JP4709986B2 - Magnetic bearing shaft system - Google Patents

Description

The present invention relates to a magnetic bearing shaft system having an inclination. This system consists of a shaft and a magnetic bearing. In particular, the magnetic bearing of the present invention comprises a magnetic bearing, one or more displacement sensors and a control system, an auxiliary bearing, and a support structure having an inclination.

  When using a magnetic bearing shaft system to lift the shaft and drive it safely, various clearances are required. In general, the deflection of the shaft itself due to its large weight falls into the category of large ones. With the use of tilted support structures, these clearances can be greatly reduced by combining the center line of the magnetic bearing with the center line of the shaft in a steady state.

  By using a magnetic bearing shaft system having an inclination, the clearance is reduced, and it is possible to improve the performance of the magnetic bearing, improve the shaft support performance and reliability, simplify the system, and improve the efficiency of the equipment used. The present invention brings a great effect to the magnetic bearing field from the viewpoints of capacity and economy, and raises the prospect of the technology for the current and future utilization systems.

  The magnetic bearing has features such as no lubrication oil and no friction, and has advantages over the conventional oil bearing and rolling bearing. This is suitable as a bearing for rotating equipment installed in nuclear facilities where mixing of lubricant around the core is disliked.

  Unlike other bearings, the magnetic bearing needs to set a clearance (gap or static gap) called an air gap. In order to operate safely without contact between the shaft and the bearing, further clearance is required. When obtaining the clearance, since it is a heavy object, it is necessary to consider the bending of the shaft with a large bend, vibration due to rotation, and the like. Furthermore, it is necessary to determine the clearance in consideration of the auxiliary bearing as an alternative bearing.

Due to this severe restriction on clearance, the use of magnetic bearings is limited in both capability and controllability. First, the magnetic bearing load needs to be inversely proportional to the square of the clearance distance until the magnetism is saturated. Also, the controllability is significantly deteriorated due to the magnetic leakage from the gap due to the increase of the clearance distance. In past literature, a clearance of 3.5 mm is required to use a magnetic bearing for a generator in a nuclear facility (Non-Patent Document 1). This value is far from 2.0 mm, which is considered optimal.
Takizuka, T., et al., 2004. R & D on the power conversion system for gas turbine high temperature reactors. Journal of Nuclear Engineering and Design 233 (2004) 329-346.

  The present invention solves the above-mentioned problems by installing the support structure for installing the magnetic bearing at an angle. Reduce or eliminate misalignment of the center line (misalignment between the shaft axis and magnetic bearing axis or auxiliary bearing axis) caused by shaft deflection by tilting the support structure, and reduce or eliminate the required clearance for deflection. It becomes possible.

  Setting the magnetic bearing system at an angle is a practical and economical solution, and is particularly effective when using heavy and bendable shafts. The tilted installation increases the capacity of the magnetic bearing, reduces the stress of the constituent material, and increases the controllability. This leads to an improvement in economy and an improvement in capacity.

  The present invention raises important advances and technical prospects of current and future utilization systems with regard to the state of the art in the field of magnetic bearings in practicality and economy.

  The magnetic bearing shaft system according to the present invention comprises a shaft and a magnetic bearing unit. The magnetic bearing unit includes a magnetic bearing, one or a plurality of displacement measuring sensors, an auxiliary bearing, and a support structure that can be installed at an inclination. There are no special bearings and shafts, and there are no restrictions on the load. Further, there is no restriction on the method for adjusting the unbalance.

In the present invention, during normal operation, the magnetic bearing imparts buoyancy to the shaft and adjusts unbalance and vibration related to rotation. That is, various clearances are reduced by inclining and installing the bearing support structure so that the magnetic bearing center line is aligned with the center line of the shaft. The sensor accurately and independently provides displacement and movement within the shaft bearing. The signal from the sensor is used for shaft positioning and vibration control. The auxiliary bearing is an auxiliary bearing at the time of failure of the magnetic bearing. Since the clearance between the auxiliary bearing and the shaft is smaller than the clearance between the magnetic bearing and the shaft, it is possible to avoid contact of the shaft with the magnetic bearing when the magnetic bearing fails.

  An alternative embodiment of the present invention can improve the capacity of the magnetic bearing system and improve the installation by tilting the auxiliary bearing by tilting the support structure to the required angle with respect to the shaft centerline. . In another alternative embodiment of the present invention, the clearance for various magnetic bearings is greatly increased by minimizing misalignment between the center line of the magnetic bearing and auxiliary bearing and the center line of the shaft by tilting the support structure. Can be reduced.

An outline of a magnetic bearing system which is a reference technique of the present invention is shown in FIG. The system comprises a shaft 7 and a magnetic bearing unit 8. During operation, the magnetic bearing unit 8 floats the shaft 7 and adjusts vibration and unbalance caused by the rotation of the shaft 7.

  More specifically, the magnetic bearing unit 8 includes a magnetic bearing 9, an inner sensor 11, an outer sensor 12, an auxiliary bearing 10, and a support structure 15 of the magnetic bearing 9 that measures displacement and generates a control signal. The center line 20 of the magnetic bearing unit 8 is related to the center line of the magnetic bearing 9 and the center line of the auxiliary bearing 10. The center line of the magnetic bearing 9 coincides with the center line 20 of the magnetic bearing unit 8.

  The magnetic bearing 9 gives buoyancy to the shaft 7. When the shaft 7 rotates, the magnetic bearing 9 adjusts vibration and unbalance caused by the rotation of the shaft 7. The inner sensor 11 and the outer sensor 12 accurately and independently give the displacement and movement necessary for flying. The signal from the sensor is used to control the shaft position and vibration. The auxiliary bearing 10 is an alternative bearing that supports the shaft 7 when the magnetic bearing 9 fails. The auxiliary bearing 10 resists the fall of the shaft 7 when the magnetic bearing 9 fails, and prevents the shaft 7 from contacting the magnetic bearing 9.

In a steady state, the shaft 7 is deflected by gravity. The angle between the shaft centerline 17 when bent and the shaft centerline 16 when there is no deflection is defined as a deflection angle (θ ₁ ) 27.

  In order to eliminate this deflection causing the possibility of contact with the magnetic bearing 9, the bearing support structure 15 is tilted along the center line 20 of the magnetic bearing unit 8 along the inclination due to the deflection of the shaft 7.

The angle at the time of the tilt installation is defined as a tilt angle (θ ₂ ) 29 of the magnetic bearing 9. The clearance (b) 31 between the auxiliary bearing 10 and the shaft 7 is one of the design items of the auxiliary bearing 10 and is expressed by the following equation using the actual displacement inclination 28 and the basic clearance (b ₀ ) 25.

Here, L is the width 26. The basic clearance (b ₀ ) 25 is determined mainly based on the centrifugal force of the shaft, thermal expansion, manufacturing error, compliance, and the amount of wear of the auxiliary bearing.
On the other hand, the magnetic bearing 9 is designed based on the clearance 32, and the clearance 32 is the sum of the following three clearances. One is the movement distance 21 between the initial center line 17 of the shaft 7 and the center line 18 when contacting the auxiliary bearing, and the second is the center line of the shaft when deformed by elasticity after contacting the auxiliary bearing. An elastic deformation 22 corresponding to a movement distance from 17 to the center line 19 at the end, and a third is an allowable clearance 23, which mainly includes centrifugal force, thermal expansion, manufacturing error, and the like. The required clearance 32 of the magnetic bearing 9 is predicted from the following equation.

Where K _a is the elastic deformation coefficient of the shaft.
Similarly, the clearance 36 at the center of the shaft 7 is the sum of the two clearances. One is the movement distance 33 between the initial center line 17 of the shaft 7 and the center line 18 at the center of the shaft when contacting the auxiliary bearing. The second is when the elastic deformation occurs after contacting the auxiliary bearing. This is an elastic deformation 35 corresponding to the moving distance from the center line 17 of the shaft to the center line 19 at the end. The minimum clearance of the shaft is expressed by the following formula.

Here K _c is the elastic deformation coefficient at the center of the shaft.
The quantities L and θ ₁ in the formulas (1) to (3) are usually important for heavy and elastic shafts. As a result, the clearances a, b, and c when using the magnetic bearing derived from the equations (1) to (3) are large values. In general, if the clearance is large, the economic efficiency and machine performance deteriorate.

On the other hand, from equation (1) to (3), by approaching tilting the corners 29 (theta ₂₎ on the deflection angle 27 (theta ₁₎ of the shaft, thereby making it possible to effectively reduce the clearance a, b, and c is there. From this fact, the clearance can be effectively reduced by tilting the magnetic bearing system .

FIG. 2 is an overview of a further reference technique of the present invention, and FIG. 1 and their similar parts are designated by the same reference numerals and will not be described in detail. As shown in FIG. 2, the auxiliary bearing 10 is tilted at an angle of 30 by tilting the support structure. If the sizing of the auxiliary bearing is an important design factor, the tilted installation of the auxiliary bearing 10 reduces the clearance 31 and provides flexibility in installation.

FIG. 3 is an overview of an embodiment of the present invention , and FIG. 2 and similar parts are designated by the same reference numerals and will not be described in detail. As shown in FIG. 3, the inclined installation of the support structure 15, (equal to the angle 27) the magnetic bearing 9 and the auxiliary bearing 10, respectively the angle 29 and angle 30 inclined, the center of each of the magnetic bearing 9 and the auxiliary bearing 10 Align the line with the center line 17 of the shaft. As a result, the clearances 31, 32, and 36 are greatly reduced. The present invention has two unique advantages. The first point is that the clearance 32 of the magnetic bearing 9 becomes uniform with respect to the length direction of the bearing, thereby forming a uniform magnetic field. As for the second point, if the clearance is uniform, the position information to be measured is the same for the sensor 11 and the sensor 12, and therefore one can be reduced.
[The invention's effect]

  The present invention capable of reducing the clearance of the magnetic bearing has the ability to bring great benefits in terms of cost and performance. One important advantage is that by reducing the clearance of the magnetic bearing, the capacity is increased and, as a result, the size and cost of the magnetic bearing system can be reduced. Until the magnetic flux density is saturated, the required load is inversely proportional to the square of the distance.

  Another advantage is that the controllability can be increased by reducing the clearance of the magnetic bearing. FIG. 4 shows the magnetic bearing clearance dependence of the magnetic bearing stiffness, and shows the stiffness response of a magnetic bearing having two different clearances. Higher rigidity is shown with a smaller clearance. That is, when the rotating shaft has two types of large and small air gaps of 2.5 mm and 3.5 mm, the rigidity of the magnetic bearing increases as the rotational frequency increases, and the smaller the air gap, The bearing rigidity is large, and it is shown that the shaft is not easily eccentric with respect to the load change.

  At the same time, by using the present invention for equipment using magnetic bearings, the performance of the equipment is improved. FIG. 5 shows the dependency of the compressor efficiency on the magnetic bearing clearance. In the compressor, the relationship between the clearance at the shaft blade tip and the compressor efficiency is shown. By reducing the clearance at the shaft tip by 1 mm, the efficiency is improved by about 3%. That is, the smaller the gap at the shaft blade tip, the higher the efficiency of the compressor.

  Specific embodiments of the invention are presented in the figures and description. These schemes described the principles and practical application of the invention in order to make use of the invention in various forms and to enable other technologies suitable for a particular use. It should not be construed as limiting the scope of the invention described in detail, and in fact many modifications and changes are possible from a learning standpoint. For example, many variations are possible, including having a different number of bearings, different types of bearings such as journals, thrusts, multi-shafts, and additionally having a balancing mechanism. Similarly, the change relates to the overall layout of the equipment that uses it, and is not limiting. Thus, the present invention should be determined by its legal equivalents.

Schematic of a magnetic bearing shaft system when the magnetic bearing and the shaft centerline are aligned by tilting the support structure . FIG. 2 is a schematic view of the magnetic bearing shaft system of FIG. 1 when the auxiliary bearing is tilted together with the magnetic bearing by tilting the support structure . FIG. 2 is a schematic view of the magnetic bearing shaft system of FIG. 1 when the magnetic bearing and auxiliary bearing are aligned with the centerline of the shaft by tilting the support structure in accordance with a specific plan of the present invention . The figure which shows the magnetic bearing clearance dependence of magnetic bearing rigidity. The figure which shows the magnetic bearing clearance dependence of compressor efficiency.

7: Shaft 8: Magnetic bearing unit 9: Magnetic bearing 10: Auxiliary bearing 11: Inner sensor 12: Outer sensor 15: Support structure 16: Shaft center line 17 without deflection 17: Shaft center line 18 when bent : Center line 19 of the shaft when contacting the auxiliary bearing 19: Center line 20 from the center line 17 to the end of the shaft due to elasticity 20: Center line 21 of the magnetic bearing unit 22: Movement distance 22 from the center line 18: Elastic deformation 23: acceptable clearance 25: basic clearance 26: width 27: angle 28 of the center line 17 of the shaft when deflected with respect to the shaft center line 16 in the absence of deflection: actual displacement 29: tilted magnetic bearing angles 30: inclination of the auxiliary bearing Angle 31: Clearance between the clearance of the auxiliary bearing and the shaft 32: Clearance 33: Distance 3 of movement of the center line until contact with the auxiliary bearing 3 : Moving distance of the center line in until the end of after contact with the auxiliary bearing 36: clearance in the middle portion of the shaft

Claims (8)

A magnetic bearing unit comprising a shaft and a magnetic bearing unit, wherein the magnetic bearing unit floats the shaft, a control device that controls the displacement and movement of the shaft, an auxiliary bearing that floats the shaft as an alternative bearing when the magnetic bearing fails, And having a support structure,
The support structure tilts and fixes the magnetic bearing and the auxiliary bearing such that the center line of each of the magnetic bearing and the auxiliary bearing coincides with the center line of the shaft that is bent when floating. Bearing shaft system.   The magnetic bearing shaft system according to claim 1, wherein the magnetic bearing shaft system includes one or more magnetic bearing units, and a sensor that measures displacement and movement of the shaft and provides a control signal to a control device.   The magnetic bearing shaft system according to claim 1, wherein the magnetic bearing shaft system is a bearing that receives the magnetic bearing in a cylindrical shape in parallel with the rotating shaft, and is used as a journal bearing that acts on a radial blur of the shaft center. The magnetic bearing shaft system according to claim 1, wherein the magnetic bearing is a bearing that receives a projecting portion from a rotating shaft and is used as a thrust bearing that acts on a blur parallel to the axis.   The magnetic bearing shaft system according to claim 1, wherein the magnetic bearing is used as a journal bearing and a thrust bearing.   The magnetic bearing shaft system according to claim 1, wherein one or more of the magnetic bearings are used.   The magnetic bearing shaft system according to claim 1, wherein the shaft has one or more shafts via a coupling.   2. The magnetic bearing shaft system according to claim 1, wherein an additional balance adjusting mechanism is used in the magnetic bearing system.

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