Crankshaft System Analysis Based On The Finite Element And Multi-body Dynamics

As one of the most important parts of the internal combustion engine, crankshaft plays an irreplaceable role in the work of the internal combustion engine. Meanwhile, crankshaft has a complex structure, bears large and alternating forces and is prone to stress concentration, leading to the occurrence of complex deformation and severe vibration. So strength and vibration analysis of the crankshaft has become a key issue in the development of the internal combustion engine. In this paper, using the finite element and multi-body dynamics method combined to analyze the crankshaft system of a 12-cylinder V-type medium speed diesel engine.Firstly, establishing the relevant models as required. Using Hypermesh software to mesh hexahedral grids, and subdivide meshes of the transition fillets between Journals and crank arms. After that, building a complete multi-body dynamics shafting model in AVL EXCITE software according to the working principle of this engine and the connection relationship between various parts.Secondly, conducting multi-body dynamics analysis. Getting force conditions of each main journal through the analysis of main journal forces, gaining large axial center deviations of each main journal and their corresponding angular coordinates through orbit analysis, and obtaining the unevenness of the rotor speed fluctuation, which turns out to meet the design requirements.Thirdly, carrying out crankshaft torsional vibration calculation and analysis. Writing a MATLAB program based on the Holtz method and using it to calculate the natural frequencies and mode shapes of free vibration. Employing the multi-body dynamics model to analyze forced torsional vibration, getting torsion angle displacements and harmonic amplitudes of the crankshaft free end under various conditions. By comparison, it turns out that 1 order amplitude under the rated conditions is the biggest and its single-stage peak-to-peak value is 0.244° CA, meeting the engineering requirements.Lastly, calculating the crankshaft fatigue strength and taking effective measures to optimize it. Through stress recovery, finding out that the maximum stress point is located at the fillet between the sixth rod journal and the end of the crank arm. Utilizing fatigue strength formulas to check the strength of this point and getting the comprehensive safety factor is 1.64. Changing location of the thrust bearing from the sixth main journal to the seventh main journal, searching the maximum stress point and checking its safety again. After calculation, getting a new comprehensive safety factor and its value is 1.84, increasing by 9.5% compared to the original.