Multi-objective Optimization Design And NVH Performance Research Of An Electric Vehicle Body Structure

In recent years,the level of car designed and manufacturing has been continuously improved,and people’s demand for cars is not limited to its role as a means of transportation.The degree of comfort in the car driving experience has gradually become a key factor to consider when choosing car products.NVH performance is one of the most important indicators of comfort.Various excitations received by the car during driving will transmit vibrations to the interior of the vehicle through the body structure,and are received by drivers and passengers in the form of ear sound pressure and somatosensory vibration.Therefore,NVH performance level is inextricably linked to the body structure performance.This paper takes an electric vehicle as the research object,and analyzes the basic performance of its body structure and the noise and vibration performance inside the vehicle.Through the multi-objective structural optimization design method,the overall torsional stiffness of the BIP can meet the target value and NVH performance inside the vehicle is improved.The main research contents of the paper are as follows:Firstly,carrying out a standardized mesh division and parts connection simulation of an electric vehicle BIP by the finite element method,a finite element model of the BIP that conformed to the engineering specification was established.The stiffness and modal of its basic structure performance were analyzed and evaluated.The overall trend of body stiffness and deformation is smooth,and the structural stiffness distribution is uniform.The BIP bending stiffness and the first-order overall bending-torsional mode meet the design target value,while the torsional stiffness is slightly lower than the target value,so the body structure needs to be optimized.Secondly,the opening and closing parts,steering mechanism,body accessories,etc.were added to the BIP in order to establish the finite element model of the trimmed body.The finite element model of the acoustic cavity system was established with the structure enclosing the interior space of the vehicle,and its modal performance was analyzed for reference on vehicle interior acoustics research.Based on the sound-structure coupling theory,the acoustic cavity system model and the trimmed body model were combined into a body-acoustic cavity coupled finite element model.The noise transfer function and vibration transfer function were respectively analyzed in the sound-structure coupling model and the trimmed body model.By applying unit excitation to each key attachment point of the vehicle body,the sound pressure and vibration acceleration situation of each response point inside the vehicle under different paths were preliminarily analyzed.Finally,the sensitivity analysis method was used to screen out the design variables with higher relative sensitivity values of torsional stiffness and lower relative sensitivity values of other properties from many parts of the BIP;Obtained by using the Hammersley method to carry out the experimental design of the design variables,the point test matrix helped to construct an approximate model of the Kriging response surface;Then a multi-objective optimization mathematical model was established with the objectives of maximizing torsional stiffness and minimizing mass,and flexural stiffness and first-order overall bending-torsional mode as constraints.Through the multi-objective genetic algorithm,the overall optimal solution that conforms to multiple optimization objectives and constraints was found.The optimization results show that the modal and stiffness performances of the BIP model are improved and meet the design target values under the consideration of the lightweight requirements of the body.The compliance rate of peak sound pressure and peak vibration acceleration at the response points under each transfer path increased,and the noise and vibration performance inside the vehicle was significantly improved.