Experimental and Numerical Modal Analysis of 6 Cylinders Diesel Crankshaft 2011-36-0358

The crankshaft dynamic behavior of internal combustion engines are deeply influenced by its geometry and modal parameters. The modal density of a 6 cylinder crankshaft is high and, therefore, it is necessary the evaluation of its several modal parameters during the crankshaft development. This paper presents the calculation of modal parameters such as: natural frequencies, modal shapes and damping factors; of a 6 cylinder in line crankshaft from a Diesel engine. Two approaches are conducted, firstly, a numeric calculation based on finite element method to collect the free body shape modes and its natural frequencies, respectively. Successively, an experiment is realized by the use of an electro-dynamic shaker to excite the structure, and accelerometers to measure the acceleration in 21 interest points of crankshaft geometry. The 3 directions FRFs are presented for each point, and also, the estimation of modal parameters obtained by tools like CMIF, Stabilization Diagram and Polymax. Gathering the results, it is possible to correlate experimental and numerical shape modes and natural frequencies, and at last, the estimated damping factors are used to construct the Rayleigh curve, used in dynamic analyses.