Patent ID: 8079299

Claim:
An upper part of a composite piston, comprising: a piston crown, a ring wall that is formed onto the piston crown, in the direction facing away from the piston crown, on the radial outer surface of which wall a ring belt is disposed, an outer recess formed into the underside facing away from the piston crown, which recess is delimited radially on the outside by the ring wall, and radially on the inside by a ring rib formed onto the underside of the upper part, an inner contact surface formed by the underside of the ring rib ( 15 , 21 ) and oriented radially, and an outer contact surface ( 3 ) formed by the underside of the ring wall ( 25 ) and oriented radially, wherein the inner contact surface has a groove-shaped profile having an average roughness depth between R z 10 and R z 30 .