MAGNETIC BEARING FOR RADIAL AND AXIAL LOAD WITH REPULSIVE PERMANENT MAGNETS

The subject of the invention is a magnetic bearing, composing a stator and a rotor with mandrel, and both its stator and rotor having a permanent magnet.

The need for bearings with an antifriction and airborne rotor arose a long time ago, in equipment running at especially high rotary speed. There was also an intention to produce a magnetic bearing by way of utilising the repulsive effect of magnets with like poles and generating adequate magnetic fields. But practical implementation proved to be difficult because owing to the repulsive effect the inadequately produced stator simply throws the rotor off. The bearing capacity of the magnetic bearing is not indifferent either: it primarily depends on the strength of the permanent magnets that produce the magnetic field. Only in recent years has technical development facilitated the production of high strength and small size permanent magnets.

Several solutions are widely known for the production of magnetic bearings. The following paragraphs give an overview of the most interesting methods that represent the current situation.

The German publication document No. DE 3243641 introduces a bearing designed with a pair of semicircular permanent magnetic cores where the vertical position of the rotor is assigned with a special sensor and the effect displayed by the strength of the permanent magnets can, when the need arises, be increased or decreased with an electromagnet. The disadvantage of the solution is that a special built-in toroidal coil, an electro-magnetic control system needs to be applied to keep the bearing in the central position and ensure its undisturbed course.

The German publication document DE 10022061 introduces a magnetic bearing designed for high-speed vacuum pumps, turbo condensers, etc. In accordance with the description, this consists of two magnetic bearings and in both the stator and the rotor are made up of a set of cores comprising permanent magnets. It is a heavy-duty bearing,

yet it comes with the disadvantage of a complicated structure, moreover its operation requires moderating cores and axial sensors.

The German publication document DE 102 24 100 proposes a solution to produce revolving and linear magnetic bearings. This bearing consists of various types of carrier, reinforcing, centring and hybrid magnets. Following from the description, the proposed bearing is actually an active magnetic bearing as it is also built with a Torque motor. In this solution again, the required performance needs several special elements, for example a centring magnet and a position sensor.

The German publication document DE 10022061 introduces the wind motor version of the above solution. It comes with the same advantages as the above.

The German publication document DE 103333733 proposes ring-shaped magnetic bearing elements placed in or beside one another and slit at minimally one place, to be used to produce magnetic fields of various strengths and directions. But no instructions are given as to how to design a bearing therefrom.

The above examples highlight the general concerns of the well-known magnetic bearings, as complicated technical solutions are required to produce an exact bearing support compensated in position and to guarantee course accuracy in the micrometer range as well.

The objective of the solution proposed in the invention is to meet the expectations of magnetic bearings without the need to build in complicated control systems, centring magnets or special sensors.

The invention is based on recognising that if the stator of the magnetic bearing is designed so that its magnetic lines of force ensphere the rotor, the severe requirements of magnetic bearings will be met with a relatively simple method.

The main idea of the solution proposed in the invention is that the stator of the magnetic bearing has at least two, basin-form shouldered bodies which are magnetised to opposing polarities and one of them — the bottom shouldered body - forms a basin, while the other — the upper shouldered body — forms a counter-basin, the magnetic fields of these shouldered bodies ensphere the rotor of the magnetic bearing, the mandrel is led through the central part of the rotor, moreover the bottom part of the rotor is magnetised to a polarity identical with that of the surface of the opposite basin and the upper part of the rotor to the polarity of the similarly opposite counter-basin. The shouldered form of the stator can ensure - without any special centring magnet - that the rotor runs exactly centrally, which will prevent the rotor to slip.

In the solution proposed in the invention it is preferable to build the shouldered bodies, i.e. the basin and the counter-basin, in separate adjustable racks and to supply the racks with a device suitable to adjust the distance of the shouldered bodies from one another. Such a device can for instance be three adjusting bolts fitted at 120° angles from one another.

It is also preferable in the invention to make the rotor flat, disc-shaped. But the rotor outlined in the invention can also have an ellipsoid or double-cone - with opposing bases - shape, yet it should definitely comprise two parts of different polarity and be magnetised so, separated along the plane perpendicular to the mandrel.

In one of the designs of the magnetic bearing proposed in the invention the inner of the basin and the counter-basin is circular and identical in diameter.

In another design of the magnetic bearing proposed in the invention the basin and the counter-basin are different in size and design, but identical in inner diameter.

As concerns the invention it is also preferable if the inner side of the shoulder for both the basin and the counter-basin, as well as the outside margin of the disc-shaped rotor are adapted to one another and have an outward shoulder shape. For ellipsoid or other

shaped rotors the inner of the stator is ellipsoid or reflects the negative shape of the otherwise shaped rotor.

It is especially preferable to approximate the adapted surfaces as close as possible, therefore the opposing surfaces should be designed nearly identically.

In still another design of the magnetic bearing proposed in the invention it is especially preferable if at least either the basin or the counter-basin is formed of separate permanent magnet sectors.

Moreover, following from the invention, the separate permanent magnet sectors are placed at such a distance from one another so as to make a uniform magnetic field.

As concerns the invention it is also preferable to fit the separate permanent magnet sectors with a shoulder. These shouldered permanent magnet sectors compose the basin or the counter-basin or both.

In another preferable design of the invention the permanent magnet sectors are formed so as to twist them around their longitudinal axis at a maximally 90° angle in both directions.

The magnetic bearing proposed in the invention is introduced in detail in drawings wherein:

Figure 1 shows the sectional drawing of the magnetic bearing proposed in the invention, where the stator is built of a basin and counter-basin made of basin-form shouldered bodies, and the rotor is flat, disc-shaped,

Figure 2 shows the top view of the magnetic bearing introduced in Figure I ₅

Figure 3 shows the basin of the stator comprising permanent magnet sectors,

Figure 4 shows the sectional drawing of a shouldered permanent magnet sector,

Figure 5 shows the top view of the basin introduced in Figure 3, where the built-in permanent magnet sectors are fixed to the rack.

Figure 1 shows clearly that the magnetic bearing has a stator 1 and a rotor 2, the latter comprising the mandrel 5. The stator 1 of the magnetic bearing has at least two, basin- form shouldered bodies. The two, basin-form shouldered bodies seem to share an identical design but are actually magnetised to the opposing polarity. The bottom shouldered body is the basin 3 that supports and holds the magnetic bearing, while the other, the upper shouldered body is the counter-basin 4 that holds off and leads the rotor 2 of the magnetic bearing. The magnetic fields of the basin-form shouldered bodies tend to ensphere the rotor 2 of the magnetic bearing. The magnetic lines of force are not specifically shown in Figure 1. The mandrel 5 is led through the middle of the rotor 2. The bottom part 6, generally the whole bottom part of the rotor 2 is magnetised to a polarity identical with that of the upper surface 8 of the opposing basin 3, while the upper part 7, generally the whole upper part of the rotor 2 to the polarity identical with the bottom surface 9 of the opposing counter-basin 4.

Following from the above and presuming the proper setting, the repulsive effect of the identically polarised magnets generates, without any special centring magnets and sensors, a force field which will hold the rotor 2 in the middle and almost floating while rotating.

For the benefit of simplifying the proper setting procedure, the invention proposes to build the shouldered bodies in a separately adjusted rack 10, and to supply the shouldered bodies with a device 11 fit to adjust their distance from one another, i.e. the bolt shown in the Figure.

In Figure 1 the rotor 2 is flat and disc-shaped, but it can also have other shapes, for instance ellipsoid or double cone. In Figure 1 the inner of the basin 3 and the counter- basin 4 is circular and identical in diameter. But they can also differ in size and design but share an identical diameter. Figure 1 shows clearly that the inner side 14 of the shoulder 12 of both the basin 3 and the counter-basin 4, just as the outside margin 13 of the flat and disc-shaped rotor 2 are adapted to each other and have an outward shoulder shape. The Figure demonstrates that adaptation generates identically shaped profiles and

nearly parallel alignment. The air gap between them can consequently be reduced to the minimum.

Figure 2 shows the top view of the magnetic bearing introduced in Figure 1.

Figure 3 shows a magnetic bearing designed in line with the invention where the basin 3 is made up of several separate permanent magnet sectors 15 which are fitted with a shoulder 12. In Figure 3 the sectors 15 are placed closely beside. The invention proposes to place them at such a maximum distance from one another whereby the individual sectors 15 could still make a uniform magnetic field as regards the effect on the rotor 2.

Figure 4 shows the sectional drawing of a sector 15, with clear views of the shoulder 12 and its inner side 14, as well as the longitudinal axis 16.

Figure 5 shows the top view of the basin 3 built in the rack 10, as introduced in Figure 3. This Figure represents clearly that the sectors 15 that constitute the basin 3 are steadily fixed into the rack 10 with the retaining bolt 17.

Although not represented in any Figure, the invention also proposes a design where the permanent magnet sectors 15 are formed so as to twist them around their longitudinal axis 16 at a maximally 90° angle in both directions. The shortest distance between the sectors 15 depends on how their revolving can be ensured, in this solution.

The magnetic bearing proposed in the invention, similar to the other like-type bearings, can also be cooled by air blow, if the need arises, which will not influence operation.

The advantages of the solution proposed in the invention are summarised as follows: by way of applying a basin-form shouldered design but lacking any separate sensors or centring magnets such a magnetic bearing is produced that gives plenty of chances to choose the dimensions of the permanent magnets used, which helps adjust the magnetic force of the bearing always according to use. The rotor similarly has a relatively simple

design, it is a round, flat, disc-shaped permanent magnet. The magnetic bearing can be adjusted to comply with the relevant technical conditions without any special electromagnet, by way of changing the distance between the racks.

Subject to use, the dimensions of the magnets can differ within the same bearing, so an asymmetric magnetic bearing can also be developed.