Warehouse structure

Abstract

Storage structure (S), with: a housing (3) having a cylindrical section (3c) having a bearing hole (3b); a connecting hole (3e) formed and configured in the housing (3) to allow a connection between the bearing hole (3b) and a lubricating oil supply oil passage (3d); a rolling bearing (15) which is arranged in the bearing hole (3b), wherein a shaft (13) is inserted through the rolling bearing (15); a damping groove (39b) which is formed in at least one of an outer circumferential surface of an outer ring (35a) of the rolling bearing (15) or an inner circumferential surface (3f) of the bearing hole (3b) such that it extends in a circumferential direction of the shaft (13); and an oil drain hole (3k) having one end connected to the damping groove (39b) and another end open to an outside of the cylinder section (3c); characterized in that a gap is formed between the outer circumferential surface of the outer ring (35a) and the inner circumferential surface (3f) of the bearing hole (3b), so that lubricating oil flows to the end surfaces (35e, 35f) of the outer ring (35a) in an axial direction of the shaft (13), and a smallest flow cross-sectional area of ​​the oil drain hole, which is smallest with respect to a flow cross-sectional area of ​​the oil drain hole (3k), is equal to or smaller than an area obtained by subtracting a smallest gap area of ​​one side, which is smallest with respect to a gap area defined between the outer ring (35a) and the inner circumferential surface (3f) of the bearing hole (3b) on one side of the damping groove (39b) in the axial direction of the shaft (13), and a smallest gap area of ​​the other side, which is smallest with respect to a gap area defined between the outer ring (35a) and the inner circumferential surface (3f) of the bearing hole (3b) on the other side of the damping groove (39b) in the axial direction, from a smallest flow cross-sectional area of ​​the connecting hole, which is smallest with respect to a flow cross-sectional area of ​​the connecting hole (3e).

Description

Technical field

[0001] The present disclosure relates to a storage structure. This application claims the priority benefit of Japanese patent application JP 2018-140461A, which was filed on July 26, 2018. State of the art

[0002] A bearing structure comprises a housing, rolling bearings, and a shaft. The rolling bearings are arranged in a bearing bore formed in the housing. The shaft is inserted through the inner rings of the rolling bearings. Patent reference 1 discloses a bearing structure in which circumferential grooves are formed in the outer rings of the rolling bearings. Lubricating oil is supplied to the circumferential grooves of the outer rings. The lubricating oil supplied to the circumferential groove forms an oil film damping between an inner circumferential surface of the bearing bore and an outer circumferential surface of the outer ring. The oil film damping is configured to dampen vibration of the shaft. Patent reference 2 discloses a bearing structure according to the preamble of claim 1. Patent references 3 to 5 disclose further prior art. Citation list of patent literature Patent literature 1: JP 2005 - 171 796 A1 Patent literature 2: US 2017 / 0 102 003 A1 Patent literature 3: US 2018 / 0 135 698 A1 Patent literature 4: DE 11 2016 003 287 T5 Patent literature 5: DE 11 2016 003 110 T5 Summary Technical Problem

[0003] However, if the lubricating oil accumulates excessively in the circumferential groove, the properties of the rolling bearing (hereinafter referred to simply as "bearing properties") may be deteriorated due to a mass effect.

[0004] The present disclosure has the purpose of providing a bearing structure that is capable of limiting a deterioration of the bearing properties. Solution to the problem

[0005] The problem mentioned above is solved by a bearing structure according to claim 1. To solve the problem mentioned above, according to one embodiment of the present disclosure, a bearing structure is provided comprising: a housing having a cylindrical section having a bearing hole; a rolling bearing arranged in the bearing hole, with a shaft being inserted through the rolling bearing; a damping groove formed in at least one of an outer circumferential surface of an outer ring of the rolling bearing or an inner circumferential surface of the bearing hole such that it extends in a circumferential direction of the shaft; and an oil drain hole having one end communicating with the damping groove and another end opening to an outside of the cylindrical section.

[0006] A gap is formed between the outer circumferential surface of the outer ring and the inner circumferential surface of the bearing bore, allowing lubricating oil to flow to the end faces of the outer ring in an axial direction of the shaft. The housing has a connecting hole that allows a connection between the bearing bore and a lubricating oil supply passage, and wherein a smallest flow cross-sectional area of ​​the oil drain hole, which is smallest with respect to a flow cross-sectional area of ​​the oil drain hole, can be equal to or smaller than an area obtained by defining a smallest gap area on one side, which is smallest with respect to a gap area defined between the outer ring and the inner circumferential surface of the bearing bore on one side of the damping groove in the axial direction of the shaft, and a smallest gap area on the other side, which is smallest with respect to a gap area defined between the outer ring and the inner circumferential surface of the bearing bore on one side of the damping groove in the axial direction of the shaft.The area defined between the outer ring and the inner circumferential surface of the bearing hole on the other side of the damping groove in the axial direction is subtracted from the smallest flow cross-sectional area of ​​the connecting hole, which is smallest with respect to a flow cross-sectional area of ​​a connecting hole.

[0007] One end of the oil drain hole can be located at a position of the bearing hole on a bottom side in a vertical direction.

[0008] The housing can have a lubricating oil discharge passage on a lower side in the vertical direction with respect to the bearing hole, and a line of extension of a central axis of the oil drain hole can intersect with a housing wall surface facing the lubricating oil discharge passage.

[0009] The outer ring can be designed to be rotatable with respect to the bearing hole. Effects of the invention

[0010] According to the present disclosure, it is possible to limit the deterioration of the bearing properties. Brief description of the drawings Fig. Figure 1 is a schematic sectional view to illustrate a turbocharger. Fig. Figure 2 is an extracted view to show a section defined by the single-point catenary lines of Fig. 1 is displayed. Fig. 3 is a sectional view of an outer ring of Fig. 2 when viewed in a direction indicated by arrow III. Fig. Figure 4 is a schematic sectional view to illustrate a storage structure of a modification example. Description of the embodiments

[0011] An embodiment of the present disclosure will now be described with reference to the accompanying drawings. The dimensions, materials, and specific numerical values ​​represented in the embodiment are merely examples used for ease of understanding and do not limit the present disclosure unless expressly stated otherwise. Elements that have substantially the same functions and configurations herein and in the drawings are designated by the same reference numerals to avoid redundant descriptions. Representations of elements with no direct relation to the present disclosure have been omitted.

[0012] Fig. Figure 1 is a schematic sectional view illustrating a turbocharger TC. A description is given below, while a direction indicated by the in Fig. The arrow L shown in section 1 corresponds to the left side of the turbocharger TC. This direction is indicated by the arrow shown in section 1. Fig. The arrow R shown in section 1 corresponds to the right side of the turbocharger TC. As shown in Fig. As shown in Figure 1, the turbocharger TC has a turbocharger main body 1. The turbocharger main body 1 has a bearing housing (housing) 3, a turbine housing 5, and a compressor housing 7. The turbine housing 5 is coupled to a left side of the bearing housing 3 by a fastening mechanism 9. The compressor housing 7 is coupled to a right side of the bearing housing 3 by fastening screws 11.

[0013] A projection 3a is formed on an outer circumferential surface of the bearing housing 3. The projection 3a is located on the side of the turbine housing 5. The projection 3a extends radially forward of the bearing housing 3. A projection 5a is formed on an outer circumferential surface of the turbine housing 5. The projection 5a is located on the side of the bearing housing 3. The projection 5a extends radially forward of the turbine housing 5. The bearing housing 3 and the turbine housing 5 are strap-fastened by the fastening mechanism 9. The fastening mechanism 9 is, for example, a G-type coupling. The fastening mechanism 9 is configured to clamp the projections 3a and 5a.

[0014] The bearing housing 3 has a cylindrical section 3c with a bearing hole 3b. The bearing hole 3b passes through the turbocharger TC in both a clockwise and counterclockwise direction. The cylindrical section 3c is essentially cylindrical. A shaft 13 is inserted through the bearing hole 3b. A pair of rolling bearings 15 are accommodated in the bearing hole 3b. The rolling bearings 15 are, for example, ball bearings. The shaft 13 is supported by the rolling bearings 15. The rolling bearings 15 rotatably support the shaft 13. A turbine impeller 17 is provided at a left end section of the shaft 13. The turbine impeller 17 is rotatably mounted in the turbine housing 5. A compressor impeller 19 is provided at a right end section of the shaft 13. The compressor impeller 19 is rotatably mounted in the compressor housing 7.

[0015] An intake opening 21 is formed in the compressor housing 7. The intake opening 21 is located on the right side of the turbocharger TC. The intake opening 21 is connected to an air cleaner (not shown). A diffuser flow passage 23 is defined by the opposing surfaces of the bearing housing 3 and the compressor housing 7. The diffuser flow passage 23 increases the air pressure. The diffuser flow passage 23 has an annular shape. The diffuser flow passage 23 communicates with the intake opening 21 via the compressor impeller 19 on a radially inner side.

[0016] A compressor screw flow passage 25 is formed in the compressor housing 7. The compressor screw flow passage 25 has an annular shape. With respect to the diffuser flow passage 23, the compressor screw flow passage 25 is located, for example, on an outer side in a radial direction of the shaft 13. The compressor screw flow passage 25 is connected to an intake port of a power unit (not shown) and the diffuser flow passage 23. When the compressor impeller 19 rotates, air is drawn from the intake port 21 into the compressor housing 7. During its flow, the drawn-in air is pressurized and accelerated by the blades of the compressor impeller 19. The pressurized and accelerated air is pressurized again in the diffuser flow passage 23 and the compressor screw flow passage 25. The pressurized air is then directed to the intake opening of the engine.

[0017] A discharge port 27 is formed in the turbine housing 5. The discharge port 27 is open on the left side of the turbocharger TC. The discharge port 27 is connected to an exhaust gas cleaning device (not shown). A turbine screw flow passage 29 and a connecting flow passage 31 are formed in the turbine housing 5. The turbine screw flow passage 29 has an annular shape. With respect to the connecting flow passage 31, the turbine screw flow passage 29 is located, for example, on an outer side in a radial direction of the turbine impeller 17. The turbine screw flow passage 29 is connected to a gas inlet port (not shown). Exhaust gas discharged from an exhaust manifold (not shown) of the engine is directed to the gas inlet port. The connecting flow passage 31 is connected to the turbine screw flow passage 29.The connecting flow passage 31 is connected to the discharge opening 27 via the turbine impeller 17 on a radially inner side. Thus, the exhaust gas, which is directed from the gas inlet opening to the turbine screw flow passage 29, is guided through the connecting flow passage 31 and the turbine impeller 17 to the discharge opening 27. As the exhaust gas flows through the discharge opening 27, it rotates the turbine impeller 17.

[0018] A rotational force from the turbine impeller 17 is transmitted via the shaft 13 to the compressor impeller 19. As the compressor impeller 19 rotates, the air pressure is increased, as described above. In this way, the air is directed to the intake port of the engine.

[0019] Fig. 2 is a partial view to show a section defined by the single-point catenary lines of Fig. 1 is displayed. As in Fig. As shown in Figure 2, the turbocharger TC has a bearing structure S. The bearing structure S includes the cylinder section 3c of the bearing housing 3, the shaft 13, the pair of rolling bearings 15 and a spacer 33.

[0020] A lubricating oil supply oil passage 3d (see Fig. 1) is formed in the bearing housing 3. The lubricating oil supply passage 3d is located on an upper side in the vertical direction with respect to the bearing hole 3b (upper side of Fig. 2) Lubricating oil, pumped from a pump (not shown), is introduced into the lubricating oil supply passage 3d. A pair of connecting holes 3e is formed between the lubricating oil supply passage 3d and the bearing hole 3b. The pair of connecting holes 3e are spaced apart in an axial direction of the shaft 13 (hereinafter referred to simply as the "axial direction"). The connecting hole 3e has one end connected to the lubricating oil supply passage 3d and another end connected to the bearing hole 3b. For example, the connecting end of the connecting hole 3e that connects to the bearing hole 3b is formed at a top position of the bearing hole 3b in the vertical direction. The connecting holes 3e allow a connection between the lubricating oil supply passage 3d and the bearing hole 3b.

[0021] The pair of rolling bearings 15 is arranged in the bearing hole 3b. The pair of rolling bearings 15 are spaced apart from each other in the axial direction. In the following, when the pair of rolling bearings 15 is referred to separately, the rolling bearing 15 on a left side of Fig. 2 (side of turbine impeller 17 (see Fig. 1)) designated as “turbine-side bearing 35”. The rolling bearing 15 on a right side of Fig. 2 (side of compressor impeller 19 (see Fig. 1)) is referred to as “compressor-side bearing 37”.

[0022] The turbine-side bearing 35 comprises an outer ring 35a, an inner ring 35b, rolling elements 35c, and a cage 35d. The inner ring 35b is mounted on an outer circumferential surface of the shaft 13. The inner ring 35b rotates integrally with the shaft 13. The outer ring 35a is arranged on a radially outer side relative to the inner ring 35b. The outer ring 35a is positioned opposite an inner circumferential surface 3f of the bearing bore 3b. The outer ring 35a is located in a position opposite the connecting bore 3e in a radial direction of the shaft 13 (hereinafter referred to simply as the "radial direction"). A damping section 39, which will be described later, is formed in an outer circumferential surface of the outer ring 35a.

[0023] The multitude of rolling elements 35c is arranged between the outer ring 35a and the inner ring 35b. The multitude of rolling elements 35c is arranged along one direction of rotation of the shaft 13 (hereinafter referred to simply as the "direction of rotation" or "circumferential direction"). The cage 35d is configured to hold the multitude of rolling elements 35c. The intervals of the multitude of rolling elements 35c in the circumferential direction are maintained by the cage 35d at predetermined intervals.

[0024] The compressor-side bearing 37 comprises an outer ring 37a, an inner ring 37b, rolling elements 37c, and a cage 37d. The inner ring 37b is mounted on the outer circumferential surface of the shaft 13. The inner ring 37b rotates integrally with the shaft 13. The outer ring 37a is arranged on a radially outer side relative to the inner ring 37b. The outer ring 37a is positioned opposite the inner circumferential surface 3f of the bearing bore 3b. The outer ring 37a is located in a position radially opposite the connecting bore 3e. A damping section 41, which will be described later, is formed in an outer circumferential surface of the outer ring 37a.

[0025] The multitude of rolling elements 37c is arranged between the outer ring 37a and the inner ring 37b. The multitude of rolling elements 37c is arranged along the circumference. The cage 37d is configured to hold the multitude of rolling elements 37c. The intervals of the multitude of rolling elements 37c in the circumferential direction are maintained at predetermined intervals by the cage 37d.

[0026] The pair of rolling bearings 15, for example, is a pair of angular contact bearings. In Fig. Figure 2 shows the center lines (hereinafter also referred to as "connecting lines") representing the contact angles of the angular contact bearings, indicated by the two-point catenary lines. The connecting line is inclined with respect to a line (plane) perpendicular to the axial direction of shaft 13 (forming a contact angle). In addition to the radial loads of shaft 13, the angular contact bearings experience shear loads. The pair of angular contact bearings experiences shear loads in directions opposite to each other. The pair of angular contact bearings is, for example, arranged in a duplex combination facing each other on both sides (a combination in which the contact angles form directions of lines that diverge from each other towards the side of the outer ring).

[0027] The outer ring 35a of the turbine-side bearing 35 has an end surface 35e and an end surface 35f at both ends in the axial direction. The end surface 35e is located on the side of the outer ring 35a where the pair of rolling bearings 35 are spaced apart. The end surface 35f is located on the side of the outer ring 35a where the pair of rolling bearings 15 are positioned close together. The end surface 35e has a thickness greater than that of the end surface 35f. The inner ring 35b has an end surface 35g and an end surface 35h at both ends in the axial direction. The end surface 35g is located on the side of the inner ring 35b where the pair of rolling bearings 15 are positioned close together. The end surface 35h is located on one side of the inner ring 35b, on which the pair of rolling bearings 15 are spaced apart. The end surface 35g has a thickness greater than that of the end surface 35h.

[0028] As described above, the outer ring 35a and the inner ring 35b each have a thickness (a thickness in the radial direction) that differs in the axial direction at both end faces. The outer diameter of the inner ring 35b increases from the side of the turbine impeller 17 (see Fig. 1) to the side of the compressor impeller 19 (see Fig. 1) The inner diameter of the outer ring 35a increases from the side of the turbine impeller 17 to the side of the compressor impeller 19.

[0029] The outer ring 37a of the compressor-side bearing 37 has an end surface 37e and an end surface 37f at both ends in the axial direction. The end surface 37e is located on the side of the outer ring 37a where the pair of rolling bearings 15 are spaced apart. The end surface 37f is located on the side of the outer ring 37a where the pair of rolling bearings 15 are closer together. The end surface 37e has a thickness greater than that of the end surface 37f. The inner ring 37b has an end surface 37g and an end surface 37h at both ends in the axial direction. The end surface 37g is located on the side of the inner ring 37b where the pair of rolling bearings 15 are closer together. The end surface 37h is located on one side of the inner ring 37b, on which the pair of rolling bearings 15 are spaced apart. The end surface 37g has a thickness greater than that of the end surface 37h.

[0030] As described above, the outer ring 37a and the inner ring 37b each have a thickness (a thickness in the radial direction) that differs in the axial direction at both end faces. The outer diameter of the inner ring 37b increases from the side of the compressor impeller 19 (see Fig. 1) to the side of the turbine impeller 17 (see Fig. 1) The inner diameter of the outer ring 37a increases from the side of the compressor impeller 19 to the side of the turbine impeller 17.

[0031] The configuration described above, in which the thicknesses at the two end faces differ in the axial direction, can only be applied to any one of the outer rings 35a and 37a and the inner rings 35b and 37b. For example, the two end faces of the outer rings 35a and 37a can have different thicknesses in the axial direction, and the two end faces of the inner rings 35b and 37b can have the same thickness in the axial direction. Furthermore, the configuration in which the thickness at the two end faces differs in the axial direction, as described above, is not a significant configuration. The outer rings 35a and 37a and the inner rings 35b and 37b can have the same thickness at both end faces in the axial direction.

[0032] The spacer (an inner ring spacer) 33 is arranged between the inner ring 35b and the inner ring 37b. The spacer 33 is an annular element. The shaft 13 is inserted through the spacer 33. The outer diameter of the spacer 33 is smaller than the outer diameter of the end faces 35g and 37g of the inner rings 35b and 37b. However, the outer diameter of the spacer 33 can be equal to or larger than the outer diameter of the end faces 35g and 37g of the inner rings 35b and 37b. This description describes the case in which the spacer 33 is provided between the inner ring 35b and the inner ring 37b. However, a spring and a spring retainer can be provided instead of the spacer 33.

[0033] No spacer (an outer ring spacer), spring, or spring retainer is provided between the outer ring 35a and the outer ring 37a. That is, no retaining element configured to hold the outer rings 35a and 37a is provided between them. Therefore, the outer rings 35a and 37a are rotatable (freely rotatable) in the circumferential direction with respect to the bearing bore 3b. When the shaft 13 rotates, the inner rings 35b and 37b rotate concurrently with the shaft 13. The rolling elements 35c and 37c rotate along with the rotation of the inner rings 35b and 37b. The rolling elements 35c and 37c move in the circumferential directions of the inner rings 35b and 37b. The outer rings 35a and 37a rotate together with the rotation and movement of the rolling elements 35c and 37c or together with the flow of the lubricating oil in the circumferential direction of the shaft 13.At this time, the rotational speed of the outer rings 35a and 37a is slower than the rotational speed of the inner rings 35b and 37b.

[0034] The shaft 13 has a small-diameter section 13a, a large-diameter section 13b, and a reduced-diameter section 13c. The inner rings 35b and 37b are mounted on the small-diameter section 13a. The large-diameter section 13b has a diameter larger than that of the small-diameter section 13a and is formed integrally with the shaft 13. The reduced-diameter section 13c has a diameter smaller than that of the small-diameter section 13a and is formed integrally with the shaft 13. The large-diameter section 13b is located to the left of the small-diameter section 13a. Fig. 2. The reduced-diameter section 13c is located on the right side of the small-diameter section 13a. Fig. 2.

[0035] The large-diameter section 13b can, however, be formed from an element that is separate from the small-diameter section 13a. The large-diameter section 13b can be configured to be detachable from the small-diameter section 13a. The reduced-diameter section 13c can be formed from an element that is separate from the small-diameter section 13a. The reduced-diameter section 13c can be configured to be detachable from the small-diameter section 13a. The outer diameter of the large-diameter section 13b is equal to or greater than the outer diameter of the end face 35h of the inner ring 35b. The inner ring 35b is positioned by the large-diameter section 13b.

[0036] An oil launcher element 43 is mounted on the diameter-reduced section 13c. The oil launcher element 43 is configured to distribute the lubricating oil to the radially outer side. The oil launcher element 43 is configured to contain leakage of the lubricating oil to the side of the compressor impeller 19 (see Fig. 1).

[0037] The oil launcher element 43 has a large-diameter section 43a. The large-diameter section 43a has a diameter larger than that of the small-diameter section 13a. The outer diameter of the large-diameter section 43a is equal to or greater than the outer diameter of the end face 37h of the inner ring 37b. The inner ring 37b is positioned by the oil launcher element 43. The maximum outer diameter of the large-diameter section 43a is equal to the maximum outer diameter of the large-diameter section 13b. In this description, the meaning of "equal" includes exactly the same and "exactly the same" includes deviations within the range of tolerances (machining accuracies, assembly errors, and the like). However, the maximum outer diameter of the large-diameter section 43a may differ from the maximum outer diameter of the large-diameter section 13b.

[0038] A side wall section 3g is formed on the bearing housing 3. With respect to the outer ring 35a, the side wall section 3g is located on the side where the pair of rolling bearings 15 are spaced apart (the side of the turbine impeller 17 (see figure). Fig. 1)). The side wall section 3g projects from the inner circumferential surface 3f of the bearing bore 3b towards the radially inner side. The side wall section 3g has an opposing surface 3h. The opposing surface 3h lies opposite the end surface 35e of the outer ring 35a in the axial direction.

[0039] A sealing plate 45 is mounted on the radially outer side of the bearing housing 3 with respect to the oil launcher element 43. The sealing plate 45 has an opposing surface 45a. The opposing surface 45a is axially opposite the end surface 37e of the outer ring 37a. The sealing plate 45 is configured to contain the leakage of lubricating oil from the bearing bore 3b to the side of the compressor impeller 19 (see Fig. 1).

[0040] The inner ring 35b, the spacer 33, the inner ring 37b, the oil launcher element 43 and the compressor impeller 19 (see Fig. 1) are inserted sequentially from an end section of the shaft 13 on the side of the compressor impeller 19. A fastening screw is attached to the end section of the shaft 13 on the side of the compressor impeller 19. A compression load (an axial force) is applied in the axial direction to the inner ring 35b, the spacer 33, the inner ring 37b, the oil launcher element 43, and the compressor impeller 19. The inner ring 35b, the spacer 33, and the inner ring 37b are clamped by the axial force between the large-diameter section 13b and the oil launcher element 43 and rotate integrally with the shaft 13.

[0041] The damping section 39 is formed in the outer circumferential surface of the turbine-side bearing 35 (of the outer ring 35a). The damping section 41 is formed in the outer circumferential surface of the compressor-side bearing 37 (of the outer ring 37a). The damping sections 39 and 41 are located opposite the inner circumferential surface 3f of the bearing bore 3b.

[0042] The damping section 39 has two annular projections 39a. The two annular projections 39a are formed on the outer circumferential surface of the outer ring 35a such that they are spaced apart from each other in the axial direction. The two annular projections 39a project from the outer ring 35a towards its radially outer side. The two annular projections 39a extend in an annular shape over the entire circumference of the outer circumferential surface of the outer ring 35a. A damping groove 39b is defined between the two annular projections 39a. The damping groove 39b extends in an annular shape over the entire circumference of the outer circumferential surface of the outer ring 35a.

[0043] The damping section 41 has two annular projections 41a. The two annular projections 41a are formed on the outer circumferential surface of the outer ring 37a such that they are spaced apart from each other in the axial direction. The two annular projections 41a project from the outer ring 37a towards its radially outer side. The two annular projections 41a extend in an annular shape over the entire circumference of the outer circumferential surface of the outer ring 37a. A damping groove 41b is formed between the two annular projections 41a. The damping groove 41b extends in an annular shape over the entire circumference of the outer circumferential surface of the outer ring 37a. The damping grooves 41b and 41b extend in the circumferential direction of the shaft 13.

[0044] On the inner circumferential surface 3f of the bearing hole 3b, the connecting hole 3e is open between positions facing the two annular projections 39a. On the inner circumferential surface 3f of the bearing hole 3b, the connecting hole 3f is open between positions facing the two annular projections 41a. This means that the damping grooves 39b and 41b are radially opposite the connecting holes 3e. The connecting holes 3e are connected to the damping grooves 39b and 41b.

[0045] The lubricating oil is supplied to the connecting holes 3e from the lubricating oil supply passage 3d (see Fig. 1) supplied. The lubricating oil enters through the connecting holes 3e and is supplied to the damping grooves 39b and 41b. The lubricating oil flows circumferentially through the damping grooves 39b and 41b. The lubricating oil flows through gaps (spaces) between the two ring projections 39a and 41a and the inner circumferential surface 3f of the bearing bore 3b. The lubricating oil forms oil films (oil film damping) between the outer circumferential surface of the outer rings 35a and 37a and the inner circumferential surface 3f of the bearing bore 3b. The oil film damping is configured to dampen vibration of the shaft 13.

[0046] The damping effect of the shaft 13's vibration can be modified (adjusted) by changing the shapes of the two ring projections 39a and 41a. The damping effect of the shaft 13's vibration can be changed without altering the shapes of the entire outer rings 35a and 37a. Therefore, it is easy to design the outer rings 35a and 37a, which have the damping sections 39 and 41.

[0047] Between the two ring projections 39a, the ring projection 39a is located on the side of the turbine runner 17 (see Fig. 1) referred to as the “first projection 39aa”. Between the two ring projections 39a, the ring projection 39a is located on the side of the compressor impeller 19 (see Fig. 1) referred to as “second projection 39ab”. Between the two ring projections 41a, the ring projection 41a on the side of the compressor impeller 19 is referred to as “first projection 41aa”. Between the two ring projections 41a, the ring projection 41a on the side of the turbine impeller 17 is referred to as “second projection 41ab”.

[0048] The second projections 39ab and 41ab are located relative to the first projections 39aa and 41aa in a direction in which the pair of rolling bearings 15 approaches. The axial width of the first projections 39aa and 41aa is smaller than the axial width of the second projections 39ab and 41ab, respectively.

[0049] The lubricating oil supplied to the damping grooves 39b and 41b flows circumferentially along these grooves. Once the damping grooves 39b and 41b are filled with lubricating oil, the oil flows over the first projections 39aa and 41aa and the second projections 39ab and 41ab, and axially between the outer circumferential surface of the outer rings 35a and 37a and the inner circumferential surface 3f of the bearing bore 3b. At this point, the lubricating oil flows more easily (with less resistance) through the gap between the first projections 39aa and 41aa and the inner circumferential surface 3f of the bearing bore 3b than through the gap between the second projections 39ab and 41ab and the inner circumferential surface 3f of the bearing bore 3b. Therefore, the lubricating oil supplied to the damping grooves 39b and 41b flows easily from the sides of the first projection 39a and 41aa.

[0050] Accordingly, the amount of lubricating oil flowing on the sides of the end faces 35e and 37e of the outer rings 35a and 37a is ensured. The lubricating oil flows on the sides of the end faces 35e and 37e, so that the outer rings 35a and 37a are pressed by the lubricating oil towards the side on which the pair of rolling bearings 15 approach each other. The outer rings 35a and 37a are pressed towards the side on which the pair of rolling bearings 15 approach each other, thereby stabilizing the positions of the turbine-side bearing 35 and the compressor-side bearing 37. However, the width of the first projections 39aa and 41aa in the axial direction can be equal to or greater than the width of the second projections 39ab and 41ab in the axial direction.

[0051] Groove sections 35i are formed in the end face 35e. The groove sections 35i extend from the outer circumferential surface through the outer ring 35a to the inner circumferential surface. Groove sections 37i are formed in the end face 37e. The groove sections 37i extend from the outer circumferential surface through the outer ring 37a to the inner circumferential surface. However, the groove sections 35i and 37i cannot be formed in both outer rings 35a and 37a. For example, the groove sections 35i can be formed in the outer ring 35a, and the groove sections 37i cannot be formed in the outer ring 37a. Furthermore, the groove sections 35i cannot be formed in the outer ring 35a, and the groove sections 37i can be formed in the outer ring 37a.

[0052] Fig. Figure 3 is a sectional view of the outer ring 35a of Fig. 2 when viewed in a direction indicated by arrow III. It should be noted that the shape of the groove section 35i in the outer ring 35a is the same as the shape of the groove section 37i in the outer ring 37a. Therefore, a description of the shape of the groove section 35i in the outer ring 35a is now given, and a description of the shape of the groove section 37i in the outer ring 37a is omitted.

[0053] As in Fig. As shown in Figure 3, the groove section 35i extends along the radial direction of the outer ring 35a. However, the groove section 35i can extend inclined with respect to the radial direction. The groove section 35i has a left-side surface 35ia, a right-side surface 35ib, and a bottom surface 35ic. The left-side surface 35ia and the right-side surface 35ib extend along the radial direction of the outer ring 35a. The bottom surface 35ic is a flat surface that is parallel to the radial direction of the outer ring 35a and parallel to the end surface 35e.

[0054] The circumferential width of the groove section 35i (that is, the distance between the left-hand surface 35ia and the right-hand surface 35ib) is constant regardless of its position in the radial direction. However, the circumferential width of the groove section 35i can be modified according to its position in the radial direction. For example, the circumferential width of the groove section 35i can be modified to decrease from the radially inner side to the radially outer side. Furthermore, the circumferential width of the groove section 35i can be modified to increase from the radially inner side to the radially outer side.

[0055] A plurality of groove sections 35i are formed in the circumferential direction of the end surface 35e. In this embodiment, four groove sections 35i are arranged at 90° intervals in the circumferential direction of the end surface 35e. However, the number of groove sections 35i is not limited to four; it is only required that the number of groove sections 35i be one or more. Furthermore, the intervals of the groove sections 35i in the circumferential direction are not limited to the same intervals and can be unequal intervals.

[0056] Returning to Fig. 2 The lubricating oil, which escapes from the first projection 39aa of the two ring projections 39a, flows downwards through the gap between the end surface 35e of the outer ring 35a and the opposite surface 3h of the side wall section 3g. The lubricating oil flows downwards through the gap between the groove sections 35i in the outer ring 35a and the opposite surface 3h of the side wall section 3g.

[0057] Similarly, the lubricating oil escaping from the first projection 41aa of the two ring projections 41a flows downwards through the gap between the end face 37e of the outer ring 37a and the opposite face 45a of the sealing plate 45. The lubricating oil flows downwards through the gap between the groove sections 37i in the outer ring 37a and the opposite face 45a of the sealing plate 45. The groove sections 35i and 37i are configured to allow the lubricating oil to be easily guided from the radially outer side to the radially inner side of the outer rings 35a and 37a. The lubricating oil, which is guided to the radially inner side of the outer rings 35a and 37a, comes into contact with the rolling elements 35c and 37c. The groove sections 35i and 37i efficiently direct the lubricating oil to the rolling elements 35c and 37c.

[0058] The end faces 35e and 37e of the outer rings 35a and 37a function as a shear bearing surface. A shear load is applied to the side of the compressor impeller 19 (see Fig. 1) is applied from the end surface 37e of the outer ring 37a to the opposite surface 45a of the sealing plate 45. A shear load is applied to the side of the turbine impeller 17 (see Fig. 1) is applied from the end surface 35e of the outer ring 35a to the opposite surface 3h of the side wall section 3g. The vibration of the shaft 13 in a thrust direction is dampened by the lubricating oil in the gap between the end surfaces 35e and 37e and the opposite surfaces 3h and 45a.

[0059] The lubricating oil that lubricates the rolling elements 35c and 37c flows out to a central section of the inner circumferential surface 3f of the bearing bore 3b. A first oil drain hole 3i is formed in the central section of the inner circumferential surface 3f of the bearing bore 3b. The first oil drain hole 3i has one end that opens to the inner circumferential surface 3f of the bearing bore 3b and another end that opens to an outer surface of the cylinder section 3c. The first oil drain hole 3i extends through the cylinder section 3c to a lower side (bottom of Fig. 2) in the vertical direction. The first oil drain hole 3i is configured to allow the lubricating oil in the bearing hole 3b to be discharged to an outer surface of the bearing hole 3b. Accordingly, the lubricating oil flowing towards the central section of the inner circumferential surface 3f of the bearing hole 3b passes through the first oil drain hole 3i and is discharged from the bearing hole 3b.

[0060] The lubricating oil discharged from bearing hole 3b (cylindrical section 3c) flows vertically downwards towards the lower side relative to bearing hole 3b (cylindrical section 3c). A lubricating oil discharge passage (lubricating oil discharge opening) 3j is formed vertically in the lower side of the bearing housing 3 relative to bearing hole 3b (cylindrical section 3c). The lubricating oil flowing downwards relative to bearing hole 3b passes through the lubricating oil discharge passage 3j and is discharged from the bearing housing 3.

[0061] If excessive amounts of lubricating oil accumulate in the damping grooves 39b and 41b, the bearing characteristics of the pair of rolling bearings 15 may be deteriorated due to a mass effect. In this respect, the cylinder section 3c in this embodiment has a second oil drain hole (an oil drain hole) 3k, which is provided separately from the first oil drain hole 3i. The second oil drain hole 3k is provided, for example, at a position on the inner circumferential surface 3f of the bearing bore 3b that is opposite the damping groove 39b. The second oil drain hole 3k has one end that communicates with the damping groove 39b and another end that opens to the outside of the cylinder section 3c. The second oil drain hole 3k is configured to allow the lubricating oil in the damping groove 39b to be discharged to the outside of the cylinder section 3c. Accordingly, the second oil drain hole 3k can prevent excessive accumulation of lubricating oil in the damping groove 39b.As a result, a deterioration of the bearing properties of the turbine-side bearing 35 can be contained.

[0062] A connecting opening (one end) of the second oil drain hole 3k, which communicates with the damping groove 39b, is formed at a position on the bearing hole 3b on its lowest side in the vertical direction. Accordingly, the connecting opening of the second oil drain hole 3k is formed at a position on the bearing hole 3b that is circumferentially furthest from the position where the bearing hole 3b and the connecting hole 3e communicate with each other. The lubricating oil supplied from the connecting hole 3e to the damping groove 39b cools the outer circumferential surface of the outer ring 35a and the inner circumferential surface 3f of the bearing hole 3b as it flows along the damping groove 39b. That is, the lubricating oil can accumulate heat as it flows from the connecting hole 3e to the second oil drain hole 3k.The connecting opening of the second oil drain hole 3k is formed at the position of the bearing hole 3b on the bottom side in the vertical direction, so that the lubricating oil can effectively cool the rolling bearings 15 and the bearing housing 3.

[0063] The amount of lubricating oil supplied from the connecting holes 3e to the bearing hole 3b is determined according to the flow cross-sectional areas of the connecting holes 3e. The amount of lubricating oil discharged from the second oil drain hole 3k to the outside of the cylinder section 3c is determined according to the flow cross-sectional area of ​​the second oil drain hole 3k. In this embodiment, the connecting holes 3e and the second oil drain hole 3k each have a constant inner diameter. However, the connecting holes 3e and the second oil drain hole 3k may each have a section with a variable inner diameter.

[0064] The amount of lubricating oil flowing over the first projections 39aa and 41aa is determined according to the gap areas defined between the outer circumferential surface of the first projections 39aa and 41aa and the inner circumferential surface 3f of the bearing bore 3b. The amount of lubricating oil flowing over the second projections 39ab and 41ab is determined according to the gap area defined between the outer circumferential surface of the second projections 39ab and 41ab and the inner circumferential surface 3f of the bearing bore 3b.

[0065] Here, the flow cross-sectional area that is smallest with respect to the flow cross-sectional area of ​​the second oil drain hole 3k is referred to as the "smallest flow cross-sectional area of ​​the oil drain hole". The flow cross-sectional area that is smallest with respect to the flow cross-sectional area of ​​the connecting hole 3e is referred to as the "smallest flow cross-sectional area of ​​the connecting hole". The gap area that is smallest with respect to the gap area defined between the outer circumferential surface of the outer rings 35a and 37a and the inner circumferential surface 3f of the bearing hole 3b on one side of the damping grooves 39b and 41b in the axial direction of the shaft 13 is referred to as the "smallest gap area of ​​one side".The gap area which is smallest with respect to the gap area defined between the outer circumferential surface of the outer rings 35a and 37a and the inner circumferential surface 3f of the bearing hole 3b on the other side of the damping grooves 39b and 41b in the axial direction of the shaft 13 is referred to as the “smallest gap area of ​​the other side”.

[0066] In this case, the smallest flow cross-sectional area of ​​the oil drain hole is equal to or smaller than the area obtained by subtracting the smallest gap area on one side and the smallest gap area on the other side from the smallest flow cross-sectional area of ​​the connecting hole. If the smallest flow cross-sectional area of ​​the oil drain hole satisfies the aforementioned condition, oil film damping between the outer circumferential surface of the outer rings 35a and 37a and the inner circumferential surface 3f of the bearing hole 3b is readily established. As a result, the vibration of the shaft 13 can be damped by the oil film damping. Conversely, if the smallest flow cross-sectional area of ​​the oil drain hole does not satisfy the aforementioned condition, it is difficult to establish oil film damping between the outer circumferential surface of the outer rings 35a and 37a and the inner circumferential surface 3f of the bearing hole 3b.Therefore, the vibration of shaft 13 can be difficult to dampen.

[0067] The second oil drain hole 3k extends along a central axis CA, which is defined by a dashed line in Fig. 2 is shown. The lubricating oil discharged from the second oil drain hole 3k flows downwards along the central axis CA of the second oil drain hole 3k towards the lower side in the vertical direction. The extension line of the central axis CA of the second oil drain hole 3k is directed towards the side of the turbine housing 5 with respect to the lubricating oil discharge passage 3j (see Fig. 1) The extension line of the central axis CA of the second oil drain hole 3k intersects a housing wall surface 3m facing the lubricating oil discharge port 3j. Accordingly, the second oil drain hole 3k allows the lubricating oil to come into contact with the housing wall surface 3m. The lubricating oil is thus able to cool the housing wall surface 3m. The housing wall surface 3m is located, for example, on the side of the turbine housing 5 with respect to the lubricating oil discharge port 3j. Therefore, the lubricating oil discharged from the second oil drain hole 3k can cool the turbine housing 5 through the housing wall surface 3m.

[0068] In this embodiment, the outer rings 35a and 37a are arranged so that they are rotatable (freely rotatable) relative to the bearing hole 3b in the circumferential direction of the shaft 13. The outer rings 35a and 37a are arranged so that they are rotatable relative to the bearing hole 3b, allowing the pair of rolling bearings 15 to achieve a squeezing effect (a spring effect) and a wedge effect of the lubricating oil. The squeezing effect is a phenomenon whereby, due to the flow and compression of the lubricating oil, resistance forces are generated on the outer rings 35a and 37a when the vibrating outer rings 35a and 37a approach the bearing hole 3b. The wedge effect is a phenomenon in which the lubricating oil is drawn to the position where the outer rings 35a and 37a and the bearing hole 3b approach each other when the outer rings 35a and 37a rotate, and thereby resistance forces are generated on the outer rings 35a and 37a due to a flow and compression of the lubricating oil.Accordingly, in the bearing structure S of this embodiment, compared to the case where the outer rings 35a and 37a are configured to be non-rotatable with respect to the bearing hole 3b, the vibration of the shaft 13 can be absorbed (damped). Furthermore, the retaining element configured to hold the outer rings 35a and 37a (a pin to prevent rotation) is not required, thus reducing the number of components.

[0069] In the bearing structure S of this embodiment, the damping sections 39 and 41 are formed in the outer rings 35a and 37a. That is, the outer rings 35a and 37a are used as damping elements. Since the outer rings 35a and 37a are used as damping elements, it is not necessary to arrange a separate annular frame element (a so-called oil film damping element) in the bearing bore 3b. Because the damping elements are formed in the outer rings 35a and 37a, the weight of the damping elements can be reduced compared to the case where the oil film damping element is provided separately. Since the weight of the damping elements is reduced, it is possible to increase the damping force for the vibration of the shaft 13.

[0070] In this embodiment, a description is given of an example in which the second oil drain hole 3k is arranged at the position opposite the damping groove 39b in the inner circumferential surface 3f of the bearing hole 3b. However, the configuration is not limited to this, and the second oil drain hole 3k can be arranged at a position opposite the damping groove 41b in the inner circumferential surface 3f of the bearing hole 3b. In this case, the second oil drain hole 3k has one end that communicates with the damping groove 41b and another end that opens to the outside of the cylinder section 3c. Furthermore, a plurality of second oil drain holes 3k can be arranged at positions opposite the damping groove 39b and the damping groove 41b in the inner circumferential surface 3f of the bearing hole 3b.This means that it is only required that the second oil drain hole 3k is located in a position opposite at least one of the damping groove 39b or the damping groove 41b in the inner circumferential surface 3f of the bearing hole 3b. (Modification example)

[0071] Fig. Figure 4 is a schematic sectional view illustrating a configuration of a bearing structure Sa of a modification example. Components that are essentially equivalent to those of the bearing structure S of the embodiment mentioned above are designated by the same reference numerals, and a description thereof has been omitted. As in Fig. As shown in Figure 4, in the bearing structure Sa of this modification example, a pair of rolling bearings 115 are arranged in the bearing bore 3b. The pair of rolling bearings 115 comprises a turbine-side bearing 135 and a compressor-side bearing 137. The turbine-side bearing 135 has an outer ring 135a. The outer ring 135a is separated from the outer ring 35a (see Figure 4). Fig. 2) differs from the embodiment mentioned above only in that the two ring projections 39a and the damping groove 39b (see Fig. 2) are not formed. The compressor-side bearing 137 has an outer ring 137a. The outer ring 137a is separated from the outer ring 37a (see Fig. 2) differs from the embodiment mentioned above only in that the two ring projections 41a and the damping groove 41b (see Fig. 2) are not trained.

[0072] Damping grooves 139b and 141b are formed in the inner circumferential surface 3f of the bearing bore 3b (of the cylindrical section 3c) of this modification example. Damping grooves 139b and 141b each have one end connected to the connecting hole 3e and another end open to the inner circumferential surface 3f of the bearing bore 3b. Damping grooves 139b and 141b extend in an annular shape around the entire circumference of the inner circumferential surface 3f of the bearing bore 3b. Damping grooves 139b and 141b extend circumferentially around the shaft 13. Damping grooves 139b and 141b are located in the bearing bore 3b at positions opposite the outer rings 135a and 137a. The connecting holes 3e are connected to the damping grooves 139b and 141b. The connecting holes 3e are configured to allow lubricating oil to be supplied to the damping grooves 139b and 141b.The lubricating oil supplied to the damping grooves 139b and 141b flows into gaps between the outer circumferential surface of the outer rings 135a and 137a and the inner circumferential surface 3f of the bearing bore 3b. The lubricating oil forms oil films (oil film damping) between the outer circumferential surface of the outer rings 135a and 137a and the inner circumferential surface 3f of the bearing bore 3b.

[0073] The second oil drain hole 3k has one end connected to the damping groove 139b and the other end open to the outside of the cylinder section 3c. The second oil drain hole 3k is configured to allow the lubricating oil in the damping groove 139b to drain to the outside of the cylinder section 3c. Accordingly, the second oil drain hole 3k can prevent excessive accumulation of lubricating oil in the damping groove 139b. As a result, deterioration of the bearing characteristics of the turbine-side bearing 135 can be prevented.

[0074] One embodiment of the present disclosure has been described with reference to the accompanying drawings, but the present disclosure is not limited to the embodiments mentioned above. It is evident that a person skilled in the art can conceive of various modifications and alterations within the scope of the claims, and those examples are to be understood as falling within the technical scope of the present disclosure.

[0075] In the embodiment mentioned above, a description has been given of an example in which the damping grooves 39b and 41b are formed in the outer rings 35a and 37a. Furthermore, in the modification example described above, a description has been given of an example in which the damping grooves 139b and 141b are formed in the inner circumferential surface 3f of the bearing bore 3b. However, the configuration is not limited to this, and the damping grooves 39b, 41b, 139b, and 141b can be formed in both the outer circumferential surface of the outer rings 35a and 37a and the inner circumferential surface 3f of the bearing bore 3b. This means that the damping grooves 39b, 41b, 139b and 141b can be formed in at least one of the outer circumferential surface of the outer rings 35a and 37a or the inner circumferential surface 3f of the bearing hole 3b.

[0076] In the embodiment and modification example mentioned above, a description has been given of the example in which one end of the second oil drain hole 3k is formed at the position of the bearing hole 3b on the lowest side in the vertical direction. However, the configuration is not limited to this, and one end of the second oil drain hole 3k can be formed in the bearing hole 3b at a position that is on the upper vertical side relative to the lowest position in the vertical direction. However, in the bearing hole 3b, one end of the second oil drain hole 3k is formed at a position that differs from where the connecting hole 3e is connected.

[0077] In the embodiment and modification example mentioned above, a description has been given of the example in which the single second oil drain hole 3k is connected to the damping groove 39b or 139b. However, the configuration is not limited to this, and the second oil drain hole 3k can be connected to the damping groove 39b or 139b at a plurality of positions in the circumferential direction. That is, a plurality of second oil drain holes 3k can be arranged in the circumferential direction. The plurality of second oil drain holes 3k can be arranged at equal or unequal intervals in the circumferential direction.

[0078] In the embodiment and modification example mentioned above, a description has been given of an example in which the extension line of the central axis CA of the second oil drain hole 3k intersects the housing wall surface 3m. However, the configuration is not limited to this, and the extension line of the central axis CA of the second oil drain hole 3k may not intersect the housing wall surface 3m. For example, the lubricating oil discharge passage 3j can be arranged on the extension line of the central axis CA of the second oil drain hole 3k.

[0079] In the embodiment and modification example mentioned above, a description has been given of the example in which the outer rings 35a, 37a, 135a and 137a of the rolling bearings 15 and 115 are provided such that they are rotatable with respect to the bearing bore 3b. However, the configuration is not limited to this, and the outer rings 35a, 37a, 135a and 137a of the rolling bearings 15 and 115 can be provided such that they are not rotatable with respect to the bearing bore 3b.

[0080] In the embodiment and modification example mentioned above, a description has been given of the example in which the rolling bearings 15 are angular contact bearings. However, the configuration is not limited to this and the rolling bearings 15 can, for example, be deep groove ball bearings or self-aligning ball bearings.

[0081] In the embodiment and modification example mentioned above, a description has been given of the example in which the rolling bearings 15 are arranged in a duplex combination facing both sides. However, the configuration is not limited to this, and the rolling bearings 15 can be arranged in a so-called duplex combination facing both sides (a combination in which the contact angles form directions of lines that diverge from each other towards the side of the inner ring).

[0082] In the embodiment and modification example mentioned above, a description has been given of the case in which the two rolling bearings 15 are provided in the bearing hole 3b such that they are spaced apart from each other in the axial direction. However, the configuration is not limited to this, and a single rolling bearing 15 can be arranged. Furthermore, a plurality of (three or more) rolling bearings 15 can be arranged in the bearing hole 3b.

[0083] In the embodiment and modification example mentioned above, a description has been given of the example in which the bearing structure S is applied to the turbocharger TC. However, the bearing structure S is not limited to the turbocharger TC and is applicable to various rotary machines. Commercial applicability

[0084] The present disclosure can be used for the warehouse structure. Reference symbol list

[0085] CA: Centerline, S: Bearing structure, Sa: Bearing structure, 3: Bearing housing (case), 3b: Bearing hole, 3c: Cylinder section, 3d: Lubricating oil supply passage, 3e: Connecting hole, 3f: Inner circumferential surface, 3j: Lubricating oil discharge passage, 3k: Second oil drain hole (oil drain hole), 3m: Housing wall surface, 13: Shaft, 15: Rolling bearing, 35a: Outer ring, 37a: Outer ring, 39b: Damping groove, 41b: Damping groove, 115: Rolling bearing, 135a: Outer ring, 137a: Outer ring, 139b: Damping groove, 141b: Damping groove

Claims

[1] Storage structure (S), with: a housing (3) having a cylindrical section (3c) having a bearing hole (3b); a connecting hole (3e) formed and configured in the housing (3) to allow a connection between the bearing hole (3b) and a lubricating oil supply oil passage (3d); a rolling bearing (15) which is arranged in the bearing hole (3b), wherein a shaft (13) is inserted through the rolling bearing (15); a damping groove (39b) which is formed in at least one of an outer circumferential surface of an outer ring (35a) of the rolling bearing (15) or an inner circumferential surface (3f) of the bearing hole (3b) such that it extends in a circumferential direction of the shaft (13); and an oil drain hole (3k) having one end connected to the damping groove (39b) and another end open to an outside of the cylinder section (3c); characterized by , that a gap is formed between the outer circumferential surface of the outer ring (35a) and the inner circumferential surface (3f) of the bearing hole (3b), so that lubricating oil flows to the end surfaces (35e, 35f) of the outer ring (35a) in an axial direction of the shaft (13), and a smallest flow cross-sectional area of ​​the oil drain hole, which is smallest with respect to a flow cross-sectional area of ​​the oil drain hole (3k), is equal to or smaller than an area obtained by subtracting a smallest gap area of ​​one side, which is smallest with respect to a gap area defined between the outer ring (35a) and the inner circumferential surface (3f) of the bearing hole (3b) on one side of the damping groove (39b) in the axial direction of the shaft (13), and a smallest gap area of ​​the other side, which is smallest with respect to a gap area defined between the outer ring (35a) and the inner circumferential surface (3f) of the bearing hole (3b) on the other side of the damping groove (39b) in the axial direction, from a smallest flow cross-sectional area of ​​the connecting hole, which is smallest with respect to a flow cross-sectional area of ​​the connecting hole (3e). [2] Bearing structure (S) according to claim 1, wherein one end of the oil drain hole (3k) is formed at a position of the bearing hole (3b) on a bottom side in a vertical direction. [3] Bearing structure (S) according to claim 1 or 2, wherein the housing (3) has a lubricating oil delivery passage (3j) on a lower side in the vertical direction with respect to the bearing hole (3b) and wherein a line of extension of a central axis (CA) of the oil drain hole (3k) intersects a housing wall surface (3m) facing the lubricating oil delivery oil passage (3j). [4] Bearing structure (S) according to one of claims 1 to 3, wherein the outer ring (35a) is provided such that it is rotatable with respect to the bearing hole (3b).

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