Abstract: The bendingtorsional coupling dynamic model of the crankshaft system in combustion engine was presented by considering varied inertia， mass eccentricity and nonlinear friction damping force. Numerical integration methods were adopted to analyze the effects of the mass eccentricity and rotate speed on the dynamic performance， and the characteristics of amplitude frequency responses were obtained based on the harmonic balance method. It is shown that the harmonic balance method coincides well with the numerical method. The damping between the cylinder and piston can produce significant inhibition of system response amplitude. The motion stability can be effectively improved by reducing the eccentric of crankshaft system.

Key words: crankshaft system, varied inertia, bendingtorsional coupling, nonlinear vibration, harmonic balance method, amplitude frequency response