WO2009124657A1

WO2009124657A1 - Magnetic bearing and method for producing a bearing race suitable therefore

Info

Publication number: WO2009124657A1
Application number: PCT/EP2009/002155
Authority: WO
Inventors: Friedrich LÖSER; Jörg ROLLMANN; Wolfgang Claus; Uwe-Otto Breucker; Qinghua Zheng; Markus Bauer
Original assignee: Thyssenkrupp Transrapid Gmbh; Rothe Erde Gmbh
Priority date: 2008-04-07
Filing date: 2009-03-25
Publication date: 2009-10-15
Also published as: DE102008017984A1

Abstract

The invention relates to a magnetic bearing having a bearing race (12), a plurality of electromagnets (2) disposed along the circumference thereof, and at least one distance sensor (7) per electromagnet (2). According to the invention, the bearing race (12) is designed substantially isotropically with regard to the magnetic and/or thermal properties thereof, at least in the circumferential direction. This is achieved according to the invention in that a seamlessly produced block having a center hole is processed by ring rolling.

Description

Magnetic bearing and method for producing a suitable bearing ring

The invention relates to a magnetic bearing specified in the preamble of claim 1 and a method for producing a suitable bearing ring.

Magnetic bearings are used for non-contact storage of rotational bodies by means of attached to this circular bearing rings. They are characterized by the fact that they work wear-free and do not require any lubricants. Preferred applications are therefore z. B. the vacuum and medical technology. For example, magnetic cardiac pumps for heart surgery are known.

The non-contact bearing of the bearing rings takes place in that their distances from the electromagnets carrying them are continuously determined by means of sensors, the actual values obtained are compared with distance nominal values, the resulting difference values are fed to a control circuit and with these the currents in the windings of the electromagnets are regulated in that the distance actual values remain substantially constant.

For the preparation of the bearing rings of magnetic bearings z. For example, starting from rolled elec- troble sheets, which are formed by punching and provided with center holes and then stacked and interconnected. It is also known, from Starting larger steel parts and then bring them by turning and milling in the desired shape.

A common feature of such bearing rings is that their magnetic properties, viewed in the circumferential direction, are not isotropic. It is believed that this magnetic anisotropy u. a. The result is that the electrical steel or steel parts used as starting materials are provided during the previous, running in linear steps rolling processes with microstructures, which have a uniform structure only in the rolling direction, however, are designed differently in all deviating directions. Possibly for the same reason bearing rings of the type described also have a locally different behavior with temperature fluctuations. These may be during operation of the magnetic bearing z. B. due to changes in ambient temperature or also result from the fact that the gap control and / or the inductive abgesch- scans the gap leads to eddy currents in the bearing rings.

If bearing rings of this type comparatively small outer diameter of z. B. about 100 mm, as z. B. applies consistently to the previously known magnetic bearings, the magnetic and thermal anisotropy plays no significant role. Since small bearing rings with concentricity deviations of less than z. B. 10 μ. can be produced, given optimum thicknesses up to 0.5 mm despite unavoidable magnetic and thermal anisotropies no regulatory technical problems. However, a very different situation exists when bearing rings with large outer diameters of z. B. 500 mm and more, in particular z. B. of up to 1000 mm are needed, as z. B. would be desirable for the use of magnetic bearings in medical scanners. Such large bearing rings could indeed with concentricity deviations of z. B. 50 μ to 100 μ, which would be sufficient for the scheme without increasing the gap thickness. As a result of the unavoidable magnetic and thermal ametropias, however, such large additional fluctuations of the magnetic and thermal properties occur here both in the measurement of the gap, if it is inductive, and in the control of the magnetic force, that in order to compensate for this, increased gaps must be provided between the bearing rings and the electromagnets or between the rotor and the stator in order to create a reserve which takes into account the increased gap dynamics and to avoid undesired contact. This enlargement of the gap thickness to a value which is greater than that corresponding to the smallest possible gap thickness for geometrical reasons has the consequence that the constructional and financial outlay for the electromagnets, sensors and regulators is undesirably increased.

Based on this, the technical problem underlying the invention, the magnetic bearing of the type described initially in such a way that it allows the use of comparatively small gap thicknesses even if bearing rings with large diameters of z. B. 500 mm and more are provided so that magnetic bearings with large diameters can be operated economically. In addition, a method for producing suitable for this purpose bearing rings to be proposed.

To solve this problem serve the characterizing features of claims 1 and 4. In addition, the invention provides the application according to claim 9 before.

The invention is based on the idea that the described disadvantages, which are particularly noticeable in the use of magnetic bearings with large diameters, can be circumvented by using, in contrast to the prior art, bearing rings which have a substantially circular-symmetrical material structure and thus also have magnetic and / or thermal properties that are essentially the same everywhere along its circumference. As a result, the previously unavoidable, caused by anisotropies fluctuations are largely eliminated. In addition, a fundamentally different from the previous manufacturing process method for the preparation of the bearing rings is proposed, which ensures in the extent required here a uniform formation of the magnetic properties. In that regard, the invention also in the application of Methods hitherto used for other purposes for producing bearing rings for magnetic bearings.

Further advantageous features of the invention will become apparent from the dependent claims.

The invention will be explained in more detail below in connection with the accompanying drawings of an embodiment. Show it:

Fig. 1 shows schematically a magnetic bearing with a conventionally made bearing ring;

FIG. 2 shows two diagrams illustrating the dependencies of gap signals and magnetic forces on the angle of rotation of the bearing ring when using a bearing ring which is assumed to be perfectly circular but magnetically and thermally anisotropic; FIG.

3 shows schematically a magnetic bearing with a bearing ring produced according to the invention; and

Fig. 4 of FIG. 2 corresponding diagrams for a likewise assumed to be perfectly circular, but inventively designed bearing ring.

Fig. 1 shows schematically a magnetic bearing with a designed as an inner ring and rotor bearing ring 1 and an outer ring and outer ring shown as outer ring, of which only four electromagnets 2 are indicated. Each electromagnet 2 has a conventional core 3 and a coil 4 wound thereon. Magnetic pole faces 5 of the cores 3 are associated with a peripheral or radial surface 6 of the bearing ring 1 and, as usual, can have concave contours adapted to their contour. The structure of all electromagnets 2 is suitably the same, so that only one electromagnet 2 needs to be described.

The bearing ring 1 consists of a ferromagnetic material and is radially centered and guided by the electromagnets 2 in a conventional manner. Furthermore can the bearing ring 1 z. B. attached to the circumference of a disc made of a non-ferromagnetic material, in particular shrunk onto these and / or attached to a rotary body to be stored. Normally, at the two ends of a rotor such a, a radial bearing forming bearing ring 1 is mounted, while in a central part of the rotor another, not shown bearing ring is arranged, which serves as thrust bearing and with peripheral edge portions of its end or axial surfaces further Electromagnet opposite. Also not shown is the drive, by means of which the rotor and thus the bearing rings 1 are set in rotation. For this purpose, customary agents known to those skilled in the art can be used.

As FIG. 1 further shows, each electromagnet 2 is assigned a preferably inductive sensor 7, which measures the actual values of the thickness of an air gap 8 which, during operation of the magnetic bearing, ie. H. when turning the bearing ring 1, between the circumferential or radial surface 6 and the Polfächen 5 of the associated electromagnet 2 forms. The output signal of the sensor 7 is supplied to a control device 9 shown in a simplified manner and compared in this with a predetermined desired value. From the difference between the two signals, a control signal is derived, which is supplied to a current through the coil 4 controlling current source. As a result, the coil current and thus the magnetic force acting on the bearing ring 1 at the location of the sensor 2 are controlled such that the thickness of the gap 8 substantially assumes the desired desired value despite any geometric imbalances in the bearing ring 1. This type of regulation is preferably the same for all electromagnets 2.

By lines Ia a hatching for the bearing ring 1 is indicated in Fig. 1, that the microstructure due to a rolling process is homogeneous only in a certain preferred direction, but in directions transverse thereto. This has an effect both on the size of the inductively determined measuring signal of the sensor 7 and on the magnetic force generated by the coil current, as FIG. 2 shows. In the upper part of Fig. 2 is schematically the dependence of the gap signal u from the rotational angle θ of the bearing ring 1, in the lower part, however, the dependence of the electromagnet second developed and exerted on the bearing ring 1 magnetic force F from the rotational angle θ of the bearing ring 1 shown. For both cases, it is assumed that the bearing ring 1 and in particular its radial surface 6 is ideally circular. It follows that actually for all angles θ a gap signal u = U ₀ would have to be obtained, which corresponds to the desired target value of the gap thickness, and therefore by means of a along the entire circumference of the bearing ring 1 held constant current io a substantially constant magnetic force F ₀ would have to be obtained, which is required to maintain the desired gap thickness.

In fact, however, FIG. 2 shows that, in spite of a geometrically ideal gap, on the one hand the sensor signal u fluctuates as a function of the rotational angle θ along a curve 10. On the other hand, acting on the bearing ring 1 at constant current I ₀ no constant, but along a curve 11 fluctuating magnetic force F. This means that the control device 9 a fluctuating in the sense of the curve 10 and thus erroneous sensor signal is communicated, even if the gap thickness geometric has the ideal value, and that, moreover, a current i through the coils 4 does not produce a constant but a magnetic force F fluctuating along the curve 11. Both have their cause in the above-mentioned, magnetic and / or thermal anisotropy, which causes in Fig. 1, that the microstructure is at least at locations of some of the electromagnets 2 other than at locations of other electromagnets 2. A solution of the existing control task is severely hampered in this way.

According to the invention, therefore, it is proposed to use a bearing ring 12 (FIG. 3) which, unlike the prior art, has a substantially isotropic design in the circumferential direction with regard to its magnetic and / or thermal properties. This is indicated in FIG. 3 by circular lines 14 which are intended to represent a circular symmetry of the magnetic and thermal properties. Incidentally, the arrangement according to FIG. 3 is identical to that in FIG. 1, for which reason the same reference numerals are used for the same parts. To ensure circumferentially uniform structure structures and thus homogeneous magnetic properties of the bearing ring 14 is preferably made of a seamless ring produced, which is brought by ring rolling in its final form. Of course, the process of ring rolling is well known to those skilled in the art. What is new here, however, is the result sought by ring rolling. So far, the ring rolling is used exclusively for the production of certain geometric dimensions with small concentricity deviations. Essential for the invention, however, is that the ring rolling apparently also microstructures are obtained which lead to the desired, at each location of the circumference of the bearing ring 1 substantially the same magnetic or thermal or even both magnetic and thermal properties.

The results achieved with the bearing ring 12 according to the invention are shown in FIG. 4 in a manner corresponding to FIG. 2. Since, according to the invention, a bearing ring 12 is used, which is preferably substantially isotropic in the circumferential direction, both in magnetic and in thermal terms, the curves 10 and 11 shown in FIG. 2 are almost completely eliminated-ideal geometric circular shape of an outer peripheral surface 15 in turn , The sensor signal u has rather along the entire circumference of the bearing ring 12 has a substantially constant value U ₀ corresponding to a substantially constant gap thickness, while a constant current io generates a substantially constant, independent of the rotational angle θ magnetic force F ₀ , the z. B. corresponds exactly to the magnetic force required to maintain the desired gap. In addition, these properties are obtained over a wide temperature range, so that changes in the room temperature od. Like. Have no influence on the scheme.

To produce the bearing rings 12 according to the invention, it is preferable to use a solid steel block or the like which has the desired thickness (eg 20 mm to 50 mm) and a uniformly round peripheral surface 15. Such a block may, for. B. by casting, forging or otherwise prepared and already provided during its production with a center hole. Alternatively, you can the center hole are also attached in a later step in the finished block. Subsequently, the peripheral surface 15 is homogenized with respect to the magnetic and thermal properties in the circumferential direction, as indicated in Fig. 3 by the circular lines 14. As far best suited for this purpose seems to be a processing of the peripheral surface 15 by ring rolling. Such machining of seamlessly made annular components is known in the manufacture of large diameter roller bearing rings and is used there to produce circumferential surfaces with very high concentricity accuracy. However, it is surprising that such a method is also suitable for providing the peripheral surface 15 in the sense of the invention with a rotationally symmetrical homogeneity in magnetic and / or thermal terms. This makes it possible, even magnetic bearing whose bearing rings 12 large diameter of z. B. 500 mm and more, operate with a comparatively small air gap, since the above-mentioned, due to the previous anisotropy required reserve can be omitted. As a result, even magnetic bearings with large diameters can be operated economically. Since the power requirement of the electromagnets 2 decreases proportionally with the square of the thickness of the air gap, less powerful electromagnets and less expensive control devices are required.

In a corresponding manner, it can be proceeded when it comes to the production of thrust bearings instead of the radial bearings described, since in particular a ring rolling process can be carried out both with radial and with axial rolls. An Axialwalzprozess leads in the relevant for the distance measurement and storage parts of the end faces of the bearing rings to the same isotropic conditions, as described above for the processing of the peripheral surface 15 with radial rollers.

Suitable starting materials for producing the rolled rings are both unalloyed or low-alloyed steels and high-alloyed steels. If necessary, it is possible to subsequently refine the finished bearing rings by treatment with suitable temperatures. The invention is not limited to the described embodiment, which can be modified in many ways. For example, the bearing rings need not have rectangular or square cross-sections. In particular, the ring rolling is also suitable for the production of bearing rings with others, eg. B. L-shaped cross-sections and / or different surface profiling. Furthermore, it is clear that the bearing rings, in deviation from the above description, can also be used as outer rings and that, instead of the four electromagnets shown, more or less than four electromagnets can be used both externally and internally as required. Instead of inductive sensors other sensors can be used, for. For example, those who work with optical means. Finally, it is understood that the various features may be applied in combinations other than those described and illustrated.

Claims

claims

1. magnetic bearing with a ferromagnetic rotatably mounted bearing ring (12), a plurality of along its circumference arranged electromagnet (2) and at least one distance sensor (7) per solenoid (2), characterized in that the bearing ring (12) with respect to its magnetic and / or thermal properties at least in the circumferential direction is substantially isotropically formed ring.

2. Magnetic bearing according to claim 1, characterized in that the bearing ring (12) consists of a seamlessly made ring.

3. Magnetic bearing according to claim 1 or 2, characterized in that the bearing ring (12) is produced by ring rolling.

4. A method for producing a bearing ring (12) for magnetic bearing, wherein first a solid, seamless round, provided with a center hole block is produced, characterized in that the block in terms of its magnetic and / or thermal properties by ring rolling in its circumferential direction is homogenized.

5. The method according to claim 4, characterized in that it is used for the production of bearing rings (12) with outer diameters of at least 500 mm.

6. The method according to claim 4 or 5, characterized in that the bearing ring (12) is refined by treatment with preselected temperatures.

7. The method according to any one of claims 4 to 6, characterized in that the block is produced by casting.

8. The method according to any one of claims 4 to 9, characterized in that the block is produced by forging and subsequent punching.

9. Application of ring rolling for the production of bearing rings (12) for magnetic bearings with circumferentially isotropic magnetic and thermal properties and with large diameters.