Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1996-01-11
1997-05-27
Dougherty, Thomas M.
Electrical generator or motor structure
Dynamoelectric
Rotary
310 90, 505876, 505903, 505905, H02K 700
Patent
active
056335474
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method, and apparatus for employing a method, of changing the stiffness of magnetic bearings. The invention relates in particular to magnetic bearings in which at least one of the constituent parts is formed by a superconductor.
BACKGROUND OF THE INVENTION
Magnetic bearings have several potential advantages over, the more conventional, rolling element bearings. These advantages are obtained from the fact that in a magnetic bearing (unlike a rolling element bearing) there need be no contact between moving elements. Eliminating contact eliminates friction which in turn eliminates the need for lubrication. Friction also causes energy losses, wear and noise. Thus a magnetic bearing, potentially, is more efficient (in terms of energy loss), has a longer life-time, and is quieter than a rolling element bearing. These are the principal advantages to be gained from magnetic bearings.
Magnetic bearings however suffer from a major disadvantage when compared to rolling element bearings. That disadvantage is the stiffness of the bearing. Stiffness refers to the behaviour of the bearing when subjected to varying loads and specifically how much movement or "play" is induced in the bearing by a varying load. In a rolling element bearing where there is metal to metal contact the stiffness is very high as play is resisted by the metal itself. In a magnetic bearing however the resistive force is a function of the density of the magnetic field. When the load on a magnetic bearing is increased therefore the bearing will move until the magnetic field density has increased sufficiently. If the magnetic field is only changing slowly the bearing will have to move a large distance for this to happen and the bearing will have a low stiffness.
It is known to vary the magnetic field density by varying the current in the coils of an electromagnetic bearing, however this is not possible with magnetic bearings which use superconductors.
SUMMARY OF THE INVENTION
Accordingly the present invention seeks to provide a magnetic bearing in which the stiffness of the magnetic bearing is controllable.
Accordingly the present invention provides a magnetic bearing for supporting and allowing relative movement in a first directional sense between a first member and a second member, the magnetic bearing comprising first magnetic means mounted on the first member and second magnetic means mounted on the second member, the first and second magnetic means producing a magnetic field therebetween to oppose loads which cause the first and second members to move relative to each other with directional components perpendicular to the first directional sense, and means arranged to change the cross-sectional area of the magnetic field between the first and second magnetic means when the magnitude of the load changes so as to control the stiffness of the magnetic bearing.
Preferably the means arranged to change the cross-sectional area of the magnetic field comprises means to move the first and second magnetic means relative to each other to change the cross-sectional area of the magnetic field.
Preferably the relative movement of the first and second magnetic means has a directional component transverse to the direction of the load which causes the first and second members to move with directional components perpendicular to the first directional sense.
The second magnetic means may be mounted on the second member by at least one parallel strip hinge, each parallel strip hinge comprising at least two members arranged parallel to each other, a first end of each member is hinged to the second magnetic means and a second end of each member is hinged to the second member, whereby the parallel strip hinge rotates about its hinges on the second member to change the cross-sectional area of the magnetic field while maintaining the first and second magnetic means parallel. The at least one parallel strip hinge may be arranged at an angle to the direction of the load. The second magnetic means may comprise a plu
REFERENCES:
patent: 3407749 (1968-10-01), Frig
patent: 4300807 (1981-11-01), Poubeau
patent: 5010563 (1991-04-01), Laurent et al.
Rao et al., "Comparative Asessment of Single-Axis Force Generation Machanisms for Superconductiving Suspensions", Proceedings of the 25th Intersociety Energy Conversion Engineering Conference, vol. 6, 12 Feb. 1992, New York, USA, pp. 149-153, XP214875.
Marinescu et al., "Passive Axial Stabilization of a Magnetic Radial Bearing by Superconductors", IEEE Transactions on Magnetics, vol. 25, No. 5, Sep. 1989, New York, USA, pp. 3233-3235, XP69079.
Dougherty Thomas M.
Rolls-Royce PLC
Tamai Karl I. E.
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