Fully coupled rigid internal combustion engine dynamics and vibration - Part I: Model development

Robust predictions of engine vibration are important for preliminary design of new engines and new vehicles, and in setting component tolerances, vibr ation modeling of internal combustion engines is commonly based on a one-wa y-coupling assumption between the engine's moving internal components and t he vibrating engine block. This assumption causes Coriolis and gyroscopic i nteractions to be neglected, and leads to a vibration model that does not p roperly conserve energy. This paper presents a new seven-degree-of-freedom model for low frequency engine vibrations that does not utilize the one-way -coupling assumption. The model is based on fully coupled rigid-body dynami cs for the pistons, connecting rods, crankshaft, flywheel, and engine block . Predictions from the new model are compared to those from nit equivalent one-way-coupled model for poorly balanced (one-cylinder) and well-balanced (inline sir-cylinder) engines. Predicted mount forces are dissimilar for th e poorly balanced engine bur are nearly the same for the well-balanced engi ne. In addition, the new model is found to properly conserve energy and acc ount for gravitational forces.