WO2001031213A1

WO2001031213A1 - Rotary machine having active magnetic bearing mounted therein

Info

Publication number: WO2001031213A1
Application number: PCT/JP1999/005878
Authority: WO
Inventors: Naohiko Takahashi; Haruo Miura; Yasuo Fukushima; Hideo Nishida; Kazuki Takahashi
Original assignee: Hitachi, Ltd.
Priority date: 1999-10-25
Filing date: 1999-10-25
Publication date: 2001-05-03

Abstract

Rotary machines operated at high speeds or high peripheral speeds often use active magnetic bearings both as radial bearings and as thrust bearings because of their advantage of requiring no lubricating oil. In other words, a rotary shaft rotating at high speed is supported by active radial bearings at two axial places and by an active thrust bearing between these radial bearings or at a place spaced from the radial bearings toward the shaft end. Magnetic leakage occurs from the thrust magnetic bearing. The magnetic field produced by this magnetic leakage could form a magnet using the rotary shaft and casing as the core. Therefore, the thrust bearing magnetic loop is provided on the outer periphery thereof with a shield member disposed adjacent the radial magnetic bearing for shielding the magnetic loop so as to prevent a magnetic loop being formed from the radial magnetic bearing. The shield member has only to be nonmagnetic and will provide high advantages if disposed in the smallest clearance.

Description

Specification

Rotating machine with active magnetic bearing

Branch art

The present invention relates to a rotating machine equipped with an active magnetic bearing, and more particularly to a rotating machine suitable for mounting an active magnetic bearing on both a thrust bearing and a radial bearing.

Background art

Due to the advantage of not using lubricating oil, magnetic bearings are beginning to be used to support the rotors of turbo compressors, which are high-speed rotating machines. Magnetic bearings of the turbo compressor, if _c turbocompressor supporting by floating a rotor comprising an impeller in the air Ri by the electromagnetic force, the force is the bearing load becomes rather large because a large, permanent Magnet bearings do not have sufficient bearing load capability. Therefore, an active magnetic bearing using an electromagnet is used for the magnetic bearing.

Active magnetic bearings support the rotor with the attraction of the electromagnets, so two electromagnets are placed facing each other across the rotor, and the attraction of the two magnets is balanced to position the rotor at a certain position. Has emerged. In order to keep the rotor floating stably, the attractive force of the magnet is controlled according to the movement of the rotor. As a result, a sensor that measures the displacement of the rotating machine port over time using an active magnetic bearing and a control circuit that controls the attractive force generated by the magnet in response to the displacement signal measured by this sensor are required. ing.

However, when a magnetic bearing is used, the performance of the bearing may be degraded due to leakage of magnetic flux. In order to prevent this, conventionally, the casing that covers the entire rotating machine is often made of non-magnetic stainless steel. Such an example is described in Japanese Patent Application Laid-Open No. Hei 9-330395 and Japanese Patent Application Laid-Open No. Hei 10-307359.

Among rotating machines, in the case of relatively small vacuum pumps, manufacturing the entire casing with non-magnetic stainless steel or aluminum alloy has advantages such as corrosion prevention, etc. It is informative. However, turbo compressors, especially For compressors with a capacity of 80 kW or more, demagnetizing the entire casing is not only expensive but also disadvantageous in that the number of processing steps increases.

On the other hand, in the above-mentioned conventional example using a passive type magnetic bearing represented by a permanent magnet magnetic bearing, the leakage of magnetic flux only reduces the magnetic flux that can be used effectively and causes a decrease in performance. The effect of the magnetic flux is small. Therefore, it is only necessary to create a holder for the magnetic bearing so as to contain the magnetic flux generated by the magnetic bearing. Japanese Patent Application Laid-Open No. 0339395 / Japanese Patent Application Laid-Open No. H10-1733259 does not take this into consideration.

The present invention has been made in view of the above-mentioned disadvantages of the related art, and has as its object to realize a high-speed rotating machine supported by an active magnetic bearing with improved reliability. Another object of the present invention is to prevent a thrust bearing from adversely affecting the control of a rotating machine.

Yet another object of the present invention is to prevent magnetization of a rotor-casing in a high-speed rotating machine supported by an active magnetic bearing. Disclosure of the invention

A first feature of the present invention to achieve the above object is that, in a rotating machine having a plurality of active magnetic bearings, an outer circumferential side of a magnetic loop formed by a plurality of active magnetic bearings in a multiplex manner And a blocking member for blocking the loop. A second feature of the present invention to achieve the above object is a rotating machine equipped with an active magnetic bearing including a pair of active radial magnetic bearings and an active thrust bearing, the thrust bearing comprising: It has a blocking member for blocking a magnetic loop formed outside of a plurality of formed magnetic loops.

Preferably, a pair of radial magnetic bearings are arranged on both sides of the thrust bearing; a blocking member is provided on at least one outer peripheral side of the pair of radial magnetic bearings. A third feature of the present invention to achieve the above object is that a rotating shaft, centrifugal impellers disposed at both ends of the rotating shaft, a motor rotor formed at an intermediate portion of the rotating shaft, Also, a casing for holding a motor stator forming a motor is provided, an active radial magnetic bearing is arranged between the impeller and the motor rotor, and a thrust magnetic bearing is provided between the pair of radial magnetic bearings. The radial magnetic bearing is provided with a magnetic loop blocking means provided on at least one outer peripheral side of the radial magnetic bearing.

Preferably, the shut-off means is made of a non-magnetic material; the rotating machine has a rated power of 80 to 250 kW; a touchdown bearing of a ball bearing is arranged between the rotating shaft and the casing; The outer periphery of the finger-down bearing was covered with a non-magnetic material; the non-magnetic material was made of stainless steel.

A fourth feature of the present invention to achieve the above object is that a rotating shaft, a motor rotor formed at an intermediate portion of the rotating shaft, a centrifugal impeller attached to both ends of the rotating shaft, An impeller has a suction port for introducing gas from outside the machine and a casing having a discharge port for introducing gas compressed by the centrifugal impeller to the outside of the machine. An active radial magnetic bearing is provided between each impeller and the motor rotor. In a rotating machine equipped with an active magnetic bearing in which an active thrust bearing is arranged on one side of the radial magnetic bearing, a magnetic loop interrupting means is provided on at least one outer peripheral side of the radial magnetic bearing. is there.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of a rotating machine equipped with an active magnetic bearing according to one embodiment of the present invention, and FIG. 2 is a view showing a magnetic loop generated by the active thrust magnetic bearing. FIG. 3 is a longitudinal sectional view of an embodiment of the active thrust magnetic bearing. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows details of a rotating part of a two-stage centrifugal compressor which is an example of the rotating machine according to the present invention. The details are shown in a longitudinal sectional view. In the two-stage centrifugal compressor 30, the first-stage centrifugal impeller 32a and the second-stage centrifugal impeller 32b are directly attached to both ends of the rotating shaft 31 that is the rotor of the motor 41. Have been. Radial magnetic bearings 33a, 33b are provided inside the rotor 31's two impellers 32a, 32b at the mounting positions, and the radial magnetic bearings 33a, 33b are provided. The rotor 31 is rotatably supported by 3b.

The radial magnetic bearings 33a and 33b are provided with radial sensors 42a and 42b for measuring the radial displacement of the rotor 31, respectively. In addition, the axial thrust generated in the two-stage compressor can be supported axially inside the radial magnetic bearing 33b on the side of the second-stage impeller 32b located on the right side in Fig. 1. The thrust magnetic bearings 34a and 34b are arranged with the thrust disk 3la formed on the rotor 31 interposed therebetween. This thrust bearing is provided with a thrust sensor 143 for measuring the axial displacement of the rotor 31.

A motor rotor 31b having a permanent magnet rotor 40 is formed at the center of the rotor 31. The motor rotor 31b faces the rotor 31b with a slight gap. 3 7 are arranged. A permanent magnet motor 41 is constituted by the motor stator 37 and the motor rotor. The outer periphery of the motor stator 37 is held by a water-cooled jacket 45, and the motor stator 37, the rotor 31 and everything else are accommodated in a casing 38c.

The centrifugal impellers 32a and 32b attached to both ends of the rotor 31 are open shroud impellers without a shroud wall. The open shroud surface of each centrifugal impeller 32a, 32b is held by the casing 38c, and the inner casing 38a, 38b held inside the casing. And a small gap is formed between them. Auxiliary bearings 39a and 39b are disposed axially outside the radial magnetic bearings 33a and 33b. The auxiliary bearings 39a and 39b are not energized because the magnetic bearings 33a and 33b are not energized, and the rotor 31 does not operate. This is to prevent contact with 38b etc. During the operation of the compressor, the radial magnetic bearings 33a and 33b lift the rotor 31. Thus, the rotation is controlled without the auxiliary bearings 39a and 39b coming into contact with the rotor 31. The gap formed between the auxiliary bearings 39a, 39b and the rotor 31 during operation is limited to the air gap of the motor and radial magnetic bearings 33a, 33b and the shroud gear of the impeller. Smaller than

In the radial magnetic bearings 33a and 33b of the two-stage centrifugal compressor configured as described above, electromagnetic steel sleeves are fitted to the rotor 31 and the rotor part 31 of the magnetic bearing is used. c, 3 I d. On the other hand, the stay portions 33c and 33d facing the rotor portion also have magnetic steel sheets. A magnetic circuit is formed between the magnetic steel sheets in the stay sections 33c and 33d and the magnetic steel sheets in the rotor section. Four magnetic circuits are formed on one radial bearing unit with the rotor interposed, and the four attractive forces of up, down, left, and right are controlled to lift the rotor.

Similarly, in the thrust bearings 34a and 34b of the two-stage centrifugal compressor, an electromagnet is arranged with the disk 31a formed on the rotor 31 interposed between the disk and the core on the stator side. To form a magnetic circuit. The disk is attracted by these two electromagnets, and by controlling the force, the axial position is controlled so that the rotor 31 does not contact the stays 38a, 38b, etc. .

By the way, in the radial bearing, most of the magnetic flux passes through the electromagnetic steel plate of the rotor, the electromagnetic steel plate of the stator, and the gear gap of the electromagnetic steel plate of the stator, and almost all other parts. Almost no leakage. On the other hand, in the thrust bearing, there is a high possibility that the magnetic flux leaks to the casing 38c and the rotating shaft 31 other than the bearing.

For example, a typical thrust magnetic bearing coil has a simple circular shape, with the rotor passing through the center. In this thrust magnetic bearing, the magnetic flux tends to pass through the center of the coil. Therefore, if the rotor is arranged at the center of the coil, the rotor acts as an iron core, and magnetic flux passes through the rotor. The magnetic flux passing through the rotor further forms a magnetic flux loop passing through the casing of the compressor, and eventually, the entire machine becomes an electromagnet. To avoid this problem, the stator of the thrust magnetic bearing has an E-shape in longitudinal section. Then, two coils are inserted per one stator, and the directions of the currents are reversed. When the thrust bearing is configured in this way, the direction of the magnetic field is reversed between the casing portion located on the outer diameter side of the coil and the rotating shaft portion located on the inner diameter side. It is erased to zero. As a result, the generated magnetic flux is confined inside the bearing.

Thrust bearings with such a structure are advantageous in that they can confine magnetic flux, but they require a large bearing facing area, so they can be used for low-speed and large rotating machines, but they can be used for high-speed small It is difficult to apply to a simple machine. For this reason, in the present invention which has been downsized at high speed, a C-shaped thrust bearing having a simple structure is employed as the thrust bearing as shown in detail in FIG.

However, in a centrifugal compressor, the magnitude of magnetization may need to be several gauss or less. Therefore, in a centrifugal compressor equipped with magnetic bearings, it is required to minimize the magnetization generated in parts other than the bearings. In the past, in order to prevent magnetization, the casing was made of a non-magnetic material such as stainless steel to shield the magnetism. However, in this case, the manufacturing cost of the compressor increased significantly due to the high cost of casing.

If the casing is made of a magnetic material such as steel without demagnetizing the casing, the magnetic flux generated from the thrust bearing will pass through the casing and magnetize the casing. According to the results of the magnetic field analysis by the present inventors, it was found that many magnetic fluxes passed through the stator part of the radial bearing. The part having the smallest magnetic gap among the gap between the rotating shaft and the stator is a so-called bearing gear formed between the bearing and the rotor in the radial bearing. Magnetic flux tends to collect in the bearing gap with the narrowest gap. As a result, the stator of the radial bearing serves as a path for magnetic flux, and the rotor and casing are connected in a magnetic circuit. In this case, the control of the radial bearing is adversely affected, and in the worst case, the radial bearing becomes uncontrollable. As described above, magnetizing the casing and the like has a significant effect on the levitation control of the centrifugal compressor. Therefore, in the present invention, the radial magnetic bearings 33a and 33b constituting the radial bearing portion and the thrust bearing portion as described below are respectively provided with the bearing housings 35a and 35a. Fixed to 5b. Then, insert rings 44a and 44b made of non-magnetic stainless steel between the radial magnetic bearings 33a and 33b and the bearing housings 35a and 35b. . This stainless steel ring acts as a magnetic shield material, that is, a blocking member for the magnetic loop.

One thrust magnetic bearing 34 a is fixed to a bearing holder 36. The other thrust magnetic bearing 34b is fixed to the bearing housing 35b or the stainless steel ring 43b. Fig. 3 shows the details of this thrust magnetic bearing.

When the centrifugal compressor rotates at a high speed, the centrifugal stress generated in the thrust disk 31a increases. Therefore, the diameter of the thrust disk 31a needs to be as small as possible. Therefore, in this embodiment, a C-shaped magnet shown in FIG. 3 is employed. In order to reduce the diameter of the thrust disk 31a, that is, to position the bearing surface as far as possible to the inner diameter side, the stator yoke is extended as far as possible to the inner diameter side.

This C-shape is different from the E-shape, and each magnet constituting the thrust magnetic bearing has only one coil. Therefore, the magnetic flux leaking to the outside cannot be canceled out positively. However, in the electromagnets facing each other across the thrust disk 31a, if the current directions are opposite to each other and the magnitudes are the same, leakage of magnetic flux to the outside is reduced. Normally, since a thrust load is applied, the current of one of the electromagnets increases, and a magnetomotive force that causes magnetic leakage occurs.

The shape of the coil used for the thrust magnetic bearings 34a and 34b is a simple circle centered on the axis of the rotor 31. When a current flows through the coil of the thrust magnetic bearing, the stator core of the thrust magnetic bearing and the thrust disk 31a are displaced. Magnetic fluxes 51a and 51b are generated as they pass. Since a gap exists between the steel core of the thrust magnetic bearing and the thrust disk, an attractive force corresponding to the magnetic flux density is generated in the gap.

The steel cores of the thrust magnetic bearings 34a and 34b are paired by narrowing the thrust disk 31a. Therefore, an arbitrary force is generated in the axial direction by adjusting the coil current applied to the stators of the two thrust magnetic bearings 34a and 34b. The coil current is adjusted using a magnetic bearing controller (not shown). The magnetic bearing controller adjusts the magnetic bearing so that the rotor is always positioned at a certain position while suppressing the displacement and vibration of the rotor caused by disturbances. For this purpose, the displacement signal of the rotor measured by the displacement sensor is input to the magnetic bearing controller. The magnetic bearing controller has a power amplifier that supplies current to the bearing coil and an arithmetic function for feedback control. In this way, the amount of coil current to be applied is calculated for the momentarily changing behavior of the rotor.

As described above, in the thrust bearing, the directions of the currents flowing through the two coils are opposite to each other so that the influence of the magnetism does not leak to the outside as much as possible. In the steady state, when there is no thrust load, the same current flows through the two coils in different directions. In this case, when the force is balanced, the magnetism that leaks to the outside is also minimized. The current required to achieve this steady state is called the bias current. Bias current loads the magnetic bearing with a static tension to improve the linearity of current and force.

In a real machine, the magnitudes of the two coil currents are never the same due to the existence of fluid thrust and unbalance of the gap. Therefore, magnetic leakage occurs according to the current difference. Conventionally, as described above, the entire casing was made of a non-magnetic material such as stainless steel to magnetically shield to reduce the influence of the magnetic leakage. However, this leads to increased costs. The use of non-magnetic materials is very effective for magnetic shielding. However, if this causes cost, a configuration is possible that allows magnetic shielding without making the entire casing non-magnetic. The present invention is the result of studying whether or not it is possible. The present invention has found a very effective magnetic shielding method using a minimum of non-magnetic material.

The details of the magnetic shielding method of the present invention are shown below. The nonmagnetic material covers only the outer periphery of the stator core of the radial magnetic bearings 33a and 33b. When the currents 51a and 51b flowing through the two coils of the thrust magnetic bearings 34a and 34b become unbalanced, as shown in Fig. 2, the magnetic field due to the unbalanced state causes A magnetic flux loop 52a, 52b having a magnetic path formed by the stator core of the radial magnetic bearings 33a, 33b, the rotating shaft 31 and the casing 38c is formed. Like the thrust magnetic bearings 34a and 34b, the radial magnetic bearings 33a and 33b have a small gap between the step iron core and the rotating shaft 31 so that the magnetic flux can easily pass through. This creates a magnetic circuit that passes through the gap. Therefore, magnetization of the casing is prevented by preventing magnetic flux from passing through the iron core of the radial bearing.

FIG. 1 shows an example of this embodiment. A blocking member made of a non-magnetic material is inserted between the stator core of the radial bearing and the casing. In this way, the magnetic loop passing through the radial bearing can be interrupted.

Here, the radial bearing has a magnetic circuit for generating a bearing attraction in the radial direction. This radial bearing suction action and the non-magnetic material inserted around the outer periphery of the radial bearing stator can be considered completely separate. This indicates that the insertion of a non-magnetic material makes the independence of the suction action of the radial bearing more complete.

In other words, unless a non-magnetic material is inserted, the magnetic flux generated by the thrust bearing passes through the radial bearing. As a result, the position control of the rotor by the radial bearing is affected by the operation of the thrust bearing. Inserting a non-magnetic material outside the radial bearing not only prevents the magnetization of the casing, but also has the effect of making the radial bearing independent of the thrust bearing control.

In the centrifugal compressor, the portions where the gap between the stator and the rotating shaft 31 is narrow include not only the magnetic bearings but also the motors 31b and 41, and the impellers 32a and 32b. And auxiliary bearings 39a and 39b. For the reasons described above, the outer peripheral portion of the motor The outer periphery of the inner casing 38a, 38b and the outer ring of the auxiliary bearing 39a, 39b must also be made of non-magnetic material.

However, in a high-speed rotating machine represented by the centrifugal compressor shown in Fig. 1, the motor stator generates heat corresponding to the driving force, and the heat is cooled around the outer periphery of the motor stator 41 to cool this heat. Is equipped with a water-cooled jacket 45. Since the water-cooling jacket 45 uses a non-magnetic material such as stainless steel or brass from the viewpoint of corrosion prevention, it is not necessary to insert another non-magnetic material around the outer periphery of the motor stator.

Considering the demagnetization of the inner casings 38a, 38b, the impellers 32a, 32b themselves are made of non-magnetic materials such as titanium alloy or aluminum alloy for high speed and high peripheral speed. Since magnetic material is used, it is not necessary to use non-magnetic material until inner casing. Although ball bearings are generally used for the auxiliary bearings 39a and 39b, it is not necessary to insert a non-magnetic material outside the outer ring if the rolling elements are ceramic. When a steel rolling element is used, magnetic flux passes through the rolling element. Therefore, as in the case of the radial bearing described above, nonmagnetic materials 46a and 46b are inserted outside the outer ring.

In the above embodiment, the radial magnetic bearings are arranged on both sides, and the thrust magnetic bearings are arranged between them. As described above, such a configuration is not preferable because a magnetic leakage loop is easily formed by the magnetomotive force generated by the thrust magnetic bearing. However, this arrangement is preferred to take full advantage of the radial bearing's damping capabilities. To avoid magnetic leakage due to the thrust magnetic bearings or due to structural limitations of the rotating machine, when the thrust magnetic bearings are not located between the radial magnetic bearings but are located outside the radial magnetic bearings Can be done as follows

In this case, the magnetic leakage is considered to be small. However, if there is anything other than the radial magnetic bearing that easily becomes a magnetic path, magnetic leakage occurs due to the thrust magnetic bearing. For example, if the auxiliary bearing is located outside the thrust magnetic bearing, the auxiliary bearing becomes a magnetic path and magnetic leakage occurs. In this case, as described above, a ceramic ball bearing is used for the auxiliary bearing, or the outside of the outer ring is non-magnetic. The formation of a magnetic path is prevented by covering with a ring of a conductive material.

As described above, according to the present invention, in the magnetic bearing for supporting the rotating machine, it is not necessary to manufacture the entire casing with a non-magnetic material, so that the magnetic bearing and the magnetic bearing are mounted at low cost. A rotating machine can be realized.

Claims

The scope of the claims

1. In a rotating machine equipped with a plurality of active magnetic bearings, a blocking member for blocking a loop on an outer peripheral side in a magnetic loop formed by the plurality of active magnetic bearings in a multiplex manner is provided. A rotating machine equipped with an active magnetic bearing.

2. In a rotary machine equipped with an active magnetic bearing having a pair of active radial magnetic bearings and an active thrust bearing, a rotating machine is provided with a plurality of magnetic loops formed by the thrust bearings. A rotary machine equipped with an active magnetic bearing, comprising a blocking member that blocks a formed magnetic loop.

3. The rotating machine according to claim 2, wherein the pair of radial magnetic bearings are arranged on both sides of the thrust bearing.

4. The rotating machine according to claim 2, wherein the blocking member is provided on at least one outer peripheral side of the pair of radial magnetic bearings.

5. A rotating shaft, centrifugal impellers disposed at both ends of the rotating shaft, a motor rotor formed at an intermediate portion of the rotating shaft, and a casing for holding a motor stator that forms a motor together with the motor rotor. An active radial magnetic bearing is disposed between the impeller and the motor rotor, and a thrust magnetic bearing is disposed between the pair of radial magnetic bearings. At least one of the radial magnetic bearings is provided. A rotating machine equipped with an active magnetic bearing, characterized in that a magnetic loop blocking means is provided on the outer peripheral side of the rotary machine.

6. The rotating machine according to claim 5, wherein said blocking means is made of a non-magnetic material.

7. The rotary machine equipped with an active magnetic bearing according to claim 5, wherein the rotary machine has a rated power of 80 to 250 kW.

8. The touchdown bearing of a ball bearing is disposed between the rotating shaft and the casing, and the outer periphery of the touchdown bearing is covered with a non-magnetic material. A rotating machine equipped with the active type magnetic bearing according to the above.

9. The rotating machine equipped with an active magnetic bearing according to claim 6, wherein the non-magnetic material is stainless steel.

10. A rotating shaft, a motor rotor formed at an intermediate portion of the rotating shaft, centrifugal impellers mounted on both ends of the rotating shaft, and a suction port for introducing gas to the centrifugal impeller from outside the machine. And a casing having a discharge port for guiding the gas compressed by the centrifugal impeller to the outside of the machine. An active radial magnetic bearing is provided between each impeller and the motor rotor. In a rotating machine equipped with an active magnetic bearing in which a thrust bearing is arranged, an active magnetic bearing characterized in that at least one of the radial magnetic bearings is provided with a magnetic loop shut-off means on an outer peripheral side thereof. Rotating machine equipped with.