Patent ID: 7219641

Claim:
A piston for internal combustion engines, comprising: a lower part that forms a skirt region, and an upper piston part that forms a piston head and a ring region; anti-fatigue bolts connecting said upper piston part with said lower piston part; compression sleeves enaged in bores of the lower piston part, each bolt contacting one end of one of said compression sleeves, wherein a contact surface of each compression sleeve contacts a contact surface of the lower piston part; wherein the contact surface of the lower piston part has a shape of spheroid having the general formula x 2 /a 2 +y 2 /a 2 +z 2 /c 2 =1, wherein x, y, and z define coordinate axes of the spheroid and a and c define a radius of the bore and of a semiaxis of the spheroid in a direction z, where a<c; wherein the coordinate axis z of the spheroid corresponds with longitudinal axii of the antifatigue bolt, a longitudinal axis of the bore and a longitudinal axis of the compression sleeve; and wherein the contact surface of the compression sleeve has the shape of a sphere having the general formula x 2 +y 2 +z 2 =r k 2 , whereby r k is a radius of the sphere and r k <a.