Patent ID: 7721688

Claim:
A variable compression ratio internal combustion engine comprising: a cylinder block having a cylindrical cylinder bore that extends through the cylinder block in a predetermined bore center axis direction, and that houses a piston; a cylinder head fixed to the cylinder block so as to cover one of opening portions of the cylinder bore; a crankcase that is disposed at a side of the cylinder block opposite from the cylinder head, and that is movable relative to the cylinder block in the center axis direction of the cylinder bore, and that rotatably supports a crankshaft that is linked to the piston; and a variable compression ratio mechanism that changes a capacity of a combustion chamber defined by a bore wall surface that defines the cylinder bore, a head lower surface that is a cylinder block-side surface of the cylinder head, and a piston top surface that is a head lower surface-side surface of the piston, the variable compression ratio mechanism including a block-side force-receiving portion extending outward from an outer wall surface of the cylinder block, a first penetration hole disposed in a region on an upper wall surface of the crankcase that intersects with a plane that contains the bore center axis, the block-side force-receiving portion being moveable within the penetration hole in a vertical direction, and a linkage portion that changes a distance between the block-side force-receiving portion and the crankcase in the bore center axis direction while contacting each of the block-side force-receiving portion and the crankcase, wherein the cylinder block has a deformation-suppressing structure that restrains a deformation of the wall surface of the cylinder bore caused by a bore wall surface stress that occurs in the bore wall surface at a position of intersection between the bore wall surface and a pressing straight line that passes through a predetermined pressing position and that is a straight line parallel to a predetermined pressing direction as the block-side force-receiving portion receives by the linkage portion a force in a direction from the cylinder block toward the crankcase so that the block-side force-receiving portion presses the outer wall surface at the pressing position in the pressing direction, and wherein the variable compression ratio mechanism of the variable compression ratio internal combustion engine includes a second penetration hole located in an upper portion of the wall of the crankcase as a hole of an eccentric shaft of the crankcase, and the block-side force-receiving portion is rotatably driven in the hole of an eccentric shaft.