JP5760680B2 - Radial foil bearing - Google Patents

Description

  The present invention relates to a radial foil bearing.

  Conventionally, as a bearing for a high-speed rotating body, a radial bearing that is used by being extrapolated to a rotating shaft is known (for example, see Patent Document 1). As such a radial bearing, a radial foil bearing including a thin plate-like top foil that forms a bearing surface and a back foil that elastically supports the top foil is well known (for example, Patent Document 2). reference). As a back foil of the radial foil bearing, a bump foil obtained by forming a thin plate into a corrugated plate is mainly used.

  Such a radial foil bearing is in a state in which the top foil is in close contact with the rotating shaft (a state in which the rotating shaft is tightened) from the time when the rotating shaft is not rotated to the time of starting, but the rotating shaft rotates faster. As a result, the surrounding fluid is caught between the top foil and the rotating shaft to form a fluid lubricating film. When the fluid lubricating film generates a sufficient film pressure, the top foil is pushed outward and the rotating shaft rotates in a non-contact state with the top foil.

  Then, the fluid lubricant film generates heat by being sheared between the rotating shaft and the top foil. For this reason, conventionally, the radial foil bearing is cooled by flowing a working fluid along the axial direction of the bearing on the back side of the bump foil or by providing a water cooling channel outside the bearing. That is, the fluid lubricating film is indirectly cooled by cooling the outside of the bump foil.

JP 2001-65570 A Japanese Patent Laid-Open No. 03-163213

  However, in radial foil bearings, the lubricating fluid in the central portion in the axial direction is difficult to escape to the outside of the bearing, and the cooled fluid around the bearing is difficult to flow into the central portion. When the cooling is insufficient as described above, the thermal expansion of the radial foil bearing and the rotating shaft increases, and the tightening (preload) of the radial foil bearing with respect to the rotating shaft becomes strong, and the bearing (top foil) may be seized.

  Further, the pressure distribution of the fluid lubrication film in the bearing axial direction has a mountain shape with the center portion of the bearing as the apex. Therefore, the radial foil bearing mainly exhibits the load capacity at the apex, that is, at the center of the bearing. However, since the bearing surface (top foil) receives a reaction force of the pressure of the fluid lubrication film, the top foil is recessed outward at the center of the bearing. For this reason, the load capacity exhibited by the radial foil bearing is significantly lower than the assumed load capacity, for example, about 50% in design.

Further, when the fluid lubricating film is not sufficiently grown, such as at the time of start-up or low-speed rotation, the top foil comes into contact with the rotating shaft and wear progresses due to rubbing.
The present invention has been made in view of the above circumstances, and its purpose is to improve cooling performance to prevent bearing seizure, reduce top foil deflection, suppress load capacity reduction, and wear. An object of the present invention is to provide a suppressed radial foil bearing.

The radial foil bearing of the present invention is a radial foil bearing that is extrapolated to a rotating shaft and supports the rotating shaft,
A cylindrical top foil disposed to face the rotating shaft, and a back foil disposed radially outside the top foil,
A plurality of oblique grooves are formed on the surface of the top foil that faces the rotation shaft, from the rear to the front in the rotation direction of the rotation shaft and from the center of the top foil in the axial direction to both edge sides. And
A land portion is formed between the oblique grooves and between the end portion on the edge side of the oblique groove and the edge.

According to this radial foil bearing, a plurality of oblique grooves are formed on the surface facing the rotation axis of the top foil, so that the ambient fluid drawn from between the start end and the end of the top foil by the rotation of the rotation shaft Then, it flows along the longitudinal direction of the oblique groove from the axial center portion of the bearing toward both side edges. Accordingly, the cooling fluid around the bearing flows into the axial center portion to cool the center portion, and the hot lubricating fluid in the center portion is discharged toward both end edges, so that the cooling performance is high. Thus, seizure of the bearing is prevented.
In addition, since the lubricating fluid discharged from the axially central portion toward the both side edges generates a strong fluid lubricating film pressure when getting over the land portion, the load capacity can be satisfactorily exhibited at the both end portions. become. And since the strong fluid lubricating film pressure is generated at both end portions in this way, unlike the conventional case, the top foil is not greatly recessed at the central portion in the axial direction, and the pressure of the fluid lubricating film is distributed to the both end portions. As a result, the top foil is slightly recessed at both ends. Therefore, a reduction in load capacity is suppressed.
In addition, since the load capacity is satisfactorily exhibited at both end portions, the rigidity is increased with respect to the relative inclination of the bearing with respect to the rotating shaft.
Furthermore, since a plurality of oblique grooves are formed on the surface of the top foil that faces the rotation axis, since the surrounding fluid already exists in the oblique grooves when the rotation shaft is started, the rotation shaft Even when the rotational speed is low, the fluid lubricating film is easily formed. Therefore, the time for the top foil to rub against the rotating shaft is shortened, and the progress of wear is suppressed.

Further, in the radial foil bearing, a central groove extending along a circumferential direction of the top foil is formed in the oblique direction on the surface of the top foil facing the rotation shaft in the axial center portion of the top foil. It is preferable to be formed in communication with the groove.
In this way, the ambient fluid drawn from between the beginning and end of the top foil flows in the circumferential direction of the bearing along the central groove, so that the bearing can be cooled better.

Further, in the radial foil bearing, it is preferable that a through hole penetrating the top foil is formed in the top foil so as to communicate with the oblique groove at a central portion in an axial direction of the top foil. .
If it does in this way, ambient fluid will be taken in from the space | gap between top foil and back foil through a through-hole, and will further flow toward a both-ends part through an oblique groove | channel. Therefore, the bearing is cooled substantially uniformly throughout the circumferential direction of the bearing.

  According to the radial foil bearing of the present invention, it is possible to improve the cooling performance and prevent the bearing from being seized, to reduce the deflection of the top foil to suppress the load capacity reduction and to further suppress the wear.

It is a mimetic diagram showing an example of a turbo machine to which a radial foil bearing concerning the present invention is applied. It is a figure which shows schematic structure of 1st Embodiment of the radial foil bearing which concerns on this invention, (a) is a longitudinal cross-sectional view, (b) is a cross-sectional view. (A) is a perspective view which shows the top foil provided in the rotating shaft, (b) is an expanded view of the inner surface of a top foil. It is a figure which shows the longitudinal cross-sectional view of the radial foil bearing shown to Fig.2 (a), and the graph which shows the distribution of the pressure (dynamic pressure) of the fluid lubricating film corresponding to this. It is a figure which shows schematic structure of 2nd Embodiment of the radial foil bearing which concerns on this invention, (a) is a longitudinal cross-sectional view, (b) is an expanded view of the inner surface of a top foil. It is a figure which shows schematic structure of 2nd Embodiment of the radial foil bearing which concerns on this invention, (a) is a longitudinal cross-sectional view, (b) is an expanded view of the inner surface of a top foil.

  Hereinafter, a radial foil bearing of the present invention will be described in detail with reference to the drawings. In the following drawings, the scale of each member is appropriately changed in order to make each member a recognizable size.

  FIG. 1 is a side view showing an example of a turbo machine to which a radial foil bearing of the present invention is applied. In FIG. 1, reference numeral 1 denotes a rotary shaft, 2 denotes an impeller provided at a tip portion of the rotary shaft, and 3 denotes a main shaft. It is a radial foil bearing which concerns on invention. Although only one radial foil bearing is shown in FIG. 1, normally, two radial foil bearings are provided in the axial direction of the rotating shaft 1 to constitute a support structure for the rotating shaft 1. . Therefore, it is assumed that two radial foil bearings 3 are also provided in this embodiment. However, the radial foil bearing 3 of the present invention is also applicable to a form in which only one is provided for the rotating shaft 1.

A thrust collar 4 is fixed to the rotary shaft 1 on the side where the impeller 2 is formed, and a thrust bearing 5 is disposed on each side of the thrust collar 4 so as to face the thrust collar 4. ing.
The impeller 2 is disposed in the housing 6 on the stationary side, and has a tip clearance 7 between the impeller 2 and the housing 6.
A radial foil bearing 3 is externally attached to the rotary shaft 1 on the center side of the thrust collar 4.

  FIGS. 2A and 2B are views showing a first embodiment of a radial foil bearing applied to the turbomachine having such a configuration. The radial foil bearing 3 according to the first embodiment is a cylindrical one that is extrapolated to the rotating shaft 1 and supports the rotating shaft 1, and has a cylindrical top foil 10 that is disposed to face the rotating shaft 1. The back foil 11 is disposed outside the top foil 10 in the radial direction, and the bearing housing 12 is disposed outside the back foil 11 in the radial direction.

The bearing housing 12 has a cylindrical shape that constitutes an extrapolation of the radial foil bearing 3, and the back foil 11 and the top foil 10 are inserted therein.
The back foil 11 is formed of a foil (thin plate) and elastically supports the top foil 10. Examples of such a back foil 11 include a bump foil, a spring foil described in JP 2006-57652 A, JP 2004-270904 A, and the like, and JP 2009-299748 A. A back foil or the like is used. In FIG. 2, a bump foil will be described as an example. As shown in FIG. 2 (b), the bump foil is formed by forming a foil (thin plate) into a corrugated plate shape and further forming and arranging it in a cylindrical shape along the inner peripheral surface of the bearing housing 12. Here, the bump foil (back foil) 11 formed in a corrugated plate shape alternately has a mountain portion in contact with the bearing housing 12 and a valley portion in contact with the top foil 10 along the circumferential direction of the radial foil bearing 3. Forming. As a result, the back foil 11 forms a fluid passage by a crest or a trough in the axial direction of the radial foil bearing 3.

  The top foil 10 has a back foil 11 attached to the outer surface (rear surface) of the top foil 10. As shown in FIG. 2A, the foil starting end 10 a side is bent outward and is formed on the bearing housing 12. By being locked in a groove (not shown), the bearing housing 12 is held and fixed in the bearing housing 12 without rotating. The foil end 10b is disposed in the vicinity of the foil start end 10a with a predetermined gap. The back foil 11 is attached to the outer surface of the top foil 10 so that the back foil 10 11 also has a predetermined gap between its start and end.

Further, the top foil 10 is formed with a plurality of oblique grooves 13 on the inner surface thereof, that is, the surface facing the rotation shaft 1 as shown in FIGS.
As shown in FIG. 3 (a) showing the appearance of the top foil 10 and FIG. 3 (b) in which the inner surface of the top foil 10 is developed, the oblique groove 13 is from the rear in the rotational direction (arrow direction) of the rotary shaft 1. As it goes forward, the top foil 10 is formed from the center (in the present embodiment, the center line CL in the axial direction) in the axial direction (the direction perpendicular to the rotational direction of the rotary shaft 1) to both edge sides. Yes. That is, the oblique groove 13 is formed and arranged in line symmetry on one side and the other side in the axial direction with the axial center line CL as a symmetry line.

  Although these oblique grooves 13 differ depending on the size of the radial foil bearing 3, for example, about 10 to 30 center lines CL are formed on only one side of the center line CL in the circumferential direction (rotating direction of the rotating shaft 1). About 20 to 60 are formed on both sides. A space between adjacent oblique grooves 13 is a non-groove forming portion, that is, an inter-groove land portion 14. The oblique groove 13 is formed by forming the inner surface of the metal thin plate-like top foil 10 into a groove having a depth of about several tens of μm by etching or the like. On the other hand, the inter-groove land portion 14 is constituted by the inner surface of the top foil 10 and is relatively formed by forming the oblique groove 13.

The diagonal grooves 13 and the inter-groove land portions 14 are not particularly limited, but the width ratio is, for example, about 2: 1 to 1: 2.
Further, as shown in FIG. 3B, the oblique groove 13 is preferably formed so that an angle with respect to the axial direction, that is, an inclination angle θ with respect to a line orthogonal to the center line CL is about 10 ° to 35 °. More preferably, it is formed at about 15 ° to 20 °, more preferably about 17 °. By setting the angle to 10 ° or more, the lubricating fluid urged by the rotational force of the rotating shaft 1 can be made to flow well in the rotating direction of the rotating shaft 1 along the oblique groove 13, and the radial foil bearing. 3 can be cooled more extensively. On the other hand, by setting the angle to 35 ° or less, the lubricating fluid flows favorably toward the end portion in the axial direction along the oblique groove 13, and the heated lubricating fluid is supplied to the radial foil bearing 3 as will be described later. It becomes possible to discharge well to the outside.

  In addition, each of the oblique grooves 13 is formed toward one end edge of the top foil 10, but does not extend to the end edge and stops before the end edge. Thus, an edge side land portion 15 is formed between the end portion (closed end) of the oblique groove 13 and the end edge. Similarly to the inter-groove land portion 14, the edge side land portion 15 is also formed by the inner surface of the top foil 10, and is relatively formed by forming the oblique groove 13.

  Although the length L1 in the axial direction of the oblique groove 13 on one side across the center line CL is not particularly limited, the length L1 in the axial direction of the top foil 10 is, for example, (2L / 5) to (L / 4) about. Therefore, the width L2 (= L / 2−L1) in the axial direction of the edge side land portion 15 is set to about (L / 10) to (L / 4). By forming the length L1 of the oblique groove 13 and the width L2 of the edge-side land portion 15 in such a range, the fluid flowing through the oblique groove 13 is once clogged by the edge-side land portion 15, and thereafter As a result, the high membrane pressure is generated.

Next, the operation of the radial foil bearing 3 having such a configuration will be described.
In a state where the rotating shaft 1 is stopped, the top foil 10 is in close contact with the rotating shaft 1 by being biased toward the rotating shaft 1 by the back foil 11. However, in the present embodiment, since the oblique groove 13 is formed on the inner surface of the top foil 10, the surrounding fluid (for example, air) already exists in the oblique groove 13 even when the rotating shaft 1 is stopped. ing.

  When the rotating shaft 1 is started, it starts rotating at a low speed at first, and then gradually accelerates and rotates at a high speed. Then, ambient fluid is drawn in from between the foil start end 10a and the foil end 10b of the top foil 10, and flows between the top foil 10 and the rotary shaft 1 to form a fluid lubricating film here. In addition, since the surrounding fluid existed in the oblique groove 13 from the beginning between the top foil 10 and the rotating shaft 1, the surrounding fluid in the oblique groove 13 is obtained even at a stage where the rotational speed of the rotating shaft 1 is low. And the ambient fluid that has flowed in are combined to easily form a fluid lubricating film. When the fluid lubricating film generates a sufficient film pressure, the top foil 10 is pushed outward and the rotating shaft 1 rotates in a non-contact state with the top foil 10.

  Further, the fluid lubricating film formed in this way generates heat by being sheared between the rotating shaft 1 and the top foil as the rotating shaft 1 rotates at high speed. However, in the present embodiment, the ambient fluid drawn from between the foil start end 10a and the foil end end 10b of the top foil 10 is directed from the center line CL toward both side edges along the length direction of the oblique groove 13. It begins to flow. Therefore, since the cooled fluid around the bearing flows into the axial central portion to cool the central portion, and the hot lubricating fluid in the central portion is discharged toward both side edges, it is high. A cooling effect can be obtained.

  In addition, since the lubricating fluid discharged from the central portion in the axial direction toward both side edges generates a strong fluid lubricating film pressure when getting over the edge-side land portion 15, the load capacity is exhibited well at both side ends. Will come to be. FIG. 4 is a graph showing the pressure (dynamic pressure) distribution of the fluid lubricating film formed between the top foil 10 and the rotating shaft 1 of the radial foil bearing 3 of the present embodiment. In FIG. 4, the horizontal axis indicates the position of the top foil 10 in the axial direction, and the vertical axis indicates the pressure (dynamic pressure) of the fluid lubricating film (higher as it goes upward).

  In FIG. 4, the solid line indicates the pressure (dynamic pressure) of the fluid lubrication film by the radial foil bearing 3 of the present embodiment, and the broken line indicates the fluid lubrication film by the conventional radial foil bearing in which the oblique grooves 13 are not formed. The pressure (dynamic pressure) is shown. Conventionally, it has a mountain shape with the center of the bearing at the apex, and exhibits a high load capacity at the center of the bearing, whereas in this embodiment, the lubricating fluid flowing through the oblique groove 13 is as described above. Since a strong fluid lubricating film pressure is generated when the end-land side land portion 15 is climbed over, the load capacity is satisfactorily exhibited at both end portions of the radial foil bearing 3.

  A part of the surrounding fluid drawn from between the foil start end 10 a and the foil end 10 b does not follow the length direction of the oblique groove 13, but extends around the top foil 10 along the rotation direction of the rotary shaft 1. Flow in the direction. Therefore, when flowing from the oblique groove 13 to the inter-groove land portion 14 and overcoming this, a strong fluid lubricating film pressure is generated. Thereby, although the radial foil bearing 3 of this embodiment exhibits high load capability in the both ends as shown in FIG. 4, it also exhibits load capability also in the center part.

In such a radial foil bearing 3, since the high cooling effect is obtained by the oblique groove 13, the seizure is prevented well.
Further, since the surrounding fluid exists in the oblique groove 13 at the time of starting and the fluid lubricating film is easily formed even at the stage where the rotational speed of the rotating shaft 1 is low, the top foil 10 comes into contact with the rotating shaft 1. The time for rubbing is shortened and the progress of wear can be suppressed.

  Further, since the load capacity is satisfactorily exhibited at both end portions of the radial foil bearing 3, unlike the conventional case, the top foil is not greatly recessed at the axial center portion, and the pressure of the fluid lubricating film is increased at both end portions. As a result, the top foil 10 is gradually recessed at both end portions. Therefore, a reduction in load capacity can be significantly suppressed as compared with the conventional case. For example, in the conventional radial foil bearing shown by the broken line in FIG. 4, the load capacity to be exhibited is, for example, about 50% in design, whereas the radial foil bearing of the present embodiment shown by the solid line in FIG. 3, the load capacity to be exhibited is, for example, about 80% in design, and the decrease in load capacity is greatly suppressed.

In addition, when the top foil is recessed outward at the center of the bearing as in the prior art, both ends in the axial direction face inward, and uneven wear tends to occur at both ends. However, in this embodiment, the top foil Such a partial wear is also prevented since 10 becomes slightly recessed at both end portions.
Further, the conventional radial foil bearing mainly exerts the load capacity in the central portion in the axial direction, and thus supports the rotating shaft 1 at one place, whereas the radial foil bearing 3 of the present embodiment has both end portions. Since the rotary shaft 1 is supported at two locations, the support capacity of the radial foil bearing 3 increases with respect to the inclination of the rotary shaft 1 and the rotary shaft 1 swings ( Even when precession occurs), the inclination of the rotating shaft 1 can be minimized.

FIGS. 5A and 5B are views showing a second embodiment of the radial foil bearing 3 applied to the turbomachine shown in FIG.
The radial foil bearing shown in FIGS. 5A and 5B is different from the radial foil bearing shown in FIGS. 2 and 3 in the structure of the top foil.

  That is, the top foil 20 in the radial foil bearing shown in FIGS. 5A and 5B has an axial center of the surface of the top foil 20 facing the rotating shaft 1 as shown in FIG. 5B. A central groove 21 is formed in the portion along the center line CL. The central groove 21 is formed to have a width of about 1 to 2 times the width of the oblique groove 13, and the depth thereof is the same as that of the oblique groove 13.

  Under such a configuration, in the radial foil bearing having the top foil 20, the surrounding fluid drawn from between the foil start end 20 a and the foil end 20 b is moved along the central groove 21. Since it flows in the circumferential direction of the bearing, the bearing is cooled better. Therefore, by obtaining a higher cooling effect, the seizure is surely prevented.

FIGS. 6A and 6B are views showing a third embodiment of the radial foil bearing 3 applied to the turbomachine shown in FIG.
The radial foil bearing shown in FIGS. 6A and 6B is different from the radial foil bearing shown in FIGS. 2 and 3 in the structure of the top foil.

  That is, the top foil 30 in the radial foil bearing shown in FIGS. 6A and 6B penetrates through the top foil 30 at the axial center of the top foil 30 as shown in FIG. 6B. A plurality of through holes 31 are formed in communication with the oblique groove 13. These through holes 31 are formed so that the inner diameter thereof is substantially the same as the width of the oblique groove 13.

  Under such a configuration, in the radial foil bearing provided with the top foil 30, the surrounding fluid is taken in through the through hole 31 from the gap between the top foil 30 and the back foil 11, It flows through the oblique groove 13 toward the both end portions of the bearing. Accordingly, the radial foil bearing is cooled almost uniformly in the entire circumferential direction, whereby a higher cooling effect can be obtained, and the seizure is reliably prevented.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.
For example, in the above-described embodiment, the radial foil bearing 3 according to the present invention is configured by including the bearing housing 12, but without the bearing housing 12, the back is directly or indirectly included in the housing that accommodates the rotating shaft. You may make it arrange | position the radial foil bearing 3 which consists of foil and a top foil.

DESCRIPTION OF SYMBOLS 1 ... Rotary shaft, 3 ... Radial foil bearing, 10 ... Top foil, 10a ... Foil start end, 10b ... Foil end, 11 ... Back foil (bump foil), 13 ... Oblique groove, 14 ... Inter-land land part (land part) ), 15... Edge side land portion (land portion), 20... Top foil, 20 a... Foil start end, 20 b .. foil end, 21 .. center groove, 30.

Claims (3)

A radial foil bearing that is extrapolated to a rotating shaft and supports the rotating shaft,
A cylindrical top foil disposed to face the rotating shaft, and a back foil disposed radially outside the top foil,
A plurality of oblique grooves are formed on the surface of the top foil that faces the rotation shaft, from the rear to the front in the rotation direction of the rotation shaft and from the center of the top foil in the axial direction to both edge sides. And
A radial foil bearing, wherein a land portion is formed between the oblique grooves and between the end portion on the end edge side of the oblique groove and the edge.   A central groove extending along the circumferential direction of the top foil is formed on the surface of the top foil facing the rotation axis so as to communicate with the oblique groove at the axial center of the top foil. The radial foil bearing according to claim 1, wherein:   2. The radial according to claim 1, wherein a through-hole penetrating the top foil is formed in the top foil in a center portion in an axial direction of the top foil so as to communicate with the oblique groove. Foil bearing.

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