Magnetic bearing assembly

Details Magnetic bearing assembly Magnetic bearing assembly

2002-03-15

2003-04-01

Dougherty, Thomas M. (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S090000, 30, C505S903000

Reexamination Certificate

active

06541885

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Applicants claim priority under 35 U.S.C. §119 of German Application No. 100 34 922.6 filed Jul. 18, 2000. Applicants also claim priority under 35 U.S.C. §120 of PCT/DE01/02602 filed Jul. 17, 2001. The international application under PCT article 21(2) was not published in English.
The invention relates to a magnetic bearing assembly of a rotor in a stator comprising at least one magnetic bearing that has a stator part and a rotor part which, in the operating position, is arranged coaxially thereto without contacting said stator part. The bearing effective area of the rotor part is formed by a radial exciting system containing permanent magnets, whereas the stator part has a high-temperature superconductor that concentrically surrounds the radial exciting system while maintaining an annular air gap.
Such an embodiment is disclosed, for example in DE 197 27 550 A1. Said earlier publication discloses, among other things, a magnetic bearing in connection with which the rotor is supported in two magnetic bearings, which axially oppose each other and are formed in a mirror-imaged manner in relation to one another with respect to their shape of truncated cones. A defined cooling method is described for such a magnetic double bearing, which is understood to be the type of transition leading into the superconducting state. According to said method, one of the two magnetic bearings is cooled first and subsequently the other magnetic bearing. While being driven to cold, the rotor is first displaced with its one bearing segment into the one magnetic bearing up to the stop, and subsequently into the other magnetic bearing up the stop. After both magnetic bearings have cooled down, an axial tensioning of the two-effective bearing segments of the rotor is obtained. According to a modified method for driving the rotor into its operating position with the use of a magnetic double bearing, a rotor with a vertical axle is employed, which is displaced upwards into the upper magnetic bearing until the rotor part comes to rest against its stator part, whereupon both magnetic bearings are driven to cold simultaneously and the rotor is subsequently released.
The following terms have come into use linguistically for three different cooling methods:
Cooling without field (zero field cooling)=ZFC.
Cooling under the operational field in the operational position, or with displacement into the operational position (operational field cooling)=OFC and (operational field cooling with offset)=OFCo; or
cooling while approaching the exciter magnet as closely as possible (maximum field cooling)=MFC.
The feature that all of said methods have in common is that the structural component to be supported, for example the rotor of a machine, has to be shifted after cooling from a cooling position into the operational position by forces, e.g. by its own weight or by the operational load. Because of the non-linear spring characteristic of the bearing, which is frequently progressive at OCC, OFCo, ZFC, but degressive at MFC, said shift requires a minimum distance in order to arrive at a working point with adequate rigidity. It is often required in this connection as a secondary condition that the working point of the bearing coincides with the geometric center line of the housing of the bearing. In many cases of application, however, said available degree of freedom of the rotor is highly limited for constructional reasons. The consequence thereof is that the required rigidity of the bearing at the working point has to be adjusted by an accordingly sized surface. This, however, results in unnecessarily high costs and unpractical dimensions of the bearing.
Therefore, the problem is based on the problem of enhancing the specific rigidity of superconducting bearings while avoiding the drawbacks described above.
Based on a magnetic bearing of the type specified above, said problem is solved according to the invention in that the high-temperature superconductor is divided in at least two circle segment-shaped HTSC partial shells which, when the bearing is hot, can be displaced with respect to each another in a radial direction by an actuator, from a position in which each HTSC partial shell has a first radial distance from the radial exciting system, into a working position having a second, smaller radial distance (operating gap) from the radial exciting system.
For compensating the weight of the rotor it may be useful if the two half-shells, in their hot position, have different first radial distances from the radial exciting system.
Furthermore, the magnetic bearing as defined by the invention may be characterized by an additional axial bearing in connection with which two axial exciting systems arranged opposing each other with an axial distance from each other. Said systems each are fitted with permanent magnets, forming an axially directed, circular disk-shaped effective bearing area of the rotor part, with a plane, circular disk-shaped HTSC axial bearing disk arranged coaxially in relation to the rotor part being associated with each of said effective bearing areas as the stator parts, whereby said HTSC axial bearing disks can be displaced away from each other by an actuator in the axial direction after the transition into the superconducting state, from a position in the hot state of the bearing, in which each HTSC axial bearing disk has a first axial distance from the associated axial exciting system, into a working position with a second, smaller axial distance from the axial exciting system.
Additional features of the invention are the objects of the dependent claims and are explained in greater detail in connection with further advantages of the invention with the help of exemplified embodiments.


REFERENCES:
patent: 5633547 (1997-05-01), Coombs
patent: 5710469 (1998-01-01), Ries
patent: 197 27 550 (1998-02-01), None
patent: 0 526 325 (1993-02-01), None
M. Komori et al. (1997) “Vibration Suppression of a Disk-Shaped Superconductor with PD Control”, Cryogenics, IPC Science and Technology Press Ltd., Guildford, GB, vol. 37 No. 4, pp. 195-199.

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