Study On Crankshaft-body Coupling Vibration For Multiple Cylinder Diesel

As the main power source at present,the diesel engines are widely used in the industries of engineering,energy and shipbuilding.With the development of manufacturing technology,the requirements of vibration and noise are stricter.As the core component of the diesel engine,the crankshaft is subjected to the cylinder pressure and inertial force of the crank-link mechanism,and the load of it will make the engine body vibrate.Therefore,the coupling effect between the crankshaft and engine body is very important to analyze the vibration and noise of diesel engine.In this paper,a finite element model of the multi-cylinder diesel engine is built according to the actual structure,which contains the cylinder,air cooler,air intake and exhaust system,oil pan and engine body.The modal analysis is carried out and analyzing the influence of the coupling effect between the crankshaft and engine body on the inherent frequency.Analyzing the difference of crank-link mechanism load under the rigid crankshaft and flexible crankshaft,the result shows that the crank-link mechanism produces additional unbalance force under the flexible crankshaft,which makes the crank-link mechanism load increase;According to the actual position of the load,loading them into the corresponding position of the FEM model and the transient dynamics analysis is carried out.Comparing the simulation results with the experimental data,it is found that the simulation results under the flexible crankshaft are closer to the experimental data.Then establishing the acoustic simulation model by the boundary element method,making the node displacement of the engine body to be the input source and obtaining the radiation noise at the location of 1 meter from the engine body.It is found that the radiation noise under the flexible crankshaft is closer to the experimental data;on this basis,making the crank-link mechanism load under the flexible crankshaft to be the input source and Comparing the vibration and radiation noise of the engine body model and the crankshaft-body model,it is found that the vibration and noise is lower under the crankshaft-body model.Based on the above results of the vibration and noise,the crank-link mechanism load is divided to the cylinder pressure and the inertial force of the crank-link mechanism,then calculating the vibration contribution of every excitation loading on the crankshaft-body model,the result shows that the cylinder pressure is the main factor on the vibration;In order to analyze the influence of the crankshaft balance on the vibration and noise,the simulation of vibration and noise under 3 different firing orders is carried out.The result shows that there is great influence of the crankshaft balance on the vibration and noise,but not the whole diesel engine.Therefore,the study will provide important theoretical support for the vibration damping and noise reduction of the multi-cylinder diesel engine.