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 d2B/dZ2. 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
d2B/d2z, consequently increasing the load capacity and the
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 d2B/d2Z 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.