A study on the dynamic characteristics of the main bearing cap damper and crankshaft coupling system with experimental validation

The vibration caused by the main bearing load has always been difficult to control effectively, making it one of the main vibration sources of the diesel engine and even the entire ship. In this study a main bearing cap damper is designed based on the principle of an integrated squeeze film damper to attenuate the main bearing load before its transmission to the engine block. To verify the function of the main bearing cap damper, a coupled dynamic model of the dampers with the crankshaft system is developed to study the attenuation characteristics. Timoshenko beam elements are used to construct a multi-throw crankshaft model. The input forces boundary condition is determined using the piston-connecting rod mechanism. And the mixed lubrication boundary condition is determined based on the hydrodynamic lubrication and micro-asperity contact models. The simulation results show that the peak reductions of the main bearing loads in the time domain for each journal could exceed 38.5%. And the effective load attenuation in the frequency domain is across the entire frequency range up to 10 kHz, with an average attenuation of more than 5 dB. In addition, the simulation results are verified through a dynamic experiment on a motor-driven crankshaft system. The predicted main bearing load exhibited excellent consistency with the measured results. Moreover, the attenuation function of the damper is experimentally verified. The best attenuation effect is observed in Journal 4, with a maximum attenuation of 49.4% in the time domain and 20 dB in the frequency domain. These findings verify the effectiveness of the main bearing cap damper, this provides a new control method for the vibration and noise of marine diesel engines.