| The lightweight design of chassis components has a positive significance for improving automobile fuel economy.The subframe is an important part of the chassis structure of the car.It can increase the rigidity of the suspension connection and optimize the ride comfort of the vehicle.At present,the lightweight design of the front sub-frame of a car mainly depends on the experience of engineers.The design efficiency is low and the weight reduction effect is not ideal.Based on multibody dynamics,finite element analysis,structural optimization design and signal processing theory,this dissertation proposes an efficient lightweight design scheme for the subframe.And applying this scheme to a lightweight design project of the front subframe of a certain car.First of all,six extreme working conditions were selected according to the strength design standards provided by the OEM.Using the commercial multibody dynamics software Adams / Car,the vehicle model and the road surface model of the test site corresponding to the limit conditions were established,and the strength load spectrum of each hard point of the subframe was obtained by simulation.A method for determining the load boundary conditions based on the strength analysis of the load spectrum of the limit working condition is proposed,which provides a reliable load boundary condition for the subframe strength performance check in the subsequent lightweight design process.By selecting the appropriate element type and simulating the sub-frame welding seams,bushings and bolts and other main connections,the subframe finite element model is established.Based on the finite element theory,strength analysis,rigidity analysis of the mounting points considering the rigid body displacement of the subframe and free modal analysis of the subframe are provided,which provide design directions for lightweighting the subframe.The subframe structure was improved and the finite element model was rebuilt.The material of the subframe was replaced,and the true stress-strain curve of the new material was obtained through multiple sets of material tensile tests.Using strength analysis based on material nonlinearity and free modal analysis to take sample points,approximate models of strength and modal response are established.The mathematical model of plate thickness optimization was established and the optimization algorithm was used to determine the best plate thickness combination of the subframe.The weight of the subframe was reduced by 2 kg,and a weight reduction effect of 10.3% was achieved while meeting the requirements of strength,stiffness,and modal performance.The subframe free modal test was carried out to obtain the test modal parameters to verify the reliability of the subframe finite element model,and the strength test of the suspension mounting point was carried out to verify the strength performance of the subframe suspension mounting point;In order to check the durability of the subframe after the lightweight design,the load spectrum of the endurance working conditions of each hard point of the subframe is edited.The durability performance of the subframe sheet metal structure was analyzed using the strain life method,and the durability performance of the weld seam structure was analyzed using the nominal stress method.The time-domain reduction of the subframe durability load spectrum was performed which ensures that the structural hazard points before and after the reduction were consistent and the fatigue life was similar.The six-channel durability test of the subframe was conducted using the programmed load spectrum,and the results showed that the fatigue life of the subframe is 1.9 times the endurance cycle,which meets the design requirements of 1.5 times the endurance cycle. |
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