Method of making an engine block using coated cylinder bore liners
Reference Number: N 01-02
Inventors: Rao, V. Durga Nageswar; Rose, Robert Alan; Yeager, David Alan; Kabat, Daniel Michael
It is an object of this invention to provide a method of making engine blocks with coated cylinder bore liners that: (a) eliminates many preparatory steps of prior methods; (b) imparts greater concentricity of the coating thereby reducing machining of the final coating surface; and (c) uses more economical coating materials to promote superior anti-friction characteristics.
In particular, the method comprises essentially: (a) casting a metallic engine block having one or more cylinder bores; (b) fabricating a thin walled liner for each bore, the liner being constituted of extruded metallic tubing, preferably of the same material as that of the block, having a cleansed inner surface, a wall thickness controlled to within .+-.10 microns, the outer diameter of the liner being slightly greater (35.+-.5 microns) than the internal diameter of the cylinder bores of the block that is to receive the liners; (c) relatively rotating the liner with respect to one or more nozzles for applying a plurality of materials to the internal surface of the liner, the materials comprising first a metal texturing fluid that is applied at high pressures to expose fresh metal of the surface, secondly a bond coating material that is thermally sprayed to form a metallurgical bond with the liner internal surface, and a top coat of anti-friction material that is adheringly plasma sprayed to the bond coating; (d) honing the coated internal surface to remove up to 150 microns of top coating, leaving a finish surface that is concentric to the tube axis within .+-.15 microns; and (e) interference fitting the coated liner to the cylinder bore by freezing the liner while maintaining the block at or above ambient temperature to permit implanting of the liner. By modifying the composition of the top coating, the bond coating may be eliminated and still achieve adequate bond strength.
In another aspect the invention is an aluminum engine block, comprising: (a) a cast aluminum alloy body having one or more precision formed cylinder bores; (b) an extruded aluminum liner fitting in the bore with an interference fit, the liner having an inner surface coated with a coating system prior to implantation; and (c) the coating system comprises a top coat of plasma sprayed iron based particles which, by themselves or by the presence of additional particles, provide solid lubrication properties.