JP2021148290A - Crankshaft and method for setting position of counterweight - Google Patents

Abstract

To provide a crank shaft capable of reducing friction between a second main journal and a third main journal, and a method for setting a position of a counterweight.SOLUTION: A crankshaft 1 is for an in-line three-cylinder engine. Seen from an axial direction of a rotation axis X, a phase of a reference line extending downward from the rotation axis X is defined as a reference position B, a phase of a straight line connecting the rotation axis X and the center of gravity of a third counterweight 5c is defined as a third weight position C, and a phase of a straight line connecting the rotation axis X and the center of gravity of a fourth counterweight 5d is defined as a fourth weight position D. The third weight position C is set on the advance angle side and the fourth weight position D is set on the retard angle side with respect to the reference position B.SELECTED DRAWING: Figure 1

Description

The present invention relates to a crankshaft for an in-line 3-cylinder engine and a method for setting the position of a counterweight of the crankshaft.

Patent Document 1 discloses a crankshaft for an in-line 3-cylinder engine including 1st to 3rd cylinders. The counterweight for the 1st cylinder is offset to the advance side, and the counterweight for the 3rd cylinder is offset to the retard side. In the balance weight for the first cylinder, the leading side portion has a larger diameter than the lagging side portion. In the balance weight for the third cylinder, the lagging side portion has a larger diameter than the advancing side portion. According to the crankshaft of the same document, the two counterweights for the second cylinder can be omitted. Therefore, the weight of the crankshaft can be reduced.

Japanese Unexamined Patent Publication No. 2012-247044

The crankshaft for an in-line 3-cylinder engine has four main journals (Nos. 1 to 4 main journals). Each of the four main journals is rotatably supported by bearings. When the crankshaft rotates, friction (friction loss, energy loss due to friction) is generated between the four main journals and the four bearings, respectively.

Here, in the case of a crankshaft in which two counterweights (3rd counterweight and 4th counterweight) for the 2nd cylinder are omitted as shown in Patent Document 1, among the 1st to 4th main journals, The friction of the 2nd main journal and the 3rd main journal in the center becomes large. In particular, when the piston rises in the second cylinder, the friction of the second main journal and the third main journal becomes large.

That is, when the piston rises in the No. 2 cylinder, an upward inertial force (centrifugal force) is applied to the crankpin (No. 2 crankpin) for the No. 2 cylinder. In the case of a crankshaft in which the 3rd counterweight and the 4th counterweight are omitted, it is difficult to offset the inertial force, so that the friction of the 2nd main journal and the 3rd main journal becomes large. Therefore, an object of the present invention is to provide a crankshaft capable of reducing friction of the 2nd main journal and the 3rd main journal with respect to a crankshaft in which the 3rd counterweight and the 4th counterweight are not arranged. do. Another object of the present invention is to provide a method for setting the position of the counterweight of the crankshaft.

In order to solve the above problems, the crankshaft of the present invention includes four main journals rotatably supported by a bearing, three crank pins arranged eccentrically with respect to the main journal, and the main journal and the crank. For an in-line 3-cylinder engine that is equipped with six crank shoulders that connect pins and six counter weights that are connected to the crank shoulders via the main journal, and that can rotate around the central axes of the four main journals as rotation axes. The four main journals are the first to fourth main journals, the three crankpins are the first to third crankpins, and the six cranks are, in order from the auxiliary drive end. The shoulders are the 1st to 6th crank shoulders, and the 6 counter weights are the 1st to 6th counter weights. The direction in which the No. 2 piston corresponding to the No. 2 crank pin moves from the top dead point to the bottom dead point is downward, and when viewed from the axial direction of the rotation axis, the reference line extending downward from the rotation axis. When the phase is viewed from the reference position and the axial direction of the rotation axis, the phase of the straight line connecting the rotation axis and the center of gravity of the third counter weight is the rotation when viewed from the third weight position and the axial direction of the rotation axis. The phase of the straight line connecting the shaft and the center of gravity of the 4th counter weight is set as the 4th weight position, the 3rd weight position is on the advance side, and the 4th weight position is the retard angle with respect to the reference position. It is characterized in that each is set on the side.

In order to solve the above problem, in the method of setting the position of the counter weight of the present invention, the direction in which the second piston moves from the bottom dead center to the top dead center is set as the upward direction, and the second piston moves in the upward direction. A translational load calculation step for calculating the translational load acting on each of the 2nd main journal and the 3rd main journal when moving, and the 2nd main when the 2nd piston moves in the upward direction. The moment calculation step for calculating the moment acting on each of the journal and the third main journal, the translational load acting on the second main journal, and the third weight position are set so that the moment becomes smaller. It is characterized by having the translational load acting on the third main journal and a weight position setting step for setting the fourth weight position so that the moment becomes smaller.

According to the crankshaft and counterweight position setting method of the present invention, the third weight position is set to the advance angle side with respect to the reference position. Therefore, the translational load and moment acting on the No. 2 main journal can be reduced with respect to the crankshaft in which the No. 3 counterweight is not arranged. Therefore, the friction of the second main journal can be reduced.

Further, the 4th weight position is set on the retard side of the reference position. Therefore, the translational load and moment acting on the No. 3 main journal can be reduced with respect to the crankshaft on which the No. 4 counterweight is not arranged. Therefore, the friction of the third main journal can be reduced.

FIG. 1 is a perspective view of a crankshaft according to an embodiment of the present invention. FIG. 2 is a right side view of the crankshaft. FIG. 3 is a cross-sectional view taken along the line III-III of FIG. FIG. 4 is a cross-sectional view taken along the IV-IV direction of FIG. FIG. 5 is an enlarged view in the frame V of FIG. FIG. 6A is a vertical cross-sectional view of Comparative Example 1. FIG. 6B is a vertical cross-sectional view of Comparative Examples 2 to 4. FIG. 7A is a graph showing the relationship between the amount of mass change and mass efficiency of Examples 1 to 3 and Comparative Examples 1 to 4. FIG. 7B is a graph showing the relationship between the amount of mass change and the friction reduction rate in Examples 1 to 3 and Comparative Examples 1 to 4. FIG. 8 is a graph showing the relationship between the amount of mass change in Examples 1 to 3 and Comparative Example 1 and the NV reduction rate in the horizontal direction.

Hereinafter, embodiments of the method for setting the positions of the crankshaft and counterweight of the present invention will be described.

(Crankshaft configuration)
First, the configuration of the crankshaft of this embodiment will be described. FIG. 1 shows a perspective view of the crankshaft of the present embodiment. FIG. 2 shows a right side view of the crankshaft. As shown in FIGS. 1 and 2, the crankshaft 1 is for an in-line 3-cylinder engine. The crankshaft 1 includes four main journals 2a to 2d, three crank pins 3a to 3c, six crank shoulders 4a to 4f, six counterweights 5a to 5f, and a flange 6. In the phase diagram at the front end of FIG. 1, the crank pins 3a to 3c are indicated by white circles, and the counterweights 5a to 5f are indicated by black circles.

A crank pulley (not shown) is attached to the front end (auxiliary drive end) of the crankshaft 1. A flywheel (not shown) is attached to the flange 6 at the rear end of the crankshaft 1.

The four main journals 2a to 2d are arranged in a row in the front-rear direction (axial direction). The central axis of the main journals 2a to 2d is the rotation axis X of the crankshaft 1. The rotation axis X extends in the front-rear direction. The bearing 90 is a so-called slide bearing and is attached to a cylinder block (not shown). Each of the main journals 2a to 2d is rotatably supported around the axis of the rotating shaft X by a bearing 90 via an oil film.

The three crank pins 3a to 3c are arranged eccentrically in the radial direction (diameter direction with respect to the rotation axis X) with respect to the four main journals 2a to 2d. The three crank pins 3a to 3c are arranged so as to be offset from each other by 120 °.

Pistons (not shown) are attached to the crankpins 3a to 3d via connecting rods (not shown). The piston (not shown) can reciprocate in the cylinder (not shown) in the vertical direction (the direction connecting the top dead center and the bottom dead center).

The six crank shoulders 4a to 4f connect the main journals 2a to 2d and the crank pins 3a to 3c in the radial direction, respectively. The six counterweights 5a to 5f are connected to the crank shoulders 4a to 4f via the rotation axis X.

Hereinafter, from the front side to the rear side, the four main journals 2a to 2d are the first to fourth main journals 2a to 2d, and the three crank pins 3a to 3c are the first to third crank pins 3a to 3c. , 6 crank shoulders 4a to 4f are 1st to 6th crank shoulders 4a to 4f, 6 counterweights 5a to 5f are 1st to 6th counterweights 5a to 5f, and 3 pistons are 1st to 3rd. They are called the number pistons.

(Position of counterweights 1 to 6)
Next, the positions (phase, circumferential position) and shapes of the 1st to 6th counterweights 5a to 5f will be described. The first counterweight 5a and the second counterweight 5b are arranged at the same position with respect to the rotation axis X. Similarly, the 5th counterweight 5e and the 6th counterweight 5f are arranged at the same position with respect to the rotation axis X. The reference position B, which will be described later, the 5th counterweight 5e and the 6th counterweight 5f, and the 1st counterweight 5a and the 2nd counterweight 5b are arranged 120 ° apart from each other with respect to the rotation axis X. There is. The first counterweight 5a, the second counterweight 5b, the fifth counterweight 5e, and the sixth counterweight 5f each have a fan shape.

FIG. 3 shows a cross-sectional view taken along the direction III-III of FIG. FIG. 4 shows a cross-sectional view taken along the IV-IV direction of FIG. In FIG. 3, the bearing 90 is omitted. As shown in FIGS. 1, 3, and 4, the No. 3 counterweight 5c and the No. 4 counterweight 5d are arranged at different positions with respect to the rotation axis X.

As shown in FIGS. 3 and 4, the front side (paper surface, clockwise direction) of the rotation axis X is the advance angle side, and the rear side (paper surface, counterclockwise direction) of the rotation direction is the retard angle side. Further, when viewed from the front side (axial direction of the rotation axis X), the phase of the reference line extending downward from the rotation axis X is set to the reference position B, and the center of gravity of the rotation axis X and the third counter weight 5c (in the present embodiment). In this case, the phase of the straight line connecting the center in the circumferential direction is defined as the third weight position C, and the phase of the straight line connecting the rotation axis X and the center of gravity of the fourth counter weight 5d is defined as the fourth weight position D.

As shown in FIG. 3, the third weight position C is arranged so as to be offset to the advance angle side with respect to the reference position B. Further, as shown in FIG. 4, the fourth weight position D is arranged so as to be offset to the retard side with respect to the reference position B. Here, the reference position B is 0 °, the advance side is the + side, and the retard side is the − side with respect to the reference position B. The third weight position C is set at a position included in the range of 19.9 ° or more and 24.6 ° or less. The fourth weight position D is set to a position included in the range of -13.7 ° or more and -19.9 ° or less. That is, the 3rd counterweight 5c and the 4th counterweight 5d are offset in the circumferential direction (rotational direction). The third counterweight 5c and the fourth counterweight 5d each have a fan shape.

(How to set the position of the counterweight)
Next, a method of setting the position of the counterweight of the present embodiment will be described. In the counterweight position setting method, the third weight position C and the fourth weight position D are set. Further, the mass and shape of the 3rd counterweight 5c and the 4th counterweight 5d are set. The counterweight position setting method includes a translational load calculation step, a moment calculation step, and a weight position setting step. The counterweight position setting method is executed by CAE (Computer Aided Engineering) analysis. FIG. 5 shows an enlarged view in the frame V of FIG.

In the translational load calculation step, when the 2nd crankpin 3b rises (specifically, when the 2nd piston corresponding to the 2nd crankpin 3b moves from the bottom dead center to the top dead center, the top dead center occurs. The translational loads Fb and Fc acting on each of the 2nd main journal 2b and the 3rd main journal 2c (when located in the immediate vicinity of the point) are calculated.

That is, the 3rd main journal 2c has inertial force (centrifugal force) from the 2nd crank pin 3b adjacent to the front side, the 4th counterweight 5d, and the 3rd crank pin 3c and the 5th counterweight 5e adjacent to the rear side. ) Is added. The combined inertial force of these inertial forces is the translational load Fc. The translational load Fc acts on the No. 3 main journal 2c in the upward direction (specifically, the direction including the upward component and orthogonal to the rotation axis X). Similarly, an upward translational load Fb is applied to the second main journal 2b. In this step, the translational loads Fb and Fc are calculated.

In the moment calculation step, the moments Mb and Mc acting on each of the 2nd main journal 2b and the 3rd main journal 2c when the 2nd crank pin 3b rises are calculated. As shown in FIG. 1, an axis orthogonal to the rotation axis X and extending in the vertical direction (stroke direction of the second piston) is perpendicular to the vertical axis Z, the rotation axis X, and the vertical axis Z and extends in the left-right direction. Is the horizontal axis Y. As shown in FIGS. 1 and 5, when the 2nd crank pin 3b is raised, the 3rd main journal 2c is in the clockwise direction (toward the 2nd crank pin 3b) when viewed from the right side around the horizontal axis Y. Moment Mc is added in the upward direction). Similarly, a moment Mb is applied to the No. 2 main journal 2b in a counterclockwise direction (a direction ascending toward the No. 2 crank pin 3b) when viewed from the right side around the horizontal axis Y. In this step, the moments Mb and Mc are calculated.

In the weight position setting step, the third weight position C shown in FIG. 3 and the fourth weight position D shown in FIG. 4 are set. Further, the mass and shape of the third counterweight 5c and the mass and shape of the fourth counterweight 5d are set. Specifically, by adjusting the mass and shape of the 3rd weight position C and the 3rd counterweight 5c, the direction and magnitude of the translational load Fb and the moment Mb acting on the 2nd main journal 2b shown in FIG. 5 can be adjusted. adjust. The mass and shape of the 3rd weight position C and the 3rd counterweight 5c are set so that the translational load Fb and the moment Mb are comprehensively reduced. Similarly, by adjusting the mass and shape of the 4th weight position D and the 4th counterweight 5d, the direction and size of the translational load Fc and the moment Mc acting on the 3rd main journal 2c shown in FIG. 5 are adjusted. .. The mass and shape of the 4th weight position D and the 4th counterweight 5d are set so that the translational load Fc and the moment Mc are totally small. Based on the counterweight position setting method described above, the mass and shape of the third weight position C and the third counterweight 5c are set, and the mass and shape of the fourth weight position D and the fourth counterweight 5d are set.

(Action effect)
Next, the effects of the crankshaft and counterweight position setting methods of the present embodiment will be described. As shown in FIG. 3, the third weight position C is set on the advance angle side with respect to the reference position B. Therefore, the translational load Fb and the moment Mb acting on the second main journal 2b shown in FIG. 5 can be reduced with respect to the crankshaft in which the third counterweight 5c is not arranged. Therefore, the friction of the second main journal 2b can be reduced.

Further, as shown in FIG. 4, the fourth weight position D is set on the retard side with respect to the reference position B. Therefore, the translational load Fc and the moment Mc acting on the No. 3 main journal 2c shown in FIG. 5 can be reduced with respect to the crankshaft in which the No. 4 counterweight 5d is not arranged. Therefore, the friction of the 3rd main journal 2c can be reduced.

Further, as is clear from the CAE analysis described later, the crankshaft of the present embodiment (the third weight position C is set on the advance angle side and the fourth weight position D is set on the retard angle side with respect to the reference position B, respectively. According to the crankshaft 1), the 2nd main journal 2b and the 3rd main are compared to the crankshaft in which the 3rd counterweight 5c and the 4th counterweight 5d are both set to the reference position B (in the same phase). The friction of the journal 2c can be reduced. Therefore, the total value of friction of all the main journals 2a to 2d can be reduced.

The third weight position C shown in FIG. 3 is set in the range of 19.9 ° or more and 24.6 ° or less. Therefore, the translational load Fb and the moment Mb acting on the second main journal 2b can be further reduced. However, even if the 3rd weight position C is less than 19.9 ° and exceeds 24.6 °, the conventional crankshaft (crankshaft without the 3rd counterweight 5c and 4th counterweight 5d, rectangular shape) The translational load Fb and moment Mb acting on the 2nd main journal 2b can be reduced with respect to the crankshaft in which the 3rd counterweight 5c and the 4th counterweight 5d are set at the same position (in the same phase). can.

The fourth weight position D shown in FIG. 4 is set in the range of -13.7 ° or more and -19.9 ° or less. Therefore, the translational load Fc and the moment Mc acting on the No. 3 main journal 2c can be further reduced. However, even when the 4th weight position D is less than -13.7 ° and exceeds -19.9 °, the translational load Fc and the moment Mc that act on the 3rd main journal 2c with respect to the conventional crankshaft. Can be made smaller.

Further, as shown in FIGS. 3 and 4, the 3rd counterweight 5c and the 4th counterweight 5d have a fan shape. Therefore, the counterweight of the present embodiment has a mass with respect to the conventional crankshaft (crankshaft in which the rectangular third counterweight 5c and the fourth counterweight 5d are set at the same position (in the same phase)). High efficiency (friction reduction rate per gram of mass of crankshaft 1). Therefore, it is possible to reduce the friction of the second main journal 2b and the third main journal 2c while reducing the weight of the crankshaft 1.

The counterweight position setting method of the present embodiment includes a translational load calculation step, a moment calculation step, and a weight position setting step. Therefore, the mass and shape of the 3rd weight position C and the 3rd counterweight 5c can be set so that the translational load Fb and the moment Mb, that is, the friction of the 2nd main journal 2b are reduced. Similarly, the mass and shape of the 4th weight position D and the 4th counterweight 5d can be set so that the translational load Fc and the moment Mc, that is, the friction of the 3rd main journal 2c are reduced.

Further, according to the counterweight position setting method of the present embodiment, the mass increase of the crankshaft 1 is suppressed with respect to the conventional crankshaft (crankshaft not provided with the third counterweight 5c and the fourth counterweight 5d). On the other hand, the friction of the 2nd main journal 2b and the 3rd main journal 2c can be reduced.

Further, according to the counterweight position setting method of the present embodiment, the conventional crankshaft (crankshaft in which the rectangular third counterweight 5c and the fourth counterweight 5d are set at the same position (in the same phase)) is used. On the other hand, the friction of the 2nd main journal 2b and the 3rd main journal 2c can be reduced while reducing the weight of the crankshaft 1.

(others)
The embodiment of the method for setting the position of the crankshaft and the counterweight of the present invention has been described above. However, the embodiment is not particularly limited to the above embodiment. It is also possible to carry out in various modified forms and improved forms that can be performed by those skilled in the art.

The third weight position C (the position of the center of gravity of the third counterweight 5c) and the center of the third counterweight 5c in the circumferential direction shown in FIG. 3 may be the same or different. For example, when a thinned portion (hole or the like) is set in the third counterweight 5c for weight reduction, the center of gravity and the center in the circumferential direction may be different. The same applies to the fourth weight position D shown in FIG.

The shape of the 3rd counterweight 5c and the 4th counterweight 5d is not particularly limited. It may be fan-shaped, rectangular, or the like. When the shape of the third counterweight 5c and the fourth counterweight 5d is a fan shape, the mass efficiency is higher than when the shape is a rectangular shape. Therefore, it is possible to reduce the friction of the second main journal 2b and the third main journal 2c while reducing the weight of the crankshaft 1. However, even if the shape of the 3rd counterweight 5c and the 4th counterweight 5d is rectangular, the 3rd weight position C is on the advance side and the 4th weight position D is on the retard side with respect to the reference position B. By setting each of them, the friction of the 2nd main journal 2b and the 3rd main journal 2c can be reduced. The shapes and positions (phases) of the other counterweights 5a, 5b, 5e, and 5f are not particularly limited. Any shape and position may be used as long as the rotation of the crankshaft 1 can be balanced.

The relationship between the translational load calculation step and the moment calculation step in the counterweight position setting method is not particularly limited. A moment calculation step may be performed before the translational load calculation step. The translational load calculation step and the moment calculation step may be performed in parallel.

The stroke direction of the second piston (vertical direction in FIG. 2) is not particularly limited. It may be vertical, horizontal, or intersecting the vertical and horizontal directions. An engine and a battery (secondary battery, fuel cell, etc.) may be used together. The driving object of the engine may be an automobile, a motorcycle, or the like.

Hereinafter, CAE analysis for verifying the friction reduction effect of the crankshaft and the NV (Noise Vibration) reduction effect in the horizontal direction of the present invention will be described. In the analysis of the friction reduction effect, a total of seven models of Examples 1 to 3 and Comparative Examples 1 to 4 were used. In the analysis of the NV reduction effect in the horizontal direction, a total of four models of Examples 1 to 3 and Comparative Example 1 were used.

First, the shapes of Examples 1 to 3 and Comparative Examples 1 to 4 will be described. FIG. 6A shows a vertical sectional view of Comparative Example 1. FIG. 6B shows a vertical sectional view of Comparative Examples 2 to 4. The cross-sectional positions of FIGS. 6 (A) and 6 (B) correspond to those of FIG. In FIGS. 6 (A) and 6 (B), the parts corresponding to those in FIG. 3 are indicated by the same reference numerals.

Examples 1 to 3 are the crankshaft 1 shown in FIGS. 1 and 2. As shown in FIG. 6A, Comparative Example 1 is a crankshaft 1 in which the third counterweight 5c and the fourth counterweight 5d are omitted from the crankshafts 1 shown in FIGS. 1 and 2. As shown in FIG. 6B, in Comparative Examples 2 to 4, in the crankshaft 1 shown in FIGS. 1 and 2, the 3rd counterweight 5c and the 4th counterweight 5d are changed from a fan shape to a rectangular shape (counter weights). This is a crankshaft 1 changed to a shape in which both edges in the circumferential direction extend linearly in the vertical direction). Further, Comparative Examples 2 to 4 are crankshafts 1 in which the third counterweight 5c and the fourth counterweight 5d are arranged at the same position (in the same phase). That is, the 3rd weight position C and the 4th weight position D coincide with the reference position B. Table 1 shows the specifications of Examples 1 to 3 and Comparative Examples 1 to 4.

In Table 1, "CW" indicates "counterweight". As shown in Table 1, based on Comparative Example 1, the mass of Comparative Example 2 is increased by 1600 g, that of Comparative Example 3 is 1200 g, and that of Comparative Example 4 is 800 g. Similarly, based on Comparative Example 1, the mass of Example 1 is increased by 1600 g, that of Example 2 is increased by 1200 g, and that of Example 3 is increased by 800 g.

The amount of mass change in Examples 1 to 3 and Comparative Examples 2 to 4 is mainly due to the mass change of the 3rd counterweight 5c and the 4th counterweight 5d. However, if the rotational balance of the crankshaft 1 is lost due to the mass change of the 3rd counterweight 5c and the 4th counterweight 5d, the 1st counterweight 5a and the 2nd counterweight 5b are appropriately used to maintain the rotational balance. The masses of the 5th counterweight 5e and the 6th counterweight 5f are also changed.

Next, the analysis result of the friction reduction effect will be described. The friction reduction effect was evaluated by the friction reduction rate. FIG. 7A shows the relationship between the amount of mass change and the mass efficiency of Examples 1 to 3 and Comparative Examples 1 to 4. The mass efficiency on the vertical axis is the friction reduction rate with respect to Comparative Example 1 per gram of mass of the crankshaft 1. The friction reduction rate is the total value of the friction reduction rates of all the main journals 2a to 2d. The mass efficiency is the amount of change in mass efficiency with respect to Comparative Example 1 when the mass efficiency of Comparative Example 1 is 100%. The mass change amount on the horizontal axis is the mass change amount (mass increase amount) of the crankshaft with respect to Comparative Example 1.

As shown in FIG. 7A, the mass efficiency of Examples 1 to 3 and Comparative Examples 2 to 4 is higher than that of Comparative Example 1. Further, the smaller the amount of change in mass with respect to Comparative Example 1, the higher the mass efficiency. Further, when the crankshafts 1 having the same mass are compared with each other by paying attention to Examples 1 to 3 and Comparative Examples 2 to 4, Example 1 is more than Comparative Example 2, and Example 2 is more than Comparative Example 3. Example 3 has higher mass efficiency than Comparative Example 4.

FIG. 7B shows the relationship between the amount of mass change and the friction reduction rate of Examples 1 to 3 and Comparative Examples 1 to 4. The friction reduction rate on the vertical axis is the amount of change in the friction reduction rate with respect to Comparative Example 1 when the friction reduction rate of Comparative Example 1 is 100%. The friction reduction rate is the total value of the friction reduction rates of all the main journals 2a to 2d. The amount of change in mass on the horizontal axis is the same as in FIG. 7 (A).

As shown in FIG. 7B, the friction reduction rates of Examples 1 to 3 and Comparative Examples 2 to 4 are higher than those of Comparative Example 1. Further, the larger the amount of change in mass with respect to Comparative Example 1, the higher the friction reduction rate. Further, when the crankshafts 1 having the same mass are compared with each other by paying attention to Examples 1 to 3 and Comparative Examples 2 to 4, Example 1 is more than Comparative Example 2 and Example 2 is more than Comparative Example 3. Example 3 has a higher friction reduction rate than Comparative Example 4.

Summarizing the above, with respect to Comparative Example 1 (crankshaft 1 in which the third counterweight 5c and the fourth counterweight 5d are omitted) shown in FIG. 6 (A), the second main journal 2b is according to Examples 1 to 3. Since the friction of the third main journal 2c can be reduced, the total value of the friction of all the main journals 2a to 2d can be reduced.

Further, with respect to Comparative Examples 2 to 4 (crankshaft 1 in which the third counterweight 5c and the fourth counterweight 5d are rectangular and have the same phase) shown in FIG. 6B, according to Examples 1 to 3. When comparing crankshafts 1 with the same mass, the friction of the 2nd main journal 2b and the 3rd main journal 2c can be reduced, so that the total value of the friction of all the main journals 2a to 2d should be reduced. Can be done. That is, friction can be reduced with higher mass efficiency.

Next, the analysis result of the NV reduction effect in the horizontal direction will be described. The horizontal NV reduction effect was evaluated by the horizontal NV reduction rate (hereinafter, appropriately abbreviated as "NV reduction rate"). The "horizontal direction" corresponds to the extending direction (horizontal direction) of the horizontal axis Y shown in FIG. That is, the "horizontal direction" is a direction parallel to the bottom surface of the cylinder block and perpendicular to the extending direction of the rotation axis X (extending direction of the crankshaft 1).

The NV reduction rates of Examples 1 to 3 and Comparative Example 1 were obtained by the following procedures, respectively. The rotation speed (engine rotation speed) of the crankshaft 1 was set to 2800 rpm (rotation per minute). The in-cylinder pressure of each of the three cylinders was 10 MPa. First, Th side (thrust side. Left side shown in FIG. 1. Side pressure is applied from the outer peripheral surface of the piston to the inner peripheral surface of the cylinder after the piston passes the top dead center), ATh side (anti-thrust side. Right side shown in FIG. 1). The horizontal acceleration (hereinafter, appropriately abbreviated as “acceleration”) in the vicinity of each main journal 2a to 2d of the bottom rail of the cylinder block on the opposite side of the Th side in the horizontal direction was output. That is, a total of 8 acceleration points (4 points on the Th side and 4 points on the ATh side) were output.

Next, the square root, that is, the effective value of the squared average value of each of the accelerations at eight locations (specifically, the acceleration waveforms for one rotation (one cycle) of each main journal 2a to 2d) was calculated. Subsequently, the average value of the effective values at eight locations was calculated. In this way, the average value of the effective values was calculated for each of Examples 1 to 3 and Comparative Example 1.

Then, the NV reduction rate of each of Examples 1 to 3 and Comparative Example 1 was calculated. Specifically, the average value of the effective values of Comparative Example 1 as a reference is Av0, the average value of the effective values of Example 1 is Av1, the average value of the effective values of Example 2 is Av2, and the effective value of Example 3 is. The NV reduction rate of Example 1 was calculated by the following formula (1), where the average value of Aav3 was used.
NV reduction rate = {1- (Av1 / Av0)} x 100 ... Equation (1)

The NV reduction rate of Comparative Example 1 is Av0 for Av1 of the formula (1), the NV reduction rate of Example 2 is Av2 for Av1 of the formula (1), and the NV reduction rate of Example 3 is Av1 of the formula (1). It was calculated by substituting Av3 into.

FIG. 8 shows the relationship between the amount of mass change in Examples 1 to 3 and Comparative Example 1 and the NV reduction rate in the horizontal direction. The NV reduction rate on the vertical axis is the amount of change in the NV reduction rate with respect to Comparative Example 1 when the NV reduction rate of Comparative Example 1 is 100%. The amount of change in mass on the horizontal axis is the same as in FIGS. 7 (A) and 7 (B). As shown in FIG. 8, the NV reduction rate is higher in all of Examples 1 to 3 than in Comparative Example 1. Further, the larger the amount of change in mass with respect to Comparative Example 1, the higher the NV reduction rate.

1: Crankshaft, 2a to 2d: 1 to 4 main journals, 3a to 3c: 1 to 3 crankpins, 4a to 4f: 1 to 4 crank shoulders, 5a to 5f: 1 to 4 Counter weight, 6: Flange, B: Reference position, C: No. 3 weight position, D: No. 4 weight position, Fb: Translational load, Fc: Translational load, Mb: Moment, Mc: Moment, X: Rotation axis, Y : Horizontal axis, Z: Vertical axis

Claims (4)

Four main journals rotatably supported by bearings and
Three crank pins arranged eccentrically with respect to the main journal,
Six crank shoulders connecting the main journal and the crank pin,
Six counterweights connected to the crank shoulder via the main journal,
A crankshaft for an in-line 3-cylinder engine that can rotate around the central axis of the four main journals as a rotation axis.
From the auxiliary drive end, the four main journals are the 1st to 4th main journals, the 3 crank pins are the 1st to 3rd crank pins, and the 6 crank shoulders are the 1st to 6th crank pins. It is a crank shoulder, and the six counterweights are the 1st to 6th counterweights.
The front side in the rotation direction of the rotation axis is the advance angle side, and the rear side in the rotation direction is the retard angle side.
The direction in which the 2nd piston corresponding to the 2nd crankpin moves from the top dead center to the bottom dead center is downward.
When viewed from the axial direction of the rotation axis, the phase of the reference line extending downward from the rotation axis is set as the reference position.
When viewed from the axial direction of the rotation axis, the phase of the straight line connecting the rotation axis and the center of gravity of the third counter weight is set to the third weight position.
When viewed from the axial direction of the rotation axis, the phase of the straight line connecting the rotation axis and the center of gravity of the No. 4 counter weight is set as the No. 4 weight position.
The crankshaft is characterized in that the third weight position is set on the advance angle side and the fourth weight position is set on the retard angle side with respect to the reference position. The reference position is 0 °, the advance side is the + side, and the retard side is the-side with respect to the reference position.
The third weight position is set in the range of 19.9 ° or more and 24.6 ° or less, and the fourth weight position is set in the range of -13.7 ° or more and -19.9 ° or less in claim 1. The described crankshaft. The direction in which the second piston moves from the bottom dead center to the top dead center is defined as the upward direction.
A translational load calculation step for calculating the translational load acting on each of the second main journal and the third main journal when the second piston moves upward.
A moment calculation step for calculating the moment acting on each of the 2nd main journal and the 3rd main journal when the 2nd piston moves upward.
The third weight position is set so that the translational load acting on the second main journal and the moment become smaller, and the translational load acting on the third main journal and the moment become smaller. The weight position setting step to set the weight position and
The method for setting the position of the counterweight of the crankshaft according to claim 1 or 2. In the weight position setting step, the translational load acting on the second main journal, the mass of the third counterweight is set so that the moment becomes smaller, and the translational load acting on the third main journal, said. The method for setting the position of the counterweight according to claim 3, wherein the mass of the fourth counterweight is set so that the moment becomes small.

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