Abstract: A piston 2 for an internal combustion engine includes side wall portions 12 connecting skirt portions 10 to pin boss portions 6 so as to support the skirt portions 10 in a direction perpendicular to an axis 8 of the pin boss portions. The skirt supporting stiffness of each side wall portion 12 is gradually changed in an axial direction of the piston 2 so as to have a maximum stiffness at a lower end portion of the side wall portions b 12 and to decrease in the direction upwardly away from the lower end portion of the side wall portion 12. Due to this structure, the skirt portion 10 is unlikely to be deformed at its lower end portion so that a clearance between the skirt portion 10 and a cylinder bore surface 20 is maintained small. Further, the skirt portion 10 has a soft structure at the shoulder of the skirt portion 10 so that a shock at the shoulder will be decreased to prevent breakage of an oil membrane from happening at the upper portion of the skirt portion 10.

Abstract: A piston for an internal combustion engine including a crown, a skirt and bosses. The skirt has a circumferentially extending faucet rib in a lower portion of the skirt and reinforcing ribs which extend in a thrust and thrust-opposing direction of the piston from the bosses straight to the faucet rib. Reinforcing ribs increase the rigidity of piston in the thrust and thrust-opposing direction and suppress parmanent deformation of the skirt in the thrust and thrust-opposing direction, resulting in decreasing slapping sounds in a piston and cylinder structure without sticking of a piston with a cylinder bore.

Abstract: An internal combustion engine includes a cylinder block, a piston and a piston ring. The cylinder block includes at least one cylinder bore which includes a cylinder bore surface. The piston is located within the cylinder bore of the cylinder block so as to be displaceable upwardly and downwardly in the longitudinal direction of the cylinder bore. The piston includes at least one annular groove which has at least one inclined surface such that a bottom of the annular groove is located lower than an outer edge of the annular groove. The piston ring includes an outer peripheral portion and an inner peripheral portion. The inner peripheral portion of the piston ring is located within the annular groove of the piston for sliding engagement with the inclined surface of the annular groove of the piston.

Abstract: An exhaust gas recirculating type diesel engine wherein part of the exhaust gas is recirculated from its exhaust system to its intake system. An annular groove is formed on the circumferential surface of the piston, and a ring for preventing small particles generated within the combustion chamber from being transferred is engaged within the annular groove.