Patent ID: 7127981

Claim:
A coupling structure for coupling a piston and a connecting rod, comprising: a protrusion formed on a rear surface of a crown of the piston and having a downwardly opening concavity and a semi-spherical concavity formed in a bottom of the downwardly opening concavity, said downwardly opening concavity having a cylindrical inner surface extending from the bottom to an open end of the downwardly opening concavity in concentric relation to the semi-spherical concavity, and a threaded portion formed on the cylindrical inner surface and having a female thread extending from the open end toward the bottom of the downwardly opening concavity; a substantially spherical small end formed at one end of the connecting rod; a holder having a spherical inner surface and holding the substantially spherical small end of the connecting rod slidably in a substantially spherical space defined by its inner surface and the semi-spherical concavity of the protrusion; and a fixing ring having a cylindrical outer surface including a threaded portion formed thereon and having a male thread engaging with the threaded portion of the protrusion for securing the holder to the protrusion of the piston, wherein first and second clearances are formed respectively between the cylindrical inner surface of the protrusion and an adjacent first outer surface of the holder and between an inner surface of the fixing ring and an adjacent second outer surface of the holder so that the holder is in abutment with the bottom of the downwardly opening concavity.