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In most high-speed engines, the crankshaft systems can become one of the most dangerous excitation sources. Since the crankshaft has significant kinetic and elastic (potential) energy, and is subjected directly to the impulsive excitation forces, significant engine structure noise and vibrations can often be caused. However, all excitation forces would be transmitted from the rotating crankshaft system to the engine structure only through the crankshaft main bearings. To investigate the excitation interaction between the crankshaft system and the engine structure, and the correlation between the crankshaft vibrations and the engine structure noise and vibrations, three phenomena were measured: (1) the crankshaft three-dimensional vibration behavior, (2) the vibration behavior of each crank journal main bearing, and (3) the engine structure noise at 1 m from the engine side.

The coupling behavior of the torsional, bending, and longitudinal vibrations in the crankshaft is described. The incidental excitation forces under crankshaft torsional vibration due to reciprocating and rotating masses are derived theoretically. Experiments on the coupling behavior of the crankshaft vibrations and the excitation behavior in the engine structure were performed in a four-cylinder automotive engine; their results are discussed.