Patent ID: 7377238

Claim:
A variable compression ratio device of an internal combustion engine, comprising: a piston including a piston inner part connected to a connecting rod via a piston pin, and a piston outer part which is fitted on an outer periphery of the piston inner part so as to be only slidable in an axial direction and which is movable between a low compression ratio position L near the piston inner part and a high compression ratio position H near a combustion chamber, with an outer end surface of the piston outer part facing the combustion chamber; a cam mechanism provided between the piston inner part and the piston outer part, and alternately moving the piston outer part to the low compression ratio position L and the high compression ratio position H; and an actuator provided at the piston inner part for operating the cam mechanism; the cam mechanism including a lift member supported by the piston inner part and moved by the actuator alternately to a lift release position A and a lift position B, a plurality of first cam top portions projectingly provided integrally on a top surface of the lift member and a plurality of second cam top portions projectingly provided on an undersurface of a head part of the piston outer part; in the lift release position A of the lift member, the first cam top portions and the second cam top portions are meshed with each other to move the piston outer part to the low compression ratio position, and in the lift position B of the lift member, the first cam top portions and the second cam top portions cause their top surfaces to abut on each other to move the piston outer part to the high compression ratio position H; wherein a skirt part is slidably guided by an inner peripheral surface of a cylinder bore of an engine B and is integrally formed at the piston inner part, and a peripheral wall of the piston outer part, to which piston rings are fitted, is terminated directly above the skirt part, wherein the piston outer part is engaged with the piston pin such that the piston outer part is slidable relative to the piston inner part alone an axis of the piston, while rotation of the piston outer part relative to the piston inner part around the axis of the piston is inhibited.