JP7127380B2 - Multi-link piston crank mechanism for internal combustion engine - Google Patents

Description

The present invention relates to a multi-link piston crank mechanism for an internal combustion engine.

an upper link, one end of which is connected to a piston via a piston pin; a lower link, which is connected to the other end of the upper link via an upper pin and to a crankpin of a crankshaft via a bearing metal; a control link supported swingably on the engine body side, the other end of which is connected to the lower link via a control pin, the lower link having a crankpin bearing for holding a bearing metal. is well known in the prior art.

In the lower link of such a double-link type piston crank mechanism, there is a possibility that a load acting on the lower link, in which the bearing metal rotates with respect to the crankpin bearing portion, may occur during operation of the engine.

For example, Patent Literature 1 discloses a technique for suppressing internal rotation of the bearing metal by providing a protrusion on the inner peripheral surface of the bearing metal and increasing the surface pressure of the bearing metal against the crankpin bearing portion.

JP 2012-241852 A

However, when the surface pressure of the bearing metal against the crankpin bearing portion increases, there is a problem that the bearing metal is likely to deteriorate. In other words, there is room for further improvement in order to suppress adduction of the bearing metal while suppressing deterioration of the bearing metal.

A multi-link piston crank mechanism for an internal combustion engine according to the present invention has a second link connected to a crankpin via a bearing metal, and the inner peripheral surface of the crankpin bearing portion and the outer peripheral surface of the bearing metal At least one of the surface roughness on the side on which the load input from the crankpin due to the combustion load acts, and the surface roughness on the side on which the load input from the crankpin due to the combustion load does not act It's bigger than it is. The side on which the load input from the crankpin due to the combustion load acts includes at least the position on which the load input from the crankpin acts. The position where the load input from the crankpin acts is a position corresponding to the 1 o'clock direction of the inner peripheral surface of the crankpin bearing portion when viewed from the center of the crankpin bearing portion when viewed in the axial direction of the crankshaft.

According to the present invention, it is possible to suppress so-called internal rotation in which the bearing metal rotates with respect to the crankpin bearing portion without increasing the surface pressure of the bearing metal with respect to the crankpin bearing portion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram schematically showing the schematic configuration of a multi-link type piston crank mechanism for an internal combustion engine according to a first embodiment of the present invention; 1 is a front view of a lower link, which is a main part of a multi-link type piston crank mechanism for an internal combustion engine according to the present invention; FIG. FIG. 2 is an explanatory view schematically showing an enlarged crank pin bearing portion and bearing metal of a lower link of a multiple link type piston crank mechanism for an internal combustion engine according to the present invention; FIG. 6 is an explanatory view schematically showing the general configuration of a multiple link type piston crank mechanism for an internal combustion engine according to a second embodiment of the present invention;

An embodiment of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is an explanatory view schematically showing the schematic configuration of a multi-link type piston crank mechanism 1 for an internal combustion engine of a first embodiment to which the present invention is applied.

An internal combustion engine having the multi-link type piston crank mechanism 1 is mounted on a vehicle such as an automobile, for example.

The multi-link type piston crank mechanism 1 is roughly composed of a piston 2, an upper link 4 as a first link, a lower link 7 as a second link, and a control link 9 as a third link.

Piston 2 is rotatably connected to one end of upper link 4 via piston pin 3 .

The other end of the upper link 4 is rotatably connected to one end side of the lower link 7 via an upper pin 5 as a first connecting pin.

The lower link 7 is rotatably connected to the crankpin 6a of the crankshaft 6. As shown in FIG. Specifically, the lower link 7 is connected to the crankpin 6a via a bearing metal 17, which will be described later.

One end of the control link 9 is rotatably connected to the other end side of the lower link 7 via a control pin 8 as a second connecting pin.

The other end of the control link 9 is rotatably connected to an eccentric shaft portion 10a of a control shaft 10 supported on the engine body side.

The control shaft 10 is arranged parallel to the crankshaft 6 and is rotatably supported by, for example, a cylinder block (not shown).

In other words, the other end of the control link 9 rotatably connected to the eccentric shaft portion 10a of the control shaft 10 is supported swingably on the engine body side. The center axis of the eccentric shaft portion 10a is eccentric to the rotation center of the control shaft 10 by a predetermined amount.

The multi-link type piston crank mechanism 1 connects a piston 2 and a crankpin 6a of a crankshaft 6 with a plurality of links.

By rotating the control shaft 10 to change the position of the eccentric shaft portion 10a, the double-link piston crank mechanism 1 can change the position of the piston 2 at the top dead center, thereby changing the mechanical compression ratio of the internal combustion engine. can do.

The control shaft 10 regulates the degree of freedom of the lower link 7, and is rotationally driven by an actuator such as an electric motor.

The multi-link type piston crank mechanism 1 can also be configured so that the compression ratio is not variable by fixing the position of the eccentric shaft portion 10a. That is, instead of the control shaft 10, the multi-link piston crank mechanism 1 may be configured as a fixed compression ratio mechanism by rotatably connecting the other end of the control link 9 to a support pin supported on the engine body side. It is possible.

2 is a front view of the lower link 7. FIG. The lower link 7 has a cylindrical crankpin bearing portion 11 in the center that fits onto the crankpin 6a. Further, the lower link 7 has a pair of upper pin bearings 12 and a pair of control pin bearings 13 on opposite sides of the crank pin bearings 11 by approximately 180°. The upper pin bearing portion 12 corresponds to a first connecting pin bearing portion. The control pin bearing portion 13 corresponds to a second connecting pin bearing portion.

The lower link 7 as a whole forms a parallelogram close to a rhombus. The lower link 7 has a lower link upper 15 as a second link upper including the upper pin bearing 12 and a second link upper including the control pin bearing 13 on a dividing plane 14 passing through the center (central axis) C of the crankpin bearing 11 . It is formed by being divided into two parts (two members), a lower link lower 16 as a two-link lower.

The lower link upper 15 and the lower link lower 16 are formed by forging, casting, or the like of carbon steel.

The dividing surface 14 consists of a single plane including the central axis C of the crankpin bearing portion 11 and serves as a mating surface between the lower link upper 15 and the lower link lower 16 .

The crankpin bearing portion 11 is fitted with the crankpin 6a via a pair of semi-cylindrical bearing metals 17 .

The crankpin bearing portion 11 has an upper side bearing portion 18 on the lower link upper 15 side and a lower side bearing portion 19 on the lower link lower 16 side.

That is, the inner peripheral surface 11 a of the crankpin bearing portion 11 is composed of the upper inner peripheral surface 18 a of the upper side bearing portion 18 and the lower inner peripheral surface 19 a of the lower side bearing portion 19 .

The crankpin bearing portion 11 is fitted with the crankpin 6a via a pair of semi-cylindrical bearing metals 17 .

A bearing metal 17 is held on each of the upper side inner peripheral surface 18a and the lower side inner peripheral surface 19a. That is, the bearing metal 17 is held on the inner peripheral surface 11 a of the crankpin bearing portion 11 .

An inner peripheral surface 17a of the bearing metal 17 rotatably supports the crank pin 6a. The bearing metal 17 is held by the inner peripheral surface 11 a of the crankpin bearing portion 11 at its outer peripheral surface 17 b.

Here, in the specification of the present application, the cylindrical surface where the inner peripheral surface 11a of the crankpin bearing portion 11 and the outer peripheral surface 17b of the bearing metal 17 meet is called a bearing surface 21 for convenience of explanation.

The dividing surface 14 is inclined with respect to the lower link width direction along a straight line connecting the center of the upper pin bearing portion 12 and the center of the control pin bearing portion 13 as viewed in the axial direction of the crankshaft. In other words, dividing surface 14 is inclined with respect to a plane including the central axis of upper pin bearing portion 12 and the central axis of control pin bearing portion 13 .

In this embodiment, the upper pin bearing portion 12 side in the lower link width direction is one end side of the lower link 7 , and the control pin bearing portion 13 side in the lower link width direction is the other end side of the lower link 7 .

The lower link upper 15 and the lower link lower 16 are fastened to each other by a pair of bolts (not shown) that are inserted in opposite directions after the crankpin bearing portion 11 is fitted on the crankpin 6a. Furthermore, the lower link upper 15 and the lower link lower 16 are fastened by two bolts arranged on both sides of the crankpin bearing portion 11 . Note that the lower link upper 15 and the lower link lower 16 may be fastened with two or more bolts.

In the above-described prior art, a protruding portion is provided on the inner peripheral surface of the bearing metal to increase the surface pressure of the bearing metal against the crankpin bearing portion, thereby suppressing the internal rotation of the bearing metal. The adduction of the bearing metal means that the bearing metal rotates with respect to the crankpin bearing portion during engine operation.

In order to suppress the internal rotation of the bearing metal by abolishing the protruding portion of the conventional technology, the surface roughness of the outer peripheral surface of the bearing metal 17 and the inner peripheral surface 11a of the crankpin bearing portion 11 is increased (roughened). Then, it is conceivable to increase the coefficient of friction of the bearing surface 21 described above.

However, the surface roughness of the outer peripheral surface 17b of the bearing metal 17 and the inner peripheral surface 11a of the crankpin bearing portion 11 is roughened over the entire circumference, and the friction coefficient is increased over the entire circumference of the bearing surface 21. is not preferable because it causes the following three problems.

The first problem is that the wear caused by the relative motion caused by the difference in deformation between the lower link 7 and the bearing metal 17 occurs over the entire circumference of the bearing surface 21. 17, the decrease in surface pressure (bearing metal back surface pressure) occurs over the entire circumference of the bearing surface 21, resulting in internal rotation.

The second problem is that by increasing the surface roughness of the outer peripheral surface 17b of the bearing metal 17 and the inner peripheral surface 11a of the crankpin bearing portion 11, the effect of stress concentration increases, and the stress concentration is increased. It is more likely to crack and break.

The third problem is that in the outer peripheral surface 17b of the bearing metal 17 and the inner peripheral surface 11a of the crankpin bearing portion 11, the larger the range (circumferential direction range) in which the surface roughness is increased, the lower the dimensional accuracy. It is to do.

Therefore, if the surface roughness of the outer peripheral surface 17b of the bearing metal 17 or the inner peripheral surface 11a of the crankpin bearing portion 11 is roughened, it is desirable to make it as small as possible in the circumferential direction.

Loads F1, F2, and F3 due to combustion loads act on the lower link 7 during engine operation in directions indicated by arrows in FIG. 2, for example.

Due to these loads F1, F2, and F3, the bearing surface 21 generally has a higher surface pressure on the lower link upper 15 side. Further, even if these loads F1, F2, and F3 are input to the bearing surface 21, the surface pressure generally decreases on the lower link lower 16 side.

That is, the bearing metal 17 generally has a higher surface pressure on the lower link upper 15 side and a generally lower surface pressure on the lower link lower 16 side due to these loads F1, F2, and F3. Further, the crankpin bearing portion 11 generally has a higher surface pressure on the lower link upper 15 side and a lower surface pressure on the lower link lower 16 side due to these loads F1, F2, and F3.

Therefore, if the outer peripheral surface 17b of the bearing metal 17 and the inner peripheral surface 11a of the crankpin bearing portion 11 are roughened on the lower link upper 15 side and not roughened on the lower link lower 16 side, Adduction can be suppressed while suppressing the above three problems.

The load F1 is an input load acting from the upper link 4 to the upper pin bearing portion 12 of the lower link 7 due to the combustion load. A load F2 is an input load acting on the crankpin bearing portion 11 of the lower link 7 and the bearing metal 17 from the crankpin 6a due to the combustion load, and is applied to the upper side bearing portion 18 of the lower link upper 15 side and the lower link upper side. It acts on the bearing metal 17 on the 15 side. A load F3 is an input load that acts on the control pin bearing portion 13 of the lower link 7 from the control link 9 due to the combustion load.

Also, the input positions of the loads F1, F2, and F3 change when the link geometry of the multi-link piston crank mechanism 1 changes, such as when the mechanical compression ratio of the internal combustion engine changes. However, even if the link geometry of the multi-link piston crank mechanism 1 changes, the bearing surface 21 generally has a higher surface pressure on the lower link upper 15 side due to the loads F1, F2, and F3, and generally has a higher surface pressure on the lower link lower 16 side. pressure becomes lower.

Furthermore, the inventors of the present application conducted a new analysis to clarify the mechanism of adduction of the bearing metal 17 . Specifically, the correlation between the coefficient of friction of the bearing surface 21 and the adduction of the bearing metal 17 was analyzed.

As a result, it was found that the amount of internal rotation (shift amount) of the bearing metal 17 differs depending on the position along the circumferential direction of the bearing surface 21 .

It was also found that the direction of internal rotation of the bearing metal 17 differs depending on the position along the circumferential direction of the bearing surface 21 .

Furthermore, it was found that the bearing surface 21 has a portion (region) where the amount of adduction of the bearing metal 17 does not change regardless of the friction coefficient of the bearing surface 21 .

Specifically, as shown in FIG. 3 , the bearing surface 21 on the lower link upper 15 side has a substantially constant amount of internal rotation along the circumferential direction of the bearing surface 21 regardless of the friction coefficient of the bearing surface 21 . It has been found that the bearing surface 21 is divided into a region A1 and a region B1 in which the amount of adduction decreases as the friction coefficient of the bearing surface 21 increases. The bearing surface 21 on the lower link lower 16 side has, along the circumferential direction of the bearing surface 21, an area A2 in which the amount of internal rotation is substantially constant regardless of the friction coefficient of the bearing surface 21, and an inner It was found to be divided into regions B2 and B3 where the amount of rotation is reduced.

FIG. 3 is an explanatory view schematically showing an enlarged crank pin bearing portion 11 and bearing metal 17 of the lower link 7 in the posture shown in FIG. In other words, in FIG. 3, the load F1 is input so as to be orthogonal to the dividing surface 14, the load F2 is input to the crankpin bearing portion 11 at the position shown in FIG. 2 schematically shows regions A1, A2, B1, B2, and B3 when input is applied to the control pin bearing portion 13 at positions as shown in FIG.

Here, a straight line L is a straight line parallel to the acting direction (input direction) of the load F1 and passing through the center C of the crankpin bearing portion 11 when viewed in the axial direction of the crankshaft. When viewed from the center C of the crankpin bearing portion 11, the lower link upper 15 side of this straight line L is the 12 o'clock direction, and the lower link lower 16 side is the 6 o'clock direction.

The load F2 is input to the bearing surface 21 in the substantially 1 o'clock direction when viewed from the center C of the crankpin bearing portion 11 in FIG.

A region A1 is a portion of the bearing surface 21 located between the 9 o'clock direction and the 10 o'clock direction when viewed from the center C of the crankpin bearing portion 11 in FIG.

A region B1 is a portion of the bearing surface 21 located between the 10 o'clock direction and the 3 o'clock direction when viewed from the center C of the crankpin bearing portion 11 in FIG. In other words, the region B1 is a predetermined range of the bearing surface 21 on the lower link upper 15 side that includes the input position of the load F2. A region A1 is a region of the bearing surface 21 on the lower link upper 15 side other than the predetermined range (region B1) including the input position of the load F2.

A region A2 is a portion of the bearing surface 21 located between the 4 o'clock direction and the 5 o'clock direction when viewed from the center C of the crankpin bearing portion 11 in FIG.

A region B2 is a portion of the bearing surface 21 located between the 3 o'clock direction and the 4 o'clock direction when viewed from the center C of the crankpin bearing portion 11 in FIG.

A region B3 is a portion of the bearing surface 21 positioned between the 5 o'clock direction and the 9 o'clock direction when viewed from the center C of the crankpin bearing portion 11 in FIG.

Therefore, in the first embodiment, in the bearing surface 21 on the side of the lower link upper 15 where the surface pressure is high, the surface roughness is increased (roughened) only in the area B1, and the surface roughness in the area A1 is decreased ( finely). Further, in the bearing surface 21 on the side of the lower link lower 16 where the surface pressure is low, the surface roughness is made small (fine) in all ranges (areas A2, B2, B3).

That is, the surface roughness of the region B1 of the bearing surface 21 is made larger (rougher) than the surface roughness of the regions A1, A2, B2, and B3.

Specifically, the surface roughness is increased in a predetermined range (region B1) including the input position of the load F2, of the upper-side inner peripheral surface 18a of the upper-side bearing portion 18 of the lower link upper 15 to which the load F2 is input. , the surface roughness of areas other than the predetermined range (area A1) is reduced. The lower inner peripheral surface 19a of the lower bearing portion 19 of the lower link lower 16, to which the load F2 is not applied, has a reduced surface roughness in all ranges (areas A2, B2, B3) along the circumferential direction.

Since the input position of the load F2 to the bearing surface 21 on the lower link upper 15 side changes due to changes in the link geometry of the multiple link type piston crank mechanism 1, etc., the specific range of the region B is the appropriate value for each actual machine. determined by

A region B1 of the bearing surface 21 has a large surface roughness by machining (for example, grinding using a tool).

Areas A1, A2, B2, and B3 of the bearing surface 21 only need to have a surface roughness small enough to be ground with a general grindstone. No machining is required.

As a result, adduction of the bearing metal 17 can be suppressed without increasing the surface pressure of the bearing metal 17 against the crankpin bearing portion 11 over the entire circumference.

In order to increase the surface roughness of the region B1 of the bearing surface 21, in addition to the portion corresponding to the region B1 of the upper side inner peripheral surface 18a, the portion corresponding to the region B1 of the outer peripheral surface 17b of the bearing metal 17 may also be machined.

Further, in increasing the surface roughness of the region B1 of the bearing surface 21, only the portion of the outer peripheral surface 17b of the bearing metal 17 corresponding to the region B1 may be machined.

Other embodiments of the present invention will be described below. It should be noted that the same reference numerals are given to the same components as those of the above-described embodiment, and redundant explanations will be omitted.

FIG. 4 is an explanatory diagram schematically showing the schematic configuration of a multi-link type piston crank mechanism 30 for an internal combustion engine of a second embodiment to which the present invention is applied.

The multiple link type piston crank mechanism 30 has substantially the same configuration as the multiple link type piston crank mechanism 1 of the first embodiment described above, but the lower link upper 33 has the upper pin bearing portion 12 and the control pin bearing portion 13. The lower link 32 is divided as shown.

That is, the lower link 32 has a lower link upper 33 as a second link upper including the upper pin bearing 12 and the control pin bearing 13 on the dividing surface 31 formed of a single plane including the central axis of the crankpin bearing 11 . and a lower link lower 34 as a second link lower consisting of other parts.

The dividing surface 31 of the second embodiment is substantially parallel to a straight line connecting the center of the upper pin bearing portion 12 and the center of the control pin bearing portion 13 as viewed in the axial direction of the crankshaft. In other words, the dividing surface 31 is substantially parallel to a plane including the central axis of the upper pin bearing portion 12 and the central axis of the control pin bearing portion 13 .

The crankpin bearing portion 11 in the second embodiment has an upper side bearing portion 35 on the lower link upper 33 side and a lower side bearing portion 36 on the lower link lower 34 side. In other words, the inner peripheral surface 11 a of the crankpin bearing portion 11 is composed of the upper inner peripheral surface 35 a of the upper bearing portion 35 and the lower inner peripheral surface 36 a of the lower bearing portion 36 .

Loads F1, F2, and F3 due to combustion loads act on the lower link 32 during engine operation, for example, in directions indicated by arrows in FIG.

Due to these loads F1, F2, and F3, the bearing surface 21 generally has a higher surface pressure on the lower link upper 33 side and a generally lower surface pressure on the lower link lower 34 side.

In the second embodiment, the surface roughness of the upper side inner peripheral surface 35a of the upper side bearing portion 35 of the lower link upper 33 to which the load F2 is input is measured in a predetermined range including the input position of the load F2. The surface roughness outside the predetermined range is reduced. Further, the surface roughness of the lower inner peripheral surface 36a of the lower bearing portion 36 of the lower link lower 34 to which the load F2 is not applied is reduced over the entire range along the circumferential direction.

The double-link type piston crank mechanism 30 of the second embodiment can also achieve substantially the same effects as the multiple-link type piston crank mechanism 1 of the first embodiment described above.

In the second embodiment, in order to increase the surface roughness of the bearing surface 21, both the upper side inner peripheral surface 35a and the outer peripheral surface 17b of the bearing metal 17 may be machined. Further, in order to increase the surface roughness of the bearing surface 21, only the outer peripheral surface 17b of the bearing metal 17 may be machined.

For the bearing surface 21, simply, the surface roughness on the lower link upper 15, 33 side, where the surface pressure is generally increased by the loads F1, F2, and F3, is increased, and the surface pressure is increased by the loads F1, F2, and F3. It is only necessary to reduce the surface roughness of the lower link lower 16, 34 side where the That is, the bearing surface 21 changes the surface roughness of the lower link uppers 15 and 33, which are the sides to which the load F2 is applied (input side), to the lower link lowers 16, 34, which are the sides to which the load F2 is not applied (input side). It is also possible to simply make it larger than the surface roughness of the side. That is, the bearing surface 21 may simply have the surface roughness on the input direction side of the load F2 larger than the surface roughness on the side opposite to the input direction of the load F2.

In other words, the upper-side inner peripheral surfaces 18a, 35a of the upper-side bearing portions 18, 35 of the lower link uppers 15, 33, which are the members of the lower link uppers 15, 33 and the lower link lowers 16, 34 on the side on which the load F2 acts. may be larger than the surface roughness of the lower inner peripheral surfaces 19a, 36a of the lower bearing portions 19, 36 of the lower link lowers 16, 34.

Alternatively, the surface roughness of the outer peripheral surface 17b of the bearing metal 17 held by the upper side bearing portions 18, 35 of the lower link uppers 15, 33 is adjusted to the surface roughness of the bearings held by the lower side bearing portions 19, 36 of the lower link lowers 16, 34. It may be made larger than the surface roughness of the outer peripheral surface 17b of the metal 17 .

Alternatively, the surface roughness of the upper-side inner peripheral surfaces 18a, 35a is made larger than the surface roughness of the lower-side inner peripheral surfaces 19a, 36a, and the outer peripheral surface of the bearing metal 17 held by the upper-side bearing portions 18, 35 The surface roughness of 17 b may be made larger than the surface roughness of the outer peripheral surface 17 b of the bearing metal 17 held by the lower side bearing portions 19 and 36 .

Even in these cases, it is possible to suppress adduction of the bearing metal 17 while suppressing the three problems described above.

DESCRIPTION OF SYMBOLS 1...Multi-link type piston crank mechanism 2...Piston 3...Piston pin 4...Upper link (first link)
5... Upper pin (first connecting pin)
6... Crankshaft 6a... Crank pin 7... Lower link (second link)
8... Control pin (second connecting pin)
9 … Control link (third link)
Reference Signs List 10 Control shaft 10a Eccentric shaft portion 11 Crank pin bearing portion 11a Inner peripheral surface 12 Upper pin bearing portion 13 Control pin bearing portion 14 Split surface 15 Lower link upper 16 Lower link lower 17 Bearing metal 17a Inside Peripheral surface 17b... Outer peripheral surface 18... Upper side bearing portion 18a... Upper side inner peripheral surface 19... Lower side bearing portion 19a... Lower side inner peripheral surface 21... Bearing surface

Claims (3)

A first link having one end connected to a piston via a piston pin, and a first link connected to the other end of the first link via a first connecting pin and connected to a crankpin of a crankshaft via a bearing metal. a second link; and a third link having one end connected to the second link via a second connecting pin and the other end supported by the engine body,
The second link has a crankpin bearing,
The bearing metal is held on the inner peripheral surface of the crankpin bearing,
At least one of the inner peripheral surface of the crankpin bearing portion and the outer peripheral surface of the bearing metal has surface roughness on the side on which the load input from the crankpin due to the combustion load acts. Due to this, the surface roughness of the side on which the load input from the crankpin does not act is made larger,
The side on which the load input from the crankpin due to the combustion load acts includes at least the position on which the load input from the crankpin acts,
The position where the load input from the crankpin acts is a position corresponding to the 1 o'clock direction of the inner peripheral surface of the crankpin bearing portion when viewed from the center of the crankpin bearing portion when viewed in the axial direction of the crankshaft. A multi-link piston crank mechanism for an internal combustion engine, characterized by: The second link is divided into two members, a second link upper part and a second link lower part, by a mating surface formed by a plane including the central axis of the crankpin bearing portion,
surface roughness of the inner peripheral surface of the crankpin bearing portion of the member on the side on which the load input from the crankpin due to the combustion load acts among the two members of the second link upper and the second link lower; is made larger than the surface roughness of the inner peripheral surface of the crankpin bearing portion of the member on the side on which the load input from the crankpin due to the combustion load does not act. A multi-link piston crank mechanism for an internal combustion engine. The second link is divided into two members, a second link upper part and a second link lower part, by a mating surface formed by a plane including the central axis of the crankpin bearing portion,
Among the two members of the second link upper and the second link lower, the inner peripheral surface of the crankpin bearing portion of the member on the side on which the load input from the crankpin due to the combustion load acts , increasing the surface roughness of a predetermined range along the circumferential direction of the input position of the load input from the crankpin due to the combustion load and both sides thereof, and decreasing the surface roughness other than the predetermined range;
The surface of the inner peripheral surface of the crankpin bearing portion of the member on the side on which the load input from the crankpin due to the combustion load does not act among the two members of the second link upper and the second link lower. 2. A multi-link piston crank mechanism for an internal combustion engine according to claim 1, characterized in that the roughness is reduced.

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