Manufacturing method of connecting rod

Abstract

To provide a method for manufacturing a connecting rod, which can reduce axial force at the time of screw fixation while suppressing misalignment of a cap part and a rod part at the time of screw fixation.SOLUTION: A method for manufacturing a connecting rod, which is disclosed in the present specification, includes a step of preparing a semi-finished product formed with a through-hole for a crankshaft, a laser processing step, and a breaking step. In the laser processing step, a plurality of laser marks are formed in the inner surface of the through-hole of the semi-finished product along the axial direction of the through-hole. In the breaking step, using the plurality of laser marks as starting points, the semi-finished product is divided into a rod part having a portion of the inner surface of the through-hole and a cap part having the other portion of the inner surface of the through-hole. In the laser processing step, a first processing condition is applied in a part of a range in the axial direction to form the laser mark, and a second processing condition different from the first processing condition is applied in the other part of the range in the axial direction to form the laser mark or to omit formation of the laser mark.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a method for manufacturing a connecting rod. [Background technology]

[0002] Patent Document 1 discloses a method for manufacturing a connecting rod, which includes the following steps. (1) A step of preparing a semi-finished product (referred to as a base material in Patent Document 1) in which a through hole for a crankshaft is formed. (2) A laser processing step for forming a plurality of laser marks (referred to as holes in Patent Document 1) in the through hole of the semi-finished product along the axial direction of the through hole. (3) A breaking process in which the semi-finished product is divided, starting from the multiple laser marks, into a rod portion having a part of the inner surface of the through hole and a cap portion having another part of the inner surface of the through hole. (4) A process of fastening the rod portion and cap portion separated in the breaking process with screws. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-113145 A Summary of the Invention [Problem to be solved by the invention]

[0004] When the processing conditions in the laser processing step are changed, the laser marks formed change. When the laser marks formed change, the surface shape of the fractured surface after fracture in the fracture step changes. For example, when the pitch at which the laser marks are formed is fine, the surface of the fractured surface becomes smooth. On the other hand, when the pitch at which the laser marks are formed is large, the surface of the fractured surface becomes rough.

[0005] If the surface of the fractured surface is smooth, the cap part and the rod part can be fixed with a small axial force when they are fixed with a screw. On the other hand, the frictional force generated at the mating surface between the cap part and the rod part (i.e., the fractured surface) is small, so that the cap part is likely to rotate relative to the rod part when they are fixed with the screw. As a result, the position of the cap part is likely to shift relative to the position of the rod part, leading to a decrease in assembly accuracy.

[0006] On the other hand, if the surface of the fractured surface is rough, the frictional force generated at the mating surface described above increases, so that the cap part is less likely to rotate relative to the rod part, and misalignment between the two is suppressed. However, the rougher the surface of the fractured surface is, the greater the axial force required to screw the cap part and the rod part together.

[0007] This specification provides a method for manufacturing a connecting rod that can reduce the axial force applied when the screws are fastened while suppressing misalignment between the cap portion and the rod portion when the screws are fastened. [Means for solving the problem]

[0008] The method for manufacturing a connecting rod disclosed in this specification includes a step of preparing a semi-finished product having a through hole of a crankshaft, a laser processing step, and a breaking step. In the laser processing step, a plurality of laser marks are formed on the inner surface of the through hole of the semi-finished product along the axial direction of the through hole. In the breaking step, the semi-finished product is divided into a rod part having a part of the inner surface of the through hole and a cap part having another part of the inner surface of the through hole, starting from the plurality of laser marks. In the laser processing step, the laser marks are formed by applying first processing conditions to a portion of the range in the axial direction, and the laser marks are formed by applying second processing conditions different from the first processing conditions to another portion of the range in the axial direction, or the formation of the laser marks is omitted.

[0009] In the above-mentioned manufacturing method, in the laser processing step, a first processing condition is applied to a part of the range in the axial direction, and a second condition different from the first processing condition is applied to another part of the range. Alternatively, the formation of the laser mark itself may be omitted in the other part of the range. This allows the surface shape of the fractured surface formed in the semi-finished product after the fracture step to be changed along the axial direction of the through hole rather than being uniform. That is, the surface of the fractured surface can be made relatively smooth (or flat) in a part of the range, while the surface of the fractured surface can be made relatively rough (or non-flat) in another part of the range. This allows the axial force required for screwing to be reduced while suppressing the positional deviation between the cap part and the rod part when they are fixed with a screw.

[0010] In the above-mentioned manufacturing method, the plurality of laser marks may further include a group of laser marks arranged along a first locus on the inner surface on one side in a first direction perpendicular to the axial direction, and a group of laser marks arranged along a second locus on the inner surface on the opposite side in the first direction. The first locus may have a convex shape displaced from both ends toward the cap portion toward the center, and the second locus may have a convex shape displaced from both ends toward the rod portion toward the center.

[0011] Suppose that both the first locus and the second locus are convex shapes displaced toward the cap part. In this case, at both axial end portions, the circumferential length of the inner surface formed in the cap part after the breaking process is shorter than the circumferential length of the inner surface formed in the rod part, and is less than the length of the semicircle. As described above, the cap part and the rod part, which are divided from each other, are fixed to each other by screws or the like in a subsequent process. At this time, two divided plain bearings are disposed on the inner surfaces of the cap part and the rod part, respectively. If the divided plain bearings each have a semicylindrical shape, and the circumferential length of the inner surface formed in the cap part is less than the length of the semicircle, both end portions in the circumferential direction of the plain bearing simultaneously protrude toward the inner surface formed in the rod part. In this state, when the cap part and the rod part are fixed to each other, the both end portions of the plain bearing protruding from the cap part may come into contact with the rod part at the same time, which may damage the plain bearing. In contrast, according to the configuration according to the present technology described above, the circumferential length of the inner surface of each of the cap part and the rod part can be the length of a semicircle, regardless of the axial position. As a result, both circumferential end portions of the divided plain bearing do not protrude from the inner surface of the through hole at the same time in either the cap portion or the rod portion. Therefore, even if one end of the plain bearing protruding from the rod portion comes into contact with the cap portion, the plain bearing will rotate passively, thereby avoiding or reducing damage to the plain bearing.

[0012] Also, a manufacturing method according to another embodiment includes a step of preparing a semi-finished product having a through hole of a crankshaft, a laser processing step of forming a plurality of laser marks on an inner surface of the through hole of the semi-finished product along an axial direction of the through hole, and a breaking step of dividing the semi-finished product into a rod portion having a part of the inner surface of the through hole and a cap portion having another part of the inner surface of the through hole, starting from the plurality of laser marks. In this case, the plurality of laser marks may include a group of laser marks arranged on the inner surface along a first locus on one side in a first direction perpendicular to the axial direction, and a group of laser marks arranged on the inner surface along a second locus on the opposite side in the first direction, and the first locus may have a convex shape displaced from both ends toward the cap portion side toward the center, and the second locus may have a convex shape displaced from both ends toward the rod portion side toward the center.

[0013] Details and further improvements of the technology disclosed in this specification are described in the following "Forms for Carrying Out the Invention". [Brief description of the drawings]

[0014] [Figure 1] 1 is a front view of a connecting rod manufactured by a manufacturing method according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a front view of a semi-finished product in a laser processing step of the manufacturing method according to the embodiment. [Diagram 3] 13 is a front view of the cap portion and the rod portion in a breaking step of the manufacturing method of the embodiment. FIG. [Figure 4] 1A and 1B are a cross-sectional view and a plan view of a semi-finished product on which a group of laser marks is formed by the laser processing step of the manufacturing method of the embodiment, respectively, after the product has been broken. [Diagram 5] 13 is a cross-sectional view of a semi-finished product on which a group of laser marks is formed according to a first modified example. [Figure 6] 13 shows a cross-sectional view of a semi-finished product on which a group of laser marks is formed according to a second modified example. [Figure 7] 13 is a cross-sectional view of a semi-finished product on which a group of laser marks is formed according to a third modified example. [Figure 8]13 is a cross-sectional view of a semi-finished product on which a group of laser marks is formed according to a fourth modified example. [Figure 9] FIG. 13 is a side view of the inner surface of a through hole in which a group of laser marks is formed according to a fifth modified example. [Figure 10] FIG. 13 is a side view of the inner surface of a through hole in which a group of laser marks is formed according to a sixth modified example. [Figure 11] FIG. 13 is a side view of the inner surface of a through hole in which a group of laser marks is formed according to a seventh modified example. [Figure 12] FIG. 13 is a side view of the inner surface of a through hole in which a group of laser marks is formed according to an eighth modified example. [Figure 13] FIG. 13 is a side view of the inner surface of a through hole in which a group of laser marks is formed according to a ninth modified example. [Figure 14] FIG. 13 is a front view of a semi-finished product in a laser processing step of the manufacturing method according to the second embodiment. [Figure 15] FIG. 13 is a side view of the inner surface of a through hole in which a group of laser marks is formed in the second embodiment. [Figure 16] 16 shows a cross-sectional view of the connecting rod taken along line XVI-XVI in FIG. 15. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A method for manufacturing a connecting rod according to an embodiment (hereinafter, sometimes simply referred to as a manufacturing method) will be described with reference to the drawings. First, a connecting rod 10 manufactured by the manufacturing method according to the embodiment will be described with reference to Fig. 1. In the following, to facilitate understanding, the positive side of the Z-axis direction in the coordinate system shown in the drawings may be simply referred to as "upper", and the opposite negative side of the Z-axis direction may be simply referred to as "lower".

[0016] The connecting rod 10 includes a cap portion 10c and a rod portion 10r. The cap portion 10c is fixed to the rod portion 10r from above by two bolts 2. The cap portion 10c and the rod portion 10r abut against each other at a mating surface 4. A shaft through hole 10s is formed at the upper end of the connecting rod 10. A piston through hole 10p is formed at the lower end of the connecting rod 10. The connecting rod 10 is a component that constitutes an engine mounted on a vehicle. When assembled into the engine, a crankshaft (not shown) is inserted into the shaft through hole 10s. Similarly, a piston (not shown) is connected to the piston through hole 10p. The connecting rod 10 converts the reciprocating motion of the piston connected to the piston through hole 10p into the rotational motion of the crankshaft that passes through the shaft through hole 10s.

[0017] 2 and 3, a manufacturing method for manufacturing the connecting rod 10 will be described below. This manufacturing method includes a preparation step, a laser processing step, a breaking step, and an assembly step. In the preparation step, a semi-finished product 10о that will be the base material of the connecting rod 10 is prepared. As shown in FIG. 2, a shaft through hole 10s is already formed in the semi-finished product 10о at the preparation step stage.

[0018] In the laser processing step, a laser processing device 20 forms a group of laser marks 8 on the inner surface of the shaft through hole 10s. The group of laser marks 8 is composed of a plurality of laser marks. The laser processing device 20 irradiates the inner surface of the shaft through hole 10s with a plurality of lasers 22 while moving along the axial direction of the shaft through hole 10s (i.e., the forward and backward direction in the plane of FIG. 2). The laser processing device 20 forms the group of laser marks 8 on the inner surface of the shaft through hole 10s along the axial direction of the shaft through hole 10s. The laser processing device 20 irradiates the laser 22 on both sides in the X-axis direction (i.e., the left and right sides in the plane of FIG. 2). The laser processing device 20 forms the group of laser marks 8 at two opposing locations on the inner surface of the shaft through hole 10s.

[0019] In the breaking step, the upper side of the semi-finished product 10о (i.e., the part corresponding to the cap part 10c) is pulled upward while the lower side of the semi-finished product 10о (i.e., the part corresponding to the rod part 10r) is fixed. As described with reference to FIG. 2, the laser mark group 8 formed in the laser processing step is formed on the inner surface of the shaft through hole 10s. The laser mark group 8 is composed of a plurality of laser marks. The strength of the part where the laser mark group 8 is formed on the inner surface of the shaft through hole 10s is locally weakened. Therefore, when the upper side of the semi-finished product 10о is pulled upward, the semi-finished product 10о is broken starting from the laser mark group 8. As a result, as shown in FIG. 3, the semi-finished product 10о is divided into the cap part 10c having a part of the upper side of the inner surface of the shaft through hole 10s and the rod part 10r having a part of the lower side.

[0020] As shown in Figs. 2 and 3, the semi-finished product 10о has a bolt hole 2h extending in the vertical direction. An upper part of the bolt hole 2h is formed by the cap portion 10c, and a lower part of the bolt hole 2h is formed by the rod portion 10r. In the assembly process, the rod portion 10r is placed on one side of the crankshaft (not shown), and the cap portion 10c is placed on the other side. As a result, the crankshaft is inserted into the shaft through hole 10s. Thereafter, as described with reference to Fig. 1, the cap portion 10c and the rod portion 10r are fixed by the two bolts 2. In this way, the manufacturing method of the embodiment manufactures a connecting rod 10 (see Fig. 1) in which the crankshaft is inserted into the shaft through hole 10s by the preparation process, the laser processing process, the breaking process, and the assembly process.

[0021] When the bolt 2 (see FIG. 1) is fastened in the assembly process, the cap portion 10c tends to rotate together with the bolt 2 in the axial direction of the shaft through hole 10s. As described above, the cap portion 10c and the rod portion 10r are formed by breaking the semi-finished product 10о. For this reason, the cap fracture surface 11c of the cap portion 10c and the rod fracture surface 11r of the rod portion 10r cannot be formed with a shape (e.g., a positioning boss) that restricts the rotation of the cap portion 10c. When the cap portion 10c and the rod portion 10r are fixed by the bolt 2, the cap portion 10c is likely to rotate relative to the rod portion 10r. That is, the position of the cap portion 10c is likely to shift relative to the position of the rod portion 10r in the assembly process.

[0022] As one method for suppressing the misalignment of the cap portion 10c and the rod portion 10r, it is considered to roughen the surfaces of the cap fracture surface 11c of the cap portion 10c and the rod fracture surface 11r of the rod portion 10r. For example, when the surface of the cap fracture surface 11c is rough and fine protrusions are formed on the surface, recesses that fit with the protrusions of the cap fracture surface 11c are formed on the surface of the fractured rod fracture surface 11r. In other words, when the surfaces of the cap fracture surface 11c and the rod fracture surface 11r are rough, the position of the cap portion 10c is less likely to be misaligned with respect to the position of the rod portion 10r.

[0023] However, if the surfaces of the cap fracture surface 11c and the rod fracture surface 11r become rough, a large axial force is required when the bolt 2 is fastened in the assembly process.

[0024] The relationship between the laser marks formed in the laser processing step of the manufacturing method of the embodiment and the surface shape of the fractured surface formed by breaking starting from the laser marks will be described with reference to Fig. 4. Fig. 4(A) is a cross-sectional view at the position of the rod fractured surface 11r where the laser marks 8 were formed in the laser processing step. The hatching in Fig. 4(A) indicates the actual cross section of the semi-finished product 10о.

[0025] As shown in Fig. 4(A), the laser mark group 8 includes a first laser mark group 8a and a second laser mark group 8b. The first laser mark group 8a, which is provided in the center of the semi-finished product 10о in the axial direction 10a of the shaft through hole 10s, has the laser marks formed at a fine pitch. The second laser mark group 8b, which is provided at both ends of the semi-finished product 10о in the axial direction 10a, has the laser marks formed at a larger pitch than the first laser mark group 8a. That is, the laser mark group 8 is formed at a fine pitch in a part of the range in the axial direction 10a, and is formed at a pitch larger than the fine pitch in another part of the range.

[0026] FIG. 4(B) shows the shape of the surface of the rod fracture surface 11r observed from the L1 direction in FIG. 3 for the rod portion 10r obtained by dividing the semi-finished product 10о on which the laser mark group 8 in FIG. 4(A) is formed in the above-mentioned fracture process. As shown in FIG. 4(B), the first fracture surface 11a formed from the first laser mark group 8a among the rod fracture surfaces 11r has a smooth surface. On the other hand, the second fracture surface 11b formed from the second laser mark group 8b among the rod fracture surfaces 11r has a rough surface. As mentioned above, the second fracture surface 11b with a rough surface regulates the positions of the cap portion 10c and the rod portion 10r in the assembly process, but increases the axial force when the bolt 2 is tightened. On the other hand, the first fracture surface 11a with a smooth surface reduces the axial force when the bolt 2 is tightened. In this way, the manufacturing method of the embodiment can suppress an increase in the axial force by restricting the position of the cap portion 10c (see FIG. 1) and the rod portion 10r in a part of the range of the rod fracture surface 11r in the axial 10a direction and smoothing the other part of the range in the axial 10a direction. As shown in FIG. 4(B), the manufacturing method of the embodiment can effectively suppress an increase in the axial force when the bolt 2 (see FIG. 1) is fastened by smoothing the peripheral portion of the bolt hole 2h to which the axial force is applied when the bolt 2 (see FIG. 1) is fastened in the rod fracture surface 11r. In addition, the manufacturing method of the embodiment can suppress a positional deviation between the cap portion 10c (see FIG. 1) and the rod portion 10r by roughening the surface of the end portion in the axial 10a direction of the semi-finished product 10о, which has a small contribution to the axial force.

[0027] The processing conditions of the laser processing step for forming the laser marks that serve as starting points in the breaking step are not limited to those shown in Fig. 4(A). Modified examples of the processing conditions of the laser processing step will be described with reference to Figs. 5 to 13.

[0028] In the laser processing step of the first modification, as shown in Fig. 5, a first laser mark group 8a with a fine pitch is formed at the end of the laser mark group 80, and a second laser mark group 8b with a pitch larger than that of the first laser mark group 8a is formed in the center of the laser mark group 80. As a result, the manufacturing method of the first modification can suppress the positional deviation between the cap portion 10c (see Fig. 1) and the rod portion 10r in the peripheral portion of the bolt hole 2h to which the axial force is applied when the bolt 2 is fastened, of the rod fracture surface 11r, when the axial force is large when the bolt 2 is fastened. In addition, the manufacturing method of the first modification can smooth the surface of the end portion in the axial 10a direction of the semi-finished product 10о, and suppress the axial force when the bolt 2 is fastened from increasing more than necessary.

[0029] In the laser processing step of the second modified example, as shown in FIG. 6, the laser mark group 81 is divided into two in the axial 10a direction, and a first laser mark group 8a with a minute pitch is formed on one side, and a second laser mark group 8b is formed on the other side with a pitch larger than that of the first laser mark group 8a. As described with reference to FIG. 2, in the laser processing step, the laser processing device 20 irradiates multiple lasers 22 while moving along the axial 10a direction. Therefore, in the laser processing step of the second modified example, the laser processing device 20 changes the pitch at which the laser 22 is irradiated once. On the other hand, in the laser processing steps of the above-mentioned embodiment and the first modified example, the laser processing device 20 changes the pitch at which the laser 22 is irradiated twice. In the manufacturing method of the second modified example, the laser processing step can be simplified compared to the laser processing step in which the semi-finished product 10о is divided into three in the axial 10a direction to form the laser mark groups 8, 80 in which the pitch of the laser marks is changed. In the laser processing step of the second modified example, as shown in Fig. 6, the first laser mark group 8a is formed on the negative side in the Y axis direction (i.e., the upper side of the paper in Fig. 6), and the second laser mark group 8b is formed on the positive side in the Y axis direction (i.e., the lower side of the paper in Fig. 6). However, in another modified example, the second laser mark group 8b may be formed on the negative side in the Y axis direction, and the first laser mark group 8a may be formed on the positive side in the Y axis direction.

[0030] In the laser processing step of the third modified example, as shown in FIG. 7, the first laser mark group 8a with a minute pitch is formed only around the bolt hole 2 in the axial direction 10a, and no laser marks are formed at both ends in the axial direction 10a. That is, in the manufacturing method of the third embodiment, the first laser mark group 8a is formed in a part of the semi-finished product 10о in the axial direction 10a in the laser processing step, and no laser mark group is formed in another part of the axial direction 10a. Even in the semi-finished product 10о in which the laser mark group 82 is formed in a part of the axial direction 10a, the semi-finished product 10о is divided into the rod portion 10r and the cap portion 10c (see FIG. 3) starting from the partially formed first laser mark group 8a. For this reason, the formation of the laser mark group may be omitted in another part of the axial direction 10a.

[0031] The fracture surface in the area where the formation of the laser marks is omitted has a rougher surface than the fracture surface starting from the first laser marks 8a with fine pitch. Therefore, the fracture surface in the area where the formation of the laser marks is omitted can suppress the positional deviation of the cap portion 10c and the rod portion 10r when the bolt 2 (see FIG. 1) is fastened. In the laser processing step of the third modified example, the time required to form the laser marks can be shortened by shortening the length of the laser marks to be formed in the axial direction 10a.

[0032] 8, the laser processing step of the fourth modified example may form the first group of laser marks 8a with a fine pitch only on the end portion in the axial 10a direction of the semi-finished product 10о, and omit the formation of the group of laser marks around the bolt hole 2. As a result, similar to the group of laser marks 80 of the second modified example described with reference to FIG. 5, when the axial force during fastening is large, it is possible to suppress misalignment between the cap portion 10c (see FIG. 1) and the rod portion 10r in the peripheral portion of the bolt hole 2h on the rod fracture surface 11r to which the axial force is applied when the bolt 2 is fastened.

[0033] A manufacturing method of a further modified example will be described with reference to Figs. 9 to 13. Figs. 9 to 13 show the vertical positions of the laser marks formed on the inner surface of the shaft through hole 10s observed from the L2 direction in Fig. 2. In the embodiment and modified example described with reference to Figs. 4 to 8, in the laser processing step, the laser marks are formed flat along the axial direction 10a of the shaft through hole 10s (i.e., parallel to the axial direction 10a). The inventors have found that, while repeating breaking experiments with laser marks formed under various processing conditions, even if the laser marks are formed non-flat (i.e., inclined with respect to the axial direction 10a), the semi-finished product 10о can be broken starting from the inclined laser marks. That is, in this specification, the "laser processing step of forming a plurality of laser marks along the axial direction of the through hole" includes a laser processing step of forming parallel laser marks along the axial direction 10a of the shaft through hole 10s and a laser processing step of forming laser marks varying along the axial direction 10a of the shaft through hole 10s.

[0034] In the laser processing step of the fifth modified example, as shown in FIG. 9, the laser mark group 84 includes a first laser mark group 8a and a third laser mark group 8c. The first laser mark group 8a and the third laser mark group 8c are both formed with a minute pitch. The third laser mark group 8c is formed so as to be inclined upward toward the positive side of the Y axis direction (i.e., the right side of the paper surface of FIG. 9). The first laser mark group 8a is formed parallel to the axis 10a direction (i.e., the Y axis direction). That is, the laser processing step of the fifth modified example forms the first laser mark group 8a with a minute pitch parallel to the axis 10a direction in a partial range in the axis 10a direction. The laser processing step of the fifth modified example forms the third laser mark group 8c with a minute pitch inclined with respect to the axis 10a direction in another partial range in the axis 10a direction. As described above, the surface of the fracture surface broken starting from the first laser mark group 8a becomes smooth, suppressing an increase in the axial force when the bolt 2 (see FIG. 1) is tightened. On the other hand, the fracture surface that is fractured starting from the third laser mark group 8c that is inclined with respect to the axis 10a direction is inclined with respect to the axis 10a direction. The fracture surface that is inclined with respect to the axis 10a direction restricts the rotation of the cap portion 10c (see FIG. 1) when the bolt 2 is fastened. The fracture surface that is inclined with respect to the axis 10a direction can suppress the positional deviation between the cap portion 10c and the rod portion 10r. Note that in FIG. 9 to FIG. 11, the first laser mark group 8a and the axis 10a are shown shifted in the vertical direction to facilitate understanding. However, the actual first laser mark group 8a is formed at the same position as the axis 10a in the vertical direction.

[0035] 10, the laser mark group 85 formed in the laser processing step of the sixth modified example may further include a fourth laser mark group 8d in addition to the first laser mark group 8a and the third laser mark group 8c. In this case, the fourth laser mark group 8d may be formed at a minute pitch and inclined upward toward the negative Y-axis direction (i.e., the left side of the paper surface of FIG. 10). The fracture surface broken from the first laser mark group 8a formed parallel to the axis 10a direction at the center of the laser mark group 85 suppresses an increase in the axial force when the bolt 2 (see FIG. 1) is fastened. The fracture surface broken from the third laser mark group 8c and the fourth laser mark group 8d formed at the end of the laser mark group 85 in the axis 10a direction is inclined with respect to the axis 10a direction. By forming a group of laser marks 85 in the laser processing step and providing inclined fracture surfaces at both ends of the semi-finished product 10о (see FIG. 2) in the axial direction 10a, it is possible to suppress misalignment between the cap portion 10c and the rod portion 10r.

[0036] Furthermore, as shown in Fig. 11, the laser mark group 86 formed in the laser processing step of the seventh modified example may include a fifth laser mark group 8e that is inclined downward toward the negative Y-axis direction in the axial 10a direction (i.e., the left side of the paper surface in Fig. 11) instead of the fourth laser mark group 8d of the laser mark group 85. The fifth laser mark group 8e is also formed with a minute pitch like the fourth laser mark group 8d. The fracture surface broken starting from the fifth laser mark group 8e is inclined with respect to the axial 10a direction. By forming the laser mark group 86 in the laser processing step and providing inclined fracture surfaces at both ends of the axial 10a direction of the semi-finished product 10о, it is possible to suppress misalignment between the cap portion 10c and the rod portion 10r.

[0037] Also, as shown in FIG. 12, the laser mark group 87 formed in the laser processing step of the eighth modified example may include a sixth laser mark group 8f and a seventh laser mark group 8g that are inclined with respect to the axis 10a direction. The sixth laser mark group 8f is inclined downward toward the Y axis direction positive side of the axis 10a direction (i.e., the right side of the paper in FIG. 12). The seventh laser mark group 8g is inclined upward toward the Y axis direction positive side of the axis 10a direction (i.e., the right side of the paper in FIG. 12). The sixth laser mark group 8f and the seventh laser mark group 8g intersect at the center of the axis 10a direction of the semi-finished product 10о. The laser mark group 87 does not include a laser mark group parallel to the axis 10a direction. Both the sixth laser mark group 8f and the seventh laser mark group 8g are formed with a minute pitch. The fracture surface that is fractured starting from the sixth laser mark group 8f and the seventh laser mark group 8g is inclined with respect to the axis 10a direction. By forming a group of laser marks 87 in the laser processing step and providing inclined fracture surfaces on both ends of the semi-finished product 10o in the axial direction 10a, it is possible to suppress misalignment between the cap portion 10c and the rod portion 10r.

[0038] Furthermore, as shown in FIG. 13, the laser mark group 88 formed in the laser processing step of the ninth modified example may include three seventh laser mark groups 8h and three eighth laser mark groups 8i inclined with respect to the axis 10a direction. The seventh laser mark group 8h is inclined downward toward the Y axis direction positive side of the axis 10a direction (i.e., the right side of the paper in FIG. 13). The eighth laser mark group 8i is inclined upward toward the Y axis direction positive side of the axis 10a direction (i.e., the right side of the paper in FIG. 12). In the laser mark group 88, the seventh laser mark group 8h and the eighth laser mark group 8i are alternately arranged in the axis 10a direction. The fracture surface broken at the starting point of the multiple laser mark groups inclined with respect to the axis 10a direction is inclined with respect to the axis 10a direction. By forming the laser mark group 88 in the laser processing step and increasing the number of fracture surfaces inclined with respect to the axis 10a direction, the positional deviation between the cap part 10c and the rod part 10r can be further suppressed.

[0039] (Second Example) Hereinafter, the manufacturing method of the second embodiment will be described with reference to Figs. 14 to 16. Fig. 14 shows a front view of the semi-finished product 10o in the laser processing step. The laser processing step in the second embodiment is basically the same as the laser processing step described in Fig. 2. In the manufacturing method of the second embodiment, the laser processing device 20 irradiates both of the multiple lasers 22 in a straight line. That is, both of the multiple lasers 22 are irradiated by the laser processing device 20 along a direction perpendicular to the axis 10a. The laser processing device 20 moves inside the shaft through hole 10s along the direction of the axis 10a (i.e., the direction toward the back of the paper in Fig. 14) while rotating along the arrow R around the axis 10a.

[0040] Fig. 15(A) shows a group of laser marks arranged by the laser 22 on the positive side in the X-axis direction of the inner surface of the shaft through hole 10s (i.e., the side in the direction of the arrow L3 in Fig. 14). Fig. 15(B) shows a group of laser marks arranged by the laser 22 on the negative side in the X-axis direction of the inner surface of the shaft through hole 10s (i.e., the side in the direction of the arrow L4 in Fig. 14). That is, Fig. 15(A) shows a first locus 90a drawn by the laser 22 on the inner surface on the right side in the left-right direction of the connecting rod 10, and Fig. 15(B) shows a second locus 90b drawn by the laser 22 on the inner surface on the left side.

[0041] As shown in FIG. 15(A), the first locus 90a includes a first inclined portion 91 and a second inclined portion 92. The first inclined portion 91 is inclined from an end P1 located on the cap portion 10c side of the shaft 10a toward the center of the first locus 90a so as to approach the shaft 10a. The first inclined portion 91 is connected to the second inclined portion 92 at the end on the center side of the first locus 90a. The second inclined portion 92 is inclined from an end P2 located on the cap portion 10c side of the shaft 10a toward the center of the first locus 90a so as to approach the shaft 10a. As a result, the first locus 90a has a V-shape that is displaced downward from both ends P1 and P2 in the axial direction toward the center. In other words, the first locus 90a has a convex shape that is displaced toward the rod portion 10r side.

[0042] A first inclination angle θ1 is formed between the first inclined portion 91 and the axis 10a. A second inclination angle θ2 is formed between the second inclined portion 92 and the axis 10a. In this embodiment, the first locus 90a has a symmetric shape in the direction of the axis 10a with respect to the midline C1 in the axial direction of the semi-finished product 10о. As a result, the first inclination angle θ1 is equal to the second inclination angle θ2.

[0043] Similarly, as shown in FIG. 15(B), the second locus 90b includes a third inclined portion 93 and a fourth inclined portion 94. The third inclined portion 93 is inclined from an end P3 located on the rod portion 10r side of the shaft 10a toward the center of the second locus 90b so as to approach the shaft 10a. The third inclined portion 93 is connected to a fourth inclined portion 94 at an end on the center side of the second locus 90b. The fourth inclined portion 94 is inclined from an end P4 located on the rod portion 10r side of the shaft 10a toward the center of the second locus 90b so as to approach the shaft 10a. As a result, the second locus 90b has a V-shape that is displaced from both ends P1 and P2 in the axial direction toward the cap portion 10c toward the center. In other words, the second locus 90b has a convex shape that protrudes upward.

[0044] A third inclination angle θ3 is formed between the third inclined portion 93 and the axis 10a. A fourth inclination angle θ4 is formed between the fourth inclined portion 94 and the axis 10a. In this embodiment, the second locus 90b has a symmetric shape in the direction of the axis 10a with respect to the midline C1 in the axial direction of the semi-finished product 10о. As a result, the third inclination angle θ3 is equal to the fourth inclination angle θ4.

[0045] As described with reference to FIG. 14, the laser processing device 20 rotates in the direction of the arrow R while irradiating a plurality of lasers 22 extending in a straight line in the left-right direction. As a result, the laser 22 irradiated in the direction of the arrow L3 (i.e., the right direction) in FIG. 14 and the laser 22 irradiated in the direction of the arrow L4 (i.e., the left direction) are displaced point-symmetrically with respect to the axis 10a. Therefore, as shown in FIG. 15, the first trajectory 90a has a symmetric shape with respect to the second trajectory 90b with respect to the axis 10a. In other words, the V-shape drawn by the first trajectory 90a and the V-shape drawn by the second trajectory 90b have the same shape, although the displacement directions are opposite to each other. Therefore, the first inclination angle θ1 is equal to the third inclination angle θ3, and the second inclination angle θ2 is equal to the fourth inclination angle θ4.

[0046] With reference to FIG. 16, a connecting rod 10 manufactured by the manufacturing method of this embodiment will be described. A sliding bearing 31 is disposed inside a shaft through hole 10s of the connecting rod 10. The sliding bearing 31 has a cylindrical shape extending along the axis 10a of the shaft through hole 10s. A crankshaft 40 is disposed inside the sliding bearing 31. The sliding bearing 31 is a member that fixes the crankshaft 40 rotatably to the connecting rod 10. A gap 50 is provided between the sliding bearing 31 and the inner surface of the shaft through hole 10s. This gap 50 is filled with oil to reduce friction between the inner surface of the shaft through hole 10s and the outer surface 31s of the sliding bearing 31.

[0047] The plain bearing 31 is composed of a cap side member 31c and a rod side member 31r, which are formed by dividing a cylindrical shape in half. Therefore, each member 31c, 31r has a semi-cylindrical shape. When the plain bearing 31 and the connecting rod 10 are fixed to the crankshaft 40, the rod portion 10r and the rod side member 31r are disposed below the crankshaft 40. Next, the cap portion 10c and the cap side member 31c are disposed above the crankshaft 40. After that, the bolts 2 (see FIG. 1) are fastened from above in the assembly process. This allows the plain bearing 31 and the connecting rod 10 to be fixed so as to cover the entire circumference of the crankshaft 40, which has a cylindrical shape.

[0048] As described above, the cap portion 10c and the rod portion 10r are formed by breaking the semi-finished product 10о. As shown in FIG. 16, the boundaries E1 and E2 of the mating surfaces 4 of the portions 10c and 10r are exposed on the inner surface of the shaft through hole 10s. The boundaries E1 and E2 are prone to have steps due to burrs formed during the breaking process and misalignment of the portions 10c and 10r caused during the assembly process. The steps may damage the outer surface 31s of the sliding bearing 31. If the outer surface 31s is damaged, the outer surface 31s becomes rough. As a result, the oil filling the gap 50 becomes less likely to flow, and the rotation efficiency of the crankshaft 40 may decrease.

[0049] If each of the trajectories 90a, 90b has a V-shape that protrudes upward, each of the boundaries E1, E2 will be displaced upward by a distance D1 with respect to the median line C2. In that case, the circumferential distance between the boundaries E1, E2 on the cap portion 10c side will be shorter than half the inner circumference of the shaft through hole 10s. As described above, the sliding bearing 31 is disposed inside the shaft through hole 10s. When the circumferential distance between the boundaries E1, E2 on the cap portion 10c side becomes shorter, both circumferential ends of the sliding bearing 31 will simultaneously protrude toward the rod portion 10r side of the inner surface of the shaft through hole 10s. In this case, the outer surface 31s of the upper portion of the sliding bearing 31 (particularly, the cap side member 31c) is likely to interfere with the rod portion 10r. In particular, when the rod portion 10r interferes with each of the boundaries E1, E2, the outer surface 31s is likely to be damaged. That is, when each of the tracks 90a, 90b has a V-shape that protrudes upward, the outer surface 31s of the sliding bearing 31 is easily damaged.

[0050] In the manufacturing method of this embodiment, the first locus 90a has a V-shape that protrudes upward, and the second locus 90b has a V-shape that protrudes downward. As a result, as shown in Fig. 16, the boundary E1 located on the positive side of the X-axis direction (i.e., the right side of the paper in Fig. 16) is displaced upward by a distance D1 with respect to the midline C2 passing through the axis 10a. On the other hand, the boundary E2 located on the opposite side (i.e., the left side of the paper in Fig. 16) is displaced downward by a distance D2 with respect to the midline C2 passing through the axis 10a. That is, according to the manufacturing method of this embodiment, the circumferential distance between the boundaries E1 and E2 on the cap portion 10c side is likely to be maintained at half the inner circumference of the shaft through hole 10s.

[0051] Furthermore, as described above, the first locus 90a and the second locus 90b have point-symmetric shapes with respect to the axis 10a. Therefore, the distance D1 is equal to the distance D2. That is, the circumferential distance between the boundaries E1 and E2 on the cap portion 10c side is maintained at half the inner circumference of the shaft through hole 10s. This makes it difficult for one member 31c, 31r of the sliding bearing 31 to protrude from one inner surface side of each portion 10c, 10r to the other inner surface side. That is, the outer surface 31s of the sliding bearing 31 and each boundary E1, E2 are unlikely to interfere with each other. That is, according to the manufacturing method of this embodiment, damage to the outer surface 31s of the sliding bearing 31 can be reduced compared to a configuration in which the above-mentioned loci 90a, 90b both have a V-shaped shape displaced toward the cap portion 10c side. Furthermore, as described above, by each of the tracks 90a and 90b having an inclined portion, it is possible to suppress misalignment between the cap portion 10c and the rod portion 10r.

[0052] The points to note about the embodiment and each modified example are described below. The surface shapes of the cap fracture surface 11c and the rod fracture surface 11r formed in the fracture process vary depending on the material, shape, and environmental temperature constituting the semi-finished product 10о, and the tensile load and speed in the fracture process. Therefore, the processing conditions of the above-mentioned modified examples may be combined and applied as the processing conditions for the laser processing process. In addition, the length of the shaft through hole 10s of each laser mark group in the axial 10a direction and the angle of inclination with respect to the axial 10a can also be changed.

[0053] In the second embodiment, the loci 90a, 90b have a shape symmetrical in the direction of the axis 10a with respect to the midline C1, but in a modified example, the loci 90a, 90b may have an asymmetric shape.

[0054] Furthermore, the shape of each of the trajectories 90a, 90b is not limited to a V-shape, but may be, for example, a W-shape, which has multiple inclined portions displaced toward the cap portion 10c toward the center, and multiple inclined portions displaced toward the rod portion 10r toward the center.

[0055] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0056] 2: Bolt 2h : Bolt hole 4:Mating surface 8: Laser marks 10: Connecting rod 10c: Cap part 10p: Piston through hole 10r: Rod section 10s: Shaft through hole 10о: Semi-finished products 11a: 1st fracture surface 11b: Second fracture surface 11c: Cap fracture surface 11r: Rod fracture surface 20: Laser processing equipment 22: Laser 31: Plain bearing 31c: Cap side member 31r: Rod side member 31s: External surface 40: Crankshaft 50: Gap 90a: 1st trajectory 90b:Second trajectory 91: 1st slope part 92:Second slope part 93:Third slope part 94: 4th slope E1, E2: Boundary part P1~P4: Edge

Claims

1. A method for manufacturing a connecting rod, comprising the steps of: preparing a semi-finished product having a through hole for a crankshaft; a laser processing step of forming a plurality of laser marks on an inner surface of the through hole of the semi-finished product along an axial direction of the through hole; A breaking process is provided in which the semi-finished product is divided into a rod portion having a part of the inner surface of the through hole and a cap portion having another part of the inner surface of the through hole, starting from the plurality of laser marks; In the laser processing step, the laser mark is formed by applying first processing conditions to a portion of the range in the axial direction, and the laser mark is formed by applying second processing conditions different from the first processing conditions to another portion of the range in the axial direction, or the formation of the laser mark is omitted; The plurality of laser marks include A laser mark group is arranged on the inner surface along a first locus on one side in a first direction perpendicular to the axial direction, and a laser mark group is arranged on the inner surface along a second locus on the opposite side in the first direction, the first locus has a convex shape displaced from both ends toward a center portion toward the cap portion, The second locus has a convex shape displaced from both ends toward the center toward the rod portion.

2. A method for manufacturing a connecting rod, comprising the steps of: preparing a semi-finished product having a through hole for a crankshaft; a laser processing step of forming a plurality of laser marks on an inner surface of the through hole of the semi-finished product along an axial direction of the through hole; A breaking process is provided in which the semi-finished product is divided into a rod portion having a part of the inner surface of the through hole and a cap portion having another part of the inner surface of the through hole, starting from the plurality of laser marks; The plurality of laser marks include A laser mark group is arranged on the inner surface along a first locus on one side in a first direction perpendicular to the axial direction, and a laser mark group is arranged on the inner surface along a second locus on the opposite side in the first direction, the first locus has a convex shape displaced from both ends toward a center portion toward the cap portion, The second locus has a convex shape displaced from both ends toward the center toward the rod portion.

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