NVH Performance Analysis And Optimization Of A Passenger Car Exhaust Systems

This paper,including following five parts,focuses on the NVH performance analysis and optimization of automobile exhaust systems based on software simulations.1.The finite element model of a exhaust system established in Hyper Mesh is imported into MSC.NASTRAN to conduct free and constrained modal analysis.The modal frequencies and mode shapes of each order are obtained.It was found that the main vibration mode mainly presents a bending mode when the frequency value is in the range of20 Hz through 200 Hz.2.The Average Driving Degree of Freedom Displacement(ADDOFD)method was used to optimize the three hanging point orientations of the exhaust system.The new hanging point positions are basically designed on nodes of the main modes of each order or not far away from node positions.Compared with the hanging position before the improvement,it is obvious that the new hanging position is more realistic and helps to reduce the transmission of vibration of the exhaust system to the vehicle body.3.The noise reduction performance of the muffler was discussed by Virtual.lab considering different insertion and different bias.The acoustic transmission loss curves of them under different conditions are obtained.It was found that the performance of mufflers with insert is better than ones without insert.The noise frequency eliminated is about an even multiple of the fundamental frequency when the insertion length is 1/4 of the longitudinal dimension of the muffler cavity.Similarly,when the insertion length is 1/2 of the longitudinal dimension of the muffler cavity,the noise frequency eliminated is about odd multiple of the fundamental frequency.However,whether the muffler is biased or not has little effect on its own muffling ability.4.The research on the response of the exhaust system engine under the main order excitation is generally divided into the frequency response analysis and the motion envelope analysis.The results of frequency response analysis and modal analysis are compared with each other,which proves the correctness of the analysis.In the motion envelope analysis,the ADAMS software was used to simulate the motion interference with the vehicle body and its accessories under extreme conditions,so as to avoid the vibration and noise problems caused by the motion interference of the exhaust system.The wear and tear of the system due to interference.5.The stiffness of rubber lifting lugs was optimized by calculating the vibration attenuation rate under the engine main order excitation.It is proved that reducing the stiffness value can improve the vibration isolation efficiency.