Patent ID: 7066118

Claim:
A compression ratio changing device in an internal combustion engine, comprising: a piston inner element to a connecting rod through a piston pin, a piston outer element which is fitted over an outer periphery of said piston inner element for sliding movement only in an axial direction with respect to the piston inner element, with an outer end face of the piston outer element exposed to a combustion chamber, said piston outer element capable of being moved between a lower-compression ratio position (L) close to said piston inner element and a higher-compression ratio position (H) close to said combustion chamber, a bulking member interposed between said piston inner and outer elements and capable of being moved between a non-bulking position (A) where said bulking member permits the movement of said piston outer element to the lower-compression ratio position (L), and a bulking position (B) where said piston outer element retained in the higher-compression ratio position, and an actuator for operating said bulking member alternately in the non-bulking position (A) and the bulking position (B), wherein said bulking member and said actuator are constructed so that said piston outer element is permitted to be moved, during reciprocal movements of said piston inner and outer elements, between the lower-compression ratio position (L) and the higher-compression ratio position (H) by natural external forces applied to said piston inner and outer elements to move these elements axially away from and toward each other, and wherein said bulking member is interposed between said piston inner and outer elements so as to be capable of turning about axes of said piston inner and outer elements between the non-bulking position (A) and the bulking position (B), and a first cam and a second cam are formed into a convex shape on axially opposed surfaces of said bulking member and one of said piston inner and outer elements, and have flat top faces for abutting against each other, when said bulking member has reached the bulking position (B), and precipice faces extending downwards substantially vertically from circumferentially opposite side edges of said top faces to roots of the cams.