The adoption of the diesel engine EGR systems, and increased uses of alcohol in spark ignited engines require wear resistant and low maintenance valve trains.
Silicon nitride ceramic inserts were pressureless-sintered and successfully die-cast in rocker arms contacting the overhead cams in the valve trains. As fired, the insert sliding surface was fine and precise, eliminating any further processing. The comosite structure was machined with the sliding surface as a reference plane.
Beside inherent high wear resistance, these lighter inserts reduced inertial forces of the trains and the torque required to drive the cams. The hard, brittle ceramics and a softer, more elastic aluminum alloy made the structure more durable and reliable.
The process of development includes characterization, screening, manufacturing and quality control of the materials, and determination of wear resistance and reliability for this new structure.