US Patent 7243445 Ball and socket 3D cushioning system

The invention relates to a sliding element for a shoe sole. The sliding element includes an upper sliding surface and a lower sliding surface, wherein the lower sliding surface is arranged below the upper sliding surface so as to be slideable in at least two directions. The upper sliding surface can form a lower side of an upper heel cup and the lower sliding surface can form an upper side of a lower heel cup, wherein the upper heel cup and the lower heel cup have corresponding substantially spherical shapes. Complex multi-dimensional sliding and cushioning movements between the upper sliding surface and the lower sliding surface are made possible by the corresponding three-dimensional shapes of the two substantially spherical surfaces.