Internal combustion engine piston

Claim 1

A piston for an internal combustion engine, comprising: a circular steel upper head element having an upper surface defining the entire piston face and a lower surface which are axially spaced to form a first thickness; a circular light alloy lower skirt element having a radially outer surface, an upper surface covered by said lower surface of said upper element, said lower element including at least one first circumferential groove on the peripheral surface thereof; means for securing said upper and lower elements to one another; an annular U-shaped cavity defined in said upper surface of said lower element adjacent said peripheral surface, said cavity extending axially at least to a position closely adjacent said at least one first circumferential groove; an annular U-shaped second groove defined in said lower surface of said upper element and facing said cavity to form a dead space, said second groove extending axially towards said upper surface of said upper element by a distance sufficient that the upper extremity of said second groove is separated from said upper surface of said upper element by less than said first thickness, wherein only said lower element includes at least one of said first grooves and wherein said upper and lower elements are centered only by contacting circumferential surfaces adjacent the peripheries of said upper and lower elements, said contacting circumferential surfaces acting to seal said dead space, further including: at least one boss extending from said lower surface of said upper element in an area radially inward from said second groove; at least one second cavity on said upper surface of said lower element, each said second cavity corresponding to one said at least one boss; radially extending contact surfaces between said upper and lower elements, said radially extending contact surfaces consisting only of said at least one boss and corresponding cavity; and a threaded hole in said upper element at each said at least one boss, wherein said means for securing is engaged between at least one said second cavity and threaded hole.