Piston Assembly Including A Polymer Coating With Hard Particles Applied to Sliding Surfaces

A piston assembly, comprising:

• a piston body formed of a metal material and including a plurality of first cross bores each presenting a piston sliding surface;
• said piston body including an upper crown portion and a pin boss formation depending from and integral with said upper crown portion;
• said pin boss formation including one of said first cross bores;
• said piston body including a skirt extending longitudinally from said upper crown portion;
• said skirt including a pair of said first cross bores each presenting said piston sliding surface and axially aligned with said first cross bore of said pin boss formation;
• said first cross bore of said pin boss formation being disposed between said pair of first cross bores of said skirt;
• a connecting rod including a shaft having a small end formed with a second cross bore for aligning with the first cross bores of the piston body;
• said second cross bore presenting a rod sliding surface;
• a wrist pin extending through said first cross bores and said second cross bore to join said skirt to said upper crown portion and said piston body to said connecting rod;
• said wrist pin including a pin sliding surface facing toward said rod sliding surface;
• a coating disposed on at least one of said sliding surfaces;
• said coating including a polymer matrix with hard particles disposed throughout said polymer matrix;
• said coating including said polymer matrix in an amount of at least 40.0 vol. %, based on the total volume of said coating;
• said polymer matrix having a melting point of at least 210° C.;
• said polymer matrix including at least one of polyarylate, polyetheretherketone (PEEK), polyethersulfone (PES), polyamide imide (PAI), polyimide (PI), expoxy resin, polybenzimidazole (PBI), and silicone resin;
• said coating including said hard particles in an amount of 0.1 to 20.0 vol. %, based on the total volume of said coating;
• said hard particles having a hardness of at least 600 HV/0.5 at a temperature of 25° C. and a D50 particle size by volume not greater than 10.0 microns;
• said hard particles including at least one of a metal nitride, metal carbide, metal oxide, metal silicide, metal boride, metal phosphide, intermetallic compound, metal oxynitrides, metal carbonitride, metal oxycarbide, and a metal powder of Ag, Pb, Au, SnBi and/or Cu;
• said coating including at least one solid lubricant in an amount of 5.0 to 40.0 vol. %, based on the total volume of the coating;
• said solid lubricant including at least one of a metal sulfide, hexagonal boron nitride (h-BN), PTFE;
• and
• said coating having a thickness of 4 to 20 microns.