Abstract: An engine piston has a crown portion generated about a longitudinal piston axis and, extending axially form the crown, a pair of gudgeon pin bosses defining a pin axis and spaced apart at opposite sides of an orthogonal thrust axis. A circumferentially discontinuous skirt defines lateral thrust and non-thrust bearing regions, respectively, centered on the thrust axis, each joined by convexly bowed reinforcement ribs to the bosses. The bearing region on the non-thrust side of the piston is circumferentially shorter than thrust region, reducing piston mass to one side of the piston, and the reinforcement ribs are offset in pin axis direction where they intersect the bosses. Mass reducing recesses are formed in the underside of the crown between the unskirted periphery reinforcement ribs and bosses, the offset ribs permitting the recesses to extend further and to permit greater reduction in mass.

Abstract: An engine piston (10) has a crown portion (12) generated about a longitudinal piston axis (14) and, extending axially from the crown, a pair of gudgeon pin bosses (26, 28) defining a pin axis (30) and spaced apart at opposite sides of an orthogonal thrust axis (40). A circumferentially discontinuous skirt defines lateral thrust and non-thrust bearing regions (34, 36), respectively, centered on the thrust axis, each joined by convexly bowed reinforcement ribs (62, 64, 66, 68) to the bosses. The bearing region (36) on the nun-thrust side of the piston is circumferentially shorter than thrust region (34), reducing piston mass to one side of the piston, and the reinforcement ribs are offset in pin axis direction where thy intersect the bosses. Mass reducing recesses (106, 108) are formed in the underside of the crown between the unskirted periphery (37), reinforcement ribs and bosses, the offset ribs (66, 68) permitting the recesses to extend further as at (110) and permit greater reduction in mass.