Radial Foil Bearings

Abstract

To provide a radial foil bearing that can readily acquire a desired performance and improves assemblability.SOLUTION: A radial foil bearing 1 includes: a top foil 2 surrounding a periphery of a shaft and facing the shaft in a radial direction; a bump foil 3 disposed in a radial outside of the top foil 2; and a cylindrical housing 4 disposed in a radial outside of the bump foil 3 and accommodating the top foil 2 and the bump foil 3. The bump foil 3 is pressed onto an inner peripheral surface 4a of the housing 4 by magnetic force.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a radial foil bearing. [Background technology]

[0002] Radial foil bearings have been known as bearings for high-speed rotation. A radial foil bearing includes a top foil that surrounds the shaft, which is the bearing object, a bump foil disposed radially outward of the top foil, and a cylindrical housing that accommodates the top foil and bump foil. The bump foil is made elastic by, for example, forming a thin plate into a corrugated shape with alternating peaks and valleys. The bump foil elastically supports the top foil to allow for flexural deformation of the top foil when subjected to the load of the shaft. The top foil supports the shaft without contact due to the wedge effect formed between the top foil and the shaft, and the elastic deformation of the bump foil damps rotational vibration of the shaft.

[0003] However, if the bump foil is crushed by the shaft due to rotational vibration of the shaft, beyond the elastic deformation range and into the plastic deformation range, the bump foil will be deformed. This can damage not only the radial foil bearing, but also the shaft and load-side mechanical components. For this reason, various techniques have been proposed to increase the spring rigidity of the bump foil. For example, a technique has been proposed in which the bump foil is made into a mesh-like structure by weaving multiple wires (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-227240 Summary of the Invention [Problem to be solved by the invention]

[0005] However, simply increasing the spring stiffness of the bump foil makes it difficult to adjust the spring stiffness and obtain the desired spring stiffness, which makes it difficult for the radial foil bearing to adequately damp the rotational vibration of the shaft, making it difficult to obtain the desired performance of the radial foil bearing. Furthermore, increasing the spring rigidity of the bump foil may result in a deterioration in the assembly efficiency of the bump foil.

[0006] Therefore, the present invention provides a radial foil bearing that can easily achieve desired performance and improve assembly efficiency. [Means for solving the problem]

[0007] In order to solve the above problems, the radial foil bearing of the present invention comprises a top foil that surrounds the shaft and faces the shaft radially, a bump foil that is arranged radially outside the top foil, and a cylindrical housing that is arranged radially outside the bump foil and that accommodates the top foil and the bump foil, and is characterized in that the bump foil is pressed against the inner surface of the housing by magnetic force.

[0008] This configuration increases the frictional resistance of the bump foil against the housing. This allows the radial foil bearing to adequately damp the rotational vibration of the shaft without increasing the spring rigidity of the bump foil itself. Furthermore, minute movements of the top foil and bump foil generate a damping effect due to eddy currents, further damping the rotational vibration of the shaft. This allows the desired performance of the radial foil bearing to be achieved. Furthermore, since there is no need to increase the spring rigidity of the bump foil, the assembly of the bump foil can be improved. The magnetic force also increases the strength with which the top foil and bump foil are attached to the housing, preventing the top foil and bump foil from shifting when the shaft is inserted into the radial foil bearing, providing a highly reliable radial foil bearing.

[0009] In the above configuration, the bump foil may be pressed against the inner circumferential surface of the housing by a permanent magnet.

[0010] This configuration allows the bump foil to be pressed against the inner peripheral surface of the housing by magnetic force with a simple structure, thereby easily increasing the frictional resistance of the bump foil against the housing.

[0011] In the above configuration, at least one of the top foil and the bump foil may be made of a magnetic material, and the housing may be formed by the permanent magnet.

[0012] This configuration increases the variety of configurations for pressing the bump foil against the housing by magnetic force, and makes it easy to increase the frictional resistance of the bump foil against the housing.

[0013] In the above configuration, the housing may be made of a magnetic material, and at least one of the top foil and the bump foil may be made of a magnetic material, and the permanent magnet may be embedded in the housing.

[0014] This configuration increases the variety of configurations for pressing the bump foil against the housing by magnetic force, and makes it easy to increase the frictional resistance of the bump foil against the housing.

[0015] In the above configuration, the housing may be made of a magnetic material, and the bump foil may be formed by the permanent magnet.

[0016] This configuration increases the variety of configurations for pressing the bump foil against the housing by magnetic force, and makes it easy to increase the frictional resistance of the bump foil against the housing.

[0017] In the above configuration, the housing may be made of a magnetic material and may include the permanent magnet disposed radially inside the bump foil.

[0018] This configuration increases the variety of configurations for pressing the bump foil against the housing by magnetic force, and makes it easy to increase the frictional resistance of the bump foil against the housing.

[0019] In the above configuration, the housing may be made of a non-magnetic material, and at least one of the top foil and the bump foil may be made of a magnetic material, and the permanent magnet may be disposed radially outward of the bump foil.

[0020] This configuration increases the variety of configurations for pressing the bump foil against the housing by magnetic force, and makes it easy to increase the frictional resistance of the bump foil against the housing. [Effects of the Invention]

[0021] According to the present invention, the radial foil bearing can easily achieve the desired performance and can be easily assembled. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a cross-sectional view taken along the radial direction of a radial foil bearing according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view taken along the axial direction of a radial foil bearing according to an embodiment of the present invention. [Figure 3] FIG. 10 is a perspective view of a housing according to a first modified example of the present invention. [Figure 4]FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] 10A to 10C are plan views showing the development of bump foils in a second modified example of the present invention, and (a) to (c) show the difference in the magnetization direction of the bump foils. [Figure 6] FIG. 10 is a perspective view of a radial foil bearing according to a third modified example of the present invention. [Figure 7] FIG. 10 is a perspective view of a radial foil bearing according to a fourth modified example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Next, an embodiment of the present invention will be described with reference to the drawings.

[0024] <Radial foil bearing> Fig. 1 is a cross-sectional view taken along the radial direction of a radial foil bearing 1. Fig. 2 is a cross-sectional view taken along the axial direction of the radial foil bearing 1. 1 and 2, the radial foil bearing 1 is mounted, for example, by fitting to a structure (not shown), and rotatably supports the shaft 100. In the following description, the direction parallel to the rotation axis C of the shaft 100 will be simply referred to as the axial direction. The radial direction of the shaft 100 will be simply referred to as the radial direction. The rotation direction of the shaft 100 will be simply referred to as the circumferential direction.

[0025] The radial foil bearing 1 comprises a top foil 2 that surrounds the shaft 100, a bump foil 3 that is arranged radially outside the top foil 2, and a cylindrical housing 4 that is arranged radially outside the bump foil 3. The top foil 2 is formed into a cylindrical shape by curving a thin metal plate so as to fit the outer circumferential surface of the shaft 100. The top foil 2 faces the shaft 100 in the radial direction.

[0026] An outer flange portion 2a that protrudes radially outward is bent and formed at each axial end of the top foil 2. The outer diameter of the outer flange portion 2a is the same as the outer diameter of the housing 4. However, this is not limited to this, and the outer diameter of the outer flange portion 2a may be any diameter greater than the inner diameter of the housing 4.

[0027] When assembling the top foil 2 to the housing 4, an outer flange portion 2a is formed on only one of the axial ends of the top foil 2. After inserting the top foil 2 into the housing 4 in this state, an outer flange portion 2a is formed on the other of the axial ends of the top foil 2. The outer flange portion 2a limits the movement of the top foil 2 in the axial direction.

[0028] The bump foil 3 is formed by bending a thin magnetic plate into a corrugated shape and then curving it to fit the outer peripheral surface of the top foil 2. As a result, the bump foil 3 has peaks 5 and valleys 6 arranged alternately in the circumferential direction. The peaks 5 are formed in an arc shape that convex radially inward. The radially outer outer surface 6a of the valleys 6 forms the outer peripheral surface of the bump foil 3.

[0029] The housing 4 is formed of a permanent magnet, and the top foil 2 and bump foil 3 are housed within the housing 4. The housing 4 magnetically attracts the bump foil 3 to the inner circumferential surface 4a of the housing 4. Specifically, the outer surfaces 6a of the valley portions 6 of the bump foil 3 are attracted to the inner circumferential surface 4a of the housing 4. In other words, the bump foil 3 is pressed against the inner circumferential surface 4a of the housing 4 by the magnetic force of the housing 4. As a result, the frictional resistance of the valley portions 6 of the bump foil 3 against the housing 4 is increased compared to when there is no magnetic force.

[0030] In this embodiment, the magnetization direction of the housing 4 is the axial direction. That is, the north pole and south pole are aligned in the axial direction with the axial center of the housing 4 as the boundary. However, the magnetization direction of the housing 4 is not limited to this, and various directions are possible. For example, the magnetization direction of the housing 4 may be the radial direction. The housing 4 may be magnetized with multiple poles in the axial and circumferential directions.

[0031] <Function of Radial Foil Bearings> Next, the operation of the radial foil bearing 1 will be described. When the shaft 100 rotates, a fluid lubrication film (not shown) is formed between the top foil 2 and the shaft 100. At this time, a load acting on the shaft 100 is applied via the fluid lubrication film, causing the top foil 2 to be pushed radially outward. When the bump foil 3 receives the load from the top foil 2, the peaks 5 at the load-receiving locations are elastically deformed, expanding their circumferential width.

[0032] Additionally, the height of the ridges 5 is reduced, allowing for deflection of the top foil 2. That is, the reduction in the height of the ridges 5 creates an area that can accommodate the deflected portion of the top foil 2. Therefore, the radial foil bearing 1 has a variable shape for its bearing surface (top foil 2), and forms an appropriate fluid lubrication film according to the load. Furthermore, when the bump foil 3 elastically deforms under load, slippage occurs between the bump foil 3 and the top foil 2 or the housing 4. Therefore, when vibration occurs in the shaft 100, friction caused by this slippage dissipates the vibration energy, and the rotational vibration of the shaft 100 is damped.

[0033] Here, the bump foil 3 is pressed against the inner peripheral surface 4a of the housing 4 by the magnetic force of the housing 4. As a result, the frictional resistance of the valley portion 6 of the bump foil 3 against the housing 4 is increased compared to when there is no magnetic force. As a result, the spring rigidity of the bump foil 3 is increased artificially, and the vibration damping effect of the shaft 100 is improved. Furthermore, if the bump foil 3 is misaligned with respect to the housing 4, eddy currents are generated by this slight movement of the bump foil 3. This eddy current generates a damping effect, which suppresses the movement of the bump foil, thereby further damping the rotational vibration of the shaft 100.

[0034] As described above, according to the embodiment described above, the frictional resistance of the bump foil 3 against the housing 4 can be increased compared to when the housing 4 has no magnetic force. This makes it possible to properly damp the rotational vibration of the shaft 100 using the radial foil bearing 1 without increasing the spring rigidity of the bump foil 3 itself. This makes it possible to obtain the desired performance of the radial foil bearing 1.

[0035] For example, if the top foil 2 is also made of a magnetic material, a damping effect due to eddy currents is generated by minute movements of the top foil 2 relative to the housing 4. This further damps the rotational vibration of the shaft 100. As a result, the desired performance of the radial foil bearing 1 can be further achieved.

[0036] Furthermore, since there is no need to increase the spring rigidity of the bump foil 3, it is possible to improve the ease of assembly of the bump foil 3. The magnetic force also increases the fixing force of the bump foil 3 to the housing 4, which also reduces displacement of the bump foil 3 when inserting the shaft 100 into the radial foil bearing 1. This makes it possible to provide a highly reliable radial foil bearing 1.

[0037] For example, if the top foil 2 is also made of a magnetic material, the magnetic force of the housing 4 will increase the strength with which the top foil 2 is fixed to the housing 4. This makes it possible to more reliably prevent the top foil 2 from shifting when the shaft 100 is inserted into the radial foil bearing 1. This makes it possible to provide a radial foil bearing 1 with even higher reliability.

[0038] In order to press the bump foil 3 against the housing 4 by magnetic force, the bump foil 3 is made of a magnetic material and the housing 4 is made of a permanent magnet. This makes it possible to easily increase the frictional resistance of the bump foil 3 against the housing 4 with a simple structure.

[0039] In the above embodiment, the bump foil 3 is formed of a magnetic material and the housing 4 is formed of a permanent magnet in order to press the bump foil 3 against the housing 4 by magnetic force. However, this is not limited to this, and various configurations can be adopted to press the bump foil 3 against the housing 4 by magnetic force. For example, the following modified configurations can be adopted.

[0040] [First Modification] Fig. 3 is a perspective view of the housing 4 in the first modified example. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. In the following description, the same features as those in the above-described embodiment are given the same reference numerals and will not be described again (the same applies to the following modified examples). As shown in Figures 3 and 4, the housing 4 does not have to be entirely made of a permanent magnet, but may be partially made of a permanent magnet. More specifically, the housing 4 is made of a magnetic material. A recess 7 is formed on the inner circumferential surface 4a of the housing 4. The recess 7 is formed over most of the inner circumferential surface 4a of the housing 4 in the axial direction.

[0041] A filler 8 is provided in the recess 7 of the housing 4 so as to fill the recess 7. The filler 8 is a non-magnetic material such as resin. A permanent magnet 9 is provided at the axial center of the housing 4. The permanent magnet 9 is formed in a ring shape to correspond to the shape of the housing 4. In this embodiment, the magnetization direction of the permanent magnet 9 is in the axial direction. That is, the north pole and south pole are aligned in the axial direction with the axial center of the permanent magnet 9 as the boundary. However, the magnetization direction of the permanent magnet 9 is not limited to this, and various directions are possible. For example, the magnetization direction of the permanent magnet 9 may be in the radial direction. The permanent magnet 9 may be magnetized with multiple poles in the axial and circumferential directions.

[0042] With this configuration, the bump foil 3 forms a magnetic path through which the magnetic flux of the permanent magnet 9 passes. As a result, the permanent magnet 9 presses the bump foil 3 against the inner circumferential surface 4a (filler 8) of the housing 4. This provides the same effects as the above-described embodiment. In addition, this configuration allows for an increased variety of configurations for pressing the bump foil 3 against the housing 4 by magnetic force. It is desirable that the top foil 2 is also made of a magnetic material, which allows the desired performance of the radial foil bearing 1 to be obtained more effectively.

[0043] In the above-described embodiment and first modified example, the case where at least the bump foil 3 is made of a magnetic material has been described. However, this is not limited to this, and either the top foil 2 or the bump foil 3 may be made of a magnetic material, and the other may be made of a non-magnetic material. For example, the bump foil 3 may be made of a non-magnetic material, and the top foil 2 may be made of a magnetic material. The magnetic force of the housing 4 attracts the top foil 2 to the housing 4, which results in the bump foil 3 being pressed against the inner circumferential surface 4a of the housing 4.

[0044] In the first modified example described above, the permanent magnet 9 is ring-shaped. However, this is not limiting, and a configuration in which multiple segment-type permanent magnets 9 are arranged in the circumferential direction may also be used. The housing 4 may also be magnetized by multiple permanent magnets 9 arranged in a so-called Halbach array magnet arrangement. In this case, it is desirable that the permanent magnets 9 are formed so as to face at least the valley portions 6 of the bump foil 3 in the radial direction. It is desirable that one permanent magnet 9 be large enough to face two to three valley portions 6 in the radial direction.

[0045] [Second Modification] Figure 5 is a plan view of the bump foil 3 in the second modified example, with (a) to (c) showing the difference in the magnetization direction of the bump foil 3. In Figures 5(a) to 5(c), the up-down direction on the paper coincides with the axial direction, and the left-right direction on the paper coincides with the circumferential direction. 5(a) to 5(c), the bump foil 3 may be formed of a permanent magnet instead of the housing 4. In this case, the housing 4 is made of a magnetic material.

[0046] The magnetization direction of the bump foil 3 may be the circumferential direction as shown in Figure 5(a). The magnetization direction of the bump foil 3 may be the axial direction as shown in Figure 5(b). If the magnetization direction of the bump foil 3 is the circumferential direction, it may be multi-polarized as shown in Figure 5(c). Alternatively, it may be multi-polarized in the axial direction, or in both the circumferential and axial directions. Even in this configuration, the same effects as those of the above-described embodiment can be achieved, and the variations in the configuration for pressing the bump foil 3 against the housing 4 by magnetic force can be increased.

[0047] [Third Modification] Fig. 6 is a perspective view of the radial foil bearing 1 showing a configuration in which the bump foil 3 is pressed against the housing 4 by magnetic force in a third modified example. In Fig. 6, the bump foil 3 and the housing 4 are shown in an expanded state for ease of understanding. As shown in FIG. 6, instead of forming the housing 4 with a permanent magnet, a separate permanent magnet 10 may be used.

[0048] The permanent magnet 10 is disposed on the valley portion 6 on the radially inner side of the bump foil 3. The permanent magnet 10 is formed in a plate shape on the valley portion 6 over the entire axial direction. The housing 4 is made of a magnetic material, and the bump foil 3 is made of a non-magnetic material, such as stainless steel.

[0049] With this configuration, the valley portions 6 of the bump foil 3 are pressed against the inner peripheral surface 4a of the housing 4 by the permanent magnet 10. This provides the same effects as the above-described embodiment. In addition, it is possible to increase the variety of configurations for pressing the bump foil 3 against the housing 4 by magnetic force. Because the housing 4 and the bump foil 3 are not made of permanent magnets, the housing 4 and the bump foil 3 can be formed inexpensively and easily.

[0050] [Fourth Modification] 7 is a perspective view of the radial foil bearing 1 showing a configuration in which the bump foil 3 is pressed against the housing 4 by magnetic force in the fourth modified example. FIG. 7 corresponds to the above-mentioned FIG. As shown in FIG. 7, the fourth modified example differs from the third modified example described above in that the position of the permanent magnet 10 is different.

[0051] That is, the permanent magnet 10 may be disposed on the outer peripheral surface 4b of the housing 4. In other words, the permanent magnet 10 may be disposed radially outside the bump foil 3. It is desirable that the permanent magnet 10 is disposed in a position radially opposite the valley portion 6 of the bump foil 3. In this case, the housing 4 is made of a non-magnetic material. This is to prevent the magnetic flux of the permanent magnet 10 from leaking into the housing 4. The bump foil 3 is made of a magnetic material.

[0052] With this configuration, the valley portions 6 of the bump foil 3 are pressed against the inner peripheral surface 4a of the housing 4 by the permanent magnet 10. This provides the same effects as the above-described embodiment. In addition, it is possible to increase the variety of configurations for pressing the bump foil 3 against the housing 4 by magnetic force. Because the housing 4 and the bump foil 3 are not made of permanent magnets, the housing 4 and the bump foil 3 can be formed inexpensively and easily.

[0053] In the fourth modified example described above, the permanent magnet 10 is disposed on the outer peripheral surface 4b of the housing 4. However, this is not limited to this, and it is sufficient that the permanent magnet 10 is disposed radially outside the bump foil 3. For example, a part of the housing 4 may be the permanent magnet 10. The permanent magnet 10 may be embedded in the housing 4.

[0054] The present invention is not limited to the above-described embodiment, and includes various modifications to the above-described embodiment without departing from the spirit of the present invention. For example, the radial foil bearing 1 may be configured by combining the above-described embodiments and modifications.

[0055] In the above embodiment, the bump foil 3 is formed by bending a thin plate into a corrugated shape. However, this is not limiting, and the bump foil 3 may be formed to be elastically deformable so as to allow for the bending deformation of the top foil 2. For example, the bump foil 3 may be formed in a mesh shape. [Explanation of symbols]

[0056] 1...Radial foil bearing 2...Top foil 3...Bump foil 4. Housing 9,10...Permanent magnets

Claims

1. a top foil that surrounds the shaft and faces the shaft in a radial direction; a bump foil disposed radially outward of the top foil; a cylindrical housing disposed radially outside the bump foil and accommodating the top foil and the bump foil; Equipped with The bump foil is pressed against the inner circumferential surface of the housing by the magnetic force of a permanent magnet. A radial foil bearing characterized by:

2. At least one of the top foil and the bump foil is made of a magnetic material, The housing is formed by the permanent magnet.

2. The radial foil bearing according to claim 1 .

3. the housing is magnetic; At least one of the top foil and the bump foil is made of a magnetic material, The permanent magnet is embedded in the housing.

2. The radial foil bearing according to claim 1 .

4. the housing is magnetic; the bump foil is formed by the permanent magnet; 2. The radial foil bearing according to claim 1 .

5. the housing is magnetic; the bump foil is a non-magnetic material; The permanent magnet is disposed radially inside the bump foil.

2. The radial foil bearing according to claim 1 .

6. the housing is non-magnetic; At least one of the top foil and the bump foil is made of a magnetic material, the permanent magnet is disposed radially outside the bump foil; 2. The radial foil bearing according to claim 1 .

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