Development of Advanced Silicon Nitride Valves for Combustion Engines and Some Practical Experience on the Road

Abstract

ABSTRACTOne major goal of automotive engineers actually is to reduce fuel consumption and emissions of present internal combustion engines. First promissing results have been achieved by the substitution of conventional by silicon nitride valves. The weight reduction of about 60 % per valve is corresponding with lower inertia and spring forces, which lead to improved emissions, reduced fuel consumptions as well as high performances of the engines. Applying statistical methods, two advanced silicon nitride materials have been developed, concerning their application as “cool” inlet valves and “hot” exhaust valves, respectively. Using high quality powders and combined optimum processing parameters, 4-point-bending strength of more than 1200 MPa (room temperature) and 870 MPa (1000 °C), resp., have been realized. Weibull moduli of more than 30 have been reproduced. Grinding of valves produced from these materials has economically been demonstrated by drastically reducing the machining times. Some results of road tests as well as of simulated engine tests from cooperations with different automotive companies are presented in detail.