Fully Coupled Rigid Internal Combustion Engine Dynamics and Vibration—Part I: Model Development

Abstract

Robust predictions of engine vibration are important for preliminary design of new engines and new vehicles, and in setting component tolerances. Vibration modeling of internal combustion engines is commonly based on a one-way-coupling assumption between the engine’s moving internal components and the vibrating engine block. This assumption causes Coriolis and gyroscopic interactions to be neglected, and leads to a vibration model that does not properly 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 dynamics for the pistons, connecting rods, crankshaft, flywheel, and engine block. Predictions from the new model are compared to those from an equivalent one-way-coupled model for poorly balanced (one-cylinder) and well-balanced (inline six-cylinder) engines. Predicted mount forces are dissimilar for the poorly balanced engine but are nearly the same for the well-balanced engine. In addition, the new model is found to properly conserve energy and account for gravitational forces.