Cooling structure of superconducting motor

In a cooling structure of a superconducting motor in which a superconducting coil is attached to a rotor, grooves are concavely provided on an outer surface of a rotating shaft that penetrates and is fixed to the rotor. A refrigerant is circulated through a refrigerant circulation pipe disposed inside the grooves to that the superconducting coil is cooled by the refrigerant.

This is a U.S. National Stage application of PCT/JP2005/023125, filed Dec. 16, 2005, which claims priority to Japanese application 2004-374707, filed Dec. 24, 2004, the disclosures of which are both incorporated herein in their entirety by reference.

TECHNICAL FIELD

The present invention relates to a cooling structure of a superconducting motor. More specifically, the present invention relates to a structure for efficiently cooling a superconducting coil attached to a rotor of a drive motor mounted on ships, such as a government ship and a passenger ship.

BACKGROUND ART

In recent years, the development of a ship driven by electrically driving a motor has been advanced in view of suppressing a depletion of fuel resources, such as a gasoline, and an environmental deterioration due to exhaust gas. Specifically, a superconducting motor disclosed in JP-A-6-006907 (Patent Document 1) may be employed, thereby eliminating copper loss in a superconducting coil and achieving high efficiency. Additionally, a miniaturization of the motor itself and a high-power output can be achieved.

Meanwhile, when driving a superconducting motor, a superconducting coil is required to be cooled to an ultra-low temperature (e.g., 77 kelvins). Thus, means for cooling is especially important, and a simple and efficient cooling structure is being required.

Particularly, when cooling a superconducting coil attached to a rotor disposed at a center of a motor, it is inefficient to cool it from outside the motor. Therefore, it is difficult to sufficiently cool the superconducting coil in such a case.

JP-A-2002-58207 (Patent Document 2) provides a structure in which a hollow portion is formed through a rotating shaft of a motor and a refrigerant is passed through the hollow portion to cool a coil attached to a rotor. This structure enables an efficient cooling of the coil attached to the rotor to a necessary temperature even in a case where the coil attached to the rotor is a superconducting coil.

However, in the structure disclosed in Patent Document 2, a center of the rotating shaft needs to be drilled to form the hollow portion. Particularly, in a case of a large motor, such as a series-coupled synchronous type motor used to drive a ship, it is difficult to form a long hollow portion through a long rotating shaft.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

The present invention has been made in view of the above problems, and it is an object thereof to provide a simple cooling structure of a superconducting motor which can efficiently cool a superconducting coil attached to a rotor.

Means for Solving the Problems

To solve the above problems, the present invention provides a cooling structure of a superconducting motor having a superconducting coil attached to a rotor, the cooling structure comprising:

a rotating shaft penetrating through and fixed to the rotor; and

a refrigerant circulation tube through which a refrigerant for cooling the superconducting coil circulates,

wherein a groove is formed on an outer surface of the rotating shaft, and the refrigerant circulation path is disposed inside the groove.

According to the above configuration, the groove is provided on the outer surface of the rotating shaft instead of providing a hollow portion through a center of the rotating shaft, and the refrigerant circulation tube is disposed inside the groove. Thus, the cooling structure can easily be provided, as compared with the case where the hollow portion is provided through the rotating shaft.

As the motor becomes large, the rotating shaft becomes long accordingly, and it becomes more difficult to form a long hollow portion through a center of the rotating shaft. Therefore, the cooling structure of the present invention may be suitably employed in a large superconducting motor in particular.

Also, since the refrigerant circulation tube is disposed inside the groove and is exposed to an outer side of the rotating shaft, the refrigerant circulation tube can be brought into a direct contact with the rotor and can be placed close to the superconducting coil attached to the rotor. Consequently, cooling effect can be enhanced as compared with the case where the refrigerant circulation tube is provided on a center line of the rotating shaft.

A material of the superconducting coil may be bismuth-based or yttrium-based high-temperature superconducting materials.

The refrigerant circulation tube may include:

a first pipe having a first outgoing path section and a first returning path section that are coupled to a supply source of the refrigerant for cooling the superconducting coil;

a second pipe having a second outgoing path section communicated with the first outgoing path section of the first pipe and a second returning path section communicated with the first returning path section of the first pipe, wherein the second pipe is fixed to an axial end of the rotating shaft and is rotatably coupled to the first pipe; and

a refrigerant circulation pipe having a third outgoing path section communicated with the second outgoing path section of the second pipe and a third returning path section communicated with the second returning path section of the second pipe.

According to the above configuration, the refrigerant for cooling the superconducting coil is circulated from the supply source to the first outgoing path section of the first pipe, the second outgoing path section of the second pipe, the refrigerant circulation pipe, the first returning path section of the second pipe, and the returning path section of the first pipe in this order, whereby the superconducting coil attached to the rotor can be cooled by the refrigerant circulated through the refrigerant circulation pipe that is disposed inside the groove of the rotating shaft.

The groove may include a first longitudinal groove section, a second longitudinal groove section, and a coupling groove section,

the first longitudinal groove section and the second longitudinal groove section are formed along an axial direction of the rotating shaft at symmetric positions with respect to an axis of the rotating shaft,

the coupling groove section is formed along a circumferential surface of the rotating shaft at a front end position of the rotating shaft,

wherein the refrigerant circulation pipe may further have a turnaround section which is disposed inside the coupling groove section and couples the third outgoing path section and the third returning path section.

The above configuration can be easily implemented only by forming the groove on the outer surface of the rotating shaft and arranging the refrigerant circulation pipe within the groove. Thus, the manufacturing efficiency of the superconducting motor can be enhanced a cost can be reduced.

In a case where it is required to further enhance the cooling effect, the groove inside which the refrigerant circulation pipe is disposed may be formed spirally along a circumferential direction other than along the axial direction of the rotating shaft, and for example, a refrigerant circulation pipe of an accordion-type that is flexible may be disposed so as to be wound around the rotating shaft, whereby a length of the refrigerant circulation pipe becomes long. Thus, the superconducting coil can efficiently be cooled in a wide range in the circumferential direction thereof.

In order to prevent the temperature of the refrigerant from rising, circumferential surfaces of the first pipe and the second pipe may be surrounded by heat-insulating means in a region other than a region in which the rotor is disposed.

The heat insulating means maybe implemented by surrounding the first pipe and the second pipe with an outer tube and providing a vacuum heat-insulating layer inside the outer tube. Alternatively, the first pipe and the second pipe may be covered by an adiabatic material.

The first pipe is coupled to the supply source of the refrigerant so that the first pipe is fixed, while the second pipe is attached to the rotating shaft so that the second pipe rotates. Therefore, the first pipe and the second pipe needs to be rotatably coupled.

According to the present invention, a first flange projected from a coupling end of the first pipe and a second flange projected from a coupling end of the second pipe may be provided, wherein the first and the second flanges are rotatably in contact with each other, and spring means for biasing the first and the second flanges in respective contacting directions may be provided.

According to the above configuration, even when the first pipe and the second pipe are somewhat misaligned, an opening in the misaligned coupling end of one of the pipes is covered by the flange corresponding to the other pipe. Thus, the refrigerant can be prevented from leaking. Moreover, the flanges contacting against each other are pushed by the spring means in their contacting directions. Thus, a gap between the flanges that are contacting each other can be eliminated, thereby preventing the refrigerant leakage.

As the refrigerant for cooling the superconducting coil, liquid nitrogen, neon, or helium may be used.

When the liquid nitrogen is used as the refrigerant, the superconducting coil can be cooled to an ultra-low temperature at which the superconducting coil is in a superconducting state.

Liquid nitrogen, whose temperature has been raised by cooling the superconducting coil, can be reused as the refrigerant by being cooled by another cooling unit. In a case where liquid nitrogen is vaporized, the vaporized liquid nitrogen may be externally discharged.

The superconducting motor may be either an axial type in which stators are disposed opposite to each other in the axial direction of the rotor so that a direction of a magnetic flux of the superconducting coil is directed in the axial direction, or a radial type in which the rotor is provided inside a hollow portion of a stator having an annular cross section so that the direction of the magnetic flux of the superconducting coil is directed in a radial direction.

In a case where the superconducting motor is the axial type, the refrigerant circulation pipe disposed inside the groove on the outer surface of the rotating shaft can be drawn out from the groove in the vicinity of the rotor so as to extend along a side surface of the rotor toward the vicinity of the superconducting coil attached to the rotor. Thus, the refrigerant circulation pipe can be disposed in the vicinity of the superconducting coil so that the cooling effect to the superconducting coil can be enhanced.

Advantages of the Invention

As described above, according to the present invention, the cooling structure for cooling the superconducting coil attached to the rotor is provided by forming the groove on the outer surface of the rotating shaft and disposing the refrigerant circulation tube inside the groove, instead of forming a hollow portion at the center of the rotating shaft. Thus, the cooling structure can easily be formed, as compared with the case where the hollow portion is provided in the rotating shaft.

Also, the refrigerant circulation tube is exposed to the outer surface of the rotating shaft. Thus, the refrigerant can be circulated at a position closer to the superconducting coil attached to the rotor than the case where a refrigerant circulation is provided on the center line of the rotating shaft. Consequently, cooling effect can be enhanced.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 to 4show a first embodiment of the invention. A superconducting motor10may be used as a propulsion motor of a ship.

As shown inFIGS. 1 and 2, the superconducting motor10includes a stator16and a rotor17which is rotatably disposed inside a hollow portion of the stator16, and it is a radial type in which a direction of a magnetic flux of a superconducting coil22attached to the rotor17is directed in a radial direction.

The rotor17is formed in a cylindrical shape, and may be made of a powder magnetic material. A rotating shaft23penetrates through a center of the rotor17and is fixed thereto. The rotating shaft23extends towards the exterior of the stator16through bearings18and21.

The superconducting coil22(or field coil) made of a superconducting material is fixed to the rotor17. As the superconducting material, bismuth-based or yttrium-based high temperature superconducting materials may be suitably used.

On the other hand, the stator16may be formed of a powder magnetic material such as an iron powder on which insulating coating is applied. As shown inFIG. 2, the stator16has a cross section of an annular shape. Armature coils19formed by a normal conducting material such as copper wires, and are attached onto an inner circumferential surface of the stator16at angular intervals of 120 degrees in a circumferential direction. Three-phase alternating currents that are phase-shifted from one another are supplied to the respective armature coils19to generate a rotating magnetic field, thereby rotating the rotor17.

As shown inFIGS. 2 and 3, a pair of grooves24and25is concavely formed along the entire length in an axial direction of the rotor17, symmetrically with respect to the central axis of the rotating shaft23. The pair of grooves24and25(a first groove section and a second groove section) is coupled to each other at a position corresponding to an end portion of the rotor17(the left side inFIG. 1) through a groove26(a coupling section) that is concavely provided along the circumferential direction of the rotating shaft23. A refrigerant circulation pipe33, in which liquid nitrogen is circulated, is disposed inside these grooves24,25, and26.

An outgoing path section33A and a returning path section33B of the refrigerant circulation pipe33are disposed inside the pair of grooves24and25, respectively. A turnaround section33C, through which the refrigerant circulation pipe33is turned from the outgoing path section33A to the returning path section33B, is disposed inside the groove26provided between the grooves24and25. The liquid nitrogen serving as a refrigerant circulates through the refrigerant circulation pipe33including the outgoing path section33A, the returning path section33B, and the turnaround portion33C that are continuously formed, whereby the superconducting coil22attached to the rotor17is cooled.

Together with the refrigerant circulation pipe33, a first pipe31and a second pipe32communicated with the first pipe31are provided as cooling means.

The first pipe31has an outgoing path section31A and a returning path section31B, which are coupled to a liquid nitrogen tank11serving as a supply source of a refrigerant (the liquid nitrogen in the embodiment) for cooling the superconducting coil.

The refrigerant for cooling the superconducting coil is not limited to liquid nitrogen, and neon and helium may be used as the refrigerant.

The second pipe32also has an outgoing path section32A and a returning path section32B, which are respectively communicated with and are rotatably coupled to the outgoing path section31A and the return passage31B of the first pipe31. The second pipe32is fixed to one of the axial ends of the rotating shaft23, and as shown inFIG. 3, a part of the second pipe32extending from the one end of the rotating shaft23to the rotor17is disposed inside the grooves24and25that are concavely provided on the rotating shaft23.

Outer circumferential surfaces of the first pipe31and the second pipe32are surrounded with outer-tubes34and36for vacuum insulation, thereby providing heat insulating means having vacuum heat-insulating layers35and37.

As described above, as for the refrigerant circulation pipe33disposed inside the grooves24,25, and26of the rotating shaft32, the outgoing path section33A and the returning path section33B are communicated with the outgoing path section32A and the returning path section32B of the second pipe, respectively. No heat insulating means is provided for the refrigerant circulation pipe33so that the superconducting coil22is cooled by a cold heat of the liquid nitrogen at this non-adiabatic portion, the cold heat being transmitted through the rotor17.

More specifically, as shown inFIG. 4, a coupling end of the first pipe31, which is coupled to the second pipe32, is disposed such that the outgoing path section31A is placed on the same line as the center line of the rotating shaft23, the outer circumference of the returning path section3lA is surrounded by the returning path section31B, and the outer circumference of the returning path section31B is surrounded by the outer-tube34for vacuum insulation.

Similarly, a coupling end of the second pipe32, which is coupled to the first pipe31, is disposed such that the outgoing path section32A is placed on the same line as the centerline of the rotating shaft23, the outer circumference of the returning path section32A is surrounded by the returning path section32B, and that the outer circumference of the returning path section32B is surrounded by the outer-tube36for vacuum insulation.

Thus, at the coupling ends of the first pipe31and the second pipe32, the outgoing path section31A and the returning path section31B of the first pipe31are disposed face the outgoing path section32A and the returning path section32B of the second pipe32, respectively. Consequently, the liquid nitrogen flowing out from the liquid nitrogen tank11circulates the outgoing path section31A of the first pipe31, the outgoing path section32A of the second pipe32, the refrigerant circulation pipe33, the returning path section32B of the second pipe32, and the returning path section31B of the first pipe31in this order.

At the coupling ends of the first pipe31and the second pipe32, flanges31A-1,31B-1,32A-1and32B-1are provided to protrude towards the outer circumferential side, and the flanges31A-1and32A-1are made to contact against each other while the flanges31B-1and32B-1are made to contact against each other. The flanges31B-1and32B-1contacting against each other are covered with a cover38, and springs39attached inside the cover38pushes the flanges31B-1and32B-1in respective contacting directions from respective sides.

According to the above configuration, instead of providing a hollow portion in the center of the rotating shaft23, the grooves24,25, and26are provided on the outer surface of the rotating shaft23, and the refrigerant circulation pipe33, in which the liquid nitrogen serving as the refrigerant is circulated, is disposed inside the grooves24,25, and26. Thus, the cooling structure can easily be formed, as compared with the case where a hollow portion is provided in the rotating shaft23.

Moreover, since the refrigerant circulation pipe33is placed closer to the outer surface than the case where the refrigerant circulation pipe33is provided on the center line of the rotating shaft23, the refrigerant circulation pipe33can be disposed closer to the superconducting coil22so that a cooling effect can be enhanced.

As shown inFIG. 5, an end31A-1aof the flange31A-1projecting at the coupling end of the outgoing path section31A of the first pipe31and an end32A-1aof the flange32A-1projecting at the coupling end of the outgoing path section32A of the second pipe32may be bent toward the rotor so that the end32A-1aof the flange32A-1is covered with the end31A-1aof the other flange31A-1, whereby a refrigerant leakage at the coupling portions can be more surely prevented.

FIGS. 6 and 7show a second embodiment of the invention.

The difference from the first embodiment is that the second embodiment is a motor of an axial type in which the stators are placed opposite to each other in the axial direction of the rotor, whereby a direction of a magnetic flux of the superconducting coil is directed in the axial direction.

In a superconducting motor50according to this embodiment, a pair of stators53and54is arranged so as to face each other on respective sides a rotor52fixed to a rotating shaft51with a predetermined gap being provided the respective sides of the rotor52.

The rotor52is formed with a through hole52aat a shaft center portion thereof, and the rotating shaft51is inserted through and fixed to the through hole52a, whereby the rotor52and the rotating shaft51are corotated.

Magnetic field element mounting holes52bare formed on the rotor52at intervals in a circumferential direction around the axis thereof. Superconducting coils55for magnetic field are fitted into and fixed in each of the magnetic field element mounting holes52bso that the direction of the magnetic flux is directed in the axial direction.

The rotating shaft51penetrates though symmetrical disk-shaped stators53and54via bearings. A plurality of armature coils56and57formed of normal conducting materials (e.g., copper wires) is arranged on the surfaces of the stators53and54at intervals in a circumferential direction around the axis thereof. One end of each of the armature coils56and57is fixed to the surface of the stator53or54on a side facing the rotor with an adhesive agent, and the armature coils56and57are protruded toward the rotor52in the axial direction.

Similarly to the first embodiment, grooves58and59are concavely provided on an outer surface of the rotating shaft51at symmetrical positions, but a circumferential groove of the first embodiment which couples the grooves58and59is not provided. Alternatively, a refrigerant circulation pipe61of the refrigerant circulation tube disposed inside the grooves58and59is drawn out from the groove at a groove end on the side of the rotor52, and is arranged to extend along a side surface of the rotor52. The refrigerant circulation pipe61is alternately arranged on an outer side (a circumferential edge side of the rotor52) and an inner side (a side of the rotating shaft51) of the superconducting coils55attached to the rotor52so as to be disposed in the vicinity of the superconducting coil55. Namely, as shown inFIG. 7, the refrigerant circulation pipe61is arranged through a space between the adjacent superconducting coils55, a space between the superconducting coil55and the circumferential edge of the rotor52, a space between the adjacent the superconducting coils55, and a space between the superconducting coil55and the rotating shaft51in this order. The refrigerant circulation pipe61may be attached to the side surface of the rotor52with an adhesive agent, or may be disposed inside a groove formed on the rotor52.

According to the above configuration, even for the axial-type motor, the superconducting coil attached to the rotor can be cooled by the cooling structure that is formed by disposing the refrigerant circulation pipe inside the groove provided on the outer surface of the rotating shaft. Also, because the refrigerant circulation pipe61is drawn out from the grooves58and59on the rotating shaft51, and the drawn-out refrigerant circulation pipe61is disposed in the vicinity of the superconducting coils55, the cooling effect the superconducting coils55can be enhanced.

Since the first pipe, the second pipe, and the remaining configurations of the refrigerant circulation tube are similar to those of the refrigerant circulation tube of the first embodiment, explanation thereof will be omitted.

FIG. 8shows a modified example of the second embodiment.

In this modified example, superconducting coils55are attached along the circumference of a rotor52. A refrigerant circulation pipe61drawn out form grooves58and59of a rotating shaft51is arranged along an inner side (a side of the rotating shaft51) of the superconducting coils55.

According to the above configuration, the refrigerant circulation pipe61is disposed in the vicinity of the superconducting coils55so that the cooling effect the superconducting coils55can be enhanced.

INDUSTRIAL APPLICABILITY

The motor device according to the present invention can suitably be used as a power source for large ships or the like which require high power output. Specifically, when an axial gap type of motor as shown inFIG. 6is applied for a series-coupled synchronous type configuration, in which stators and rotors are alternately stacked on a rotating shaft so that the stators and the rotors are arranged in a high density, and in which high temperature superconducting bulk magnets are attached to the respective rotors and are cooled by a refrigerant circulated through a refrigerant circulation tube provided on the rotating shaft, high-power output of the motor can be maintained. Accordingly, such a motor can suitably be used as a propulsion motor for large ships, such as a government ship or a passenger ship.