US Patent 7730828 Rotor recess with scupper slots and free casting

A piston for an internal combustion engine includes a piston head provided with an annular field, and a piston shaft arranged beneath the annular field. The piston shaft has shaft surfaces and a recess surface which is arranged around a bolt borehole and set back in relation to an outer diameter of the piston. At least one cavity is provided in the region of the lowest annular groove for oil flow in the direction of the recess surface during the movement of the piston and the at least one cavity is arranged outside an especially stressed region above the bolt borehole.