JP2008303890A - Variable compression ratio internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable compression ratio internal combustion engine capable of preventing deformation of a wall surface forming a cylinder bore. <P>SOLUTION: An internal combustion engine 10 is provided with a variable compression ratio mechanism 50 comprising a case side bearing forming part 51, a block side bearing forming part 52, and a shaft-like driving part 53. The case side bearing forming part is formed on an upper part of a crankcase 30. The block side bearing forming part is extended to an outer side on a lower end of an outer wall surface 20c of a cylinder block 20. The block side bearing forming part is connected to the case side bearing forming part by the shaft like driving part. Further, a vertical position of a bore wall surface on an end of the crankcase 30 side is same with a vertical position of the outer wall surface 20c of the cylinder block 20 on the end of the crankcase 30 side (block outer wall surface lower end), or is in a position on a cylinder head side compared to the position of the block outer wall surface lower end. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a variable compression ratio internal combustion engine capable of changing a compression ratio that is a ratio of a maximum value to a minimum value of a volume of a combustion chamber that changes with movement of a piston.

  Conventionally, there has been proposed a variable compression ratio internal combustion engine that changes a compression ratio by moving a cylinder block in an axis line (center axis) direction of a cylinder bore (hereinafter also simply referred to as “vertical direction”) with respect to a crankcase. ing. For example, as shown in FIGS. 15 and 16, one of such variable compression ratio internal combustion engines can move in the vertical direction relative to the cylinder block 910 and the cylinder block 910 below the cylinder block 910. A crankcase 920 and a variable compression ratio mechanism 930 are provided.

  The cylinder block 910 is formed with four cylinder bores 911 arranged linearly. Each cylinder bore 911 houses a piston 912 as shown in FIGS. The piston 912 is connected to the crankshaft 921 shown in FIG. The crankshaft 921 is rotatably supported by a crankcase 920. Further, the variable compression ratio internal combustion engine includes a cylinder head 940 as shown in FIG. The cylinder head 940 is fixed on the cylinder block 910.

  The variable compression ratio mechanism 930 includes a block-side bearing forming portion 931, a case-side bearing forming portion 932 (932a, 932b), and a shaft-like drive portion 933. The block side bearing forming portion 931 is also referred to as a block side force receiving portion. The case side bearing forming portion 932 is also referred to as a case side force receiving portion.

  The block-side bearing forming portion 931 extends outward from the outer wall surface 913 in a region including an end portion on the crankcase 920 side (lower end portion of the cylinder block 910) of the outer wall surface (side wall surface) 913 of the cylinder block 910. As described above, it is fixed to the outer wall surface 913.

  The case side bearing forming portion 932a is formed in the upper part of the crankcase 920. The case side bearing forming portion 932b is fixed to the case side bearing forming portion 932a. The case side bearing forming portion 932a and the case side bearing forming portion 932b constitute a case side bearing forming portion 932 as shown in FIG.

The shaft-like drive portion 933 includes a plurality of eccentric cam portions, and includes a cylindrical bearing hole formed in the block-side bearing formation portion 931, a case-side bearing formation portion 932a, and a case-side bearing formation portion 932b. It is arranged to pass through a cylindrical bearing hole formed in the side bearing forming portion 932. Then, as shown in FIGS. 17A and 17B, the shaft driving unit 933 is rotated around a predetermined axis by a driving device (not shown). At this time, the shaft-like drive portion 933 rotates while abutting (engaging) with the surfaces forming the cylindrical bearing holes formed in the block-side bearing forming portion 931 and the case-side bearing forming portion 932, The distance D in the central axis (axis) direction (vertical direction) BC of the cylinder bore 911 between the position of the bearing forming portion 931 and the position of the case side bearing forming portion 932 is changed. The longer the distance D, the longer the distance between the cylinder block 910 and the crankcase 920, so that the combustion chamber volume (minimum value of the combustion chamber volume) when the piston 912 is at the top dead center is increased. . Therefore, the compression ratio is low. Thus, according to the internal combustion engine, the compression ratio can be changed (see, for example, Patent Document 1).
JP 2003-206871 A

  As shown in FIG. 18, when the mixed gas burns in the combustion chamber formed by the wall surface forming the cylinder bore 911, the lower surface 941 of the cylinder head 940, and the top surface of the piston 912, the pressure of the gas in the combustion chamber Becomes extremely high. By this pressure, the lower surface 941 of the cylinder head 940 is pushed upward by the force F0a, and the top surface of the piston is pushed downward by the force F0b. Thereby, an upward force F1a is applied to the cylinder block 910 to which the cylinder head 940 is fixed, while a downward force F1b is applied to the crankcase 920 that supports the crankshaft 921 connected to the piston 912. Is added. As a result, the portion on the crankcase 920 side of the surface forming the bearing hole of the block-side bearing forming portion 931 is pushed downward by receiving the force F2 from the shaft-like drive portion 933.

  As described above, since the end of the cylinder block 910 on the cylinder head 940 side is fixed to the cylinder head 940, the rigidity is high. On the other hand, since the end of the cylinder block 910 on the crankcase 920 side is not fixed to the crankcase 920, the rigidity is relatively low. Further, since the force F2 acts at a position away from the outer wall surface 913 to which the block-side bearing forming portion 931 is fixed, it tends to bend the lower end portion of the cylinder block 910 inward. It acts on the cylinder block 910 as a force (bending moment).

  In other words, of the outer wall surface 913 of the cylinder block 910, the end on the crankcase 920 side (the lower end of the block outer wall surface) in the region where the block-side bearing forming portion 931 is fixed is oriented inward of the cylinder block 910. A pressing force F3 in the (pressing direction) is applied. By this pressing force F3, the wall surface forming the cylinder bore 911 is deformed inward of the cylinder bore 911 as shown by the dotted line DF. As a result, the frictional force between the wall surface forming the cylinder bore 911 and the piston 912 increases and fuel consumption deteriorates, or the amount of lubricating oil flowing into the combustion chamber increases and the lubricating oil is wasted. There was a fear of it.

  The present invention has been made to address the above-described problems, and an object of the present invention is to provide a variable compression ratio internal combustion engine capable of preventing the wall surface forming the cylinder bore from being deformed.

In order to achieve such an object, a variable compression ratio internal combustion engine according to the present invention provides:
A cylinder bore that is a cylindrical hole penetrating in a predetermined bore central axis direction is formed, and a cylinder block that houses a piston in the cylinder bore, and is fixed to the cylinder block so as to cover one of the opening portions of the cylinder bore. The cylinder head is disposed on the opposite side of the cylinder head with respect to the cylinder block, and is movable relative to the cylinder block in the bore central axis direction, and the crankshaft connected to the piston is rotatable. And a crankcase that is supported by a bore wall surface that forms the cylinder bore, a head lower surface that is a surface of the cylinder head on the cylinder block side, and a piston top surface that is a surface of the piston on the lower surface side of the head Equipped with a variable compression ratio mechanism that changes the volume of the combustion chamber formed A variable compression ratio internal combustion engine.

  The variable compression ratio mechanism includes a block-side force receiving portion extending outward from an outer wall surface of the cylinder block, and the block-side force receiving portion while contacting the block-side force receiving portion and the crankcase. A connecting portion that changes a distance in the bore central axis direction between the crankcase and the crankcase.

  Further, the cylinder block has a lower end of the bore wall surface, which is an end of the bore wall surface on the crankcase side, at an end on the crankcase side of the outer wall surface of the cylinder block from which the block side force receiving portion extends. It is configured to be the same position as the position of the lower end of the outer wall surface of the block or the position on the cylinder head side relative to the position of the lower end of the outer wall surface of the block.

  According to this, the position of the end on the crankcase side of the bore wall surface (the lower end of the bore wall surface) is the position of the end on the crankcase side of the outer wall surface of the cylinder block from which the block side force receiving portion extends (the lower end of the block outer wall surface). Or the position closer to the cylinder head than the position of the lower end of the outer wall surface of the block. Therefore, when the portion including the bore wall surface of the crankcase side end portion (block lower end portion) of the cylinder block is bent inward of the cylinder block by the pressing force, the lower end of the bore wall surface is inward of the cylinder bore. The distance that can be moved can be made shorter than when the lower end of the bore wall surface is located closer to the crankcase than the lower end of the outer wall surface of the block. As a result, the degree to which the bore wall surface is deformed by the pressing force can be reduced.

Another variable compression ratio internal combustion engine according to the present invention is:
A plurality of cylinder bores, which are cylindrical holes penetrating in a predetermined bore center axis direction, are formed in a straight line in a cylinder arrangement direction orthogonal to the bore center axis direction, and a piston is placed in each cylinder bore. A cylinder block to be accommodated, a cylinder head fixed to the cylinder block so as to cover one of the opening portions of the cylinder bore, and disposed opposite to the cylinder head with respect to the cylinder block and to the cylinder block A crankcase that is relatively movable in the bore central axis direction and rotatably supports a crankshaft connected to the piston, and a bore wall surface that forms the cylinder bore and the cylinder block side of the cylinder head The lower surface of the head and the surface of the piston on the lower surface side of the head A variable compression ratio internal combustion engine having a variable compression ratio mechanism for changing the volume of the combustion chamber formed by the that the piston top surface.

  The variable compression ratio mechanism is configured to be external to the outer wall surface in a region including a part of the intersection line between a plane perpendicular to the cylinder arrangement direction and passing through the central axis of the cylinder bore and the outer wall surface of the cylinder block. The block side force receiving portion extending in the direction of the block, and the distance between the block side force receiving portion and the crankcase in the bore central axis direction between the block side force receiving portion and the crankcase. A connecting portion to be changed.

  The cylinder block is formed between a bore central axis arrangement plane including the cylinder arrangement direction and the bore central axis direction in a cross section obtained by cutting the cylinder block along a plane orthogonal to the cylinder arrangement direction, and an outer wall surface of the cylinder block. The bore center axis arrangement plane and the block side force receiving portion in a cross section obtained by cutting the cylinder block in a plane perpendicular to the cylinder arrangement direction and passing through the block side force receiving portion extend. It is comprised so that the part shorter than the distance between the same outer wall surface in the position which is may be included.

  That is, this cylinder block has a thick part including a part where the block-side force receiving part extends and a thin part composed of other parts. As a result, the rigidity at the position where the block side force receiving portion extends is higher than the rigidity at other positions. Therefore, the cylinder block is not easily deformed even when the pressing force is applied. That is, it is possible to reduce the degree to which the bore wall surface is deformed by the pressing force while suppressing an increase in the weight of the cylinder block.

Furthermore, another variable compression ratio internal combustion engine according to the present invention is:
The block-side force receiving portion receives a force in the direction from the cylinder block toward the crankcase by the connecting portion, so that the block-side force receiving portion presses the outer wall surface in a predetermined pressing direction at a predetermined pressing position. Therefore, the bore wall stress, which is a stress generated on the bore wall surface at a position where a straight line passing through the same push position and parallel to the push direction intersects the bore wall surface, Stress reducing means for making the outer wall stress smaller than the outer wall stress, which is the stress generated in the outer wall surface, may be provided.

  That is, in such an internal combustion engine, when the mixed gas burns in the combustion chamber, a force in the direction from the cylinder block to the cylinder head (upward) is applied to the cylinder head, and the piston moves from the piston to the piston. A force in the direction toward the crankshaft (downward) is applied, and as a result, the block side force receiving portion is pulled downward by the crankcase via the connecting portion. As a result, the block-side force receiving portion presses the outer wall surface in a predetermined pressing direction at a predetermined pressing position in the outer wall surface of the cylinder block (see force F3 described above). As a result, stress is generated in the cylinder block. Of these stresses, the stress (bore wall stress) generated on the bore wall surface at a position where a straight line passing through the pushing position and parallel to the pushing direction intersects the bore wall surface is removed at the pushing position by the stress reducing means. It is made smaller than the stress (outer wall surface stress) generated on the wall surface.

  Therefore, the degree of deformation of the bore wall surface due to the stress can be reduced as compared with the case where no stress reducing means is provided. As a result, since the frictional force between the bore wall surface and the piston does not become excessive, fuel consumption can be prevented from deteriorating, and the amount of lubricating oil flowing into the combustion chamber does not become excessive, so that the lubricating oil is wasted. It is possible to prevent consumption.

  In this case, the stress reducing means is a position within the surface on the crankcase side of the cylinder block, and when the same surface is viewed from the bore central axis direction, the block side force receiving portion and the bore wall surface It is preferable to be formed of slit-shaped grooves formed in the cylinder block so as to open at a position therebetween.

  According to this, when the block-side force receiving portion presses the outer wall surface of the cylinder block as described above, the outer wall surface stress is substantially equal to the outer wall surface side portion (outer wall surface side portion) with respect to the groove portion of the cylinder block. The same magnitude of stress is generated, and this outer wall surface portion is deformed. Thereby, an outer wall surface side part generate | occur | produces the force resisting the force (pressing force) which a block side receiving part presses an outer wall surface. As a result, the stress transmitted to the portion on the bore wall surface side (bore wall surface side portion) with respect to the groove portion is smaller than the outer wall surface stress. Thereby, the said bore wall surface stress becomes small compared with the case where the said groove part is not formed. As a result, the degree of deformation of the bore wall surface due to the bore wall stress can be reduced.

On the other hand, when the cylinder block includes a hollow cylindrical cylinder liner having an inner wall surface constituting the bore wall surface,
The stress reducing means has higher rigidity than a portion of the cylinder block excluding the cylinder liner, and a position on the pressing straight line between the block side force receiving portion and the cylinder liner. It may be constituted by a reinforcing member arranged in the cylinder block so as to pass through and surround the cylinder liner around the bore central axis.

  According to this, when the block-side force receiving portion presses the outer wall surface of the cylinder block as described above, the outer wall surface stress and the portion on the outer wall surface side (outer wall surface side portion) with respect to the reinforcing member of the cylinder block are reduced. Stresses of approximately the same magnitude are generated. At this time, since the rigidity of the reinforcing member is higher than the rigidity of the cylinder block, due to the rigidity of the reinforcing member, the stress transmitted to the bore wall surface side portion (bore wall surface side portion) is smaller than the outer wall surface stress. . Thereby, the said bore wall surface stress becomes small compared with the case where the said reinforcement member is not arrange | positioned. As a result, the degree of deformation of the bore wall surface (cylinder liner) due to the bore wall surface stress can be reduced.

<First Embodiment>
Embodiments of a variable compression ratio internal combustion engine according to the present invention will be described below with reference to the drawings. As shown in FIG. 1, the variable compression ratio internal combustion engine 10 includes a cylinder block 20 and a crankcase 30.

<< Cylinder block >>
The cylinder block 20 is made of aluminum. As shown in FIGS. 1 to 3, the cylinder block 20 has a substantially rectangular upper surface 20a and a lower surface 20b having short sides and long sides and side surfaces parallel to the long side direction (in this specification, “outer wall surface” It is also referred to as “.” 20 c. Hereinafter, in this specification, a direction from the upper surface 20a of the cylinder block 20 toward the lower surface 20b is referred to as a downward direction, and a direction from the lower surface 20b of the cylinder block 20 to the upper surface 20a is referred to as an upward direction.

  The cylinder block 20 is formed with four cylindrical through holes penetrating in a direction orthogonal to the upper surface 20a and the lower surface 20b (that is, the vertical direction, also referred to as the bore central axis direction). These through holes are linearly arranged in the long side direction (cylinder arrangement direction) of the cylinder block 20. In each through hole, a hollow cylindrical cylinder liner 20d having the same outer diameter as the through hole is coaxially disposed (press-fit or cast).

  The cylinder liner 20d is made of cast iron. A cylindrical space formed by the inner wall surface of the cylinder liner 20d is referred to as a cylinder bore 21. The lower end (end on the crankcase 30 side) of the cylinder liner 20d is included in a plane including the lower surface 20b of the cylinder block 20. That is, the position in the vertical direction of the lower end (the lower end of the bore wall surface) of the inner wall surface (the wall surface forming the cylinder bore 21) of the cylinder liner 20d is the lower end of the outer wall surface 20c of the cylinder block 20 (the lower end of the block outer wall surface). It is the same position as the position in the up-down direction.

Lubricating oil in an oil pan (not shown) attached to the lower part of the crankcase 30 is supplied to the bore wall surface.
FIG. 4 is a cross-sectional view of the variable compression ratio internal combustion engine 10 taken along a plane including a 4-4 line passing through the central axis (bore central axis) BC of the cylinder bore 21 shown in FIG. 1 and orthogonal to the cylinder arrangement direction. As shown, one cylindrical piston 22 is accommodated in each cylinder bore 21. A piston ring for scraping off excess lubricant on the bore wall surface is disposed on the side surface of each piston 22.

  The cylinder block 20 is formed with a cooling water passage 23 for flowing cooling water. The cooling water passage 23 is a groove disposed around the cylinder liner 20 d and opens to the upper surface 20 a of the cylinder block 20.

<< Crankcase >>
As shown in FIG. 1, the crankcase 30 supports the crankshaft 31 in a rotatable manner and accommodates the crankshaft 31. The crankcase 30 is disposed below the cylinder block 20 so that the axial direction of the crankshaft 31 coincides with the cylinder arrangement direction. Each piston 22 is connected to the crankshaft 31 via a connecting rod 32 shown in FIG. With such a configuration, the reciprocating motion of each piston 22 is converted into the rotational motion of the crankshaft 31.

<< Cylinder head >>
Further, the variable compression ratio internal combustion engine 10 includes a 5-5 line passing between the cylinder bores 21 and the cylinder bores 21 shown in FIGS. 4 and 1, and the variable compression ratio internal combustion engine 10 on a plane orthogonal to the cylinder arrangement direction. As shown in FIG. 5, which is a cross-sectional view taken along a line, a cylinder head 40 is provided. The cylinder head 40 is fixed to the upper surface 20 a of the cylinder block 20 (that is, the side opposite to the crankcase 30 with respect to the cylinder block 20) so as not to move with respect to the cylinder block 20.

  As shown in FIG. 4, the cylinder head 40 is formed with a plurality of recesses 40 a 1 that open to the cylinder block 20 side surface (head lower surface) 40 a of the cylinder head 40 and correspond to each of the cylinder bores 21. ing. Each recess 40a1 is connected to a wall surface (bore wall surface) forming one cylinder bore 21 corresponding to each recess 40a1 in a state where the cylinder head 40 is fixed to the cylinder block 20. That is, the cylinder head 40 is fixed to the cylinder block 20 so as to cover one (upper side) of the opening portion of the cylinder bore 21. The recess 40a1 of the head lower surface 40a, the bore wall surface, and the surface of the piston 22 on the cylinder head 40 side (piston top surface) form a combustion chamber 41 for each cylinder bore 21 (for each cylinder).

  As shown in FIG. 4, the cylinder head 40 is formed with an intake port 42 communicating with the combustion chamber 41 and an exhaust port 43 communicating with the combustion chamber 41 for each cylinder. In the cylinder head 40, an intake valve 42 a that opens and closes the intake port 42, an exhaust valve 43 a that opens and closes the exhaust port 43, and a spark plug 44 that generates a spark in the combustion chamber 41 are disposed for each cylinder. Yes.

  In addition, the variable compression ratio internal combustion engine 10 is provided with fuel injection means (not shown). By injecting fuel with the fuel injection means, a mixed gas containing fuel and air is burned via the intake port 42. The chamber 41 is supplied.

<< Variable compression ratio mechanism >>
Further, the variable compression ratio internal combustion engine 10 includes a variable compression ratio mechanism 50 as shown in FIGS. The variable compression ratio mechanism 50 is a mechanism provided one by one near each side surface (outer wall surface) 20 c of the cylinder block 20. The variable compression ratio mechanism 50 on one side surface (outer wall surface) 20c and the variable compression ratio mechanism 50 on the other side surface 20c are symmetric with respect to the bore center axis arrangement plane including the bore center axes BC of all cylinders. . Therefore, only the variable compression ratio mechanism 50 on one side surface 20c will be described.

  As shown in FIG. 1, the variable compression ratio mechanism 50 includes a case-side bearing forming part 51, a block-side bearing forming part 52, and a shaft-like driving part 53. The case side bearing forming portion 51 is also referred to as a case side force receiving portion. The block side bearing forming portion 52 is also referred to as a block side force receiving portion. Furthermore, the axial drive part 53 comprises the connection part.

<Case side bearing formation part>
The case side bearing forming portion 51 includes a flat vertical wall portion 51a and a plurality of cap portions 51b.
The vertical wall portion 51 a constitutes the upper side wall of the crankcase 30. The vertical wall 51a faces the side surface (outer wall surface) 20c of the cylinder block 20 and covers a part of the outer wall surface 20c in a state where the cylinder block 20 is disposed on the crankcase 30. .

  A plurality of (four in this example) corresponding to each of the cylinder bores 21 in a state where the vertical wall portion 51a penetrates in the thickness direction and the cylinder block 20 is disposed on the crankcase 30. Through-hole 51a1 is formed. Each through hole 51a1 is arranged in a region including a position where a plane that includes the central axis (bore central axis) BC of one corresponding cylinder bore 21 and intersects the cylinder arrangement direction and the vertical wall portion 51a. Has been. A cross section in which the vertical wall 51a is cut by a plane perpendicular to the cylinder arrangement direction at a position between the through hole 51a1 and the through hole 51a1 formed in the vertical wall 51a. A recess 51a2 having a semicircular shape is formed. The center of the semicircle of each recessed part 51a2 is arrange | positioned coaxially.

  One cap 51b corresponds to each of the recesses 51a2 of the vertical wall 51a. Each cap portion 51b is fixed to the vertical wall portion 51a so as to cover one corresponding concave portion 51a2 of the vertical wall portion 51a. In each cap portion 51b, in a state where the cap portion 51b is fixed to the vertical wall portion 51a, the cap portion 51b is cut by a plane that is a recess opened toward the vertical wall portion 51a and is orthogonal to the cylinder arrangement direction. A recessed portion 51b1 having a semicircular shape in the cross section is formed. The semicircular diameter of the recess 51b1 is the same as the semicircular diameter of the recess 51a2.

  With this configuration, the case-side bearing forming portion 51 is arranged in the cylinder arrangement direction by the concave portion 51a2 of the vertical wall portion 51a and the concave portion 51b1 of the cap portion 51b in a state where the cap portion 51b is fixed to the vertical wall portion 51a. A plurality of cylindrical bearing holes 51c that penetrates and are arranged coaxially are formed.

<Block side bearing forming part>
The block-side bearing forming portion 52 is composed of a plurality (four in this example) of members corresponding to each of the through holes 51a1 of the vertical wall portion 51a. Each block-side bearing forming portion 52 is fixed to the lower end portion of the outer wall surface 20c of the cylinder block 20 in a state of being inserted into the through hole 51a1 of the vertical wall portion 51a. That is, each block-side bearing forming portion 52 extends outward from the outer wall surface 20c of the cylinder block 20 and includes a plane including the central axis of the corresponding one of the cylinder bores 21 and orthogonal to the cylinder arrangement direction. The cylinder block 20 is disposed in a region including a part of the line of intersection with the outer wall surface 20c.

  The vertical length of the block-side bearing forming portion 52 is shorter than the vertical length of the through hole 51a1 of the vertical wall portion 51a. With such a configuration, the block-side bearing forming portion 52 can move in the vertical direction within the through hole 51a1 of the vertical wall portion 51a. That is, the crankcase 30 can be moved relative to the cylinder block 20 in the vertical direction (bore central axis direction).

  Each block-side bearing forming portion 52 is formed with a cylindrical bearing hole 52a penetrating in the cylinder arrangement direction. Each bearing hole 52a is arranged coaxially. The diameter of each bearing hole 52a is larger than the diameter of the bearing hole 51c.

<Axial drive unit>
As shown in FIGS. 1, 4, and 5, the shaft-like drive portion 53 has a plurality of fixed portions each corresponding to each of the rod-shaped eccentric shaft portion 53 a and the bearing hole 51 c of the case-side bearing forming portion 51. A plurality of movable cam portions 53c corresponding to each of the cam portions 53b, the bearing holes 52a of the block side bearing forming portion 52, and a worm gear 53d are provided.

  Each fixed cam portion 53b is a cylindrical member having substantially the same diameter as the bearing hole 51c of the case-side bearing forming portion 51. The length of each fixed cam portion 53b in the axial direction is substantially the same as the length in the axial direction of one corresponding bearing hole 51c of the case side bearing forming portion 51. Each fixed cam portion 53b is formed with a through-hole that penetrates in the axial direction at a position deviated (eccentric) from its central axis and has a columnar through-hole having substantially the same diameter as the eccentric shaft portion 53a. .

  Each movable cam portion 53c is a columnar member having substantially the same diameter as the bearing hole 52a of the block side bearing forming portion 52. The length in the axial direction of each movable cam portion 53 c is substantially the same as the length in the axial direction of one corresponding bearing hole 52 a of the block-side bearing forming portion 52. Each movable cam portion 53c is formed with a cylindrical through-hole having a diameter substantially the same as that of the eccentric shaft portion 53a, which is a through-hole penetrating in the axial direction at an eccentric position.

  The fixed cam portion 53b and the movable cam portion 53c are alternately arranged with the fixed cam portions 53b and the movable cam portions 53c one by one, and the through holes of the fixed cam portions 53b and the through holes of the movable cam portions 53c are arranged coaxially. And it attaches to the eccentric shaft part 53a in a state where the eccentric shaft part 53a is passed through each through hole. Screw holes (not shown) are formed in the fixed cam portion 53b and the eccentric shaft portion 53a. The fixed cam portion 53b and the eccentric shaft portion 53a are arranged so that the respective fixed cam portions 53b do not rotate with respect to the eccentric shaft portion 53a, and all the fixed cam portions 53b are arranged coaxially. It is fixed by a screw (not shown) that is inserted through. On the other hand, the movable cam portion 53c is rotatable with respect to the eccentric shaft portion 53a.

  The worm gear 53d is fixed to the fixed cam portion 53b so as not to rotate with respect to the eccentric shaft portion 53a and to be coaxial with the fixed cam portion 53b. The worm gear 53d is rotationally driven by meshing with an output portion of a motor (not shown).

  In the shaft-like drive portion 53, each fixed cam portion 53b is accommodated in one corresponding bearing hole 51c of the case-side bearing forming portion 51 and is in contact with the wall surface forming the bearing hole 51c in the bearing hole 51c. And each movable cam portion 53c is accommodated in one corresponding bearing hole 52a of the block-side bearing forming portion 52 and is in contact with the wall surface forming the bearing hole 52a. It is supported by the case side bearing formation part 51 and the block side bearing formation part 52 so that it can rotate within 52a.

<Operating principle of variable compression ratio mechanism>
Here, a change in the compression ratio accompanying the rotation of the worm gear 53d will be described with reference to FIG.

  As shown in FIG. 6A, when the central axis of the eccentric shaft portion 53a is located immediately below the central axis FC of the fixed cam portion 53b, that is, the central axis of the eccentric shaft portion 53a is the fixed cam portion 53b. The central axis of the eccentric shaft portion 53a, the central axis FC of the fixed cam portion 53b, and the central axis MC of the movable cam portion 53c are arranged on the same straight line in this order, The distance in the vertical direction between the central axis FC of the fixed cam portion 53b and the central axis MC of the movable cam portion 53c is the shortest. Accordingly, since the distance in the vertical direction between the crankcase 30 and the cylinder block 20 is also the shortest, the compression ratio is the highest.

  In this state, when the right worm gear 53d in FIG. 6A is rotated counterclockwise (in the direction of arrow A) and the left worm gear 53d is rotated in the clockwise direction (in the direction of arrow B), the right side The central axis of the eccentric shaft portion 53a moves counterclockwise around the central axis FC of the fixed cam portion 53b, and the central axis of the left eccentric shaft portion 53a rotates clockwise around the central axis FC of the fixed cam portion 53b. Moving. At this time, all the movable cam portions 53c cannot move in the left-right direction due to the rigidity of the cylinder block 20.

  Accordingly, the right movable cam portion 53c rotates counterclockwise in the bearing hole 52a while abutting against the wall surface forming the bearing hole 52a of the block-side bearing forming portion 52, and pushes up the block-side bearing forming portion 52. Further, the left movable cam portion 53 c rotates in the bearing hole 52 a in a clockwise direction while abutting against a wall surface forming the bearing hole 52 a of the block-side bearing forming portion 52, thereby pushing up the block-side bearing forming portion 52. Then, by continuing the rotation drive of the worm gear 53d, the variable compression ratio mechanism 50 is in the state of the center axis of the eccentric shaft portion 53a and the center axis of the fixed cam portion 53b as shown in FIG. It reaches the state where FC and the left-right direction are lined up.

  In the state shown in FIG. 6B, the distance in the vertical direction between the central axis FC of the fixed cam portion 53b and the central axis MC of the movable cam portion 53c is longer than that shown in FIG. Become. Therefore, the compression ratio is lower than that shown in (A).

  Further, by continuing the rotational drive of the worm gear 53d, the central axis of the right eccentric shaft portion 53a moves counterclockwise around the central axis FC of the fixed cam portion 53b, and the central axis of the left eccentric shaft portion 53a. Moves clockwise around the central axis FC of the fixed cam portion 53b. Accordingly, the right movable cam portion 53c rotates clockwise in the bearing hole 52a while abutting against the wall surface forming the bearing hole 52a of the block side bearing forming portion 52, and pushes up the block side bearing forming portion 52. Further, the left movable cam portion 53 c rotates in the bearing hole 52 a counterclockwise while abutting against the wall surface forming the bearing hole 52 a of the block side bearing forming portion 52, and pushes up the block side bearing forming portion 52. Then, the state of the variable compression ratio mechanism 50 reaches the state shown in FIG.

  In the state shown in FIG. 6C, the central axis FC of the fixed cam portion 53b, the central axis of the eccentric shaft portion 53a, and the central axis MC of the movable cam portion 53c are arranged on the same straight line in this order. The distance in the vertical direction between the central axis FC of 53b and the central axis MC of the movable cam portion 53c is the longest (that is, the state shown in FIG. 6A and the state shown in FIG. 6B). Longer than the state.) Accordingly, since the distance in the vertical direction between the crankcase 30 and the cylinder block 20 is also the longest, the compression ratio is the lowest.

  Thus, as the right worm gear 53d rotates counterclockwise and the left worm gear 53d rotates clockwise (the state of the variable compression ratio mechanism 50 is shown in (C) to (C)). As it goes to the state), the compression ratio decreases.

  On the other hand, if the rotation direction of the worm gear 53d is opposite to that described above, the compression ratio increases as the worm gear 53d rotates, contrary to the case described above. That is, in the state shown in (C), when the right worm gear 53d is rotated in the clockwise direction and the left worm gear 53d is rotated in the counterclockwise direction, the central axis of the right eccentric shaft portion 53a becomes the fixed cam portion. While moving clockwise around the central axis FC of 53b, the central axis of the left eccentric shaft portion 53a moves counterclockwise around the central axis FC of the fixed cam portion 53b.

  Therefore, the right movable cam portion 53c rotates counterclockwise in the bearing hole 52a while abutting against the wall surface forming the bearing hole 52a of the block-side bearing forming portion 52, and pushes down the block-side bearing forming portion 52. Further, the left movable cam portion 53c rotates clockwise in the bearing hole 52a while abutting against the wall surface forming the bearing hole 52a of the block side bearing forming portion 52, and pushes down the block side bearing forming portion 52.

Therefore, by continuing the rotational drive of the worm gear 53d, the state of the variable compression ratio mechanism 50 reaches the state shown in (B), and further continues to the state shown in (A).
Thus, as the right worm gear 53d rotates in the clockwise direction and the left worm gear 53d rotates in the counterclockwise direction (the state of the variable compression ratio mechanism 50 is changed from the state shown in (C) to (A). Since the distance in the up-and-down direction between the crankcase 30 and the cylinder block 20 is shortened (toward the state), the compression ratio increases.

  Thus, the compression ratio of the variable compression ratio internal combustion engine 10 is changed by changing the distance between the crankcase 30 and the cylinder block 20 in the vertical direction (bore central axis direction) by rotationally driving the worm gear 53d. Is changed.

<Slit groove>
Further, as shown in FIGS. 3 and 4, the cylinder block 20 includes a plurality of slit-like stress reducing grooves 24 as stress reducing means, each corresponding to each of the block side bearing forming portions 52. Is formed. Each stress reducing groove 24 is a position in the lower surface 20b of the cylinder block 20, and one block side bearing formation corresponding to each stress reducing groove 24 when the lower surface 20b is viewed from the bore central axis direction. It opens at a position (region) between the portion 52 and the bore wall surface that forms the cylinder bore 21 disposed at a position closest to the block-side bearing forming portion 52. The shape of the opening of each stress reducing groove 24 is an elongated rectangular shape having a long side slightly longer than the length of the block-side bearing forming portion 52 in the cylinder arrangement direction and an extremely short short side perpendicular to the long side. is there.

  The depth of each stress reducing groove 24 is slightly longer than half the length of the block-side bearing forming portion 52 in the vertical direction, as shown in FIG.

<Action>
In the variable compression ratio internal combustion engine 10 according to the first embodiment configured as described above, when the mixed gas formed in the combustion chamber 41 burns, the pressure of the gas in the combustion chamber 41 becomes extremely high. By this pressure, as shown in FIG. 7, the head lower surface 40a is pushed upward by the force F0a, and the top surface of the piston 22 is pushed downward by the force F0b. Thus, an upward force F1a is applied to the cylinder block 20 to which the cylinder head 40 is fixed, while a downward force F1b is applied to the crankcase 30 that supports the crankshaft 31 connected to the piston 22. Is added. As a result, the portion on the crankcase 30 side of the wall surface forming the bearing hole 52a of the block side bearing forming portion 52 receives the force F2 from the shaft-like drive portion 53 and is pushed downward.

  Since this force F2 acts at a position away from the outer wall surface 20c to which the block-side bearing forming portion 52 is fixed, let's bend the lower end of the cylinder block 20 inward of the cylinder block 20. Acting on the cylinder block 20 as a force (bending moment). In other words, in the outer wall surface 20c of the cylinder block 20 at the end on the crankcase 30 side in the region where the block side bearing forming portion 52 is fixed (the lower end of the block outer wall surface, the pressing position) A pressing force F3 in a direction (pressing direction) toward is applied. That is, the block-side bearing forming portion (block-side force receiving portion) 52 presses the outer wall surface 20 c in the pressing direction at the lower end portion in the outer wall surface 20 c of the cylinder block 20.

  As a result, the stress (outer wall surface stress) generated in the outer wall surface 20 c at the pressing position is substantially equal to the stress on the outer wall surface 20 c side of the cylinder block 20 on the outer wall surface 20 c side (outer wall surface surface). The outer wall surface side portion is deformed as indicated by the dotted line DF. Thereby, the outer wall surface side portion generates a force that resists the force (pressing force) F3 that the block side bearing forming portion 52 presses the outer wall surface 20c.

  As a result, the stress transmitted to the portion closer to the bore wall surface (bore wall surface side portion) than the stress reducing groove 24 is smaller than the outer wall surface stress. As a result, a straight line passing through the pressing position of the stress generated in the cylinder block 20 by the pressing force F3 and parallel to the pressing direction is generated on the bore wall surface at a position where it intersects the bore wall surface. The stress (bore wall stress) is smaller than that when the stress reducing groove 24 is not formed. As a result, the degree of deformation of the bore wall surface due to the bore wall stress can be reduced.

  As a result, since the frictional force between the bore wall surface and the piston 22 does not become excessive, fuel consumption can be prevented from deteriorating, and excess lubricating oil can be reliably scraped off by the piston ring. It is possible to prevent the amount of the lubricating oil flowing into 41 from being excessive, and to prevent the lubricating oil from being wasted.

  Further, according to the variable compression ratio internal combustion engine 10 according to the first embodiment, the cylinder in which the block side bearing forming portion 52 extends is located at the position in the vertical direction of the end of the bore wall surface on the crankcase 30 side (bottom wall bottom end). The position of the outer wall surface 20c of the block 20 is the same as the position in the vertical direction of the end on the crankcase 30 side (lower end of the outer wall surface of the block). Therefore, when the pressing force F3 is extremely large, even if the bore wall surface side portion of the end (block lower end) of the cylinder block 20 on the crankcase 30 side is bent inward of the cylinder block 20, the bore The distance by which the lower end of the wall surface is moved inward of the cylinder block 20 can be made shorter than when the lower end of the bore wall surface is located closer to the crankcase 30 than the lower end of the outer wall surface of the block. As a result, the degree to which the bore wall surface is deformed by the pressing force F3 can be reduced.

<Modification of First Embodiment>
In the first embodiment, the stress reducing groove is formed at a position away from the cylinder liner 20d in the cylinder block 20, but may be formed adjacent to the cylinder liner 20d.

  In this case, for example, FIG. 9 is a cross-sectional view of the cylinder block 20 cut along a plane including the line 9-9 in FIGS. 8 and 8 which is a front view of the lower surface 20b of the cylinder block 20 and perpendicular to the cylinder arrangement direction. As shown in FIG. 4, the lower end portion of the wall surface forming the through hole of the cylinder block 20 has a bore center axis arrangement plane P1 from the bore center axis arrangement plane P1 including the bore center axis BC of all the cylinders to the same wall surface. A wide portion 61 is formed in which the distance L1 in the orthogonal direction is longer than the distance L2 at the upper end of the wall surface.

The wide portion 61 is formed from the bore center axis BC to the bore center axis arrangement plane when the cylinder block 20 is formed with the same through hole as the columnar through hole formed in the cylinder block 20 according to the first embodiment. The wall surface on which the through hole is formed is formed so as to form a cylindrical hole having a straight line BC1, BC1 as a central axis that is a predetermined distance in the direction orthogonal to P1 and parallel to the bore central axis BC. Therefore, it can be formed easily.
A stress reducing groove 24-1 is formed by the wide portion 61 and the outer wall surface of the cylinder liner 20d. That is, according to such a configuration, the stress reducing groove 24-1 can be easily formed.

  Further, the stress reducing groove may be provided so as to surround the cylinder liner 20d. In this case, for example, as shown in FIG. 10 which is a front view of the lower surface 20b of the cylinder block 20, the lower end portion of the wall surface forming the through hole of the cylinder block 20 has a diameter larger than the diameter of the upper end portion of the wall surface. The large-diameter portion 62 having the structure is configured.

The large-diameter portion 62 is coaxial with the bore center axis BC in a state where the cylinder block 20 has the same through-hole as the cylindrical through-hole formed in the cylinder block 20 according to the first embodiment, and It can be easily formed by scraping the wall surface forming the through hole so as to form a cylindrical hole having a diameter larger than the diameter of the through hole.
The large diameter portion 62 and the outer wall surface of the cylinder liner 20d form a stress reducing groove 24-2. That is, according to such a configuration, the stress reducing groove 24-2 can be easily formed.

  In addition, the stress reducing groove in the first embodiment and its modification may be filled with an elastic body such as rubber.

Second Embodiment
Next, a variable compression ratio internal combustion engine according to a second embodiment of the present invention will be described. The variable compression ratio internal combustion engine according to the second embodiment is different from the variable compression ratio internal combustion engine 10 according to the first embodiment only in that a reinforcing member is provided as a stress reduction means instead of the stress reduction groove portion 24. . Hereinafter, this difference will be mainly described.

  The cylinder block 20 of the variable compression ratio internal combustion engine 10 includes the 12-12 line in FIGS. 11 and 11 which is a front view of the lower surface 20b of the cylinder block 20, and the cylinder block 20 on a plane orthogonal to the cylinder arrangement direction. As shown in FIG. 12, which is a cut sectional view, the lower end of the wall surface that forms each of the plurality of through holes formed in the cylinder block 20 has a large diameter that is larger than the diameter of the upper end portion of the wall surface. A diameter portion 63 is provided.

  The length of the large-diameter portion 63 in the vertical direction (bore central axis direction) is approximately 1/3 of the length of the block-side bearing forming portion 52 in the vertical direction. The length of the large-diameter portion 63 in the vertical direction is from about ¼ of the vertical length of the block-side bearing forming portion 52 to the total length of the block-side bearing forming portion 52 in the vertical direction. Or may be longer than the entire length.

  A reinforcing member 64 having the same shape as this space is press-fitted into a space formed by the large-diameter portion 63 and the outer wall surface of the cylinder liner 20d. That is, the reinforcing member 64 passes through the position between the block-side bearing forming portion 52 and the cylinder liner 20d on the pressing straight line, and surrounds the cylinder liner 20d around the bore center axis BC. The cylinder block 20 is provided. In addition, the reinforcing member 64 is made of a material (in this example, steel and cast iron) having a rigidity higher than that of a part of the cylinder block 20 excluding the cylinder liner 20d (in this example, a part made of aluminum). Etc.).

  According to the variable compression ratio internal combustion engine 10 according to the second embodiment configured as described above, when the block-side bearing forming portion 52 presses the outer wall surface 20c of the cylinder block 20 as described above, A stress having the same magnitude as the outer wall surface stress is generated at a portion (outer wall surface side portion) closer to the outer wall surface 20c than the reinforcing member 64. At this time, since the rigidity of the reinforcing member 64 is higher than the rigidity of the cylinder block 20, the rigidity of the reinforcing member 64 causes a portion closer to the bore wall surface than the reinforcing member 64 (bore wall surface side portion, that is, the cylinder liner 20d). The transmitted stress is smaller than the external wall stress. As a result, the bore wall stress is reduced as compared with the case where the reinforcing member 64 is not provided. As a result, the degree of deformation of the bore wall surface due to the bore wall stress can be reduced.

  In addition, the said 2nd Embodiment may be further equipped with the groove part 24 for stress reduction with which 1st Embodiment mentioned above is equipped.

<Third Embodiment>
Next, a variable compression ratio internal combustion engine according to a third embodiment of the present invention will be described. The variable compression ratio internal combustion engine according to the third embodiment is related to the first embodiment only in that the stress reducing groove 24 is not formed and the cylinder block has a thick part and a thin part. This is different from the variable compression ratio internal combustion engine 10. Hereinafter, this difference will be mainly described.

  The outer wall surface 20c of the cylinder block 20 of the variable compression ratio internal combustion engine 10 includes a line 14-14 in FIGS. 13 and 13 which is a front view of the lower surface 20b of the cylinder block 20, and is a plane orthogonal to the cylinder arrangement direction. As shown in FIG. 14, which is a sectional view of the cylinder block 20, a plurality of convex portions 65 corresponding to the cylinder bores 21 are formed.

  The top surface of each convex portion 65 is a plane parallel to a portion of the outer wall surface 20c where the convex portion 65 is not formed. Each convex portion 65 is a plane including the central axis BC of one cylinder bore 21 corresponding to each convex portion 65 and a part of the plane orthogonal to the cylinder arrangement direction intersects with the top surface of each convex portion 65. And it is located in the lower end part of the outer wall surface 20c. A block-side bearing forming portion 52 is fixed to the top surface of each convex portion 65.

  That is, each block-side bearing forming portion 52 extends outward from the outer wall surface 20c of the cylinder block 20 (the top surface of the convex portion 65), and one cylinder bore corresponding to each block-side bearing forming portion 52 is provided. 21 is arranged in a region including a part of the intersection line CL between the plane including the central axis BC and perpendicular to the cylinder arrangement direction and the outer wall surface 20c of the cylinder block 20.

  With such a configuration, as shown in FIG. 13, the cylinder block 20 is cut at a plane that is perpendicular to the cylinder arrangement direction and passes through a portion of the outer wall surface 20 c where the convex portion 65 is not formed. A distance D1 between the bore center axis arrangement plane P2 including the cylinder arrangement direction and the bore center axis direction in the cross section and the outer wall surface 20c of the cylinder block 20 is a plane orthogonal to the cylinder arrangement direction and out of the outer wall surface 20c. It is shorter than the distance D2 between the bore center axis arrangement plane P2 and the outer wall surface 20c of the cylinder block 20 in a cross section obtained by cutting the cylinder block 20 along a plane passing through the portion where the convex portion 65 is formed.

  Furthermore, as shown in FIG. 14, the bore center in a cross section obtained by cutting the cylinder block 20 along a plane that is orthogonal to the cylinder arrangement direction and that passes through a portion of the outer wall surface 20c where the convex portion 65 is formed. A distance D1 between the shaft arrangement plane P2 and a portion of the outer wall surface 20c of the cylinder block 20 where the convex portion 65 is not formed is the bore center axis arrangement plane P2 and the outer wall surface 20c of the cylinder block 20 in the same cross section. It is shorter than the distance D2 between the part in which the convex part 65 is formed.

  That is, according to the above configuration, the cylinder block 20 has a distance between the bore central axis arrangement plane P2 and the outer wall surface 20c of the cylinder block 20 in a cross section obtained by cutting the cylinder block 20 along a plane orthogonal to the cylinder arrangement direction. The bore center axis arrangement plane P2 and the block side bearing forming portion 52 are extended in a cross section obtained by cutting the cylinder block 20 in a plane perpendicular to the cylinder arrangement direction and passing through the block side bearing forming portion 52. A portion that is shorter than the distance D2 between the outer wall surface 20c (that is, the top surface of the convex portion 65) is included.

  According to the variable compression ratio internal combustion engine 10 according to the third embodiment configured as described above, the cylinder block 20 has higher rigidity than the other positions at the position where the block-side bearing forming portion 52 extends. It has become. Therefore, the cylinder block 20 is not easily deformed even when the pressing force F3 is applied. That is, it is possible to reduce the degree of deformation of the bore wall surface by the pressing force F3 while suppressing an increase in the weight of the cylinder block 20.

  In addition, this invention is not limited to said each embodiment, A various modification can be employ | adopted within the scope of the present invention. For example, the block side bearing forming portion 52 may be formed integrally with the cylinder block 20. Moreover, the block side bearing formation part 52 may be arrange | positioned above the edge (lower end) by the side of the crankcase 30 of the outer wall surface 20c.

1 is a schematic perspective view of a variable compression ratio internal combustion engine according to a first embodiment of the present invention. It is a perspective view from the upper part of the cylinder block shown in FIG. FIG. 2 is a perspective view from below of the cylinder block shown in FIG. 1. FIG. 4 is a cross-sectional view of the variable compression ratio internal combustion engine cut along a plane along line 4-4 in FIG. 1. FIG. 5 is a cross-sectional view of the variable compression ratio internal combustion engine cut along a plane along line 5-5 in FIG. 1. It is the figure which showed typically the change of the compression ratio by driving the variable compression ratio mechanism shown in FIG. It is the figure which showed typically the deformation | transformation of the cylinder block by the force applied to a cylinder block when combustion generate | occur | produces in the combustion chamber shown in FIG. It is the schematic which looked at the cylinder block of the variable compression ratio internal combustion engine which concerns on the modification of 1st Embodiment of this invention from the downward direction. It is sectional drawing which cut | disconnected the cylinder block in the plane along 9-9 line of FIG. It is the schematic which looked at the cylinder block of the variable compression ratio internal combustion engine which concerns on the modification of 1st Embodiment of this invention from the downward direction. It is the schematic which looked at the cylinder block of the variable compression ratio internal combustion engine which concerns on 2nd Embodiment of this invention from the downward direction. It is sectional drawing which cut | disconnected the cylinder block in the plane along the 12-12 line | wire of FIG. It is the schematic which looked at the cylinder block of the variable compression ratio internal combustion engine which concerns on 3rd Embodiment of this invention from the downward direction. It is sectional drawing which cut | disconnected the cylinder block in the plane along the 14-14 line | wire of FIG. It is a schematic perspective view of the conventional variable compression ratio internal combustion engine. FIG. 16 is a perspective view from above of the cylinder block shown in FIG. 15. FIG. 16 is a diagram schematically showing a change in compression ratio when the variable compression ratio mechanism shown in FIG. 15 is driven. It is the figure which showed typically the deformation | transformation of the cylinder block by the force applied to a cylinder block when combustion generate | occur | produces in the combustion chamber shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Variable compression ratio internal combustion engine, 20 ... Cylinder block, 20b ... Lower surface, 20c ... Outer wall surface, 20d ... Cylinder liner, 21 ... Cylinder bore, 22 ... Piston, 24 ... Stress reduction groove part, 30 ... Crankcase, 31 ... Crank Shaft, 40 ... cylinder head, 41 ... combustion chamber, 50 ... variable compression ratio mechanism, 51 ... case side bearing forming portion, 51c ... bearing hole, 52 ... block side bearing forming portion, 52a ... bearing hole, 53 ... shaft drive 53a ... eccentric shaft part, 53b ... fixed cam part, 53c ... movable cam part, 53d ... worm gear, 61 ... wide part, 62 ... large diameter part, 63 ... large diameter part, 64 ... reinforcing member, 65 ... convex part , BC: bore central axis, F3: pressing force, FC: central axis of fixed cam portion, MC: central axis of movable cam portion.

Claims (2)

A cylinder bore that is a cylindrical hole penetrating in a predetermined bore central axis direction is formed, and a cylinder block that houses a piston in the cylinder bore, and is fixed to the cylinder block so as to cover one of the opening portions of the cylinder bore. The cylinder head is disposed on the opposite side of the cylinder head with respect to the cylinder block, and is movable relative to the cylinder block in the bore central axis direction, and the crankshaft connected to the piston is rotatable. And a crankcase that is supported by a bore wall surface that forms the cylinder bore, a head lower surface that is a surface of the cylinder head on the cylinder block side, and a piston top surface that is a surface of the piston on the lower surface side of the head Equipped with a variable compression ratio mechanism that changes the volume of the combustion chamber formed A variable compression ratio internal combustion engine,
The variable compression ratio mechanism includes a block-side force receiving portion extending outward from an outer wall surface of the cylinder block, a block-side force receiving portion and the crankcase, and the block-side force receiving portion. A connecting portion for changing a distance in the bore central axis direction between the crankcase and the crankcase,
The cylinder block is a block in which a position of a lower end of the bore wall surface which is an end of the bore wall surface on the crankcase side is an end on the crankcase side of an outer wall surface of the cylinder block from which the block side force receiving portion extends. A variable compression ratio internal combustion engine configured to be the same position as a lower end of the outer wall surface or a position closer to the cylinder head than a position of the lower end of the outer wall surface of the block. A plurality of cylinder bores, which are cylindrical holes penetrating in a predetermined bore center axis direction, are formed in a straight line in a cylinder arrangement direction orthogonal to the bore center axis direction, and a piston is placed in each cylinder bore. A cylinder block to be accommodated, a cylinder head fixed to the cylinder block so as to cover one of the opening portions of the cylinder bore, and disposed opposite to the cylinder head with respect to the cylinder block and to the cylinder block A crankcase that is relatively movable in the bore central axis direction and rotatably supports a crankshaft connected to the piston, and a bore wall surface that forms the cylinder bore and the cylinder block side of the cylinder head The lower surface of the head and the surface of the piston on the lower surface side of the head A variable compression ratio internal combustion engine having a variable compression ratio mechanism for changing the volume of the combustion chamber formed by the that the piston top surface,
The variable compression ratio mechanism is configured to be external to the outer wall surface in a region including a part of the intersection line between a plane perpendicular to the cylinder arrangement direction and passing through the central axis of the cylinder bore and the outer wall surface of the cylinder block. The block side force receiving portion extending in the direction of the block, and the distance between the block side force receiving portion and the crankcase in the bore central axis direction between the block side force receiving portion and the crankcase. A connecting part to be changed,
The cylinder block is formed between a bore central axis arrangement plane including the cylinder arrangement direction and the bore central axis direction in a cross section obtained by cutting the cylinder block along a plane orthogonal to the cylinder arrangement direction, and an outer wall surface of the cylinder block. The bore center axis arrangement plane and the block side force receiving portion in a cross section obtained by cutting the cylinder block in a plane perpendicular to the cylinder arrangement direction and passing through the block side force receiving portion extend. A variable compression ratio internal combustion engine configured to include a portion that is shorter than a distance from the outer wall surface at a certain position.

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