JP2007003000A - Connecting rod, internal combustion engine equipped therewith and automobile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a split type connecting rod formed of a titanium alloy to secure sufficient rigidity while suppressing an extra increase in weight. <P>SOLUTION: The titanium alloy split type connecting rod comprises a rod body part 10 and an large end part 30 provided at one end of the rod body part 10. The large end part 30 is cut and split into a rod portion 33 connected to one end of the rod body part 10 and a cap portion 34 to be joined to the rod portion 33. The rod portion 33 and the cap portion 34 each have a cut surface F in protruded/recessed shape. A difference in height between the highest portion and the lowest portion of the cut surface F is 230 μm or greater. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a connecting rod made of titanium alloy, and more particularly to a split type connecting rod made of titanium alloy in which a large end portion is divided. The present invention also relates to an internal combustion engine or a motor vehicle provided with such a connecting rod.

  In an internal combustion engine of a motor vehicle, a member called a connecting rod (or connecting rod) is used to connect a crankshaft and a piston. FIG. 42 shows a conventional connecting rod 401. The connecting rod 401 has a rod-shaped rod body 410, a small end 420 provided at one end of the rod body 410, and a large end 430 provided at the other end of the rod body 410.

  The small end portion 420 has a through hole (piston pin hole) 425 for allowing a piston pin to pass through, and is connected to the piston. On the other hand, the large end portion 430 has a through hole (crank pin hole) 435 through which the crank pin is passed, and is connected to the crank shaft.

  The large end portion 430 is divided into a rod portion 433 that is continuous with one end of the rod body portion 410 and a cap portion 434 that is coupled to the rod portion 433 by a bolt 440. FIG. 43 shows the connecting rod 401 with the bolt 440 removed. A bolt hole 432 into which the bolt 440 is screwed is formed in the large end portion 430 so as to penetrate both the rod portion 433 and the cap portion 434.

  The connecting rod 401 shown in FIGS. 42 and 43 is called a split connecting rod because the large end portion 430 is divided into the rod portion 433 and the cap portion 434 as described above.

  Conventionally, steel has been widely used as a material for connecting rods, but in recent years, it has been proposed to use a titanium alloy for reducing the weight of connecting rods (for example, Non-Patent Document 1). However, since titanium alloys have material characteristics different from those of steel, the following problems occur when a split connecting rod is formed using a titanium alloy.

  The longitudinal elastic modulus (Young's modulus) of the titanium alloy is around 100 GPa to 110 GPa, which is about half of the longitudinal elastic modulus of steel. Thus, titanium alloys are distorted approximately twice as much as steel when the same stress is applied. For this reason, when a titanium alloy is used as the material for the split connecting rod, the shape similar to that of the steel connecting rod is low in rigidity, and the large end portion is greatly deformed during use.

  The deformed large end is schematically shown in FIG. As can be seen from FIG. 44, due to the inertial force acting on the connecting rod, the rod portion at the large end is deformed so as to sag inward, and the roundness of the crankpin hole is reduced. As a result, there arises a problem that friction loss (friction loss) is increased and bearing metal disposed in the crank pin hole at the large end portion is seized to the crank pin.

In order to prevent such problems from occurring, conventional titanium alloy connecting rods ensure rigidity by suppressing the deformation of the large end by making the large end thicker than steel connecting rods. Yes. FIG. 45 schematically shows a connecting rod 501 made of titanium alloy disclosed in Non-Patent Document 1. As can be seen from FIG. 45, the shoulder portions 531a and 531b of the rod portion 533 (portions extending on both sides from the rod main body portion 510) are significantly thickened.
Toshihiko Matsubara, “Development of Free-cutting Titanium Alloy Connecting Rod”, Titanium / Zirconium, October 1991, Vol. 39, No. 4, p. 175-184

  However, increasing the thickness increases the weight of the connecting rod, so that the effect of reducing the weight by using a titanium alloy having a small specific gravity is reduced.

  The present invention has been made in view of the above problems, and an object of the present invention is to ensure sufficient rigidity while suppressing an increase in extra weight in a split connecting rod made of titanium alloy.

  The connecting rod according to the present invention is formed of a titanium alloy, and includes a rod main body portion and a large end portion provided at one end of the rod main body portion and having a through hole, and the large end portion is formed on the rod main body portion. A split type connecting rod divided into a rod part continuous to the one end and a cap part coupled to the rod part, wherein the rod part and the cap part each have a fractured surface having an uneven shape. The difference in height between the highest part and the lowest part of the fracture surface is 230 μm or more, whereby the above object is achieved.

  In a preferred embodiment, the rod portion and the cap portion include inclusions in the vicinity of the fracture surface.

  In a preferred embodiment, the titanium alloy includes a rare earth element and sulfur, and the inclusion is a compound of a rare earth element and sulfur.

  In a preferred embodiment, the titanium alloy includes 0.05 wt% or more and 0.7 wt% or less of a rare earth element and 0.05 wt% or more and 0.2 wt% or less of sulfur.

  In a preferred embodiment, the longitudinal direction of the inclusions forms an angle of 0 ° or more and 30 ° or less with respect to the mating surface of the rod portion and the cap portion.

  In a preferred embodiment, the longitudinal direction of the inclusion is substantially parallel to the mating surface.

  In a preferred embodiment, the metal flow in the vicinity of the mating surface is substantially parallel to the longitudinal direction of the inclusion.

  In a preferred embodiment, the longitudinal direction of the inclusion is substantially perpendicular to the mating surface of the rod portion and the cap portion.

  An internal combustion engine according to the present invention includes a connecting rod having the above-described configuration, thereby achieving the above object.

  The motor vehicle according to the present invention includes the internal combustion engine having the above-described configuration, thereby achieving the above object.

  The connecting rod made of titanium alloy according to the present invention is a split type connecting rod in which a large end portion is broken and divided into a rod portion continuing to one end of the rod main body portion and a cap portion coupled to the rod portion. The rod part and the cap part each have a fractured surface having an uneven shape, and the difference in height between the highest part and the lowest part of the fractured surface is 230 μm or more. Therefore, the fracture surfaces can be firmly fitted to each other, and the rigidity of the large end can be sufficiently increased. Therefore, deformation of the large end can be suppressed without increasing the thickness of the rod portion.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As will be described in detail below, the connecting rod according to the present invention is a split type connecting rod formed by a fracture method (sometimes referred to as a “breaking split type”). The fracture method is a method in which a large end portion is integrally formed and then divided into a rod portion and a cap portion by brittle fracture. Conventionally, the fracture method has not been used for connecting rods made of titanium alloy. This is because the titanium alloy has high toughness, and it has been considered that it is extremely difficult to perform a fracture method that requires brittle fracture on a connecting rod made of titanium alloy. For example, the fracture method is not used for the titanium alloy connecting rod disclosed in Non-Patent Document 1. Conventionally, when forming a split connecting rod made of titanium alloy, the rod portion and the cap portion are formed separately, or the large end portion is integrally formed and then cut by machining.

  1 and 2 show a connecting rod 1 made of a titanium alloy in the present embodiment. FIG. 1 and FIG. 2 are a perspective view and a plan view, respectively, schematically showing the connecting rod 1 before breaking division.

  As shown in FIGS. 1 and 2, the connecting rod 1 includes a rod-shaped rod main body 10, a small end 20 provided at one end of the rod main body 10, and a large provided at the other end of the rod main body 10. And an end 30.

  A through hole (referred to as a “piston pin hole”) 25 through which the piston pin passes is formed in the small end portion 20. On the other hand, a through-hole (referred to as “crank pin hole”) 35 through which the crank pin is passed is formed in the large end portion 30. The crank pin hole 35 is typically larger in diameter than the piston pin hole 25.

  The large end portion 30 has shoulder portions 31 a and 31 b extending from the rod main body portion 10 on both sides. Further, a bolt hole 32 is formed in the large end portion 30 as shown in FIG. The bolt hole 32 in the present embodiment is a bottomed hole that extends from the cap portion 34 side toward the rod portion 33 side and has a bottom surface 32 s inside the rod portion 33.

  In the following description, the direction in which the rod body 10 extends is referred to as “longitudinal direction”, and the direction of the central axis of the crankpin hole 35 (shown by a one-dot chain line in FIG. 1) is referred to as “axial direction”. . A direction orthogonal to the longitudinal direction and the axial direction is referred to as a “width direction”. In the drawings, the longitudinal direction is indicated by an arrow Z, the axial direction is indicated by an arrow X, and the width direction is indicated by an arrow Y.

  As shown in FIGS. 1 and 2, the rod portion 33 and the cap portion 34 are integrally formed in the large end portion 30 before the fracture division. The large end portion 30 is broken and divided along a planned fracture surface A that is parallel to the axial direction X and the width direction Y (that is, orthogonal to the longitudinal direction Z). The planned fracture surface A is set so as to pass through the central axis of the crankpin hole 35, for example.

  FIG. 3 shows the connecting rod 1 after fracture division. The large end portion 30 of the connecting rod 1 is divided into a rod portion 33 continuing to the other end of the rod main body portion 10 and a cap portion 34 coupled to the rod portion 33 by a coupling member (here, a bolt 40).

  By the fracture division, the fracture surface F having a fine concavo-convex shape is formed in each of the rod portion 33 and the cap portion 34. By bringing the fracture surface F of the rod portion 33 and the fracture surface F of the cap portion 34 into contact with each other and screwing the bolt 40 into the bolt hole 32, the rod portion 33 and the cap portion 34 are coupled to each other.

  As described above, the connecting rod 1 in the present embodiment is a fracture split type connecting rod. In the fracture split type connecting rod 1, the fracture surfaces F of the rod portion 33 and the cap portion 34 have complementary concave and convex shapes, so that the rod portion 33 and the cap portion 34 are accurately positioned. Moreover, when the unevenness | corrugation of the torn surface F fits, the coupling | bonding of the rod part 33 and the cap part 34 becomes firm, and the rigidity of the big end part 30 whole improves. In particular, since it is possible to receive not only the rod portion 33 but also the cap portion 34, the force for indenting the rod portion 33 inward, it is possible to suppress the deformation as shown in FIG.

  As a result of the inventor of the present invention actually making and studying titanium alloy connecting rods of various specifications, the difference in height between the highest part and the lowest part of the fracture surface F is 230 μm or more (more preferably 300 μm or more). By doing so, it was found that the fractured surfaces F could be fitted more firmly and the rigidity of the large end portion 30 could be sufficiently increased. Therefore, by setting the height difference of the fracture surface F to 230 μm or more, the deformation of the large end portion 30 can be effectively suppressed without increasing the thickness of the rod portion 33 as shown in FIG.

  In the connecting rod 1 according to the present embodiment, as described above, since the rigidity of the rod portion 33 is increased by the difference in height of the fracture surface F being 230 μm or more, it is sufficient even if the shoulder portions 31a and 31b are not thickened. Rigidity can be ensured. FIG. 4 shows an enlarged view of the vicinity of the shoulders 31a and 31b of the connecting rod 1. As shown in FIG. For comparison, FIG. 4 also shows the shape of the connecting rod 501 in which the rod portion 533 shown in FIG. As can be seen from FIG. 4, in the connecting rod 1 in the present embodiment, the thickness of the shoulder portions 31a and 31b is smaller than that of the connecting rod 501 shown in FIG. 45, and the weight is reduced accordingly.

  In order to increase the height difference of the fracture surface F so that it is 230 μm or more as described above, it is preferable that the rod portion 33 and the cap portion 34 include inclusions in the vicinity of the fracture surface F. FIG. 5 is a photomicrograph showing a cross section of a connecting rod actually produced as described later. As shown in FIG. 5, inclusions 8 are present in the matrix of the titanium alloy. The inclusion 8 has an anisotropic shape, for example, a needle shape (fiber shape) or an ellipse shape as shown in FIG. The length of the inclusion 8 is typically about 10 μm to 400 μm. The inclusion 8 illustrated in FIG. 5 is a rare earth element and sulfur compound.

  If the rod part 33 and the cap part 34 include the inclusion 8 in the vicinity of the fracture surface F (that is, in the vicinity of the planned fracture surface A before the fracture split), the inclusion 8 promotes brittle fracture, so the fracture Relatively large irregularities are easily formed on the cross section F. Therefore, it becomes easy to sufficiently increase the height difference of the fracture surface F to 230 μm or more.

  6 and 7 show the cross-sectional curve (surface roughness) of the fracture surface of the connecting rod of the prototype including the inclusion 8. Moreover, in FIG. 8, the cross-sectional curve (surface roughness) of a torn surface is shown about the connecting rod of the comparative example which does not contain the inclusion 8. FIG. The surface roughness shown in FIGS. 6, 7 and 8 is a plot of the roughness in the width direction Y.

  From comparison between FIG. 6 and FIG. 7 and FIG. 8, it can be seen that the inclusion 8 includes a larger difference in height of the fracture surface. Specifically, the height difference of the fracture surface (maximum height Ry calculated by JIS B0601-1994) is about 299 μm in the prototype shown in FIG. 6 and about 232 μm in the prototype shown in FIG. In the comparative example shown in FIG.

  In addition, the connecting rods of these prototypes and comparative examples were actually incorporated into the engine, and an engine test was conducted. In the connecting rod of the comparative example whose sectional curve is shown in FIG. 8, the deformation of the large end portion is large, and seizure of the bearing metal to the crank pin may occur. On the other hand, such seizure did not occur in the connecting rod of the prototype whose cross-sectional curves are shown in FIGS. 6 and 7. Also from this result, it is understood that the deformation of the large end portion 30 can be suppressed by setting the height difference of the fracture surface to 230 μm or more.

  For reference, FIG. 9 shows a cross-sectional curve of a fracture surface of a fractured connecting rod made of steel. In the example shown in FIG. 9, the height difference of the fracture surface is about 88 μm. As can be seen from this, by including inclusions 8 in the connecting rod 1 made of titanium alloy, it is possible to give the fracture surface F a significantly larger (specifically, twice or more) height difference than before. it can.

  Moreover, according to examination of this inventor, it turned out that the fracture | rupture division | segmentation of the connecting rod 1 made from a titanium alloy can be performed more easily and more reliably by orienting the longitudinal direction of the inclusion 8 to a predetermined direction. .

  FIG. 10 shows an example in which the inclusion 8 has a preferable breakability in the longitudinal direction. FIG. 10 is a diagram schematically showing the state of the inclusion 8 in the vicinity of the mating surface P between the rod portion 33 and the cap portion 34. In this figure, the inclusion 8 in the cross section B near the mating surface P is shown in the drawing. It is shown enlarged in the lower right.

  In the specification of the present application, the “mating surface” between the rod portion 33 and the cap portion 34 is not an actual fracture surface F including fine irregularities formed on the surfaces of the rod portion 33 and the cap portion 34, but a fracture division. It refers to a virtual surface P that coincides with the planned fracture surface A in the previous connecting rod 1. In the present embodiment, as shown in FIG. 1, the fracture split is performed along the planned fracture plane A that is orthogonal to the longitudinal direction Z (that is, parallel to the axial direction X and the width direction Y). It is a plane orthogonal to the longitudinal direction Z and parallel to the axial direction X and the width direction Y. Note that the planned fracture surface A and the mating surface P are not limited to those exemplified here. The planned fracture surface A and the mating surface P may not be orthogonal to the longitudinal direction Z, and may not be parallel to the axial direction X and the width direction Y.

  In the example shown in FIG. 10, the inclusion 8 extends substantially parallel to the mating surface P. In other words, the inclusions 8 are arranged so that the longitudinal direction thereof is substantially parallel to the mating surface P. Here, the inclusion 8 in the cross section of the cap portion 34 is shown, but also in the cross section of the rod portion 33, the longitudinal direction of the inclusion 8 is substantially parallel to the mating surface P.

  FIG. 11 shows a metal flow (also referred to as “fiber flow”) of the connecting rod 1 including the inclusions 8 as shown in FIG. Metal flow is a flow of metal structure found in forged products, and is also called forging line. When the cut surface of the forged product is corroded, the metal flow is visually recognized as a fibrous metal structure.

  As schematically shown by the solid line MF in FIG. 11, the metal flow in the vicinity of the mating surface P is substantially parallel to the mating surface P. Therefore, the metal flow in the vicinity of the mating surface P is substantially parallel to the longitudinal direction of the inclusion 8. Thus, the inclusions 8 are typically arranged so that the longitudinal direction thereof follows the metal flow. This is considered to be because inclusions 8 extend following the flow of the metal structure when the metal flow is formed. Therefore, the longitudinal direction of the inclusion 8 can be made substantially parallel to the mating surface P by setting the metal flow substantially parallel to the mating surface P, as will be described later.

  From the viewpoint of ease of mold design, improvement in strength, and improvement in yield, it is also conceivable to design so that the metal flow is parallel to the longitudinal direction of the connecting rod, as shown in FIG. However, in order to break and divide the large end portion of the connecting rod designed in this way, brittle fracture must be performed so as to cross the metal flow, that is, to cut the fibrous metal structure.

  On the other hand, as shown in FIG. 11, when the metal flow is substantially parallel to the mating surface P (the planned fracture surface A before the fracture split), the fracture split can be performed so as not to cross the metal flow. Therefore, fracture splitting can be easily performed in a connecting rod made of a titanium alloy having high toughness.

  Furthermore, as shown in FIG. 10, when the inclusion 8 whose longitudinal direction is substantially parallel to the mating surface P is included in the vicinity of the mating surface P between the rod portion 33 and the cap portion 34, it is easier to split the fracture. In addition, it can be performed more reliably. This is considered to be because the inclusion 8 having an anisotropic shape serves as the starting point of the break, thereby promoting the brittle break along the plane parallel to the longitudinal direction of the inclusion 8.

  In addition, although the case where the longitudinal direction of the inclusion 8 and the metal flow are substantially parallel to the axial direction X is illustrated here (FIGS. 10 and 11), the present invention is not limited to this. The longitudinal direction and metal flow of the inclusions 8 need only be substantially parallel to the mating surface P, and may be directed to any orientation in the mating surface P. The longitudinal direction of the inclusion 8 and the metal flow may be substantially parallel to the width direction Y (that is, substantially orthogonal to the axial direction X) as shown in FIGS. X and width direction Y may be crossed.

  However, from the viewpoint of more effectively suppressing the deformation of the large end portion 30 during operation, the longitudinal direction of the inclusion 8 is shown in FIG. 10 rather than being substantially parallel to the width direction Y as shown in FIG. As shown, it is preferably substantially parallel to the axial direction X. As a result of the inclusion 8 having an anisotropic shape being the starting point of fracture, the irregularities of the fracture surface F tend to be formed such that the ridge line extends in parallel to the longitudinal direction of the inclusion 8. Therefore, when the longitudinal direction of the inclusion 8 is set substantially parallel to the axial direction X, the unevenness of the fracture surface F is also formed so that the ridge line extends parallel to the axial direction X. Therefore, the rigidity with respect to the force (the force acting in parallel with the width direction Y orthogonal to the axial direction X) that causes the rod portion 33 of the large end portion 30 to be squeezed inward becomes higher, as shown in FIG. Deformation can be suppressed more effectively.

  Further, the longitudinal direction of the inclusion 8 and the metal flow may be inclined as long as the angle is relatively small with respect to the mating surface P as shown in FIG. If the angle θ formed by the longitudinal direction of the inclusion 8 and the mating surface P is 0 ° or more and 30 ° or less, the fracture division can be easily performed as compared with the conventional case. The reason for this will be described with reference to FIGS.

  As shown in FIG. 16A, when the angle θ formed by the longitudinal direction of the inclusion 8 and the mating surface P is 90 °, the fracture occurs along the plane perpendicular to the metal flow. For this reason, it is necessary to perform fracture division so as to cut the fibrous metal structure.

  On the other hand, as shown in FIG. 16 (b), when the longitudinal direction of the inclusion 8 is inclined at a relatively small angle with respect to the mating surface P, it breaks along the surface intersecting the metal flow. However, the fracture can be performed more easily than in the case shown in FIG. This is the number of fibrous structures to be cut, as can be seen from comparing the number of solid lines MF that schematically show the metal flow across the mating surface P in FIGS. 16 (a) and 16 (b). This is because there are fewer. For example, as illustrated in FIG. 16B, when the angle θ formed by the longitudinal direction of the inclusion 8 and the mating surface P is 30 °, the number of fibrous structures to be cut is approximately ½. .

  In addition, as shown in FIG. 16C, when the angle θ between the longitudinal direction of the inclusion 8 and the metal flow and the mating surface P is 0 °, the fracture occurs along the plane parallel to the metal flow. Will do. For this reason, it is possible to more easily carry out break division.

  Thus, by setting the angle θ between the longitudinal direction of the inclusion 8 and the mating surface P to be 0 ° or more and 30 ° or less, the number of fibrous structures to be broken as compared to the case where θ = 90 ° is obtained. Can be reduced to about ½ or less, and therefore, the fracture division can be performed sufficiently easily.

  Further, as shown in FIG. 2, the large end portion 30 of the connecting rod 1 in the present embodiment extends as a bolt hole 32 from the cap portion 34 side toward the rod portion 33 side, and has a bottom surface 32 s inside the rod portion 33. The bottomed hole which has is formed. Accordingly, the portion corresponding to the bottom of the bolt hole 32 serves to reinforce the rod portion 33, so that the rigidity of the rod portion 33 can be increased as compared with the case where the through hole is formed as the bolt hole.

  From the viewpoint of realizing higher rigidity, it is preferable that the thickness of the portion corresponding to the bottom of the bolt hole 32 is larger than a certain level. Specifically, the shortest distance from the bottom surface 32s of the bolt hole 32 to the outer surface of the rod portion 33 is preferably 3 mm or more, and more preferably 4 mm or more.

  Note that through holes may be formed as bolt holes. Even if the bolt hole is a through hole, sufficient rigidity can be ensured if the height difference of the fracture surface F is 230 μm or more.

  Next, the manufacturing method of the connecting rod 1 in this embodiment is demonstrated. Here, the manufacturing method will be described using the connecting rod 1 shown in FIGS. 17 and 18 as an example. FIGS. 17 and 18 are diagrams showing the connecting rod 1 before breaking and dividing, and specifically show an example of a preferable structure formed on the inner peripheral surface of the crankpin hole 35. Hereinafter, this structure will be briefly described, and subsequently, a method for manufacturing the connecting rod 1 will be described.

  A fracture starting groove 50 extending in the axial direction X is formed on the inner peripheral surface of the crankpin hole 35. The fracture start groove 50 is located at the center of the portion where the inner peripheral surface of the crankpin hole 35 and the planned fracture surface A intersect. The fracture starting groove 50 is formed in each of the mutually opposing positions on the inner peripheral surface of the crankpin hole 35.

  Further, on both sides of the fracture starting groove 50, bearing locking grooves 51 for locking a bearing metal functioning as a bearing are formed. The bearing locking groove 51 prevents the bearing metal from rotating. Each bearing locking groove 51 includes a concave portion having a curved bottom surface, and is provided so as to extend in the circumferential direction of the crankpin hole 35. The bottom surface of the bearing locking groove 51 is curved in an arc shape with a cross section perpendicular to the axial direction X.

  Further, notches 52 are respectively provided on both sides of the bearing locking groove 51. Each notch 52 has a curved bottom surface and is provided so as to extend in the circumferential direction of the crankpin hole 35. The bottom surface of each notch 52 is curved in an arc shape with a cross section perpendicular to the axial direction X. Further, chamfered portions 53 extending in the circumferential direction of the crankpin hole 35 are provided by chamfering the edge portion of the crankpin hole 35.

  Then, the manufacturing method of this connecting rod 1 is demonstrated. FIG. 19 is a flowchart showing the manufacturing method in the present embodiment.

  First, an element body of the connecting rod 1 including the rod main body portion 10, the small end portion 20, and the large end portion 30 is formed by forging using a titanium alloy (step S1). For example, a titanium alloy ingot is prepared, and the ingot is hot-forged to form plate-like members 60 and 62 as shown in FIGS. Thereafter, the plate-like members 60 and 62 are cut out as indicated by dotted lines in FIGS. The longitudinal direction of the inclusions 8 and the metal flow are formed along the deformation direction in plastic processing such as rolling or forging. Therefore, by forming the connecting rod body so that the direction of plastic deformation and the longitudinal direction of the connecting rod body are orthogonal to each other, the longitudinal direction of the inclusions 8 and the metal flow are changed to the planned fracture surface A (the divided mating surface P). It can be made substantially parallel to. The method for forming the connecting rod body is not limited to the hot forging exemplified here, and may be cold forging or machining from a rolled material.

  In this embodiment, a titanium alloy having a composition of Ti-3Al-2V-S-REM (rare earth elements, specifically, La and Ce are used) (for example, DAT52F manufactured by Daido Steel Co., Ltd.) is used as the material titanium alloy. Use. In the present specification, the titanium alloy includes titanium as a main component, and contains at least one of Al, V, Fe, Mo, Cr and C (preferably at least Al) of 0.5 wt% or more and 10.0 wt%. % Refers to an alloy added in an amount of less than 1%.

  By using a titanium alloy containing a rare earth element and sulfur, these compounds can be present as inclusions in the titanium alloy, and as described above, the fracture division can be easily performed. Thereby, the height difference of the fracture surface F can be easily set to 230 μm or more. In order to form inclusions in the titanium alloy, the content of rare earth elements (eg, La, Ce, Pr, Nd) is preferably 0.05 wt% or more and 0.7 wt% or less, and the sulfur content Is preferably 0.05 wt% or more and 0.2 wt% or less.

  Further, a titanium alloy containing 2.5 wt% or more and 6.75 wt% or less of aluminum and 1.6 wt% or more and 4.5 wt% or less of vanadium is excellent in hardness. It is possible to improve brittleness and facilitate brittle fracture.

  Next, the connecting rod 1 is machined (step S2). FIG. 22 is a flowchart showing detailed steps of machining. First, the thickness surface (surface perpendicular to the axial direction X) of the connecting rod 1 is ground (step S21), and subsequently, the piston pin hole 25 and the crankpin hole 35 are formed in the small end portion 20 and the large end portion 30, respectively. (Step S22).

  Next, the bearing locking groove 51 is formed on the inner peripheral surface of the crank pin hole 35 of the large end 30 (step S23), and then the notches 52 are formed on both sides of the bearing locking groove 51 (step S24). ). Subsequently, a chamfered portion 53 is formed at the edge of the crankpin hole 35 (step S25). The piston pin hole 25, the crank pin hole 35, the bearing locking groove 51, the cutout portion 52, and the chamfered portion 53 are formed by cutting.

  Thereafter, a bottomed hole is formed as a bolt hole 32 in the large end portion 30 (step S26). The bolt holes 32 are formed by cutting using a drill, for example. Typically, the bolt hole 32 is formed such that the shortest distance from the bottom surface 32s of the bolt hole 32 to the outer surface of the rod portion 33 is about 0.5 mm to 5 mm (preferably 3 mm or more). .

  Finally, the fracture starting groove 50 is formed on the inner peripheral surface of the crankpin hole 35 (step S27). In this embodiment, the break starting groove 50 is formed by wire cut electric discharge machining.

  In the wire cut electric discharge machining, a conductive wire is disposed along the axial direction X of the inner peripheral surface of the crankpin hole 35, and a pulse-like high voltage is provided between the conductive wire and the inner peripheral surface of the crankpin hole 35. Is applied. Accordingly, corona discharge is caused between the conductive wire and the inner peripheral surface of the crankpin hole 35, and the inner peripheral surface of the crankpin hole 35 is scraped into a linear shape. As a result, a fracture starting groove 50 that extends linearly in the axial direction X is formed at the center of the inner peripheral surface of the crankpin hole 35. According to the wire cut electric discharge machining, the break starting groove 50 can be simultaneously formed in the plurality of connecting rods 1. Therefore, production efficiency is improved. The fracture starting groove 50 may be formed by other machining such as laser machining or cutting.

  Further, grinding of the thickness surface of the connecting rod 1, formation of the piston pin hole 25 and crank pin hole 35, formation of the bearing locking groove 51, formation of the notch portion 52, formation of the chamfered portion 53, formation of the bolt hole 32, and The formation of the break starting groove 50 is not limited to the order illustrated in FIG. 22 and can be performed in any order. For example, the bearing locking groove 51, the cutout portion 52, and the chamfered portion 53 may be formed after the formation of the fracture starting groove 50.

  Subsequently, heat treatment is performed on the connecting rod 1 (step S3 in FIG. 19). In this embodiment, annealing treatment, solution treatment, and aging treatment are sequentially performed. An example of each processing condition is shown in Table 1. Table 1 also shows the Rockwell hardness (HRC) of the connecting rod 1 for each of the annealing treatment, the solution treatment and the aging treatment.

  From the viewpoint of improving the strength of the connecting rod 1 and facilitating brittle fracture, the Rockwell hardness after the heat treatment is preferably 33 HRC or more.

  Subsequently, a surface hardening process is performed on the connecting rod 1 (step S4), and then an internal thread process is performed in the bolt hole 32 of the large end 30 (step S5). The surface hardening treatment is performed, for example, by coating the surface of the connecting rod 1 with chromium nitride by the PVD method. In addition, you may perform a surface hardening process after grinding of the internal peripheral surface mentioned later (step S8).

  Next, the large end portion 30 of the connecting rod 1 is broken and divided into the rod portion 33 and the cap portion 34 (step S6).

  FIG. 23 shows an example of the breaking division technique. As shown in FIG. 23, the convex portions of the sliders 200 and 201 that are movable in the horizontal direction are inserted into the crank pin holes 35 of the large end portion 30 of the connecting rod 1, and the wedge 202 is inserted between the convex portions of the sliders 200 and 201. Driving with the weight 203. As a result, the large end portion 30 of the connecting rod 1 is broken and divided into the rod portion 33 and the cap portion 34 along the planned fracture surface A, starting from the fracture starting groove 50.

  In addition, it is preferable to cool the large end 30 to a predetermined temperature or lower (for example, −40 ° C. or lower) in advance before the step of breaking and dividing the large end 30. The large end 30 can be cooled, for example, by immersing the connecting rod 1 in liquid nitrogen. By performing such a cooling step before the fracture splitting step, the fracture split of the connecting rod 1 made of titanium alloy can be easily performed.

  Conventionally, such a cooling process has been performed on a steel fracture split type connecting rod. In the case of steel connecting rods, the temperature at which the fracture mode when a load is applied changes from ductile fracture to brittle fracture (called the “ductility-brittle transition temperature”) is below room temperature. This is because break division can be easily performed.

  However, in a titanium alloy, this ductile-brittle transition temperature is originally above room temperature. Therefore, it seems that the meaning of performing the cooling process does not seem at first glance. However, when the present inventor dared to perform the cooling step without being bound by such common technical knowledge, it was experimentally confirmed that the fracture splitting of the titanium alloy connecting rod is facilitated. The reason for this is presumed that fracture splitting was facilitated by a slight decrease in toughness.

  Subsequently, by inserting the bolt 40 into the bolt hole 32 in a state where the fracture surface F of the rod portion 33 and the fracture surface F of the cap portion 34 are in contact with each other, the rod portion 33 and the cap portion 34 are connected. Assembling (step S7 in FIG. 19).

  Next, the inner peripheral surfaces of the piston pin hole 25 at the small end portion 20 and the crank pin hole 35 at the large end portion 30 of the assembled connecting rod 1 are ground (step S8). In this way, the split connecting rod 1 is manufactured.

  Then, the rod part 33 and the cap part 34 are disassembled by removing the bolt 40 from the large end part 30 of the assembled connecting rod 1 (step S9). Finally, the disassembled rod part 33 and cap part 34 are assembled to the crankpin of the crankshaft (step S10).

  In the manufacturing method of the present embodiment, as described above, a connecting rod whose longitudinal direction of inclusions is substantially parallel to the plane to be broken is prepared, and the breaking division is performed on the connecting rod, so that the breaking division can be easily performed. it can. In addition, since the connecting rod including inclusions is prepared in the vicinity of the planned fracture surface, it is easy to sufficiently increase the height difference of the fracture surface.

  FIGS. 24A to 24E show photographs of fracture surfaces of the large end portion 30 of the connecting rod 1 actually manufactured. 24 (b), (c) and (d) are enlarged photographs of the parts 24B, 24C and 24D surrounded by a circle in FIG. 24 (a), and FIG. 24 (e) is the same as FIG. ) An enlarged photograph of a portion 24E surrounded by a circle inside. The inclusions 8 and the metal flow are parallel to the axial direction X (up and down direction on the paper surface). As shown in FIGS. 24 (a) to 24 (e), a brittle fracture surface having fine irregularities is obtained over the entire surface of the fracture surface F, and it can be seen that fracture splitting was suitably performed. Further, it can be seen that the uneven ridge line extends substantially parallel to the axial direction X, and the uneven ridge line extends parallel to the longitudinal direction of the inclusions 8. When the height difference of the fracture surface F was measured, it was 230 μm or more.

  In the present embodiment, the case where a connecting rod in which the longitudinal direction of inclusions is substantially parallel to the planned fracture surface is illustrated, but the longitudinal direction of the inclusion is an angle of 30 ° or less with respect to the planned fracture surface. As long as it is, it may be inclined. If the angle between the longitudinal direction of the inclusions and the mating surface is 0 ° or more and 30 ° or less, the fracture division can be easily performed.

  In addition, as shown in FIG. 25, the longitudinal direction of the inclusion 8 may be substantially perpendicular to the mating surface P. When the longitudinal direction of the inclusion 8 is substantially perpendicular to the mating surface P, the metal flow is substantially parallel to the longitudinal direction Z of the connecting rod 1 (see FIG. 12). Strength is improved. Specifically, the fatigue strength is improved by 5 to 10% with respect to the stress in the direction in which the axis of the connecting rod 1 is bent. In addition, the mold design is facilitated and the yield is improved.

  Even when the metal flow is substantially parallel to the longitudinal direction Z of the connecting rod 1, since the rod portion 33 and the cap portion 34 include the inclusion 8 in the vicinity of the fracture surface F, the height difference of the fracture surface F is sufficiently large. It is easy to increase the thickness to 230 μm or more.

  FIG. 26, FIG. 27 and FIG. 28 show cross-sectional curves (surface roughness) of the fracture surface of the connecting rod including a metal flow substantially parallel to the longitudinal direction Z. FIG. 26 and FIG. 27 show the surface roughness of the connecting rod of the prototype including the inclusion 8 whose longitudinal direction is substantially perpendicular to the mating surface P, and FIG. 28 shows the comparative example not including the inclusion 8. It shows the surface roughness of the connecting rod.

  From comparison between FIG. 26, FIG. 27, and FIG. 28, it can be seen that the inclusion 8 includes a larger difference in height of the fracture surface. Specifically, the difference in height of the fracture surface is about 279 μm in the prototype example shown in FIG. 26 (the composition of the titanium alloy material is Ti-3Al-2V), and the prototype example shown in FIG. Ti-3Al-2V) is about 248 μm, while the comparative example shown in FIG. 8 (the composition of the material titanium alloy is Ti-6Al-4V) is about 85 μm.

  The connecting rods of these prototypes and comparative examples were actually assembled to the engine, and an engine test was conducted. In the connecting rod of the comparative example whose sectional curve is shown in FIG. 28, seizure of the bearing metal to the crankpin may occur. On the other hand, in the connecting rod of the prototype whose cross-sectional curves are shown in FIG. 26 and FIG. 27, such seizure did not occur as a result of suppressing the deformation of the large end 30.

  In the case where the metal flow is substantially perpendicular to the mating surface P, the fracture split is less than in the case where the metal flow is substantially parallel to the mating surface P (or inclined at a relatively small angle). Since it becomes difficult, it is preferable to increase the breaking division speed and to give larger energy.

  In the present embodiment, as shown in FIGS. 17 and 18, a fracture starting groove 50, a bearing locking groove 51, and a notch 52 are formed on the inner peripheral surface of the crankpin hole 35. It is more preferable that these are formed in such a shape that the stress at the time of fracture division concentrates on the fracture starting groove 50, because "double cracking" at the time of fracture division can be prevented. This will be described in more detail below.

  29A, 29B, and 29C show cross-sectional shapes of the fracture starting point groove 50, the notch 52, and the bearing locking groove 51, respectively.

  As shown in FIG. 29 (a), the fracture starting groove 50 is composed of a substantially parallel surface and a semicircular bottom surface. The depth H1 of the fracture starting groove 50 is, for example, 0.5 mm, and the curvature radius R1 of the bottom surface is, for example, 0.1 mm.

  As shown in FIG. 29 (b), the notch 52 is formed of an arc-shaped bottom surface. The depth H2 of the notch 52 is, for example, 0.5 mm, and the curvature radius R2 of the bottom surface is, for example, 6.5 mm.

  As shown in FIG. 29 (c), the bearing locking groove 51 is composed of an arc-shaped bottom surface. The depth H3 of the bearing locking groove 51 is, for example, 1.6 mm, and the curvature radius R3 of the bottom surface is, for example, 6.5 mm.

  The depth H2 of the notch 52 and the depth H3 of the bearing locking groove 51 are equal to or greater than the depth H1 of the fracture starting groove 50. In the present embodiment, the depth H2 of the notch 52 is substantially equal to the depth H1 of the fracture start groove 50, and the depth H3 of the bearing locking groove 51 is greater than the depth H1 of the fracture start groove 50. Further, the curvature radius R2 of the bottom surface of the notch 52 is larger than the curvature radius R1 of the bottom surface of the fracture start groove 50, and the curvature radius R3 of the bottom surface of the bearing locking groove 51 is the curvature radius of the bottom surface of the fracture start groove 50. Greater than R1.

  In general, the stress concentration coefficient α is obtained by the following equation (1). In Equation (1), H represents the depth of the notch, and R represents the radius of curvature of the notch.

α = 1 + 2√ (H / R) (1)
When the depth H1 of the fracture starting groove 50 is 0.5 mm and the radius of curvature R1 is 0.1 mm, the stress concentration factor α is 5.5 from the above equation (1). When the depth H2 of the notch 52 is 0.5 mm and the radius of curvature R2 is 6.5 mm, the stress concentration factor α is 1.6 from the above equation (1). When the depth H3 of the bearing locking groove 51 is 1.6 mm and the curvature radius R3 is 6.5 mm, the stress concentration factor α is 2.0 from the above equation (1).

  As described above, the stress concentration factor of the fracture starting groove 50 is larger than the stress concentration factors of the notch 52 and the bearing locking groove 51.

  Therefore, stress concentrates in the fracture starting groove 50 on the inner peripheral surface of the crankpin hole 35, and the stress concentration is relaxed in the notch 52 and the bearing locking groove 51. As a result, stress is concentrated at the center of the inner peripheral surface of the crankpin hole 35.

  Here, the operation of the break starting groove 50 and the notch 52 at the time of breaking the large end 30 will be described in more detail. First, how the fracture proceeds at the large end 30 when the notch 52 is not provided will be described with reference to FIGS. 30 to 33, and then, when the notch 52 is provided. A state in which the breakage proceeds in the large end portion 30 will be described with reference to FIGS. 34 to 36.

  In the large end portion 30 shown in FIG. 30, a pair of bearing locking grooves 51 are formed on both sides of the fracture starting groove 50 formed in the central portion of the inner peripheral surface of the crankpin hole 35. The fracture starting groove 50 is also formed outside the bearing locking groove 51 (both ends of the inner peripheral surface of the crankpin hole 35).

  Usually, the stress tends to concentrate on the thin portion and the end portion. Since the bolt hole 32 is provided in the central portion of the large end portion 30, the central portion of the inner peripheral surface of the crankpin hole 35 is a thin portion. Therefore, stress concentrates on the central portion and both end portions of the inner peripheral surface of the crankpin hole 35.

  Therefore, in the large end portion 30 shown in FIG. 30, there are three break starting points: a break starting groove 50 at the center of the inner peripheral surface of the crankpin hole 35 and a break starting groove 50 at both ends. As a result, as indicated by arrows in FIG. 30, the breakage progresses from the center portion and both end portions of the inner peripheral surface of the crankpin hole 35.

  In this case, as shown in FIG. 31 and FIG. 32, the fracture surface a formed by the fracture from the central portion of the inner peripheral surface of the crankpin hole 35 and the fracture from both ends of the inner peripheral surface of the crankpin hole 35 When the fracture surface b is formed at a different height, a region 350 where the fracture surface a and the fracture surface b overlap with each other is generated as shown in FIG. .

  In addition, as shown in FIG. 32, the inner peripheral surface of the crankpin hole 35 is ground to the DD line in a later step. Further, in the conventional method for manufacturing the split connecting rod, the edge of the crankpin hole 35 is chamfered to the line EE in the step after the fracture split.

  Next, as shown in FIG. 33 (b), when the rod portion 33 and the cap portion 34 are separated, a step is generated at the junction M between the fracture surface a and the fracture surface b. As shown in FIG. 31, the merge portion M is generated at a position closer to the crankpin hole 35 than the center line L1 in the width direction Y of the large end portion 30.

  Thereafter, as shown in FIG. 33 (c), after the rod portion 33 and the cap portion 34 are assembled, the inner peripheral surface of the crankpin hole 35 is ground to the line DD. When the rod part 33 and the cap part 34 are disassembled, as shown in FIG. 33 (d), the broken piece 341 is missing from the region 350 where the fracture surface a and the fracture surface b overlap.

  On the other hand, in the large end portion 30 shown in FIG. 34, a pair of bearing locking grooves 51 are formed on both sides of the fracture starting groove 50 formed in the central portion of the inner peripheral surface of the crankpin hole 35. Cutout portions 52 are formed outside the bearing locking grooves 51 (both ends of the crankpin hole 35). Further, a chamfered portion 53 is formed at the edge of the crankpin hole 35.

  Since the stress concentration coefficient of the notch 52 is smaller than the stress concentration coefficient of the fracture starting groove 50, the stress concentration at both ends of the crankpin hole 35 is relaxed. Further, since the chamfered portion 53 is formed at the edge of the crankpin hole 35, stress concentration at the edge of the crankpin hole 35 is alleviated. Therefore, stress concentrates on the central portion of the inner peripheral surface of the crankpin hole 35.

  Therefore, in the example shown in FIG. 34, the starting point of the break is one place in the central portion of the inner peripheral surface of the crankpin hole 35. As a result, as indicated by an arrow in FIG. 34, the breakage proceeds from one place at the center of the inner peripheral surface of the crankpin hole 35.

  In this case, as shown in FIG. 35, the fracture surface F is formed by the fracture from the central portion of the inner peripheral surface of the crankpin hole 35. As shown in FIG. 36 (a), the rod portion 33 and the cap portion 34 are broken and divided by a single fracture surface F, and a double crack does not occur.

  Therefore, as shown in FIG. 36B, when the rod portion 33 and the cap portion 34 are separated, no step is generated on the fracture surface F.

  Thereafter, as shown in FIG. 36C, after the rod portion 33 and the cap portion 34 are assembled, the inner peripheral surface of the crankpin hole 35 is ground to the line DD. As shown in FIG. 36 (d), even when the rod portion 33 and the cap portion 34 are disassembled, the missing pieces do not occur.

  Thus, when the notch 52 is provided, as shown in FIG. 35, a plurality of regions are formed in the region between the center line L1 in the width direction Y of the large end 30 and the inner peripheral surface of the crankpin hole 35. There are no overlapping areas of fracture surfaces. When there is no overlapping region of a plurality of fracture surfaces in a region between at least the tangent L2 of the bolt hole 32 parallel to the axial direction X and the inner peripheral surface of the crankpin hole 35, the inner peripheral surface of the crankpin hole 35 It is possible to prevent fragments from being lost during grinding.

  As described above, when a structure is formed on the inner peripheral surface of the crankpin hole 35 such that the starting point of breakage is one place on the inner peripheral surface of the crankpin hole 35, the large end 30 is formed by one fracture surface F. Since the rod part 33 and the cap part 34 are broken and divided, the occurrence of double cracks can be prevented. Accordingly, it is possible to prevent a large protruding portion from being generated on the fracture surface F and to prevent a piece from being lost from the fracture surface F. As a result, high roundness and roundness are obtained at the time of assembling the rod portion 33 and the cap portion 34, and the occurrence rate of defective products is reduced.

  In addition, the structure formed in the inner peripheral surface of the crankpin hole 35 is not limited to what was illustrated here.

  In the large end portion 30 shown in FIG. 37, a pair of bearing locking grooves 51 are formed on both sides of the fracture starting groove 50 formed in the center of the inner peripheral surface of the crankpin hole 35, and the crankpin hole A chamfered portion 53 is formed at the edge of 35. In the outer part of the bearing locking groove 51, the fracture starting groove 50 and the notch 52 are not formed but are flat.

  Since the stress concentration coefficient of the flat surface is smaller than the stress concentration coefficient of the fracture starting groove 50, the stress concentration at both ends of the inner peripheral surface of the crankpin hole 35 is relaxed. Further, since the chamfered portion 53 is formed at the edge of the crankpin hole 35, stress concentration at the edge of the crankpin hole 35 is alleviated. Therefore, stress concentrates on the central portion of the inner peripheral surface of the crankpin hole 35.

  Therefore, the starting point of breakage is one place at the center of the inner peripheral surface of the crankpin hole 35. As a result, as indicated by an arrow in FIG. 37, the breakage proceeds from one central portion of the inner peripheral surface of the crankpin hole 35.

  In this case, a fracture surface is formed by the fracture from the central portion of the inner peripheral surface of the crankpin hole 35. Accordingly, the large end portion 30 is broken and divided into the rod portion 33 and the cap portion 34 by one fracture surface, so that double cracking does not occur.

  38, a notch 52 is formed at the center of the inner peripheral surface of the crankpin hole 35, and a pair of bearing locking grooves 51 are formed on both sides of the notch 52. In the large end 30 shown in FIG. Has been. A fracture starting groove 50 is formed outside one bearing locking groove 51, and a further notch 52 is formed outside the other bearing locking groove 51. Further, a chamfered portion 53 is formed at the edge of the crankpin hole 35.

  In this case, stress concentration at the central portion and the end portion where the notch portion 52 is provided in the inner peripheral surface of the crankpin hole 35 is alleviated. Further, since the chamfered portion 53 is formed at the edge of the crankpin hole 35, stress concentration at the edge of the crankpin hole 35 is alleviated. Therefore, stress concentrates on the end of the inner peripheral surface of the crankpin hole 35 where the fracture starting groove 50 is formed.

  Therefore, the starting point of breakage is one place on one end of the inner peripheral surface of the crankpin hole 35. As a result, as shown by an arrow in FIG. 38, the breakage proceeds from one place on one end of the inner peripheral surface of the crankpin hole 35.

  In this case, a fracture surface is formed by fracture from one end of the inner peripheral surface of the crankpin hole 35. Accordingly, the large end portion 30 is broken and divided into the rod portion 33 and the cap portion 34 by one fracture surface, so that double cracking does not occur.

  In the large end portion 30 shown in FIG. 39, a pair of bearing locking grooves 51 are formed on both sides of the fracture starting groove 50 formed in the central portion of the inner peripheral surface of the crankpin hole 35. A notch 52 is formed outside the stop groove 51. A chamfered portion 53 is not formed at the edge of the crankpin hole 35.

  Since the stress concentration factor of the notch 52 is smaller than the stress concentration factor of the fracture starting groove 50, the stress concentration at the both ends of the inner peripheral surface of the crankpin hole 35 is relaxed. Therefore, stress concentrates on the central portion of the inner peripheral surface of the crankpin hole 35.

  Therefore, the starting point of breakage is one place at the center of the inner peripheral surface of the crankpin hole 35. As a result, as indicated by an arrow in FIG. 39, the breakage proceeds from one central portion of the inner peripheral surface of the crankpin hole 35.

  In this case, a fracture surface is formed by the fracture from the central portion of the inner peripheral surface of the crankpin hole 35. Accordingly, the large end portion 30 is broken and divided into the rod portion 33 and the cap portion 34 by one fracture surface, so that double cracking does not occur.

  The connecting rod 1 in this embodiment is widely used in various internal combustion engines (engines) for motor vehicles and machines. In FIG. 40, an example of the engine 100 provided with the connecting rod 1 in this embodiment is shown.

  The engine 100 includes a crankcase 110, a cylinder block 120, and a cylinder head 130.

  A crankshaft 111 is accommodated in the crankcase 110. The crankshaft 111 has a crankpin 112 and a crank web 113.

  A cylinder block 120 is provided on the crankcase 110. The cylinder block 120 is fitted with a cylindrical cylinder sleeve 121, and the piston 122 is provided so as to reciprocate within the cylinder sleeve 121.

  A cylinder head 130 is provided on the cylinder block 120. The cylinder head 130 forms a combustion chamber 131 together with the piston 122 and the cylinder sleeve 121 of the cylinder block 120. The cylinder head 130 has an intake port 132 and an exhaust port 133. An intake valve 134 for supplying air-fuel mixture into the combustion chamber 131 is provided in the intake port 132, and an exhaust valve 135 for exhausting the combustion chamber 131 is provided in the exhaust port. .

  Piston 122 and crankshaft 111 are connected by connecting rod 1. Specifically, the piston pin 123 of the piston 122 is inserted into the through hole (piston pin hole) of the small end portion 10 of the connecting rod 1, and the crankshaft 111 is inserted into the through hole (crank pin hole) of the large end portion 20. The crank pin 112 is inserted, and the piston 122 and the crankshaft 111 are connected to each other. A bearing metal 114 is provided between the inner peripheral surface of the through hole of the large end portion 20 and the crank pin 112. The bearing metal 114 is locked by the bearing locking groove 51.

  Since the engine 100 shown in FIG. 40 has the split type connecting rod 1 made of titanium alloy in the present embodiment, it is possible to realize light weight, high fuel consumption, and high output.

  FIG. 41 shows a motorcycle including the engine 100 shown in FIG.

  In the motorcycle shown in FIG. 41, a head pipe 302 is provided at the front end of the main body frame 301. A front fork 303 is attached to the head pipe 302 so as to be able to swing in the left-right direction of the vehicle. A front wheel 304 is rotatably supported at the lower end of the front fork 303.

  A seat rail 306 is attached so as to extend rearward from the upper rear end of the main body frame 301. A fuel tank 307 is provided on the main body frame 301, and a main seat 308 a and a tandem seat 308 b are provided on the seat rail 306.

  A rear arm 309 extending rearward is attached to the rear end of the main body frame 301. A rear wheel 310 is rotatably supported at the rear end of the rear arm 309.

  The engine 100 shown in FIG. 40 is held at the center of the main body frame 301. For the engine 100, the connecting rod 1 in the present embodiment is used. A radiator 311 is provided in front of the engine 100. An exhaust pipe 312 is connected to the exhaust port of the engine 100, and a muffler 313 is attached to the rear end of the exhaust pipe 312.

  A transmission 315 is connected to the engine 100. A drive sprocket 317 is attached to the output shaft 316 of the transmission 315. The drive sprocket 317 is connected to the rear wheel sprocket 319 of the rear wheel 310 via a chain 318. Transmission 315 and chain 318 function as a transmission mechanism that transmits the power generated by engine 100 to the drive wheels.

  Since the motorcycle shown in FIG. 41 includes the engine 100 using the connecting rod 1 in the present embodiment, suitable performance can be obtained.

  According to the present invention, in a split type connecting rod made of a titanium alloy, it is possible to ensure sufficient rigidity while suppressing an increase in excess weight.

  The connecting rod made of titanium alloy according to the present invention is widely used in various internal combustion engines (for example, engines for motor vehicles).

It is a perspective view which shows typically the state before the fracture | rupture division | segmentation of the connecting rod in suitable embodiment of this invention. It is a front view which shows typically the state before the fracture | rupture division | segmentation of the connecting rod in suitable embodiment of this invention. It is a perspective view showing typically the state after fracture division of a connecting rod in a suitable embodiment of the present invention. It is a figure which shows the shoulder part periphery of a connecting rod in suitable embodiment of this invention. It is a microscope picture of the inclusion contained in the connecting rod in suitable embodiment of this invention. It is a graph which shows the cross-sectional curve of a torn surface about the connecting rod (prototype example) containing an inclusion. It is a graph which shows the cross-sectional curve of a torn surface about the connecting rod (prototype example) containing an inclusion. It is a graph which shows the cross-sectional curve of a torn surface about the connecting rod (comparative example) which does not contain an inclusion. It is a graph which shows the cross-sectional curve of a torn surface about a steel fracture split type connecting rod. It is a figure which shows typically the mode of the inclusion in the joint surface vicinity of a rod part and a cap part. It is a figure which shows typically the metal flow of the connecting rod in suitable embodiment of this invention. It is a figure which shows typically the metal flow of the conventional connecting rod. It is a figure which shows typically the mode of the inclusion in the joint surface vicinity of a rod part and a cap part. It is a figure which shows typically the metal flow of the connecting rod in suitable embodiment of this invention. It is a figure for demonstrating the relationship between the longitudinal direction of an inclusion, and a mating surface. (A)-(c) is a figure for demonstrating the suitable range of the angle | corner which the longitudinal direction of an inclusion and the mating surface make. It is a perspective view which shows typically the state before the fracture | rupture division | segmentation of the connecting rod in suitable embodiment of this invention. It is a perspective view which expands and shows a part of connecting rod shown in FIG. It is a flowchart which shows the manufacturing method of the connecting rod in suitable embodiment of this invention. It is a figure which shows an example of the aspect which cuts out the element | base_body of a connecting rod from a plate-shaped member. It is a figure which shows an example of the aspect which cuts out the element | base_body of a connecting rod from a plate-shaped member. It is a flowchart which shows the detailed process of machining. It is sectional drawing which shows an example of the method of fracture | rupture division | segmentation. (A)-(e) is a photograph which shows the fracture surface of the large end part of the connecting rod actually produced as an experiment. (B), (c) and (d) are enlarged photographs of the parts 24B, 24C and 24D surrounded by the circle in (a), and (e) is surrounded by the circle in (b). It is an enlarged photograph of the part 24E. It is a figure which shows typically the mode of the inclusion in the joint surface vicinity of a rod part and a cap part. It is a graph which shows the cross-sectional curve of a torn surface about the connecting rod (prototype example) containing an inclusion. It is a graph which shows the cross-sectional curve of a torn surface about the connecting rod (prototype example) containing an inclusion. It is a graph which shows the cross-sectional curve of a torn surface about the connecting rod (comparative example) which does not contain an inclusion. (A) is sectional drawing which shows the shape of a fracture | rupture origin groove | channel, (b) is sectional drawing which shows the shape of a notch part, (c) is sectional drawing which shows the shape of a bearing latching groove. It is a figure for demonstrating progress of the fracture | rupture in the fracture | rupture planned surface of the large end part in which the notch part is not provided. It is a figure which shows the state of the torn surface of the big end part in which the notch part is not provided. It is an enlarged view of the C section in FIG. (A)-(d) is sectional drawing which shows typically the process from the fracture | rupture of the large end part in which the notch part is not provided to grinding of an internal peripheral surface. It is a figure for demonstrating the progress of the fracture | rupture in the planned fracture | rupture surface of the large end part in which the notch is provided. It is a figure which shows the state of the torn surface of the large end part in which the notch part is provided. (A)-(d) is sectional drawing which shows typically the process from the fracture | rupture of the large end part in which the notch part is provided to grinding of an internal peripheral surface. It is a schematic diagram which shows progress of the fracture | rupture in the fracture | rupture planned surface of the large end part which has another structure suitable for prevention of a double crack. It is a schematic diagram which shows progress of the fracture | rupture in the fracture | rupture planned surface of the large end part which has another structure suitable for prevention of a double crack. It is a schematic diagram which shows progress of the fracture | rupture in the fracture | rupture planned surface of the large end part which has another structure suitable for prevention of a double crack. It is sectional drawing which shows typically an example of the engine provided with the connecting rod in suitable embodiment of this invention. FIG. 41 is a cross-sectional view schematically showing a motorcycle including the engine shown in FIG. 40. It is a front view which shows the conventional split type connecting rod typically. It is a front view which shows typically the state which removed the volt | bolt of the split type connecting rod shown in FIG. It is a figure which shows typically a mode that the big end part is deform | transforming at the time of an engine driving | operation. It is a front view which shows the conventional split type connecting rod typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Connecting rod 8 Inclusion 10 Rod main-body part 20 Small end part 25 Piston pin hole 30 Large end part 31a, 31b Shoulder part 32 Bolt hole 32s Bottom face of bolt hole 33 Rod part 33a Protruding part 34 Cap part 35 Crank pin hole 40 Bolt 50 Break start groove 51 Bearing locking groove 52 Notch 53 Chamfer 100 Engine

Claims (10)

Formed from titanium alloy,
The rod body,
Provided at one end of the rod main body, and a large end having a through hole,
The large end portion is a split-type connecting rod divided into a rod portion continuous with the one end of the rod body portion and a cap portion coupled to the rod portion,
The rod part and the cap part each have a fractured surface having an uneven shape,
A connecting rod having a height difference of 230 μm or more between the highest part and the lowest part of the fracture surface.   The connecting rod according to claim 1, wherein the rod portion and the cap portion include inclusions in the vicinity of the fracture surface.   The connecting rod according to claim 2, wherein the titanium alloy includes a rare earth element and sulfur, and the inclusion is a compound of a rare earth element and sulfur.   4. The connecting rod according to claim 3, wherein the titanium alloy contains 0.05 wt% or more and 0.7 wt% or less of a rare earth element and 0.05 wt% or more and 0.2 wt% or less of sulfur.   5. The connecting rod according to claim 2, wherein a longitudinal direction of the inclusion forms an angle of 0 ° or more and 30 ° or less with respect to a mating surface of the rod portion and the cap portion.   The connecting rod according to claim 5, wherein a longitudinal direction of the inclusion is substantially parallel to the mating surface.   The connecting rod according to claim 5 or 6, wherein a metal flow in the vicinity of the mating surface is substantially parallel to a longitudinal direction of the inclusion.   The connecting rod according to any one of claims 2 to 4, wherein a longitudinal direction of the inclusion is substantially perpendicular to a mating surface between the rod portion and the cap portion.   An internal combustion engine comprising the connecting rod according to any one of claims 1 to 8.   A motor vehicle comprising the internal combustion engine according to claim 9.