Patent ID: 6546900
Filing Date: 2003-04-15
Classification: F02B

Abstract:
A variable compression ratio mechanism for a reciprocating internal combustion engine, comprising:a connecting rod connecting a crank on a crankshaft with a piston, the connecting rod being split into an upper connecting rod portion oscillatingly linked to the piston through a piston pin and a lower connecting rod portion rotatably linked to a crankpin of the crankshaft; the upper and lower connecting rod portions being oscillatingly linked to each other through a first connecting pin; a rockable arm oscillatingly linked at one end to the lower connecting rod portion through a second connecting pin; a control mechanism shifting a center of oscillating motion of the rockable arm to vary a compression ratio of the engine; the rockable arm being oscillatingly linked at its other end via the control mechanism to a cylinder block; a piston stroke of the piston being set to be greater than two times a crank radius of the crank on the crankshaft, irrespective of whether the compression ratio is varied by the control mechanism; and a linkage having at least the upper and lower connecting rod portions, the first and second connecting pins and the rockable arm being dimensioned and laid out, so that a crankpin load acting on the crankpin is less than a crankpin load produced by a linkage that has the crankpin located on a perpendicular line at substantially a midpoint of a line segment between and including a center of the first connecting pin and a center of the second connecting pin, wherein assuming that a directed line perpendicular to both a direction of the piston stroke and an axis of rotation of the crankshaft is taken as an x-axis, a directed line parallel to the direction of the piston stroke is taken as a y-axis, a distance from the center of the first connecting pin to a plane including the axis of rotation of the crankshaft and extending in a direction of the y-axis is denoted by D1, and a distance from a center of the crankpin to the plane including the axis of rotation of the crankshaft and extending in the direction of the y-axis is denoted by D2, at top dead center of the piston an inclination angle of a link containing a line segment between and including the center of the crankpin and the center of the second connecting pin with respect to a direction of the x-axis is denoted by &agr;1, and at bottom dead center of the piston the inclination angle of the link containing the line segment between and including the center of the crankpin and the center of the second connecting pin with respect to the direction of the x-axis is denoted by &agr;2, the distance D1 is set to be greater than or equal to the distance D2 during the piston stroke from the top dead center to the bottom dead center and additionally the inclination angle &agr;1 is set to be less than or equal to the inclination angle &agr;2, irrespective of whether the compression ratio is varied by the control mechanism.