Advanced Automated Analysis Methodology for Predicting the Valve Durability

Recent advancements in IC engine and Hybrid vehicles emphasize the use of higher rated fuels with higher calorific values, leading to higher operating temperature and pressure values. This makes the design of valve train components a complex task. Typically, IC engine valves are subjected to varying stresses throughout an engine cycle. This can result in fatigue failure of valves in many applications where the supplier was deficient in advanced analysis methodologies. Considering this fact, a new technique for valve durability and life predictions has been developed using various approaches such as internal semi-empirical thermal boundary conditions calculation tool, Multibody Dynamics (MBD) and Finite Element Modelling (FEM). In this study, a bi-metallic (Stem - X45 CrSi 9 3 and Head - X50 CrMnNiNbN 21 9) exhaust valve operating under direct attack valvetrain of 1.2L inline 3-cylinder gasoline engine has been considered. Internal semi-empirical tool and literature work on gas flow has been used to predict the thermal boundary (gas side temperatures and HTCs at various locations) conditions. The predicted thermal BCs are then used to predict the temperature distribution and thermal stresses in the valve. An MBD model of the direct attack type valvetrain has been built using the Ricardo VALDYN software tool to predict the valve seating and peak lift deceleration loadings. A FEM approach has then been used to predict the stresses at various events such as 1. Firing 2. Seating and 3. Valve deceleration and the fatigue durability and life. To reduce the total iteration time and study various valve designs quickly, a script has been written which runs all the analyses sequentially and gives fatigue safety and life values at the end. The safety factor predicted in this study provides a good correlation with test data. The new design proposed after FEA calculations has an improved fatigue safety factor.