Plain bearing

Abstract

To provide a sliding bearing for hardly causing cavitation erosion on the slide surface.SOLUTION: A second half-split bearing has one oil groove and two second inclined face parts on the inner diameter side. The surfaces of the second inclined face parts each include a center region and an edge region. On a boundary between the center region and the edge region, an inflection part is formed. In the center region, a convex curve is formed at the outer diameter side of the second half-split bearing. In the edge region, a convex curve is formed at the inner diameter side. On the surface of the second inclined face part, a plurality of second peripheral grooves are formed neighboring each other. A groove center line is inclined to a vertical line toward a center line passing through the width center of the axial length of the oil groove. A groove inclination angle in the edge region is minimum at the axial end of the second inclined face part, and continuously larger as coming closer to the inflection part. A groove inclination angle in the center region is minimum at a position neighboring the groove end of the second inclined face, and continuously larger as coming closer to the inclination part.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a cylindrical sliding bearing for supporting a crankshaft of an internal combustion engine, which includes a pair of split bearings.

Background Art

[0002] The crankshaft of an internal combustion engine is supported at the lower part of the cylinder block of the internal combustion engine via a main bearing composed of a pair of split bearings at its journal part. For the main bearing, lubricating oil discharged by an oil pump is fed into a lubricating oil groove formed along the inner peripheral surface of the main bearing through a through-hole formed in the wall of the main bearing from an oil gallery formed in the cylinder block wall. Further, a first lubrication oil passage is formed to penetrate in the diameter direction of the journal part, and both ends of the first lubrication oil passage are in communication with the lubricating oil groove of the main bearing. Furthermore, a second lubrication oil passage passing through the crank arm part branches off from the first lubrication oil passage of the journal part, and this second lubrication oil passage is in communication with a third lubrication oil passage formed to penetrate in the diameter direction of the crank pin. In this way, the lubricating oil fed into the lubricating oil groove formed on the inner peripheral surface of the main bearing through the through-hole from the oil gallery in the cylinder block wall passes through the first lubrication oil passage, the second lubrication oil passage, and the third lubrication oil passage, and is supplied from a discharge port opened at the end of the third lubrication oil passage to the sliding surface between the crank pin and the connecting rod bearing composed of a pair of split bearings (see, for example, Patent Document 1). Oil is supplied between the surface of the crankshaft and the sliding surfaces of the main bearing and the connecting rod bearing.

[0003] Conventionally, for the purpose of equalizing the pressure (load) distribution on the sliding surface of a split bearing, a split bearing provided with a recess formed such that the central side is recessed rather than the end side in the axial direction of the split bearing has been proposed (see, for example, Patent Documents 2 and 3).

[0004] However, in conventional recesses, circumferential grooves are not formed on the surface of the recess, making it difficult for circumferential flow to occur in the lubricating oil within the recess. As a result, the cavity in the lubricating oil tends to diffuse outward in the axial direction of the split bearing within the recess. Furthermore, since conventional recesses are formed only by a convex curved surface extending from the sliding surface toward the outer diameter side of the split bearing (unlike the present invention), it is difficult for flow to occur that pushes the lubricating oil, including the cavity present near the axial end, toward the crankshaft within the recess where the gap between the crankshaft and the sliding surface of the split bearing is narrow. This leads to a problem where cavitation erosion is likely to occur on the surface of the recess near the axial end. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-277831 [Patent Document 2] Special Publication No. 2013-536924 [Patent Document 3] Japanese Utility Model Publication No. 2-41717 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide a sliding bearing for the crankshaft of an internal combustion engine that is less susceptible to cavitation erosion on the sliding surface near the axial end of the split bearing. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides a sliding bearing for rotatably supporting the crankshaft of an internal combustion engine, The sliding bearing has first and second split bearings that are combined to form a cylindrical shape, and the first and second split bearings have a sliding surface on the inner diameter side and a back surface on the outer diameter side. The aforementioned back surface is parallel to the axial direction of the first and second split bearings. The first and second split bearings have circumferential end faces on both sides in the circumferential direction, The first and second split bearings have axial end faces at both ends in the axial direction, The second split bearing has one oil groove on its inner diameter side, the oil groove is located between the two axial end faces of the second split bearing, extends in the circumferential direction, and has a constant axial length W1. The oil groove has groove ends at both ends in the axial direction, The sliding surface of the second split bearing has two second inclined surfaces, the second inclined surfaces are adjacent to each other along the entire circumferential length of each groove end, and have a constant axial length W2, and the surfaces of the second inclined surfaces are displaced so as to continuously approach the back surface from each axial end face towards the groove end. The surface of the second inclined surface portion includes a central region adjacent to the groove end and an edge region adjacent to the central region and located closer to each axial end face of the second split bearing than the central region. There is an inflection portion at the boundary between the central region and the edge region. The central region, in a cross-sectional view of the second split bearing in the axial direction, forms a curve that is convex toward the outer diameter side of the second split bearing. The edge region, in a cross-sectional view of the second split bearing in the axial direction, forms a curve that is convex toward the inner diameter side of the second split bearing. Multiple second circumferential grooves are formed adjacent to each other on the surface of the second inclined surface, and these multiple second circumferential grooves are formed along the entire circumferential length of the surface of the second inclined surface, and these multiple second circumferential grooves are formed along the entire width of the surface of the second inclined surface, and when viewed in cross-section in the axial direction of the second split bearing, the second circumferential grooves have curved groove surfaces, and vertices are formed between adjacent groove surfaces, and the curve connecting the vertices represents the surface of the second inclined surface. The groove width of the second circumferential groove is defined as the length of a hypothetical straight line connecting the tops on both sides of the second circumferential groove, the groove centerline is defined as a line passing through the midpoint of the length of the hypothetical straight line and extending perpendicularly to the hypothetical straight line, the groove depth of the second circumferential groove is defined as the length perpendicular to the hypothetical straight line to the position where the groove surface is furthest from the hypothetical straight line, and the position of the maximum groove depth of the second circumferential groove is located on the groove centerline. The area enclosed by the virtual straight line and the groove surface is defined as the groove cross-sectional area, and the groove width, groove depth, and groove cross-sectional area of ​​the plurality of second circumferential grooves are the same as each other, and the groove width, groove depth, and groove cross-sectional area of ​​the second circumferential grooves are the same at any position in the circumferential direction. The angle between the perpendicular line extending from the surface of the second inclined surface portion so as to be perpendicular to the axis of the split bearing and the groove center line is defined as the groove inclination angle θ1. The present invention provides a sliding bearing in which the groove centerline on the surface of the second inclined surface passes through the center of the width of the axial length of the oil groove and is inclined with respect to the perpendicular toward the centerline extending in the circumferential direction, the groove inclination angle θ1 in the edge region is minimum at the axial end of the second inclined surface and continuously increases as it approaches the inflection portion, and the groove inclination angle θ1 in the central region is minimum at a position adjacent to the groove end of the second inclined surface and continuously increases as it approaches the inflection portion.

[0008] In another embodiment of the present invention, the edge region of the second inclined surface is adjacent to the axial end face of the second split bearing.

[0009] In another embodiment of the present invention, the width W2C of the central region of the second inclined surface is 25% or more and 75% or less of the width W2 of the second inclined surface.

[0010] In another embodiment of the present invention, the depth D2 of the second inclined surface is 0.005 mm or more and 0.050 mm or less.

[0011] In another embodiment of the present invention, the groove depth D3 of the second circumferential groove is 1.5 μm or more and 10 μm or less.

[0012] In another embodiment of the present invention, the groove width W3 of the second circumferential groove is 0.05 mm or more and 0.25 mm or less.

[0013] In another embodiment of the present invention, the groove inclination angle θ1 of the second circumferential groove closest to the inflection portion of the second inclined surface is greater than the groove inclination angle θ1 of the second circumferential groove closest to the groove end by a value in the range of 0.001° to 7°.

[0014] In another embodiment of the present invention, the groove inclination angle θ1 of the second circumferential groove closest to the inflection portion of the second inclined surface is greater than the groove inclination angle θ1 of the second circumferential groove closest to the axial end of the second inclined surface by a value in the range of 0.001° to 7°.

[0015] In another embodiment of the present invention, the first split bearing has a center line that passes through the center of the width of the axial length of the first split bearing and extends in the circumferential direction, the sliding surface of the first split bearing has two first inclined surfaces, the first inclined surfaces are adjacent to the center line and have a constant axial length W5 from the center line toward each axial end face, and extend over the entire circumferential length of the first split bearing, and the surfaces of the first inclined surfaces are displaced to continuously approach the back surface toward the groove end from each axial end face, The surface of the first inclined surface portion includes a central region adjacent to the center line of the first split bearing and an edge region adjacent to the central region and located closer to each axial end face of the first split bearing than the central region. There is an inflection portion at the boundary between the central region and the edge region. The central region, in a cross-sectional view of the first split bearing in the axial direction, forms a curve that is convex toward the outer diameter side of the first split bearing. The edge region forms a convex curve on the inner diameter side of the first half bearing in a cross-sectional view in the axial direction of the first half bearing. On the surface of the first inclined surface portion, a plurality of first circumferential grooves are formed adjacent to each other. The plurality of first circumferential grooves are formed over the entire circumferential length of the surface of the first inclined surface portion. The plurality of first circumferential grooves are formed over the entire width of the surface of the first inclined surface portion. The first circumferential groove has a curved groove surface when viewed in a cross-section in the axial direction of the first half bearing. Tops are formed between adjacent groove surfaces, and a curve connecting the tops represents the surface of the first inclined surface portion. The groove width of the first circumferential groove is defined as the length of a virtual straight line linearly connecting the tops on both sides of the first circumferential groove. The groove center line is defined as a line passing through the central position of the length of the virtual straight line and extending in a direction perpendicular to the virtual straight line. The groove depth of the first circumferential groove is defined as the length in a direction perpendicular to the virtual straight line from the virtual straight line to the position where the groove surface is most separated. The position of the maximum groove depth of the first circumferential groove is located on the groove center line. The area surrounded by the virtual straight line and the groove surface is defined as the groove cross-sectional area. The groove widths, the groove depths, and the groove cross-sectional areas of the plurality of first circumferential grooves are the same as each other. The groove widths, the groove depths, and the groove cross-sectional areas of the first circumferential groove are the same at any position in the circumferential direction. An angle formed between a perpendicular line extending from the surface of the first inclined surface portion so as to be orthogonal to the axis of the half bearing and the groove center line is defined as a groove inclination angle θ2. The groove center line on the surface of the first inclined surface portion is inclined with respect to the perpendicular line toward the center line of the first half bearing. The groove inclination angle θ2 in the edge region is minimum at the axial end portion of the first inclined surface portion, and continuously increases as it approaches the bending portion. The groove inclination angle θ2 in the central region is minimum at a position adjacent to the center line of the first half bearing, and continuously increases as it approaches the bending portion.

[0016] In another embodiment of the present invention, an edge region of the first inclined surface portion is adjacent to an axial end surface of the first half bearing.

[0017] In another embodiment of the present invention, an axial length obtained by summing axial lengths W5 of the two first inclined surface portions of the first half bearing is an axial length W7, an axial length obtained by summing axial lengths W2 of the two second inclined surface portions of the second half bearing and an axial length W1 of the oil groove is an axial length W4, and the axial length W7 and the axial length W4 are the same.

[0018] In another embodiment of the present invention, a width W5C of a central region of the first inclined surface portion is 25% or more and 75% or less of a width W5 of the first inclined surface portion.

[0019] In another embodiment of the present invention, a depth D4 of the first inclined surface portion is 0.005 mm or more and 0.050 mm or less.

[0020] In another embodiment of the present invention, a groove depth D5 of the first circumferential groove is 1.5 μm or more and 10 μm or less.

[0021] In another embodiment of the present invention, a groove width W6 of the first circumferential groove is 0.05 mm or more and 0.25 mm or less.

[0022] In another embodiment of the present invention, a groove inclination angle θ2 of the first circumferential groove closest to an inflection portion of the first inclined surface portion is larger by a value in a range of 0.001° or more to 7° or less than a groove inclination angle θ1 of the first circumferential groove closest to a center line of the first half bearing.

[0023] In another embodiment of the present invention, a groove inclination angle θ2 of the first circumferential groove closest to an inflection portion of the first inclined surface portion is larger by a value in a range of 0.001° or more to 7° or less than a groove inclination angle θ2 of the first circumferential groove closest to an axial end portion of the first inclined surface portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] [Figure 1] This is a schematic diagram showing the bearing system of the crankshaft. [Figure 2] This is a view of a sliding bearing according to a first specific example of the present invention, as seen from the axial direction of the bearing. [Figure 3] Figure 2 is a plan view of the first split bearing as seen from the sliding surface side. [Figure 4] Figure 2 is a plan view of the second split bearing as seen from the sliding surface side. [Figure 5] This is a cross-sectional view AA in Figure 3. [Figure 6] Figure 4 is a cross-sectional view of BB. [Figure 7] This is an enlarged view of Figure 6. [Figure 8A] This is an enlarged cross-sectional view of the second circumferential groove (θ1 is near its minimum). [Figure 8B] This is an enlarged cross-sectional view of the second circumferential groove (θ1 is near its maximum). [Figure 9A] This is a cross-sectional view illustrating the operation of the present invention. [Figure 9B] This is a plan view illustrating the operation of the present invention. [Figure 10A] This is a cross-sectional view illustrating the operation of the present invention (CC cross-sectional view in Figure 9B). [Figure 10B] This is a plan view illustrating the operation of the present invention. [Figure 10C] This is a component breakdown diagram showing the state in which the F1(v) component of the oil flow F1 is relatively larger than the F1(h) component. [Figure 10D] This is a component breakdown diagram showing the state in which the F1(h) component of the oil flow F1 is relatively larger than the F1(v) component. [Figure 11] This is a cross-sectional view of a split bearing, different from the specific example shown. [Figure 12] This is a plan view of the first split bearing according to a second specific example of the present invention, as seen from the sliding surface side. [Figure 13] Figure 12 is a cross-sectional view of the DD. [Figure 14] This is an enlarged view of Figure 13. [Figure 15A]This is an enlarged cross-sectional view of the first circumferential groove (θ2 is near its minimum). [Figure 15B] This is an enlarged cross-sectional view of the first circumferential groove (θ2 is near its maximum). [Figure 16A] This is a cross-sectional view illustrating the operation of the present invention. [Figure 16B] This is a plan view illustrating the operation of the present invention. [Figure 17A] This is a cross-sectional view illustrating the operation of the present invention (EE cross-sectional view in Figure 16B). [Figure 17B] This is a plan view illustrating the operation of the present invention. [Figure 17C] This is a component breakdown diagram showing the state in which the F1(v) component of the oil flow F1 is relatively larger than the F1(h) component. [Figure 17D] This is a component breakdown diagram showing the state in which the F1(h) component of the oil flow F1 is relatively larger than the F1(v) component. [Figure 18] This is a cross-sectional view of a split bearing, different from the specific example shown. [Modes for carrying out the invention]

[0025] The first specific example of the present invention will be described below with reference to the drawings.

[0026] Figure 1 schematically shows a bearing device 1 of an internal combustion engine. This bearing device 1 comprises a journal portion 6 supported at the lower part of the cylinder block 8, a crankpin 5 formed integrally with the journal portion 6 and rotating about the journal portion 6, and a connecting rod 2 that transmits reciprocating motion from the internal combustion engine to the crankpin 5. Furthermore, the bearing device 1 includes a main bearing 4 that rotatably supports the journal portion 6 and a connecting rod bearing 3 that rotatably supports the crankpin 5, as sliding bearings that support the crankshaft.

[0027] Although the crankshaft has multiple journal sections 6 and multiple crankpins 5, for the sake of explanation, only one journal section 6 and one crankpin 5 will be shown in the diagram. In Figure 1, the positional relationship in the depth direction of the paper is such that the journal section 6 is at the back of the paper and the crankpin 5 is at the front.

[0028] The journal section 6 is pivotally supported in the lower part 82 of the cylinder block of the internal combustion engine via a main bearing 4, which is composed of a pair of split bearings 41 and 42. In Figure 1, the upper split bearing 42 has an oil groove 42a formed along the entire length of its inner circumferential surface. The journal section 6 also has a lubrication oil passage 6a that penetrates in the diametrical direction, and when the journal section 6 rotates in the direction of arrow X, the inlet openings 6c at both ends of the lubrication oil passage 6a alternately communicate with the oil groove 42a of the main bearing 4.

[0029] The crankpin 5 is pivotally supported in the big end housing 21 of the connecting rod 2 (rod-side big end housing 22 and cap-side big end housing 23) via a connecting rod bearing 3, which is composed of a pair of split bearings 31 and 32.

[0030] As described above, lubricating oil discharged by the oil pump is sent to the main bearing 4 from the oil gallery formed in the cylinder block wall through a through-hole formed in the wall of the main bearing 4 into the oil groove 42a formed along the inner circumferential surface of the main bearing 4.

[0031] Furthermore, a first lubrication passage 6a is formed through the journal portion 6 in the diametrical direction, and the inlet opening 6c of the first lubrication passage 6a is in communication with the lubrication groove 42a. A second lubrication passage 5a is formed branching from the first lubrication passage 6a of the journal portion 6 and passing through the crank arm portion (not shown), and the second lubrication passage 5a is in communication with a third lubrication passage 5b formed through the crank pin 5 in the diametrical direction.

[0032] In this way, the lubricating oil is supplied through the first lubricating oil passage 6a, the second lubricating oil passage 5a, and the third lubricating oil passage 5b, and then from the discharge port 5c at the end of the third lubricating oil passage 5b into the gap formed between the crankpin 5 and the connecting rod bearing 3.

[0033] First example The following describes an example in which the sliding bearing of the present invention is applied to a connecting rod bearing 3. However, the present invention is not limited to a connecting rod bearing 3 and can also be applied to a main bearing 4.

[0034] Figure 2 shows a first specific example of a sliding bearing (connecting rod bearing 3) according to the present invention. The connecting rod bearing 3 is formed by butting the circumferential end faces 76 of a pair of first split bearings 31 and second split bearings 32 together to form a cylindrical shape overall. The surface forming the inner circumferential surface of the cylindrical shape is the sliding surface 7, and the surface forming the outer circumferential surface is the back surface.

[0035] The wall thickness of the first split bearing 31 and the second split bearing 32 is constant in the circumferential direction. However, the wall thickness may be maximum at the center in the circumferential direction and continuously decrease toward both end faces 76, 76 in the circumferential direction.

[0036] In small internal combustion engines for passenger cars and commercial vehicles, the outer diameters of the first split bearing 31 and the second split bearing 32 are approximately 30 mm to 150 mm, the axial width is approximately 10 mm to 50 mm, and the wall thickness is approximately 1.5 mm to 3 mm. In medium-sized internal combustion engines for industrial use, the outer diameter is approximately 150 mm to 350 mm, the axial width is approximately 50 mm to 150 mm, and the wall thickness is approximately 3 mm to 8 mm. Note that these dimensions are examples and other dimensions are possible.

[0037] Figure 3 is a view of the first split bearing 31 from the sliding surface 7 side. The first split bearing 31 has axial end faces 7E, 7E.

[0038] Figure 5 is a cross-sectional view of the first split bearing 31 as seen from section AA (axial section) in Figure 3. The sliding surface 7 of the first split bearing 31 is parallel to the back surface of the first split bearing in the axial section.

[0039] Figure 4 is a view of the second split bearing 32 from the sliding surface 7 side. The second split bearing 32 has axial end faces 7E, 7E. The second split bearing 32 also has an oil groove 32a extending in the circumferential direction formed on the sliding surface 7, and the oil groove 32a has groove ends 32E, 32E at both ends in the axial direction. The oil groove 32a opens to both circumferential end faces 76, 76 of the second split bearing 32. Here, a center line WC2 is defined that passes through the center of the width of the axial length of the second split bearing 32 and extends in the circumferential direction. Also, a center line 32C is defined that passes through the center of the width of the axial length of the oil groove 32a and extends in the circumferential direction. Here, the center line WC2 of the second split bearing 32 is aligned with the center line 32C of the oil groove 32a. Note that the oil groove 32a may be formed to open to at least one of the circumferential end faces 76, 76.

[0040] Figure 6 is a cross-sectional view of the second split bearing 32 as seen from the BB cross-section (axial cross-section) of Figure 4. The sliding surface 7 of the second split bearing 32 has two adjacent second inclined surfaces 71, 71 that extend along the entire circumferential length of both ends 32E, 32E of the oil groove 32a, and the two second inclined surfaces each have a surface 71S, 71S. Each surface 71S, 71S of the second inclined surface is displaced continuously from the axial ends 71E, 71E of the second inclined surface toward the ends 32E, 32E of the oil groove, approaching the back surface of the second split bearing 32. Here, the axial ends 71E, 71E of the second inclined surface are adjacent to the axial end faces 7E, 7E of the second split bearing 32.

[0041] Next, the axial cross-sectional shape of the second split bearing 32 will be described in detail using Figures 7, 8A, and 8B.

[0042] Figure 7 is an enlarged view of Figure 6 and shows the axial cross-sectional shape of the second split bearing 32. The second inclined surface portion 71 includes a central region 711 adjacent to the groove end 32E and an edge region 712 adjacent to the central region 711 and located closer to the axial end face 7E of the second split bearing than the central region 711. There is an inflection portion 71P at the boundary between the central region 711 and the edge region 712. Here, the second inclined surface portion 71, the central region 711, and the edge region 712 each have a constant axial length W2, W2C, and W2E, respectively. Also, the sum of the axial lengths W1 of the two second inclined surfaces W2, W2 and the oil groove 32a of the second split bearing 32 is W4.

[0043] Here, the oil groove 32a has a rectangular cross-section consisting of a groove width W1 and a groove depth D1. The groove width W1 is defined as the distance parallel to the back surface of the second split bearing 32. The groove depth D1 is defined as the distance from the groove end 32E of the oil groove 32a to the bottom surface of the oil groove 32a in a direction perpendicular to the back surface of the second split bearing 32. Here, the groove width W1 is approximately 10% to 30% of the axial width of the second split bearing 32, and the groove depth D1 is approximately 30% to 70% of the wall thickness of the second split bearing 32. Note that these dimensions are examples, and other dimensions can be used.

[0044] The width W2 of the second inclined surface is defined as the distance parallel to the back surface of the second split bearing 32. The width W2 of the second inclined surface is decomposed into the width W2C of the central region and the width W2E of the edge region. Here, the width W2C of the central region is 25% or more and 75% or less of the width W2 of the second inclined surface.

[0045] The central region 711 has a curve that is convex toward the outer diameter side of the second split bearing 32. The edge region 712 has a curve that is convex toward the inner diameter side of the second split bearing 32. The depth D2 of the second inclined surface is maximum at the portion adjacent to the groove end 32E of the oil groove and minimum (zero) at the axial end 71E of the second inclined surface. The depth D2 of the second inclined surface is defined as the length from the axial end 71E of the second inclined surface to the groove end 32E of the oil groove in a direction perpendicular to the back surface of the second split bearing 32. Here, the depth D2 of the second inclined surface is between 0.005 mm and 0.050 mm.

[0046] Multiple second circumferential grooves 72 are formed adjacent to each other on the surface 71S of the second inclined surface of the second split bearing 32. The multiple second circumferential grooves 72 extend parallel to the circumferential direction and are formed along the entire circumferential length of the surface 71S. Furthermore, the second circumferential grooves 72 are formed along the entire width of the surface 71S. It is permissible for the second circumferential grooves 72 to be slightly inclined (maximum 1°) with respect to the circumferential direction of the second split bearing 32. For ease of understanding, the second circumferential grooves 72 are depicted in an exaggerated manner in each drawing.

[0047] The second circumferential groove 72 has a curved groove surface 721 when viewed in the axial cross-section of the second split bearing 32. A vertex 722 is formed between the concave surfaces 721 of adjacent second circumferential grooves 72. The curve connecting the vertices 722 represents the surface 71S of the second inclined surface. Microscopically, there are no flat regions on the surface 71S of the second inclined surface.

[0048] Figures 8A and 8B show enlarged views of the second circumferential groove 72 in Figure 7. Figure 8A shows the shape of the second circumferential groove 72 near the groove end 32E of the oil groove in the central region 711 of the second inclined surface portion 71, and the shape of the second circumferential groove 72 near the axial end 71E of the second inclined surface portion in the edge region 712. Figure 8B shows the shape of the second circumferential groove 72 near the inflection portion 71P in the central region 711 of the second inclined surface portion 71, and the shape of the second circumferential groove 72 near the inflection portion 71P in the edge region 712. The groove width W3 of the second circumferential groove 72 is defined as the length of a virtual straight line 723 that linearly connects the tops 722 on both sides of the second circumferential groove 72. The groove centerline 724 is defined as a line that passes through the midpoint of the length of the virtual straight line 723 and extends perpendicular to the virtual straight line 723. The groove depth D3 of the second circumferential groove 72 is defined as the length from the virtual straight line 723 to the point where the groove surface 721 is furthest away, perpendicular to the virtual straight line 723. The position of the maximum groove depth D3 of the second circumferential groove 72 lies on the groove centerline 724. Here, the groove depth D3 of the second circumferential groove 72 is between 1.5 μm and 10 μm. The groove width W3 of the second circumferential groove 72 is between 0.05 mm and 0.25 mm.

[0049] The area enclosed by the virtual straight line 723 and the groove surface 721 is defined as the groove cross-sectional area 72A. The groove width W3, groove depth D3, and groove cross-sectional area 72A of each second circumferential groove 72 are the same as those of the other. Furthermore, the groove width W3, groove depth D3, and groove cross-sectional area 72A of the second circumferential groove 72 are the same at any position in the circumferential direction.

[0050] Furthermore, the shape of the groove surface 721 of each second circumferential groove 72 is formed symmetrically with respect to the groove centerline 724. The two groove cross-sectional areas that divide the groove cross-sectional area 72A of each second circumferential groove 72 by the groove centerline 724 are equal to each other.

[0051] The angle between the perpendicular line VL1, which extends from the surface 71S of the second inclined surface portion so as to be perpendicular to the axis of the second split bearing 32, and the groove centerline 724 of the second circumferential groove 72 is defined as the groove inclination angle θ1. The groove centerlines 724 of all second circumferential grooves 72 on the second inclined surface portion 71 are inclined toward the centerline 32C of the oil groove 32a with respect to the perpendicular line VL1.

[0052] In the central region 711 of the second inclined surface portion 71, the second circumferential groove 72 closest to the groove end 32E of the oil groove has the smallest groove inclination angle θ1 (see Figure 8A), and the second circumferential groove 72 closest to the inflection portion 71P has the largest groove inclination angle θ1 (see Figure 8B). Therefore, the groove inclination angle θ1 continuously increases as it approaches the inflection portion 71P from the groove end 32E of the oil groove (as it moves outward in the axial direction). Here, the groove inclination angle θ1 of the second circumferential groove 72 closest to the inflection portion 71P of the second inclined surface portion 71 is greater than the groove inclination angle θ1 of the second circumferential groove closest to the groove end 32E by a value in the range of 0.001° to 7°.

[0053] In the edge region 712 of the second inclined surface portion 71, the second circumferential groove 72 closest to the inflection portion 71P has the maximum groove inclination angle θ1 (see Figure 8B), and the second circumferential groove 72 closest to the axial end portion 71E of the second inclined surface portion has the minimum groove inclination angle θ1 (see Figure 8A). Therefore, the groove inclination angle θ1 continuously decreases as it approaches the axial end portion 71E of the second inclined surface portion from the inflection portion 71P (as it moves axially outward). Here, the groove inclination angle θ1 of the second circumferential groove 72 closest to the inflection portion 71P of the second inclined surface portion 71 is greater than the groove inclination angle θ1 of the second circumferential groove 72 closest to the axial end portion 71E of the second inclined surface portion 71 by a value in the range of 0.001° to 7°.

[0054] The connecting rod bearing 3 in this specific example is formed by butting the circumferential end faces 76 of a pair of first split bearings 31 and second split bearings 32 together to form a cylindrical shape overall. The split bearings 31 and 32 may have a sliding layer made of Cu bearing alloy or Al bearing alloy. Alternatively, they may have a sliding layer made of Cu bearing alloy or Al bearing alloy on a backing layer made of Fe alloy. Furthermore, they may have a sliding layer consisting of a surface portion made of Cu bearing alloy or Al bearing alloy and one of the soft Bi, Sn, or Pb, or an alloy mainly composed of these metals, or a surface portion made of a resin composition mainly composed of synthetic resin, which is positioned on the sliding surface side of the bearing alloy.

[0055] Next, the operation of the sliding bearing 3 of the present invention will be explained with reference to Figures 9A to 10D.

[0056] During operation of an internal combustion engine, the gap S between the surface of the crankpin 5 and the sliding surface 7 of the second split bearing 32 is constantly fluctuating due to the effects of the explosion pressure in the cylinder and the centrifugal force associated with the rotation of the crankshaft. Furthermore, the lubricating oil present in the gap S near the axial center of the sliding surface 7 of the first split bearing 31 flows over the circumferential end face 76 and into the gap S near the axial center of the second split bearing 32 as the crankpin 5 rotates. At this time, the lubricating oil passes through a discontinuity formed by the sliding surface 7 of the first split bearing 31 and the oil groove 32a of the second split bearing 32. As a result, turbulence of the lubricating oil occurs in the oil groove 32a near the circumferential end face 76, and a cavity 9 is created in the lubricating oil due to pressure fluctuations.

[0057] Figure 9A shows a cross-sectional view of the connecting rod bearing 3 near the circumferential end face 76. Figure 9B shows Figure 9A viewed from the sliding surface 7 side. Figures 9A and 9B show the state in which the sliding surface 7 of the connecting rod bearing 3 and the surface of the crankpin 5 move from a separated state to a relatively close state during the operation of the internal combustion engine. When the sliding surface 7 and the surface of the crankpin 5 move from a separated state to a relatively close state, the lubricating oil present in the gap S is pressed toward the sliding surface 7 side. As a result, the cavity 9 created in the oil groove 32a moves toward the inside side of the oil groove 32a (the outer diameter side of the second split bearing 32) together with the lubricating oil.

[0058] Figure 10A is a cross-section of CC in Figure 9B, showing the vicinity of the second inclined surface 71. Here, the flow of lubricating oil, including the cavity 9 which has moved as if being pushed into the oil groove 32a, reverses direction when it reaches the bottom of the oil groove 32a, creating a backflow R. This is because the lubricating oil cannot move toward the outer diameter side of the second split bearing 32 beyond the bottom of the groove. Therefore, the lubricating oil, including the cavity 9, moves as if being pushed toward the axial end face 7E side of the second split bearing 32.

[0059] Furthermore, when the surface of the crankpin 5 approaches the sliding surface 7, the oil flowing circumferentially through the gap S between the surface 71S of the second inclined surface and the surface of the crankpin 5 is pressed by the surface of the crankpin 5 toward the interior of the multiple second circumferential grooves 72 on the surface 71S of the second inclined surface. The oil in each second circumferential groove 72 is pushed by the oil flowing in from behind, increasing its pressure and not only flows circumferentially within the second circumferential groove 72 but also flows toward the crankpin 5 (reverse flow), forming an oil flow F1. Here, the groove centerline 724 of each second circumferential groove 73 on the surface 71S of the second inclined surface is inclined toward the centerline 32C of the oil groove 32a. Therefore, the oil flow F1 flowing out from within the second circumferential groove 72 mainly flows inclined toward the surface of the crankpin 5 and toward the centerline 32C of the oil groove 32a. Furthermore, at this time, an oil flow F2 is formed in the circumferential direction in the gap S between the surface 71S of the second inclined surface portion and the surface of the crankpin 5, accompanying the surface of the rotating crankpin 5 (see Figure 10B. Figure 10B is a view of Figure 10A from the sliding surface 7 side of the second split bearing 32).

[0060] The cavity 9, pushed out by the reverse flow R, is carried along with the lubricating oil through the gap S towards the front side in the rotational direction Z of the crankpin by the oil flows F1 and F2. Since the central region 711 of the second inclined surface portion 71 where the cavity 9 is located has a curve that is convex toward the outer diameter side of the second split bearing 32, the oil flow F1 has the following components.

[0061] As shown in Figures 10C and 10D, the oil flow F1 is decomposed into a component F1(v) directed toward the surface side of the crankshaft 5 and a component F1(h) directed toward the center line 32C side of the oil groove 32a. In the central region 711, the oil flow F1 flowing out from the second circumferential groove 72 near the groove end 32E of the oil groove of the second inclined surface portion 71 has a relatively large F1(v), as shown in Figure 10C.

[0062] On the other hand, in the central region 711, the oil flow F1 flowing out from the second circumferential groove 72 near the inflection portion 71P of the second inclined surface portion 71 has a relatively large F1(h), as shown in Figure 10D.

[0063] In the central region 711, the flow component of the oil flow F1 flowing out from the second circumferential groove 72 located between the groove end 32E and the inflection portion 71P continuously changes from the flow component shown in Figure 10C to the flow component shown in Figure 10D, moving from the groove end 32E toward the inflection portion 71P (towards the axially outward direction of the second split bearing 32). With this structure, the oil flow F1 in the central region 711 of the second inclined surface portion 71 presses the lubricating oil present in the central region 711, together with the cavity 9, toward the center line 32C of the oil groove 32a and toward the surface of the crankpin 5. As the pressure of the lubricating oil in the pressed central region 711 increases, the cavity 9 contained within the lubricating oil collapses prematurely within the central region 711 due to the return of pressure. Therefore, the cavity 9 is prevented from flowing into the edge region 712 of the second inclined surface portion 71. Therefore, the cavity 9 collapses near the surface 71S of the edge region 712 where the gap S narrows, preventing cavitation erosion from occurring on the surface 71S of the edge region 712. At this time, the cavity 9 in the central region 711 is pushed up towards the surface of the crankpin 5 along with the lubricating oil, and is separated from the surface 71S of the central region 711. Also, on the side of the center line 32C of the oil groove 32a where the cavity 9 is pressed and moved, the depth D2 of the second inclined surface is deepest. Therefore, when the cavity 9 collapses in the central region 711, the occurrence of cavitation erosion on the surface 71S of the central region 711 and the groove surface 721 is prevented.

[0064] Furthermore, since the edge region 712 of the second inclined surface portion 71 has a curve that is convex toward the inner diameter side of the second split bearing 32, the oil flow F1 has the following components.

[0065] In the edge region 712, the oil flow F1 flowing out from the second circumferential groove 72 near the inflection portion 71P of the second inclined surface portion 71 has a relatively large F1(h), as shown in Figure 10D.

[0066] On the other hand, in the edge region 712, the oil flow F1 flowing out from the second circumferential groove 72 near the axial end 71E of the second inclined surface portion has a relatively large F1(v), as shown in Figure 10C.

[0067] Therefore, even if the cavity 9 in the central region 711 does not completely collapse within the central region 711, and some flows into the edge region 712, near the inflection portion 71P of the edge region 712, the cavity 9 is pressed toward the center line 32C of the oil groove 32a along with the lubricating oil. In this way, there is an effect of pushing the cavity 9 that has flowed into the edge region 712 back into the central region 711. Furthermore, even if the cavity 9 reaches near the axial end 71E of the edge region 712, near the axial end 71E of the edge region 712, the cavity 9 is pressed toward the surface side of the crankpin 5 along with the lubricating oil. Therefore, it is possible to collapse the cavity 9 by repressure within the gap S spaced apart from the surface 71S of the edge region 712, and the occurrence of cavitation erosion on the surface 71S of the edge region 712 and the groove surface 721 is prevented.

[0068] The width W2C of the central region of the second inclined surface is preferably 25% or more and 75% or less of the width W2 of the second inclined surface. If the width W2C of the central region is less than 25% of the width W2 of the second inclined surface, the cavity 9 is less likely to be pressed toward the surface side of the crankpin 5 together with the lubricating oil near the groove end 32E of the oil groove 32. As a result, the cavity 9 is more likely to collapse in the gap S close to the surface 71S of the central region 711, and cavitation erosion is more likely to occur on the surface 71S of the central region 711 and the groove surface 721 near the groove end 32E. If the width W2C of the central region exceeds 75% of the width W2 of the second inclined surface, the cavity 9 is less likely to be pressed toward the surface side of the crankpin 5 together with the lubricating oil near the axial end 71E of the second inclined surface. Therefore, the cavity 9 is prone to collapse within the gap S near the surface 71S of the edge region 712, and cavitation erosion is likely to occur on the surface 71S of the edge region 712 and the groove surface 721 near the axial end 71E.

[0069] The depth D2 of the second inclined surface is preferably 0.005 mm or more and 0.050 mm or less. If the depth D2 of the second inclined surface is less than 0.005 mm, even if the cavity 9 is pressed by the oil flow F1, the gap S between the surface 71S of the second inclined surface and the surface of the crankpin 5 is narrow, making it easy for the cavity 9 to collapse near the surface 71S of the second inclined surface, and cavitation erosion to occur in that area. If the depth D2 of the second inclined surface exceeds 0.050 mm, oil film breakdown is likely to occur in the second inclined surface, and seizure is likely to occur.

[0070] The groove depth D3 of the second circumferential groove 72 is preferably 1.5 μm or more and 10 μm or less. The groove width W3 of the second circumferential groove 72 is preferably 0.05 mm or more and 0.25 mm or less. If the groove depth D3 of the second circumferential groove 72 exceeds 10 μm, or if the groove width W3 exceeds 0.25 mm, the oil flow F1 will be weakened. Also, if the groove depth D3 of the second circumferential groove 72 is less than 1.5 μm, or if the groove width W3 is less than 0.05 mm, the amount of oil flow F1 flowing from each second circumferential groove 72 into the gap S between the surface 71S of the second inclined surface and the surface of the crankpin 5 will be reduced. As a result, the cavity 9 may not be sufficiently pressed.

[0071] Preferably, the groove inclination angle θ1 of the second circumferential groove 72 closest to the inflection portion 71P of the second inclined surface portion 71 is greater than the groove inclination angle θ1 of the second circumferential groove 72 closest to the groove end portion 32E by a value in the range of 0.001° to 7°. If the groove inclination angle θ1 of the second circumferential groove 72 closest to the inflection portion 71P is greater than the groove inclination angle θ1 of the second circumferential groove 72 closest to the groove end portion 32E by a value of less than 0.001°, the F1(h) component of the oil flow F1 flowing out from the second circumferential groove 72 of the central region 711 becomes insufficient. As a result, the cavity 9 is less likely to be pressed toward the center line 32C side of the oil groove 32a, and the cavity 9 is more likely to flow out into the edge region 712. Furthermore, if the groove inclination angle θ1 of the second circumferential groove 72 closest to the inflection portion 71P is greater than the groove inclination angle θ1 of the second circumferential groove 72 closest to the groove end 32E by more than 7°, the F1(v) component of the oil flow F1 flowing out from the second circumferential groove 72 in the central region 711 becomes insufficient. As a result, the cavity 9 is less likely to be pressed toward the surface side of the crankpin 5, and the cavity 9 is more likely to collapse near the surface 71S and groove surface 721 of the central region 711.

[0072] Preferably, the groove inclination angle θ1 of the second circumferential groove 72 closest to the inflection portion 71P of the second inclined surface portion 71 is greater than the groove inclination angle θ1 of the second circumferential groove 72 closest to the axial end portion 71E of the second inclined surface portion 71 by a value in the range of 0.001° to 7°. If the groove inclination angle θ1 of the second circumferential groove 72 closest to the inflection portion 71P is greater than the groove inclination angle θ1 of the second circumferential groove 72 closest to the axial end portion 71E of the second inclined surface portion 71 by less than 0.001°, the F1(h) component of the oil flow F1 flowing out from the second circumferential groove 72 near the inflection portion 71P of the edge region 712 becomes too small. As a result, it becomes difficult to push the cavity 9 into the central region 711, and the cavity 9 is more likely to collapse within the edge region 712. Furthermore, if the groove inclination angle θ1 of the second circumferential groove 72 closest to the inflection portion 71P is greater than the groove inclination angle θ1 of the second circumferential groove 72 closest to the axial end portion 71E of the second inclined surface portion 71 by more than 7°, the cavity 9 is less likely to be pushed up toward the surface side of the crankpin 5. As a result, the cavity 9 is more likely to collapse near the surface 71S and groove surface 721 of the edge region 712.

[0073] At any position in the circumferential direction, each second circumferential groove 72 formed in the second inclined surface portion 71 has the same groove depth D3, groove width W3, and groove cross-sectional area 72A. Because each second circumferential groove 72 of the second inclined surface portion 71 has the same groove depth D3, groove width W3, and groove cross-sectional area 72A, when the crankshaft 5 surface approaches the sliding surface 7 during operation of the internal combustion engine, the pressure of the oil pressed into and flowing into each second circumferential groove 72 increases almost simultaneously and equally, and an oil flow F1 that flows back from each second circumferential groove 72 towards the gap S between the surface 71S of the second inclined surface portion 71 and the surface of the crankpin 5 is formed almost simultaneously. As a result, the cavity 9 is pressed evenly toward the center line 32C side of the oil groove 32a, making it easy to stably collapse the cavity 9 on the surface side of the crankshaft 5 near the center line 32C of the oil groove 32a.

[0074] Furthermore, during operation of the internal combustion engine, when the sliding surface 7 and the surface of the crankpin 5 move from a close position to a separated position, the cavity 9 in the gap S moves along with the lubricating oil in a direction away from the sliding surface 7 (towards the surface of the crankpin 5) following the surface of the crankpin 5. Also, as the gap S expands, the cavity 9 in the central region 711 or the edge region 712 collapses at a position sufficiently separated from the surface 71S of the second inclined surface and the groove surface 721, and cavitation erosion does not occur on the surface 71S of the second inclined surface and the groove surface 721.

[0075] Unlike the configuration of this specific example, if the groove centerline 724 of the second circumferential groove 72 is inclined toward the axial end face 7E of the second split bearing rather than toward the centerline 32C of the oil groove 32a with respect to the perpendicular VL1, when the surface of the crankpin 5 approaches the sliding surface 7, although there is an effect of pushing the lubricating oil and cavity 9 toward the surface of the crankpin 5, the flow of the lubricating oil and cavity 9 is pushed outward in the axial direction, so the cavity 9 is likely to flow into the edge region 712.

[0076] Figure 11 is a cross-sectional view of a split bearing with a configuration different from that of this specific example. In Figure 11, the surface 71S of the second inclined surface does not have an inflection portion 71P, and is formed only by a curve that is convex toward the outer diameter side. Furthermore, the second circumferential groove 72 is not formed on the surface 71S of the second inclined surface. In such a case, no oil flow F1 toward the center line 32C side of the oil groove 32a occurs in the lubricating oil in the gap S between the surface 71S of the second inclined surface and the surface of the crankpin 5. Therefore, the lubricating oil containing the cavity 9 pushed out by the backflow R tends to diffuse outward in the axial direction of the second split bearing 32, and the cavity 9 tends to reach the vicinity of the axial end 71E of the second inclined surface. Therefore, cavitation erosion is likely to occur on the surface 71S near the axial end 71E.

[0077] Furthermore, unlike the configuration of this specific example, if the groove depth D3, groove width W3, and groove cross-sectional area 72A of each second circumferential groove 72 of the second inclined surface portion 71 are not constant, the pressure of the oil that is pressed into and flows into each second circumferential groove 72 when the surface of the crankshaft 5 approaches the sliding surface 7 will not be the same at the same time, and an oil flow F1 that flows backward from each second circumferential groove 72 towards the gap S between the surface 71S of the second inclined surface portion 71 and the surface of the crankpin 5 will not be formed almost simultaneously. Alternatively, in the second circumferential groove 72 with a relatively large groove depth D3, groove width W3, and groove cross-sectional area 72A among the multiple second circumferential grooves 72, the pressure of the incoming oil will not be high, and therefore no oil flow F1 will be formed (the oil will flow circumferentially within the second circumferential groove 72). Therefore, the cavity 9 is less likely to be stably pressed against the surface side of the crankshaft 5 near the center line 32C of the oil groove 32a, and cavitation erosion may occur on the surface 71S and the groove surface 721.

[0078] Second example Next, a second specific example of the present invention will be described. The second specific example has the same configuration as the first specific example, except for the configuration of the first split bearing 31 which will be described below.

[0079] Figure 12 is a view of the first split bearing 31 in the second specific example, seen from the sliding surface 7 side. The first split bearing 31 has axial end faces 7E, 7E. Here, a center line WC1 is defined that passes through the center of the width of the axial length of the first split bearing 31 and extends in the circumferential direction.

[0080] Figure 13 is a cross-sectional view of the first split bearing 31 as seen from the DD section (axial section) of Figure 12. The sliding surface 7 of the first split bearing 31 has two first inclined surfaces 73, 73 adjacent to the centerline WC1 of the first split bearing. The two first inclined surfaces each have a surface 73S, 73S. Each surface 73S, 73S of the first inclined surface is displaced from the axial ends 73E, 73E of the first inclined surface toward the centerline WC1 of the first split bearing, and is continuously displaced toward the back surface of the first split bearing 31.

[0081] Next, the axial cross-sectional shape of the first split bearing 31 will be described in detail using Figures 14, 15A, and 15B.

[0082] Figure 14 is an enlarged view of Figure 13 and shows the axial cross-sectional shape of the first split bearing 31. The first inclined surface portion 73 includes a central region 731 adjacent to the centerline WC1 of the first split bearing, and an edge region 732 adjacent to the central region 731 and located closer to the axial end face 7E of the first split bearing than the central region 731. There is an inflection portion 73P at the boundary between the central region 731 and the edge region 732. Here, the first inclined surface portion 73, the central region 731, and the edge region 732 each have constant axial lengths W5, W5C, and W5E, respectively. Also, the sum of the axial lengths W5, W5 of the two first inclined surface portions 73, 73 of the first split bearing 31 is W7.

[0083] The width W5 of the first inclined surface is defined as the distance parallel to the back surface of the first split bearing 31. The width W5 of the first inclined surface is decomposed into the width W5C of the central region and the width W5E of the edge region. Here, the width W5C of the central region is 25% or more and 75% or less of the width W5 of the first inclined surface.

[0084] The central region 731 has a curve that is convex to the outer diameter side of the first split bearing 31. The edge region 732 has a curve that is convex to the inner diameter side of the first split bearing 31. The depth D4 of the first inclined surface is maximum at the portion adjacent to the center line WC1 of the first split bearing and minimum (zero) at the axial end 73E of the first inclined surface. The depth D4 of the first inclined surface is defined as the length from the axial end 73E of the first inclined surface to the intersection of the center line WC1 of the first split bearing and the surface 73S in a direction perpendicular to the back surface of the first split bearing 31. Here, the depth D4 of the first inclined surface is between 0.005 mm and 0.050 mm.

[0085] Multiple first circumferential grooves 74 are formed adjacent to each other on the surface 73S of the first inclined surface of the first split bearing 31. The multiple first circumferential grooves 74 extend parallel to the circumferential direction and are formed along the entire circumferential length of the surface 71S. The first circumferential grooves 73 are formed along the entire width of the surface 71S. The first circumferential grooves 74 are permitted to be slightly inclined (maximum 1°) with respect to the circumferential direction of the first split bearing 31. For ease of understanding, the first circumferential grooves 74 are depicted in an exaggerated manner in each drawing.

[0086] The first circumferential groove 74 has a curved groove surface 741 when viewed in an axial cross-section of the first split bearing 31. A vertex 742 is formed between the concave surfaces 741 of adjacent first circumferential grooves 74. The curve connecting the vertices 742 represents the surface 73S of the first inclined surface. Microscopically, there are no flat regions on the surface 73S of the first inclined surface.

[0087] Figures 15A and 15B show enlarged views of the first circumferential groove 74 in Figure 14. Figure 15A shows the shape of the first circumferential groove 74 near the center line WC1 of the first half-bearing in the central region 731 of the first inclined surface portion 73, and the shape of the first circumferential groove 74 near the axial end 73E of the first inclined surface portion in the edge region 732. Figure 15B shows the shape of the first circumferential groove 74 near the inflection portion 73P in the central region 731 of the first inclined surface portion 73, and the shape of the first circumferential groove 74 near the inflection portion 73P in the edge region 732. The groove width W6 of the first circumferential groove 74 is defined as the length of a virtual straight line 743 that linearly connects the tops 742 on both sides of the first circumferential groove 74. The groove center line 744 is defined as a line that passes through the midpoint of the length of the virtual straight line 743 and extends perpendicular to the virtual straight line 743. The groove depth D5 of the first circumferential groove 74 is defined as the length from the virtual straight line 743 to the point where the groove surface 741 is furthest away, perpendicular to the virtual straight line 743. The position of the maximum groove depth D5 of the first circumferential groove 74 lies on the groove centerline 744. Here, the groove depth D5 of the first circumferential groove 74 is between 1.5 μm and 10 μm. The groove width W6 of the first circumferential groove 74 is between 0.05 mm and 0.25 mm.

[0088] The area enclosed by the virtual straight line 743 and the groove surface 741 is defined as the groove cross-sectional area 74A. The groove width W6, groove depth D5, and groove cross-sectional area 74A of each first circumferential groove 74 are the same as those of the others. Furthermore, the groove width W6, groove depth D5, and groove cross-sectional area 74A of the first circumferential groove 74 are the same at any position in the circumferential direction.

[0089] Furthermore, the shape of the groove surface 741 of each first circumferential groove 74 is formed symmetrically with respect to the groove centerline 744. The two groove cross-sectional areas that divide the groove cross-sectional area 74A of each first circumferential groove 74 by the groove centerline 744 are equal to each other.

[0090] The angle between the perpendicular line VL2, which extends from the surface 73S of the first inclined surface portion so as to be perpendicular to the axis of the first half-bearing 31, and the groove centerline 744 of the first circumferential groove 74 is defined as the groove inclination angle θ2. The groove centerlines 744 of all first circumferential grooves 74 on the first inclined surface portion 73 are inclined with respect to the perpendicular line VL2 toward the centerline WC1 of the first half-bearing.

[0091] In the central region 731 of the first inclined surface portion 73, the first circumferential groove 74 closest to the centerline WC1 of the first split bearing has the smallest groove inclination angle θ2 (see Figure 15A), and the first circumferential groove 74 closest to the inflection portion 73P has the largest groove inclination angle θ2 (see Figure 15B). Therefore, the groove inclination angle θ2 increases continuously as it approaches the inflection portion 73P from the centerline WC1 of the first split bearing (as it moves outward in the axial direction). Here, the groove inclination angle θ2 of the first circumferential groove 74 closest to the inflection portion 73P of the first inclined surface portion 73 is greater than the groove inclination angle θ2 of the first circumferential groove closest to the centerline WC1 of the first split bearing by a value in the range of 0.001° to 7°.

[0092] In the edge region 732 of the first inclined surface portion 73, the first circumferential groove 74 closest to the inflection portion 73P has the maximum groove inclination angle θ2 (see Figure 15B), and the first circumferential groove 74 closest to the axial end portion 73E of the first inclined surface portion has the minimum groove inclination angle θ2 (see Figure 15A). Therefore, the groove inclination angle θ2 continuously decreases as it approaches the axial end portion 73E of the first inclined surface portion from the inflection portion 73P (as it moves axially outward). Here, the groove inclination angle θ2 of the first circumferential groove 74 closest to the inflection portion 73P of the first inclined surface portion 73 is greater than the groove inclination angle θ2 of the first circumferential groove 74 closest to the axial end portion 73E of the first inclined surface portion 73 by a value in the range of 0.001° to 7°.

[0093] Furthermore, the axial length W7, which is the sum of the axial lengths W5, W5 of the two first inclined surfaces 73, 73 of the first split bearing 31, and the axial length W4, which is the sum of the axial lengths W1 of the two second inclined surfaces W2, W2 and the oil groove 32a of the second split bearing 32, are made to be the same length.

[0094] Next, the operation of the sliding bearing 3 of the present invention will be explained with reference to Figures 16A to 17D.

[0095] During operation of the internal combustion engine, the lubricating oil in the oil groove 32a of the second split bearing 32 flows beyond the circumferential end face 76 into the gap S near the centerline WC1 of the first split bearing 31. If the lubricating oil in the oil groove 32a contains a cavity 9, the cavity 9 flows into the gap S near the centerline WC1 of the first split bearing 31 along with the flow of lubricating oil.

[0096] Figure 16A shows a cross-sectional view of the connecting rod bearing 3 near the circumferential end face 76. Figure 16B shows Figure 16A viewed from the sliding surface 7 side. Figures 16A and 16B show the state in which the sliding surface 7 of the connecting rod bearing 3 and the surface of the crankpin 5 move from a separated state to a relatively close state during the operation of the internal combustion engine. When the sliding surface 7 and the surface of the crankpin 5 move from a separated state to a relatively close state, the lubricating oil present in the gap S is pressed toward the sliding surface 7. As a result, the cavity 9 that has flowed into the gap S near the center line WC1 of the first split bearing 31 moves toward the sliding surface 7 of the first split bearing 31 together with the lubricating oil.

[0097] Figure 17A is the EE cross-section of Figure 16B, showing the vicinity of the first inclined surface 73. When the surface of the crankpin 5 approaches the sliding surface 7, the oil flowing circumferentially through the gap S between the surface 73S of the first inclined surface and the surface of the crankpin 5 is pressed by the surface of the crankpin 5 toward the interior of the multiple first circumferential grooves 74 on the surface 73S of the first inclined surface. The oil in each first circumferential groove 74 is pushed by the oil flowing in from behind, increasing its pressure and not only flows circumferentially within the first circumferential groove 74, but also flows toward the crankpin 5 side (reverse flow), forming an oil flow F1. Here, the groove centerlines 744 of each first circumferential groove 74 on the surface 73S of the first inclined surface are inclined toward the centerline WC1 of the first split bearing. Therefore, the oil flow F1 flowing out from the first circumferential groove 74 flows mainly at an inclination toward the surface side of the crankpin 5 and toward the centerline WC1 of the first split bearing. At the same time, an oil flow F2 is formed that flows circumferentially through the gap S between the surface 73S of the first inclined surface portion and the surface of the crankpin 5, accompanying the surface of the rotating crankpin 5 (see Figure 17B. Figure 17B is a view of Figure 17A from the sliding surface 7 side of the first split bearing 31).

[0098] Here, a central region 731 of the first inclined surface is formed near the center line WC1 of the first split bearing 31. Therefore, the cavity 9 that flows from the oil groove 32a of the second split bearing 32 into the gap S near the center line WC1 of the first split bearing 31 is carried along with the lubricating oil by the oil flows F1 and F2 to the front side in the rotational direction Z of the crankpin within the gap S. Since the central region 731 of the first inclined surface has a curve that is convex toward the outer diameter side of the first split bearing 31, the oil flow F1 has the following components.

[0099] As shown in Figures 17C and 17D, the oil flow F1 is decomposed into a component F1(v) directed toward the surface side of the crankshaft 5 and a component F1(h) directed toward the centerline WC1 side of the first split bearing 31. In the central region 731, the oil flow F1 flowing out from the first circumferential groove 74 near the centerline WC1 of the first split bearing 31 has a relatively large F1(v) component, as shown in Figure 17C.

[0100] On the other hand, in the central region 731, the oil flow F1 flowing out from the first circumferential groove 74 near the inflection portion 73P of the first inclined surface portion 73 has a relatively large F1(h), as shown in Figure 17D.

[0101] In the central region 731, the flow component of the oil flow F1 flowing out from the first circumferential groove 74 located between the centerline WC1 and the inflection portion 73P of the first split bearing 31 continuously changes from the flow component shown in Figure 17C to the flow component shown in Figure 17D, moving from the centerline WC1 of the first split bearing 31 toward the inflection portion 73P (towards the axially outward direction of the first split bearing 31). With this structure, the oil flow F1 in the central region 731 of the first inclined surface portion 73 presses the lubricating oil present in the central region 731, together with the cavity 9, toward the centerline WC1 of the first split bearing 31 and toward the surface of the crankpin 5. As the pressure of the lubricating oil in the pressed central region 731 increases, the cavity 9 contained within the lubricating oil collapses prematurely within the central region 731 due to the return of pressure. Therefore, the cavity 9 is prevented from flowing into the edge region 732 of the first inclined surface portion 73. Therefore, the cavity 9 collapses near the surface 73S of the edge region 732 where the gap S narrows, preventing cavitation erosion from occurring on the surface 73S of the edge region 732. At this time, the cavity 9 in the central region 731 is pushed up towards the surface of the crankpin 5 along with the lubricating oil, and is separated from the surface 73S of the central region 731. Also, the depth D4 of the first inclined surface is deepest on the side of the centerline WC1 of the first split bearing 31 where the cavity 9 is pressed and moved. Therefore, when the cavity 9 collapses in the central region 731, the occurrence of cavitation erosion on the surface 73S of the central region 731 and the groove surface 741 is prevented.

[0102] Furthermore, since the edge region 732 of the first inclined surface portion 73 has a curve that is convex towards the inner diameter side of the first split bearing 31, the oil flow F1 has the following components.

[0103] In the edge region 732, the oil flow F1 flowing out from the first circumferential groove 74 near the inflection portion 73P of the first inclined surface portion 73 has a relatively large F1(h), as shown in Figure 17D.

[0104] On the other hand, in the edge region 732, the oil flow F1 flowing out from the first circumferential groove 74 near the axial end 73E of the first inclined surface portion has a relatively large F1(v), as shown in Figure 17C.

[0105] Therefore, even if the cavity 9 in the central region 731 does not completely collapse within the central region 731, and some flows into the edge region 732, near the inflection portion 73P of the edge region 732, the cavity 9 is pressed toward the centerline WC1 of the first split bearing 31 along with the lubricating oil. In this way, there is an effect of pushing the cavity 9 that has flowed into the edge region 732 back into the central region 731. Furthermore, even if the cavity 9 reaches near the axial end 73E of the edge region 732, near the axial end 73E of the edge region 732, the cavity 9 is pressed toward the surface side of the crankpin 5 along with the lubricating oil. Therefore, it is possible to collapse the cavity 9 by repressure within the gap S spaced apart from the surface 73S of the edge region 732, and the occurrence of cavitation erosion on the surface 73S and groove surface 741 of the edge region 732 is prevented.

[0106] The width W5C of the central region of the first inclined surface is preferably 25% or more and 75% or less of the width W5 of the first inclined surface. If the width W5C of the central region is less than 25% of the width W5 of the first inclined surface, the cavity 9 is less likely to be pressed toward the surface side of the crankpin 5 together with the lubricating oil near the center line WC1 of the first split bearing. As a result, the cavity 9 is more likely to collapse in the gap S close to the surface 73S of the central region 731, and cavitation erosion is more likely to occur on the surface 73S and groove surface 741 of the central region 731 near the center line WC1 of the first split bearing. If the width W5C of the central region exceeds 75% of the width W5 of the first inclined surface, the cavity 9 is less likely to be pressed toward the surface side of the crankpin 5 together with the lubricating oil near the axial end 73E of the first inclined surface. Therefore, the cavity 9 is prone to collapse within the gap S near the surface 73S of the edge region 732, and cavitation erosion is likely to occur on the surface 73S of the edge region 732 and the groove surface 741 near the axial end 73E.

[0107] The depth D4 of the first inclined surface is preferably 0.005 mm or more and 0.050 mm or less. If the depth D4 of the first inclined surface is less than 0.005 mm, even if the cavity 9 is pressed by the oil flow F1, the gap S between the surface 73S of the first inclined surface and the surface of the crankpin 5 is narrow, making it easy for the cavity 9 to collapse near the surface 73S of the first inclined surface, and cavitation erosion to occur in that area. If the depth D4 of the first inclined surface exceeds 0.050 mm, oil film breakdown is likely to occur in the first inclined surface, and seizure is likely to occur.

[0108] The groove depth D5 of the first circumferential groove 74 is preferably 1.5 μm or more and 10 μm or less. The groove width W6 of the first circumferential groove 74 is preferably 0.05 mm or more and 0.25 mm or less. If the groove depth D5 of the first circumferential groove 74 exceeds 10 μm, or if the groove width W6 exceeds 0.25 mm, the oil flow F1 will be weakened. Also, if the groove depth D5 of the first circumferential groove 74 is less than 1.5 μm, or if the groove width W6 is less than 0.05 mm, the amount of oil flow F1 flowing from each first circumferential groove 74 into the gap S between the surface 73S of the first inclined surface and the surface of the crankpin 5 will be reduced. As a result, the cavity 9 may not be sufficiently pressed.

[0109] Preferably, the groove inclination angle θ2 of the first circumferential groove 74 closest to the inflection portion 73P of the first inclined surface portion 73 is greater than the groove inclination angle θ2 of the first circumferential groove 74 closest to the centerline WC1 of the first split bearing 31 by a value in the range of 0.001° to 7°. If the groove inclination angle θ2 of the first circumferential groove 74 closest to the inflection portion 71P is greater than the groove inclination angle θ2 of the first circumferential groove 74 closest to the centerline WC1 of the first split bearing 31 by a value of less than 0.001°, the F1(h) component of the oil flow F1 flowing out from the first circumferential groove 74 of the central region 731 becomes insufficient. As a result, the cavity 9 is less likely to be pressed toward the centerline WC1 side of the first split bearing 31, and the cavity 9 is more likely to flow out into the edge region 732. Furthermore, if the groove inclination angle θ2 of the first circumferential groove 74 closest to the inflection portion 73P is greater than the groove inclination angle θ2 of the first circumferential groove 74 closest to the centerline WC1 of the first split bearing 31 by more than 7°, the F1(v) component of the oil flow F1 flowing out from the first circumferential groove 74 of the central region 731 becomes insufficient. As a result, the cavity 9 is less likely to be pressed toward the surface side of the crankpin 5, and the cavity 9 is more likely to collapse near the surface 73S and groove surface 741 of the central region 731.

[0110] Preferably, the groove inclination angle θ2 of the first circumferential groove 74 closest to the inflection portion 73P of the first inclined surface portion 73 is greater than the groove inclination angle θ2 of the first circumferential groove 74 closest to the axial end portion 73E of the first inclined surface portion 73 by a value in the range of 0.001° to 7°. If the groove inclination angle θ2 of the first circumferential groove 74 closest to the inflection portion 73P is greater than the groove inclination angle θ2 of the first circumferential groove 74 closest to the axial end portion 73E of the first inclined surface portion 73 by less than 0.001°, the F1(h) component of the oil flow F1 flowing out from the first circumferential groove 74 near the inflection portion 73P of the edge region 732 becomes too small. As a result, it becomes difficult to push the cavity 9 into the central region 731, and the cavity 9 is more likely to collapse within the edge region 732. Furthermore, if the groove inclination angle θ2 of the first circumferential groove 74 closest to the inflection portion 73P is greater than the groove inclination angle θ2 of the first circumferential groove 74 closest to the axial end portion 73E of the first inclined surface portion 73 by more than 7°, the cavity 9 is less likely to be pushed up toward the surface side of the crankpin 5. As a result, the cavity 9 is prone to collapse near the surface 73S and groove surface 741 of the edge region 732.

[0111] At any position in the circumferential direction, each first circumferential groove 74 formed on the first inclined surface portion 73 has the same groove depth D5, groove width W6, and groove cross-sectional area 74A. Because each first circumferential groove 74 of the first inclined surface portion 73 has the same groove depth D5, groove width W6, and groove cross-sectional area 74A, when the surface of the crankshaft 5 approaches the sliding surface 7 during operation of the internal combustion engine, the pressure of the oil pressed into and flowing into each first circumferential groove 74 increases almost simultaneously and equally, and an oil flow F1 that flows backward from each first circumferential groove 74 towards the gap S between the surface 73S of the first inclined surface portion 73 and the surface of the crankpin 5 is formed almost simultaneously. As a result, the cavity 9 is pressed evenly toward the center line WC1 of the first split bearing 31, making it easy to stably collapse the cavity 9 on the surface side of the crankshaft 5 near the center line WC1 of the first split bearing 31.

[0112] Furthermore, in this specific example, the axial length W7, which is the sum of the axial lengths W5, W5 of the two first inclined surfaces 73, 73 of the first split bearing 31, and the axial length W4, which is the sum of the axial lengths W1 of the two second inclined surfaces W2, W2 and the oil groove 32a of the second split bearing 32, are the same length. Therefore, the following effects are achieved. In other words, when the lubricating oil in the gap S between the sliding surface 7 of the first split bearing 31 and the crankpin 5 flows beyond the circumferential end face 76 and into the gap S between the sliding surface 7 of the second split bearing 32 and the crankpin 5 (or conversely, when the lubricating oil in the gap S between the sliding surface 7 of the second split bearing 32 and the crankpin 5 flows beyond the circumferential end face 76 and into the gap S between the sliding surface 7 of the first split bearing 31 and the crankpin 5), similar oil flows F1 and F2 are formed in the first split bearing 31 and the second split bearing 32. As a result, the flow of lubricating oil is stabilized, preventing turbulence of the lubricating oil when it crosses the circumferential end face 76, and effectively preventing the formation of a cavity 9 when it crosses the circumferential end face 76.

[0113] Furthermore, during operation of the internal combustion engine, when the sliding surface 7 and the surface of the crankpin 5 move from a close position to a separated position, the cavity 9 in the gap S moves along with the lubricating oil in a direction away from the sliding surface 7 (towards the surface of the crankpin 5) following the surface of the crankpin 5. Also, as the gap S expands, the cavity 9 in the central region 731 or the edge region 732 collapses at a position sufficiently separated from the surface 73S of the first inclined surface and the groove surface 741, and cavitation erosion does not occur on the surface 73S of the first inclined surface and the groove surface 741.

[0114] Unlike the configuration of this specific example, if the groove centerline 744 of the first circumferential groove 74 is inclined toward the axial end face 7E of the first split bearing 31 rather than toward the centerline WC1 of the first split bearing 31 with respect to the perpendicular VL2, when the surface of the crankpin 5 approaches the sliding surface 7, although there is an effect of pushing the lubricating oil and cavity 9 toward the surface of the crankpin 5, the flow of the lubricating oil and cavity 9 is pushed outward in the axial direction, so the cavity 9 is likely to flow into the edge region 732.

[0115] Figure 18 is a cross-sectional view of a split bearing with a configuration different from that of this specific example. In Figure 18, the surface 73S of the first inclined surface does not have an inflection portion 73P, and is formed only by a curve that is convex toward the outer diameter side. Furthermore, the first circumferential groove 74 is not formed on the surface 73S of the first inclined surface. In such a case, no oil flow F1 toward the centerline WC1 side of the first split bearing 31 is generated in the lubricating oil in the gap S between the surface 73S of the first inclined surface and the surface of the crankpin 5. Therefore, the lubricating oil including the cavity 9 tends to diffuse outward in the axial direction of the first split bearing 31, and the cavity 9 tends to reach the vicinity of the axial end 73E of the first inclined surface. Therefore, cavitation erosion is likely to occur on the surface 73S near the axial end 73E.

[0116] Furthermore, unlike the configuration of this specific example, if the groove depth D5, groove width W6, and groove cross-sectional area 74A of each first circumferential groove 74 of the first inclined surface portion 73 are not constant, the pressure of the oil that is pressed into and flows into each first circumferential groove 74 when the surface of the crankshaft 5 approaches the sliding surface 7 will not be the same at the same time, and an oil flow F1 that flows backward from each first circumferential groove 74 towards the gap S between the surface 73S of the first inclined surface portion 73 and the surface of the crankpin 5 will not be formed almost simultaneously. Alternatively, in the first circumferential groove 74, where the groove depth D5, groove width W6, and groove cross-sectional area 74A are relatively large among the multiple first circumferential grooves 74, the pressure of the incoming oil will not be high, and therefore no oil flow F1 will be formed (the oil will flow circumferentially within the first circumferential groove 74). Therefore, the cavity 9 is less likely to be stably pressed against the surface side of the crankshaft 5 near the center line WC1 of the first split bearing 31, and cavitation erosion may occur on the surface 73S and groove surface 741. [Explanation of Symbols]

[0117] 1. Bearing device 2 connecting rods 21. Large end housing 22 Rod-side big end housing 23. Cap-side big end housing 3 Connecting rod bearings 31 First split bearing 32 Second split bearing 32a Oil groove 32C Centerline of the oil groove in the axial direction 32E Groove end 4 Main bearings 41 First split bearing 42 Second split bearing 42a Oil groove 5 Crankpin 5a Lubrication oil path 5b Lubrication oil path 5c outlet 6. Journal Section 6a Lubrication oil path 6c Inlet opening 7. Sliding surface 7E Axial end face 71 2nd slope section 711 Central area of ​​the second inclined surface 712 Edge region of the second inclined surface 71E Axial end of second inclined surface section 71P Inflection section of the second inclined surface 71S Surface of the second inclined surface 72 Second circumferential groove 721 Groove surface of the second circumferential groove 722 Top of the second circumferential groove 723 Virtual straight line of the second circumferential groove 724 Centerline of the second circumferential groove 72A Groove cross-sectional area of ​​the second circumferential groove 73 1st slope section 731 Central area of ​​the first inclined surface 732 Edge region of the first inclined surface 73E Axial end of first inclined surface section 73P Inflection part of the first inclined surface part 73S Surface of the first inclined surface 74 1st circumferential groove 741 Groove surface of the first circumferential groove 742 Top of the first circumferential groove 743 Virtual straight line of the first circumferential groove 744 Centerline of the first circumferential groove 74A Groove cross-sectional area of ​​the first circumferential groove 76 Circumferential end face 8 Cylinder Block 81 Cylinder block upper part 82 Lower part of cylinder block D1 Groove depth D2 Depth of the second inclined surface D3 Groove depth of the second circumferential groove D4 Depth of the first inclined surface D5 Groove depth of the first circumferential groove R backflow VL1 Perpendicular to the second split bearing VL2 Perpendicular to the first split bearing WC1 Axial centerline of the first split bearing WC2 Second Split Bearing Axial Method Centerline W1 Groove width W2 Axial length of the second inclined surface W2C Axial length of the second central region W2E Axial length of the second edge region W3 Groove width of the second circumferential groove W4 is the axial length of W1 + W2 × 2. W5 Axial length of the first inclined surface W5C Axial length of the first central region W5E Axial length of the first edge region W6 Groove width of the first circumferential groove Axial length of W7 W5×2 Rotation direction of the X journal section Z crankpin rotation direction θ1 Groove inclination angle of the second circumferential groove θ2 Groove inclination angle of the first circumferential groove

Claims

1. A sliding bearing for rotatably supporting the crankshaft of an internal combustion engine, The sliding bearing has first and second split bearings that are combined to form a cylindrical shape, and the first and second split bearings have a sliding surface on the inner diameter side and a back surface on the outer diameter side. The aforementioned back surface is parallel to the axial direction of the first and second split bearings. The first and second split bearings have circumferential end faces on both sides in the circumferential direction, The first and second split bearings have axial end faces at both ends in the axial direction, The second split bearing has one oil groove on its inner diameter side, the oil groove is located between the two axial end faces of the second split bearing, extends in the circumferential direction, and has a constant axial length W1. The oil groove has groove ends at both ends in the axial direction, The sliding surface of the second split bearing has two second inclined surfaces, the second inclined surfaces are adjacent to each other along the entire circumferential length of each groove end, and have a constant axial length W2, and the surfaces of the second inclined surfaces are displaced so as to continuously approach the back surface from each axial end face towards the groove end. The surface of the second inclined surface portion includes a central region adjacent to the groove end and an edge region adjacent to the central region and located closer to each axial end face of the second split bearing than the central region. There is an inflection portion at the boundary between the central region and the edge region. The central region, in a cross-sectional view of the second split bearing in the axial direction, forms a curve that is convex toward the outer diameter side of the second split bearing. The edge region forms a curve that is convex toward the inner diameter side of the second split bearing in a cross-sectional view in the axial direction of the second split bearing. Multiple second circumferential grooves are formed adjacent to each other on the surface of the second inclined surface, and these multiple second circumferential grooves are formed along the entire circumferential length of the surface of the second inclined surface, and these multiple second circumferential grooves are formed along the entire width of the surface of the second inclined surface, and when viewed in cross-section in the axial direction of the second split bearing, the second circumferential grooves have curved groove surfaces, and vertices are formed between adjacent groove surfaces, and the curve connecting the vertices represents the surface of the second inclined surface. The groove width of the second circumferential groove is defined as the length of a virtual straight line connecting the tops on both sides of the second circumferential groove, the groove centerline is defined as a line passing through the midpoint of the length of the virtual straight line and extending perpendicularly to the virtual straight line, the groove depth of the second circumferential groove is defined as the length perpendicular to the virtual straight line from the virtual straight line to the position where the groove surface is furthest away, and the position of the maximum groove depth of the second circumferential groove is located on the groove centerline. The area enclosed by the virtual straight line and the groove surface is defined as the groove cross-sectional area, and the groove width, groove depth, and groove cross-sectional area of ​​the plurality of second circumferential grooves are the same as each other, and the groove width, groove depth, and groove cross-sectional area of ​​the second circumferential grooves are the same at any position in the circumferential direction. The angle between the perpendicular line extending from the surface of the second inclined surface portion so as to be perpendicular to the axis of the split bearing and the groove center line is defined as the groove inclination angle θ1. A sliding bearing in which the groove centerline on the surface of the second inclined surface passes through the center of the width of the axial length of the oil groove and is inclined with respect to the perpendicular toward the centerline extending in the circumferential direction, the groove inclination angle θ1 in the edge region is minimum at the axial end of the second inclined surface and continuously increases as it approaches the inflection portion, and the groove inclination angle θ1 in the central region is minimum at a position adjacent to the groove end of the second inclined surface and continuously increases as it approaches the inflection portion.

2. The sliding bearing according to claim 1, wherein the edge region of the second inclined surface portion is adjacent to the axial end face of the second split bearing.

3. The sliding bearing according to claim 1 or 2, wherein the width W2C of the central region of the second inclined surface is 25% or more and 75% or less of the width W2 of the second inclined surface.

4. The sliding bearing according to claim 1 or 2, wherein the depth D2 of the second inclined surface portion is 0.005 mm or more and 0.050 mm or less.

5. The sliding bearing according to claim 1 or 2, wherein the groove depth D3 of the second circumferential groove is 1.5 μm or more and 10 μm or less.

6. The sliding bearing according to claim 1 or 2, wherein the groove width W3 of the second circumferential groove is 0.05 mm or more and 0.25 mm or less.

7. The sliding bearing according to claim 1 or 2, wherein the groove inclination angle θ1 of the second circumferential groove closest to the inflection portion of the second inclined surface is greater than the groove inclination angle θ1 of the second circumferential groove closest to the groove end by a value in the range of 0.001° or more and 7° or less.

8. The sliding bearing according to claim 1 or 2, wherein the groove inclination angle θ1 of the second circumferential groove closest to the inflection portion of the second inclined surface is greater than the groove inclination angle θ1 of the second circumferential groove closest to the axial end of the second inclined surface by a value in the range of 0.001° or more and 7° or less.

9. The first split bearing has a center line, which passes through the center of the width of the axial length of the first split bearing and extends in the circumferential direction, and the sliding surface of the first split bearing has two first inclined surfaces, which are adjacent to the center line and have a constant axial length W5 from the center line toward each axial end face, and extend over the entire circumferential length of the first split bearing, and the surface of the first inclined surfaces is displaced so as to continuously approach the back surface toward the groove end from each axial end face, The surface of the first inclined surface portion includes a central region adjacent to the center line of the first split bearing and an edge region adjacent to the central region and located closer to each axial end face of the first split bearing than the central region. There is an inflection portion at the boundary between the central region and the edge region. The central region, in a cross-sectional view of the first split bearing in the axial direction, forms a curve that is convex toward the outer diameter side of the first split bearing. The edge region, in a cross-sectional view of the first split bearing in the axial direction, forms a curve that is convex toward the inner diameter side of the first split bearing. Multiple first circumferential grooves are formed adjacent to each other on the surface of the first inclined surface, and these multiple first circumferential grooves are formed along the entire circumferential length of the surface of the first inclined surface, and these multiple first circumferential grooves are formed along the entire width of the surface of the first inclined surface, and when viewed in cross-section in the axial direction of the first split bearing, the first circumferential grooves have a curved groove surface, and vertices are formed between adjacent groove surfaces, and the curve connecting the vertices represents the surface of the first inclined surface. The groove width of the first circumferential groove is defined as the length of a virtual line connecting the tops on both sides of the first circumferential groove, the groove centerline is defined as a line passing through the midpoint of the length of the virtual line and extending perpendicularly to the virtual line, the groove depth of the first circumferential groove is defined as the length perpendicular to the virtual line from the virtual line to the position where the groove surface is furthest away, and the position of the maximum groove depth of the first circumferential groove is located on the groove centerline. The area enclosed by the aforementioned imaginary line and the groove surface is defined as the groove cross-sectional area. The groove width, groove depth, and groove cross-sectional area of ​​the plurality of first circumferential grooves are all the same, and the groove width, groove depth, and groove cross-sectional area of ​​the first circumferential grooves are the same at any position in the circumferential direction. The angle between the perpendicular line extending from the surface of the first inclined surface portion so as to be perpendicular to the axis of the split bearing and the groove center line is defined as the groove inclination angle θ2. The sliding bearing according to claim 1 or 2, wherein the groove centerline on the surface of the first inclined surface is inclined with respect to the perpendicular to the centerline of the first split bearing, the groove inclination angle θ2 in the edge region is minimum at the axial end of the first inclined surface and continuously increases as it approaches the inflection portion, and the groove inclination angle θ2 in the central region is minimum at a position adjacent to the centerline of the first split bearing and continuously increases as it approaches the inflection portion.

10. The sliding bearing according to claim 9, wherein the edge region of the first inclined surface portion is adjacent to the axial end face of the first split bearing.

11. The sliding bearing according to claim 9, wherein the sum of the axial lengths W5, W5 of the two first inclined surfaces of the first split bearing is the axial length W7, the sum of the axial lengths W2, W2 of the two second inclined surfaces of the second split bearing and the axial length W1 of the oil groove is the axial length W4, and the axial length W7 and the axial length W4 are the same.

12. The sliding bearing according to claim 9, wherein the width W5C of the central region of the first inclined surface is 25% or more and 75% or less of the width W5 of the first inclined surface.

13. The sliding bearing according to claim 9, wherein the depth D4 of the first inclined surface portion is 0.005 mm or more and 0.050 mm or less.

14. The sliding bearing according to claim 9, wherein the groove depth D5 of the first circumferential groove is 1.5 μm or more and 10 μm or less.

15. The sliding bearing according to claim 9, wherein the groove width W6 of the first circumferential groove is 0.05 mm or more and 0.25 mm or less.

16. The sliding bearing according to claim 9, wherein the groove inclination angle θ2 of the first circumferential groove closest to the inflection portion of the first inclined surface is greater than the groove inclination angle θ1 of the first circumferential groove closest to the center line of the first split bearing by a value in the range of 0.001° or more and 7° or less.

17. The sliding bearing according to claim 9, wherein the groove inclination angle θ2 of the first circumferential groove closest to the inflection portion of the first inclined surface is greater than the groove inclination angle θ2 of the first circumferential groove closest to the axial end of the first inclined surface by a value in the range of 0.001° or more and 7° or less.

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