Using Modal Analysis of Supported Crankshafts to Assess their Dynamic Characteristics in the Early Phase of Engine Development

The main purpose of the paper is to show the possibility of assessing the dynamic properties of crankshaft in the early design phase of engine development, without performing dynamic forced response simulation. This is achieved by carrying out modal analysis of crankshaft under existing boundary conditions, namely by taking the radial stiffness in main bearings and the masses of moving conrods and pistons into account. The spectra of eigenfrequencies and corresponding mode shapes as a result of such supported modal analysis are compared to those of free modal analysis, emphasizing the influence of the boundary conditions. To easily identify the modes and to compare them with each other, kinetic energy-based method is used, alongside visualization and animation of mode shapes. The examples of crankshafts considered in the paper are taken from model catalog of virtual engines of six different sizes and configurations, being compared to that of in-line 4-cylinder engine as the reference case. All types of modal analysis are performed on structured FE models of crankshafts using software tool AVL EXCITE™ Shaft Modeler.