Optimization Design Of Vehicle Body Structure Based On NTF Analysis

With the rapid development of the automotive industry,the comfort,safety,emissions of vehicle have also been greatly improved,and the problem of vehicle interior noise has become increasingly prominent.The excitation of the engine and road surface are transmitted to the body through various parts of the chassis,which causing vibration of the vehicle body that coupled with the cavity,then forms interior noises.This paper establishes the finite element model of body-in-white and Trimmed-body of an SUV.Then makes stiffness analysis and modal analysis of body-in-white,modal analysis of acoustic cavity and Trimmed-body.Identifying the dangerous paths through the noise transfer function analysis and input point interance analysis,and then determin the most deformed body by modal contribution analysis and the operational deflection shape analysis.The vibration of the board parts is reduced by optimizing the structure and installing a dynamic vibration absorber that can reduce the interior noise.1)Building a finite element analysis model of the SUV body structure.The finite element analysis model of the body-in-white is established according to the modeling specification and the simplification principle;the finite element analysis of the trimmed-body is composed of assembling the closure model,the dashboard simplified model,the steering system model,the front subframe model and other interior parts and vehicle accessory models.2)Stiffness and modal analysis of the vehicle body structures.Analyze the bodyin-white,the trimmed-body and the acoustic cavity and obtain the basic distribution of the modal frequency of the vehicle body structures and the basic dynamic performance of the acoustic cavity in the car.The bending stiffness and torsional stiffness of the body-in-white are analyzed,and the bending stiffness and torsional stiffness curves of the left and right side beams and longitudinal beams of the body-in-white are obtained,and the bending stiffness and torsional stiffness of the body-in-white are calculated to determine the good stiffness performance of the body structure to ensure the NVH performance.3)Transfer function analysis of the trimmed-body.The 20 attachment points that between the vehicle body and the components such as the engine,chassis and exhaust system are regarded as the excitation points.Each excitation point is divided into three directions: X,Y and Z.A total of 60 excitation conditions are used to perform the noise transfer function.Through the analysis of the noise transfer function,the dangerous condition of the vehicle’s acoustic response exceeding the target line is identified,and then the cause of the noise inside the vehicle is determined by the Input-Point-Inertance analysis of the attachment point.Finally,through the modal contribution analysis and operational deflection shape analysis,the body panels that contribute the most to the noise response in the vehicle are found.4)The optimized design of the body structure enables low noise control inside the car.Based on the vibration characteristics and acoustic radiation theory of simple support plates,the vibration characteristics and acoustic radiation of simply supported plates are studied from the aspects of thickness,number of punch bars,number of reinforcement bars and curved panels.Combined with the research results,the optimized components are optimized,and three optimization schemes are customized.Finally,the dynamic vibration absorber is installed at the maximum deformation of the inner panel of the left rear sub-board and squeezing the plate at the right rear bumper hole and increasing the solder joint are the optimal solution.The optimization scheme reduces the noise inside the car by an average of 4.8 dB at the frequence of 105 Hz.