NVH Performance Analysis And Optimization Study Of A New Passenger Car

Consumers’pursuit of vehicle comfort is enhanced.In addition to considering the cost performance and safety performance of vehicles,they also pay attention to the various performances of vehicles,including the overall vehicle noise,vibration and Harshness.Poor vehicle NVH performance will not only reduce the comfort of passengers,but also lead to the reduction of other performance.About one-third of vehicle failures are inextricably related to NVH problems.Therefore,it is one of the research hotspots of vehicle NVH to study and optimize the noise and vibration performance of the vehicle to improve the vehicle performance and improve the comfort of the vehicle.Hyper Mesh is used to establish the finite element models of a new passenger car,and modal analysis is used to calculate and analyze the free modal of the body-in-white and verify the modal test in this thesis.Then,the origin dynamic stiffness method is used to analyze the origin dynamic stiffness of the key attachment points of the body-in-white,and the NVH performance of the body-in-white is improved through the empirical structure optimization.Secondly,the free modal analysis of the interior body is carried out,and the transfer function method is used to analyze the vibration transfer function of the interior body,and the substandard or weak performance is optimized.The free mode of the acoustic cavity is analyzed to grasp the sound pressure distribution inside the vehicle.At the same time,the noise transfer function of the acoustic-solid coupling model is analyzed,and the acoustic contribution of the body panel is analyzed to determine the eight panels as the optimization object.Finally,the corresponding approximate model established by Isight is used to optimize the panels’thickness T₁～T₈ as the design variable,the peak sound pressure SPL₁～SPL₁₃and the body mass minimization as the objective function,and the overall first-order torsional modal frequency f₁ and the overall first-order bending modal frequency f₂ of the interior body as the constraints,and the multi-objective optimization of body NVH performance is carried out based on the second-generation non-dominated sorting optimization algorithm.It is shown that except for some indexes of peak sound pressure SPL₁～SPL₁₃,the other performance indexes have met the target requirements.（1）The overall first-order torsional modal frequency（36.70 Hz）,the front-end yaw modal frequency（40.48 Hz）and the overall first-order bending modal frequency（43.89Hz）of the body-in-white are increased to 38.31 Hz,44.72 Hz and 54.88 Hz respectively,and the modal performance of the body-in-white is improved.At the same time,the dynamic stiffness of the origin of the key attachment points has met the target requirements,and the vibration input to the body has been controlled to a certain extent.（2）After structural optimization and multi-objective optimization,the overall first-order torsional modal frequency of the interior body is increased to 29.98 Hz,the overall first-order bending frequency is increased to 34.22 Hz,the concerned modes of the rear door are improved to a certain extent,the vibration transfer function performance of the interior body meets the requirements,and the NVH performance of the interior body is improved.（3）After multi-objective optimization,although the peak sound pressure at the response point of the acoustic-solid coupling model SPL₁～SPL₁₃is still higher than the target value of 60d B,the optimized peak sound pressure is basically reduced,and some of the peak sound pressure has reached the standard.The body mass is reduced to 891.8kg,which is 4.4 kg lower than that before optimization,and the lightweight rate is 0.5%.The NVH performance of the vehicle can be effectively improved based on the combination of empirical structure optimization and genetic algorithm multi-objective optimization,thereby improving the comfort of the occupants in the vehicle.