 ′, and if enough output is obtained, the demonstration system  10  is configured so that it may be driven upward (indicated with an arrow B) by propeller blades  11  attached to the rotor to thereby levitate. 
     A structure of the demonstration system  10  of this outer rotor-type superconducting induction motor  1 ′ will be described below. 
     Indicated with  12  in  FIG. 2  is a base. This base  12  is formed in a disc shape, and provided on its central top side are a pair of pole-shaped linear guides  13  standing in parallel and spaced apart by a certain distance. These linear guides  13  act as vertical guides for the induction motor  1 ′ when the outer rotor-type induction motor  1 ′ is driven upward (arrow B) by propulsion of the propeller blades  11 . 
     A stator  14  is retained on the linear guides  13  slidably in an up-down direction. This stator  14  is formed of a cylindrical member with its top and bottom openings being closed, and a superconducting armature coil  15  is disposed on the inner surface of an outer circumferential wall section of the stator  14 . This stator  14  has a structure of a vacuum container having a predetermined degree of vacuum (e.g., from about 10-5 to about 10-6 Torr) in order to maintain a cooling temperature of the superconducting armature coil  15 . The superconducting armature coil  15  is connected to a power supply lead  17  for supplying electric power from the electric generator  4  ( FIG. 1 ), and the power supply lead  17  is guided out of the stator  14  from its bottom. 
     Also, a rotor  18  having a cylindrical main body is externally fitted over the stator  14  with a gap of a predetermined dimension between the rotor  18  and the stator  14 . Between the rotor  18  and the stator  14  at the top and bottom ends thereof, bearings indicated with  19 ,  20  are inserted. 
     This rotor  18  is constituted with a complex with small thickness consisting of a highly electrically conductive material layer  22  consisting of a highly conductive non-magnetic material, such as copper, aluminum or the like, disposed on a surface opposing the stator  14 ; and a magnetic material layer  23  consisting of highly magnetically permeable iron or the like for returning magnetic flux, which magnetic material layer  23  disposed of immediately outside of the highly electrically conductive material layer  22 , wherein the rotor  18  has an extremely light weight construction. In other words, magnetic flux intersecting the highly electrically conductive material layer  22  is increased by the magnetic material layer  23 , facilitating an increase of induced current in the highly electrically conductive material layer, and therefore, an increase of torque. 
     However, it should be noted that if the magnetic material layer  23  is thickened, it will increase the system&#39;s weight. 
     Also, the propeller blades  11  are provided on the outer circumferential surface of this rotor  18 . A base section  11   a  of each of the propeller blades  11  is secured by welding, and distal ends  11   b  of the propeller blades  11  extending outward along diametrical directions of the rotor  18  are provided around periphery of this rotor  18  at regular intervals. 
     In such a configuration, if the superconducting armature coil  15  provided on the stator  14  is energized, the rotor  18  may be rotationally driven by a rotational torque in the rotor  18  generated by a rotating magnetic field created by the armature coils  15 . This in turn rotate the propeller blades  11  in a direction indicated with an arrow C to thereby allow the induction motor  1 ′ to levitate. 
     Note that although it is concerned that the temperature of the rotor  18  rises in the above configuration, this problem may be addressed by the propeller blades  11  functioning as radiation fins as well. 
     The present inventors confirmed that an effective output efficiency is obtained through demonstration experiments such as ones related to the above problem, and continued other experiments to complete the present invention. 
     (Inner Rotor-Type Superconducting Induction Motor) 
       FIG. 3  is a schematic view showing an inner rotor-type superconducting induction motor  1 ″. 
     This induction motor  1 ″ comprises a stator frame  26 ; a stator  28  secured to the stator frame  26  for maintaining superconducting armature coils  27  thereon; a power supply lead  29  connected to the top of the armature coils  27  for feeding them electricity; a rotor  30  rotationally retained about an vertical axis and facing the inner surface of the coils  27 ; a central axis  31  extending upward from the rotor  30  to above the stator  28  and rotationally retained in the center of top wall of the stator frame  26 ; and propeller blades  32  provided at the top end of the central axis  31 . 
     The stator frame  26  is formed of any material, preferably a material with a thermally-insulating function. This stator frame  16  comprises a cylindrical (or rectangular) outer circumferential wall  26   a  as well as a top wall section  26   b  and a bottom wall section  26   c  for closing an upper opening and a lower opening of the outer circumferential wall  26   a . Inside this stator frame  26 , a container  33  is secured for retaining liquid nitrogen. This stator frame  26  is adapted to have a structure of vacuum space of a predetermined degree of vacuum (e.g., from about 10-5 to about 10-6 Torr) in order to maintain a cooling temperature of the superconductor filling the armature coil  33 . 
     Here, the container  33  is formed of a material which is an electric insulator generating no eddy current loss and having mechanical strength at a low temperature, such as a FRP. However, this material is not limited to FRPs and may be of other materials having similar characteristics. 
       FIG. 4  shows a top view of the stator  28  secured to the container  33  in the stator frame  26 ; and  FIG. 5  shows a perspective view of the stator  28 . 
     The stator  28  comprises a cylindrical main body  35  and superconducting armature coils  36  attached to the main body  35 . 
     The main body  35  is formed of a FRP and, as shown in  FIG. 4 , its cross section has a shape having a hexagonal profile and having a central cylindrical through-hole. Thus, as shown in  FIG. 5 , an inner circumferential surface of this main body  35  is formed in a tubular shape having a certain diameter, and an outer circumferential surface of this main body  35  is formed to be divided into six rectangular sides in its circumferential direction. 
     Also, one superconducting armature coil  36  is secured to each of the six rectangular sides, and therefore, six superconducting armature coils  36  in total are secured along the outer circumference of the main body  35 . 
       FIG. 6  shows a top view ( FIG. 6A ) and a plan view ( FIG. 6B ) of one of the superconducting armature coils  36 . Each of the superconducting armature coils  36  of this embodiment example does not use a core made of a material with high magnetic permeability such as iron, but is constructed only with a FRP core  37  and a superconducting coiling wire  38  wound around the FRP core  37 , thus enabling this structure to increase its magnetic flux density. The superconducting coiling wire  38  is, as shown in  FIG. 7  ( FIG. 7A ,  FIG. 7B ), a thin and narrow ribbon-like RE-based (yttrium-based) high-temperature superconducting wire. However, the superconducting wire is not limited to the above shape and material, and other superconducting wires, such as bismuth-based superconducting materials may be used. 
     The stator  28  with the superconducting armature coils  36  attached thereto is secured in the central section of the container  33 , as shown in  FIG. 3 . The container  33  is filled with a refrigerant, and the superconducting armature coils  36  are cooled using refrigerant immersion cooling. 
     Note that the armature coils  36  may be connected in series or in parallel. 
     Also, the rotor  30  disposed inside the inner diameter of the stator  28  is a cylindrical member, as shown in  FIG. 8 , and has an outer diameter smaller than the inner diameter of the stator  28  (main body  35 ). As in the example of  FIG. 1 , this rotor  30  is constituted with a complex consisting of an electrically conductive material layer  39  of aluminum, copper or the like, disposed on a surface opposing the stator  14 ; and a magnetic material layer  40  with high magnetic permeability for returning magnetic flux, which magnetic material layer  40  laminated on an inner surface of the electrically conductive material layer  39 , wherein the rotor  30  has an extremely light weight construction. 
     Also, as shown in  FIG. 9 , lid bodies  42 ,  43  are attached at the top and bottom of the rotor  30 , respectively, and the central axis  31  is inserted vertically through these lid bodies  42 ,  43  and the rotor  30  along the central axis of the rotor  30 . 
       FIG. 10  is a schematic view showing an inner rotor-type induction motor unit assembled by inserting the rotor  30  into the stator  28 . 
     Other Stator Embodiments 
     The above stator  28  of the inner rotor-type induction motor  1 ″ was an example where six armature coils were attached on the outer surface of the main body  35 , but the present invention is not limited by this configuration. 
     In an example shown in  FIG. 11A ,  FIG. 11B  of  FIG. 11 , a main body  35 ′ is larger than the main body  35 , and  12  armature coils  36 ′ are secured on an inner surface side of the main body  35 ′. According to such a configuration, larger output may be obtained. 
     Other Rotor Embodiments 
     The above-described embodiment was an example where the stator  28  side was made to be superconductive while the rotor  30  was not and configured as a light cylindrical body, but if a rotor indicated with  30 ′ below is used as in  FIG. 12 , the rotor  30  may be made superconductive while keeping the operation effect of the present invention to enable higher efficiency and output of the induction motor. 
     The rotor  30 ′ comprises superconducting wires  45  embedded vertically in an electrically conductive material layer  39 ′ (a layer formed of copper) on an outer side of the rotor  30 ′, and short-circuit rings  46 ,  47  attached at the top and bottom, respectively, to connect the superconducting wires  45 . The embedding of the superconducting wires  45  into the rotor  30 ′ may improve the shielding current density (increase shielding current) induced by the magnetic flux linking to the rotor  30 ′, and even when a rotor  30 ′ has a small thickness, it may induce a large current. Accordingly, the torque increases to thereby enable an improved output density of the superconducting induction motor. 
     Also, in this embodiment, the superconducting wires  45  are respectively fitted in grooves  39   a  provided in an electrically conductive material layer  39 ′ made of copper, and the grooves are curved in one direction at their tops and bottoms. Thus, the shielding current may be configured to flow in loops, and characteristic degradation (decline of a critical current value) of the superconducting wires may be prevented. 
       FIG. 12  and  FIG. 13  are diagrams respectively illustrating a structure of and steps for assembling the electrically conductive material layer  39 ′ having the grooves  39   a.    
     In this embodiment, the rotor (electrically conductive material layer  39 ′) is by separately shaping and assembling ring-shaped parts  50 ,  51  having curved grooves  39   b ,  39   c , and a part  52  structuring a midsection. Note that the depth direction of the grooves  39   a - 39   c  is adapted to provide a slightly angled or skewed relative to the radial direction. They are configured to be capable of suppressing harmonic wave torques, electromagnetic excitation force. 
     Also, as shown in  FIG. 13 , the rotor  30 ′ is completed by fitting the ribbon-shaped superconducting wires  45  into the grooves  39   a - 39   c , with each of the upper and lower ends of the superconducting wires  45  curved to fit the shape of the grooves  39   a - 39   c , and then, attaching the short-circuit rings  46 ,  47  onto the upper and lower ends. 
     Note that each of the short-circuit rings  46 ,  47  is configured in a ring shape by winding a ribbon-shaped superconducting wire  53  in a horizontal direction along a circumference of each copper ring  52  having the same thickness as a width of the wire  45  so that the short-circuit rings  46 ,  47  respectively have the same width as the thickness of the main body. 
     Also, note that the superconducting wire does not need to be embedded into the rotor, but may be affixed to the surface of the rotor. In this case, as indicated with the numeral  54  in  FIG. 15 , it is preferred that the superconducting wires are arranged in a mesh-like manner with some of the superconducting wires provided in a circumferential direction intersecting with the others provided in a direction parallel to a central axis line, and that the superconducting wires are provided at predetermined intervals to thereby cover the entire surface of the electrically conductive material layer of the rotor. 
     (Other Application Examples of Superconducting Induction Rotating Machine) 
       FIG. 16  shows an example of a superconducting induction rotating machine of the present invention applied to a liquid feed pump for liquid nitrogen or liquid hydrogen. 
     In other words, as shown in  FIG. 16A , B, the liquid feed pump  55  of this embodiment is disposed in the midsection of a liquid feed pipe  56 . 
     In this example, a stator  57  of an induction rotating machine as the liquid feed pump  55  is secured to the liquid feed pipe  56 , and a cylindrical rotor  58  is disposed in the liquid feed pipe, and is retained by the rotor  57  through bearings, which is not shown, while opposing superconducting armature coils  59 . 
     The rotor  58  is formed as a complex in a similar manner to that of the aforementioned embodiments, but is configured in such a way that a liquid flows through the liquid feed pipe inside an inner diameter section of the rotor  58 . Also, propeller fins  60  are secured in the inner diameter section of this rotor  58 . 
     This example is configured so that liquid nitrogen flowing inside the liquid feed pipe  56  is used to cool the superconducting armature coil  59 . Thus, the structure of the stator of the induction motor may be simplified. 
     Also, when the liquid feed pipe  56  is long, a plurality of the liquid feed pumps  55  are disposed at predetermined intervals. In this case, since the refrigerant flowing through the liquid feed pipe is used to cool the superconducting armature coil  59 , there is no need to provide additional means for cooling. 
     Therefore, it is effective to use this liquid feed pump for a refrigerant supply system of the fully superconducting system shown in  FIG. 1 . 
       FIG. 17  shows an example incorporating the superconducting induction motor of the present invention into a compact passenger vehicle. 
     A configuration of this case uses outer rotor-type superconducting induction motors  1 ′ similar to the one shown in  FIG. 2 , and tires (tread bodies)  61  are directly attached to outer circumferential surfaces of a rotor  18 , as shown in  FIG. 17 . Thus, self-propelling tires  61  may be configured. 
     Also, according to a passenger vehicle  62  with a plurality of the tires  61  attached thereto, compact mobility with a very simple configuration may be provided. 
     According to such a structure, when the rotors are rotationally driven, an induction rotating machine of this embodiment may drive and feed liquid through liquid feed pipes. 
     Although various embodiments of the present invention have been described, it should be understood that the present invention is not be limited to the above-described embodiments, and various changes and modifications may be made without departing from the scope and spirit of the invention. 
     For example, although the system shown in  FIG. 1  was applied to an aircraft in the above one embodiment, it is not limited to these examples and may be applied to any objects requiring propulsion. For example, the system may be applied to a passenger vehicle ( FIG. 17 ) or a train. 
     Also, while one of the above embodiments used propeller blades/fins for generating propulsion, any means for generating propulsion by rotation of a rotor may be used. Further, when these blades or fins are used as means for dissipating heat, any configurations for increasing surface areas may be used, such as a honeycomb structure. 
     Also, when transmitting a driving force of the superconducting induction motor of the present invention by contacting with an object such as the ground, the present invention is no limited to using tires, as shown in  FIG. 17 , and caterpillars or gears may be attached as propulsion generation bodies. 
     DESCRIPTION OF THE REFERENCE NUMBERS 
     
         
         
           
               1 . Superconducting induction motor 
               2 . Fully superconducting system 
               3 . Gas turbine engine 
               4 . Superconducting electric generator 
               5 . Superconducting inverter/Superconducting cable 
               6 . Freezing machine 
               10 . Demonstration system 
               11 . Propeller blades 
               11   a . Base section 
               11   b . Distal end 
               12 . Base 
               13 . Linear guide 
               14 . Stator 
               15 . Superconducting armature coil 
               16 . Stator frame 
               17 . Power supply lead 
               18 . Rotor 
               22 . Highly electrically conductive material layer 
               23 . Magnetic material layer 
               25 . Armature coil 
               26 . Stator frame 
               26   a . Outer circumferential wall 
               26   b . Top wall section 
               26   c . Bottom wall section 
               27 . Superconducting armature coils 
               28 . Stator 
               29 . Power supply lead 
               30 . Rotor 
               31 . Central axis 
               32 . Propeller blades 
               33 . Container 
               35 . Main body 
               36 . Superconducting armature coils 
               37 . Core 
               38 . Superconducting coiling wire 
               39 . Electrically conductive material layer 
               40 . Magnetic material layer 
               42 ,  43 . Lid bodies 
               45 . Superconducting wire 
               46 ,  47 . Short-circuit rings 
               52 . Copper ring 
               53 . Superconducting wire 
               54 . Superconducting wire 
               55 . Liquid feed pump 
               56 . Liquid feed pipe 
               57 . Stator 
               58 . Rotor 
               59 . Superconducting armature coils 
               60 . Propeller fins 
               61 . Tires 
               62 . Passenger vehicle (compact mobility)