Superconducting bearing device

Abstract: A superconducting bearing device comprises an annular permanent magnet portion 2 disposed concentrically with a rotary body 1 in the form of a vertical shaft, and superconductors 8 opposed to the lower end face of the magnet portion 2 and vertically spaced apart therefrom. The permanent magnet portion 2 comprises a disk 4 fixedly mounted on the rotary body 1, and annular permanent magnets 6a, 6b arranged on the disk 4 at a spacing radially of the rotary body 1. Each of the magnets 6a, 6b has upper and lower ends magnetized to polarities opposite to each other, and the adjacent magnets 6a, 6b are magnetized to polarities opposite to each other at the upper ends, as well as at the lower ends. The radial spacing between the magnets 6a, 6b is optimized in accordance with the radial dimension (width) of the magnets 6a, 6b. This improves the device in load capacity and rigidity and prevents the deflection of axis of the rotary body 1, enabling the bearing device to support the rotary body 1 in a noncontact state with good stability.

Description: The present invention relates to superconducting bearing devices, for example, for use in hydraulic machines and machine tools which require high-speed rotation, power storage apparatus for storing excessive electric power as converted to kinetic energy of a flywheel, or gyroscopes The EP 0 322 693 A deals with a radial superconducting bearing device disposing the arrangement of a rotor in a bore of a stator. The rotor is at least in part made of permanent magnetic material having its magnetic axis extending along the rotary axis of the rotor. The stator consists of superconducting material. The WO 90/03524 A discloses an axial bearing element employing a superconductor element. A plurality of permanent magnets is provided in a disclike hetero polar configuration without spacing between the permanent magnets. The permanent magnets are magnetized in the axial direction. The JP 01295019 A discloses an axial superconducting bearing device wherein annular permanent magnets are provided on a stationary member in a heteropolar configuration with a spacing between them in the radial direction. The permanent magnets are magnetized in the axial direction. The EP 0 467 34.1 A of applicant describes a superconducting bearing having an annular permanent magnet portion concentrically arranged on a rotary body and a superconducter surrounding the permanent magnet portion and spaced apart therefrom. A plurality of annular permanent magnets is arranged on a disk at a spacing in radial direction. This document is not pre-published with respect to the present application. In recent years, superconducting bearing devices capable of supporting a rotary body in a noncontact state have been developed as bearing devices permitting high-speed rotation of the rotary body and having high rigidity. It is thought that such superconducting bearing devices comprise, for example, an annular permanent magnet disposed concentrically with a rotary body and having axially opposite ends magnetized to polarities opposite to each other, and an annular superconductor opposed to the end face of the magnet and spaced apart therefrom axially of the rotary body. However, the superconducting bearing device has the problem of being insufficient in rigidity with respect to the direction of the rotation axis and in load capacity. Another problem encountered is that the device is unable to support the rotary body in a noncontact state with good stability because the axis of the rotary body deflects owing to insufficient rigidity. These problems are thought attributable to the following reason. The magnetic field strength H and magnetic flux density B of the permanent magnet are in inverse proportion to the distance from the magnet and decrease with an increase in the distance. Suppose the distance between the superconductor and the permanent magnet is Z, the apparent magnetic susceptibility of the superconductor is M, the field strength of the permanent magnet is H and the flux density of the magnet is B. The force of magnetic repulsion between the superconductor and the permanent magnet is in proportion to the product of the susceptibility M and the gradient of field strength dH/dZ or to the product of the susceptibility M and the gradient of flux density dB/dZ. The rigidity is proportional to the product of the susceptibility M and d 2 B/dZ 2 . However, the gradient of field strength dH/dZ or the gradient of flux density dB/dZ of the annular permanent magnet is not great sufficiently, hence insufficient rigidity and load capacity. An object of the present invention is to overcome the foregoing problems and to provide a superconducting bearing device capable of supporting a rotary body in a noncontact state with good stability by preventing the deflection of the axis of the rotary body. To comply with this object, the bearing according to the invention is characterized by the features of claim 1. The present invention accordingly provides a superconducting bearing device which comprises an annular permanent magnet portion disposed concentrically with a rotary body, and a superconductor opposed to the outer periphery of the permanent magnet portion and spaced apart therefrom radially of the rotary body, the permanent magnet portion comprising a disk fixedly mounted on the rotary body, and a plurality of annular permanent magnets arranged on the disk at a spacingwith respect to each other in the axial direction of the rotary body, each of the permanent magnets having radially opposite sides magnetized to polarities opposite to each other, the permanent magnets adjacent to each other being magnetized to polarities opposite to each other at their same sides with respect to the radial direction. Preferably, the spacing between the annular permanent magnets is 0.2 to 1.0 times the thickness of the magnets as measured axially thereof. In this case, a magnetic flux produced from the positive pole of one magnet and directed toward the negative pole of the same magnet upon reversion is added to a magnetic flux produced from the positive pole of another pole. This gives a strengthened magnetic flux and increases the gradient of flux density dB/dZ and d 2 B/d 2 z, consequently increasing the load capacity and the rigidity. Therefore, the deflection of the axis of the rotary body can be prevented, enabling the device to support the rotary body in a noncontact state with good stability. Experiments have shown that the reversion of the magnetic flux starts to become pronounced in a space at a distance of 0.3 times the magnet width from the magnetic pole in the axial direction and at least 0.2 times the width radially away therefrom. Accordingly when two magnets are arranged too closely, the magnetic flux produced from the positive pole of one of the magnets and the magnetic flux entering the negative pole of the other magnet will interfere with each other to produce an adverse effect. BRIEF DESCRIPTION OF THE DRAWINGS The only Figure is a diagram in vertical section showing the main portion of a superconducting bearing device as an embodiment of the invention. The present invention will be described below in greater detail with reference to the accompanying drawings. In the following description, like parts are designated by like reference numerals. The only Figure schematically shows the main portion of a superconducting bearing device as an embodiment. A permanent magnet portion 20 has a disk 21 which is formed in its outer periphery with a plurality of, for example two, annular grooves 22a, 22b vertically spaced apart. Annular permanent magnets 23a, 23b are fixedly fitted in the grooves 22a, 22b, respectively. Each of the permanent magnets 23a, 23b has radially opposite sides which are magnetized to polarities opposite to each other. The radially outer sides, as well as the inner sides, of the adjacent permanent magnets 23a, 23b are magnetized to opposite polarities. For example, the upper magnet 23a has an N pole at the outer periphery and an S pole at the inner periphery, and the lower magnet 23b has an S pole at the outer periphery and an N pole at the inner periphery. The magnetic flux distribution around the axis of rotation is so designed as to remain unaltered by rotation. Assuming that the axial dimension of the permanent magnets 23a, 23b is the thickness thereof, the spacing between the magnets 23a, 23b is preferably 0.2 to 1.0 times the thickness. A type II superconductor 24 is disposed as opposed to the outer periphery of the permanent magnet portion 20 and spaced apart therefrom radially of a rotary body 1. Incidentally, the superconductor 24 may be in the form of a complete ring or a segment of a ring. In this case, the magnetic fluxes of each of the adjacent permanent magnets 23a, 23b at the outer peripheral part of the magnet portion 20 are strengthened by those emitted by the other magnet and reversed to make the gradient of flux density dB/dZ and d 2 B/d 2 Z greater than when the permanent magnet portion comprises a single permanent magnet. This increases the force of magnetic repulsion between the magnet portion 20 and the superconductor 24. Moreover, a great force of magnetic attraction acts therebetween merely when the spacing between the magnet portion 20 and the superconductor 24 slightly increases toward the direction of axis of rotation from the distance at which the force of magnetic repulsion is in balance with the pinning force. Conversely, a great force of magnetic repulsion acts therebetween merely when the spacing slightly decreases from the distance of balance. Accordingly, a greater load capacity and improved rigidity are available. A type I superconductor, i.e., a superconductor completely preventing the penetration of magnetic fluxes may be used as the superconductor in this embodiment. In this case, the rotary body is supported in a noncontact state with respect to the radial direction utilizing the complete diamagnetic phenomenon of the superconductor. It is desired in this case to provide a superconducting bearing at a suitable position for supporting the rotary body with respect to the axial direction. The superconducting bearing device embodying the present invention is suitable for use in hydraulic machines and machine tools which require high-speed rotation, power storage apparatus for storing excessive electric power as converted to kinetic energy of a flywheel, or gyroscopes.

Claims: Superconducting bearing device comprising an annular permanent magnet portion (20) disposed concentrically with a rotary body (1) and a superconductor (24) opposed to the permanent magnet portion (20) and spaced apart therefrom. the permanent magnet portion (20) comprising a disk (21) fixedly mounted to the rotary body (1), a plurality of annular permanent magnets (23a,23b) being arranged on the disk (21), the superconductor (24) being opposed to the outer periphery of the permanent magnet portion (2), the annular permanent magnets (23a,3b) being arranged on the disk (21) at a spacing with respect to each other in the axially direction of the rotary body (1), each of the permanent magnets (23a,23b) having radially opposite sides magnetized to polarities opposite to each other, the permanent magnets adjacent to each other being magnetized to polarities opposite to each other at their same sides with respect to the radial direction. Superconducting bearing device as defined in claim 1, characterized in that the spacing between the annular permanent magnets (23a,23b) is 0,2 to 1.0 times the thickness of the magnets as measured axially thereof. Superconducting bearing device as defined in claim 1, characterized in that the disk (21) is formed on its outer peripheral face with a plurality of annular grooves (22a,22b) spaced apart axially of the rotary body, the annular permanent magnets (23a,23b) being respectively fixedly fitted in the grooves. Superconducting bearing device as defined in claim 1, characterized in that the superconductor (24) has an upper end and a lower end and all the permanent magnets (23a,23b) are arranged within a range between the upper and lower end of the superconductor in a vertical cross section.

Inventors: SHIBAYAMA MOTOAKI, TAKAHATA RYOICHI, TAKAICHI HIROSHI, SHIBAYAMA, MOTOAKI, TAKAHATA, RYOICHI, TAKAICHI, HIROSHI
Applicants: KOYO SEIKO CO, SHIKOKU RESEARCH INST INC, KOYO SEIKO CO., LTD., SHIKOKU RESEARCH INSTITUTE INCORPORATED
Application year: 1992
Main classification: F16C39
IPC codes: F16C39