Anti-loose Performance Improvement And Multi-objective Optimization Design Of Threaded Joint Structure In Automobile

Threaded connection is one of the widely used connection structures in automotive mechanical structures.The screw connection at the chassis is especially important for the safety and driving experience of the whole vehicle.Due to the complicated force,the loosening of the threaded connection at this place sometimes occurs.To this end,the overall connection reliability of the screw connection structure at the chassis of the automobile was studied in this paper,and combined with theoretical analysis,finite element simulation and experiment,multi-objective optimization and other technologies,the factors affecting the anti-looseness performance of threaded connection structure,the improvement of anti-looseness performance,and the comprehensive performance optimization of the critical connection structure of the chassis were studied.The main research contents are as follows:1.The influencing factors and influence laws of the anti-loosening performance of the threaded connection structure were studied through finite element simulation and experiment.Firstly,the influence of friction coefficient,thickness of connecting piece and thread engagement length on the looseness of connection structure under transverse alternating load were studied by finite element simulation.Secondly,the effects of friction coefficient,initial preload,equivalent friction diameter of supporting surface and anti-loosening method on the looseness of threaded connection structure were studied through transverse vibration experiment,to provide reference for the optimization of the anti-loose performance of the threaded connection structure.2.The anti-loosening performance of the threaded connection structure was optimized from three aspects: the tightening process,the minimum height of the nut and the friction coefficient of the joint surface.The theoretical and experimental research on the fastener torque method and the torque angle method were carried out.The high-precision bolt yield point capture method was proposed.Through road test,the attenuation of torque and preload after tightening by torque angle method and traditional torque method was compared.The results show that tightening with the torque angle method can significantly improve the anti-loosening performance of the threaded connection structure;Based on Alexander theory,the height of the nut was optimized by comprehensive consideration of the working load,structural size,tensile strength,performance level,partial incomplete contact and unbending load-bearing thread of the threaded joint and other factors;In order to ensure the anti-slip ability and reduce the pre-tightening loss caused by the embedding,the joint surface of the connected piece should be controlled within a certain range,and the influence of different materials and surface treatment methods on the friction coefficient of the bonding surface were determined through experiments,which provided a reference for the design of threaded connection structure.3.For the problem of loose and abnormality noise of the threaded connection of the automobile chassis,the front point of the connection between the sub-frame and the swing arm was taken as the research object,the friction coefficient of the joint surface,the length of the bushing,support thickness and bolt flange diameter were taken as design variables,and the minimum attenuation value of the axial force and overall mass of the threaded connection structure were the optimization targets,then the response surface approximation model was established.The NSGA-II algorithm was used to optimize the multi-objective design.After optimization,the axial force attenuation of the threaded connection structure was small and the connecting parts were not crushed,the overall performance of the threaded connection structure was significantly improved.