Nissan utilizes ceramics in the turbine rotor of turbochargers to improve acceleration response by reducing the inertia weight of the turbine rotor.
Since ceramic material does not yield, a high degree of localized stress will cause it to fail. Therefore, in order to be able to apply this brittle material to a high-speed rotor under high-stress conditions, silicon nitride material has been improved, and a low-stress shape employing the three-dimensional finite element method developed. Furthermore, a new technique for bonding the ceramic rotor to a metal shaft is employed in order to reduce residual stress caused by the difference in thermal expansion coefficients between the ceramic and metal materials. Since the strength of ceramics varies widely, it was necessary to confirm the reliability of the ceramic rotor and evaluate its life of fatigue.
This paper, then, describes the design philosophy, bonding method, reliability and durability of the ceramic rotor.
A turbocharger with ceramic rotor was first introduced into the automotive market in the domestic model of Nissan's 200Z last October.