JP2013011207A - Multiple linkage type piston to crank mechanism of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust variations of compression ratio in a target compression ratio with high accuracy.SOLUTION: Provided is a multiple linkage type piston to crank mechanism which changes the compression ratio by changing the position of an eccentric shaft through the rotation of a control shaft, and can adjust a top dead point position of the piston for each cylinder, by rotating an eccentric sleeve to the eccentric shaft. Each component of the multiple linkage type piston to crank mechanism is machined in advance (set in dimensions) so that: the angle of the control shaft is set at one in the highest compression ratio; and that a piston position nearly agrees with the central value designed on the piston top dead point of the piston in the highest compression ratio, when a crankshaft is fixed to have an adjustment target air cylinder in the top dead point, and when the eccentric sleeve is mounted in the eccentric shaft with the attitude being in the center of a linear characteristics area.

Description

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

  For example, Patent Document 1 discloses a first link that is pivotably coupled to a piston, and a second link that is pivotally coupled to the first link and is rotatably mounted on a crankpin of a crankshaft. A link, a control shaft having an eccentric shaft portion, and a third link that is rotatably connected to the second link via a connecting pin and is swingably connected to the eccentric shaft portion of the control shaft. In the variable compression ratio mechanism of the internal combustion engine that variably controls the compression ratio of the internal combustion engine by rotating the control shaft according to the engine operating state and changing the position of the eccentric shaft portion, the compression ratio is independently set for each cylinder. There is disclosed one in which adjustable adjusting means is provided at the lower part of the third link.

  In Patent Document 1, a bolt hole having a thread groove is provided in the lower portion of the third link, and an adjustment bolt is screwed into the bolt hole, and a pair of halves are formed in the lower portion of the third link. An eccentric sleeve bearing of structure is provided. And the outer periphery of this eccentric sleeve bearing and the front-end | tip of an adjustment bolt are engaging, and since an eccentric sleeve bearing rotates by rotating an adjustment bolt and advancing and retreating, a 3rd link and a 2nd link are connected. Fine adjustment of the distance between the connecting pin and the swing center of the lower part of the third link is possible, and the compression ratio can be finely adjusted.

JP-A-2005-69027

  However, in the variable compression ratio mechanism disclosed in Patent Document 1, there is no mention of a set compression ratio when adjusting the top dead center position of the piston and the angular posture of the eccentric sleeve. There is a possibility that variations in the compression ratio at the target compression ratio cannot be accurately adjusted, such as when the specific compression ratio is frequently used.

  Accordingly, the present invention changes the position of the eccentric shaft portion by rotating the control shaft, thereby changing the top dead center position of the piston to change the compression ratio, and rotating the eccentric sleeve relative to the eccentric shaft portion. In the multi-link piston-crank mechanism of the internal combustion engine in which the piston top dead center position can be adjusted for each cylinder, the angle of the control shaft is set to an angle corresponding to a predetermined compression ratio, and the crankshaft Is set to an angle at which the piston becomes a predetermined stroke position, and the eccentric sleeve is positioned in the center of a linear characteristic region in which the relation of the stroke position of the piston to the rotation angle of the eccentric sleeve is close to linear When the piston is assembled to the eccentric shaft portion, the stroke position of the piston is approximately equal to the design median value of the predetermined stroke position at a predetermined compression ratio. Match so on, multi-link piston - is characterized by the elements of the crank mechanism is configured.

  According to the present invention, it is possible to accurately adjust the variation in the compression ratio at the target compression ratio.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows schematic structure of the multilink type piston-crank mechanism of the internal combustion engine to which this invention was applied. The side view which shows the structure of the control shaft vicinity. The side view of a control axis. The front view of a control axis. Explanatory drawing which expanded and showed the connection part of the control link and control shaft in the multiple link type piston-crank mechanism of the internal combustion engine to which this invention was applied. It is explanatory drawing which shows the eccentric sleeve used for the multiple link type piston-crank mechanism of the internal combustion engine to which this invention was applied, (a) is a front view, (b) is a side view, (c) is a rear view. . Explanatory drawing which showed typically the relationship between the rotation angle of an eccentric sleeve, and the height change of a piston. Explanatory drawing which showed typically the relationship between the rotation angle of the eccentric sleeve in 1st Embodiment of this invention, and the height change of a piston in the case of the highest compression ratio. Explanatory drawing which showed typically the relationship between the rotation angle of the eccentric sleeve in 1st Embodiment of this invention, and the rotation angle of a control shaft. Explanatory drawing which showed typically the relationship between the rotation angle of the eccentric sleeve in 2nd Embodiment of this invention, and the height change of a piston in the case of intermediate compression ratio. Explanatory drawing which showed typically the relationship between the rotation angle of the eccentric sleeve in 2nd Embodiment of this invention, and the rotation angle of a control shaft.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. 1 and 2 show an example of a basic configuration of a multi-link piston-crank mechanism to which the present invention is applied, and shows a case where the present invention is applied to an in-line four-cylinder internal combustion engine. FIG. 1 is an explanatory diagram showing a schematic configuration of a multi-link piston-crank mechanism of an internal combustion engine, and FIG. 2 is a side view showing a configuration in the vicinity of a control shaft 6 (described later).

  The multi-link type piston-crank mechanism includes an upper link 3 and a lower link 4 that connect the piston 1 and the crankshaft 2, a control link 5 that restricts the movement of the upper link 3 and the lower link 4, and one end of the control link 5. And a control shaft 6 having an eccentric shaft portion 7 connected so as to be swingable.

  The piston 1 is slidably disposed in a cylinder 10 formed in the cylinder block 9 and is connected to one end (upper end in FIG. 1) of the upper link 3 via a piston pin 11 so as to be swingable. .

  The other end (the lower end in FIG. 1) of the upper link 3 is rotatably connected to one end of the lower link 4 via the first connecting pin 12.

  The lower link 4 is rotatably attached to the crankpin 13 of the crankshaft 2 at the center thereof.

  The crankshaft 2 includes a plurality of journal portions 14 and a crank pin 13, and the journal portion 14 serving as a rotation shaft thereof is rotatably supported by the cylinder block 9. The crank pin 13 is eccentric from the journal portion 14 by a predetermined amount, and the lower link 4 is rotatably connected thereto.

  One end (upper end in FIG. 1) of the control link 5 that restricts the movement of the lower link 4 is rotatably connected to the other end of the lower link 4 via the second connecting pin 16, and the other end (in FIG. 1). The lower end is supported by a cylinder block 9 which is a part of the internal combustion engine body so as to be swingable. The other end of the control link 5 can be displaced with respect to the main body of the internal combustion engine in order to change the compression ratio of the internal combustion engine. Specifically, a control shaft 6 extending in parallel with the crankshaft 2 is provided, and the other end of the control link 5 is rotatably fitted to an eccentric shaft portion 7 provided eccentric to the control shaft 6. That is, the swing fulcrum 17 is the center position of the eccentric shaft portion 7.

As shown in FIGS. 1 to 4, the control shaft 6 includes a main shaft portion 8 that is rotatably supported by the cylinder block 9, and an eccentric shaft portion 7 that is eccentric by a predetermined amount e _{0 with} respect to the main shaft portion 8. And have. The eccentric shaft portion 7 is set to have a larger diameter than the main shaft portion 8, and the connecting portion 26 between the eccentric shaft portion 7 and the main shaft portion 8 has a smaller diameter than either the eccentric shaft portion 7 or the main shaft portion 8. It has become. An actuator 19 such as an electric motor is attached to one end of the control shaft 6. In the present embodiment, the control shaft 6 has eccentric shaft portions 7 formed at four locations, and the control links 5 of four cylinders are connected to the eccentric shaft portions 7 respectively.

  Therefore, when the control shaft 6 is rotationally driven by the actuator 19 to change the compression ratio, the center position of the eccentric shaft portion 7 that becomes the swing fulcrum 17 of the control link 5 moves relative to the engine body. As a result, the motion constraint condition of the lower link 4 by the control link 5 changes, the stroke position of the piston 1 with respect to the crank angle changes, and the compression ratio is changed accordingly.

  Further, in this multi-link type piston-crank mechanism, the center 15 of the journal portion 14 of the crankshaft 2 is offset to the right side in FIG. 1 with respect to the bore center line L1 of the cylinder 10. Further, the main shaft portion 8 serving as the rotation shaft of the control shaft 6 passes through the center 15 of the journal portion 14 and is on the right side in FIG. 1 with respect to the journal center line L2 parallel to the bore center line L1 of the cylinder 10. In addition to being offset, it is configured to be positioned below the journal portion 14 of the crankshaft 2 in FIG.

  In other words, in the multi-link type piston-crank mechanism, the journal portion 14 of the crankshaft 2 and the main shaft portion 8 of the control shaft 6 are offset in the same direction with respect to the bore center line L1 of the cylinder 10 and controlled. The shaft 6 is configured to be positioned below the crankshaft 2.

  Here, as shown in FIGS. 5 and 6, a substantially cylindrical seamless sleeve 20 is press-fitted around the eccentric shaft portion 7 of the control shaft 6. The eccentric sleeve 20 is fixed by press-fitting based on a sufficient press-fitting allowance without rotating relative to the eccentric shaft portion 7 during engine operation. Therefore, according to the present invention, instead of adjusting the center position of the connecting pin hole (the inner periphery of the bearing metal) of the control link as in the prior art, the eccentric shaft portion 7 (the outer periphery on the shaft side) of the control shaft 6 is adjusted. The center position is adjusted.

  The eccentric sleeve 20 includes a cylindrical portion 21 that is press-fitted into the eccentric shaft portion 7, and a rotation angle adjustment portion 22 that is formed at one end of the cylindrical portion 21. The cylindrical portion 21 is an outer peripheral surface that is rotatably fitted to a cylindrical bearing metal 24 attached to the other end side of the control link 5 with respect to an inner peripheral surface 23 that faces the outer peripheral surface of the eccentric shaft portion 7. 25 is formed to be eccentric by a predetermined amount e. The rotation angle adjusting part 22 is a convex part formed in a bowl shape on the entire circumference of one end of the cylindrical part 21, and is formed so that the outer shape is a hexagon when the eccentric sleeve 20 is viewed from the axial direction. Yes.

  Here, since the eccentric sleeve 20 is press-fitted into the eccentric shaft portion 7 of the control shaft 6, the inner peripheral surface 23 of the cylindrical portion 21 of the eccentric sleeve 20 and the outer peripheral surface of the eccentric shaft portion 7 are in direct contact. There will always be a part. In other words, the gap between the inner peripheral surface 23 of the cylindrical portion 21 of the eccentric sleeve 20 and the outer peripheral surface of the eccentric shaft portion 7 is set so as not to be at least in a fluid lubrication state.

  As shown in FIG. 3, the control shaft 6 in the present embodiment has four eccentric shaft portions 7, and the eccentric shaft portions 7a and 7b are arranged from the right side in FIG. 3 with the eccentric shaft portions 7c and 7d. In FIG. 3, an eccentric sleeve 20 is assembled from the left side in FIG. This is because the outer diameters of the eccentric shaft portions 7a and 7d are set smaller than the outer diameter of the eccentric shaft portions 7b and 7c (for example, about 1 mm). However, the inner diameter of the cylindrical portion 21 of the eccentric sleeve 20 that is press-fitted into the eccentric shaft portions 7a and 7d is set smaller than the inner diameter of the cylindrical portion 21 of the eccentric sleeve 20 that is press-fitted into the eccentric shaft portions 7b and 7c. The press-fitting allowance δ (the difference between the outer diameter of the eccentric shaft portion 7 and the inner diameter of the cylindrical portion 21 of the eccentric sleeve 20) is set to be the same for all cylinders. Further, the outer diameter of the eccentric sleeve is configured to be the same for all the cylinders, and the common control link 5 can be used for all the cylinders.

The eccentric amount e corresponding to the deviation between the center of the outer diameter and the center of the inner diameter of the eccentric sleeve 20 is the same for all cylinders, and is set to the minimum amount of eccentricity necessary for adjusting the variation in the compression ratio between the cylinders. The eccentric amount e ₀ of the eccentric shaft portion 7 of the control shaft 6 with respect to the main shaft portion 8 is set to be smaller.

  In such a multi-link type piston-crank mechanism, when adjusting the compression ratio during the assembly process of the internal combustion engine, all link parts (upper link 3, lower link 4, control link 5) are assembled. Thereafter, the control shaft 6 is fixed so as not to rotate, and for example, the height of the piston 1 of each cylinder at the top dead center position is measured, and the top dead center position corresponding to the measured height and the angle of the control shaft 6 at that time The required rotation angle of the eccentric sleeve 20 of each cylinder is calculated from the comparison with the calculated piston height, and the jig is engaged with the rotation angle adjusting portion 22 of the eccentric sleeve 20 to rotate the eccentric sleeve 20 of each cylinder. To adjust the height of the piston 1. If the top dead center position is adopted and adjusted in the stroke position of the piston 1, adjustment using a jig can be easily performed.

  Here, the relationship between the rotation angle of the eccentric sleeve 20 and the height change of the piston 1 is as shown in FIG. When the control shaft 8 is fixed and only the eccentric sleeve 21 is rotated at the piston top dead center position (with the crankshaft 2 fixed so that the cylinder to be adjusted is at the top dead center position), the piston top dead center position In the process from the rotation angle at which the piston becomes the highest to the rotation angle at which the piston top dead center position becomes the lowest, the relationship of the top dead center position (height) of the piston 1 to the rotation angle of the eccentric sleeve 20 is linear (the ratio is constant). There is a region close to (linear characteristic region). In such a region close to linearity, when the height of the piston 1 is adjusted, the required adjustment amount of the piston height can be accurately converted into the rotation angle of the eccentric sleeve 20, and the rotation angle of the eccentric sleeve 21 is managed. Therefore, it becomes easy to adjust the compression ratio variation by adjusting the piston height.

  When adjusting the top dead center position of the piston 1 by rotating the eccentric sleeve 20, for example, the top dead center position of the piston 1 of each cylinder is adjusted to coincide with the design median value (design median value). In this case, in the adjusted compression ratio (if the angle of the control shaft 8 is the angle at which the top dead center position is adjusted), it is possible to make the variation in the compression ratio between the cylinders substantially zero. However, regarding the top dead center position of the piston 1 at a compression ratio other than the compression ratio at which the top dead center position of the piston 1 is adjusted, the variation among the cylinders is not zero.

  Therefore, for example, if a compression ratio other than the compression ratio when adjusting the top dead center position of the piston 1 by rotating the eccentric sleeve 20 is frequently used during operation of the internal combustion engine, the compression is less frequently used. The advantage of minimizing the variation in compression ratio between cylinders at the time of ratio is small. On the other hand, if the variation in the compression ratio between the cylinders when the compression ratio is frequently used can be minimized, the fuel efficiency performance can be improved as a whole.

  Therefore, when the internal combustion engine uses the highest compression ratio that can be achieved by the multi-link type piston-crank mechanism most during the operation, as in the first embodiment of the present invention shown in FIGS. The dimensions of each part of the multi-link type piston-crank mechanism are set. That is, the angle of the control shaft 8 is set to the angle at the maximum compression ratio, the crankshaft 2 is fixed so that the cylinder to be adjusted is at the top dead center position, and the eccentric sleeve 20 is set to the center of the linear characteristic region. Components of the multi-link type piston-crank mechanism so that the piston position substantially coincides with the design median value of the piston top dead center position at the highest compression ratio when assembled to the eccentric shaft portion 7 in such a posture. Are processed in advance (the dimensions of each part are set). In the actual assembly process, when the eccentric sleeve 20 is press-fitted into the eccentric shaft portion 7, the cylinder to be adjusted is at the top dead center position at the rotation angle when the rotation angle of the control shaft 6 is the maximum compression ratio. With the crankshaft 2 fixed, the eccentric sleeve 20 is rotated with respect to the eccentric shaft portion 7 to adjust the top dead center position of the piston 1. In the case of this example, the configuration of the multi-link type piston-crank mechanism is configured to convert the vertical movement of the control link 5 into the vertical movement of the piston 1 or the upper link 3 relatively directly. (The arrangement is close to point symmetry with the crankpin 13 as the center.) Therefore, the eccentric direction P2 of the eccentric sleeve 20 (details will be described later) intersects the longitudinal direction of the control link 5 (the control link 5 is linearly arranged). It can be moved in a generally vertical direction.

  In this first embodiment, when the eccentric sleeve 20 is press-fitted into the eccentric shaft portion 7 (before adjustment), the assembly angle of the eccentric sleeve 20 with respect to the eccentric shaft portion 7 is as shown in FIG. The relationship of the top dead center position (height) of the piston 1 with respect to the rotation angle is an angle near the center of the region (linear characteristic region) in the region close to linear (constant ratio).

  Further, as shown in FIG. 9, when the rotation angle of the control shaft 6 is the maximum compression ratio, the eccentric sleeve 20 is rotated so that the top dead center position of the piston 1 becomes the design median value. Since the compression ratio is adjusted, the higher the top dead center position compared to the lower piston top dead center position (the higher the compression ratio compared to the lower compression ratio), the center of the design. The adjusted piston top dead center position tends to approach the piston top dead center position, which is a value, and it is closest to the design median value at the highest compression ratio that is frequently used.

  In the first embodiment, as shown in FIG. 9, the eccentric direction P2 of the eccentric sleeve 20 is predetermined in the clockwise direction in FIG. 9 with respect to the eccentric direction P1 of the eccentric shaft portion 7 with respect to the main shaft portion 8. The setting of this direction is based on the relationship of the stroke position of the piston 1 with respect to the rotation angle of the eccentric sleeve 20 after taking into account the posture of the multi-link type piston-crank mechanism when the compression ratio is high. It is the one that makes it the most linear (the ratio is made the most constant). 9, 31 is the center position of the main shaft portion 8, and 32 is the center position of the eccentric sleeve 20 (center position of the outer peripheral surface 25 of the eccentric sleeve 20). The arrow indicating the eccentric direction P2 of the eccentric sleeve 20 indicates that the center position 32 of the eccentric sleeve 20 and the thickness of the eccentric sleeve 20 (tubular portion 21) are the smallest when the eccentric sleeve 20 is viewed from the front. It is located on a straight line passing through the portion and the portion where the wall thickness is the thickest. Incidentally, before adjusting the top dead center position of the piston 1 by the eccentric sleeve 20, the piston top dead center position is sandwiched by two two-dot chain lines in FIG. 9 with respect to the design median value. It will have a range of variation indicated by the range.

  In such a first embodiment, for example, when used in combination with a supercharger and the internal combustion engine frequently uses the maximum compression ratio, it is accurately adjusted so that variations in the maximum compression ratio frequently used are eliminated. Therefore, the occurrence of knocking can be suppressed, and the fuel consumption when the engine is operated at a high compression ratio, particularly at the maximum compression ratio can be improved. That is, this first embodiment is preferably applied when the compression ratio that is most desired to reduce variation is the highest compression ratio.

  In the case where the internal combustion engine uses the intermediate compression ratio between the highest compression ratio and the lowest compression ratio that can be realized by the multi-link type piston-crank mechanism most during the operation, FIG. 10 and FIG. As shown in the second embodiment of the present invention, the dimensions of each part of the multi-link type piston-crank mechanism are set. That is, the angle of the control shaft 8 is set to an angle in the intermediate compression ratio, the crankshaft 2 is fixed so that the cylinder to be adjusted is at the top dead center position, and the eccentric sleeve 20 is set to the center of the linear characteristic region. Components of the multi-link piston-crank mechanism so that the piston position substantially coincides with the design median value of the piston top dead center position at the intermediate compression ratio when assembled to the eccentric shaft portion 7 in such a posture. Are processed in advance (the dimensions of each part are set). In the actual assembly process, when the eccentric sleeve 20 is press-fitted into the eccentric shaft portion 7, the cylinder to be adjusted is positioned at the top dead center at the rotation angle when the rotation angle of the control shaft 6 is the intermediate compression ratio. With the crankshaft 2 fixed, the eccentric sleeve 20 is rotated with respect to the eccentric shaft portion 7 to adjust the top dead center position of the piston 1. In the case of this example, the configuration of the multi-link type piston-crank mechanism is configured to convert the vertical movement of the control link 5 into the vertical movement of the piston 1 or the upper link 3 relatively directly. (The arrangement is close to point symmetry with the crankpin 13 as the center.) Therefore, the eccentric direction P2 of the eccentric sleeve 20 intersects the longitudinal direction of the control link 5 (in general, the control link 5 can be moved linearly). The direction is close to vertical.

  In the second embodiment, when the eccentric sleeve 20 is press-fitted into the eccentric shaft portion 7 (before adjustment), the assembly angle of the eccentric sleeve 20 with respect to the eccentric shaft portion 7 is as shown in FIG. The relationship of the top dead center position (height) of the piston 1 with respect to the rotation angle is an angle near the center of the region (linear characteristic region) in the region close to linear (constant ratio).

  Further, as shown in FIG. 11, when the rotation angle of the control shaft 6 is the rotation angle at the intermediate compression ratio, the eccentric sleeve 20 is rotated so that the top dead center position of the piston 1 becomes the design median value. Since the compression ratio is adjusted, the closer the rotation angle of the control shaft 6 is to the rotation angle at the intermediate compression ratio, the closer to the piston top dead center position, which is the design center value. The dead center position tends to be closer to the design median value when the intermediate compression ratio is frequently used.

  In the second embodiment, as shown in FIG. 11, the eccentric direction P2 of the eccentric sleeve 20 is on the counterclockwise direction side in FIG. 11 with respect to the eccentric direction P1 of the eccentric shaft portion 7 with respect to the main shaft portion 8. The direction is set at a predetermined angle, and the setting of this orientation takes into account the posture of the multi-link piston-crank mechanism at the intermediate reduction ratio, and the relationship between the stroke position of the piston 1 with respect to the rotation angle of the eccentric sleeve 20 Is made the most linear (the ratio is made the most constant). Since the attitude of the multi-link type piston-crank mechanism is different from that of the first embodiment having a different compression ratio, the eccentric direction P2 is slightly different from that of the first embodiment. Incidentally, also in this second embodiment, before the top dead center position of the piston 1 is adjusted by the eccentric sleeve 20, two piston top dead center positions in FIG. It has a range of variation indicated by a range between two-dot chain lines.

  In such a second embodiment, for example, when mounted on a hybrid vehicle or the like and mainly operates an internal combustion engine for charging a battery, it is frequently used at an intermediate compression ratio that is larger than the minimum compression ratio. By setting the intermediate compression ratio as the intermediate compression ratio, it is possible to accurately adjust so as to eliminate variations in the frequently used intermediate compression ratio, and to improve fuel efficiency when operating at the intermediate compression ratio. Can be made. That is, this second embodiment is preferably applied to a case where the compression ratio at which the variation is most desired to be reduced is an intermediate compression ratio that is greater than the minimum compression ratio.

  In the first and second embodiments described above, the eccentric sleeve 20 reduces the variation in the compression ratio between the cylinders, and accordingly, the eccentric sleeve 20 is set to avoid interference between the intake and exhaust valves and the piston. The margin can be reduced, the ignition timing advance angle, and the EGR region can be expanded, and the fuel efficiency can be improved. And since the dispersion | variation in the compression ratio between cylinders is reduced by the eccentric sleeve 20, it becomes possible to expand a supercharging pressure area | region, and it becomes possible to improve an output and a torque.

  The eccentric sleeve 20 is press-fitted into the eccentric shaft portion 7 so that the piston top dead center position at the lowest compression ratio matches the design median value of the piston top dead center position at the lowest compression ratio. When the rotation angle is the minimum compression ratio, the eccentric sleeve 20 is rotated with respect to the eccentric shaft portion 7 and the top dead center position of the piston 1 is adjusted. From the tendency of FIGS. Since the variation in the compression ratio becomes large, it is desirable to set at least a compression ratio other than the lowest compression ratio to a compression ratio that minimizes the variation.

5 ... Control link 6 ... Control shaft 7 ... Eccentric shaft part 20 ... Eccentric sleeve

Claims (4)

A control having a plurality of link members for connecting pistons and crankshafts of an internal combustion engine, a control link for restricting movement of the plurality of link members, and an eccentric shaft portion to which one end of the control link is swingably connected A shaft and a cylindrical eccentric sleeve press-fitted into the eccentric shaft portion, and the top dead center position of the piston is changed by changing the position of the eccentric shaft portion by rotation of the control shaft. In the multi-link piston-crank mechanism of an internal combustion engine in which the top dead center position of each piston can be adjusted for each cylinder by rotating the eccentric sleeve with respect to the eccentric shaft portion as the compression ratio changes.
The angle of the control shaft is set to an angle corresponding to a predetermined compression ratio, the angle of the crankshaft is set to an angle at which the piston is at a predetermined stroke position, and the eccentric sleeve is rotated by the eccentric sleeve. Design of a predetermined stroke position at a predetermined compression ratio when the piston stroke position is assembled to the eccentric shaft portion in a posture in which the relation of the stroke position of the piston to the angle is the center of a linear characteristic region that is close to linear A multi-link piston-crank mechanism for an internal combustion engine, wherein each element of the multi-link piston-crank mechanism is configured to substantially coincide with the above median value.   2. The multi-link piston-crank mechanism for an internal combustion engine according to claim 1, wherein the predetermined compression ratio is a compression ratio larger than a minimum compression ratio that can be realized by rotating the control shaft.   The multi-link piston-crank mechanism for an internal combustion engine according to claim 1 or 2, wherein the predetermined compression ratio is a maximum compression ratio that can be realized by rotating the control shaft.   The multi-link piston-crank mechanism for an internal combustion engine according to any one of claims 1 to 3, wherein the predetermined stroke position of the piston is a top dead center position.

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