Numerical vibration study of a complex kinematics high efficiency engine

This paper discusses the prediction method of vibration of an innovative engine architecture with variable compression ratio and extended expansion. In the framework of a global optimization of the multi-cylinders architecture, this study allows to choose the best configuration regarding number of cylinders, firing order and ignition timing while minimizing number of balancing shaft. This last point is essential in order to have the best global engine efficiency. Several calculation models are used to find the best engine configuration. First of all, a rigid body dynamics simulation is used to reproduce complex kinematic of the engine and compute free forces and free moments applied to the engine block. Solutions are assessed in a calculation model which compute the displacement of the engine on its mountings while taking into account the assembly constraint of the engine into the vehicle. A FFT post processing of these displacements are compared to the order 2 displacement of a conventional reference engine. It allows to identify the main vibration harmonics to balance for each configuration. Finally, this study allows to find the optimum solution which requires the lowest number of balancer shafts to achieve a similar displacement as the reference engine.