JP2006177470A - Crankshaft of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the size of an internal combustion engine by reducing the longitudinal dimension of a crankshaft 4. <P>SOLUTION: This crankshaft 4 comprises a plurality of main journals 13 and crank pins 5, and the main journals 13 are connected to the crank pins 5 through crank webs 14. Annular recessed parts 16 are formed in the inner end faces 14a of the crank webs 14 concentrically to the crank pins 5. Though a pin boss 6a for a control pin of a lower link 6 rotatably fitted to the crank pin 5 is larger in the axial dimension, the position of the pin boss 7a corresponds to the position of the annular recessed part 16, and both ends of the pin boss 6a are passed through the inside of the annular recessed part 16. As a result, the engine can be reduced in size in the longitudinal direction without increasing intervals of the main journals 13. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement of a crankshaft constituting a piston crank mechanism of an internal combustion engine.

  As a kind of piston crank mechanism of a reciprocating internal combustion engine, a multi-link type piston crank mechanism such as Patent Documents 1 to 3 previously proposed by the present applicant is known. This includes an upper link connected to the piston pin of the piston, a lower link connecting the upper link and the crank pin of the crankshaft, one end supported to be swingable to the engine body side, and the other end to the lower link. A control link coupled to the link. The upper link and the lower link are rotatably connected to each other via an upper pin, and the control link and the lower link are rotatably connected to each other via a control pin. This multi-link type piston crank mechanism can be used as a variable compression ratio mechanism by changing the position of the swing fulcrum of the control link on the engine body side by an eccentric cam.

  In an internal combustion engine using such a multi-link type piston crank mechanism, there are more types of moving parts than an internal combustion engine having a conventional single-link type piston crank mechanism. Become more.

  Specifically, the piston and the upper link are connected via a piston pin in the same manner as a piston and a connecting rod in a general single link type piston crank mechanism, and the upper link and the lower link are connected via an upper pin. The control link and the lower link are connected via a control pin.

  The rotatable connecting portion through these pins can be the same as the structure around the piston pin in the conventional general single-link type piston crank mechanism. The structure around the piston pin may not be taken. That is, an internal combustion engine having a multi-link type piston crank mechanism has a complicated component structure, so that the living space of each part generally tends to be narrowed. In addition to the length of the pin, there is a case where the dimensions of the snap ring at both ends and the bank portion outside the snap ring groove cannot be secured in the rotary connecting portion.

In Patent Document 3, a washer having a flange portion whose outer diameter is larger than the inner diameter of the pin hole and a male screw portion coaxial with the flange portion is formed at both ends of the pin in a portion where there is no allowance for such an axial dimension. A structure has been proposed in which a pin is screwed into a female screw and a pin is prevented from coming off in the axial direction by flange portions of washers at both ends.
JP 2001-227367 A JP 2002-61501 A JP 2003-322056 A

  In the internal combustion engine having the multi-link type piston crank mechanism and the internal combustion engine having a general single link type piston crank mechanism, one of the performances generally required for the crankshaft is torsion and Increased rigidity against bending. The crankshaft is subjected to bending deformation or torsional deformation when an inertial force from a main motion system component other than the crankshaft or a load resulting from combustion is input to the crankpin. Crankshaft deformation may cause deterioration of crankshaft durability, noise, friction, etc.In particular, torsional deformation will cause torsional resonance of the crankshaft and may cause the above-mentioned problems remarkably. Many.

  In particular, in an internal combustion engine having a multi-link type piston crank mechanism, the load input to the crank pin is larger than that of a conventional internal combustion engine having a single link type piston crank mechanism due to the mechanical characteristics of the piston crank mechanism, and the torsion Deformation and bending deformation increase. That is, in an internal combustion engine equipped with a general single link type piston crank mechanism, the combustion load from the piston is input to the crank pin only through the connecting rod, whereas the multiple link type piston crank mechanism as described above. The combustion load is input to the crank pin via the upper link and the lower link in the internal combustion engine, and at that time, in the lower link, the principle of the lever with the control pin as the fulcrum, the upper pin as the power point, and the crank pin as the action point The combustion load is amplified and input to the crankpin.

  Further, in order to make the longitudinal length of the internal combustion engine as small as possible, it is required to make the distance between the main journals as small as possible. Since the length of the crank pin depends on the size of the lower link or connecting rod connected to the crank pin, the thickness of the crank web (the dimension in the axial direction of the crank shaft) should be reduced if the distance between the main journals is designed to be as small as possible. The crankshaft must be designed to be as small as possible.

  In particular, when a lower link or connecting rod of a plurality of cylinders must be connected to one crank pin in a V-type internal combustion engine or the like, the demand for the thickness of the crank web becomes increasingly severe.

  Further, the crankshaft is also required to maintain a good rotational balance. Generally, in order to cancel the rotational imbalance caused by the mass of the crankpin and the moving parts connected to the crankpin, a counterweight is installed at the opposite phase to the crankpin, but the entire crankshaft is downsized. In order to achieve this, it is necessary to make the outer diameter of the counterweight as small as possible. In that case, it is necessary to improve the balance by making the mass on the crankpin side as small as possible. Particularly in an internal combustion engine having a multi-link type piston crank mechanism, the mass of the lower link connected to the crank pin is larger than that of a connecting rod in a general single link type piston crank mechanism. Is more compelling.

  The present invention has been made for the purpose of achieving the above-described problems required for a crankshaft at a higher level.

  The invention according to claim 1 includes a main journal rotatably supported by a bearing portion of the internal combustion engine, and a crank pin to which a link component linked to the piston is rotatably attached, and the main journal and the crank pin are In a crankshaft of an internal combustion engine connected via a crank web, an annular recess is formed concentrically with the center of the crank pin on the end face of the crank web on the crank pin side.

  Therefore, the above-mentioned recess allows the crank web and the link component (for example, a general connecting rod or a lower link in the above-described multi-link piston crank mechanism) to be connected to the crank pin so as to be rotatable. Interference can be avoided, the thickness of the crank web in the axial direction of the crankshaft and the distance between the main journals can be reduced, and the internal combustion engine can be downsized in the front-rear direction.

  Further, since the crank web in the vicinity of the crank pin can be reduced in weight, it becomes easy to improve the rotation balance of the crank shaft.

  In one aspect of the present invention, as in claim 2, a plurality of link parts are rotatably connected to one crank pin.

  For example, in a configuration in which a plurality of link parts (for example, connecting rods) are connected to one crankpin as in a V-type 8-cylinder internal combustion engine, there is a strong tendency for the parts living space in the longitudinal direction of the internal combustion engine to be tight. In the present invention, as described above, interference with the link component can be avoided by the recess of the crank web as described above. In addition, because the crankpin mass increases, the rotation balance of the crankshaft per crank throw tends to deteriorate, but as described above, the recesses can improve the rotation balance of the crankshaft. It becomes easy.

  According to the crankshaft of the present invention, as in claim 3, the upper link whose one end is connected to the piston pin of the piston, the other end of the upper link is swingably connected, and is rotatable to the crank pin. The present invention can be applied to a multi-link type piston crank mechanism including a lower link to be attached and a control link having one end swingably supported on the engine body side and the other end connected to the lower link.

  In this case, it is possible to avoid interference in the longitudinal direction of the internal combustion engine between the crank web and the lower link, the crank web and the upper pin, and the crank web and the control pin. Since these parts generally have larger dimensions in the longitudinal direction of the internal combustion engine than the connecting rod of the single link type piston crank mechanism, the effect of avoiding interference is particularly effective. In particular, the upper pin and the control pin, and the bore formed in the lower link or the upper link or the control link for supporting these pins are the most in the longitudinal direction of the internal combustion engine in each component of the multi-link piston crank mechanism. Since the dimensions are increased, the internal combustion engine can be efficiently downsized in the front-rear direction by avoiding component interference at these positions.

  In the invention of claim 4, the thickness of the crank web in the crankshaft axial direction in the recess is 2/3 or more of the maximum thickness of the crank web in the same direction. With such a configuration, it is possible to suppress a decrease in the bending rigidity and torsional rigidity of the crankshaft due to the formation of the recess.

  In the invention of claim 5, the radius of the inner peripheral edge of the annular concave portion is equal to or greater than the distance between the center of the crankpin and the center of the main journal. Therefore, the concavity is formed at the minimum at the portion connecting the center of the main journal and the center of the crank pin that contributes most to the rigidity of the crankshaft, and the decrease in the bending rigidity and torsional rigidity of the crankshaft is minimized. It becomes possible to do.

  In the invention of claim 6, the stroke of the piston is greater than twice the distance between the center of the crankpin and the center of the main journal. In other words, a crank increasing shaft such as a multi-link mechanism is provided between the crank pin and the piston, and the crank arm length for realizing the necessary amount of piston stroke is a crank shaft for a single link type piston crank mechanism. Is relatively shorter. Therefore, since the overlap between the crankpin and the main journal is increased, the proportion of the crank web thickness contributing to the crankshaft rigidity is relatively small, and even if a recess is provided in the crank web, a decrease in rigidity is minimized. Can be suppressed.

  In the invention of claim 7, the distance between the center of the main journal and the center of the crankpin is 120% or less of the radius of the main journal, and the radius of the crankpin is 65% of the distance between the center of the main journal and the center of the crankpin. That's it. Therefore, since the overlap between the crankpin and the main journal is increased, the proportion of the crank web thickness contributing to the crankshaft rigidity is relatively small, and even if a recess is provided in the crank web, a decrease in rigidity is minimized. Can be suppressed.

  In the invention of claim 8, the distance from the center of the crank pin to the center of the width in the radial direction of the recess is substantially the same as the distance from the center of the crank pin to the center of the upper pin.

  Accordingly, interference between the upper pin and the pin boss part holding the upper pin and the crank web can be avoided, and even when the upper pin load increases and the length of the upper pin must be increased in the high-power internal combustion engine, It becomes possible to suppress the dimensions.

  According to a ninth aspect of the present invention, the crankshaft of the present invention is a multi-link type piston crank provided with a projecting portion projecting in the radial direction at the end portion of the upper pin in order to prevent the upper pin from falling off from the pin hole. Applied to the mechanism.

  In this configuration, the convex portion formed of the flange portion or the like can prevent the upper pin from dropping without pressing the upper pin into the pin hole, and can reduce the friction loss caused by the rotational motion between the upper link and the lower link. . In this case, the convex portion at the end of the upper pin protrudes in the longitudinal direction of the internal combustion engine from the maximum width of the pin hole (dimension in the pin axial direction). In this case, the interference between the convex portion and the crank web is This can be avoided by forming the recess.

  In the invention of claim 10, the distance from the center of the crankpin to the center of the width in the radial direction of the recess is substantially the same as the distance from the center of the crankpin to the center of the control pin.

  Therefore, especially when the control pin and the pin boss portion holding the control pin can be prevented from interfering with the crank web, the internal combustion engine is increased even when the control pin load is increased and the length of the control pin must be increased in the high output internal combustion engine. It is possible to suppress the dimension in the front-rear direction.

  In the invention of claim 11, the crankshaft of the present invention is a multi-link type in which a protrusion projecting in the radial direction is provided at the end of the control pin in order to prevent the control pin from falling off the pin hole. Applicable to piston crank mechanism.

  In this configuration, it is possible to prevent the control pin from falling off without press-fitting the control pin into the pin hole, and it is possible to reduce the friction loss caused by the rotational movement between the control link and the lower link. In this case, the protrusion at the end of the control pin protrudes in the longitudinal direction of the internal combustion engine rather than the maximum width of the pin hole (dimension in the pin axial direction). Can be avoided by forming a recess.

  In a twelfth aspect of the present invention, the total thickness of the two crank webs constituting one crank throw in the crankshaft axial direction is equal to or less than the length of the crank pin between the two. As a result, the thickness of the crank web can be minimized so that the dimension in the longitudinal direction of the internal combustion engine is minimized.

  According to the present invention, interference between a link member such as a connecting rod that is rotatably attached to a crank pin and a crank web can be avoided by the recess, and the size of the crankshaft and thus the longitudinal direction of the internal combustion engine can be reduced. it can. Moreover, since the crank web in the vicinity of the crank pin can be reduced in weight, it is easy to improve the rotation balance of the crankshaft, and a reduction in size and weight including the counterweight can be achieved.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. First, a multi-link type piston crank mechanism in which the crankshaft of this embodiment is used will be described with reference to FIGS.

  This piston crank mechanism is applied as a variable compression ratio mechanism as in the above-mentioned Patent Document 1 and the like, and the crankshaft 4 includes a plurality of main journals 13 and crank pins 5, and a cylinder block. A main journal 13 is rotatably supported by main bearing portions 11 (11a to 11e) including 12 bulkheads and bearing caps. The crankpin 5 is eccentric from the main journal 13 by a predetermined amount, and the lower link 6 is rotatably connected thereto.

  The lower link 6 is configured to be split into two members along a split surface passing through the center of the crankpin 5 so as to be assembled to the crankpin 5, and the crankpin 5 is arranged at a substantially central crankpin bearing portion. Are mated.

  The upper link 3 has a lower end side rotatably connected to one end of the lower link 6 by an upper pin 9, and an upper end side rotatably connected to the piston 1 by a piston pin 2. The piston 1 receives combustion pressure and reciprocates in the cylinder of the cylinder block 12.

  The control link 8 that restrains the movement of the lower link 6 is connected to the other end of the lower link 6 by a control pin 10 so as to be rotatable, and the lower end side is a cylinder block that becomes a part of the engine body via the control shaft 7. The lower part of 12 is rotatably connected. Specifically, the control shaft 7 is rotatably supported by the engine body and has an eccentric cam portion that is eccentric from the center of rotation, and the lower end portion of the control link 8 is rotatably fitted in the eccentric cam portion. Match. The rotational position of the control shaft 7 is controlled by a compression ratio control actuator (not shown) that operates based on a control signal from an engine control unit (not shown).

  In the variable compression ratio mechanism using the multi-link type piston crank mechanism as described above, when the control shaft 7 is rotated by the compression ratio control actuator, as disclosed in Patent Document 1, etc., the eccentric cam The swing support position of the lower end of the control link 8 changes via the part. When the swing support position of the control link 8 changes, the stroke of the piston 1 changes, and the position of the piston 1 at the piston top dead center (TDC) increases or decreases. As a result, the engine compression ratio changes.

  As shown in FIG. 6 (a cross-sectional view taken substantially along the line AA in FIG. 5), this embodiment is an in-line four-cylinder internal combustion engine, and the crankshaft 4 has five main journals 13 in five longitudinal directions. And is rotatably supported by the five main bearing portions 11a to 11e of the cylinder block 12, respectively.

  Next, the main part of the crankshaft 4 according to the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 is a side view of the crankshaft 4, which shows one cylinder of the crankshaft 4 for an in-line four-cylinder engine. FIG. 2 is a cross-sectional view taken along the line BB in FIG. 1 in which the crankshaft 4 in FIG. 1 is cut at the center in the longitudinal direction of the crankpin 5.

  As described above, the crankshaft 4 has the main journal 13 supported by the main bearing portion 11 of the cylinder block 12, and the lower link 6 is rotatably attached to the crankpin 5. In the case of the present embodiment, the crankshaft 4 is formed of a single material in which all four cylinders are continuous by, for example, forging. The crankpin 5 is eccentric with respect to the main journal 13, and the crankpin 5 and the main journal 13 are integrally connected by a crank web 14. Counter weights 15 are formed at opposite angular positions across the crank pin 5 of the crank web 14 and the center 17 of the main journal 13, and around the rotation center 17 due to the mass of the crank pin 5 and the lower link 6. It is configured to balance rotational imbalance as much as possible.

  An annular recess 16 is formed concentrically with the center 18 of the crankpin 5 on the end faces 14a of the pair of crank webs 14 facing each other, that is, the end face 14a of the crank web 14 on the crankpin 5 side. The recess 16 has a groove shape that is recessed in the axial direction of the crankshaft 4, and as shown in FIG. Has an open arc shape. By forming such a recess 16, the mass of the portion located on the crankpin 5 side around the rotation center 17 of the main journal 13 can be reduced, and the rotation balance of the crankshaft 4 can be made better. Can do.

  FIG. 3 is a cross-sectional view of the crankshaft 4 taken along a plane passing through the rotation center 17 of the main journal 13 and the center 18 of the crankpin 5 (that is, a CC cross section in FIG. 2). FIG. 3 also shows the lower link 6 connected to the crank pin 5, and the control pin 10 center of the lower link 6 is illustrated in a positional relationship that coincides with the CC line in FIG. 2. The axial total length (distance between the outer end faces) of the bifurcated pin boss portion 6 a that supports both ends of the control pin 10 of the lower link 6 is that of the bearing housing portion 6 b at the center of the lower link 6 connected to the crank pin 5. It is longer than the axial dimension, that is, protrudes to the left and right of FIG. Therefore, in the case of the crankshaft of the prior art, the interval between the inner end faces 14a of the pair of crank webs 14 must be wider than the total length of the control pin pin boss portion 6a. The center point of the radial width substantially coincides with the center position of the control pin 10. In other words, the radii from the center 18 of the crankpin 5 substantially coincide with each other. Therefore, the end of the control pin pin boss 6a passes through the annular recess 16, and the distance between the bottom surfaces of the pair of annular recesses 16 facing each other is larger than the width of the control pin pin boss 6a. Since it is sufficient to make it wide, the length of the crankshaft 4 can be shortened by the depth of the annular recess 16, and the entire internal combustion engine can be downsized in the front-rear direction. In particular, in order to optimize the surface pressure applied to the bearing portion, the axial length of the pin boss portion 6a for the control pin tends to be longer than the axial dimension of the crankpin bearing housing 6b. In an internal combustion engine having a piston crank mechanism, the effect of downsizing by the annular recess 16 is highly effective.

  In this embodiment, the annular recess 16 is formed by paying attention to the positional relationship between the control pin pin boss portion 6a of the lower link 6 and the end surface 14a of the crank web 14. However, a similar problem exists in the upper pin pin boss portion. sell. Therefore, in this case, if the annular recess 16 is formed so that the center of the radial width of the annular recess 16 coincides with the distance from the center 18 of the crank pin 5 to the center of the upper pin 9, the axial length of the pin boss portion for the upper pin is increased. The entire internal combustion engine can be reduced in size while ensuring this.

  Further, the shape of the annular recess 16 has several characteristics. In FIG. 3, the thickness t1 of the crank web 14 where the annular recess 16 is formed is 2/3 or more of the general thickness t2 of the crank web 14 where the annular recess 16 is not formed. Further, the radius of the inner peripheral edge of the annular recess 16, that is, the boundary surface 21 on the inner peripheral side (radius from the center 18 of the crankpin 5) is larger than the distance from the center 18 of the crankpin 5 to the rotation center 17 of the main journal 13. long. Due to these morphological features, despite the formation of the annular recess 16, there are sufficient members in the connecting portion 22 between the crank pin 5 and the main journal 13 that contributes most to the torsional rigidity and bending rigidity of the crankshaft 4. The thickness can be ensured, and the reduction in rigidity can be suppressed to the minimum while the effects of weight reduction, balance improvement and downsizing can be sufficiently obtained. In particular, in this embodiment, the thickness t2 of the general portion of the crank web 14 is formed so as to be shorter than the length of the crank pin 5 even if the crank webs 14 on both sides are combined, and the recess 16 is formed as described above. If it is formed in a shape that does not match the above, there is a risk that the decrease in rigidity may reach an unacceptable level.

  In the above embodiment, not only the annular recess 16 but also the overall shape of the crankshaft 4 is characterized. In this embodiment, since a multi-link type piston crank mechanism is used, the piston stroke of the internal combustion engine is more than twice the distance between the center 17 of the main journal 13 and the center 18 of the crankpin 5. The distance between the center 17 of the journal 13 and the center 18 of the crankpin 5 is 120% or less of the radius of the main journal 13, and the radius of the crankpin 5 is between the center 17 of the main journal 13 and the center 18 of the crankpin 5. It is designed to be 65% or more of the distance. With these characteristics, a sufficient thickness of the member can be secured at the connecting portion 22 that connects the crankpin 5 and the main journal 13, and the torsion and bending rigidity of the crankshaft can be sufficiently increased. It is possible.

  Next, FIG. 4 is an explanatory view of a second embodiment of the present invention applied to a single link type piston crank mechanism. Like FIG. 3, the crankshaft 4 is connected to the center 17 of the main journal 13 and the center 18 of the crankpin 5. It is sectional drawing cut | disconnected by the plane which passes through. The basic configuration of the crankshaft 4 of the second embodiment is the same as that of the first embodiment. In the second embodiment, the crankshaft 4 is applied to a V-type 8-cylinder internal combustion engine having a bank angle of 90 °. The difference is that two sets of connecting rods 23 are rotatably connected to the crankpin 5. One of the two sets of connecting rods 23 is connected to the piston of the cylinder in the right bank, and the other is connected to the piston of the cylinder in the left bank. The two connecting rods 23 of the left and right banks generally take different angles with respect to the crankshaft 4, but in this figure, for convenience, both are shown as cross-sectional views cut along the fastening surface of the rod body and the cap. It is shown. When trying to reduce the size of the V-type internal combustion engine in the front-rear direction, the pitch between the bores of the cylinders in each bank is of course reduced. It is also necessary to reduce the offset amount. Since the offset amount between the cylinder centers of both banks is the distance between the centers of the plurality of connecting rods 23 connected to the crankpin 5, the connecting rods 23 must be formed as thin as possible in order to reduce the size of the internal combustion engine. . The thickness (axial dimension) of the bearing portion 23a on the inner peripheral side of the large end portion of the connecting rod 23 fitted to the crankpin 5 can reduce the maximum surface pressure of the bearing portion if the diameter of the crankpin 5 is increased. Although it is possible to reduce the thickness, the thickness (axial dimension) of the outer peripheral side fastening portion 23b that connects the rod body and the cap is determined depending on the fastening strength of the screw, so that it is extremely thin. It is difficult to do. In this embodiment, the bearing portion 23a and the fastening portion 23b are offset in the front-rear direction (axial direction), and the positions of the portion 23c protruding in the axial direction of the fastening portion 23b and the annular recess 16 concentric with the crank pin 5 are provided. By matching these, it becomes possible to arrange a pair of connecting rods 23 without increasing the interval between the main journals 13. Further, as in the case of the first embodiment, since the annular recess 16 is formed, the weight on the crankpin 5 side is reduced, so that the rotation balance of the crankshaft 4 is improved. In a V-type internal combustion engine, since a plurality of connecting rods 23 are connected to one crankpin 5, the crankshaft 4 is more than an internal combustion engine such as an in-line four-cylinder engine in which one connecting rod is connected to one crankpin. Since the rotational balance tends to deteriorate, the balance improvement effect by the annular recess 16 is more effective in the V-type internal combustion engine.

The side view of the principal part which shows 1st Example of the crankshaft which concerns on this invention. Sectional drawing along the BB line of FIG. Sectional drawing along CC line of FIG. 2 shown in the state which assembled | attached the lower link. Sectional drawing similar to FIG. 3 which shows 2nd Example of the crankshaft which concerns on this invention. BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing of the multilink type piston crank mechanism in which the crankshaft of 1st Example is used. Sectional drawing along the AA line of FIG.

Explanation of symbols

4 ... Crankshaft 5 ... Crankpin 6 ... Lower link 10 ... Control pin 14 ... Crank web 16 ... Recess

Claims (12)

A main journal rotatably supported by a bearing portion of the internal combustion engine, and a crank pin to which a link component linked to the piston is rotatably attached, and the main journal and the crank pin are connected via a crank web In the crankshaft of an internal combustion engine,
A crankshaft for an internal combustion engine, characterized in that an annular recess is formed concentrically with the center of the crankpin on an end face of the crank web on the crankpin side.   The crankshaft of an internal combustion engine according to claim 1, wherein a plurality of link parts are rotatably connected to one crankpin.   An upper link whose one end is connected to the piston pin of the piston, a lower link where the other end of the upper link is swingably connected and rotatably attached to the crank pin, and one end swings toward the engine body side. 3. A crank for an internal combustion engine according to claim 1, wherein the crank is applied to a multi-link type piston crank mechanism having a control link that is movably supported and has the other end connected to the lower link. shaft.   The internal combustion engine according to any one of claims 1 to 3, wherein the thickness of the crank web in the crankshaft axial direction in the recess is not less than 2/3 of the maximum thickness of the crank web in the same direction. Crankshaft.   The crankshaft of an internal combustion engine according to any one of claims 1 to 4, wherein the radius of the inner peripheral edge of the annular recess is equal to or greater than the distance between the center of the crankpin and the center of the main journal.   The crankshaft of an internal combustion engine according to any one of claims 1 to 5, wherein the stroke of the piston is greater than twice the distance between the center of the crankpin and the center of the main journal.   The distance between the center of the main journal and the center of the crankpin is 120% or less of the radius of the main journal, and the radius of the crankpin is 65% or more of the distance between the center of the main journal and the center of the crankpin. The crankshaft of the internal combustion engine according to any one of claims 1 to 6.   4. The crankshaft of an internal combustion engine according to claim 3, wherein a distance from the center of the crank pin to the center of the width of the concave portion in the radial direction substantially coincides with a distance from the center of the crank pin to the center of the upper pin.   9. The multi-link type piston crank mechanism according to claim 8, wherein the upper pin is applied to a projecting portion projecting in a radial direction in order to prevent the upper pin from falling off from a pin hole. Crankshaft of internal combustion engine.   4. A crankshaft for an internal combustion engine according to claim 3, wherein a distance from the center of the crank pin to the center of the width in the radial direction of the recess substantially coincides with a distance from the center of the crank pin to the center of the control pin.   The present invention is applied to a multi-link type piston crank mechanism having a projecting portion protruding in a radial direction at an end portion of the control pin in order to prevent the control pin from falling off from a pin hole. 10 crankshafts. 12. The internal combustion engine according to claim 1, wherein the total thickness of two crank webs constituting one crank throw in the crankshaft axial direction is equal to or less than a length of a crank pin between the two crank webs. Engine crankshaft.

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