Prediction Technique for Vibration of Power-Plant with Elastic Crankshaft System

The dynamic behaviors of power-plant have much effect on interior noises and vibrations of passenger cars, especially, in the frequency range below 1000 Hz. So it is very important to estimate the vibrations of power-plant at the design stage. To predict the dynamic behaviors of power-plant including the rotating elastic crankshaft system, the time domain dynamic simulation methods have been applied, however such analyses require much time and resource of computer. In this report, the exciting forces to the cylinder block are derived in the frequency domain from both the dynamic stiffness of bearing oil films and the dynamic displacements of crankshaft journals, so that the computation time is reduced considerably. To estimate the displacements of the crankshaft journals, the vibrations of an engine crankshaft system including crank journal oil films under firing conditions are calculated using the dynamic stiffness matrix method in the frequency domain. The displacements derived in the crankshaft coordinate system are substituted into the engine block coordinate system to estimate the exciting forces to cylinder block. The dynamic stiffness of bearing oil films is calculated by applying the Sommerfeld numbers for each main bearing under operating conditions. The exciting forces in the frequency domain are calculated by applying both the displacements and the stiffness of bearing oil films. Finally, by applying those forces to the finite element model of the power-plant, the acceleration responses of power-plant vibrations are obtained.