JP4618231B2 - Internal combustion engine and its connecting rod - Google Patents

Description

  The present invention relates to a connecting rod of an internal combustion engine that is connected to a piston of the internal combustion engine, a crankshaft having a rotation shaft at a position offset from the center axis of a cylinder bore, and an internal combustion engine including the connecting rod.

  As is well known, an internal combustion engine employing a so-called offset crank structure in which the center axis of the crankshaft is offset with respect to the center axis of the cylinder bore in order to reduce the frictional resistance between the piston and the cylinder block. Is widely known. In an internal combustion engine employing such an offset crank structure, the connecting rod is substantially parallel to the central axis of the cylinder bore at the timing when the combustion pressure becomes maximum, so that the force acting on the piston from the cylinder side wall in the expansion stroke is minimized. Therefore, it is possible to suppress the occurrence of so-called piston hitting sound.

However, in such an internal combustion engine, the connecting rod and the cylinder may interfere with each other when the offset amount is set to be large to some extent.
Therefore, conventionally, as seen in Patent Document 1, for example, a connecting rod having a bent portion in which a column portion connecting a large end portion and a small end portion is bent so as to protrude to the opposite side to the offset direction has been adopted. Proposed. By adopting such a configuration, it is possible to avoid interference between the connecting rod and the cylinder even when the offset amount is set to be somewhat large.
JP 2003-172101 A

  By the way, in such a connecting rod, interference between the connecting rod and the cylinder can be surely avoided, but when a bending moment is generated in the column portion of the connecting rod due to the combustion pressure acting on the piston. In addition, stress concentration occurs in the bent portion of the column portion. In particular, when the offset crank structure is adopted, such stress concentration becomes more remarkable. For this reason, the stress concentration may cause excessive bending deformation in the bent portion, and may cause damage such as cracks in the column portion.

  The present invention has been made in view of such circumstances, and its purpose is to avoid damage such as cracks caused by excessive bending deformation of the column portion while avoiding interference with the cylinder in an internal combustion engine having an offset crank mechanism. It is an object of the present invention to provide a connecting rod capable of suppressing the occurrence of the above.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
The invention according to claim 1 is a crankshaft having a small end portion in which an insertion hole into which a piston pin provided in a piston of an internal combustion engine is inserted is formed, and a rotation shaft at a position offset from the center axis of the cylinder bore. In a connecting rod of an internal combustion engine comprising a large end portion having an insertion hole through which a crank pin is inserted, and a column portion connecting the small end portion and the large end portion, the column portion is A straight line that has a line-symmetric shape with respect to a center line that connects the centers of the insertion holes of the end and the large end, and has both sides are flat and both sides are curved. An arcuate part connecting the straight line part and the large end part, and by making the curvature of the curved surface on the side where the rotation axis is offset in the arcuate part larger than the curvature of the curved surface on the opposite side, It is summarized in that the portion located on the opposite side is formed thicker in the direction perpendicular to the axial direction of the crankpin than the portion positioned core wire on the side where the rotating shaft is offset relative .

  According to this configuration, while avoiding interference between the column portion and the cylinder block, the rigidity against bending deformation of the column portion, which is likely to increase, can be increased by adopting the offset crank structure, and cracks caused by the deformation For example, the column portion can be prevented from being damaged.

Further , according to the same configuration, for example, compared with the case where the portion located on the opposite side to the offset direction is thickened in the axial direction of the crankpin, while suppressing the increase in the weight of the connecting rod due to the thickening. The rigidity against bending deformation of the column portion can be effectively increased.

The invention according to claim 2 comprises the connecting rod according to claim 1, wherein a small end portion of the connecting rod is connected to a piston pin provided on the piston, while a large end portion is a central axis of the cylinder bore. it is summarized in that an internal combustion engine comprising coupled to a crank pin of the crankshaft with its axis of rotation to a position offset from the.

  According to this configuration, in an internal combustion engine that employs an offset crank structure, while avoiding interference between the column section and the cylinder block, the rigidity against bending deformation of the column section that is likely to increase due to the adoption of the offset crank structure is improved. Thus, it is possible to suppress the occurrence of damage to the column part such as a crack caused by the deformation.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a partial cross-sectional view of an engine showing a connecting rod and a piston, a crankshaft and the like connected thereby. As shown in FIG. 1, this engine employs a structure in which the rotation axis LC of the crankshaft is offset with respect to the center axis LB of the cylinder bore 31 formed in the cylinder block 30, a so-called offset crank structure. The crankpin 40 of the crankshaft rotates along a broken line CC in the drawing around the rotation axis LC. The cylinder bore 31 is provided with a piston 20 that reciprocates within the bore 31. The piston pin 21 of the piston 20 and the crankpin 40 of the crankshaft are connected by the connecting rod 10.

  FIG. 2A shows the front structure of the connecting rod 10 according to the present embodiment based on a comparison with a conventional connecting rod, and FIG. 2B shows the AA line of FIG. The cross-sectional structures along are shown respectively. In FIG. 2A, the shape of the connecting rod 10 according to the present embodiment is indicated by a solid line, and the shape of the conventional connecting rod is indicated by a two-dot chain line.

  As shown in FIG. 2A, the connecting rod 10 according to the present embodiment is mainly composed of a rod main body 11 and a cap 12 fastened to the rod main body 11 by a bolt 13. The rod main body 11 has a small end portion 14 formed with an insertion hole 14a through which the piston pin 21 is inserted. On the other hand, in the rod body 11, a large end portion 16 is formed by the end portion opposite to the small end portion 14 and the cap 12. The large end portion 16 has an insertion hole 16a through which the crank pin 40 is inserted by a semi-arc-shaped facing surface 11a formed on the rod body 11 side and a semi-arc-shaped facing surface 12a formed on the cap 12 side. Is formed. Here, the small end portion 14, the large end portion 16, and the insertion holes 14a and 16a have a line-symmetric shape with respect to a center line L connecting the centers of the insertion holes 14a and 16a.

  On the other hand, the rod body 11 is formed with a column portion 15 that connects the small end portion 14 and the large end portion 16. The column portion 15 is composed of a straight portion 15 a that is flat on both sides and connected to the small end portion 14, and an arcuate portion 15 b that is curved on both sides and connects the straight portion 15 a and the large end portion 16. Yes. The straight portion 15a is formed such that both side surfaces in the left-right direction in the drawing are inclined, and the thickness between both side surfaces increases linearly from the small end portion 14 downward in the drawing. The straight line portion 15a also has a line-symmetric shape with respect to the center line L. On the other hand, the arc-shaped portion 15b is formed in a curved surface having a curvature Rn1 on the right side in the drawing, that is, the side opposite to the offset direction, and on the left side in the drawing, that is, the offset direction. The side surface of this side is formed into a curved surface having a curvature Rn2 larger than the curvature Rn1. Thus, the arcuate portion 15b has an asymmetric shape with respect to the center line L. As shown in FIG. 2B, a cross-sectional view taken along line AA in FIG. 2A is such that the column portion 15 is centered by the arcuate portion 15b formed of a curved surface having such curvatures Rn1 and Rn2. The portion located on the opposite side of the portion on the offset direction side with respect to L is thicker in the direction perpendicular to the axial direction of the crank pin 40.

As shown in FIG. 2A, as a comparative example, the arc-shaped portion 115b of the conventional connecting rod is formed into a curved surface having a curvature Rn10 on both side surfaces. The curvature Rn1 is set to a value smaller than the curvature Rn10, and the curvature Rn2 is set to a value larger than the curvature Rn10. That is, between the curvature Rn1, Rn2, RN10, the magnitude relation such Rn1 <Rn10 <Rn2.

  For this reason, in the connecting rod according to the present embodiment, as compared with the conventional connecting rod, it is possible to avoid interference between a portion of the column portion 15 located on the offset direction side and the cylinder block 30, and the column. The rigidity against bending deformation of the portion 15 can also be increased.

As described above, according to the connecting rod according to the present embodiment, the following effects can be obtained.
(1) The column portion 15 is formed so that the portion located on the opposite side of the center line L is thicker than the portion located on the offset direction side. For this reason, while avoiding interference between the column portion 15 and the cylinder block 30, the rigidity against bending deformation of the column portion 15 that is likely to increase due to the adoption of the offset crank structure is enhanced, and cracks caused by the deformation, etc. It becomes possible to prevent the column portion 15 from being damaged.

  (2) The column portion 15 is formed so that a portion located on the opposite side to the offset direction is thick in a direction orthogonal to the axial direction of the crankpin 40. For this reason, for example, compared with the case where the portion located on the opposite side of the offset direction is formed thick in the axial direction of the crankpin 40, the increase in the weight of the connecting rod 10 due to the thick formation is suppressed. Thus, the rigidity against bending deformation can be effectively increased.

In addition, the said embodiment can be implemented with the following forms which changed this suitably.
As for the arc-shaped portion of the column portion 15, as shown in the sectional view of FIG. 3A, the arc-shaped portion 215 b of the column portion 15 is more than the portion located on the offset direction side with respect to the center line L. The portion located on the opposite side may be formed thick not only in the direction orthogonal to the crank pin 40 but also in the axial direction of the crank pin 40. However, in the connecting rod having such an arcuate portion 215b, the thickness of the crank pin 40 in the axial direction has to be longer than that of the conventional connecting rod. For this reason, when such a connecting rod is employed in an engine in which connecting rods are arranged adjacent to each other, for example, a V-type engine, the distance between the connecting rods is avoided in order to avoid interference between the adjacent connecting rods. There is a risk that the engine will be enlarged. For this reason, for example, in such a V-type engine, it is desirable to employ a connecting rod having the cross-sectional shape shown in the above embodiment.

  In addition, like the arcuate portion 315b shown in the cross-sectional view of FIG. 3B, a portion positioned on the opposite side of the portion positioned on the offset direction side with respect to the center line L is defined as the axis of the crankpin 40. You may make it form thickly only in a direction.

  In the above embodiment, a connecting rod having a cross-sectional shape as shown in FIG. 2B, that is, a connecting rod having a so-called I-shaped cross-section, is assumed as the cross-sectional structure along the line AA in FIG. However, a connecting rod having a cross-sectional shape as shown in FIGS. 4A and 4B, for example, a so-called H-shaped connecting rod may be used. In this case, the column portion may be formed thicker in the axial direction of the crankpin 40 than the portion located on the offset direction side with respect to the center line L. Specifically, as shown in FIG. 4 (a), a portion on the side opposite to the offset direction with respect to the center line L is arcuate so as to be thick in a direction perpendicular to the axial direction of the crankpin 40. The part 415b is formed, or as shown in FIG. 4B, the arcuate part 515b is formed so as to be thick in the axial direction of the crank pin 40.

The fragmentary sectional view of the engine concerning this embodiment. (A) The front view which shows the connecting rod concerning this embodiment based on contrast with the conventional connecting rod. (B) Sectional drawing which shows the cross-sectional structure along the AA line of Fig.2 (a). (A), (b) Sectional drawing which shows the cross-section along the AA line of FIG. 2 about the modification of the connecting rod of this embodiment. (A), (b) Sectional drawing which shows the cross-section along the AA line of FIG. 2 about the other modification of the connecting rod of this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Connecting rod, 11 ... Rod main body, 11a, 12a ... Opposite surface, 12 ... Cap, 13 ... Bolt, 14 ... Small end part, 14a, 16a ... Insertion hole, 15 ... Column part, 15a ... Linear part, 15b, 115b, 215b, 315b, 415b, 515b ... arc-shaped portion, 16 ... large end, 16a ... insertion hole, 20 ... piston, 21 ... piston pin, 30 ... cylinder block, 31 ... cylinder bore, 40 ... crankpin.

Claims (2)

A small end portion formed with an insertion hole through which a piston pin provided in a piston of an internal combustion engine is inserted, and an insertion hole through which a crank pin of a crankshaft having the rotation shaft is inserted at a position offset from the center axis of the cylinder bore In a connecting rod of an internal combustion engine comprising a large end portion formed with a column portion connecting the small end portion and the large end portion,
The column portion has a line-symmetric shape with respect to a center line that connects the centers of the insertion holes of the small end portion and the large end portion, and a straight portion connected to the small end portion with both side surfaces being flat. A curved surface on both sides of the curved surface on the side where the rotational axis is offset from the curved surface on the opposite side. The portion located on the opposite side of the portion where the rotation shaft is offset with respect to the center line is formed thicker in the direction perpendicular to the axial direction of the crank pin. A connecting rod for an internal combustion engine. A connecting rod according to claim 1, wherein a small end portion of the connecting rod is connected to a piston pin provided on the piston , and a rotating shaft is placed at a position where the large end portion is offset from the center axis of the cylinder bore. internal combustion engine comprising coupled to a crank pin of the crankshaft with.

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