Bearing device for crank shaft of internal combustion engine

Abstract

To provide a bearing device for a crank shaft of an internal combustion engine in which damage hardly occurs even when a close-in phenomenon occurs on a bearing housing during operation.SOLUTION: A bearing device of the present invention includes a crank shaft, a bearing housing, and a slide bearing made of a pair of half-split bearings. Each of the half-split bearings has an inner peripheral face and an outer peripheral face. At least one of the half-split bearings has an oil hole extending by penetrating a wall thickness of the half-split bearing, and a transition face is formed between the outer peripheral face of the half-split bearing and a peripheral edge of an outer peripheral face-side opening. In a non-installed state where the slide bearing is not installed to a bearing holding hole of the bearing housing, the peripheral edge of the outer peripheral face-side opening of the oil hole is positioned on a curvature center side of the outer peripheral face from the outer peripheral face, and a depth of the transition face becomes continuously larger from a position adjacent to the outer peripheral face toward a position adjacent to the peripheral edge of the outer peripheral face-side opening. Also, in an installed state, the outer peripheral face and the transition face of the half-split bearing are in contact with the inner peripheral face of the bearing holding hole with no gap therebetween.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a bearing device that supports a crankshaft of an internal combustion engine. [Background technology]

[0002] The crankshaft of an internal combustion engine is supported at its journal portion on the lower part of the cylinder block of the engine via a main bearing consisting of a pair of half bearings. To lubricate the main bearing, lubricating oil discharged by an oil pump is sent from an oil gallery formed in the cylinder block wall through a through-hole formed in the wall of the main bearing and into a lubricating oil groove formed along the inner surface of the main bearing. A first lubricating oil passage is formed diametrically through the journal portion, and both end openings of this first lubricating oil passage are connected to the lubricating oil groove of the main bearing. Furthermore, a second lubricating oil passage is formed branching from the first lubricating oil passage in the journal portion and passing through the crank arm portion, and this second lubricating oil passage is connected to a third lubricating oil passage formed diametrically through the crank pin. For this reason, lubricating oil is sent from the oil gallery in the cylinder block wall through a through-hole into a lubricating oil groove formed in the inner surface of the main bearing, passes through the first, second, and third lubricating oil passages, and is supplied from a discharge port at the end of the third lubricating oil passage between the crank pin and the sliding surface of a connecting rod bearing consisting of a pair of half bearings (see, for example, Patent Document 1). In this way, oil is supplied between the surface of the crankshaft and the sliding surfaces of the main bearing and connecting rod bearing. The lubricating oil supplied to the connecting rod bearing is then supplied between the piston and cylinder liner through a through-hole formed in the wall of the connecting rod bearing and a lubricating oil passage formed in the connecting rod wall.

[0003] The main bearing and connecting rod bearing, each consisting of a pair of half bearings, are each held in a cylindrical bearing retaining hole in the bearing housing. The bearing housing is made up of a pair of housing halves, each of which has a semi-cylindrical surface that becomes the bearing retaining hole when the housing halves are combined. The half bearings are held in these semi-cylindrical surfaces.

[0004] Recently, efforts to reduce the weight of internal combustion engines in order to improve fuel efficiency have led to a trend toward lower rigidity in bearing housing components such as connecting rods and engine blocks. As a result, during operation of the internal combustion engine, inertial forces acting on the bearing housing and dynamic loads from the crankshaft cause the cylindrical bearing housing's bearing retaining hole to undergo a phenomenon known as close-in, in which the bearing housing undergoes repeated elastic deformation, with the vertical inner diameter becoming larger than the horizontal inner diameter, followed by elastic deformation that returns to its cylindrical shape. (Here, the horizontal direction refers to the direction connecting the two split surfaces of the housing segments of the bearing housing, as viewed from the axial direction of the bearing retaining hole. The vertical direction refers to the direction perpendicular to the direction connecting the two split surfaces of the housing segments.) This phenomenon causes repeated, fluctuating loads in the circumferential direction to be applied to the half bearings held in each housing segment. In a half bearing consisting of a backing metal layer and a sliding layer made of an Fe alloy, there is a proposal to remove the sliding layer in the vicinity of the opening of the through hole (oil hole) in order to prevent cracking of the sliding layer in the vicinity of the opening of the through hole (oil hole) due to the load that repeatedly fluctuates in the circumferential direction of the half bearing (see, for example, Patent Document 2).

[0005] In a plain bearing equipped with a half bearing in which the sliding layer adjacent to the opening of the through hole (oil hole) has been removed, as described in Patent Document 2 above, when a close-in phenomenon occurs in the bearing housing during operation of an internal combustion engine, the backing metal layer adjacent to the through hole is likely to be damaged (cracked) due to fluctuations in the load applied circumferentially to the half bearing, and the through hole (oil hole) is likely to undergo plastic deformation, reducing the holding force of the plain bearing by the bearing housing. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-277831 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-41724 Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide a bearing device for a crankshaft of an internal combustion engine that is less susceptible to such damage during operation of the engine. [Means for solving the problem]

[0008] According to the present invention, there is provided a bearing device for supporting a crankshaft of an internal combustion engine, the bearing device comprising: a crankshaft; a bearing housing having a cylindrical bearing retaining hole; and a cylindrical plain bearing mounted on an inner peripheral surface of the bearing retaining hole; a bearing device in which the plain bearing is made up of a pair of half bearings each having a semi-cylindrical shape, each half bearing having a backing layer extending on the outer diameter side and a sliding layer extending on the inner diameter side, each half bearing having an inner circumferential surface, an outer circumferential surface and both circumferential end surfaces, the inner circumferential surface of the half bearing supporting the crankshaft, the pair of half bearings having the same axial length, at least one of the pair of half bearings having one or more oil holes extending through the wall thickness of the half bearing, and both the inner circumferential surface side opening and the outer circumferential surface side opening of the oil hole having a circular shape; a transition surface is formed between the outer peripheral surface of the half bearing and the periphery of the outer peripheral surface side opening of the oil hole, In an unmounted state where the plain bearing is not mounted on the inner peripheral surface of the bearing retaining hole, the peripheral edge of the outer peripheral surface opening of the oil hole in the half bearing is located closer to the center of curvature of the outer peripheral surface in the direction of the axial line of the oil hole than the outer peripheral surface of the half bearing, and as a result, the depth of the transition surface from the outer peripheral surface in a direction perpendicular to the outer peripheral surface increases continuously from the position adjacent to the outer peripheral surface to the position adjacent to the peripheral edge of the outer peripheral surface opening, the depth of the transition surface at the position adjacent to the peripheral edge of the outer peripheral surface opening is 5 to 50 μm, and the length of the transition surface from the position adjacent to the outer peripheral surface to the position adjacent to the peripheral edge of the outer peripheral surface opening in either radial direction of the axial line of the oil hole is 100 to 300 μm, and A bearing device is provided in which, when the plain bearing is mounted on the inner peripheral surface of the bearing retaining hole, the outer peripheral surface and transition surface of the half bearing are in contact with the inner peripheral surface of the bearing retaining hole without any gap.

[0009] According to one embodiment of the present invention, in the unwrapped state, the ratio (D1 / L2) of the depth (D1) of the transition surface at a position adjacent to the periphery of the outer peripheral surface opening to the length (L2) of the transition surface may be 0.05 to 0.20. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic diagram showing a bearing device for a crankshaft. [Figure 2] 1 is a view of a sliding bearing according to a first embodiment of the present invention in an unmounted state, viewed from the axial direction. [Figure 3] 3 is a view of the upper half bearing shown in FIG. 2 as viewed from the axial direction. [Figure 4] 3 is a plan view of the upper half bearing shown in FIG. 2, viewed from the inner peripheral surface side. FIG. [Figure 5] 3 is a plan view of the upper half bearing shown in FIG. 2, viewed from the outer circumferential surface side. FIG. [Figure 6] 3 is a view showing the vicinity of an opening of an oil hole of the half bearing shown in FIG. 2 (a view taken along arrow A in FIG. 3). [Figure 7] 6 is a cross-sectional view of the half bearing taken along line BB shown in FIG. 5. [Figure 8] FIG. [Figure 9] FIG. 4 is a view showing a bearing housing when elastically deformed. [Figure 10] 1 is a view of a plain bearing and a bearing housing according to a first embodiment of the present invention, viewed from the axial direction. [Figure 11] 11 is an enlarged cross-sectional view of part C of the sliding bearing and bearing housing shown in FIG. 10. [Figure 12A] 1 is a diagram illustrating the operation of the present invention. FIG. [Figure 12B] 1 is a diagram illustrating the operation of the present invention. FIG. [Figure 13] FIG. 4 is a view of a sliding bearing according to a second embodiment of the present invention in an unmounted state, viewed from the axial direction. [Figure 14] FIG. 14 is a view of the upper half bearing shown in FIG. 13 as viewed from the axial direction. [Figure 15]FIG. 15 is a plan view of the half bearing shown in FIG. 14, viewed from the outer circumferential surface side. [Figure 16] FIG. 16 is a cross-sectional view of the half bearing shown in FIG. 15 taken along line DD. [Figure 17] FIG. 17 is an enlarged view of a portion E of the half bearing shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, specific examples of the present invention will be described with reference to the drawings.

[0012] (First embodiment) Fig. 1 shows a schematic diagram of a bearing device 1 for an internal combustion engine. This bearing device 1 comprises a crankshaft journal portion 6 supported on the lower part of a cylinder block, a crankpin 5 of the crankshaft formed integrally with the journal portion 6 and rotating around the journal portion 6, and a connecting rod 2 that transmits reciprocating motion from the internal combustion engine to the crankpin 5. The bearing device 1 further comprises, as sliding bearings that support the crankshaft, a main bearing 4 that rotatably supports the journal portion 6, and a connecting rod bearing 3 that rotatably supports the crankpin 5.

[0013] Although the crankshaft has multiple journals 6 and multiple crankpins 5, for ease of explanation, only one journal 6 and one crankpin 5 will be illustrated here. In Fig. 1, the positional relationship in the depth direction of the page is such that the journals 6 are at the back side of the page and the crankpins 5 are at the front side.

[0014] The journal portion 6 is journaled on a bearing housing 10 (cylinder block or housing segment 101 and cap or housing segment 102) at the bottom of the cylinder block of the internal combustion engine via a main bearing 4 consisting of a pair of half bearings 41, 42. An oil groove 41a is formed along the entire length of the inner circumferential surface of the half bearing 41, which is on the upper side in FIG. 1. The journal portion 6 also has a lubricating oil passage 6a that penetrates it in the diameter direction, and when the journal portion 6 rotates in the direction of arrow X, the inlet openings 6c at both ends of the lubricating oil passage 6a alternately communicate with the oil groove 41a of the main bearing 4.

[0015] The crank pin 5 is journaled in the bearing housing 21 (rod-side big-end housing or housing segment 22A and cap-side big-end housing or housing segment 22B) of the connecting rod 2 via a connecting rod bearing 3 consisting of a pair of half bearings 31, 32, and is adapted to rotate in the direction of arrow Z.

[0016] The bearing housing 10 is made up of a pair of housing halves 101, 102. The housing halves 101, 102 have semi-cylindrical inner circumferential surfaces 24, which form cylindrical bearing retaining holes 23 when the dividing surfaces 26 of the pair of housing halves 101, 102 are butted together (see FIG. 8). The outer circumferential length of the pair of half bearings 41, 42 that make up the main bearing 4 is slightly larger than the inner circumferential length of the bearing retaining hole 23 in the bearing housing 10. Therefore, after installation, circumferential compressive stress is generated in the pair of half bearings 41, 42, and pressure is generated between the outer circumferential surfaces 8 and the inner circumferential surface 24 of the bearing retaining hole 23, securing the pair of half bearings 41, 42 in the bearing retaining hole 23 in the bearing housing 10.

[0017] Similarly, the bearing housing 21 is made up of a pair of housing segments 22A and 22B. The housing segments 22A and 22B have semi-cylindrical inner peripheral surfaces 24, which form a cylindrical bearing retaining hole 26 when the split surfaces 26 of the pair of housing segments 22A and 22B are butted together (see FIG. 8 ). The outer peripheral length of the pair of half bearings 31 and 32 that make up the connecting rod bearing 3 is slightly longer than the inner peripheral length of the bearing retaining hole 23 in the big-end housing (bearing housing) 21. Therefore, after installation, circumferential stress is generated in the pair of half bearings 31 and 32, generating pressure between the outer peripheral surfaces 8 and the inner peripheral surface 24 of the bearing retaining hole 23, securing the pair of half bearings 31 and 32 in the bearing retaining hole 23 in the big-end housing (bearing housing) 21.

[0018] As described above, to lubricate the main bearing 4, the lubricating oil discharged by the oil pump is sent from the oil gallery formed in the cylinder block wall through the oil hole 4H formed in the wall of the main bearing 4 and into the oil groove 41a formed along the inner surface of the main bearing 4.

[0019] Furthermore, a first lubricating oil passage 6a is formed through the journal portion 6 in the radial direction, and an inlet opening 6c of the first lubricating oil passage 6a is capable of communicating with the lubricating oil groove 41a. Also, a second lubricating oil passage 5a is formed branching from the first lubricating oil passage 6a of the journal portion 6 and passing through the crank arm portion (not shown), and the second lubricating oil passage 5a is connected to a third lubricating oil passage 5b formed through the crank pin 5 in the radial direction.

[0020] In this way, the lubricating oil passes through the first lubricating oil passage 6a, the second lubricating oil passage 5a, and the third lubricating oil passage 5b, and is supplied to the gap formed between the crank pin 5 and the connecting rod bearing 3 from the discharge port 5c at the end of the third lubricating oil passage 5b.

[0021] Furthermore, an oil hole 3H is formed through the wall of the connecting rod bearing 3 and communicates with a lubricating oil passage 25 formed through the wall of the connecting rod 2. Lubricating oil is supplied to the gap formed between the piston (not shown) and the cylinder liner (not shown) via the oil hole 3H of the connecting rod bearing 3 and the lubricating oil passage 25 of the connecting rod 2.

[0022] In recent internal combustion engines, weight reduction is being sought in order to improve fuel efficiency, which has led to a trend toward lower rigidity of bearing housing components such as the connecting rod 2 and engine block 101. As a result, during operation of the internal combustion engine, inertial forces acting on the bearing housing 10; 21 and dynamic loads from the crankshaft cause the cylindrical bearing retaining hole 23 of the bearing housing 10; 21 to undergo a phenomenon known as close-in, in which the bearing retaining hole 23 repeatedly undergoes elastic deformation (see FIG. 9 ) in which the vertical inner diameter DV becomes larger than the horizontal inner diameter DH, followed by elastic deformation (see FIG. 8 ) in which the bearing retaining hole 23 returns to its cylindrical shape. Here, the horizontal direction refers to the direction connecting the two dividing surfaces 26 of the housing segments 101, 102; 22A, 22B of the bearing housing 10; 21, as viewed from the axial direction of the bearing retaining hole 23. The vertical direction is a direction perpendicular to the direction connecting the dividing surfaces 26 of the housing segments 101, 102; 22A, 22B of the bearing housings 10; 21 when viewed from the axial direction of the bearing retaining hole 23.

[0023] Circumferential stress (stress in the direction compressing the circumferential length of the plain bearing 3; 4) is applied to the plain bearing 3; 4 held in the bearing retaining hole 23 of the bearing housing 10; 21. As a result, a concentrated area of ​​circumferential stress is formed around the oil hole 3H; 4H of the plain bearing 3; 4. When the inner diameter of the bearing retaining hole 23 in the bearing housing 10; 21 increases in the vertical direction, the circumferential length of the inner surface of the bearing retaining hole 23 increases, and the circumferential stress applied to the plain bearings 3; 4 decreases, while when the inner diameter of the bearing retaining hole 23 in the bearing housing 10; 21 elastically deforms to return to its cylindrical shape, the circumferential stress applied to the plain bearings 3; 4 increases. When the internal combustion engine is operating, the circumferential stress applied to the plain bearings 3; 4 fluctuates repeatedly.

[0024] In a conventional sliding bearing (see, for example, Patent Document 2) equipped with a half bearing in which the sliding layer adjacent to the opening of the oil hole on the inner peripheral surface has been removed, when the close-in phenomenon occurs in the bearing housing while the internal combustion engine is operating, fluctuations in the circumferential stress applied to the half bearing make it easy for damage (cracks) to occur in the backing metal layer adjacent to the oil hole, and the oil hole (the backing metal layer adjacent to the oil hole) undergoes plastic deformation, reducing the circumferential length of the half bearing and easily reducing the holding force of the sliding bearing by the bearing housing.

[0025] An embodiment in which the bearing device 1 of the present invention is applied to a connecting rod bearing will be described below. However, it will be understood that the application of the bearing device of the present invention is not limited to connecting rod bearings, and it may also be applied to a main bearing having a main bearing housing.

[0026] Fig. 2 shows a connecting rod bearing 3 made up of half bearings 31, 32 of the present invention, viewed from the axial direction, with the circumferential end faces 76 facing each other in an unmounted state. Fig. 3 is a view of the upper half bearing 31 shown in Fig. 2, viewed from the axial direction. Fig. 4 is a plan view of the upper half bearing 31 shown in Fig. 2, viewed from the inner peripheral surface side. Fig. 5 is a plan view of the upper half bearing 31 shown in Fig. 2, viewed from the outer peripheral surface side.

[0027] As shown in FIGS. 2 to 4 , the connecting rod bearing 3 of this embodiment is formed by butting together the circumferential end faces 76 of a pair of semi-cylindrical half bearings 31, 32 to form an overall cylindrical shape. The half bearings 31, 32 have a backing metal layer 91 extending radially outward and a sliding layer 92 extending radially inward. The backing metal layer 91 can be made of an Fe alloy such as hypoeutectoid steel or stainless steel. The sliding layer 92 can be made of a Cu bearing alloy, an Al bearing alloy, or the like. The cylindrical inner circumferential surface 7 or the outer circumferential surface 8 may have a surface portion made of one of Bi, Sn, or Pb, which is softer than the bearing alloy. Alternatively, the surface portion may be made of an alloy primarily containing one of these metals, or a resin composition primarily containing a synthetic resin.

[0028] The half bearings 31, 32 have an inner peripheral surface 7, an outer peripheral surface 8, two circumferential end faces 76, 76, and two axial end faces 7E, 7E. The pair of half bearings 31, 32 have the same inner diameter dimension, outer diameter dimension, and axial length L1.

[0029] The half bearing 31 has an oil hole 3H that penetrates the wall thickness T of the half bearing 31, and the inner surface side opening 34 and the outer surface side opening 33 of the oil hole 3H have a circular shape when viewed from the direction of the axial line CL of the oil hole.

[0030] Figure 6 is a view showing the vicinity of the outer surface side opening 33 of the oil hole 3H of the half bearing 31 shown in Figure 3 (viewed from the arrow A in Figure 3), and Figure 7 is a cross-sectional view along line BB of the half bearing shown in Figure 5.

[0031] In the non-mounted state, the peripheral edge 33e of the outer peripheral surface opening 33 of the oil hole 3H of the half bearing 31 is located on the side closer to the center of curvature C1 of the outer peripheral surface than the outer peripheral surface 8 (i.e., on the inner peripheral surface 7 side) in the direction of the axial line CL of the oil hole 3H, and a transition surface 81 is formed between the outer peripheral surface 8 and the peripheral edge 33e of the outer peripheral surface opening 33 of the oil hole 3H. The depth of the transition surface 81, which is defined as the distance from the outer peripheral surface 8 to the transition surface 81 in a direction perpendicular to the outer peripheral surface 8, increases continuously in any radial direction relative to the center C2 of the oil hole 3H from a position adjacent to the outer peripheral surface 8 to a position adjacent to the peripheral edge 33e of the outer peripheral surface-side opening 33. The depth D1 of the transition surface at the position adjacent to the peripheral edge 33e of the outer peripheral surface-side opening 33 is 5 to 50 μm. In addition, the length L2 of the transition surface 81, which is defined as the radial distance relative to the center C2 of the oil hole 3H from a position adjacent to the outer peripheral surface 8 to a position adjacent to the peripheral edge 33e of the outer peripheral surface side opening 33, is 100 to 300 μm in any radial direction relative to the center C2 of the oil hole 3H. Furthermore, the ratio (D1 / L2) of the depth D1 of the transition surface at a position adjacent to the periphery 33e of the outer peripheral surface side opening 33 to the length L2 of the transition surface is preferably 0.05 to 0.20.

[0032] In this embodiment, the wall thickness T1 of the half bearing 31 and the thickness T2 of the backing metal layer 91 are constant circumferentially except for the region of the transition surface 81. The thickness T3 of the sliding layer 92 is constant throughout the entire circumferential length of the half bearings 31, 32. Alternatively, without being limited thereto, the wall thickness T1 of the half bearing 31 and the thickness T3 of the sliding layer may be greatest at the circumferential center of the half bearings 31, 32 and decrease toward the circumferential end faces 76. In the case of a bearing device for a small internal combustion engine, such as that used in a passenger car, the wall thickness T1 of the half bearings 31, 32 may be 1 to 3 mm, the backing metal layer thickness T2 may be 0.75 to 2.85 mm, and the sliding layer thickness T3 may be 0.15 to 0.3 mm. However, the wall thickness T1, backing metal layer thickness T2, and sliding layer thickness T3 of the half bearings 31, 32 are not limited thereto and may be other dimensions.

[0033] The inner circumferential surface 7 of the half bearings 31, 32 may also have crush reliefs (not shown) at both circumferential ends. Crush reliefs are surfaces formed by radially reducing the wall thickness of the inner circumferential surface 7 in the circumferential end regions of the half bearings 31, 32. These crush reliefs are formed to absorb misalignment or deformation between the circumferential end faces 76 of the half bearings that may occur, for example, when the pair of half bearings 31, 32 are assembled into a bearing housing. Therefore, the center of curvature of the surface of the crush relief is different from the center of curvature of the inner circumferential surface 7 in other regions (see SAE J506 (items 3.26 and 6.4), DIN 1497, section 3.2, and JIS D3102). Generally, in the case of small internal combustion engine bearings for passenger cars, the depth of the crush relief on the circumferential end face of the half bearing (the distance from the original inner circumferential surface to the crush relief on the circumferential end face 76) is about 0.01 to 0.05 mm.

[0034] Furthermore, in this embodiment, the half bearing 31 has one oil hole 3H, but may have multiple oil holes 3H. Furthermore, in this embodiment, of the pair of half bearings 31, 32, only one (upper) half bearing 31 has the oil hole 3H, but the other (lower) half bearing 32 can also have an oil hole 3H.

[0035] FIG. 10 is a view of the plain bearing and the big end of the connecting rod according to the first embodiment of the present invention, viewed from the axial direction. FIG. 11 is an enlarged cross-sectional view (enlarged cross-sectional view of part C) of the plain bearing and the big end of the connecting rod shown in FIG. 10 , taken near the oil hole 3H. As shown in FIG. 10 , when the half bearings 31, 32 are installed in the bearing retaining hole 23 of the big-end housing 21, circumferential compressive stress is generated in the pair of half bearings 31, 32, causing their circumferential end faces 76 to contact each other without any gaps. The dotted line adjacent to the outer peripheral surface 8 in FIG. 11 indicates a hypothetical transition surface 81A and outer peripheral surface opening 33A that would exist if they were not displaced upon installation. In the actual installed state, the circumferential compressive stress causes the circumferential end faces 76 of the pair of half bearings 31, 32 to press against each other, displacing the transition surface 81 radially outward (in the direction of the white arrow in FIG. 11 ). This causes the transition surface 81 to contact the inner peripheral surface 24 of the bearing retaining hole 23 without any gaps, just like the outer peripheral surface 81.

[0036] 11 , when the half bearing 31 is installed in the bearing retaining hole 23 of the big-end housing 21, the transition surface 81 of the half bearing 31 is displaced radially outward, causing the inner circumferential surface 7 in the area corresponding to the transition surface 81 and the inner circumferential surface opening 34 of the oil hole 3H to also be displaced radially outward. As a result, the transition inner circumferential surface 71 is formed in a position adjacent to the inner circumferential surface opening 34 of the oil hole 3H of the half bearing 31.

[0037] If the depth D1 of the transition surface 81 at a position adjacent to the circumferential edge 33e of the outer peripheral surface opening 33 in the unmounted state is less than 5 μm or the length L2 of the transition surface 81 is less than 100 μm, the transition surface 81 will be unable to sufficiently relieve the circumferential compressive stress applied around the oil hole 3H due to elastic deformation when a close-in phenomenon occurs in the bearing retaining hole 23 of the bearing housing 10 or 21. If the depth D1 of the transition surface at a position adjacent to the circumferential edge 33e of the outer peripheral surface opening 33 in the unmounted state is more than 50 μm or the length L2 of the transition surface 81 is more than 300 μm, oil passing through the oil hole 3H may get between the outer peripheral surface 8 of the half bearing 31 and the inner peripheral surface 24 of the bearing retaining hole 23 of the bearing housing 10 or 21 when a close-in phenomenon occurs in the bearing retaining hole 23 of the bearing housing 10 or 21. If oil gets between the outer surface 8 of the half bearing 31 and the inner surface 24 of the bearing retaining hole 23, the holding force of the plain bearing 3 by the bearing retaining hole 23 will be reduced, causing the plain bearing 3 to rotate together with the rotating shaft (crank pin 5), which may make it unable to support the rotating shaft (crank pin 5; journal portion 6).

[0038] Next, the operation of the present invention will be described. As described above, during operation of the internal combustion engine, due to the inertial force applied to the bearing housing 10; 21 and the dynamic load from the crankshaft, the bearing retaining hole 23 of the cylindrical bearing housing 10; 21 undergoes a phenomenon (close-in phenomenon) in which the bearing retaining hole 23 repeatedly undergoes elastic deformation (see FIG. 9) in which the vertical inner diameter DV becomes larger than the horizontal inner diameter DH, and then returns to its cylindrical shape (see FIG. 8). Figure 12A shows an enlarged cross-sectional view, viewed from the axial direction, of the vicinity of the oil hole 3H of the half bearing 31 in the mounted state when the bearing retaining hole 23 of the bearing housing 21 has elastically deformed due to the close-in phenomenon so that the vertical inner diameter DV becomes larger than the horizontal inner diameter DH (see Figure 9), and Figure 12B shows an enlarged cross-sectional view, viewed from the axial direction, of the vicinity of the oil hole 3H of the half bearing 31 in the mounted state when the bearing retaining hole 23 of the bearing housing 21 has elastically deformed so that it returns to a cylindrical shape (see Figure 8). As shown in Figure 12A, when the bearing retaining hole 23 of the bearing housing 21 elastically deforms so that the vertical inner diameter DV becomes larger than the horizontal inner diameter DH, the circumferential length of the inner surface 24 of the bearing retaining hole 23 increases, the circumferential stress applied to the half bearing 31 decreases, and the transition surface 81 elastically deforms so as to move away from the inner surface 24 of the bearing retaining hole 23. On the other hand, as shown in Figure 12B, when the inner diameter of the bearing retaining hole 23 of the bearing housing 21 elastically deforms to return to a cylindrical shape, the circumferential stress applied to the half bearing 31 increases, and the transition surface 81 elastically deforms so that it comes into contact with the inner surface 24 of the bearing retaining hole 23 without any gaps. When the close-in phenomenon occurs, just before the circumferential load applied around the oil hole 3H increases, part of the load is consumed by the elastic deformation of this transition surface 81, preventing damage (cracks) to the sliding layer 92 and backing layer 91 near the oil hole 3H and preventing the oil hole (i.e., the sliding layer and backing layer near the oil hole) from plastically deforming and reducing the circumferential length of the half bearing. This allows the holding force of the plain bearing by the bearing housing to be maintained.

[0039] (Second embodiment) Other non-limiting embodiments of the present invention will be described below.

[0040] Fig. 13 is a view of a connecting rod bearing 3 made up of half bearings 31, 32 in an unmounted state according to a second embodiment of the present invention, viewed from the axial direction, with the circumferential end faces 76 facing each other. Fig. 14 is a view of the upper half bearing 31 shown in Fig. 13, viewed from the axial direction. Fig. 15 is a plan view of the half bearing 31 shown in Fig. 14, viewed from the outer circumferential surface side. Fig. 16 is a cross-sectional view of the half bearing 31 shown in Fig. 15 taken along line DD, and Fig. 17 is an enlarged view of part E of the half bearing 31 shown in Fig. 16.

[0041] The bearing device of the second embodiment differs only in the configuration of the upper half bearing 31 of the sliding bearing (connecting rod bearing 3), and the other configurations are the same as those of the bearing device of the first embodiment. Explanation of the configurations common to the first embodiment will be omitted.

[0042] A chamfer 34C is formed between the inner peripheral surface 7 and the peripheral edge 34e of the inner peripheral opening 34 of the oil hole 3H of the half bearing 31. Burrs may form on the edge of the inner peripheral opening 34 of the oil hole 3H during manufacturing of the half bearing 31. The chamfer 34C is formed to remove these burrs. In this embodiment, the surface of the chamfer 34C is flat, but it may also be curved.

[0043] A chamfer 33C is formed between the outer peripheral surface 8 and the periphery 33e of the outer peripheral opening 33 of the oil hole 3H of the half bearing 31. Burrs may form on the edge of the outer peripheral opening 33 of the oil hole 3H during manufacturing of the half bearing 31. The chamfer 33C is formed to remove these burrs. In this embodiment, the chamfer 33C has a curved (arcuate) surface, but it may also have a flat surface. Note that this chamfer 33C does not come into contact with the inner peripheral surface 24 of the bearing retaining hole 23 when the half bearing 31 is mounted in the bearing retaining hole 23 of the bearing housing 21. If the chamfer 33C is made too large, the strength of the backing metal layer 91 in the vicinity of the outer peripheral opening 33 of the oil hole 3H will be reduced. In order to minimize the effect on the strength of the backing metal layer 91 in the vicinity of the outer peripheral surface opening 33 of the oil hole 3H, it is preferable that the length L3 of the chamfer 33C, which is defined as the radial distance with respect to the axial line CL from a position adjacent to the outer peripheral surface 8 to a position adjacent to the periphery 33e of the outer peripheral surface opening 33, be 15% or less of the length L2 of the transition surface 81 (see Figure 17).

[0044] While the above description has been given using an example in which the bearing device of the present invention is applied to a connecting rod bearing that supports the crank pin of a crankshaft of an internal combustion engine, the bearing device of the present invention can also be applied to a main bearing that supports the journal portion of the crankshaft. The half bearings may further include, for example, oil grooves or positioning notches. The half bearings may also have chamfers at positions where the outer peripheral surface and each axial end face are adjacent, or at positions where the inner peripheral surface and each axial end face are adjacent. [Explanation of symbols]

[0045] 1 Bearing device 10 Bearing housing (for main bearing) 101 Housing division body (lower part of cylinder block) 102 Housing division body (bearing cap) 2 connecting rods 21 Bearing housing (for connecting rod bearing) 22A Housing division (rod side large end housing) 22B Housing segment (cap side large end housing) 23 Bearing retaining hole 24 Inner peripheral surface 25 Lubricating oil path 3 Connecting rod bearing 31, 32 Half bearings 3H oil hole 33 Outer surface opening 33e Periphery 34 Inner surface opening 34e Periphery 4 Main bearing 41, 42 Half bearings 41a Oil groove 4H oil hole 5 crank pin 5a, 5b Lubrication oil path 5c outlet 6 Journal Department 6a Lubrication oil path 6c Inlet opening 7 Inner surface 71 Transition inner surface 7E Axial end face 76 Circumferential end face 8 Outer surface 81 Transition plane 81A Virtual transition surface 91 Underground Gold 92 Sliding layer C1 Center of curvature of outer surface C2 Oil hole center CL Oil hole axis line D1 Depth of the transition surface L1 Axial length of half bearing L2 Length of the transition surface L3 Chamfer length T1 Half bearing wall thickness T2 Backing layer thickness T3 Thickness of sliding layer X Rotation direction of journal Z Crank pin rotation direction

Claims

1. A bearing device for supporting a crankshaft of an internal combustion engine, comprising: a crankshaft; a bearing housing having a cylindrical bearing retaining hole; and a cylindrical plain bearing mounted on an inner peripheral surface of the bearing retaining hole; a bearing device in which the plain bearing is made up of a pair of half bearings each having a semi-cylindrical shape, each half bearing having a backing layer extending on the outer diameter side and a sliding layer extending on the inner diameter side, each half bearing having an inner circumferential surface, an outer circumferential surface and both circumferential end surfaces, the inner circumferential surface of each half bearing supports the crankshaft, the pair of half bearings have the same axial length, at least one of the pair of half bearings has one or more oil holes extending through a wall thickness of the half bearing, and both the inner circumferential surface side opening and the outer circumferential surface side opening of each oil hole have a circular shape; a transition surface is formed between the outer peripheral surface of the half bearing and a periphery of the outer peripheral surface side opening of the oil hole, In an unmounted state in which the plain bearing is not mounted on the inner peripheral surface of the bearing retaining hole, the peripheral edge of the outer peripheral surface side opening of the oil hole of the half bearing is located closer to the center of curvature of the outer peripheral surface in the direction of the axial line of the oil hole than the outer peripheral surface of the half bearing, so that the depth of the transition surface from the outer peripheral surface in a direction perpendicular to the outer peripheral surface increases continuously from a position adjacent to the outer peripheral surface towards a position adjacent to the peripheral edge of the outer peripheral surface side opening, the depth of the transition surface at the position adjacent to the peripheral edge of the outer peripheral surface side opening is 5 to 50 μm, and the length of the transition surface from the position adjacent to the outer peripheral surface to the position adjacent to the peripheral edge of the outer peripheral surface side opening is 100 to 300 μm in either radial direction of the axial line of the oil hole, and a sliding bearing mounted on the inner peripheral surface of the bearing retaining hole, the outer peripheral surface and the transition surface of the half bearing being in contact with the inner peripheral surface of the bearing retaining hole without any gaps.

2. 2. The bearing device according to claim 1, wherein, in the non-mounted state, the ratio (D1 / L2) of the depth (D1) of the transition surface at a position adjacent to the periphery of the outer peripheral surface side opening to the length (L2) of the transition surface is 0.05 to 0.20.

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