JPH07174138A - Gas bearing structure - Google Patents

Abstract

PURPOSE:To provide a stable bearing characteristic by uniformly holding a thickness in an air gap part between a rotary shaft and a gas bearing even at the time of both low and high speed rotations by facilitating working. CONSTITUTION:In a gas bearing structure formed so as to support a hollow rotary shaft 11 by a gas bearing 15, the structure is formed by providing a high rigidity part 16, by which rigidity against centrifugal force of the rotary shaft 11 is increased in a central part as compared with bearing both end parts, in an internal peripheral part of the rotary shaft 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas bearing applied to rotary machines such as turbines and compressors.

[0002]

2. Description of the Related Art Conventionally, a gas bearing structure shown in FIGS. 14 to 16 has been known (Japanese Patent Publication No. 51-28775), and a till which is opposed to the outer peripheral surface of a hollow rotary shaft 1 through a minute gap. A plurality of bearing pads 2 are arranged in the circumferential direction of the rotary shaft 1, and the tilting pad 2 is pivotably supported from the rear by a pivot 3 protruding toward the center of the rotary shaft 1. 4 is provided. Then, as the rotary shaft 1 rotates, a wedge-shaped space is formed between the rotary shaft 1 and the tilting pad 2, and dynamic pressure is generated. The dynamic pressure causes the rotary shaft 1 to tilt. The pad 2 is supported in a non-contact state.

When the rotating shaft 1 rotates, the surface of the rotating shaft 1 forms a curved surface in the axial direction by centrifugal force, and when the bending of the curved surface becomes large, the rotating shaft 1 and the tilting pad 2 come into contact with each other. An unfavorable situation occurs. Therefore, as shown in FIG. 15, the inner peripheral surface of the tilting pad 2 is formed as a curved surface in consideration of expansion due to centrifugal force so that the thickness of the void portion at the center thereof is increased. Then, as shown in FIG.
Even if the shaft rotates at high speed and centrifugally expands, contact between the rotary shaft 1 and the tilting pad 2 is prevented, and the thickness of the void is made uniform to stabilize the characteristics of the bearing.

[0004]

In the above conventional gas bearing structure, the inner peripheral surface of the tilting pad 2 is formed as a curved surface in consideration of the centrifugal expansion of the rotary shaft 1. However, in the structure having such a curved surface, the thickness of the void portion is not constant in the axial direction when the rotating shaft 1 rotates at a low speed, and stable bearing characteristics cannot be obtained. Occurs. That is, when the voids are non-uniform, the bearing performance is deteriorated. Further, the inner peripheral surface of the tilting pad 2 is processed into a barrel shape to be curved. However, since the processing accuracy such as the curvature of the inner peripheral surface directly affects the dimension of the void portion, this processing accuracy is improved. Must be on the order of a few dozen microns. However, there is a problem that it is difficult to process with this accuracy.

Further, in the above gas bearing structure, the rotary shaft 1
However, if the gas bearing structure including the rotating shaft 1 is enlarged, the deformation due to the non-uniform temperature distribution of the rotating shaft 1 caused by heat generation is more dominant than the centrifugal expansion. Become. That is, between the rotating shaft 1 and the tilting pad 2 which are rotating, heat is generated due to the friction of the gas, and the heat is radiated closer to the end of the tilting pad 2 and radiated closer to the center. It's hard to do. Therefore, the rotary shaft 1
A heat distribution corresponding to this difference in the degree of heat radiation is generated in the sheet, resulting in non-uniform thermal expansion. The surface of the rotating shaft 1 forms a curved surface in the axial direction due to this non-uniform thermal expansion, in addition to the centrifugal force caused by the rotation of the rotating shaft 1. The conventional gas bearing structure described above has a problem that this thermal expansion is not taken into consideration. The present invention has been made to solve the problems of the conventional art, is easy to process, and even in low speed rotation and high speed rotation, the thickness of the gap between the rotary shaft and the gas bearing is uniform. Therefore, the present invention aims to provide a gas bearing structure capable of maintaining stable bearing characteristics and maintaining stable bearing characteristics.

[0006]

In order to solve the above-mentioned problems, the present invention provides a gas bearing structure in which a hollow rotating shaft is supported by a gas bearing. It was formed by providing a high-rigidity portion that increases the rigidity against the centrifugal force in the central portion as compared with the both end portions of the bearing portion.

[0007]

With the above structure, the amount of centrifugal expansion in the central portion of the bearing portion, which has a large amount of thermal expansion as compared with both ends of the bearing portion of the rotary shaft, is smaller than that in both ends. Become.

[0008]

An embodiment of the present invention will be described below with reference to the drawings. 1 to 5 show a gas bearing structure according to a first embodiment of the present invention, in which a tilting pad 12 opposed to the outer peripheral surface of a hollow rotary shaft 11 via a minute gap is provided in the rotary shaft 11. A plurality of, three in the present embodiment, are arranged in the circumferential direction, and the tilting pad 12 is rocked from behind by a pivot 14 supported by a frame 13 so as to project toward the center of the rotary shaft 11. A gas bearing 15 is provided, which is supported as much as possible. Also, the rotating shaft 11
The high-rigidity portion 16 formed by continuously and linearly changing the wall thickness is provided on the inner peripheral part of the bearing so that the wall thicknesses of both ends of the bearing part increase toward the center. The rigidity of the rotating shaft 11 against the centrifugal force is set to be greater in the central portion than in both end portions of the bearing portion. By rotating the rotating shaft 11 in the same manner as described above, a wedge-shaped space is formed between the rotating shaft 11 and the tilting pad 12, and dynamic pressure is generated. Are supported in a non-contact state with the tilting pad 12.

By the way, when considering only thermal expansion that occurs as a result of gas friction in the above-mentioned gap when the rotating shaft 11 rotates at high speed, the surface of the rotating shaft 11 has a central portion of the bearing portion as shown in FIG. A curved surface is formed in the axial direction so that is convex outward. Next, when only the centrifugal expansion due to the high speed rotation of the rotating shaft 11 is considered, in this embodiment, since the high rigidity portion 16 is provided on the inner peripheral portion of the rotating shaft 11, the change in the thickness of the rotating shaft 11 is changed. Based on the difference in rigidity, the rotating shaft 11 is more likely to be deformed toward both ends of the bearing part having a low rigidity as shown in FIG. 4, and is curved in the axial direction so that the surface becomes concave outward. Form a surface. In reality, since centrifugal expansion and thermal expansion occur simultaneously, the surface of the rotating shaft 11 is a combination of the convex shape shown in FIG. 3 and the concave shape shown in FIG. 4, as shown in FIG. It becomes flat in the axial direction. As a result, the thickness of the void becomes uniform in the axial direction.

On the other hand, since the facing surfaces of the rotary shaft 11 and the tilting pad 12 are formed flat in the axial direction, the thickness of the above-mentioned void becomes uniform even when the rotary shaft 11 rotates at a low speed. Therefore, stable bearing characteristics are always maintained at both high speed and low speed rotation of the rotating shaft 11. FIG. 6 shows only the vicinity of the bearing portion of the gas bearing structure according to the second embodiment of the present invention. In contrast to the first embodiment shown in FIG. Others are substantially the same except that an annular high-rigidity portion 16a formed by projecting over the entire circumference is provided. FIG. 7 shows only the vicinity of the bearing portion of the gas bearing structure according to the third embodiment of the present invention, and in contrast to the first embodiment shown in FIG. 1, instead of the high rigidity portion 16, over the entire inner circumference of the bearing portion, A high-rigidity portion 1 formed by projecting in a step-like manner such that the wall thickness increases toward the central portion.
Other than that the point 6b is provided, it is substantially the same. In the first to third embodiments, the high rigidity parts 16, 16
The a and 16b may be formed by members different from the other parts of the rotating shaft 11.

FIG. 8 shows only the vicinity of the bearing portion of the gas bearing structure according to the fourth embodiment of the present invention. In contrast to the first embodiment shown in FIG. 1, the high rigidity portion 16 is replaced by the center portion of the bearing portion. Inside the department,
Except for the point that a high-rigidity portion 16c formed by embedding an annular member having a higher rigidity than the other parts of the rotating shaft 11 is provided, the other parts are substantially the same. Then, in the second, third, and fourth embodiments, by adopting the above-mentioned configuration, the rigidity of the central portion against the centrifugal force is increased as compared with the both ends of the bearing portion of the rotating shaft 11, and the first embodiment is performed. Similar to the case of the example, the voids are kept uniform to maintain stable bearing characteristics.

Next, the gas bearing structure in which the thickness of the rotary shaft 11 is constant as shown by the two-dot chain line in FIG. 6 and the gas bearing structure according to the second embodiment shown by the solid line in FIG. The results of calculating the change in the outer diameter of the rotating shaft using the finite element method under the same conditions of the outer diameter of the rotating shaft, the number of revolutions, the material of the rotating shaft, etc. are shown in FIGS.
FIG. 10 shows the case of the second embodiment). 9 and 10, the horizontal axis represents the length of the entire bearing portion as 1, and the distance from one end of the bearing portion is expressed in the form of a ratio, and the vertical axis represents the change amount of the outer diameter due to the expansion of the rotating shaft 11. The maximum value is set to 1, and the change amount of the outer diameter is expressed in the form of a ratio to the maximum value. As is clear from the figure, in FIG. 10 in the case of the second embodiment, the maximum change amount is as small as about 60% compared to FIG. 9 in the case of a constant wall thickness, and the effect of the high rigidity portion 11a clearly appears. ing.

In the above embodiments, the gas bearing structure using the tilting pad type gas bearing has been described, but the present invention is not limited to this, and the hollow rotary shaft 11 in each of the above embodiments is used. If adopted, in addition to this,
1, a gas bearing structure using another type of dynamic pressure gas bearing 15a, and a static pressure gas bearing 1 as shown in FIG.
The present invention includes both the gas bearing structure using 5b and the gas bearing structure using the gas bearing 15c shown in FIG. 13, which uses both dynamic pressure and static pressure.

[0014]

As is apparent from the above description, according to the present invention, in a gas bearing structure in which a hollow rotary shaft is supported by a gas bearing, a centrifugal force of the rotary shaft is provided in an inner peripheral portion of the rotary shaft. A high-rigidity portion is formed to increase the rigidity with respect to the force in the central portion as compared with the both end portions of the bearing portion. Therefore, the gas bearing structure according to the present invention is easy to process,
In addition, the amount of centrifugal expansion in the central portion of the bearing portion, which has a large amount of thermal expansion compared to both ends of the bearing portion of the rotating shaft, is smaller than that in both ends, and as a result, during low speed rotation and high speed rotation. In either case, there is an effect that the thickness of the gap between the rotary shaft and the gas bearing can be kept uniform and stable bearing characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a gas bearing structure according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a partial cross-sectional view showing a shape of a bearing portion of the gas bearing structure shown in FIG. 1 after being deformed only by thermal expansion.

FIG. 4 is a partial cross-sectional view showing the shape of the bearing portion of the gas bearing structure shown in FIG. 1 after being deformed only by centrifugal expansion.

5 is a partial cross-sectional view showing the shape of the bearing portion of the gas bearing structure shown in FIG. 1 after being deformed by both centrifugal expansion and thermal expansion.

FIG. 6 is a partial cross-sectional view showing only the bearing portion of the gas bearing structure according to the second embodiment of the present invention.

FIG. 7 is a partial sectional view showing only a bearing portion of a gas bearing structure according to a third embodiment of the present invention.

FIG. 8 is a partial sectional view showing only a bearing portion of a gas bearing structure according to a fourth embodiment of the present invention.

FIG. 9 is a diagram showing a calculation result of a deformation amount of a bearing portion on a rotating shaft having a constant wall thickness.

FIG. 10 is a diagram showing a calculation result of a deformation amount of a bearing portion on a rotating shaft having a constant wall thickness.

FIG. 11 is a cross-sectional view perpendicular to the axis showing a gas bearing structure using a dynamic pressure type gas bearing other than the tilting pad type.

FIG. 12 is a cross-sectional view perpendicular to the axis showing a gas bearing structure using a static pressure type gas bearing.

FIG. 13 is a cross-sectional view perpendicular to the axis showing a gas bearing structure using a dynamic pressure combined type gas bearing.

FIG. 14 is a cross-sectional view showing a conventional gas bearing structure.

FIG. 15 is a partial cross-sectional view showing only a bearing portion in a state where the gas bearing shown in FIG. 14 is not deformed.

16 is a partial cross-sectional view showing only the bearing portion in a state where the gas bearing shown in FIG. 14 is deformed by centrifugal expansion.

[Explanation of symbols]

 11 rotating shaft 15,15a, 15b, 15c gas bearing 16,16a, 16b, 16c high rigidity part

Front page continuation (72) Inventor ▲ Yoshi ▼ Hiro Kawakawa 2-3-1, Niihama, Arai-cho, Takasago, Hyogo Pref., Takasago Works, Kobe Steel Co., Ltd. (72) Toshiaki Hirata 2-3, Niihama, Arai-cho, Takasago, Hyogo Prefecture No. 1 Inside Takasago Works, Kobe Steel, Ltd.

Claims (1)

[Claims] 1. In a gas bearing structure in which a hollow rotating shaft is supported by a gas bearing, the inner peripheral portion of the rotating shaft has a rigidity against the centrifugal force of the rotating shaft compared to both ends of the bearing portion in a central portion. The gas bearing structure is characterized in that it has a high-rigidity portion that is enlarged in the direction.