Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1993-01-15
1994-05-31
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Rotary
H02K 709
Patent
active
053172264
DESCRIPTION:
BRIEF SUMMARY
This invention relates to magnetic bearings and is in particular concerned with thrust bearings for use in conjunction with rotating shafts.
It is well-known to support a rotatable shaft by means of a magnetic bearing. It is also known to control the axial displacement of such a shaft by means of a magnetic thrust bearing, as opposed to a conventional thrust race. A magnetic thrust bearing comprises a rotor mounted on the rotable shaft whose axial displacement is to be regulated and at least one fixed stator element mounted to associated hardware. The stator element has associated with it the energising windings whereby the position controlling force is generated, and regulated, typically under the control of electronic sensing/positioning circuitry. It is usual to manufacture the rotor component from solid, iron-based alloys and the same material may be used for the stator(s). This is acceptable where the thrust load is fairly static and the rate of change of flux is not a significant factor.
However, where there are dynamic load changes accompanied by a high rate of change of flux, solid components are undesirable because of the eddy currents developed. These result in high power loss and very significant heating of the bearing components. Accordingly, a laminated construction is preferred for such applications, but if such a construction is to be effective, simple radially-directed laminations are unsatisfactory because of the reduction in magnetic surface area in the progressively radially outward direction. It will be noted that a typical lamination thickness is on the order of 0.1 to 0.25 mm. Wedge shape laminations are not a satisfactory solution, because of this fact. One proposed solution is to increase the diameter of the co-operating components, though this does not really address the further problem which arises when the respective rotor and stator laminations do not actually align with one another at their outer periphery. Where there is no alignment, there will be a high reluctance; where there is alignment, there will be a low reluctance. The overall effect is one of rapid changes leading to higher winding losses and to the generation of high frequency transients in the windings.
It is an object of this invention to minimise these problems.
According to this invention, the stator and rotor components of a magnetic thrust bearing are each of laminated construction, the laminations being curved so that their tips lie in a common cylindrical plane. The arrangement is preferably such that abutting side edges of the laminations also lie in common planes, which are disposed normal to the axis of rotation.
By curving the lamination tips (in effect) about the axis of rotation, the gap between adjacent laminations can be very considerably reduced, at the expense of overall outside diameter. If this is a problem, it can be compensated for by increasing the length of the laminations, of course, but in ordinary circumstances this will not be needed, since the arrangement of this invention results in considerably improved magnetic efficiency.
A further advantage of the invention lies in the fact that manufacture of a rotor and two stator components can be carried out from a single cylindrical assembly which is cut into three sections at right angles to its central axis.
One method of making a magnetic thrust bearing according to the invention comprises the steps of mounting a plurality of generally radially aligned laminations to a central supporting hub, bending said laminations about the axis of said hub until their distal edges lie in a common cylindrical plane, and clamping said distal edges in that plane. The method may include the step of cutting the clamped assembly into at least two portions, with the cut lying in a plane normal to said axis. Preferably, a single clamped assembly is cut into three such portions, to form the components of a complete magnetic thrust bearing. In the case of the two portions destined for use as stators, the method may also include the step of generating an axially ex
REFERENCES:
patent: 3746407 (1973-07-01), Stiles et al.
patent: 4180296 (1979-12-01), Habermann
patent: 4332428 (1982-06-01), Maruyama
patent: 4820949 (1989-04-01), Mizobuchi et al.
patent: 4958098 (1990-09-01), Sarraf
patent: 5079458 (1992-01-01), Schuster
Stephan Steven L.
The Glacier Metal Company Limited
To E.
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