JPH09269007A - Passive magnetic bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a passive magnetic bearing which does not generate vortex current when a rotor is normally positioned while avoiding rotational drug (loss), and obtains high resetting rigidity. SOLUTION: A bearing is composed of a stator and a rotor. The stator has an axial-symmetric form and generates substantially cylindrical axial magnetic field. The rotor has ring-like or disk-like conductors 24A, 24B, 24C. Each inner diameter of magnetic poles of yoke ends 20A, 20B, 20C, 20D connected to a permanent magnet 11 for generating an axial-symmetric magnetic field is a little larger than each outer diameter of the conductors 24A, 24B, 24C and a little smaller than inner diameter thereof. The magnetic pole has an angularly projected portion in the vicinity of the conductor end of the rotor, which is located near the corner of the conductors 24A, 24B, 24C of the rotor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive magnetic bearing, and in particular, the magnetic force of a stator-side magnet induces an eddy current in a rotating rotor-side conductor, and the eddy current is received from a magnetic field. The present invention relates to a magnetic bearing device in which a rotor is supported in a non-contact manner by force.

[0002]

2. Description of the Related Art As a magnetic bearing of the above-mentioned type, for example, JP-A-6-200941 and PCT / US95.
The thing disclosed by the / 03023 international patent application etc. is known. In the all-passive type magnetic bearing using the normal conductive magnet on the stator side, it is necessary to obtain the restoring rigidity by utilizing the eddy current or induced current due to the rotation of the rotor.

However, in the above-mentioned prior art method of inducing current in a multi-pole type magnetic field, eddy current is unavoidable even when the rotor is in a normal position, and thus a large rotary drag (resistance) loss is avoided. Absent. Although there is a null flux coil method even with the same induced current method, in order to prevent harmful eddy currents, the coil structure is complicated and high cost, and if the coil structure is simple, eddy current loss (heat generation, rotating drag)
There was an unavoidable drawback.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and if the rotor is in the normal position,
An object of the present invention is to provide a passive magnetic bearing that does not generate an eddy current, can avoid a rotational drag (resistance) loss, and can obtain high restoring rigidity.

[0005]

DISCLOSURE OF THE INVENTION The present invention comprises a stator and a rotor, the stator generating an axially symmetric and substantially cylindrical magnetic field in the axial direction, and the rotor having a disk-shaped conductor. It is characterized in that the outer peripheral end of the conductor is arranged in the vicinity where the change in the magnetic flux density is maximized by the radial displacement of the conductor with respect to the magnetic field.

Further, the disc-shaped conductor is formed into a ring shape, and the inner peripheral end of the ring-shaped conductor is near the maximum change in magnetic flux density due to radial displacement of the ring-shaped conductor with respect to the stator magnetic field in the axial direction. It is characterized by being placed in.

Further, the outer peripheral end of the ring-shaped conductor is arranged in the vicinity of where the change of the magnetic flux density is maximized by the radial displacement of the ring-shaped conductor with respect to the stator magnetic field.

Further, the disk-shaped conductor is characterized in that ring-shaped insulators and conductors are concentrically arranged alternately.

Further, it is composed of a stator and a rotor, the stator generates an axially symmetric, substantially cylindrical axial magnetic field, and the rotor is provided with a disc-shaped or ring-shaped conductor for generating an axially symmetric magnetic field on the stator side. The inner diameter of the magnetic pole, which is the end of the yoke connected to the permanent magnet, is made slightly larger than the outer peripheral end of the disc-shaped conductor or the ring-shaped conductor, or slightly smaller than the inner peripheral end of the ring-shaped conductor. .

Further, one ends of the facing portions of the magnetic poles are made to project in an acute angle so as to be in close proximity to each other, and are spaced apart from the other end so as to gradually widen the gap, and the conductor has its corners at the acute magnetic poles. Proximity to the tip and the conductor is arranged outside the gap.

Further, the invention is characterized in that, of the two straight lines forming the magnetic pole projecting in an acute angle, the straight line on the conductor side and the straight line on the gap side are inclined.

Further, the rotor is provided with a plurality of ring-shaped conductors in the rotation axis direction, and a magnetic pole at a yoke end connected to a permanent magnet for generating a magnetic field in the axially symmetrical axial direction on the stator side has the plurality of ring-shaped conductors. It is characterized in that it is arranged close to both ends of the outer circumference and / or the inner circumference of the conductor.

In the disk-shaped rotor, a plurality of ring-shaped conductors and ring-shaped insulators are alternately arranged, and a yoke end connected to a permanent magnet for generating an axially symmetric axial magnetic field on the stator side. The magnetic poles are arranged close to the outer peripheral edge and the inner peripheral edge corners of the plurality of ring-shaped conductors.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, in order to obtain radial restoring rigidity, the inner peripheral edge or outer peripheral edge of a rotor-side conductor disc or ring-shaped conductor plate is made axially symmetrical with respect to the rotation axis formed on the stator side. Place concentrically in a magnetic field. As a result, when the rotor rotates in the normal position, induced electromotive force is generated, but current does not flow due to axial symmetry, and axial symmetry is broken and eddy current flows only when there is radial displacement. Then, it interacts with the axially symmetric magnetic field on the stator side to generate radial restoring rigidity.

The eddy current type passive magnetic bearing generates a rotational resistance or a drag together with a restoring rigidity. When only one of the inner circumference and the outer circumference of the rotor side conductor is used, there is no problem because drag will not occur unless there is radial displacement of the rotor, but when the rotor is displaced, drag will occur at the same time as radial restoration rigidity. It is inevitable. It is known that this drag affects translational movement, which may couple with posture movement and cause instability. As a countermeasure against this, if an axially symmetric magnetic field is simultaneously provided on the inner and outer circumferences of a relatively narrow ring conductor, the adverse effect on the translational movement of the drag can be reduced. In other words, it can be limited to the influence of the difference between the inner and outer radii.

In order to increase the restoring rigidity, it is sufficient that the change in the magnetic flux density cut by the conductor with respect to the radial displacement of the conductor is rapid. For that purpose, it is necessary to devise the shape of the magnetic poles through which the magnetic flux enters and leaves the gap. In the present invention, the magnetic pole end faces are not made flat, but one end is made to have an acute angle to face each other and the vicinity thereof is set to the maximum position of the magnetic flux density, and the magnetic pole faces facing from the tip of the acute angle are made into a conical shape. It is possible to slow the radial change in density and, conversely, make the change abrupt from the sharp tip to the outside. Therefore, the conductor does not necessarily have to be sandwiched between the magnetic poles, and it suffices if the conductor is located between the magnetic poles having the acute-angled tip, and thus there is a merit that the assembly becomes easy.

If one example of applying the above-mentioned method to a high-speed rotating body such as a turbo molecular pump to perform uncontrolled magnetic levitation, a radial restoration rigid passive magnetic bearing is used as a rotor. It is unstable in the radial direction at rest or at low speed by providing two or more sets near both ends of the shaft, but stable rigidity in the radial direction can be obtained by rotating at a certain speed or more, so measure the radial direction at high speed. You can A repulsive magnet for supporting the rotor weight is provided facing the rotor and the stator side, and if necessary, a part of the rotor,
By placing magnets on both sides or one side and magnets or magnetic material for attraction on the other side so that an attraction action is generated between the stators, the axial weight when the rotor shaft is erected is supported. . If necessary, the meaning is that the sum of the rigidity against displacement in the three axial directions between the permanent magnets is zero when not rotating, so if the stable rigidity in the rotating axis direction is too large, the unstable rigidity in the radial direction increases. As a result, the load on the eddy current type passive bearing is increased, the size of the entire device is increased, and the cost is increased.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 are schematic views for explaining the principle of the present invention. In FIG. 1, a cylindrical gap 13 is provided in a magnetic circuit composed of a permanent magnet 11 on the stator side and a yoke 12 which are axially symmetric with respect to a rotation axis, and the gap 13 is formed on the rotor side, for example, a copper disk 14 or the like.
The outer peripheral edge 14 a of the magnetic field B passes through a part of the magnetic field B. The outer peripheral end 14a of the disk 14 is preferably placed at the position where the change (ΔB / Δr) in the magnetic flux density B with respect to the radial displacement Δr. Normal position of rotor (concentric with stator magnetic field)
In the case of, since the entire circumference of the disk-shaped conductor 14 cuts the uniform axisymmetric magnetic flux density B at the peripheral speed v, the induced electromotive force E E = v × B is generated, but the electromotive force in the radial direction is axisymmetric. Therefore, no current flows because there is no difference in the circumferential direction on the disc conductor 14.

FIG. 2 is a diagram showing the distribution of electromotive force and current I when the copper disk 14 is displaced to the left in FIG.
When radial displacement occurs, one of the disks (near left edge c)
Since the increase in the magnetic flux that cuts is large and the opposite side (near the right end c ') decreases conversely, the electromotive force E in the vicinity of the magnetic flux increasing position c becomes the maximum and the electromotive force E near the magnetic flux increasing position c becomes maximum. The electromotive force E'in the vicinity of the end c'is the minimum. The current I flows in the direction in which the electromotive force is generated near the maximum position c of the electromotive force, the current flows in the opposite direction near the opposite end c ′, and the current I that returns along the outer circumference of the disk flows.

FIG. 3 shows the change in the loop current when the rotational speed of the disk increases. In this case, keeping in mind that the magnetic flux density near the left end of the disk is increasing, when the rotational speed v of the disk increases, a delay occurs in the current flow due to the electrical resistance and self-inductance of the current circuit. ,
As shown in FIG. 3, one of the loop currents I _A becomes strong and is made to flow in the rotational direction. The other loop current I
_B becomes weaker and is made to flow away from the position c near the maximum magnetic flux density. As a result, these currents generate Lorentz force F = I × B as shown by the small arrow in FIG. 3 due to the interaction with the magnetic flux density B. The resultant force is resilience.

4 to 6 show examples in which the disc-shaped conductor is a ring-shaped conductor. FIG. 4 shows a case where a ring-shaped conductor 15 is attached to the outer peripheral portion of the disk-shaped conductor in FIG. An insulator 16 is provided on the inner peripheral side of the ring-shaped conductor 15.
It has become. In this example, the axial cylindrical magnetic field B formed by the magnet 11 and the yoke 12 passes through the outer peripheral end 15 a and the inner peripheral end 15 b of the ring-shaped conductor 15.

The principle of eddy current generation is exactly the same, but the magnetic flux density near c increases and the magnetic flux density near c'decreases with respect to the left displacement of the ring-shaped conductor 15. Thus, mainly four loop currents I are generated. At high speed, two current loops grow and the remaining two current loops decay and are made to flow as in FIG. 3, and the number of main current loops becomes two as shown in FIG. Then, in the vicinity of a high magnetic flux density, a restoring force as shown by a small arrow F is generated. Therefore, by adopting the ring type, the restoring rigidity can be increased at the inner peripheral edge and the outer peripheral edge as compared with the case of the simple disk, so that it will be increased. The combined use of the inner peripheral edge and the outer peripheral edge of the ring-shaped conductor is also effective for reducing the influence on translational motion.

However, the eddy current type magnetic bearing generates rotation resistance or drag together with restoration rigidity. In the present invention, there is no problem because drag does not occur unless there is radial displacement of the rotor, but when displacement occurs, it is unavoidable that drag occurs simultaneously with restoration rigidity. It is known that this drag affects translational motion, which may couple with posture motion and cause instability. As a countermeasure against this, if an axially symmetric magnetic field is provided on the inner and outer circumferences of the relatively narrow ring conductor, the adverse effect on the translational movement of the drag can be reduced. In other words, it can be limited to the influence of the difference between the inner and outer radii.

FIG. 7 shows a case where the magnetic circuit on the stator side is constructed so that the inner and outer circumferences of the ring cut magnetic flux in the same direction. In that case, the eddy current at low speed is as shown in FIG. 8, and at high speed as shown in FIG. 9, the restoring force is similarly generated.

FIG. 10 is an example in which the magnetic pole of FIG. 1 is improved, and is an enlarged view of the vicinity of the magnetic pole. This figure shows the central axis d
A cylindrical yoke 12, 12 is arranged around the magnet, and a magnetic flux B ₁ , B ₂ , B ₃ , B _4, ... Is formed between the magnetic poles protruding in an acute angle at the tip of the yoke by a permanent magnet (not shown). Is. Flux B ₁ of the gap, the B _2, B _3, B _4, etc., a representation of the path of the magnetic flux, since the magnetic flux B ₂ is the magnetic pole distance is the shortest density is maximum. Next, the magnetic flux B ₃ protruding from the gap has a larger magnetic resistance because it is longer than any of the illustrated paths, and the magnetic flux density is minimum. The magnetic flux density of the magnetic fluxes B ₁ and B ₄ is gradually decreased because the distance between the magnetic poles 12 and 12 is gradually separated from that of B ₃ . This means that the magnetic flux density change is extremely large near the magnetic flux B ₃ with respect to the radial change of the disk-shaped conductor. Therefore, the effect of the magnetic flux change (ΔB / Δr) on the radial displacement (Δr) is more effective when the outer peripheral edge of the conductor disk is placed outside the gap between the magnetic poles near the magnetic flux B ₃ than in the gap. Becomes Further, in the case of FIG. 1, for example, if the disc-shaped conductor 14 is slightly inside the magnetic pole inner peripheral surface, the magnetic circuit on the stator side and the rotor including the disc can be assembled. It will be extremely easy.

FIG. 11 shows a passive magnetic bearing in which the improved magnetic poles of FIG. 10 are stacked in three stages. A cylindrical rotor 23 having ring-shaped conductors 24A, 24B, 24C arranged axially in the lower portion around the central axis d is similarly supported by a cylindrical outer peripheral side stator and inner peripheral side stator. The outer peripheral stator has a ring-shaped permanent magnet 11, and a ring-shaped yoke 20 as well.
The structure is sandwiched by A, 20B, 20C, and 20D, and the tip of the inner peripheral end side thereof has an acute-angled magnetic pole shown in FIG. Similarly, the ring-shaped permanent magnet 11 is provided on the inner circumferential side stator as well as the ring-shaped yokes 21A, 21B, 21.
It has a structure sandwiched between C and 21D, and its tip has an acute-angled magnetic pole.

According to this structure, the ring-shaped conductor 24A,
Since it has a structure in which three stages of magnetic bearings supporting 24B and 24C are laminated, stronger bearing rigidity can be obtained. Also,
Similarly, the magnetic bearing portion can be manufactured only by inserting the cylindrical rotor between the cylindrical outer peripheral side stator and the cylindrical outer peripheral side stator, so that the assembly is easy. Incidentally, the stator may be provided only on the outer peripheral side or the inner peripheral side.

FIG. 12 shows an example in which two sets of different-diameter conductor rings are arranged on one rotor disk. On the rotor disc 30, ring-shaped conductors 31 and 32 are fixed around a central axis d with a ring-shaped insulator interposed therebetween. Ring-shaped conductor 31
The stator-side acute-angled magnetic poles are arranged so as to project from the yokes at positions facing the inner peripheral edge and outer peripheral edge corners, respectively. The upper and lower stators are cylindrical yokes 33A,
A ring-shaped permanent magnet 11 is inserted between 33B and 33C. In this structure, the rotor and the stator enter, but a large number of conductor rings can be arranged concentrically on one rotor disk, and the magnetic bearing rigidity can be increased accordingly.

FIG. 13 shows a sectional structure of a further improved main portion of the magnetic bearing. This is a modification of the structure of the magnetic pole shown in FIG. The acute-angled magnetic pole at the tip of the yoke projects inward (toward the corner portion of the rotor conductor to be supported). That is, the angle formed by the two straight lines L ₁ and L ₂ forming the acute-angled magnetic pole with the rotation axis direction d is 9
It is less than 0 °. That is, of the two straight lines L ₁ and L ₂ , the straight line L ₁ on the conductor 14 side is inclined toward the gap side.
This further increases the magnetic resistance of the magnetic flux B ₃ and reduces the magnetic flux density. Therefore, with respect to the radial displacement (Δr) between the magnetic flux B ₂ and the magnetic flux B ₃ , the change in the magnetic flux density (ΔB / Δ
r) can be further increased, and the magnetic bearing rigidity can be further increased.

FIG. 14 shows a case where the above-mentioned magnetic pole structure is applied to a magnetic bearing for supporting the disc-shaped rotor shown in FIG. FIG. 15 shows a case where the above-mentioned magnetic pole structure is similarly applied to the magnetic bearing showing the cylindrical rotor shown in FIG. 11, and in the case of the present embodiment, the cylindrical rotor has a double structure with the inner peripheral side further. Has become.

FIG. 16 is an application of the present invention for all-passive (uncontrolled) magnetic levitation which seems to be effective when external disturbance force or torque such as a flywheel or turbo molecular pump is relatively small. Here is an example. The passive magnetic bearings 40 having the structure shown in FIG. 11 are arranged near the outer circumferences of the upper and lower ends of the rotor 41. By adjusting the gap, the rotation motor 42 is provided at the center, the repulsion magnet system 43 is provided at the lower center, and the attraction magnet system 44 is provided at the upper part, so that the rotor 41 is supported not only by weight but also by stable rigidity in the rotation axis d direction. Can be set to. Although not shown, since a space is left in the vicinity of the repulsion / attraction magnets 43 and 44, a large amount of copper is arranged on the stator side thereof to form an eddy current damper. Further, a touchdown bearing 45 is arranged near this in case of low speed rotation or in case of emergency. This is because the passive magnetic bearing of this embodiment is non-contact because the rotor floats above a certain rotation speed. Although not shown, the magnetic bearings 40, 43,
It is also effective to support the stator side of 44 with a vibration absorbing function.

[0033]

According to the present invention, when the rotor rotates in a normal position, eddy current does not flow, and the problems of heat generation and rotation drag (resistance) do not occur. Further, by setting the end portion of the conductor in the vicinity of the maximum change in the magnetic flux density due to the radial displacement, it is possible to obtain high restoring rigidity of the magnetic bearing. Where the change in the magnetic flux density with respect to the radial displacement of the conductor is maximum, the acute angle is formed by making the magnetic pole structure at the tip of the yoke into an acute angle.
This can be realized by setting the angle formed by the straight line of the book with respect to the rotation axis direction to 90 ° or less.

[Brief description of drawings]

FIG. 1 is a sectional view showing a principle structure of a passive magnetic bearing of the present invention.

FIG. 2 is a plan view showing distributions of electromotive force and eddy current of a disk-shaped rotor formed by the magnetic bearing.

3 is a plan view showing the distribution of eddy currents and restoring force when the disk-shaped rotor of FIG. 2 is rotated at high speed.

FIG. 4 is a cross-sectional view of a structure in which the rotor has a ring-shaped conductor in the magnetic bearing shown in FIG.

5 is a plan view showing the distribution of electromotive force and eddy current of the ring-shaped conductor rotor in FIG.

6 is a plan view showing the distribution of eddy currents and restoring force when the ring-shaped conductor rotor of FIG. 5 is rotated at high speed.

7 is a sectional view of the structure shown in FIG. 4 in which magnetic fields in the same direction are applied to the outer peripheral edge and the inner peripheral edge of the ring-shaped conductor.

8 is a plan view showing the distribution of electromotive force and eddy current of the ring-shaped conductor rotor in FIG. 7 at low speed.

9 is a plan view showing the distribution of eddy currents and restoring force when the ring-shaped conductor rotor of FIG. 8 is rotated at high speed.

FIG. 10 is a sectional view of the magnetic pole structure of the stator according to the first embodiment of the present invention.

FIG. 11 is a cross-sectional view of a magnetic bearing structure using the magnetic pole structure.

FIG. 12 is a sectional view of a magnetic bearing structure of another embodiment using the magnetic pole structure.

FIG. 13 is a sectional view of a magnetic pole structure of the stator according to the second embodiment of the present invention.

14 is a sectional view of a magnetic bearing structure using the magnetic pole structure shown in FIG.

15 is a sectional view of a magnetic bearing structure of another embodiment using the magnetic pole structure shown in FIG.

FIG. 16 is a sectional view of a rotary machine using the passive magnetic bearing of the present invention.

[Explanation of symbols]

11 permanent magnets 12, 20A, 20B, 20C, 20D, 21A, 21
B, 21C, 21D yoke 13 Air gap 14 Disc rotor 15, 24A, 24B, 24C Ring conductor B ₁ , B ₂ , B ₃ , B ₄ Magnetic flux E Induced electromotive force I Eddy current F Restoring force

Claims (9)

[Claims] 1. A stator and a rotor, wherein the stator generates an axially symmetric and substantially cylindrical magnetic field in the axial direction, and the rotor includes a disk-shaped conductor. The passive magnetic bearing is characterized in that it is arranged in the vicinity where the change in magnetic flux density is maximized by the radial displacement of this conductor with respect to the magnetic field. 2. The disk-shaped conductor is ring-shaped, and the inner peripheral end of the ring-shaped conductor is near the maximum change in magnetic flux density due to radial displacement of the ring-shaped conductor with respect to the stator magnetic field in the axial direction. The passive magnetic bearing according to claim 1, wherein 3. The ring-shaped conductor according to claim 2, wherein an outer peripheral end of the ring-shaped conductor is arranged in the vicinity of which the change of the magnetic flux density is maximized by the radial displacement of the ring-shaped conductor with respect to the stator magnetic field. Passive magnetic bearing. 4. The passive type conductor according to claim 1, wherein the disc-shaped conductor is one in which ring-shaped insulators and conductors are concentrically arranged alternately. Magnetic bearings. 5. A stator and a rotor, the stator generating an axially symmetric and substantially cylindrical axial magnetic field, and the rotor having a disk-shaped or ring-shaped conductor for generating an axially symmetric magnetic field on the stator side. The inner diameter of the magnetic pole, which is the end of the yoke connected to the permanent magnet, is made slightly larger than the outer peripheral end of the disc-shaped conductor or the ring-shaped conductor, or slightly smaller than the inner peripheral end of the ring-shaped conductor. Passive magnetic bearing. 6. One end of each of the opposing portions of the magnetic poles projects in an acute angle and is adjacent to each other, and is spaced apart from the other end so that the gap gradually widens, and the conductor has a corner portion of the magnetic pole having the acute angle. 6. The passive magnetic bearing according to claim 5, wherein the conductor is arranged near the tip and outside the gap. 7. A magnetic pole projecting in the shape of an acute angle 2
7. The passive magnetic bearing according to claim 6, wherein among the straight lines of the book, the straight line on the conductor side is inclined toward the gap side. 8. The rotor is provided with a plurality of ring-shaped plate-shaped conductors in a rotation axis direction, and a magnetic pole at a yoke end connected to a permanent magnet for generating a magnetic field in an axially symmetric axial direction on the stator side has the plurality of rings. The passive magnetic bearing according to any one of claims 5 to 7, wherein the passive magnetic bearing is arranged close to both outer and / or inner ends of the conductor. 9. The disk-shaped rotor has a plurality of ring-shaped conductors and ring-shaped insulators arranged alternately, and a yoke end connected to a permanent magnet for generating an axially symmetric axial magnetic field on the stator side. 8. The passive magnetic bearing according to claim 5, wherein the magnetic poles are arranged in proximity to the outer peripheral end and the inner peripheral end corner of the plurality of ring-shaped conductors.