Superconducting bearing device

Abstract: A superconducing bearing device comprising a permanent magnet portion (3) provided on a rotatable member (1), and a superconductor disposed as opposed to the magnet portion (2). The permanent magnet portion (3) is so mounted on the rotatable member (1) that the rotation of the rotatable member does not alter the magnetic flux distribution around the axis of rotation of the member. The superconductor (2) permits penetration of the magnetic flux of the magnet portion thereinto, is spaced apart from the magnet portion (3) by a distance permitting a predetermined quantity of magnetic flux of the magnetic portion (3) to penetrate thereinto, and is disposed at a position not permitting the rotation of the rotatable member (1) to alter the distribution of penetrating magnetic flux.

Description: BACKGROUND OF THE INVENTION The present invention relates to superconducting bearing devices having incorporated therein a superconductor permitting penetration of a magnetic flux thereinto. Superconducting bearing devices heretofore known include, for example, the one disclosed in Unexamined Japanese Patent Publication SHO 63-243523. The superconducting bearing device disclosed includes a Type I superconductor, i.e., a superconductor preventing the penetration of magnetic flux perfectly to utilize the perfect diamagnetism of the superconductor. The device comprises a rotary shaft made of the superconductor and having its opposite ends fitted in a pair of recesses each of which is formed in a support member of magnetic material magnetized to one of the polarities, the rotary shaft being supported in a non-contacting position axially thereof. With the known superconducting bearing device, the rotaty shaft is supported in a non-contacting position utilizing perfect diamagnetism as stated above and is therefore instable with respect to a direction orthogonal to the direction of repulsion, so that the support member for supporting each end of the rotary shaft must be machined to a shape surrounding the shaft end. Furthermore,between the shaft end and the support member, the portion opposed to the shaft end axially and radially of the shaft needs to be magnetized. Accordingly, the device is cumbersome to design and make. A superconductor-magnet induced separation as described in the preamble of claims 1 and 2 and known from US 4,797,386 consists of a Type II superconducting support body made of a Type II superconducting material like barium yttrium copper oxide composition and a permanent magnet which is levitated over the superconducting support body when this arrangement is cooled down to realize a Type II superconducting state. Levitation of the permanent magnet is caused by the Meissner effect whereas a stabilization force results from field penetration in one or more regions where the magnetic field H exceeds H c1 value of the used Type II superconducting material. A superconducting bearing using this principal consists of a tubular superconducting body within which a magnetic member attached to a rotatable shaft is arranged for supporting the rotatable shaft during rotation. In this bearing radial support is obtained by the Meissner effect whereas longitudinal displacement of the magnetic member relative to the tubular superconducting body is prevented by a pinning force resulting from field penetration in one ore more regions where the magnetic field H of the magnetic member exceeds H c1 value. Another bearing system (WO 90/03534) employing a superconductor element made of Y 1 Ba 2 Cu 3 oxide includes a permanent magnet member that is not simply repelled (Meissner effect) but pinned by the magnetic field lines developed in the superconductor owing to a partial penetration of the magnetic flux. This partial penetration occurs in field portions where the magnetic field H exceeds the critical value H c1 . The magnetic member may be a rotor in the shape ofa flat donut consisting of one or more magnet elements which are magnetized in the longitudinal direction of the axis of rotation. When two or more magnetic elements are used for the rotor the polarization alternates so that an N-pole of one magnet element is adjacent to S-magnet poles of abutting magnet elements. Another magnetic bearing is known from JP-A-1-98 709 and consists of a cylindrical inner race fitted around a rotary shaft and a cylindrical outer race fitted in a housing. The inner and outer races are matching with each other and either one thereof is made of superconductive material and the other of a permanent magnet. This magnetic bearing uses the Meissner effect of the superconductive material only to stabilize a minute gap between the inner and the outer race. A further bearing (JP-A-1-69818) using a superconductor consists of an outer ring made of superconductor material and an inner magnetic ring fitted on a rotatable shaft. The outer ring comprises radial flanges extending inwardly so as to embrace the inner magnetic ring to some extend. This magnetic bearing uses also the Meissner effect of the superconductor only. Another bearing known from JP-A-1-295019 comprises superconducting plates arranged in parallel and spaced from each other which are fixed to a rotatable shaft. Three permanent magnet groups each consisting of three annular permanent magnets are arranged to face both faces of both plates of superconducting material. Each of the annular permanent magnets is magnetized so as to be polarized in parallel with the longitudinal direction of the axis of rotation whilst permanent magnets arranged adjacent to each other in the longitudinal or radial direction are magnetized so as to be antiparallel polarized. SUMMARY OF THE INVENTION The object of the present invention is to provide a superconducting bearing device adapted to support a rotatable member radially and axially by a simple construction. This object is achieved by the superconducting bearing device according to claim 1 or 2. Since the permanent magnet consisting preferably of at least two annular magnet portions polarized so that adjacent magnet poles of abutting magnet portions have the same polarity, the magnetism of one of the magnet poles repels that of another magnet pole of the same polarity causing the magnetic flux to extend axially of the rotatable shaft when the radially arranged portions are polarized in parallel with the axis of rotation. Similarly, the magnetism of one portion repels that of the other portion having the same polarity with the result that the magnetic flux expends both axially and radially of the rotatable member, when opposed side or end portions of the adjacent magnet portions have the same polarity. This permits an increased quantity of flux to penetrate into the superconductor opposing the endfaces and/or the outer periphery of the permanent magnet. Consequently, the superconductor traps an increased amount of flux to give the device an increased load capacity and enhanced rigidity. The restraining action of the magnetic flux of the permanent magnet penetrating into the superconductor stably hold the magnet and the superconductor opposed to each other and spaced apart by a predetermined distance. In this state, the rotatable shaft carrying the magnet can be rotated about its axis without resistance caused by the external magnetic field acting on the superconductor since the magnetic flux distribution is uniform with respect to the axis ofrotation and remains unchanged. Accordingly, the rotatable shaft can be supported by the superconductor in a non-contacting position radially and axially thereofwhen the magnet mounted on the rotatable shaft is merely positioned in place relative to the superconductor. Thus, the device of the invention is adapted to rotatably support the rotatable shaft with good stability by very simple construction. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation schematically showing a first superconducting bearing device; FIG. 2 is a side elevation schematically showing a second superconducting bearing device; FIG. 3 is a view in vertical section schematically showing a first embodiment of superconducting bearing device of the invention; FIG. 4 is a view in vertical section schematically showing a second embodiment of superconducting bearing device of the invention; FIG. 5 is a view in vertical section schematically showing a third embodiment of superconducting bearing device of the invention; FIG. 6 is a view in vertical section schematically showing a fourth embodiment of superconducting bearing device of the invention; FIG. 7 is a view in vertical section schematically showing a fifth embodiment of superconducting bearing device of the invention; and FIG. 8 is a view in vertical section schematically showing an sixth embodiment of superconducting bearing device of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Several embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, like parts are designated by like reference numerals. FIG. 1 schematically shows a superconducting bearing device, that comprises a solid cylindrical rotatable member 1, and a superconductor 2 in the form of a flat plate. The rotatable member 1 in its entirety is a permanent magnet portion in the form of a single permanent magnet. The rotatable member 1 has one end magnetized to an N pole, and the other end magnetized to an S pole. The superconductor 2 comprises a base plate which is prepared from a high-temperature superconducting material of the yttrium type of great pinning force, for example, YBa 2 Cu 3 O x , and which contains normally conductive particles (Y 2 Ba 1 Cu 1 ) as uniformly mixed with the superconducting material. The superconductor 2 has properties to trap the magnetic flux released from the rotatable member 1 and penetrating thereinto. The rotatable member 1 is disposed with its axis positioned horizontally and is rotatable about the axis without permitting alteration of the magnetic flux distribution around the axis despite the rotation. The superconductor 2 is opposed to the rotatable member 1 and disposed at a position spaced apart from the member 1 by a distance permitting a predetermined quantity of magnetic flux of the member 1 to penetrate into the superconductor, the superconductor 2 further being so positioned that the rotation of the member 1 will not alter the distribution of penetrating magnetic flux. The superconductor 2 has its upper surface opposed to the outer peripheral surface of the rotatable member 1 and is positioned horizontally below the rotatable member 1 in parallel thereto. When the bearing device is to be operated, the superconductor 2 is cooled by suitable cooling means and maintained in a superconducting state. If the rotatable member 1 is merely disposed horizontally above the superconductor 2 as positioned horizontally in a superconducting state, only a small quantity of magnetic flux of the member 1 penetrates into the superconductor 2, so that the member 1 is merely levitated by a repulsive force due to the Meissner effect of the superconductor 2 and is not supported stably. However, when the rotatable member 1 is disposed above the superconductor 2 in the vicinity thereof first and the superconductor 2 is thereafter cooled to the superconducting state, a large quantity of magnetic flux released from the rotatable member 1 penetrates into the superconductor 2 and is trapped in this state. Since the superconductor 2 contains pinning centers (e.g., normally conductive particles) as uniformly mixed with the superconducting material, the magnetic flux penetrating into the superconductor 2 becomes distrubuted also uniformly and is held trapped. Consequently, the rotatable member 1 is held levitated above the superconductor 2 and supported axially and radially with high stability. When the rotatable member 1 as thus supported in a non-contacting position is rotated about its axis, the magnetic flux penetrating into the superconductor 2 offers no resistance to the rotation because the magnetic flux distribution around the axis remains unchanged despite the rotation. Further because the rotation involves no frictional resistance unlike sliding or rolling bearings, the rotatable member 1 is to rotate permanently, whereas the member is influenced by air resistance and geomagnetism in actuality and therefore comes to a halt eventually. Nevertheless, such resistance to rotation is very small for the bearing device and almost negligible. If the rotatable member 1 as supported in the above non-contacting position is pushed in one direction with a force smaller than the pinning force, the member 1 shifts in this direction once, then shifts toward the original position, thus undergoing a swinging motion for some time, and thereafter comes to a stop at the original position. However, if the rotatable member 1 is pushed toward one direction with a force greater than the pinning force, the member 1 stops upon moving to a position to which it is forcibly shifted from the original position. Thus, the member 1 is restrained in the shifted position. This phenomenon occurs owing to the pinning force peculiar to the superconductor 2 of the foregoing structure. If the magnetic flux of the rotatable member 1 is held pinned to the supercontactor 2 as described above, the rotatable member 1 will always be supported with good stability by a restraining action. FIG. 2 schematically shows the main portion of another superconducting bearing device. This device is the same as the first device with respect to the structure and arrangement of the superconductor 2. The rotatable member 1, although the same as the one included in the first device, is disposed above the superconductor 2 with its axis of rotation positioned vertically. The upper surface of the superconductor 2 is opposed to the lower end face of the rotary member 1. With the exception of this feature, the second device is the same as the first. With the second device, the rotatable member 1 is also supported as levitated above the superconductor 2 as in the case of the first device. In the foregoing two devices, the arrangement of the rotatable member 1 and the superconductor 2 may be inverted. In other words, the rotatable member 1 may be disposed below the lower surface of the superconductor 2 in proximity to the superconductor 2. The rotatable member 1 is then supported as levitated as if being suspended from the superconductor 2. Alternatively, if the rotatable member 1 is opposed, as positioned obliquely, to the superconductor 2, the member 1 is held levitated in the oblique position. FIG. 3 schematically shows the main portion of another superconducting bearing device, i.e., a first embodiment of the present invention. This bearing device comprises a rotatable member 1 in the form of a vertical shaft, and a superconductor 2. A permanent magnet portion 3 in the form of a horizontal disk is mounted on the rotatable member 1 concentrically therewith, and the superconductor 2 is opposed to the lower end face of the magnet portion 3 and spaced apart therefrom axially of the rotatable member 1. The superconductor 2 is in the form of a disk having a bore, and the rotatable member 1 extends through the bore with a clearance formed in the bore around the member 1. The permanent magnet portion 3 is in the form of an integral assembly and comprises a plurality of annular permanent magnets 4a, 4b, 4c arranged at a spacing radially of the member 1, and a nonmagnetic material 5 interposed therebetween. The portion 3 is secured to the rotatable member 1. The upper and lower ends of each of the magnets 4a, 4b, 4c are magnetized to polarities opposite to each other, and all the magnets 4a, 4b, 4c are magnetized to the same polarity at their same ends. For example, the upper ends of all the magnets 4a, 4b, 4c are magnetized as N poles, and the lower ends thereof as S poles. The magnetic flux distribution around the axis of rotation is free of changes despite the rotation of the member 1. The superconductor 2 has the same properties as the one included in the first device and is disposed at a position spaced apart from the magnet portion 3 by a distance permitting a predetermined quantity of magnetic flux of the portion 3 to penetrate thereinto and which will not permit the rotation of the member 1 to alter the distribution of penetrating magnetic flux. A cooling case 22 which is cooled by a refrigerator 20 or the like via a temperature control unit 21 is fixedly provided within a housing (not shown) for the bearing device. The superconductor 2 is fixed to the cooling case 22. When the superconducting bearing device is operated, the superconductor 2 is cooled with a suitable refrigerant circulated through the cooling case 22 and maintained in a superconducting state. As in the case of the first device, the restraining action of the magnetic flux penetrating into the superconductor 2 from the permanent magnet portion 3 and trapped in the superconduct 2 holds the rotatable member 1 and the superconductor 2 opposed to each other with a predetermined spacing provided therebetween and supports the member 1 as levitated above the superconductor 2. At each end of the permanent magnet portion 3, the magnetism of one of the permanent magnets 4a, 4b, 4c repels that of another magnet of the same polarity, with the result that the magnetic flux extends to a greater extent axially of the rotatable member 1 than in the case where the permanent magnet portion has a single permanent magnet. Consequently, an increased quantity of flux penetrates into the superconductor 2 which is disposed as opposed to the lower end face of the magnet portion 3 for the superconductor 2 to trap the increased quantity of flux. This gives the device a greater load capacity and higher rigidity. In addition to the superconductor 2, second superconductors 6 may be provided as indicated in broken lines in FIG. 3. These second superconductors 6 are arranged radially outwardly of the periphery of the permanent magnet portion 3 at a distance from and as opposed to the periphery. These superconductors 6 also support the rotatable member 1, consequently giving further enhanced rigidity to the entire bearing device. These superconductors 6 may form a completely annular block or may be segments of an annular block. FIG. 4 schematically shows the main portion of another superconducting bearing device, i.e. a second embodiment. In this embodiment, superconductors 2, 6, 7 are provided as opposed respectively to the lower end face, outer peripheral surface and upper end face of a permanent magnet portion 3 on a rotatable member 1. FIG. 5 schematically shows the main portion of another superconducting bearing device, i.e., a third embodiment. This embodiment has a permanent magnet portion 8 which also comprises a plurality of annular permanent magnets 9a, 9b arranged at a spacing radially of the rotatable member 1 and a nonmagnetic material 10 interposed therebetween. The side portions of each permanent magnet 9a or 9b which are opposite radially of the rotatable member 1 are magnetized to polarities opposite to each other, and the opposed side portions of the adjacent magnets 9a, 9b are magnetized to the same polarity. For example, the inner side portion of the inner magnet 9a has N pole, the outer side portion thereof S pole, the inner side portion of the outer magnet 9b S pole, and the outer side portion thereof N pole. Three or more permanent magnets, when used, are also magnetized similarly. At the opposed side portions of the adjacent magnets 9a, 9b in this embodiment, the magnetism of one side portion repels that of the other side portion having the same polarity, with the result that the magnetic flux expands both axially and radially of the rotatable member. This permits an increased quantity of flux to penetrate into the superconductor 2 which is opposed to the lower end face of the permanent magnet portion 8. In this case, additional superconductors may also be provided as opposed to the outer peripheral surface and the upper end face of the magnet portion 8. FIG. 6 schematically shows the main portion of another superconducting bearing device, i.e., a fourth embodiment. This embodiment has a permanent magnet portion 11 in the form of an integral assembly and comprising a plurality of annular permanent magnets 12a, 12b arranged at a spacing axially of the rotatable member 1 and a nonmagnetic material 13 interposed therebetween. The side portions of each magnet 12a or 12b which are opposite axially of the rotatable member are magnetized to polarities opposite to each other, and the opposed ends of the adjacent magnets 12a, 12b are magnetized to the same polarity. For example, the upper end of the upper magnet 12a is magnetized as N pole, the lower end thereof as S pole, the upper end of the lower magnet 12b as S pole, and the lower end thereof as N pole. The same is true of the case wherein three or more permanent magnets are used. At the opposed ends of the adjacnet magnets 12a, 12b of the fourth embodiment, the magnetism of one end repels that of the other end having the same polarity, with the result that the magnetic flux expands both axially and radially of the rotatable member. This permits an increased quantity of flux to penetrate into the superconductor 2 which is opposed to the lower end face of the magnet portion 11. In this case, additional superconductors may also be provided as opposed to the outer peripheral surface and the upper end face of the permanent magnet portion 11. FIG. 7 schematically shows the main portion of another superconducting bearing device, i.e., a fifth embodiment. In this embodiment, the superconductor 2 of the third embodiment is replaced by a superconductor 6 opposed to the outer peripheral surface of the permanent magnet portion 8. As already stated with reference to the fifth embodiment, the magnetic flux expands both axially and radially of the rotatable member also in this case, with the result that an increased quantity of flux penetrates into the superconductor 6 which is disposed as opposed to the outer peripheral surface of the magnet portion 8. FIG. 8 schematically shows the main portion of another superconducting bearing device, i.e., an eighth embodiment. In this embodiment, the superconductor 2 of the sixth embodiment is replaced by a superconductor 6 opposed to the outer peripheral surface of the permanent magnet portion 11. As already described with reference to the sixth embodiment, the magnetic flux expands both axially and radially of the rotatable member also in this case, with the result that in increased quantity of flux penetrates into the superconductor 6 which is disposed as opposed to the outer peripheral surface of the magnet portion 11.

Claims: A superconducting bearing device comprising: a rotatable shaft (1); an annular permanent magnet portion (3, 8, 11) being provided around said rotatable shaft (1) integrally and concentrically therewith, and said rotatable shaft (1) not altering a magnetic flux distribution generated by said annular permanent magnet portion (3, 8, 11) around an axis of roration of said rotatable shaft (1); a cooling case (22) provided within a housing for the bearing device and creating a temperature environment for realizing a Type II superconducting state; and a Type II superconducter (2, 6, 7) being penetrated by said rotatable shaft (1) and being fixed to said cooling case (22); wherein said Type II superconductor (2, 6, 7) permitting penetration of the magnetic flux of said permanent magnet portion (3, 8, 11), being positioned so as to be spaced from said permanent magnet portion (3, 8. 11) by a distance permitting a predetermined quantity of the magnetic flux of said permanent magnet portion (3, 8, 11) to penetrate thereinto, and being positioned so as not to permit a rotation of said rotatable shaft (1) to alter the distribution of penetrating magnetic flux, characterized in that said permanent magnet portion (3, 8, 11) includes at least two annular permanent magnets (9a, 9b; 12a, 12b) magnetized to the same polarity at their adjacent ends and a nonmagnetic material (15; 13) interposed therebetween. A superconducting bearing device comprising: a rotatable shaft (1); an annular permanent magnet portion (3, 8, 11) being provided around said rotatable shaft (1) integrally and concentrically therewith, said rotatable shaft (1) not altering a magnetic flux distribution generated by said annular permanent magnet portion (3, 8, 11) around an axis of rotation of said rotatable shaft (1); a cooling case (22) provided within a housing for the bearing device and creating a temperature environment for realizing a Type II superconducting state; and a Type II superconducter (2, 6, 7) being penetrated by said rotatable shaft (1) and being fixed to said cooling case (22); wherein said Type II superconductor (2, 6, 7) permitting penetration of the magnetic flux of said permanent magnet portion (3, 8, 11), being positioned so as to be spaced from said permanent magnet portion (3, 8, 11) by a distance permitting a predetermined quantity of the magnetic flux of said permanent magnet portion (3, 8, 11) to penetrate thereinto, and being positioned so as not to permit a rotation of said rotatable shaft (1) to alter the distribution of penetrating magnetic flux, characterized in that said permanent magnet portion (3, 8, 11) includes at least two annular permanent magnets (4a, 4b, 4c) magnetized to polarites opposite each other at both axial ends and to the same polarity at their adjacent axial ends and arranged at different spacings radially of the rotatable shaft (1), and a nonmagnetic material (15; 13) interposed therebetween. A superconducting bearing device as defined in claim 1, characterized in that said annular permanent magnets (12a, 12b) of said permanent magnet portion (3, 11) have magnetic poles magnetized to polarites opposite each other at both axial ends and are arranged at a spacing axially along the rotatable shaft. A superconducting bearing device as defined in claim 1, characterized in that said annular permanent magnets (9a, 9b) of said permanent magnet portion (8) have magnetic poles magnetized to polarities opposite each other at the radially inner and outer sides and are arranged at a spacing radially of the rotatable shaft. A superconducting bearing device as defined in any one of claims 1 to 4, characterized in that said Type II superconductor (2, 7) is positioned opposite to an axial endface of said annular permanent magnet portion (3, 8, 11). A superconducting bearing device as defined in any one of claims 1 to 5, characterized in that said Type II superconductor (6) is positioned opposite said radially outer periphery of said permanent magnet portion (3, 8, 11). A superconducting bearing device as defined in any one of claims 1 to 6, characterized in that said superconductor (2, 6, 7) is a yttrium type oxide ceramic superconductor. A superconducting bearing device as defined in claim 7, characterized in that said yttrium type oxide ceramic superconductor has normally conductive particles spread uniformally as pinning points of the penetrating magnetic flux in the interior thereof. A superconducting bearing device as defined in claim 7 or 8, characterized in that the yttrium type oxide ceramic superconductor is made of YBa 2 Cu 3 O x .

Inventors: EGUCHI SHOJI, TAKAHATA RYOICHI, EGUCHI, SHOJI, TAKAHATA, RYOICHI
Applicants: KOYO SEIKO CO, KOYO SEIKO CO., LTD.
Application year: 1991
Main classification: F16C39
IPC codes: F16C39