JP2010203518A - Crankshaft structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crankshaft structure for relieving stress concentration generated in a crank pin, while reducing weight. <P>SOLUTION: This crankshaft structure has an overlap part (10) overlapping in the radial direction between the crank pin (3) and a main journal (2), and a hollow part (11) formed so as to extend in the axial direction of the crank pin (3) and the main journal (2) in an overlap area of the crank pin (3), and is characterized in that the hollow part (11) is arranged so that a thickness (D1) of an end part on the main journal center (C2) side of the crank pin (3) becomes thinner than a thickness (D2) of respective both side parts. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a crankshaft structure.

  The crankshaft is connected to a flywheel at one end. The starter meshes with a ring gear fitted to the flywheel to rotate the flywheel. The rotational force of the flywheel is converted into the reciprocating motion of the piston through the connecting rod. Once the flywheel starts to rotate, it will continue to rotate due to its own inertial force, thus making the crankshaft rotate smoothly. Thus, since the crankshaft is the main moving part of the internal combustion engine, the structure of the crankshaft is directly connected to the performance of the internal combustion engine.

  Conventionally, a crankshaft structure in which a hollow portion is provided in a crankpin or a main journal in order to reduce the weight of the crankshaft is known (particularly, Patent Document 1).

JP-A-2005-351442

  In a crankshaft having a region where the crankpin and the main journal overlap in the radial direction, when engine brakes act to cause left and right runout of the flywheel, stress concentration occurs at the base side of the crankpin. Such stress concentration may cause deterioration of the crankpin.

  The present invention has been made paying attention to such conventional problems, and an object of the present invention is to provide a crankshaft structure that can reduce stress concentration while reducing the weight while reducing the weight.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

  The present invention provides an overlap portion (10) in which a crankpin (3) and a main journal (2) overlap in a radial direction, and the crankpin (3) and the main journal in an overlap region of the crankpin (3). A hollow portion (11) formed so as to extend in the axial direction of (2), and the hollow portion (11) is a wall of an end portion of the crank pin (3) on the main journal center (C2) side. The thickness (D1) is provided so as to be thinner than the thickness (D2) on both sides thereof.

  According to the present invention, the hollow portion formed in the crankpin is provided such that the thickness of the end portion of the crankpin on the center side of the main journal is thinner than the thickness of each side portion thereof. As a result, the stress on the base side portion of the crankpin caused by the left and right surface runout of the flywheel is distributed toward the end portion on the main journal center side that is thinner than both side portions. Therefore, the stress concentration at the base portion of the crankpin can be reduced. Moreover, since a hollow part is provided, weight reduction is also possible.

It is a figure which shows the crankshaft structure of 1st Embodiment. It is a figure which shows the positional relationship of the main journal of 1st Embodiment, a crankpin, and a hollow part. It is a figure explaining the stress distribution of a crankpin.

  Hereinafter, an embodiment for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a crankshaft structure according to a first embodiment.

  The crankshaft 1 is for an inline 4-cylinder engine. The crankshaft 1 includes a main journal 2, a crankpin 3, a crank web 4, a flywheel mounting flange portion 5, and a crankshaft pulley mounting portion 6. The crankshaft 1 converts the rotational motion into a reciprocating motion of the piston via a connecting rod connected to the crankpin 3. Further, the crankshaft 1 is formed integrally by casting by forming a hollow portion 11 described later with a core.

  Those skilled in the art of engine use the expression top dead center / bottom dead center separately from the direction of gravity. In a horizontally opposed engine, etc., the top dead center is not necessarily above the gravity direction and the bottom dead center is not below the gravity direction. If the engine is inverted, the top dead center is below the gravity direction. The bottom dead center is above the gravity direction. In this specification, according to the custom, the top dead center side is up, the bottom dead center side is down, and the part of the crankshaft 1 is expressed based on the arrangement when the piston is at the top dead center. In FIG. 1, the cylinders at both ends are arranged when the piston is at top dead center. For example, the upper part of the crankpin 3 indicates the apex side of the crank arm 4 a of the crank web 4. The lower part of the crankpin 3 indicates the counterweight 4b side of the crank web 4. When the piston is at bottom dead center, it rotates 180 degrees so that the lower part of the crankpin 3 is up and the upper part of the crankpin 3 is down. Further, since the vertical direction is the axial direction of the crank web 4 (crank arm 4a), it is also expressed as the crank arm direction. Further, those skilled in the art of the engine express the crankshaft pulley mounting portion 6 of the crankshaft 1 as a front end portion and the flywheel mounting flange portion 5 as a rear end portion.

  The main journal 2 is a rotating shaft of the crankshaft 1. Although not shown, the main journal 2 is fixed to the cylinder block via a bearing and a bearing cap. In a four-cylinder engine, a total of five main journals 2 are provided between the cylinders and on the outer sides. An oil hole 2 a that is an inlet of an oil passage is provided on the outer surface of the main journal 2, and oil is supplied from the main journal 2 to the crankpin 3. The main journal 2 has an overlap portion 10 that overlaps the crankpin 3 in the radial direction. In the main journal 2, a total of four hollow portions 11 are formed in the overlap portion 10 located between the first cylinder and the second cylinder, and the third cylinder and the fourth cylinder. Details of the hollow portion 11 will be described later.

  The crankpin 3 is a shaft that is inserted into the large end hole of the connecting rod in the case of a single link mechanism, and is a shaft that is inserted into the pin hole of the lower link in the case of a multilink mechanism. The crankpin 3 is a member that connects the main journals 2 that are the main shafts of the crankshaft 1 via the crank web 4, and is eccentric with respect to the main journal 2 in the vertical direction. In the four-cylinder engine, four crankpins 3 are provided for each cylinder. The crankpin 3 has a hollow portion 11 formed in the overlap portion 10.

  Here, the hollow part 11 is demonstrated with reference to FIG. FIG. 2 is a diagram illustrating a positional relationship among the main journal 2, the crankpin 3, and the hollow portion 11. The main journal 2 and the crankpin 3 have an overlap portion 10 (overlap region = hatched portion) overlapping in the radial direction when viewed from the axial direction. The overlap portion 10 is formed by overlapping the upper side of the main journal 2 and the lower side of the crank pin 3. The overlap portion 10 is provided with a hollow portion 11. The hollow part 11 has a circular cross section and a cylindrical shape. This has the effect of suppressing stress concentration around the hollow portion 11. The hollow portion 11 extends in the axial direction from the end surface of the crank web 4 to the crank pin 3 through the main journal 2. That is, the hollow portion 11 penetrates the crank pin 3, the crank web 4 (crank arm 4 a side), the main journal 2, and the other crank web 4 (counter weight 4 b side) on the opposite side across the main journal 2. The bottom end has a bottomed shape with the bottom near the boundary between the crankpin 3 and the crank web 4 (crank arm 4a side) and opens to the outer surface (counterweight 4b side) of the crank web 4 It is. The center C11 of the hollow portion 11 is provided eccentrically downward from the center C2 of the main journal 2, and is located between the center C2 of the main journal 2 and the center C3 of the crankpin 3. Because of this positional relationship, in FIG. 2, the thickness D1 at the lower end of the crankpin 3 is thinner than the thickness D2 that is equal to each other at both ends of the crankpin 3.

  Returning again to FIG.

  The crank web 4 includes a crank arm 4a and a counterweight 4b. A total of eight crank webs 4 are provided on each side of the crank pin 3. The crank arm 4 a is a member that connects the main journal 2 and the crank pin 3. The counterweight 4b is also called a balance weight, and is provided on the opposite side of the crankpin 3 in order to improve the balance of the center of gravity that is biased toward the crankpin 3 side. A hollow portion 11 is formed in the crank arm 4a and the counterweight 4b on both sides of the main journal 2 located between the first cylinder and the second cylinder and between the third cylinder and the fourth cylinder.

  The flywheel mounting flange portion 5 is provided at the rear end portion of the crankshaft 1. The flywheel mounting flange portion 5 is mounted with a flywheel which is a disc and has a rotational inertial mass. The flywheel reduces rotation unevenness due to intermittent generation of in-cylinder combustion pressure of each cylinder.

  The crankshaft pulley mounting portion 6 is provided at the front end portion of the crankshaft 1 on the side opposite to the flywheel mounting flange portion 5. A crankshaft pulley is attached to the crankshaft pulley attaching portion 6. The crankshaft pulley drives auxiliary machinery.

  Next, the operation will be described with reference to FIG. 3A and 3B are diagrams for explaining the stress distribution of the crankpin. FIG. 3A shows the stress distribution of this embodiment, and FIG. 3B shows the conventional stress distribution. In the conventional crankshaft structure, as shown in FIG. 3 (B), the hollow portion 11 is provided concentrically and in a perfect circle with the crankpin 3, so that the wall thicknesses D1 and D2 of the crankpin are equal. A bending mode is generated at the base of the crankpin 3 due to left and right runout of the flywheel. The stress distribution at this time is concentrated due to high stress generated at the side end of the crankpin 3 (illustration of the right side of the drawing is omitted). In this embodiment, as shown in FIG. 3A, the stress distribution is smooth from the side end portion to the lower end portion of the crankpin 3.

  According to the present embodiment, the hollow portion 11 having a perfect circular cross section is eccentrically provided on the crank pin 3. The center C11 of the hollow portion 11 is decentered downward from the center C3 of the crankpin 3 in the crank arm direction. For this reason, the thickness D1 of the lower part of the crankpin 3 becomes thinner than the thickness D2 of both sides. As a result, the stress at the base of the crankpin 3 generated by the left and right surface runout of the flywheel is generated by being distributed from the side end portion to the lower end portion of the crankpin 3. Therefore, the stress concentration at the base end portion of the crankpin 3 can be relaxed, and there is no fear of deterioration from the side end portion.

  In particular, in the case of a multi-link mechanism that constitutes a variable compression ratio engine, the lower link rotates like a lever and varies the stroke amount. small. Therefore, the overlap portion 10 between the crankpin 3 and the main journal 2 is large. Further, the runout mode of the flywheel is affected by the input load applied to the crankpin 3. In the case of a multi-link mechanism, the upper link coupled to the piston pin and the crank pin 3 are linked via a lower link. The input load to the crankpin 3 due to the in-cylinder combustion pressure and the inertial force is larger than that of the single link mechanism because of the lever ratio relationship. Therefore, the runout of the flywheel is large and the stress generated in the crankpin 3 is large. Even in such a case, in this embodiment, it is possible to reduce the maximum stress value generated at the root of the crankpin 3 by reliably relaxing the stress concentration.

  Further, the hollow portion 11 is provided not only through the crankpin 3 but also through the crank web 4 and the main journal 2. Thereby, the weight of the crankshaft 1 can be significantly reduced. Further, the hollow portion 11 opens into the counterweight 4 b of the crank web 4. Therefore, the hollow portion 11 is easy to manufacture because it is formed using a core and integrally formed by casting, and then the core is taken out from the opening of the counterweight 4b.

  Further, the hollow portion 11 reduces the weight of the crankpin 3 with respect to the axis of the crankshaft 1. As a result, the weight of the counterweight 4b provided on the opposite side of the crankpin 3 and the crank arm 4a can also be reduced.

  Moreover, since the hollow part 11 has penetrated between members, it can also serve as an oil passage of the crankshaft 1.

  Without being limited to the embodiments described above, various modifications and changes are possible within the scope of the technical idea, and it is obvious that these are also included in the technical scope of the present invention.

  For example, in the embodiment, the hollow portion is provided by decentering a perfect circle, but this is not a limitation. Any shape may be used as long as the thickness of the lower portion of the crankpin is thinner than the thickness of both sides. Further, although the hollow portion is provided so as to penetrate the crankpin, the crank web, and the main journal, the stress concentration of the crankpin can be reduced even if it is provided only on the crankpin. Further, in order to further reduce the weight and relieve stress concentration, a hollow portion may be provided in addition to the crank pin. For example, in the case of the embodiment, since the hollow portion is provided at the lower portion, the second hollow portion is further provided at the upper portion. As a result, the thickness of the upper portion of the crankpin is reduced and the stress is distributed to the upper portion, so that the stress concentration is further relaxed and the weight can be reduced.

  Further, in this embodiment, the hollow portion is provided in the crankpins of all cylinders, but it may be provided only in the rearmost crankpin that is most affected by flywheel runout, or the crankpins of the rear end multiple cylinders May be provided.

  Moreover, in this embodiment, although the crankshaft structure integrally formed by casting using a core in a hollow part was assumed, it is not restricted to this. An assembled crankshaft structure in which each member is individually molded and fastened with bolts or the like may be used, or a joined crankshaft structure in which welding is performed with a high current may be used.

DESCRIPTION OF SYMBOLS 1 Crankshaft 2 Main journal 3 Crankpin 4 Crank web 4a Crank arm 4b Counterweight 10 Overlap part 11 Hollow part C2 Main journal center C3 Crankpin center C11 Hollow part center D1 Thickness D2 of crankpin lower part D2 Crankpin side Wall thickness

Claims (11)

An overlap portion in which the crankpin and the main journal overlap in the radial direction;
A hollow portion formed so as to extend in the axial direction of the crankpin and the main journal in an overlap region of the crankpin;
With
The hollow portion is provided so that the thickness of the end portion of the crankpin on the center side of the main journal is thinner than the thickness of each side portion thereof,
A crankshaft structure characterized by that. The cross section of the hollow portion is a perfect circle eccentric from the center of the hollow portion toward the center of the main journal.
The crankshaft structure according to claim 1, wherein: The hollow portion is formed so as to penetrate the crank pin, the crank arm, the main journal, and the counterweight, and its end has a bottomed shape with the crankpin as a bottom surface and opening to the counterweight.
The crankshaft structure according to claim 1 or 2, characterized in that A plurality of the hollow portions are provided in a main journal located between adjacent cylinders having different phases.
The crankshaft structure according to any one of claims 1 to 3, wherein the crankshaft structure is provided. A second hollow portion additionally provided in the crankpin;
The crankshaft structure according to any one of claims 1 to 4, further comprising: The hollow portion is provided on the crank pin at the end closest to the flywheel,
The crankshaft structure according to any one of claims 1 to 5, characterized in that: The hollow portion is provided in the crank pin of the rear end multiple cylinders on the flywheel side,
The crankshaft structure according to any one of claims 1 to 5, characterized in that: The hollow portion is a part of a crankshaft oil hole structure,
The crankshaft structure according to any one of claims 1 to 7, wherein the structure is a crankshaft structure. The crankshaft is integrally formed by casting using a core in the hollow portion.
The crankshaft structure according to any one of claims 1 to 8, wherein the structure is a crankshaft structure. The crankshaft is an assembled crankshaft,
The crankshaft structure according to any one of claims 1 to 8, wherein the structure is a crankshaft structure. The crankshaft is a joined crankshaft,
The crankshaft structure according to any one of claims 1 to 8, wherein the structure is a crankshaft structure.

Images