Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1997-01-06
1997-12-02
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Rotary
310 90, 310 64, 310 74, 2989806, 384913, 3849071, 384278, H02K 516
Patent
active
056939949
DESCRIPTION:
BRIEF SUMMARY
This invention relates to back-up bearing arrangements for magnetic bearings.
It is known to provide bearing functions for a rotating body by suspending the body, in particular a rotor thereof, in a magnetic field derived from one or more permanent magnet and/or electro-magnet.
Magnetic bearings also are employed to provide both radial support for a shaft or body and axial support, that is, as thrust bearings.
In general the radial and axial support is combined with closed loop position control wherein the axial position or deviation from a chosen position is monitored and employed to vary the current flowing in a suspension electro-magnet and restore the body to a desired position.
It is well known that magnetic bearings are employed where the rotational speed is very high, often in the region of 25-30,000 rpm, notwithstanding that the body may be heavy and rotate about a shaft of tens of centimeters diameters.
It is a feature of practical magnetic bearings that the electromagnetic control is able to function properly within a limited range displacements and/or frequency of displacements, partly due to the small air gaps employed between rotating and stationary components and the high stiffness that accommodates controlled electromagnetic suspension.
Thus there exists always the possibility of the rotor being subjected to extraneous external forces of such magnitude and/or frequency that exceed the restoring capabilities of the electromagnetic control, as well as the possibility of failure of electromagnetic forces per se, that would inevitably result in the contacting of the rotor and stationary components and damage to either or both.
Electromagnetic bearings therefore generally employ back-up bearing arrangements which are intended to run in contact for a limited continuous period, usually sufficient only until the body can be brought to rest. Frequently therefore, they have a significant degree of friction to effect braking of the body which is no longer successfully suspended magnetically. Such back-up bearings are known and applicable to both radial and axial bearings.
Typically such a back-up bearing arrangement includes a collar carried by, or formed integrally with, a rotatable shaft and other parts of the magnetic bearing that is both load bearing and thermally conductive and has one or more surface regions which are disposed with respect to a stationary bearing part so that in operation the regions run in abutment with the, stationary part. To effect a bearing function at all,the stationary part comprises a dry running bearing material having a sponge-like matrix of bronze or iron loaded with a dry lubricant such as graphite, molybdenum disulphide or tungsten disulphide.
Notwithstanding the lubricated nature of the stationary material, heat is generated by the abutment and requires to be conducted away through the collar to prevent accelerated wear of the dry bearing material due to the phenomenon of adhesive wear caused by local asperities of the collar and matrix of the bearing material welding together.
Furthermore, a degree of friction, which inevitably generates heat, is desirable in producing a braking effect on the rotating parts of the bearing to bring them to rest, so reducing the effective coeficient of friction of the dry running bearing material and/or the collar is not a solution.
However, in magnetic bearings, the high speed of rotation places emphasis on the strength of the collar material to withstand centrifugal loading. In this respect it is usual to have the collar formed from steel, notwithstanding that the conduction of heat from the abutting surfaces of the bearing arrangement is below optimum and the metals of the collar and bearing material readily melt locally to exacerbate wear.
It will be appreciated that such wear is also a function of linear speed between the surfaces, and this increases as a function of radius of a rotating body. Therefore, in the case of an axial or thrust bearing which is mounted with respect to a relatively large diameter shaft, the radially ext
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Patent Abstracts of Japan; vol. 10, No. 301 (M-525) (2357) 14 Oct. 1986.
Stephan Steven L.
The Glacier Metal Company Limited
Williams Timothy A.
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