Identification of Torsional Vibration Modal Parameters: Application on a Ferrari Engine Crankshaft

Comfort plays a very important role in the development of cars. The pistons firing order of an internal combustion engine, by nature, do not generate a constant torque on the crankshaft. At specific crankshaft speed, where the engine’s excitation frequency and the driven-system’s natural frequency coincide, torsional vibrations can excite crankshaft resonances and other dynamic phenomena within the engine or further down the driveline, potentially leading to fatigue failure of the crankshaft, or to important NVH problems. In order to achieve very high standards, the behavior of the driveline system needs to be investigated. For this reason a technique named Torsional-Order Based Modal Analysis (T-OBMA) has been developed in order to identify the torsional resonance frequencies and their related damping ratios of driveline systems during operating conditions. The technique is based on the rotational speed measurements acquired in two or more points along the driveline. The modal parameters are identified from torsional orders measured during an engine speed runup. The technique has been validated in a simulation and in an industrial test environment identifying crankshaft modal parameters on a Ferrari engine.