Magnetic support with permanent magnets for absorption of the radial bearing stresses.

p0001The invention relates to a magnetic bearing for a rotor with permanent magnets for holding the radial bearing forces, and with a stabilizer which holds the rotor in a non-contact position with respect to a stator. For this purpose, acting on the stator mounted electric coils together with rotor-mounted magnetizable parts.

p0002Magnetic bearings of this type are described in U.S. Patent 3,929,390 and the Journal of Spacecraft, Vol 17, No. 2, 1980, P. 93 - 98, known. In these magnetic bearings ring-shaped permanent magnets are attached to both ends of the rotor, cooperating with stator fixed to the annular magnet in such a manner that a radial centering force is exerted on the rotor at a radial deflection. At the same time arises in the axial direction a force instability by the permanent magnets. This force is balanced by an instability in the middle of the rotor-mounted, axially acting electromagnetic deflection cell that is charged with electric control currents corresponding to the respective axial deviation of the rotor from its axial nominal position. The deviation is detected using a noncontact sensor system which regulates the deflection cell by control current flowing through a corresponding electronic amplifier. On both sides of the deflection cell of identification affixed to the rotor ends of permanent magnets attached to the stator: fixed copper discs which cooperate with the rotor mounted permanent magnets in such a way that radial vibrations of the rotor are damped in the immediate vicinity. In contrast, the positions are in a manner known from DE-A 34 09 047 magnetic storage for those permanent magnetic bearing elements which cause the radial centering of the rotor, on both sides retain the rotor center of gravity substantially, while the deflection cell is applied to the end of the rotor shaft outside of the permanent magnetic rotor bearing , The deflection cell thereby contains several attached to the rotor permanent magnets, which cause an eddy current damping of radial vibrations of the rotor with a stator mounted on copper plate.

p0003Disadvantage of the above-described magnetic bearings is that occurring during operation of such bearings axial deformation of the rotor and in particular dimensions of the rotor enclosing the housing to which the stator magnets are fastened, may cause a substantial misalignment of the bearing system, so that in unfavorable conditions the margin the magnetic deflection cell is exceeded. The deformations mentioned occur particularly due to pressure loads on the housing when it is, for example, evacuated, or as a result of thermal stresses caused primarily by the drive motor for the rotor. On the other hand, can cause a change in length of the rotor and hence misalignment of the magnetic bearings or propulsive gas caused by friction at high rotational speeds heating of the rotor.

p0004The object of the invention is to provide a magnetic bearing whose adjustment is largely insensitive to deformations without the bearing assembly is complicated.

p0005This object of the invention is achieved in a magnetic bearing of the type described by the features specified in patent claim 1. The bearing according to the invention comprises only two self-contained bearing components, the static adjustment of a priority area storage with relatively high magnetic rigidity is determined, while a steady bearing with compared to the gravity bearing lower stiffness essentially accepts contactless stabilizing the system. The gravity bearing supports the vast majority of the rotor weight and is therefore in the region of the rotor center of gravity arranged. This division of the supporting and stabilizing function on two under different magnetic bearing is similar to the distribution of the bearing and stable isere therein functions of wing and tail of aircraft in its mode of action.

p0006Because the center of gravity bearing supports the rotor mass, the equilibrium position of the rotor in the axial direction is largely determined by gravity bearing, during deformation-induced shifts in the steady bearing because of its low rigidity only have a marginal effect on the rotor equilibrium. Preferably, the ratio of the bearing stiffness between gravity bearing and steady bearings at least 10: 1.

p0007The gravity mounting of the rotor also makes flying mounts of details possible. Such a bearing provides in addition to the favorable for the handling of the system installation clearance at the bearing-free side has the advantage that all the components of the magnetic bearing in a short and therefore dimensionally stable housing can be accommodated, in contrast to the known bearings in which the bearing components accordingly via large housing components must be connected, whose deformations, as described above, a negative effect on the magnetic bearing.

p0008With the aim to achieve a high bearing stiffness in gravity bearing, there is a gravity bearing according to claim 2 of a set of magnetic rings of hard magnetic material by rectified axial Magnenetisierung. Rotor and Statormagnetringe alternately and with regard to their magnetization direction in succession, wherein the substantially planar faces of the rotor and Statormagnetringen face in close axial distance.

p0009The arrangement of the axially magnetized rings in series connection, that is in axial attractive arrangement, compared to the in known magnetic bearings often applied repulsive magnetic devices has the advantage that the magnetic rings wrden operated at high internal magnetic flux density so that the local variations in the coercivity of the magnetic material only slightly affect the uniformity of the rotational movement of the rotor. Avoiding Eisenpolschuhen with flux concentration of the air gaps, which are used in other magnetic bearings, allowing a favorable ratio of the radial Zentriersteifigkeit the camp to its negative axial stiffness and simultaneously avoids the use of production technology unfavorable and thus costly ring magnets with radial magnetization.

p0010To further increase the rigidity of the center of gravity bearing at least one further set of magnet rings is arranged with the first set of opposite axial magnetisation according to claim 3, wherein end faces of the rotor or Statormagnetringe of the one set of end faces of the rotor or Statormagnetringe of the other set in a plane. Because of the magnetostatic circumstances opposite polarity to the bearing gaps can increase the stiffness of the bearing in relation to the magnetic material used volume disproportionately by the arrangement of concentric pole faces.

p0011The formation of concentric, coplanar pole faces can be achieved in an advantageous manner by locally different magnetization of one made of a piece of disk, claim 4. With discs of this type can reduce machining costs and reduce the installation costs of the gravity bearing.

p0012For applications in which the magnetic bearings are used with chemically aggressive gases or liquids into contact, especially when using the magnetic bearings in pumps or compressors, made of hard magnetic material magnetic rings or discs are preferably provided with a coating that the hard magnetic material against the action such media protects claim. 5

p0013In the case of the use of rare-earth-cobalt materials for the magnetic rings or magnetic disks and operating in hydrogen-containing media, the coating is advantageously made of screens and / or protective plates according to claim 6, which compounds by Schrumpfverbin or by gluing, soldering or welding to the magnetic rings or magnetic disks are mounted.

p0014In applications where a moisture barrier to prevent corrosion is required only, the magnet rings or discs according to claim 7 preferably inexpensive coated by applying a liquid phase, in particular a plastic impregnation and chemically or galvanically deposited metal layers are formed.

p0015To avoid mechanical overloading of the magnetic rings of hard magnetic material, which may occur due to centrifugal forces at high rotational speeds, these magnetic rings are bordered advantageously in a material of high tensile strength according to claim. 8 As such, preferably is a fiber composite material.

p0016Since the gravity bearing can not be canceled because of the exclusive use of permanent magnets to generate forces in its centering function, and because this gravity bearing associated with compared to the steady bearing only low dynamic stabilization tasks, can the gravity bearing shatterproof on a mechanical emergency bearing high quality in favor of a simple, inexpensive and run jack to dispense, claim 9. the centering effect of gravity bearing sufficient under otherwise normal operating conditions to capture secure the rotor after momentary radial start due to a radial impact on system resources.

p0017Advantageously and cost-effective manner the start socket is lined with a temperature-resistant plastic with good sliding properties according to claim 10th Preferably, PTFE (polytetrafluoroethylene) or polyimide can be used with Gleitstoffeinlagerungen.

p0018In a further embodiment of the invention, a sensor is provided according to claim 11 for scanning the axial rotor position, consisting of two coils of approximately the same impedance substantially. One of the coils is mounted with axial spacing opposite a marking element which is secured to one of axial ends of the rotor and is used for scanning the rotor bearings. The marking member consists of a material with high electrical and / or magnetic conductivity. The boundary surfaces of the coil and marking part are substantially flat and oriented perpendicularly with respect to the rotor axis. The second coil of the sensor is located opposite a marking attached to the stator part, which consists of an equivalent of the material of the marking portion of the rotor material. The construction of the sensor consists of two substantially identical coils is in particular in conjunction with a differential transformer in the entrance area of ​​the control amplifier is advantageous because temperature-related changes in the coil impedances are neutralized and as a result causes the sensor system no temperature-induced misalignment of the magnetic bearing.

p0019Another embodiment of the invention, a drive motor between the gravity bearing and the steady bearing 8 housed claim 12. The secured to the rotor shaft rotor of the drive motor consists essentially of permanent magnetic material with low permeability and is magnetized in the radial direction. In connection with the inventive bearing a motor with permanent-magnet rotor is the advantage of a comparatively low negative radial stiffness with low permeability compared to conventional squirrel-cage motors with high permeability iron filling. This occurs with conventional hard roller bearings not annoying in while. The overall rigidity of a magnetic bearing, especially one without radial electromagnetic control, can interfere unduly

p0020according to claim 13, a stator is provided for the drive motor to drive the permanent-magnet rotor having a conventional three-phase motors with winding and is fed from a three-phase generator or three-phase current transformers. Such a training motor stands out in an advantageous manner from that of a brushless DC motor, because it enables a higher engine efficiency. This advantage is especially true in connection with the non-contact magnetic storage to effect because of heat losses from the engine is not transmitted to the rotor, from which they can be because of the good thermal insulation of the rotor difficult to dissipate.

p0021In a further embodiment of the invention is the rotor an axially acting thrust bearing mounted, which consists of two mutually identified and fixed on the rotor shaft shoulder or spindle bearings as well as a related case can claim 14th

p0022according to claim 15 the use of the inventive bearing in conjunction with a flywheel of high-strength material is provided, in particular from a designed for high rotational speeds fiber composite material. Systems of this type are suitable in a known manner as an energy storage for uninterrupted power supplies and for Chopper with high time resolution.

p0023The rotor bearing according to the invention is mainly used for rotors of an axially and / or radially compressing gas turbine, in particular a turbo molecular pump to generate high vacuum, to claim 16. In this application, the inventive bearing is due to its simple construction and the therefrom fol lowing high operational reliability of particular importance for use for vacuum process technology to.

p0024Another use is given for spinning turbines, claim 17 for spinning turbines is particularly the cost of manufacture of the magnetic bearing due to its simple structure is advantageous.

p0025The invention will be explained in more detail with reference to embodiments. The drawing shows in detail:<ul><li>Figure 1 Magnetic storage ,: basic structure;</li><li>2a gravity bearing with magnetized in the axial direction magnetic ring set;</li><li>2b gravity bearing with two oppositely magnetized magnetic ring sets;</li><li>2c gravity bearing with magnetic disks having two concentrically arranged, annular zones of opposite axial magnetization;</li><li>3 steady bearing;</li><li>4 radial rubbing jack;</li><li>Figure 5 axial sensor; </li><li>6 drive motor;</li><li>Figure 7 Starting warehouse.</li></ul>

p0026Figure 1 schematically shows the basic structure of the magnetic storage according to the invention. A rotor 1 consisting of shaft 2 and the shaft attached machine part 3 (for example, a flywheel), is located with its axis 4 within a gravity bearing 5. The gravity bearing 5 is mounted on a bearing housing 6 which also carries a steady bearing. 7 On the bearing housing 6, a sensor 8 is mounted for scanning the axial rotor position, which is connected to the input of a control amplifier. 9 The output current of the variable gain amplifier 9 acts on the present in the steady bearing 7 deflection coils in such a way that when the axial deviation of the rotor from its predetermined contactless target position a deviation counteracting restoring force is exerted on the rotor. The variable gain amplifier 9 is preferably designed such that the rotor 1 occupies an axial position in which all acting in gravity bearing 5 static axial forces are balanced, so that under these conditions, the output current of the variable gain amplifier to zero. This will occur with sufficient dimensioning of gravity bearing 5 and the stabilizer bearing 7 in particular in the case of a vertical axis position of the whole system, in which in addition to the generated by gravity bearing 5 and the steady bearing 7 magnetostatic axial forces in addition the weight of the rotor 1 must be collected. In this case, the upward magnetic forces to the weight of larger dimensioned than the downwardly directed magnetic forces. The machine part 3 is to be connected to the shaft 2 so that the center of gravity of the rotor 1 coincides possible with the center of gravity bearing. 5

p00272a shows a half section through an embodiment of the center of gravity bearing 5. The gravity bearing has rotor magnetic rings 10 and Statormagnetringe 11 which in their dimensions substantially the same and are arranged within a preferably made of iron or other magnetically conductive material gravity bearing housing 12 in the manner in succession that rotor magnet rings 10a, 10b are located between Statormagnetringen 11a, 11b, 11c. The rotor magnet rings 10a, 10b are fixed by means of a support disk 13 on the shaft of the second The faces of the rotor and Statormagnetringe face each other in close axial distance.

p0028All rotor and Statormagnetringe 10, 11 of the center of gravity bearing 5 are made of hard magnetic material and magnetized in axially parallel direction. The rotor and Statormagnetringe are fixed to the shaft 2 or in the gravity bearing housing 12 such that they are arranged behind one another with respect to their magnetization direction 14 which is indicated in Figures 2a to 2c by arrows. thus opposite magnetic poles are opposite to the bearing gaps between the stator and rotor magnetic rings, between which a strong magnetic field with magnetic appeal builds. The attraction forces increase strongly with tighter bearing columns. In middle position, the rotor magnet rings between Statormagnetringen results in a balance of power, which, however, is extremely unstable and only by appropriate design of the stabilizing bearing 7 (Fig. 3) can be maintained.

p0029The prevailing between the end faces of the rotor and Statormagnetringe magnetic field causes a high radial restoring force between the magnetic rings. The magnetic rings must be at least such that the rotor weight can be collected. In the axial direction similar restoring forces can be generated by an axial displacement of the rotor, so that the results from the modified bearing gap widths difference magnetic forces cause the weight balance in particular with a vertical axis position.

p0030The rotor magnet rings 10a, 10b are fitted in the embodiment in protective rings 15 of a material with high tensile strength, so that they are at high rotational speeds torn not by centrifugal forces. As material for the armor rings 15 are located next to high-strength stainless steel or titanium alloys and in particular fiber-reinforced plastics such as glass, carbon or even borfaserverstärkte plastics.

p0031Fig. 2b shows a further variant of gravity bearing 5 with turn concentrically disposed rotor and Statormagnetringen, wherein a radially outboard set of rotor magnet rings 16a, 16b and Statormagnetringen 17a, 17b, 17c and an internal set of rotor magnet rings 18a, 18b and Statormagnetringen 19a, 19b, 19c are arranged adjacent. The external set of magnet rings 16, 17 and the inner set of magnet rings 18, 19 are axially magnetized in opposite directions. The end faces of all the magnetic rings are held by the rotor or Statormagnetringen each case in one plane.

p0032Based on the magnetic material volume provides such an arrangement of magnetic rings a 50% increase in bearing stiffness over that bearing assembly, as described in the embodiment of Fig. 2a. thus leaves without substantial enlargement of the outer diameter of the center of gravity bearing housing 12 with an unchanged overall length is a multiple of power reserve in gravity bearing 5 install.

p0033More extensive use of the magnetic material used has the in Fig. 2c reproduced variant of gravity bearing 5. In this gravity bearing, instead of in Fig. 2b reproduced each matched rotor and Statormagnetringe discs 20a, 20b, 21a, 21b used of hard magnetic material, the are each marked by arrows concentric annular zones of opposite magnetization and have matched to each other is formed and inserted so that the permanent magnetic areas of the discs -. in analogy to the bearing arrangement of Figure 2b - are magnetized in the outer and inner field in the opposite direction. In this magnetic bearing design are preferably all slices on back iron circuits 22, 23 is mounted, whereby the effect of the permanent magnetic zones can be further increased. In the embodiment of Fig. 2c all rotor magnetic rings is provided in its entire axial length einfassender protective ring 24 of non-magnetic material of high tensile strength.

p0034Fig. 3 shows the structure of the stabilizing bearing 7. In the housing 25 of the stabilizing bearing 7 are two electrical coils 26a, 26b inserted which cooperate with two fixed to the shaft 2 ring magnets 27a, 27b of permanent magnetic material in such a way that the rotor 1 at the axial center position of the ring magnets an axial force is transmitted in the housing 25 whose direction and amount are unambiguous and linear associated with the direction and amount of current flowing through the coils. The machining direction of the current in the coils 26a, 26b is directed oppositely.

p0035The ring magnets 27a, 27b of the stabilizer bearing 7 are mounted on supporting disks 28a, 28b and encased in protective rings 29a, 29b of a unmag material of high tensile strength. Between the ring magnets 27a, 27b protrudes an integral with the stator disc 30 of electrically highly conductive material, preferably copper, into it. In the plate 30 27b electrical eddy currents in radial vibrations of the rotor 1 by the ring magnets 27a induces. The mechanical energy contained in the vibrating motion of the rotor 1 is transmitted inductively to the disk 30 and converted into heat. In this way, the vibrations of the rotor are effectively damped.

p0036The rotation of the rotor 1 around its rotor axis 31 only negligibly small eddy currents are generated in the disk 30, because the magnetic flux of the disc does not change during this movement. The disc 30 has formed outside the gap of the ring magnets 27a, 27b a collar 32 which improves the outer short-circuit for the eddy currents, so that the vibration damping is more effective.

p0037FIG. 5 shows a section through the sensor 8, which serves to detect the axial rotor position. Two sensor coils 33, 34 with substantially the same dimensions and number of turns are fixedly mounted on the sensor housing 35th In close axial distance in front of the end face of the sensor coil 33 is located on the shaft end 36 of a marking portion 37 of electrically and / or magnetically highly conductive material, such as aluminum, steel or ferrite. The second sensor coil 34 is compared to a corresponding mark part 38 which is fixed to the sensor housing 35th In the exemplary embodiment, the marking member 38 from the same material as said marker member 37. The boundary surfaces of the sensor coils and tag parts have only a small axial distance from one another. The sensor coils 33, 34 are passed through by a high-frequency alternating current from the control amplifier 9 (see. Fig. 1) is supplied and serves to determine the coil impedances at the given AC frequency. The impedances of the sensor coils 33, 34 are then approximately equal if their distances to the boundary surfaces of the mark parts 37, 38 are approximately equal. The recovered in control amplifier 9 electrical signal is approximately equal to zero in this case. Upon axial rotor deviation signal in respect of its sign and magnitude of the direction and amount of deviation of the rotor from the neutral rotor position is clearly allocated.

p0038The axial rotor position approximately proportional signal of variable gain amplifier 9 is equipped with a phase advance. Due to this phase lead, a damping force in the axial direction is transmitted to the rotor than the desired restoring force simultaneously so that not cause particular shock loads of the magnetic bearing to the rotor axial vibration.

p0039The inventive bearing is thus in all axes stability and cushioning, is being carried out only in the direction of the rotor axis 31 of the rotor with electromagnetic deflection, however, are only effective permanent magnets in the rest.

p0040Fig. Figure 6 shows the sectional view of a drive motor 39 for driving the rotor. As a runner, the drive motor, a rotor part 40 is fixed to the shaft 2 of the rotor 1, which consists essentially of permanent magnetic material with radial magnetization. The rotor part 40 is surrounded by the motor stator without contact 41 'has a three-phase winding 41 and is fed from a polyphase alternator or three-phase converter 42nd The drive motor 39 can be attached to any free position of the shaft 2, in particular, it is located between the center of gravity bearing 5 and the steady bearing. 7

p0041Fig. 7 shows an arranged on the shaft 2 of the rotor thrust bearing 43. The thrust bearing has two fixed to the shaft 2 shoulder or spindle bearings 44, 45, which are set against each other. The shoulder or spindle bearings acting axially along with an attached to the bearing housing 6 capsule 46, which must be made up of several parts, so that the bearing in the assembled state of the startup are such be enclosed camp of the capsule that the outer faces of the bearing against contact surfaces 47 of the capsule 46 can be supported when the rotor 1 in the axial direction is flexed, a permitted contactless maximum deviation is exceeded. In such a case, in particular in case of failure of the axial stabilization function of the steady bearing 7, the start-up bearing then takes over the task of the axial support of the rotor. The contact surfaces 47 prevent further deflection of the rotor. 1

p0042When gravity bearing the rotor magnetic rings between Statormagnetringen are arranged in the embodiments. This assignment of rotor and Statormagnetringen may be designed in other ways, if only the magnetic series arrangement of magnetic zones of the magnetic rings and discs is maintained. Variable is self-evident in the magnetic bearing of the invention, the stator and rotor part. Thus it is possible without changing the bearing effect to mount the stator of the magnetic bearing on a fixed axis and fix the rotor parts on a surrounding the axis hollow shaft, which then carries the axis rotating machine part.

p0043When using the magnetic bearing for machine units, where corrosive liquids come into contact with the magnetic bearing, the magnetic rings in addition to the guard rings previously described that are shrunk, protected on their faces. Suitable for this purpose on the end face of the magnetic rings, for example, glued fenders from non-magnetic material, for example, from stainless steels. It is possible instead of the fenders also a coating of magnetic rings by galvanic deposition of protective layers of the liquid phase.

p0044For the radial limitation of the freedom of movement of the shaft 2 a run-up sleeve 48 is shown in Figure 4, which is fixed to the center of gravity bearing housing 12th The thrust sleeve 48 is preferably made of a plastic having good sliding property, for example of PTFE or polyimide with incorporated Gleitstoffen.