JP6442998B2 - Crankshaft - Google Patents

Description

  The present invention relates to a crankshaft used for a vehicle engine, for example.

  Weight reduction is one of the biggest challenges for transportation equipment such as automobiles. Among them, the crankshaft is one of the parts having the largest mass among the moving parts, and various efforts have been made such as increasing the strength of the material. Recently, attempts have been made to reduce the weight by optimizing the shape surface. For example, as in Patent Document 1, a proposal has been made to reduce the weight by providing a pair of lightening portions on a crank web connecting a journal and a pin in a crankshaft.

JP 2013-113323 A

  If the hollow portion is provided in the crank web, the rigidity of the crankshaft is naturally reduced. In this regard, in the case of the crankshaft disclosed in Patent Document 1, the depth of the lightening portion is regulated so as not to reach the inside of the pin. For this reason, it is possible to suppress a decrease in rigidity of the crankshaft by extending the pin.

  However, the requirement for weight reduction has been demanded at a higher level with time, and naturally there is an allowable limit in design for the reduction in rigidity. Under such circumstances, in order to obtain a greater lightening effect, there is a strong demand for the development of a method of providing a lightening portion for reducing the value of lowering the rigidity even with the same weight reduction. It has become. An object of the present invention is to make it possible to provide a crankshaft capable of reducing the reduction in rigidity for the size of weight reduction by the lightening part on the assumption that the lightening part is provided.

  The crankshaft according to the present invention includes a journal, a pin arranged in parallel to the journal, a shoulder portion that is interposed between the journal and the pin, is adjacent to the pin, and has a bottomed hole recessed. A crankshaft comprising: an arm having a vertical direction in the direction connecting the center of the journal and the center of the pin when viewed from the axial direction of the journal, and the pin from the center of the journal in the vertical direction. If the direction from the center of the pin toward the center of the journal in the vertical direction is the downward direction, and the direction orthogonal to the vertical direction is the horizontal direction, the depth of the hole The cross-sectional shape in a direction orthogonal to the direction includes a first base having the longest lateral length of the cross-sectional shape and a center of gravity of the cross-sectional shape. And a second base that is arranged in the upper direction or the lower direction of the first base and that connects the pair of inflection points most spaced from the first base in the lateral direction is set, Of the first base and the second base, one is the upper side, the other is the lower side arranged in the lower direction of the upper side, the length of the upper side is α, and the length of the lower side is β. It is characterized in that the relation of β ≧ 1 is established.

  Here, the “inflection point” refers to a point where the curvature changes. That is, even if the curvature sign does not change, any point where the curvature itself changes is included in the concept of the “inflection point” of the present invention. For example, a boundary between a pair of curves that curve in different directions, a boundary between a pair of curves that curve in the same direction and have different curvatures, a boundary between a pair of straight lines that have different inclinations, and a boundary between a curve and a straight line And the like are included in the concept of “inflection points” of the present invention.

  In this specification, the direction connecting the center of the journal and the center of the pin as viewed from the axial direction of the journal is defined as “vertical direction”. Also, in the vertical direction, the direction from the center of the journal to the center of the pin is defined as “upward”. Further, in the vertical direction, the direction from the center of the pin toward the center of the journal is defined as “downward”. A direction orthogonal to the vertical direction is defined as a “lateral direction”. When the crankshaft includes a plurality of pins, the above-described directions (vertical direction, upward direction, downward direction, and lateral direction) are defined for each pin.

  Preferably, the upper edge of the cross-sectional shape should have an arc shape in which the center of curvature is set in the lower direction than the upper edge. Furthermore, it is preferable that the upper edge of the cross-sectional shape has a similar arc shape to the upper edge of the shoulder portion.

  Preferably, the cross-sectional shape is similar over the entire length in the depth direction, and the area of the cross-sectional shape is preferably reduced as the hole becomes deeper.

  Preferably, an oil passage that connects the journal and the pin via the arm is further provided, a hardened layer is formed on an outer peripheral surface of the pin, and the hole is formed in the oil passage and the hardened layer. It is better to have a configuration where they are arranged so as not to interfere.

  According to the crankshaft of the present invention, a hole is provided in the shoulder portion, and the first base and the second base are disposed in the cross-sectional shape of the hole so as to face each other in the vertical direction across the center of gravity. Yes. When one of the first base and the second base is the upper side and the other is the lower side, a relationship of α / β ≧ 1 is established between the length α of the upper side and the length β of the lower side. For this reason, as will be apparent from the analysis and experiment described later, it is possible to suppress a decrease in the rigidity of the crankshaft due to the recess of the hole, compared to the case where the hole of another shape is recessed in the shoulder portion. .

  Further, the crankshaft has a lower rigidity as the hole is deeper. However, in the case of other hole shapes, the rigidity deterioration rate per unit mass tends to increase as the hole becomes deeper. On the other hand, in the crankshaft of the present invention, as will be apparent from the analysis described later, even when the hole depth is deep, the rigidity deterioration rate does not increase, and a decrease in the rigidity of the crankshaft can be suppressed.

It is an axial direction fragmentary sectional view of the crankshaft which is one Embodiment of the crankshaft of this invention. It is the II-II direction sectional drawing of FIG. It is the III-III direction sectional drawing of FIG. (A)-(f) is the cross-sectional shape of the hole of other embodiment. It is a schematic diagram of an analysis model. (A) is a perspective view of the hole of a 1st analysis model. (B) is a perspective view of the hole of the second analysis model. It is a graph which shows the relationship between (alpha) / (beta) of a 1st model and a 2nd model, and a bending rigidity deterioration rate. It is a graph which shows the relationship between the depth of a 1st model and a 2nd model, and a bending rigidity deterioration rate. (A) is the cross-sectional shape of the hole of Example 1. FIG. (B) is the cross-sectional shape of the hole of Example 2. FIG. (C) is the cross-sectional shape of the hole of Example 3. (D) is the cross-sectional shape of the hole of Comparative Example 1. (E) is the cross-sectional shape of the hole of Comparative Example 2. It is a graph which shows the relationship between (alpha) / (beta) of each sample, and a bending rigidity deterioration rate.

  Hereinafter, embodiments of the crankshaft of the present invention will be described. FIG. 1 is a partial sectional view in the axial direction of the crankshaft according to the present embodiment. FIG. 2 shows a cross-sectional view in the II-II direction of FIG. FIG. 3 shows a cross-sectional view in the III-III direction of FIG.

<Configuration of crankshaft>
First, the structure of the crankshaft 1 of this embodiment is demonstrated. The front-rear direction in FIGS. 1 to 3 corresponds to the “journal axial direction” of the present invention. The vertical direction in FIGS. 1 to 3 corresponds to the “vertical direction” of the present invention. The upward direction corresponds to the “upward direction” of the present invention for the first and fourth pins 3 from the front, and the “downward direction” of the present invention for the second and third pins 3 from the front. The downward direction corresponds to the “downward direction” of the present invention for the first and fourth pins 3 from the front, and the “upward direction” of the present invention for the second and third pins 3 from the front. The left-right direction corresponds to the “lateral direction” of the present invention.

  As shown in FIGS. 1 to 3, the crankshaft 1 of the present embodiment is a crankshaft for an inline 4-cylinder engine. The crankshaft 1 includes five journals 2, four pins 3, eight arms 4, and four oil passages 5. The journal 2 has a short-axis columnar shape extending in the front-rear direction. The journal 2 is provided with a bearing (not shown). The bearing supports the crankshaft 1 in a rotatable manner.

  The pin 3 has a short-axis columnar shape extending in the front-rear direction. A connecting rod (not shown) is attached to the pin 3 via a bearing (not shown). The first and fourth pins 3 from the front are arranged so as to be shifted upward with respect to the journal 2. For example, as shown in FIG. 2, the radial center C <b> 2 of the first pin 3 is shifted upward from the radial center C <b> 1 of the journal 2. On the other hand, the second and third pins 3 from the front are arranged so as to be shifted downward with respect to the journal 2. In order to improve wear resistance, the outer peripheral surface of the pin 3 is subjected to IH (Induction Heating) processing, that is, induction hardening. Therefore, a hardened layer 30 is formed on the outer peripheral surface of the pin 3.

  The arm 4 is interposed between the journal 2 and the pin 3. The arm 4 includes a shoulder portion 40 and a counterweight portion 41. Shoulder portions 40 are disposed on both front and rear sides of the arbitrary pin 3. A bottomed hole 400 is recessed in the shoulder portion 40. The counterweight portion 41 is disposed on the opposite side of the shoulder portion 40 in the vertical direction with the journal 2 interposed therebetween. The oil passage 5 is disposed inside the crankshaft 1. The oil passage 5 connects the journal 2 and the pin 3 via the arm 4.

<Shape of crankshaft hole>
Next, the shape of the hole 400 of the crankshaft 1 of this embodiment will be described. As shown in FIG. 3, the cross-sectional shape of the hole 400 (specifically, the cross-sectional shape in the direction orthogonal to the depth direction of the hole) A has a triangular shape that points downward. The cross-sectional shape A is similar over the entire length in the depth direction of the hole 400 (between the opening 400a and the bottom 400b shown in FIG. 1). The hole 400 is formed in the shoulder portion 40 by shearing. Due to the draft during processing, the area of the cross-sectional shape A gradually decreases as the hole 400 becomes deeper. As shown in FIG. 1, the side part 400c and the bottom part 400b of the hole 400 are connected via the round chamfered part 400d. The bottom 400b is disposed so as not to interfere with the oil passage 5 and the quenching layer 30.

  As shown in FIG. 3, the cross-sectional shape A includes an upper edge a, a lower edge b, a pair of left and right side edges c, and a pair of left and right round chamfers d. Inflection points z are arranged at the boundary between the upper edge a and the round chamfered portion d, the boundary between the round chamfered portion d and the side edge c, and the boundary between the side edge c and the lower edge b, respectively. The cross-sectional shape A is symmetric with respect to the center line in the vertical direction passing through the center of gravity G of the cross-sectional shape A.

  The upper edge a has an arc shape that swells upward. The upper edge a is similar to the upper edge of the shoulder portion 40 shown in FIG. The pair of left and right round chamfered portions d are connected to both ends of the upper edge a in the left-right direction. The left round chamfered portion d has an arc shape that swells in the left direction. The right round chamfered portion d has an arc shape that swells in the right direction. The pair of left and right side edges c are connected to the lower ends of the pair of left and right round chamfers d. The left side edge c has a linear shape extending in the lower right direction. The right side edge c has a linear shape extending in the lower left direction. The distance between the pair of left and right side edges c gradually decreases in the downward direction. The lower edge b connects the lower ends of the pair of left and right side edges c. The lower edge b has an arc shape that swells downward. The curvature of the lower edge b is larger than the curvature of the upper edge a.

<Definition of first base, second base, top, bottom>
Next, the definition of the first base, the second base, the upper side, and the lower side regarding the shape of the hole 400 will be described. As shown by a dotted line in FIG. 3, the first base L <b> 1 is set by connecting, in a cross-sectional shape A, a portion having the longest length in the left-right direction with a straight line.

  As indicated by a dotted line in FIG. 3, the second base L2 is set upward or downward with respect to the first base L1 across the center of gravity G of the cross-sectional shape A. The second base L2 is a straight line connecting the pair of inflection points Z farthest from the first base L1 (defined as such). That is, the first base L1 and the second base L2 are parallel to each other across the center of gravity G of the cross-sectional shape A.

  Of the first base L1 and the second base L2, the side arranged in the upward direction is the upper side U. The side arranged in the downward direction is the lower side D. A relationship of α / β ≧ 1 is established between the length α of the upper side U in the left-right direction and the length β of the lower side D in the left-right direction.

  In the case of the hole 400 of the present embodiment, the first base L1 connects the pair of left and right round chamfers d. The second base L2 is disposed in the downward direction of the first base L1. The second base L2 is between the pair of left and right inflection points z (specifically, the inflection point z at the boundary between the lower end of the left side edge c and the left end of the lower edge b, and the lower end and lower side of the right side edge c) And the inflection point z at the boundary with the right end of the edge b). The first base L1 corresponds to the upper side U, and the second base L2 corresponds to the lower side D. A relationship of α / β> 1 is established between the length α of the upper side U in the left-right direction and the length β of the lower side D in the left-right direction.

<Effect>
Next, the effect of the crankshaft 1 of this embodiment is demonstrated. According to the crankshaft 1 of the present embodiment, the hole 400 is recessed in the shoulder portion 40. In addition, the cross-sectional shape of the hole 400 includes a first base L1 and a second base L2 that face each other in the vertical direction across the center of gravity G. A shape of α / β> 1 is established between the length α of the upper side U (first base L1) and the length β of the lower side D (second base L2). By using such a shape, as will be apparent from the analysis and experiment described later, the reduction in the rigidity of the crankshaft 1 due to the concave formation of the hole 400 is smaller than in the case of reducing the weight with other hole shapes. .

  Further, as shown in the analysis described later, when the depth of the hole 400 becomes deeper, the rigidity deterioration rate tends to increase with respect to the mass to reduce the weight by providing the hole, but the crankshaft 1 of the present embodiment. Then, as will be apparent from the analysis described later, even if the depth of the hole 400 is increased, the rigidity deterioration rate does not increase, and a decrease in the rigidity of the crankshaft 1 can be suppressed.

  Further, the upper edge a of the cross-sectional shape A has an arc shape in which the center of curvature is set lower than the upper edge a. For this reason, compared with the case where the upper edge a is exhibiting linear form, the thickness reduction (removal allowance) of the shoulder part 40 can be increased. That is, the weight of the crankshaft 1 can be reduced. Further, the upper edge a is similar to the upper edge of the shoulder portion 40. For this reason, it is possible to suppress the occurrence of “cracking” in the hole 400.

  The cross-sectional shape A is similar over the entire length of the hole 400 in the depth direction. Further, the area of the cross-sectional shape A becomes smaller as the hole 400 becomes deeper. By setting it as such a shape, the process of the hole 400 can be performed easily.

  Further, the hole 400 is disposed so as not to interfere with the oil passage 5 and the quenching layer 30. For this reason, there is no possibility of adversely affecting the original purpose and effect of providing the oil passage 5 and the quenching layer 30.

  Moreover, in the case of the crankshaft of the above-mentioned patent document 1, in order to suppress the fall of rigidity, the depth of the lightening part is controlled by the depth which does not reach the inside of a pin. On the other hand, in the crankshaft 1 of the present embodiment, as shown in the results described later, the bottom portion 400b of the hole 400 is located inside the pin 3 because the rigidity is not easily lowered even if the hole depth is increased. Even if it is the depth which reaches | attains, rigidity fall can be suppressed small. Therefore, the weight reduction effect of the crankshaft 1 can be increased.

<Others>
The embodiment of the crankshaft of the present invention has been described above. However, the embodiment is not particularly limited to the above embodiment. Various modifications and improvements that can be made by those skilled in the art are also possible.

  The cross-sectional shape A of the hole 400 is not particularly limited. A relationship of α / β ≧ 1 may be established between the length α of the upper side U (first base L1) and the length β of the lower side D (second base L2). For example, examples of the cross-sectional shape A include a polygon (a triangle pointing downward, a trapezoid pointing downward, a square, a rectangle, etc.), and a shape in which a round chamfer is added to the vertex of the polygon.

  4A to 4F show cross-sectional shapes of holes of other embodiments. In addition, about the site | part corresponding to FIG. 3, it shows with the same code | symbol. As shown in FIGS. 4A to 4F, the upper edge a, the lower edge b, and the side edge c may be linear or may be curved (for example, an arc) that bulges outward. Further, the upper edge a, the lower edge b, and the side edge c may swell outside the cross-sectional shape A. The presence or absence of the round chamfered portion 400d is not particularly limited, but it is advantageous to provide the round chamfered portion in view of stress concentration. Instead of the arc-shaped round chamfered portion 400d, a straight planar chamfered portion may be arranged. The number of side edges c may be single or plural. For example, two upper and lower side edges c may be arranged on both the left and right sides. Similarly, the arrangement number of the upper edge a and the lower edge b may be singular or plural. The cross-sectional shape A may be configured by appropriately combining the edges (upper edge a, lower edge b, side edge c, and round chamfered portion d) shown in FIGS.

  The number of holes 400 is not particularly limited. A plurality of holes 400 may be disposed on the single shoulder portion 40. Further, the hole 400 may be disposed only in the shoulder portion 40 where the oil passage 5 is not disposed, out of the pair of shoulder portions 40 on both the front and rear sides of the arbitrary pin 3.

  It should be noted that it is necessary to balance the rotation of the crankshaft 1 by providing a thinning portion on the counterweight portion 41 corresponding to the thinning amount of the shoulder portion 40 by the hole 400. Therefore, the effect of reducing the weight can be obtained. The cross-sectional shape A may not be similar over the entire length in the depth direction of the hole 400. That is, it is only necessary that at least a part of the entire length in the depth direction of the hole 400 exhibits the cross-sectional shape A of the present invention. The configuration of the crankshaft 1 is not particularly limited. The crankshaft 1 may be a single piece (for example, a cast).

  The arrangement of cylinders of the engine in which the crankshaft 1 is used (that is, the arrangement of the pins 3 with respect to the journal 2) is not particularly limited. It may be serial, V-shaped, horizontally opposed, or the like. The number of cylinders is not particularly limited. Two, three, four, five, six, eight, ten, twelve, etc. cylinders may be used. Further, the location and number of the oil passages 5 are not particularly limited.

  Hereinafter, analysis (simulation) and experiment (demonstration experiment) performed on the crankshaft of the present invention will be described.

<Analysis>
An analysis performed on the crankshaft of the present invention will be described. In the analysis (specifically, elastic deformation analysis by FEM (Finite Element Method)), the bending stiffness deterioration rate (bending stiffness deterioration rate per unit mass) of the two analysis models 9 having different shapes of the holes 400 was compared.

[Analysis model]
First, the analysis model will be described. FIG. 5 shows a schematic diagram of the analysis model. In addition, about the site | part corresponding to FIG. 1, it shows with the same code | symbol. As shown in FIG. 5, the analysis model 9 corresponds to a part of the crankshaft 1 shown in FIG.

  FIG. 6A shows a perspective view of a hole of the first analysis model (hereinafter referred to as “first model”). FIG. 6B is a perspective view of a hole of the second analysis model (hereinafter referred to as “second model”). In addition, about the site | part corresponding to FIG. 3, it shows with the same code | symbol. 5 and 6, the depth direction of the hole 400 is indicated by an arrow Y3. As shown in FIG. 5, the depth direction Y <b> 3 is a direction orthogonal to the surface development direction of the surface 40 </ b> F (shown by a thick line in FIG. 5) of the shoulder portion 40.

  As shown in FIG. 6A, the cross-sectional shape A of the hole 400 of the first model is a trapezoidal shape that points downward. As shown in FIG. 6B, the cross-sectional shape A of the hole 400 of the second model is a shape in which the upper edge a and the lower edge b of the cross-sectional shape A of the first model hole 400 are changed from a straight shape to an arc shape. is there. The upper edge a of the second model is similar to the upper edge of the shoulder portion 40 shown in FIG. As shown by a dotted line in FIG. 6B, the bottom 400b of the second model is similar to the opening 400a. The area of the bottom part 400b is smaller than the area of the opening part 400a. The area of the cross-sectional shape A becomes smaller as the hole 400 becomes deeper. In other words, the draft angle for the mold (inclination angle of the side portion 400c with respect to the depth direction Y3) is set in the hole 400 of the second model.

[analysis method]
Next, an analysis method will be described. In the analysis, the bending stiffness and bending stiffness deterioration rate of the first model and the second model were calculated when the length α of the upper side U, the length β of the lower side D, and the depth L3 were changed. In addition to the first model and the second model, the bending stiffness and the bending stiffness deterioration rate were similarly calculated for an analysis model without holes 400 (hereinafter referred to as “non-hole model”).

  Hereinafter, a method for calculating the bending rigidity and the bending rigidity deterioration rate will be described. As shown by the white arrows Y2a and Y2b in FIG. 5, the radial and axial centers C1a and C1b of the pair of journals 2 on the front and rear sides of each model are supported so as to be rotatable (can be opened). . Then, as indicated by a hollow arrow Y1 in FIG. 5, a load was applied to each model from the portion directly above the center C2 in the radial direction and the axial direction of the pin 3.

From the following equation (1), the load is F, the displacement amount of the center C1a in the arrow Y1 direction is ΔC1a, the displacement amount of the center C1b in the arrow Y1 direction is ΔC1b, and the displacement amount of the center C2 in the arrow Y1 direction is ΔC2. The stiffness k was calculated.
k = F / [(ΔC2-{(ΔC1a + ΔC1b) / 2}] (1)

Assuming that the bending stiffness of the non-hole model is k1, the bending stiffness of the perforated model (first model and second model) is k2, and the amount of mass loss due to the hole 400 is ΔM, the bending stiffness deterioration rate R is obtained from the following equation (2). Was calculated.
R = (k1−k2) / (k1 × ΔM) (2)

[Analysis result]
Next, the analysis result will be described. FIG. 7 is a graph showing the relationship between α / β and the bending rigidity deterioration rate of the first model and the second model. In FIG. 7, the first model is indicated by a white circle and the second model is indicated by a black circle. The “bending rigidity deterioration rate” on the vertical axis is a relative value when the bending rigidity deterioration rate at the point P1 is 100. The line L4 is an approximate line by the least square method of all white circles.

  As shown in FIG. 7, it was found that the bending rigidity deterioration rate R is low when α / β ≧ 1 in both the first model and the second model. That is, it was found that if both α and β ≧ 1 were set for both the first model and the second model, the bending stiffness was less likely to be reduced as compared to the non-porous model.

  Moreover, it turned out that the bending rigidity deterioration rate R becomes lower in the second model than in the first model. That is, it was found that the bending rigidity of the second model is less likely to decrease than the first model.

  FIG. 8 is a graph showing the relationship between the depth of the first model and the second model and the bending rigidity deterioration rate. In FIG. 8, α / β ≧ 1 of the first model is a white circle, α / β <1 of the first model is a white square, and α / β ≧ 1 of the second model. Are shown by black circles and those of the second model by α / β <1 are shown by black squares. The “bending rigidity deterioration rate” on the vertical axis is a relative value when the bending rigidity deterioration rate at the point P2 is 100. The line L5 is an approximate line by the least square method of all white circles. The line L6 is an approximate line by the least square method of all white squares.

  As shown in FIG. 8, it was found that in both the first model and the second model, when α / β ≧ 1, the bending rigidity deterioration rate R is difficult to increase even when the depth L3 of the hole 400 increases. That is, if α / β ≧ 1 is set in both the first model and the second model, the depth L3 of the hole 400 becomes deeper than that in the case of reducing the weight by the hole satisfying α / β <1. However, it was found that the bending rigidity is not easily lowered.

  Further, it was found that the bending rigidity deterioration rate R is less likely to be higher in the second model than in the first model. In other words, it was found that the second model has a lower bending rigidity deterioration rate and the bending rigidity is less likely to be lower than the first model regardless of the value of the depth L3 of the hole 400.

<Experiment>
As a result of the computer simulation described above, the influence of the bending rigidity deterioration rate due to the change in the value of α / β could be predicted. An experiment to confirm was conducted. In the experiment, the bending rigidity deterioration rates of five crankshafts 1 (samples) having different shapes of the holes 400 were compared.

[sample]
First, samples (Examples 1 to 3, Comparative Examples 1 and 2) used in the experiment will be described. In each sample, in the crankshaft 1 shown in FIG. 1, the hole 400 is disposed only in the shoulder portion 40 where the oil passage 5 is not disposed, of the pair of shoulder portions 40 on both the front and rear sides of all the pins 3. did.

  FIG. 9A shows the cross-sectional shape of the hole of Example 1. FIG. FIG. 9B shows the cross-sectional shape of the hole of Example 2. FIG. 9C shows the cross-sectional shape of the hole of Example 3. FIG. 9D shows the cross-sectional shape of the hole of Comparative Example 1. FIG. 9E shows the cross-sectional shape of the hole of Comparative Example 2. In addition, about the site | part corresponding to FIG. 6, it shows with the same code | symbol.

  Α / β of the cross-sectional shape A of the hole 400 of Example 1 is 2.9, α / β of the cross-sectional shape A of the hole 400 of Example 2 is 1.1, α of the cross-sectional shape A of the hole 400 of Example 3 / Β is 1, α / β of the cross-sectional shape A of the hole 400 of Comparative Example 1 is 0.9, and α / β of the cross-sectional shape A of the hole 400 of Comparative Example 2 is 0.3.

  As shown in FIGS. 9A and 9B, the cross-sectional shape A of the hole 400 of Examples 1 and 2 is a trapezoidal shape that points downward. As shown in FIG.9 (c), the cross-sectional shape A of the hole 400 of Example 3 is a rectangular shape. As shown in FIGS. 9D and 9E, the cross-sectional shape A of the hole 400 of Comparative Examples 1 and 2 is a trapezoidal shape that points upward. However, the upper edge a and the lower edge b of each sample have an arc shape. Further, the upper edge a of each sample is similar to the upper edge of the shoulder portion 40 shown in FIG.

  The depth direction of the hole 400 of each sample is a direction orthogonal to the surface development direction of the surface 40F (shown by a thick line in FIG. 5) of the shoulder portion 40, similarly to the analysis model 9 shown in FIG. The bottom of each sample hole 400 is similar to the opening. The area of the bottom is smaller than the area of the opening. The area of the cross-sectional shape A becomes smaller as the hole 400 becomes deeper. That is, a draft angle for the mold is set in the hole 400. The depth L3 and draft of the hole 400 of each sample were unified.

[experimental method]
Next, an experimental method will be described. The experimental method is the same as the above analysis method. That is, in the experiment, the portions directly below the radial and axial centers C1a and C1b of the pair of journals 2 on the front and rear sides of the second pin 3 from the front of each sample are represented by white arrows Y2a and Y2b in FIG. As shown, it was rotatably supported. Then, as indicated by a hollow arrow Y1 in FIG. 5, a load was applied from the portion directly above the radial center of the pin 3 and the center C2 in the axial direction. And the bending rigidity of each sample and the bending rigidity deterioration rate were computed from said Formula (1) and Formula (2).

[Experimental result]
Next, experimental results will be described. FIG. 10 is a graph showing the relationship between α / β and the bending rigidity deterioration rate of each sample. The “bending rigidity deterioration rate” on the vertical axis is a relative value when the bending rigidity deterioration rate of Comparative Example 2 is set to 100. Specifically, the bending rigidity deterioration rate per 100 g of the mass of each sample is calculated, the bending rigidity deterioration rate of Comparative Example 2 is set to 100, and the bending rigidity deterioration rate of samples other than Comparative Example 2 is relative to the 100. Value.

  As shown in FIG. 10, when the bending rigidity deterioration rate R of Comparative Example 2 is set to 100, the bending rigidity deterioration rate R of Comparative Example 1 is 92, the bending rigidity deterioration rate R of Example 3 is 88, and The bending rigidity deterioration rate R was 87, and the bending rigidity deterioration rate R of Example 1 was 84. That is, it was found that the bending rigidity deterioration rate R is lower in Examples 1 to 3 than in Comparative Examples 1 and 2. It turned out that the fall of bending rigidity becomes smaller in Examples 1-3 than Comparative Examples 1,2.

  1: crankshaft, 2: journal, 3: pin, 4: arm, 5: oil passage, 9: analysis model, 30: hardened layer, 40: shoulder, 40F: surface, 41: counterweight, 400: hole 400a: opening, 400b: bottom, 400c: side, 400d: round chamfer, A: cross-sectional shape, C1: center, C1a: center, C1b: center, C2: center, D: lower side, G: center of gravity, L1: First base, L2: Second base, L3: Depth, U: Upper side, Z: Inflection point, a: Upper edge, b: Lower edge, c: Side edge, d: Round chamfer, z: Inflection point

Claims (4)

A journal,
Pins arranged parallel to the journal;
An arm interposed between the journal and the pin and having a shoulder portion adjacent to the pin and having a bottomed hole recessed;
A crankshaft comprising:
When viewed from the axial direction of the journal, the direction connecting the center of the journal and the center of the pin is the vertical direction, the direction from the center of the journal to the center of the pin in the vertical direction is the upward direction, and the vertical direction is the vertical direction. When the direction from the center of the pin toward the center of the journal is a downward direction, and the direction orthogonal to the vertical direction is a lateral direction,
In the cross-sectional shape in the direction orthogonal to the depth direction of the hole,
The point at which the curvature changes at the outer edge of the cross-sectional shape as an inflection point,
A first base having the longest lateral length of the cross-sectional shape;
Across the center of gravity of the cross-sectional shape, are arranged on the direction or the downward direction of the first base, between the pair of the inflection point of the farthest outer edge from the first base, connected to said lateral The second base to
Is set,
Of the first base and the second base, when one is the upper side, the other is the lower side arranged in the lower direction of the upper side, the length of the upper side is α, and the length of the lower side is β, A crankshaft characterized by satisfying the relationship / β ≧ 1. 2. The crankshaft according to claim 1, wherein an upper edge of the outer edge of the cross-sectional shape has an arc shape in which a center of curvature is set in the lower direction than the upper edge. The cross-sectional shape is similar over the entire length in the depth direction,
The crankshaft according to claim 1 or 2, wherein an area of the cross-sectional shape becomes smaller as the hole becomes deeper. Furthermore, an oil passage that connects the journal and the pin via the arm is provided,
A quenching layer is formed on the outer peripheral surface of the pin,
The crankshaft according to any one of claims 1 to 3, wherein the hole is disposed so as not to interfere with the oil passage and the quenching layer.

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