JP2012072817A - Foil bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foil bearing having a bearing surface whose flexibility can be easily adjusted.SOLUTION: The foil bearing includes a cylindrical external member 1, a shaft 2 inserted into the inner periphery of the external member 1, and a plurality of leaves 3 interposed between an inner peripheral face 1b of the external member 1 and an outer peripheral face 2a of the shaft 2, and each having one end mounted on the external member 1. On the inner peripheral face of each leaf 3, the bearing surface 3d is provided which forms a wedge-shaped radial bearing clearance. On each leaf 3, a protrusion 2b is provided in contact with the inner peripheral face 1b of the external member 1 at a position apart from the fixed end of the leaf 3. The side closer to the free end than the protrusion 2b of each leaf 3 is brought into contact with the free end of the other leaf 3.

Description

  The present invention relates to a foil bearing in which a thin film foil is interposed between an inner peripheral surface of an outer member and an outer peripheral surface of a shaft.

  The main shaft of a gas turbine or turbocharger is driven to rotate at high speed. Moreover, the turbine blade attached to the main shaft is exposed to high temperature. Therefore, bearings that support these main shafts are required to be able to withstand severe environments such as high temperature and high speed rotation. Oil lubricated rolling bearings and hydrodynamic pressure bearings may be used as bearings for this type of application, but if lubrication with a liquid such as lubricating oil is difficult, the auxiliary equipment of the lubricating oil circulation system from the viewpoint of energy efficiency The use of these bearings is restricted under conditions such as when it is difficult to provide a separate or when resistance due to liquid shear becomes a problem. Therefore, an air dynamic pressure bearing has attracted attention as a bearing suitable for use under such conditions.

  As an air dynamic pressure bearing, one in which both the rotating side and the fixed side bearing surfaces are made of a rigid body is generally used. However, in this type of air dynamic pressure bearing, if the radial bearing clearance formed between the rotating and stationary bearing surfaces is insufficiently managed, a self-excited so-called whirl is called when the stability limit is exceeded. Easy to touch around the spindle. Therefore, gap management according to the rotation speed used is important. In particular, in an environment such as a gas turbine or a turbocharger where the temperature changes drastically, the radial bearing gap varies due to the effect of thermal expansion, so accurate gap management becomes extremely difficult.

  A foil bearing is known as a bearing that is less likely to cause a whirl and can easily manage a gap even in an environment with a large temperature change. In the foil bearing, a bearing surface is constituted by a thin film (foil) having low rigidity with respect to bending, and the load is supported by allowing the bearing surface to bend. Normally, the inner peripheral surface of the bearing is composed of a thin plate called a top foil, and a spring-like member called a back foil is arranged on the outer diameter side to elastically support the load received by the top foil with the back foil. Yes. In this case, when the shaft rotates, an air film is formed between the outer peripheral surface of the shaft and the inner peripheral surface of the top foil, and the shaft is supported in a non-contact manner.

  Foil bearings are characterized by excellent stability because of the flexibility of the foil, an appropriate radial bearing gap is formed according to the operating conditions such as shaft rotation speed, load, and ambient temperature. It can be used at a higher speed than an air dynamic pressure bearing. In addition, the radial bearing clearance of a general dynamic pressure bearing needs to be managed in the order of 1/1000 of the shaft diameter. For example, a radial bearing clearance of about several μm needs to be always secured for a shaft having a diameter of about several millimeters. . Therefore, when taking into account manufacturing tolerances, and even thermal expansion when the temperature change is severe, strict gap management is difficult. On the other hand, in the case of a foil bearing, it is sufficient to manage a radial bearing gap of about several tens of μm, and there is an advantage that its manufacture and gap management become easy.

  As the foil bearing, a top foil is elastically supported by a cut and raised provided in a back foil (Patent Document 1), and a bearing foil is elastically supported by an elastic body formed by meshing strands (Patent Document). 2) and those having a back foil provided with a support portion that contacts the inner surface of the outer ring and does not move in the circumferential direction and an elastic portion that is elastically bent by the surface pressure from the top foil (Patent Document 3), etc. are known. is there.

  As a type of foil bearing, the back foil is not provided, the top foil is divided in the circumferential direction to form a leaf foil, and the leaf foils are provided in multiple places in the circumferential direction while overlapping the parts, and the leaf foils overlap. There is also a so-called leaf type that obtains springiness at a portion. In this leaf type foil bearing, the fixed bearing ring is divided into a plurality of arc-shaped ring members in the circumferential direction, one end of the foil is welded to the joining end of each arc-shaped ring member, and a Rayleigh step is bent on the foil. One formed (Patent Document 4), one formed by a piezo bimorph (Patent Document 5), one formed by a bimetal made of two types of metals having different linear expansion coefficients (Patent Document 6), etc. It is known.

JP 2002-364463 A JP 2003-262222 A JP 2009-299748 A Japanese Examined Patent Publication No. 2-20851 JP-A-4-54309 JP 2002-295467 A

  In a foil bearing, since the flexibility (rigidity) of the bearing surface has a great influence on the bearing performance, it is necessary to provide the bearing surface with the optimum flexibility in accordance with the design conditions and operating conditions. Among the conventional foil bearings, in the foil bearings shown in Patent Documents 1 to 3, the flexibility of the bearing surface is optimized mainly by adjusting the elastic supporting force of the back foil. However, since the structure of the back foil is generally complicated, it is difficult to adjust the elastic supporting force, and the bearing design becomes difficult.

  On the other hand, in the leaf-type foil bearings shown in Patent Documents 4 to 6, in order to adjust the flexibility of the bearing surface, it is necessary to change the material, dimensions, shape, etc. of the leaf, and it is similarly difficult to design the bearing. It becomes.

  Therefore, an object of the present invention is to provide a foil bearing in which the flexibility of the bearing surface can be easily adjusted.

  In order to achieve the above object, the present invention provides a cylindrical outer member, a shaft inserted in the inner periphery of the outer member, and a foil, and an inner peripheral surface of the outer member and an outer peripheral surface of the shaft. Are arranged at a plurality of locations in the circumferential direction between them, and have a bearing surface forming a wedge-shaped radial bearing gap, one end is fixed to a mounting member consisting of either a shaft or an outer member, and the other end is a free end A foil bearing that supports the relative rotation of the shaft and the outer member with a fluid film generated in the radial bearing gap, and a protrusion that contacts the mounting member at a position away from the fixed end of the leaf. And a free end of another leaf is brought into contact with the free end side of the protruding portion of each leaf.

  In the conventional configuration, when one end of the leaf is attached to the attachment member, this attachment position is fixed as a fulcrum of the leaf. Therefore, in order to adjust the flexibility (rigidity) of the leaf, it is unavoidable to change the material, shape, dimensions, etc. of the leaf. On the other hand, as in the present invention, if a protrusion is provided on the leaf separately from the attachment portion to the attachment member, and this protrusion is brought into contact with the attachment member, the protrusion when the protrusion elastically deforms the leaf, Become. When the free end of another leaf comes into contact with the free end side of the protrusion, elastic support force is applied to the other leaf by elastic deformation of the leaf on the free end side of the protrusion. If the position of the protrusion is moved (especially if it is moved in the circumferential direction), the leaf fulcrum position changes and the spring constant of the leaf on the free end side of the protrusion changes, so that the leaf in contact with this Furthermore, the flexibility of the bearing surface can be adjusted. This makes it possible to freely set the flexibility of the leaf only by adjusting the position of the protrusion, and the bearing design is facilitated.

  It is desirable to provide an overlap portion that overlaps the other leaf in the radial direction on the fixed end side of the leaf. Thereby, the free end of another leaf can be reliably brought into contact with the free end side of the protruding portion of the leaf. In addition, even when the leaf is partially plastically deformed from the radial bearing gap side and the protrusion is formed, the recess formed by the plastic deformation does not face the radial bearing gap, preventing the fluid film from being broken by the recess. can do. The protrusion is preferably formed over the entire axial length of the leaf.

  The above configuration can be applied not only when the outer member is an attachment member and the shaft is rotated, but also when the shaft is an attachment member and the outer member is rotated.

  During the operation of the bearing, a minute sliding in the circumferential direction occurs between the protrusion and the portion that contacts the protrusion of the mounting member. Considering the damping effect of vibration due to this sliding, it is desirable to increase the frictional force acting on the sliding part to some extent. Therefore, if the first coating is formed on any one or both of the contact portion between the projection and the projection of the attachment member, the material of the foil or outer member can be determined by appropriately selecting the coating material. Regardless of this, it is possible to obtain an optimum coefficient of friction at both sliding parts, and the degree of freedom in bearing design is increased.

  In a low-speed rotation state immediately after starting or immediately after stopping, a member facing the bearing surface of the leaf via a radial bearing gap comes into sliding contact. Accordingly, by forming the second coating on the bearing surface to reduce the friction, it is possible to reduce the friction torque immediately after starting and immediately after stopping to reduce the torque. Further, the bearing surface can be protected and wear of the bearing surface during sliding contact can be suppressed.

  The first coating and the second coating are desirably formed of materials having different friction coefficients. As the first film and the second film, any one of a DLC film, a titanium aluminum nitride film, and a diverted molybdenum film can be selected. Since the DLC coating and the titanium aluminum nitride coating are hard coatings, if they are used, in addition to reducing friction, it is possible to increase the bearing life by improving wear resistance.

  The foil bearing described above can be used for supporting a rotor of a gas turbine or a rotor of a supercharger.

  According to the present invention, the flexibility of the bearing surface can be easily adjusted by adjusting the position of the protrusion. Therefore, the bearing design suitable for the operating conditions and the design conditions becomes easy, and the cost of the foil bearing can be reduced.

It is a front view which shows one Embodiment of the foil bearing concerning this invention. It is a perspective view of the foil bearing shown in FIG. It is a front view which shows other embodiment of this invention.

  1 and 2 show an embodiment of a leaf type foil bearing according to the present invention. The foil bearing is suitable for supporting a rotor of a gas turbine or a supercharger, for example, and includes a cylindrical outer member 1 and a shaft 2 inserted into the inner periphery of the outer member 1 and coupled to the rotor. And a plurality of leaves 3 interposed in a gap between the inner peripheral surface of the outer member and the outer peripheral surface of the shaft 2.

  Each leaf 3 is formed of a metal foil, and is arranged at equal positions in the circumferential direction of the gap. The inner peripheral surface of each leaf 3 constitutes an arc-shaped bearing surface 3d that is convex on the outer diameter side, and shrinks in the rotational direction of the shaft 2 between the bearing surface 3d and the outer peripheral surface 2a of the shaft 2. A wedge-shaped radial bearing gap C is formed.

  Each leaf 3 is fixed to the outer member 1 by attaching one end thereof to the inner periphery of the outer member 1. For example, as shown in the drawing, an attachment portion 3a standing in the outer diameter direction is formed at one end portion of the leaf 3, and this attachment portion 3a is fitted and fixed in a fitting groove 1a formed on the inner periphery of the outer member 1. Thus, each leaf 3 can be fixed to the outer member 1. The attachment method of each leaf 3 to the outer member 1 is arbitrary, and can be fixed by adhesion or welding. The other end of each leaf 3 is a free end. On the fixed end side of each leaf 3, an overlap portion P is formed that overlaps in the radial direction with the free end side of another leaf 3 adjacent in the counter-rotating direction of the shaft 2.

  On the outer peripheral surface in the overlap portion P of each leaf 3, a protrusion 3b protruding in the outer diameter direction is formed. This protrusion 3b is formed by partially plastically deforming the leaf 3 from the inner diameter side to the outer diameter direction, and is constituted by a ridge formed over the entire axial length of the leaf 3, for example, as shown in FIG. Can do. In a state where each leaf 3 is attached to the outer member 1, each protrusion 3 b elastically contacts the inner peripheral surface 1 b of the outer member 1. In this state, the foil bearing shown in FIG. 1 is obtained by inserting the shaft 1 into the inner periphery of the foil 3.

  In the above configuration, when the shaft 2 is rotated in the reduction direction of the wedge-shaped radial bearing gap C, an air film is formed between the bearing surface 3d of each leaf 3 and the outer peripheral surface 2a of the shaft 2. As a result, as shown in FIG. 1, wedge-shaped radial bearing gaps C are formed at a plurality of circumferential positions around the shaft 2, and the shaft 2 can rotate in the radial direction in a non-contact state with respect to the foil 3. (The actual radial bearing gap C has a very small width of about several tens of μm, but the width is exaggerated in FIG. 1). Further, due to the flexibility of each leaf 3, the bearing surface 3 d of each leaf 3 is arbitrarily elastically deformed according to the operating conditions such as the load, the rotational speed of the shaft 2, the ambient temperature, etc. It is automatically adjusted to an appropriate width according to the conditions. Therefore, the radial bearing gap can be managed to the optimum width, and the shaft 2 can be stably supported.

  While the shaft 2 is rotating, each leaf 3 is elastically deformed to the outer diameter side by the pressure of the air film formed in the radial bearing gap C, and its free end is in the rotational direction as shown by a two-dot chain line in FIG. The adjacent leaf 3 is contacted. At this time, the leaf 3 on the outer diameter side is elastically deformed, so that the leaf 3 on the inner diameter side in contact with the leaf 3 is elastically supported and the flexibility of the bearing surface 3d is increased. Therefore, the self-adjustment ability of the width of the radial bearing gap C is enhanced, and a vibration damping effect is also obtained. Therefore, the radial bearing gap can be managed to the optimum width even under severe operating conditions such as high temperature and high speed rotation, and the shaft 2 can be stably supported.

  In the present invention, a protruding portion 3 b is provided on each leaf 3 separately from the attaching portion 3 a to the outer member 1, and the protruding portion 3 b is in contact with the outer member 1. Since this protrusion 3b serves as a fulcrum (starting point) when each leaf 3 is elastically deformed, elastic deformation of the leaf 3 occurs on the free end side from the protrusion 3b. Therefore, if the position of the protrusion 3b is moved in the circumferential direction, the spring constant of the leaf 3 can be changed on the free end side relative to the protrusion 3b, and elastic support given to other leaves 3 when the leaves are in contact with each other. The power can be adjusted. Thereby, it becomes possible to freely set the flexibility of each leaf 3 only by adjusting the position of the protrusion 3b in the circumferential direction, and the bearing design is facilitated. The position of the protrusion 3b can be adjusted within the range of the overlap portion P and within a range in which another leaf 3 can contact the free end side of the protrusion 3.

  By forming the protrusion 3b by plastic deformation, a recess is formed on the inner peripheral surface of the leaf 3, but this recess is in the range of the overlap portion P, and the recess faces the radial bearing gap C. There is nothing. Therefore, it is possible to prevent the air film from being broken by the recess and to support the shaft 2 stably.

  In the foil bearing, it is difficult to form an air film having a thickness greater than the surface roughness on the bearing surface 3d of each leaf 3 and the outer peripheral surface 2a of each shaft 2 at the time of low-speed rotation immediately before the shaft 2 is stopped or immediately after starting. . For this reason, metal contact is generated between the foil 3 and the outer peripheral surface 2a of the shaft 2, and the torque is increased. In order to reduce the torque by reducing the frictional force at this time, it is desirable to form a second coating on the bearing surface 3d of each leaf 3 to reduce the friction of the surface. As this type of coating, for example, a DLC film, a titanium aluminum nitride film, or a molybdenum disulfide film can be used. The DLC film, titanium or aluminum nitride film can be formed by CVD or PVD, and the molybdenum disulfide film can be easily formed by spraying. In particular, since the DLC film and the titanium aluminum nitride film are hard, by forming a film with them, the wear resistance of the bearing surface 3d can be improved, and the bearing life can be increased.

  Further, during the operation of the bearing, a minute sliding in the circumferential direction also occurs between the protrusion 3 b of each leaf 3 and the inner peripheral surface 1 b of the outer member 1. By forming a first coating on one or both of the sliding portion, that is, the outer surface of the protrusion 3b and the inner peripheral surface 1b of the outer member 1 in contact with the sliding portion, Abrasion can be improved. In order to improve the vibration damping effect, a certain amount of frictional force may be required at the sliding portion, and the first coating is not required to have a very low frictional property. Therefore, as the first coating, it is preferable to use a DLC film, titanium, or an aluminum nitride film that has a friction coefficient larger than that of the diverted molybdenum film but is excellent in wear resistance. For example, while using a disulfide molybdenum film as the second coating on the bearing surface 3d, a DLC film or the like is used as the first coating on the sliding portion of the protrusion 3b and the outer member 1, and the friction coefficients of the two coatings are different. This makes it possible to achieve both a reduction in torque and an improvement in the vibration damping effect.

  In the above description, the case where the shaft 2 is a rotating side member and the outer member 1 is a fixed side member in the configuration of FIG. 1 is illustrated, but conversely, the shaft 2 is a fixed side member, Even when the member 1 is a rotation side member, the configuration of FIG. 1 can be applied as it is. However, in this case, since the leaf 3 is a rotation side member, it is necessary to design the leaf 3 in consideration of the deformation of the leaf 3 due to centrifugal force.

  Further, in FIG. 1, the case where each leaf 3 is fixed to the outer member 1 is illustrated, but the leaf 3 can also be fixed to the shaft 2. FIG. 3 shows an example in which the attachment portion 3 a at one end of each leaf 3 stands up on the inner diameter side and is fitted and fixed in a fitting groove 2 b provided in the shaft 2, for example. In addition to this, the attachment portion 3a may be fixed to the shaft 2 by adhesion or welding. The outer peripheral surface of each leaf 3 constitutes an arc-shaped bearing surface 3d that is convex on the outer diameter side, and is directed in the rotational direction of the shaft 2 between the bearing surface 3d and the inner peripheral surface 1b of the outer member 1. As a result, a wedge-shaped radial bearing gap C is formed. On the fixed end side of each leaf 3, an overlap portion P that overlaps in the radial direction with the free end side of another leaf 3 adjacent in the counter-rotating direction is configured. In the overlap portion P of each leaf 3, a protrusion 3b is formed by partially plastically deforming the leaf 3 from the outer diameter side toward the inner diameter side, and the protrusion 3b contacts the outer peripheral surface 2a of the shaft 2. ing. During rotation of the outer member 1, the free ends of the other leaves adjacent to the anti-rotation direction side are in contact with the free end side of the protrusions 3 b of the leaves 3. With the above configuration, the same operation and effect as the embodiment shown in FIGS. 1 and 2 can be obtained.

  In FIG. 3, the outer member 1 is the rotating side, but the outer member 1 may be the fixed side. However, when the outer member 1 is on the fixed side, the foil 3 is on the rotating side. Therefore, when the foil 3 is designed, it is necessary to consider deformation of the foil 3 due to centrifugal force.

  The foil bearing described above can be used not only as an air dynamic pressure bearing using air as a pressure generating fluid but also as an oil dynamic pressure bearing using lubricating oil as a pressure generating fluid.

DESCRIPTION OF SYMBOLS 1 Outer member 1a Fitting groove 1b Inner peripheral surface 2 Shaft 2a Outer peripheral surface 2b Fitting groove 3 Leaf 3a Attaching part 3b Protruding part 3d Bearing surface C Radial bearing gap P Overlap part

Claims (12)

A cylindrical outer member, a shaft inserted in the inner periphery of the outer member, and a foil, which are arranged at a plurality of locations in the circumferential direction between the inner peripheral surface of the outer member and the outer peripheral surface of the shaft. A radial bearing having a bearing surface forming a wedge-shaped radial bearing gap, one end fixed to an attachment member composed of either a shaft or an outer member, and the other end being a free end. In the foil bearing that supports the relative rotation of the shaft and the outer member with the fluid film generated in the gap,
A foil bearing characterized in that a protrusion is provided on a leaf to come into contact with the mounting member at a position away from the fixed end, and the free end of another leaf is brought into contact with the free end side of the protrusion of each leaf.   The foil bearing according to claim 1, wherein an overlap portion that overlaps the other leaf in the radial direction is provided on a fixed end side of the leaf, and a protrusion is provided on the overlap portion.   The foil bearing according to claim 1, wherein the protrusion is formed by partially plastically deforming the leaf from the radial bearing gap side.   The foil bearing of any one of Claims 1-3 which formed the protrusion part over the axial direction full length of the leaf.   The foil bearing according to any one of claims 1 to 4, wherein the outer member is an attachment member and the shaft is rotated.   The foil bearing according to any one of claims 1 to 4, wherein the shaft is used as a mounting member and the outer member is rotated.   The foil bearing of any one of Claims 1-6 which formed the 1st film in any one or both among the contact parts of a projection part and the projection part of an attachment member.   The foil bearing of any one of Claims 1-7 in which the 2nd film | membrane which makes the surface low friction was formed in the bearing surface of the leaf.   The foil bearing according to claim 8, wherein the first coating and the second coating are formed of materials having different friction coefficients.   The foil bearing according to claim 8 or 9, wherein any one of a DLC film, a titanium aluminum nitride film, and a diverted molybdenum film is selected as the first film and the second film.   The foil bearing of any one of Claims 1-10 used for support of the rotor of a gas turbine.   The foil bearing of any one of Claims 1-10 used for support of the rotor of a supercharger.

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