US Patent 7954421 Lightweight piston

A piston has a piston head that is provided with a field of rings and a piston shaft which is disposed thereupon. The piston shaft is equipped with supporting shaft wall sections and rear connecting walls which interconnect the shaft wall sections, have an arched shape, and are fitted with a bolt bore. An undercut free space is provided below the annular field in the area of the bolt bore in the region of the piston head. An arched zone is disposed in the interior of the piston at the transition from the bolt bore in the direction of the shaft wall session.