| NVH is the abbreviation of Noise,Vibration and Harshness.The performance of NVH is one of the most important issues in the automotive industry.Exhaust system is an important subsystem of vehicle system,and its NVH performance has an important influence on the NVH performance of the vehicle.Therefore,the exhaust system development based on NVH performance is particularly important.This paper comes from the actual project,mainly from the two aspects of noise reduction and vibration reduction of the exhaust system development,to meet the performance of NVH.In the aspect of noise reduction,the acoustic analysis of the exhaust system is carried out and the internal structure of the muffler is designed to meet customer requirement according to the acoustic theory.Firstly,the GT-POWER model of the engine is calibrated by bench test data,and the exhaust system is replaced by the pipe which is as long as the exhaust pipe.The exhaust system is coupled with the engine to calculate the tailpipe noise.Then the spectrum of the tail tube noise is analyzed by using the professional acoustic analysis software,and the internal structure of the exhaust muffler is designed according to the results of the analysis of the tail noise frequency distribution curve.Then build a complete coupling model of the power device and exhaust muffler which can be used for simulation calculation.The noise of the tail pipe is simulated and compared with the data collected from the bench test of the exhaust muffler.Finally,these data are used to improve the plan of noise reduction.The vibration reduction is mainly based on the vibration analysis theory for the design of the exhaust system.Firstly,the free modal frequencies and mode shapes of the exhaust system are calculated by using the simplified finite element model of the exhaust system.The simulation results are compared with the measured results of the modal test,and the comparison is the natural frequency of the simulation and experiment.The method of modal judgment criterion is used to compare the correlation between the two modes,and the experimental data are used to verify the accuracy of the simulation model.On this basis,design and optimize the lug of the exhaust system.The method of Average Driving DOF Displacement is used to make preliminary determination of the hanging position of the lug.The fully constrained modal analysis is carried out and the natural frequencies of the fully constrained modes are obtained.And observe whether they avoid the engine excitation frequency to prevent resonance.Then,the static analysis of the suspension point is carried out to obtain the stress state of each suspension point.The position of the suspension is adjusted according to the force condition,so that the force on each hanging device can be uniform,in the range of allowable load.After the adjustment of the position of the hanging device,the frequency response simulation of the whole system can be carried out to determine the final program.The sensitivity analysis of the key components of the exhaust system is carried out by using the sensitivity analysis theory,and the sensitivity of the suspension position and the lifting lug stiffness to the natural mode of the exhaust system are analyzed.At last,the performance of exhaust system is tested,and the results are compared with the simulation results.Through the research of two aspects of vibration damping and noise reduction,we can improve the NVH performance of exhaust system and develop high quality products to meet customer demand. |
