| The crankshaft is one of the core moving parts of the internal combustion engine.The working state of the crankshaft directly determines the stability and reliability of the engine.In this paper,a V-type two-cylinder gasoline engine dedicated to a helicopter is taken as the research object,combined with the finite element method,multi-body dynamics theory and EHD theory,the bearing lubrication of the crankshaft and the fatigue durability of the crankshaft are calculated.By analyzing the bearing lubrication performance and crankshaft fatigue life of the crankshaft under special working conditions,the design defects of the crankshaft were found,and then a design improvement plan was proposed for the design defects of the crankshaft.Through the calculation and analysis of the improvement program,the feasibility of the improvement program is ensured,which provides a theoretical basis for the structural improvement program of the crankshaft.In the research,firstly,the finite element model of crankshaft and related parts was established through HyperMesh software,and the modal analysis of the crankshaft finite element model was carried out through ABAQUS software to verify the rationality of the grids.Through the comparison of the results of the modal analysis,it is confirmed that the error of the finite element mesh of the crankshaft is within a reasonable range,and it can be used for the calculation of the crankshaft multi-body dynamics.According to the EXCITE multi-body dynamics calculation requirements,all the finite element meshes have been reduced in substructure,and the crankshaft multi-body dynamics model has been built according to the actual engine parameters.The accuracy of the multi-body dynamics analysis model is verified by comparing the force of the crank pin with the theoretical force of the crank pin in the calculation results of multi-body dynamics.Through the comparative analysis of the calculation results of the main bearing load and the crank pin load,it is found that the unbalance of the crankshaft is too large,resulting in the sum of the two main bearing loads being much greater than the crank pin load.Through the analysis of the maximum oil film pressure and the minimum oil film thickness,it is found that the main bearing of the crankshaft has a serious shortage of lubrication during operation.According to the peak rough contact pressure curve and the surface pressure cloud diagram of the rough contact,it is found that a large rough contact pressure appears at a certain edge position during the operation of the main bearing.According to the analysis results,the balance performance and structural rigidity of the crankshaft were improved.In this study,finite element analysis with ABAQUS software was used to calculate the stress change process of the crankshaft during the working cycle.The fatigue strength of crankshaft was analyzed by FEMFAT software.Through calculation,it is found that the stress at the transition fillet of the connecting part between the crank pin of the crankshaft and the two crank arms is large and the safety factor of fatigue strength does not meet the design requirements of crankshaft fatigue life.In view of the insufficient strength of the crankshaft,this paper proposes a solution that is to increase the radius of the crank pin and reduce the inner hole of the crank pin.By calculating and adjusting the performance of the improved scheme,the optimized design of the crankshaft structure is completed.The calculation results show that after the improvement,the oil film pressure and oil film thickness of the crankshaft have been significantly improved,which meets the design and use requirements,and ensures that abnormal bearing wear will not occur during the normal operation of the engine.Compared with the original crankshaft,the maximum stress of the crankshaft has also been significantly improved,and the safety factor of fatigue strength has reached the theoretical reference value to ensure that the crankshaft will not experience fatigue damage during work. |
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