Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-04-17
2001-07-03
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C417S365000
Reexamination Certificate
active
06255752
ABSTRACT:
The invention concerns a bearing arrangement for a rotor of a fluid flow machine having at least one permanent magnet bearing for radial guidance and at least one hydrodynamic plain bearing—which carries the axial thrust of the fluid flow machine—for axial—or for axial and radial—guidance in the operating phase. The invention also concerns a use of the fluid flow machine.
It is known for the lubrication of rolling and plain bearing in fluid flow machines or turbines to be effected in many cases by the flow medium itself. The service life of the bearings lubricated in that way can be increased when using wear-resistant bearing materials such as for example silicon nitride in rolling bearings or silicon carbide in plain bearings.
The use of hydrodynamic and hydrostatic plain bearings results in a bearing arrangement without contact of the sliding surfaces in the operating phase and thus affords a bearing arrangement with a low degree of wear. Contact-free bearing arrangements are also represented by the use of electrical or magnetic forces—for example in active magnetic bearings in accordance with WO 95/13477—in bearings with superconductor materials or in permanent magnet bearings. In that respect, no lubricant is necessary to achieve the support action. Permanent magnet bearings are always used in conjunction with other kinds of bearings as, in accordance with Earnshaw's law, it is not possible for a static body to be stably supported in all three directions in space exclusively by means of permanent magnets. In most cases they are used in combination with an active magnetic bearing. Moreover in regard to active magnetic bearings there are constructions in which the rotor is radially guided by rolling bearings in the starting and stopping or run-down phases in order to suppress rotor oscillations.
Hydraulic compensating devices such as for example compensating plates which with the flow medium produce an axial thrust compensation effect are also known. To promote the axial thrust compensation effect in transient operating phases, EP 0 355 796 describes the combination of axial thrust compensation with an active magnetic arrangement. A combination of a device for axial thrust compensation with a lifting device which, by means of permanent magnets, prevents contact of the load-relief plates in the stopped condition, is to be found in EP 0 694 696. The permanent magnets in that case do not have a bearing function.
The known bearing structures suffer from a number of disadvantages. Rolling and plain bearings are heavily loaded when involving lubrication by means of media which have a poor lubricating action—for example which are of very low viscosity—and they attain only short operating lives or often have to be maintained or replaced. Other bearings suffer from the disadvantage that additional technical complication and expenditure is required for satisfactory operation of the bearings upon starting up and in part also in operation thereof: hydrostatic plain bearings require a pressure source which—for example when the bearings are used in pumps—can admittedly in the operating phase also be represented by the pump itself, but which must be present as an external component for the starting phase. A similar consideration applies in regard to hydrodynamic plain bearings whose high starting moment often has to be compensated by suitable technical measures, for example hydrostatic starting. Hydraulic compensating devices in previous design configurations also require technical arrangements, for example additional bearings, in order to compensate for the axial thrust force of the fluid flow machine in the transient operating phases and in order to prevent high starting moments, for example due to compensating plates being in contact. Active magnetic bearings require electrical power for them to operate and they need active regulation as well as additional auxiliary bearings to cover the case of failure of the magnetic bearings.
When using superconductor magnetic bearings, for example when using cryogenic—intensively cold—flow media, additional complication and expenditure is necessary in order to ensure the correct position of the rotor at temperatures above the superconducting phase of the superconductors. When using cryogenic media, with many of the above-mentioned bearings there is the risk of the rotor jamming due to impurities contained in the cryogenic medium becoming frozen on, while the machine is in the stopped condition.
In consideration of those factors the inventor set himself the aim of providing a low-wear bearing arrangement for rotors of fluid flow machines or turbines, which do not have a lubricant apart from the flow medium, wherein the rotor bearing arrangement is to be distinguished in terms of implementation thereof by a low starting torque and a low level of technical complication and expenditure.
That object is attained by the teaching of the independent claim; the appendant claims set forth desirable developments. The scope of the invention also embraces all combinations consisting of at least two of the features disclosed in the description, the drawing and/or the claims.
In accordance with the invention, in the operative position of the rotor the components of one or more permanent magnet bearing or bearings on the rotor are displaced with respect to the associated components on the housing side axially in opposite relationship to the direction of the axial thrust of the fluid flow machine out of the position of force equilibrium, and there is produced a force which is directed in opposite relationship to the axial thrust and which provides that the sliding surfaces of the hydrodynamic bearings which are operative in the operative phase are separated from each other during the starting phase and the rotor is pressed against one or more additional plain or rolling bearings; the latter provide for guidance of the rotor during the starting and stopping phases and are structurally such that, at low speeds of rotation and in the stopped condition, they have a substantially lower moment of friction than the hydrodynamic plain bearings used in the bearing arrangement.
In accordance with the invention therefore the rotor is guided radially by means of one or more permanent magnet bearings. Axial guidance is effected by one or more hydrodynamic plain bearings which act on one side, wherein the rotor of the fluid flow machine is pressed against the bearing or bearings by the axial thrust which occurs in the operating phase. If the hydrodynamic bearings are of a suitable configuration, it is also possible for radial forces to be carried by the hydrodynamic plain bearings in operation of the machine. The permanent magnet bearings serve at the same time as a lifting device for the sliding surfaces of the hydrodynamic plain bearings.
Axial displacement of the bearing elements on the rotor side relative to the bearing elements on the housing side produces a force which is directed in opposite relationship to the axial thrust and which separates the sliding surfaces of the hydrodynamic bearings from each other in the run-down or stopping phases. In the stopped condition and during the starting and stopping phases the rotor is guided by one or more plain or rolling bearings which, at low speeds of rotation and in the stopped condition, have a substantially lower frictional moment than the hydrodynamic bearings used; that minimises the starting torque of the flow machine.
For the purpose of achieving axial displacement of the rotor into the operative position in the starting phase with a low level of technical complication and expenditure, the above-mentioned axial displacement of the rotor is preferably so limited that the magnetic forces of the permanent magnet bearings which occur remain lower in the axial direction than the minimum axial thrust of the machine in operation thereof. As a result, when starting up, the rotor automatically moves into the operative position.
If limitation of the axial displacement of the rotor is not possible or is not wanted, the rotor or
Allweiler AG
Bachman & LaPointe P.C.
Dinh Le Dang
Ramirez Nestor
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