BEARING DEVICE AND ROTATING DEVICE

Abstract

A bearing device according to an embodiment is a bearing device for rotatably supporting a rotational shaft, the device including at least one rolling bearing which includes an inner race fixed to the rotational shaft, a rolling element, and an outer race for rotatably holding the rolling element with the inner race, and a casing for housing the rolling bearing, the casing including a plurality of first oil supply holes formed at intervals in a circumferential direction for supplying lubricant oil to a first gap between the rolling bearing and an inner circumferential surface of the casing. Each of the plurality of first oil supply holes satisfies:

π.Math.d.sub.1.Math.δ.sub.1<π.Math.d.sub.1.sup.2/4   (a)

, where d.sub.1 is a diameter of an outlet opening of the first oil supply hole, and δ.sub.1 is a space of the first gap.

Claims

1. A bearing device for rotatably supporting a rotational shaft, the device comprising: at least one rolling bearing which includes an inner race fixed to the rotational shaft, a rolling element, and an outer race for rotatably holding the rolling element with the inner race; and a casing for housing the rolling bearing, the casing including a plurality of first oil supply holes formed at intervals in a circumferential direction for supplying lubricant oil to a first gap between the rolling bearing and an inner circumferential surface of the casing, wherein each of the plurality of first oil supply holes satisfies:
π.Math.d.sub.1.Math.δ.sub.1<π.Math.d.sub.1.sup.2/4   (a) , where d.sub.1 is a diameter of an outlet opening of the first oil supply hole, and δ.sub.1 is a space of the first gap.

2. The bearing device according to claim 1, wherein the plurality of first oil supply holes are disposed symmetrically with respect to an axial center of the rotational shaft in a cross-section of the rotational shaft.

3. The bearing device according to claim 1, wherein, in an opposite surface opposite to the inner circumferential surface of the casing across the first gap, a first recess is formed which is configured such that a cross-sectional area thereof in a direction orthogonal to an axis of the rotational shaft decreases from a position where the cross-sectional area is maximum toward at least one side in an axial direction.

4. The bearing device according to claim 3, wherein the first recess is configured such that a depth thereof decreases toward the one side in the axial direction.

5. The bearing device according to claim 3, wherein the first recess is configured such that the cross-sectional area decreases from the position where the cross-sectional area is maximum toward each of the one side and another side in the axial direction, and is configured such that a distance from the position where the cross-sectional area is maximum to an end portion on the one side in the axial direction and a distance from the position where the cross-sectional area is maximum to an end portion on the another side in the axial direction are equal.

6. The bearing device according to claim 3, wherein the first recess is configured such that the position where the cross-sectional area is maximum is opposite to the outlet opening of the first oil supply hole.

7. The bearing device according to claim 3, wherein the at least one rolling bearing includes a plurality of rolling bearings disposed at intervals in the axial direction of the rotational shaft, wherein the bearing device further includes a cover member configured to cover respective perimeters of the plurality of rolling bearings, and wherein the opposite surface is constituted by an outer circumferential surface of the cover member.

8. The bearing device according to claim 7, wherein the casing forms a second oil supply hole for supplying the lubricant oil to a second gap between an inner surface of the casing and an axial one end surface of the cover member, and a third oil supply hole for supplying the lubricant oil to a third gap between the inner surface of the casing and an axial another end surface of the cover member, and wherein each of the plurality of first oil supply holes satisfies:
π.Math.d.sub.2.Math.δ.sub.2<π.Math.d.sub.2.sup.2/4   (b) , where d.sub.2 is a diameter of an outlet opening of the second oil supply hole, and δ.sub.2 is a space of the second gap; and
π.Math.d.sub.3.Math.δ.sub.3<π.Math.d.sub.3.sup.2/4   (c) , where d.sub.3 is a diameter of an outlet opening of the third oil supply hole, and δ.sub.3 is a space of the third gap.

9. The bearing device according to claim 8, wherein, in the axial one end surface opposite to the inner surface of the casing across the second gap, a second recess is formed which is configured such that a cross-sectional area thereof in a direction parallel to the axis of the rotational shaft decreases from a position where the cross-sectional area is maximum toward at least one side in a radial direction, and wherein, in the axial another end surface opposite to the inner surface of the casing across the third gap, a third recess is formed which is configured such that a cross-sectional area thereof in the direction parallel to the axis of the rotational shaft decreases from a position where the cross-sectional area is maximum toward the at least one side in the radial direction.

10. A bearing device for rotatably supporting a rotational shaft, the device comprising: a plurality of rolling bearings disposed at intervals in an axial direction of the rotational shaft, the rolling bearings each including an inner race fixed to the rotational shaft, a rolling element, and an outer race for rotatably holding the rolling element with the inner race; a cover member configured to cover respective perimeters of the plurality of rolling bearings; and a casing for housing the plurality of rolling bearings and the cover member, the casing forming a second oil supply hole for supplying lubricant oil to a second gap between an inner surface of the casing and an axial one end surface of the cover member, and a third oil supply hole for supplying the lubricant oil to a third gap between the inner surface of the casing and an axial another end surface of the cover member, wherein the second oil supply hole satisfies:
π.Math.d.sub.2.Math.δ.sub.2<π.Math.d.sub.2.sup.2/4   (b) , where d.sub.2 is a diameter of an outlet opening of the second oil supply hole, and δ.sub.2 is a space of the second gap, and wherein the third oil supply hole satisfies:
π.Math.d.sub.3.Math.δ.sub.3<π.Math.d.sub.3.sup.2/4   (c) , where d.sub.3 is a diameter of an outlet opening of the third oil supply hole, and δ.sub.3 is a space of the third gap.

11. The bearing device according to claim 10, wherein, in the axial one end surface opposite to the inner surface of the casing across the second gap, a second recess is formed which is configured such that a cross-sectional area thereof in a direction parallel to the axis of the rotational shaft decreases from a position where the cross-sectional area is maximum toward at least one side in a radial direction, and wherein, in the axial another end surface opposite to the inner surface of the casing across the third gap, a third recess is formed which is configured such that a cross-sectional area thereof in the direction parallel to the axis of the rotational shaft decreases from a position where the cross-sectional area is maximum toward the at least one side in the radial direction.

12. A rotating device, comprising: a rotational shaft; and the bearing device according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0031] FIG. 1 is a vertical cross-sectional view of a rotating device including a bearing device according to an embodiment.

[0032] FIG. 2 is a vertical cross-sectional view of the bearing device according to an embodiment.

[0033] FIG. 3 is a schematic view showing a supply system for supplying lubricant oil to the bearing device.

[0034] FIG. 4 is an explanatory view for describing a restoring force of a rotational shaft by a squeeze action of an oil film.

[0035] FIG. 5 is an enlarged view of an A portion in FIG. 2.

[0036] FIG. 6 is a cross-sectional view of the bearing device according to an embodiment.

[0037] FIG. 7 is a vertical cross-sectional view of the bearing device according to an embodiment.

[0038] FIG. 8 is a vertical cross-sectional view of the bearing device according to an embodiment.

[0039] FIG. 9 is a vertical cross-sectional view of the bearing device according to an embodiment.

DETAILED DESCRIPTION

[0040] Some embodiments of the present invention will be described below with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions and the like of components described or shown in the drawings as the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.

[0041] For instance, an expression of relative or absolute arrangement such as “in a direction”, “along a direction”, “parallel”, “orthogonal”, “centered”, “concentric” and “coaxial” shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance whereby it is possible to achieve the same function.

[0042] Further, for instance, an expression of a shape such as a rectangular shape or a cylindrical shape shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness or chamfered corners within the range in which the same effect can be achieved.

[0043] On the other hand, an expression such as “comprise”, “include”, “have”, “contain” and “constitute” are not intended to be exclusive of other components.

[0044] FIG. 1 is a vertical cross-sectional view of a rotating device 50 including a bearing device 10 according to a bearing device. FIG. 2 is a vertical cross-sectional view of the bearing device 10 (10A) according to an embodiment. The bearing device 10 (10A) includes at least one rolling bearing 14 for supporting a rotational shaft 12 rotatably about an axis O.sub.1, and the rolling bearing 14 is housed in a casing 16. The rolling bearing 14 is formed by an inner race 18 fixed to the rotational shaft 12, a rolling element 20, and an outer race 22 for rotatably holding the rolling element 20 with the inner race 18. The casing 16 includes a plurality of oil supply holes 24 (24a, 24b, 24c, 26d) (first oil supply holes) formed at intervals in the circumferential direction, and high-pressure lubricant oil r is supplied to a gap C.sub.1 (first gap) between the rolling bearing 14 and an inner surface 16a of the casing 16 via the plurality of oil supply holes 24 (24a to 24d). Each of the oil supply holes 24 satisfies:

π.Math.d.sub.1.Math.δ.sub.1<π.Math.d.sub.1.sup.2/4   (a)

,where d.sub.1 is a diameter of an outlet opening of the oil supply hole 24, and δ.sub.1 is a space of the gap C.sub.1.

[0045] FIG. 3 is a view showing a lubricant oil supply system, and schematically showing the rotational shaft 12 and the rolling bearing 14 as one structure (12+14). In an embodiment, the plurality of oil supply holes 24 (24a to 24d) are disposed symmetrically with respect to the axis Oi of the rotational shaft 12 in a cross-section of the rotational shaft 12. According to the present embodiment, since the plurality of oil supply holes 24 (24a to 24d) are disposed symmetrically with respect to the axis O.sub.1 of the rotational shaft 12, it is possible to equally supply the lubricant oil r to the gap C.sub.1 in the circumferential direction of the rotational shaft 12. Thus, it is possible to form a good oil film in the gap C.sub.1. For example, if the bearing device 10 (10A) is applied to a small rotating device such as a turbocharger, since the plurality of oil supply holes 24 (24a to 24d) are disposed symmetrically with respect to the axis O.sub.1 of the rotational shaft 12, it is possible to supply lubricant oil with the same pressure to the gap C.sub.1 in the circumferential direction of the rotational shaft 12. Thus, it is possible to form a uniform oil film in the gap C.sub.1 along the circumferential direction of the rotational shaft 12.

[0046] In an embodiment, as shown in FIG. 3, the plurality of oil supply holes 24 are disposed at regular intervals in the circumferential direction of the casing 16, for example. The three oil supply holes 24 are disposed at intervals of 120°, or the four oil supply holes 24 are disposed at intervals of 90° so that the supply amount of lubricant oil is uniformly distributed in the circumferential direction of the rolling bearing 14. Further, the plurality of oil supply holes 24 are disposed in a direction orthogonal to an outer circumferential surface and an inner circumferential surface of the casing 16.

[0047] If the gap C.sub.1 configures self-squeeze as in the above-described embodiment, the outlet opening of the oil supply hole 24 is formed to be the same as or smaller than the cross-sectional area of the upstream oil supply hole 24.

[0048] The above-described configuration of the bearing device 10 (10A) described so far also is also included in the bearing device 10 (10B, 10C) according to other embodiments shown in FIGS. 7 and 8 in common. Therefore, in FIGS. 7 and 8, the same members or same instruments as the bearing device 10 (10A) are indicated by the same reference numerals, respectively.

[0049] FIG. 4 is a view schematically showing the gap C.sub.1 formed between the rolling bearing 14 and the casing 16. The gap C.sub.1 satisfying the above-described expression (a) configures so-called self-squeeze for the lubricant oil r passing through the gap C.sub.1 to exert a squeeze action. Therefore, it is possible to form the good oil film in the gap C.sub.1 without using a mechanical means. If the rotational shaft 12 is eccentric in the radial direction due to a vibration or the like, a pressure loss increases in a region R.sub.1 where the gap C.sub.1 is narrowed, increasing a pressure. Therefore, a reverse restoring force from an eccentric direction acts on the rotational shaft 12, restoring the rotational shaft 12 to a side of a region R.sub.2 where the gap C.sub.1 is widened and a pressure is decreased. Thus, it is possible to hold the oil film in the gap C.sub.1, and it is possible to damp the vibration of the rotational shaft 12 even if the rotational shaft 12 vibrates.

[0050] In an embodiment, as shown in FIG. 1, the bearing device 10 is provided to rotatably support the rotational shaft 12 of the rotating device 50. The rotating device 50 according to an embodiment illustrated in FIG. 1 is a turbocharger, and the bearing device 10 is housed in the casing 16 forming a part of a bearing housing 64. The turbocharger includes a compressor 52 and a turbine 54 at both ends of the rotational shaft 12. The compressor 52 is radially provided with a plurality of compressor blades 58 around a compressor wheel 56. The turbine 54 is radially provided with a plurality of turbine blades 62 around a turbine wheel 60. In the bearing housing 64, an oil channel 68 for the lubricant oil r communicating with the oil supply holes 24 is formed. In FIG. 1, a compressor housing for housing the compressor wheel 56 and the compressor blades 58, and a turbine housing for housing the turbine wheel 60 and the turbine blades 62 are not illustrated.

[0051] In an embodiment, as shown in FIGS. 1 and 2, the rotating device 50 includes a thrust bearing 66, and the thrust bearing 66 supports a thrust load loaded on the rotational shaft 12. In FIG. 2, the casing 16 disposed opposite to the rolling bearing 14 is not necessarily a body portion of the casing 16, but also includes attachment members such as a bearing mount and a sleeve attached to the body of the casing 16. Further, some measures (not shown) for suppressing detent in the circumferential direction of the rotational shaft 12 is provided for the rolling bearing 14, as needed.

[0052] In an embodiment, as shown in FIG. 3, the high-pressure lubricant oil r is supplied to the plurality of oil supply holes 24 (24a to 24d) by a pump 28 from a lubricant oil supply source (not shown) such as a lubricant oil tank (not shown) via a pipe passage 26.

[0053] FIG. 5 is an enlarged view of an A portion in FIG. 2. FIG. 6 is a view corresponding to the A portion in another embodiment. In an embodiment, as shown in FIGS. 5 and 6, a recess 30 (30a, 30b) (first recess) is formed in the opposite surface 22a (32a) opposite to the inner surface 16a of the casing 16 across the gap C.sub.1. The opposite surface 22a (32a) indicates an outer circumferential surface 22a of the outer race 22 in the embodiment shown in FIG. 5, and indicates an outer circumferential surface 32a of a cover member 32 in the embodiments shown in FIGS. 7 and 8. The recess 30 is configured such that a cross-sectional area thereof in the direction orthogonal to the axis O.sub.1 of the rotational shaft 12 decreases from a position where the cross-sectional area is maximum toward at least one side in the axial direction of the rotational shaft 12.

[0054] In an embodiment, the recess 30 is formed into, for example, an oval shape or a rectangular shape as viewed from the side of the casing 16. In the embodiment shown in FIG. 5, the recess 30 (30a) is configured such that a depth thereof decreases toward one side in the axial direction, but can be configured such that an interval between side surfaces forming the recess (a width dimension of the recess 30) is narrowed toward one side in the axial direction, even if the depth is constant in the axial direction.

[0055] According to the present embodiment, the lubricant oil r supplied from the oil supply holes 24 to the recess 30 via the gap C.sub.1 accelerates toward the axial direction of the rotational shaft 12 along the surface of the recess 30, and a normal component force Pd is generated with respect to the surface of the recess 30 by a dynamic pressure of the lubricant oil r. The normal component force Pd becomes a force of restoring the eccentric rotational shaft 12 to a statically determinate position. Therefore, it is possible to have both of a self-squeeze effect on the oil film passing through the gap C.sub.1 and an alignment effect in the radial direction of the rotational shaft 12 by the dynamic pressure of the lubricant oil r. Thus, it is possible to hold the oil film in the recess 30, and to exert the vibration damping effect even if the rotational shaft 12 vibrates in the radial direction.

[0056] The recess 30 is disposed in the opposite surface 22a (32a) opposite to an outlet opening of at least one oil supply hole 36.

[0057] The plurality of oil supply holes 24 (24a to 24d) are preferably formed along a direction orthogonal to the outer circumferential surface of the outer race 22 at least in the vicinity of the outlet opening. Thus, it is possible to reduce the pressure loss of the lubricant oil r and to increase the normal component force Pd acting on the surface of the recess 30.

[0058] In an embodiment, as shown in FIG. 5, the recess 30 (30a) is configured such that the depth thereof decreases toward one side in the axial direction. The lubricant oil r supplied from the oil supply holes 24 to the recess 30 (30a) flows along the surface of the recess 30 (30a) and accelerates toward the axial direction, and the normal component force Pd is generated with respect to the surface of the recess 30 (30a) by the dynamic pressure of the lubricant oil r. Therefore, it is possible to further increase the self-squeeze effect by the gap C.sub.1 and the alignment effect in the radial direction of the rotational shaft 12 by the dynamic pressure of the lubricant oil r.

[0059] In an embodiment, as shown in FIG. 6, the recess 30 (30b) is configured such that a cross-sectional area thereof gradually decreases toward one side and another side in the axial direction from a position where the cross-sectional area is maximum. Further, the recess 30 (30b) is configured such that a distance L.sub.1 from a position P.sub.1 where the cross-sectional area is maximum to an end portion on the one side in the axial direction and a distance L.sub.2 from the position where the cross-sectional area is maximum to an end portion on the another side in the axial direction are equal.

[0060] If the lubricant oil r is supplied to the recess 30 (30b), the lubricant oil r is branched to the one side or the another side in the axial direction on the surface of the recess 30 (30b). Thus, depending on a position where the lubricant oil r is supplied, it is possible to generate a force of moving the rotational shaft 12 to the one side or the another side. For example, if the lubricant oil is supplied to the position where the cross-sectional area is maximum, a distribution of the normal component force Pd generated on the surface of the recess 30 (30b) along the axial direction is symmetrical about the position where the cross-sectional area is maximum. Therefore, if the rotational shaft 12 moves in the axial direction from the statically determinate position due to the vibration or the like, the distribution of the normal component force Pd generated on the surface of the recess 30 (30b) along the axial direction is asymmetric. Thus, the dynamic pressure of the lubricant oil r acting on the surface of the recess 30 (30b) in an opposite direction to the moving direction of the rotational shaft 12 increases, applying a force of restoring the rotational shaft 12 to an original statically determinate position. Therefore, in addition to the self-squeeze effect of the oil film and the alignment effect in the radial direction by the dynamic pressure of the lubricant oil r, it is possible to exert an alignment effect in a thrust direction.

[0061] In an embodiment, as shown in FIGS. 5 and 6, the recess 30 (30a, 30b) is configured such that the position where the cross-sectional area is maximum is opposite to the outlet opening of the oil supply hole 24. In addition to the technical effects by the above-described embodiments, when the rotational shaft 12 is at the statically determinate position, the lubricant oil r discharged from the outlet opening of the oil supply hole 24 is supplied to the position where the cross-sectional area of the recess 30 is maximum, making it possible to efficiently convert kinetic energy of the lubricant oil r into the dynamic pressure acting on the surface of the recess 30.

[0062] In an embodiment, it is configured such that the position P.sub.1 where the cross-sectional area of the recess 30 (30a, 30b) is maximum is opposite to a center point P.sub.2 of the outlet opening of the oil supply hole 24. That is, it is configured such that the point P.sub.1 and the center point P.sub.2 are on a perpendicular line O.sub.2. Thus, when the rotational shaft 12 is at the statically determinate position, the lubricant oil r discharged from the outlet opening of the oil supply hole 24 is accurately supplied to the position where the cross-sectional area of the recess 30 is maximum, making it possible to efficiently convert the kinetic energy of the lubricant oil r into the dynamic pressure acting on the surface of the recess 30.

[0063] FIG. 6 shows that the rolling bearing 14 moves in an arrow direction (right side in drawing) from the statically determinate position together with the rotational shaft 12, due to occurrence of the vibration of the rotational shaft 12. If the rotational shaft 12 moves from the statically determinate position to one side in the axial direction, the distribution of the normal component force Pd over the axial direction formed on the surface of the recess 30 (30b) is asymmetric as illustrated in FIG. 6. That is, the normal component force Pd generated on the surface of the recess 30 (30b) in the opposite direction to the moving direction of the rotational shaft 12 increases. By a difference in asymmetric normal component force Pd, the force of restoring the rotational shaft 12 to the original statically determinate position in the thrust direction is applied. Thus, in addition to the self-squeeze effect of the oil film by the gap C.sub.1 and the alignment effect in the radial direction by the dynamic pressure of the recess 30 (30b), it is possible to exert the alignment effect in the thrust direction.

[0064] In an embodiment, the cross-section of the recess 30 (30b) has an arc shape. Further, in an embodiment, the cross-section of the recess 30 (30b) has a symmetrical shape with respect to the perpendicular line O.sub.2 perpendicular to the outer circumferential surface of the outer race 22 passing through the point P.sub.1 at the statically determinate position. Thus, when the rotational shaft 12 is at the statically determinate position, the distribution of the normal component force Pd is symmetric with respect to the perpendicular line O.sub.2, and the normal component force Pd is balanced in the axial direction. Consequently, when the rotational shaft 12 moves in the axial direction from the statically determinate position due to the vibration or the like, the asymmetrical distribution of the normal component force Pd can sensitively be expressed, and thus the force of restoring the rotational shaft 12 can sensitively be expressed.

[0065] In an embodiment, the bearing device 10 (10B) shown in FIG. 7 includes the plurality of rolling bearings 14 (14a, 14b) disposed at intervals in the axial direction of the rotational shaft 12, and the cover member 32 is disposed so as to cover respective perimeters of the plurality of rolling bearings 14. Then, the recesses 30 are disposed in the outer circumferential surface 32a (opposite surface) of the cover member 32. Each of the recesses 30 may be the recess 30 (30a) shown in FIG. 5 or may be the recess 30 (30b) shown in FIG. 6. Since the recesses 30 are formed in the outer circumferential surface 32a of the cover member 32, the dynamic pressure of the lubricant oil r is transmitted to the plurality of rolling bearings 14 (14a, 14b) via the cover member 32. Therefore, an equal force acts on the respective rolling bearings 14 from the cover member 32, and the respective rolling bearings 14 are uniformly moved by the cover member 32, making it possible to improve the alignment effect with respect to the rotational shaft 12.

[0066] In an embodiment, if the recesses 30 (30a) are formed in the outer circumferential surface 32a of the cover member 32, the two recesses 30 (30a) are formed such that directions in which the cross-sectional areas thereof gradually decrease are opposite to each other. Thus, the normal component forces Pd in directions other than the radial direction are generated in the opposite direction in the two recesses 30 (30a), and thus cancel each other out. Therefore, an excessive force is not applied in the thrust direction.

[0067] In an embodiment, the cover member 32 basically has a cylindrical shape, and a partition wall forming the outer circumferential surface 32a can exist at least at a position opposite to the oil supply holes 24. Further, the cover member 32 internally includes a restriction part 34 for restricting an axial movement of each rolling bearing 14. The restriction part 34 includes an annular recess where the outer race 22 of the rolling bearing 14 is fitted, and the outer race 22 is fitted with the recess, thereby restricting the axial movement.

[0068] In an embodiment, in the bearing device 10 (10C) shown in FIG. 8, an oil supply hole 36 (second oil supply hole) and an oil supply hole 38 (third oil supply hole) are formed in the casing 16. The oil supply hole 36 supplies the lubricant oil r to a gap C.sub.2 (second gap) between an axial end surface 32b of the cover member 32 and an inner surface 16a of the casing 16. The oil supply hole 38 supplies the lubricant oil r to a gap C.sub.3 (third gap) between an axial end surface 32c of the cover member 32 and an inner surface 16b of the casing 16. The oil supply hole 36 satisfies:

π.Math.d.sub.2.Math.δ.sub.2<π.Math.d.sub.2.sup.2/4   (b)

, where d.sub.2 is a diameter of an outlet opening of the oil supply hole 36, and δ.sub.2 is a space of the gap C.sub.2, and the oil supply hole 38 satisfies:

π.Math.d.sub.3.Math.δ.sub.3<π.Math.d.sub.3.sup.2/4   (c)

, where d.sub.3 is a diameter of an outlet opening of the oil supply hole 38, and δ.sub.3 is a space of the gap δ.sub.3.

[0069] According to the present embodiment, self-squeeze by the squeeze action of the oil film is configured when the lubricant oil r supplied from the oil supply hole 36 and the oil supply hole 38 passes through the gap C.sub.2 and the gap C.sub.3, respectively, making it possible to form the good oil film in the gap C.sub.2 and the gap C.sub.3 without using the mechanical means. Further, even if the rotational shaft 12 moves to one side or another side in the thrust direction from the statically determinate position due to the vibration, it is possible to damp the vibration in the thrust direction and to exert the alignment effect of restoring the rotational shaft 12 to the original statically determinate position. Therefore, the bearing device 10 (10C) can have both of the alignment effect in the radial direction by self-squeeze on the lubricant oil r supplied from the oil supply holes 24, and the alignment effect in the thrust direction by self-squeeze on the lubricant oil r supplied from the oil supply holes 36 and 38.

[0070] In an embodiment, a plurality of oil supply holes 36 and 38 are formed at a regular interval in the circumferential direction of the rotational shaft 12. Further, the oil supply holes 36 and 38 are formed along a direction orthogonal to the inner circumferential surface of the casing 16 at least in the vicinity of the outlet opening. Thus, it is possible to reduce the pressure loss of the lubricant oil and to increase the normal component force Pd generated on the surfaces of recesses 40 and 42.

[0071] In an embodiment, as shown in FIG. 9, the recess 40 is formed in the axial end surface 32b of the cover member 32 opposite to the inner surface 16a of the casing 16 across the gap C.sub.2. Further, the recess 42 is formed in the axial end surface 32c of the cover member 32 opposite to the inner surface 16b of the casing 16 across the gap C.sub.3. The recesses 40 and 42 are each configured such that a cross-sectional area thereof in a direction parallel to the axis O.sub.1 of the rotational shaft 12 decreases from a position where the cross-sectional area is maximum toward at least one side in the radial direction of the rotational shaft 12.

[0072] According to the present embodiment, the lubricant oil r supplied from the oil supply hole 36 to the recess 40 accelerates toward the radial direction, generating the normal component force Pd with respect to the surface of the recess 40 by the dynamic pressure of the lubricant oil r. The normal component force Pd becomes a force of restoring the rotational shaft 12 moved in the thrust direction to the statically determinate position. The same normal component force acts also in the lubricant oil r supplied from the oil supply hole 38 to the recess 42. Therefore, in the present embodiment, it is possible to have both of the self-squeeze effect of the oil film and the alignment effect in the radial direction of the rotational shaft 12 by the dynamic pressure of the lubricant oil r. Thus, it is possible to exert the vibration damping effect even if the rotational shaft 12 vibrates in the radial direction. Therefore, the bearing device 10 (10C) can have both of the self-squeeze effect on the oil film supplied from the oil supply holes 24 and the alignment effect in the radial direction by the recess 30, and the self-squeeze effect on the oil film supplied from the oil supply holes 36 and 38 and the alignment effect in the thrust direction by the recesses 40 and 42.

[0073] In an embodiment, the recesses 40 and 42 have the same shape as the recess 30 (30a) or the recess 30 (30b). Thus, it is possible to exert the alignment effect in the radial direction by the normal component force Pd generated on the surface of the recess 30 (30a, 30b).

[0074] In an embodiment, in the bearing device 10 (10C) shown in FIG. 8, the oil supply holes 24 and the recess 30 may be omitted, and only the oil supply holes 36 and 38 may be provided. Thus, self-squeeze by the squeeze action of the oil film is configured when the lubricant oil r supplied from the oil supply holes 36 and 38 passes through the gap C.sub.2 and the gap C.sub.3, respectively. Thus, it is possible to form the good oil film in the gap C.sub.2 and the gap C.sub.3 without using the mechanical means, and even if the rotational shaft 12 moves to one side or another side in the thrust direction from the statically determinate position due to the vibration, it is possible to damp the vibration in the thrust direction and to exert the alignment effect of restoring the rotational shaft 12 to the original statically determinate position.

[0075] In an embodiment, as shown in FIG. 9, the oil supply holes 24 and the recess 30 may be omitted, and only the oil supply holes 36 and 38, and the recesses 40 and 42 may be provided. Thus, it is possible to have both of the self-squeeze effect on the oil film by the gap C.sub.2 and C.sub.3, and the alignment effect in the radial direction of the rotational shaft 12 by the dynamic pressure of the lubricant oil r. Thus, it is possible to exert the vibration damping effect even if the rotational shaft 12 vibrates in the radial direction. Therefore, a thrust bearing provided for the rotational shaft can be omitted, in some cases.

[0076] Since the rotating device 50 shown in FIG. 1 includes the bearing device 10 according to each embodiment described above, it is possible to form self-squeeze by the squeeze action of the lubricant oil film in the gap between the rolling bearing 14 and the casing 16 for housing the rolling bearing 14. Thus, it is possible to suppress radial eccentricity of the rotational shaft 12 due to the vibration, making it possible to exert the vibration damping effect of the rotational shaft 12.

[0077] The turbocharger has been taken as an example of the rotating device shown in FIG. 1. However, each embodiment described above is also applicable to another rotating device including the rotational shaft.

INDUSTRIAL APPLICABILITY

[0078] According to some embodiments, in a rotating device including a rotational shaft, if the rotational shaft is supported by a rolling bearing, it is possible to effectively suppress a vibration without using a mechanical means.

REFERENCE SIGNS LIST

[0079] 10 (10A, 10B, 10C) Bearing device [0080] 12 Rotational shaft [0081] 14 (14a, 14b) Rolling bearing [0082] 16 Casing [0083] 16a, 16b Inner surface [0084] 18 Inner race [0085] 20 Rolling element [0086] 22 Outer race [0087] 22a Outer circumferential surface (opposite surface) [0088] 24 (24a, 24b, 24c, 24d) Oil supply hole (first oil supply hole) [0089] 26 Pipe passage [0090] 28 Pump [0091] 30 (30a, 30b) Recess (first recess) [0092] 32 Cover member [0093] 32a Outer circumferential surface (opposite surface) [0094] 32b, 32c Axial end surface [0095] 34 Restriction part [0096] 36 Oil supply hole (second oil supply hole) [0097] 38 Oil supply hole (third oil supply hole) [0098] 40 Recess (second recess) [0099] 42 Recess (third recess) [0100] 50 Rotating device [0101] 52 Compressor [0102] 54 Turbine [0103] 56 Compressor wheel [0104] 58 Compressor blade [0105] 60 Turbine wheel [0106] 62 Turbine blade [0107] 64 Bearing housing [0108] 66 Thrust bearing [0109] 68 Oil channel [0110] C.sub.1 Gap (first gap) [0111] C.sub.2 Gap (second gap) [0112] C.sub.3 Gap (second gap) [0113] O.sub.1 Axis [0114] O.sub.2 Center line [0115] P.sub.2 Center point [0116] Pd Normal component force [0117] r Lubricant oil