Identification of Torsional Damping Coefficients for Internal Combustion Engine Crankshafts

In order to solve the difficulty of selecting the damping coefficients in torsional vibration theoretical analysis of internal combustion engine (ICE) crankshafts, an identification method of torsional damping coefficients of main crankshafts components was proposed based on the modal damping ratio of crankshafts angular vibration. In this method, the multi-mass system of crankshafts was simplified to an equivalent torsion pendulum system, and the relationship between the modal damping ratio of crankshafts angular vibration and the torsional damping coefficient of each crankshaft component was derived by vibratory energy theory. Thus, if the damping ratio of crankshafts angular vibration is given, the main torsional damping coefficients of crankshafts could be identified by analyzing the damping property of crankshafts torsional vibration and selecting a proper mode of angular vibration. As a case study, the damping coefficients of a 4-and a 6-cylinder diesel engine were identified by simulation and experiment. The results show that the identified torsional damping coefficients of the main crankshafts components obtained by simulation have a maximum error of 4.89%compared to the experimental one. This demonstrates the validity of the proposed identification method.