Effect of Inertia Variation Due to Reciprocating Parts and Connecting Rod on Coupled Free Vibration of Crankshaft

The inertia due to reciprocating parts and connecting rods, as felt by the crankshaft, varies with the crank angle. The effect of inertia variation on torsional free vibration of crankshafts has been studied extensively. In this paper, the effect on combined torsional and bending free vibrations is examined. Single-cylinder engine crankshaft geometry is considered for the study. The results indicate that the inertial coupling, introduced by the reciprocating parts and connecting rod, significantly influences the free vibration characteristics, particularly when the natural frequencies of the crankskahft are closely spaced. The results suggest that, under such conditions, modeling the crankshaft as a pure torsional system would involve considerable error.