Rotary sliding bearing and manufacturing method thereof

Abstract

To provide a rotary slide bearing and its manufacturing method, excellent in resistance against seizure by smoothly discharging a lubricant held in recessed portions.SOLUTION: A plurality of recessed portions 22 are formed on an outer surface of a shaft member 2, and an inclination angle θ2 of an inner face 24 at a rear part with respect to a rotating direction of the shaft member 2 is determined to be larger than an inclination angle θ1 of an inner face 23 at a front part with respect to the rotating direction of the shaft member 2, in the recessed portion 22.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a rotary plain bearing and a method for manufacturing the same. [Background technology]

[0002] A bearing member is known that forms a texture consisting of circular recesses with a diameter of 0.01 to 1.0 mm and a depth of 0.001 to 0.1 mm on the inner sliding surface of a main bearing that supports the crankshaft of an automobile engine or a connecting rod bearing that supports the crankpin, thereby reducing the contact area with the crankshaft or crankpin and thereby reducing frictional resistance (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-207108 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the recess formed on the sliding surface is too deep, the lubricating oil held in the recess cannot be smoothly discharged, resulting in a state of boundary lubrication, which means that a sufficient oil film cannot be formed between the shaft member and the bearing member, which can cause seizure.

[0005] The problem to be solved by the present invention is to provide a rotary plain bearing that has excellent seizure resistance by smoothly discharging lubricating oil held in recesses, and a method for manufacturing the same. [Means for solving the problem]

[0006] The present invention provides The laser light is irradiated at an angle toward the front side of the rotation direction of the shaft member with respect to the radial direction of the shaft member,The above problem is solved by forming a plurality of recesses on the outer surface of the shaft member, and making the inclination angle of the inner surface of each recess at the rear side relative to the rotation direction of the shaft member larger than the inclination angle of the inner surface at the front side relative to the rotation direction of the shaft member. [Effects of the Invention]

[0007] According to the present invention, since the lubricating oil held in the recessed portion can be smoothly discharged, it is possible to provide a rotary plain bearing with excellent seizure resistance and a method for manufacturing the same. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a front view showing a crankshaft to which an embodiment of the rotary plain bearing of the present invention is applied. [Figure 2] 2 is an enlarged view of a crank pin at part II in FIG. 1. FIG. [Figure 3] 10 is an enlarged front view showing an example of forming a recess according to the present invention. FIG. [Figure 4] 2A to 2C are an enlarged front view, a partially cutaway perspective view, and a cross-sectional view showing a recess and an uneven surface on the inner surface of the recess according to the present invention. [Figure 5] 1(a) to 1(c) are enlarged cross-sectional views showing examples of the shape of recesses according to the present invention. [Figure 6] 1A is an enlarged cross-sectional view illustrating the effect of the recess according to the present invention, and FIG. 1B is an enlarged cross-sectional view illustrating the effect of the recess according to a comparative example of the present invention. [Figure 7A] 1A to 1C are front views showing an example of a method for forming a recess according to the present invention. [Figure 7B] 1A to 1C are side views showing an example of a method for forming a recess according to the present invention. [Figure 7C] FIG. 7C is an enlarged cross-sectional view showing a portion VIIC of FIG. 7B. [Figure 7D] FIG. 7D is an enlarged cross-sectional view showing the state of the crank pin after the recess shown in FIG. 7C is formed. [Figure 8] 7(a) to 7(c) are enlarged cross-sectional views each showing an example of a method for grinding or polishing the sliding contact surface of the crank pin from the state of FIG. 7D. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a front view showing a crankshaft 1, which is one embodiment of a rotary plain bearing of the present invention. The rotary plain bearing of the present invention and its manufacturing method are not particularly limited, but can be applied to rotary plain bearings that include shaft members such as crank journals 11 and crank pins 12 of a crankshaft 1 of an automobile engine. The illustrated crankshaft 1 is a crankshaft for a four-cylinder engine, and includes crank journals 11 supported by bearing members on the engine side, crank pins 12 connected to connecting rods of pistons, crank arms 13 connecting crank journals 11 and crank pins 12, and balance weights 14 for reducing the inertial force generated by the reciprocating motion of the pistons.

[0010] The crank journal 11, which serves as a shaft member constituting the rotary plain bearing of this embodiment, is supported by the engine block via a half-shaped metal bearing (not shown). The crank pin 12, which also serves as a shaft member constituting the rotary plain bearing of this embodiment, is connected to the piston connecting rod via a half-shaped metal bearing (not shown). These metal bearings constitute the bearing members of the rotary plain bearing of this embodiment. The crank journal 11 and the metal bearing, and the crank pin 12 and the metal bearing, are slidable via lubricating oil.

[0011] Figure 2 is an enlarged view of the crank pin 12 in part II of Figure 1. The symbol CL indicates the central axis of the crank pin 12. Hereinafter, the crank pin 12 will be described as an example of a shaft member of the rotary plain bearing of the present invention, and the crank pin 12 will also be referred to as the shaft member 2. However, the present invention can be applied to a shaft member according to the present invention by giving the crank journal 11 a similar configuration in addition to the crank pin 12. The crank pin 12 will be described as rotating in the direction of the arrow with the central axis CL as the center of rotation relative to the connecting rod and the metal bearing.

[0012] As shown in Fig. 2, in the crankpin 12, which is a solid shaft member 2, the entire outer surface of the crankpin 12 serves as a sliding surface 21 with a metal bearing (not shown), and a plurality of recesses 22 are formed evenly or uniformly over the entire sliding surface 21. Fig. 3 is a front view showing an example of the formation of the recesses 22 according to the present invention, and the left-right direction in the drawing is the extension direction of the central axis CL of the crankpin 12. Fig. 3 shows three recesses 22, and indicates dimensions L1 and L2 of the opening ends of the recesses 22 and dimensions M1 and M2 relating to the positional relationship between the opening ends of the three recesses 22.

[0013] The dimensions of the opening end of one recess 22 are not particularly limited, but for example, as shown in FIG. 3, the long side L1 is 0.26 mm ± 0.02 mm (240 to 280 μm), the short side L2 is 0.025 mm ± 0.015 mm (10 to 40 μm), both ends are semicircular, and the space between them is rectangular, and the depth L3 (see FIG. 4) is 0.01 mm ± 0.005 mm (5 to 15 μm). Also, as shown in FIG. 3, the distance M1 along the long sides between two adjacent recesses is 1.3 mm ± 0.2 mm, and the distance M2 along the short sides is 2.6 mm ± 0.5 mm. Due to these dimensional relationships, the area ratio of the opening end of the recess 22 to the area of ​​the sliding surface 21 of the crankpin 12 is 0.26% ± 0.05%, which improves the wettability of the lubricating oil and enhances the retention of the lubricating oil.

[0014] The recesses 22 in one row along the central axis CL of the crank pin 12 and the recesses 22 in the rows above and below it may be arranged such that the positions of the open ends are staggered, as shown in Fig. 3. This is to ensure that the recesses 22 that hold lubricating oil are evenly arranged. The recesses 22 may also be formed using other known dimensions and arrangements.

[0015] 4A and 4B are diagrams showing examples of recess 22 and the formation of an uneven surface on the recess inner surface according to the present invention. Similar to FIG. 3, FIG. 4A is a front view showing the open end of recess 22. Similarly, FIG. 4B is a cross-sectional view taken along line BB. FIG. 4C is a partially cross-sectional perspective view taken along line CC. As shown in FIG. 4B, recess 22 includes four inner surfaces: a front inner surface 23 and a rear inner surface 24 extending from a pair of opposing long sides of the open end toward the bottom, and a left side surface 25 and a right side surface 25 extending from a pair of opposing semicircular circumferences of the open end toward the bottom, as shown in FIG. 4C. Regarding the front, rear, left, and right sides of recess 22, the downstream side and the upstream side are referred to as the front and rear, respectively, relative to the rotational direction of crankpin 12, respectively. Furthermore, the left side and the right side are referred to as the left and right sides, respectively, relative to the rotational direction of crankpin 12. For example, in Fig. 4(A), the crank pin 12 rotates from top to bottom on the paper, so the recess 22 shown in the figure also moves (rotates) from top to bottom on the paper. In this case, the bottom of the paper is the front, the top is the rear, the right side is the left, and the left side is the right.

[0016] As shown in Fig. 4(B) and Fig. 5(a) to (c), the recess 22 according to the present invention is formed so that the inclination angle θ2 of the rear inner surface 24 relative to the rotation direction of the crankpin 12 is larger than the inclination angle θ1 of the front inner surface 23 relative to the rotation direction of the crankpin 12. Note that the inclination angle of the inner surface of the recess 22 refers to the angle with a line that is parallel to the opening end of the recess 22 and passes through the bottom, as shown in Fig. 5(a) to (c), or in other words, the angle with a line that is tangent to the opening end of the recess 22. When the crankpin 12 rotates from right to left as shown in Fig. 5, the lubricating oil flows relatively from the left toward the right, passing through the front inner surface 23 and the rear inner surface 24 of the recess 22. More specifically, the lubricating oil on the front sliding surface 21 of the recess 22 flows from the front opening end 231 along the front inner surface 23, is retained at the bottom of the recess 22, then rises along the rear inner surface 24 and is discharged from the rear opening end 241 to the rear sliding surface 21 of the recess 22.

[0017] When the lubricating oil flows into, is held in, and is discharged from the recess 22, if the front inner surface 23 and the rear inner surface 24 have the same or identical shape, the lubricating oil is less likely to be discharged to the sliding surface 21 at the rear of the recess 22. That is, as in the comparative example shown in FIG. 6(b), when the lubricating oil flows downward from the front opening end 231 along the front inner surface 23 (dotted arrow), the lubricating oil flows smoothly. On the other hand, when the lubricating oil flows upward along the rear inner surface 24 toward the rear opening end 241, if the vertical stress is small, the lubricating oil swirls as it rises (solid arrow), making it less likely to flow upward.

[0018] In contrast, as shown in Fig. 6(a), the recess 22 according to the present invention is formed such that the inclination angle θ2 of the rear inner surface 24 is greater than the inclination angle θ1 of the front inner surface 23, so that the inclination of the rear inner surface 24 is steeper than that of the front inner surface 23. When the rear inner surface 24 is steep, the rear inner surface 24 acts as a weir against the lubricating oil (dotted arrow) flowing from the front opening end 231 along the front inner surface 23, and can cause the lubricating oil to rise vertically (solid arrow). Therefore, the lubricating oil easily flows along the rear inner surface 24 to the rear opening end 241 and is smoothly discharged to the sliding surface 21 at the rear of the recess 22.

[0019] The inclination angle θ2 of the rear inner surface 24 may be greater than the inclination angle θ1 of the front inner surface 23 (i.e., θ2 > 45 degrees), as shown in FIG. 5(b), and is not particularly limited. However, the closer the rear inner surface 24 is to perpendicular to the bottom of the recess 22, the more likely stress acting vertically on the lubricant is to be generated. Therefore, the inclination angle θ2 is preferably set to 70 degrees to 90 degrees. In this case, the inclination angle θ2 may be set according to the depth of the recess 22, such that the inclination angle θ2 approaches 90 degrees as the depth of the recess 22 increases. This makes it easier for the lubricant retained in the recess 22 to be discharged more smoothly. As shown in FIG. 5(c), the shape of the recess 22 may be composed of five inner surfaces, including a bottom surface 26 connecting the front inner surface 23 and the rear inner surface 24. The bottom surface 26 may be flat or arc-shaped to maintain the flow rate of the lubricant. This improves the retention of lubricating oil that has flowed in from the front inner surface 23, while allowing the lubricating oil to be smoothly discharged by the rear inner surface 24, which is steeper than the front inner surface 23.

[0020] 4(C), of the four inner surfaces constituting the recess 22, at least the rear inner surface 24 has a vertically streaked uneven surface extending from the open end of the recess 22 to the bottom. When this vertically streaked uneven surface is formed on the rear inner surface 24 from which the lubricating oil is discharged, it acts as a guide for the lubricating oil, making it easier for the lubricating oil to flow toward the upper rear open end 241, thereby allowing the lubricating oil to be discharged more smoothly. However, the vertically streaked uneven surface is not an essential component of the present invention and may be omitted as necessary.

[0021] FIG. 7A is a front view showing an example of a method for forming the recess 22 according to the present invention, where the symbol CL indicates the central axis of the crankpin 12. The recess 22 according to the present invention can also be formed by plastic processing such as forging or rolling. However, this method increases the frequency of tool replacement, such as a punch. Therefore, it is preferable to form the recess 22 by irradiating it with laser light. By using laser light, it is possible to relatively easily and stably form a complex shape in which the inclination angle θ1 of the front inner surface 23 of the recess 22 is small while the inclination angle θ2 of the rear inner surface 24 is approximately vertical. Furthermore, forming the recess 22 by irradiating it with laser light softens the open end of the recess 22 due to the tempering effect that occurs during cooling after the laser irradiation, thereby improving durability.

[0022] When forming recesses 22 by irradiating laser light, recesses 22 may be formed by a relative slight oscillation between the laser light and crankpin 12. However, to shorten the processing time, it is preferable to irradiate by scanning with an overlapping pulsed laser spot light. For example, using a laser marking device 3 shown in Fig. 7A, the pulsed laser spot light is scanned along the central axis CL of crankpin 12 so that the spot diameter D of spot light 32 of laser light 31 on sliding surface 21 of crankpin 12 is 0.025 mm ± 0.015 mm.

[0023] The crankpin 12 is fixed and not rotated about the central axis CL until a row of recesses 22 is formed along the central axis CL of the crankpin 12. After one row of recesses 22 is formed, the crankpin 12 is rotated slightly about its central axis CL to the next row, and the pulsed laser spot light is again scanned along the central axis CL of the crankpin 12. To form one recess 22, the pulsed laser spot light is scanned little by little along the central axis CL of the crankpin 12 so that the pulsed laser spot light overlaps, as shown in the center diagram of FIG. 7A . As a result, one recess 22 is formed as shown in the right diagram of the same figure. However, laser processing is a method of processing a pocket by melting metal, and the inner surface 24 behind the recess 22 is a surface where the molten metal has solidified. Therefore, even without special processing, an uneven surface with vertical stripes extending from the open end to the bottom is formed by the laser marks.

[0024] 7B is a side view showing an example of a method for forming recesses 22 according to the present invention, and FIG. 7C is an enlarged cross-sectional view showing portion VIIC of FIG. 7B. When recesses 22 are formed using a pulsed laser spot light, as shown in FIG. 7B, the laser marking device 3 is scanned while tilted at an angle α with respect to the central axis CL of the crankpin 12. More specifically, as shown in FIG. 7C, the irradiation angle of the laser light is tilted at the angle α forward in the rotation direction of the crankpin 12 with respect to the radial direction of the crankpin 12. This causes the inclination angle of the rear inner surface 24 of recesses 22 to be larger than the inclination angle of the front inner surface 23, making it possible to form the front inner surface 23 as a gently sloping surface and the rear inner surface 24 as a substantially vertically sloping surface.

[0025] Figure 7D shows the state of crank pin 12 after recess 22 has been formed by the method shown in Figures 7A to 7C. Shaft member 2 of the rotary plain bearing of the present invention may be used as a bearing with recess 22 formed in the method shown in Figures 7A to 7C, but may also be subjected to the following grinding or polishing process as needed.

[0026] As shown in FIG. 7D , when the recess 22 is formed by irradiating a laser beam, the molten metal solidifies, forming a molten layer in the recess 22. This molten layer often rises at the open ends 231 and 241 of the recess 22, forming burrs 28. If these burrs 28 remain on the crankpin 12 in the finished product, they could damage the metal bearing. Therefore, they are removed by grinding or polishing the sliding surface 21 of the crankpin 12. In particular, the burrs 28 at the open ends 231 and 241 of the recess 22 formed by laser processing are molten layers with low hardness and are therefore brittle, and can be easily removed by grinding or polishing. Removing the burrs 28 at the open ends 231 and 241 of the recess 22 prevents damage to the metal bearing and improves its durability.

[0027] 8(a) to 8(c) are enlarged cross-sectional views showing an example of a method for grinding or polishing the sliding surface 21, which is the outer surface of the crankpin 12. FIG. 8(b) shows a state after grinding or polishing has been performed from the state shown in FIG. 8(a), and FIG. 8(c) shows a state after further grinding or polishing has been performed from the state shown in FIG. 8(b). After forming multiple recesses 22 in the crankpin 12 according to this embodiment, as shown in FIG. 8(a), an abrasive 4 such as abrasive paper is brought into contact with the sliding surface 21 of the crankpin 12, and the crankpin 12 side is rotated. This causes grinding or polishing of the open ends of the recesses 22, particularly the open ends 231 and 241 of the pair of long sides. Note that the sliding surface 21 of the crankpin 12 and the abrasive 4 may be fixed on the crankpin 12 side and rotated on the abrasive 4 side, or both the crankpin 12 and the abrasive 4 may be rotated in opposite directions. The grinding or polishing amount in this step is preferably such that burrs 28 protruding from the sliding contact surface 21 become flush with the sliding contact surface 21 .

[0028] 8(b) shows a state in which the burrs 28 generated at the opening end 231 of the front inner surface 23 have been ground or polished until they become flush with the sliding surface 21. As shown in FIG. 7D, when the irradiation angle of the laser light is tilted forward in the rotation direction of the crank pin 12 and scanned, the burrs 28 generated at the rear opening end 241 become larger than the burrs 28 generated at the front opening end 231. Therefore, when the sliding surface 21 is ground or polished, the burrs 28 generated at the front opening end 231 are removed before the burrs 28 generated at the rear opening end 241, and become flush with the sliding surface 21.

[0029] FIG. 8( c ) shows a state in which the burr 28 generated at the front opening end 231 has been removed, and then the burr 28 generated at the rear opening end 241 has been ground or polished until it is flush with the sliding surface 21. As shown in FIG. 8( c ), when the burr 28 generated at the rear opening end 241 has been ground or polished until it is flush with the sliding surface 21, the curvature of the front inner surface 23 is greater than the curvature of the rear opening end 241, resulting in a gentle slope. This slope allows the lubricating oil to smoothly flow from the front opening end 231 along the front inner surface 23. In contrast, the curvature of the rear inner surface 24 is smaller, so the rear opening end 241 maintains its effect as a dam for the lubricating oil, while the slight curvature of the rear opening end 241 allows the lubricating oil to smoothly drain to the sliding surface 21 behind the recess 22. This gives the recess 22 a shape that allows for excellent inflow and discharge of lubricating oil.

[0030] As described above, according to the rotary plain bearing of this embodiment, the shaft member 2 has a plurality of recesses 22 on its outer surface, and the inclination angle θ2 of the inner surface 24 of the recesses 22 on the rear side relative to the rotation direction of the shaft member 2 is greater than the inclination angle θ1 of the inner surface 23 on the front side relative to the rotation direction of the shaft member 2, so that the lubricating oil held in the recesses can be smoothly discharged. As a result, a rotary plain bearing with excellent seizure resistance can be provided.

[0031] Furthermore, according to the rotary sliding bearing of this embodiment, the inclination angle θ2 of the rear inner surface 24 relative to the rotation direction of the shaft member 2 is 70 to 90 degrees, which allows the lubricating oil held in the recessed portion to be discharged even more smoothly.

[0032] Furthermore, according to the rotary sliding bearing of this embodiment, at least the rear inner surface 24 of the recess 22 relative to the rotation direction of the shaft member 2 is made into an uneven surface with vertical stripes extending from the open end of the recess 22 to the bottom, and the uneven surface acts as a guide for the lubricating oil to be drawn out, making it easier for the lubricating oil to be directed toward the rear open end 241 located above, thereby allowing the lubricating oil to be discharged more smoothly.

[0033] Furthermore, according to the rotary sliding bearing of this embodiment, of the opening ends 231, 241 of the recess 22, the curvature of the front opening end 231 relative to the rotation direction of the shaft member 2 is greater than the curvature of the rear opening end 241 relative to the rotation direction of the shaft member 2, allowing the lubricating oil to flow in smoothly. Furthermore, while the effect of the rear inner surface 24 as a dam for the lubricating oil is maintained, the slight curvature of the rear opening end 241 allows the lubricating oil to be smoothly discharged to the sliding surface 21 at the rear of the recess 22. As a result, the recess has a shape that allows excellent inflow and discharge of the lubricating oil.

[0034] Furthermore, according to the manufacturing method for a rotary plain bearing of this embodiment, laser light is irradiated at an angle toward the front in the rotational direction of the shaft member 2 relative to the radial direction of the shaft member 2, and multiple recesses 22 are formed on the outer surface of the shaft member 2. This makes it possible to relatively easily and stably form a complex shape in which the inclination angle θ1 of the front inner surface 23 of the recesses 22 is small, while the inclination angle θ2 of the rear inner surface 24 is approximately vertical.

[0035] Furthermore, according to the method for manufacturing a rotary plain bearing of this embodiment, a laser beam is irradiated onto at least the inner surface 24 of the recess 22 on the rear side in the direction of rotation of the shaft member 2 to form an uneven surface in the form of vertical stripes extending from the open end of the recess 22 to the bottom, thereby reducing the need to change tools for forging or rolling. Also, the uneven surface can be easily formed.

[0036] Furthermore, according to the manufacturing method for the rotary plain bearing of this embodiment, the recesses 22 and the uneven surface are formed simultaneously by irradiating the outer surface of the shaft member 2 with overlapping pulsed laser spot light, so that the processing time (takt time) can be shortened and the recesses 22 and the uneven surface can be easily formed.

[0037] Furthermore, according to the manufacturing method for the rotary plain bearing of this embodiment, after forming the multiple recesses 22, the outer surface of the shaft member 2 is ground or polished along the rotation direction of the shaft member 2 to remove the molten layer (burr 28) that has formed at the opening ends 231, 241 of the recesses 22, thereby suppressing damage to the metal bearing and improving durability.

[0038] Furthermore, according to the method for manufacturing a rotary plain bearing of this embodiment, after the molten layer (burr 28) is removed by grinding or polishing, the outer surface of the shaft member 2 is further ground or polished along the rotational direction of the shaft member 2, so that the curvature of the front open end 231 relative to the rotational direction of the shaft member 2 is made greater than the curvature of the rear open end 241 relative to the rotational direction of the shaft member 2. This allows the lubricating oil to flow in smoothly, and furthermore, while the effect of the rear inner surface 24 as a dam for the lubricating oil is maintained, the slight curvature of the rear open end 241 allows the lubricating oil to be smoothly discharged to the sliding surface 21 behind the recess 22, resulting in a recess shape that is excellent in terms of the inflow and discharge properties of the lubricating oil. [Explanation of symbols]

[0039] 1...Crankshaft 11...Crank journal 12...Crank pin 13...Crank arm 14...Balance weight 2...Shaft member 21…Sliding surface 22...recess 23...Front inner surface 24...Rear inner surface 25...Side 26...Bottom 3...Laser marking device 31...Laser light 32...Spot light 4...Abrasive material CL…Center axis line

Claims

1. A rotary plain bearing having a bearing member and a shaft member that is in sliding contact with the bearing member via lubricating oil, The laser beam is irradiated at an angle toward the front side in the rotation direction of the shaft member with respect to the radial direction of the shaft member, thereby forming a plurality of recesses on the outer surface of the shaft member; A method for manufacturing a rotary plain bearing, wherein the inclination angle of the inner surface of the recess on the rear side relative to the rotation direction of the shaft member is formed to be larger than the inclination angle of the inner surface on the front side relative to the rotation direction of the shaft member.

2. A method for manufacturing a rotary plain bearing as described in claim 1, wherein the inclination angle of the rear inner surface relative to the rotation direction of the shaft member is formed to be between 70 degrees and 90 degrees.

3. 3. A method for manufacturing a rolling plain bearing according to claim 1 or 2, wherein a laser beam is irradiated onto at least an inner surface of the recess on a rear side relative to the rotation direction of the shaft member, to form an uneven surface in the form of vertical stripes extending from the open end of the recess to the bottom.

4. 4. A method for manufacturing a rotary plain bearing according to claim 3, wherein the recesses and the uneven surface are formed simultaneously by irradiating the outer surface of the shaft member with pulsed laser spot light in an overlapping manner.

5. 5. The method for manufacturing a rotary plain bearing according to any one of claims 1 to 4, wherein, after forming the plurality of recesses, the outer surface of the shaft member is ground or polished along the rotation direction of the shaft member, and a molten layer formed at the open ends of the recesses is removed.

6. 6. A method for manufacturing a rotary plain bearing according to claim 5, wherein, after removing the molten layer by the grinding or polishing, the outer surface of the shaft member is further ground or polished along the rotational direction of the shaft member, so that the curvature of the front open end in the rotational direction of the shaft member is made larger than the curvature of the rear open end in the rotational direction of the shaft member.

7. 7. The method for manufacturing a rotary plain bearing according to claim 1, wherein the shaft member is a crank journal or crank pin of a crankshaft of an automobile engine.

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