In recent years, compact direct injection diesel engines for passenger cars have been expected for global warming prevention. And the developments of these engines with high power and good efficiency have been increasing mainly in Europe and Japan. An engine piston is one of significant internal parts to improve engine performance and is required to have more improved properties, such as design flexibility of combustion chamber and durability for increasing heat and mechanical load, than current ones. The piston with selectively reinforced top ring groove can meet these requirements. But it needs large-sized manufacturing equipment for special casting process with high pressure such as squeeze casting, so it has disadvantages such as higher manufacturing cost and low flexibility of design. We developed reinforcements that are easy to infiltrate and have good wearing property as composites and low-pressure infiltration process " Air-assisted infiltration process " based on gravity die-casting. The developed techniques can provide the maximum features of selectively reinforced piston. In developed process, much lower pressure about 1 MPa for infiltration than in the squeeze casting is practicable. Diesel pistons made by developed techniques achieve superior mechanical and wearing property with reasonable costs. The developed pistons have been adopted for new compact direct injection diesel engines (RFDI-TD) of which mass production was started from April 1998.
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