Study On Optimization Of Vibration And Noise Of Exhaust System Of A Vehicle

Over the past two decades,the number of passenger cars in China's cities has exploded.The resulting traffic noise problems are becoming more and more serious,and the urban environment has been greatly negatively affected.As one of the main problems of environmental pollution,noise pollution has attracted more and more attention.From the source of noise pollution,traffic noise occupies a very important part.When a car is driving on the road,it will emit unpleasant noise because of the external work of the internal combustion engine,the vibration caused by the contact between the tire and the road surface,and the friction caused by the air resistance.People's daily production,life and health will be seriously affected by car noise.With the development of automobile emission technology,the air pollution caused by automobiles is less and less.Noise pollution has gradually become the biggest pollution caused by automobiles to the environment.In this paper,combined with the original exhaust system of a specific vehicle,the performance of exhaust NVH is optimized from two aspects of vibration and noise.Aiming at the vibration performance of target vehicle exhaust system,firstly,the weighted displacement is calculated according to ADDOFD,and the theoretical optimal position of the hook is determined according to the calculation results.On this basis,four and five lifting ears schemes are proposed,and the feasibility of the two schemes is verified by 1G force balance calculation.After determining the scheme,the whole method is used to predict the modal of the hook,and the reliability of the scheme is verified by comparing with the experiment.According to the parameters set in the early stage of development,the first vertical bending mode,lateral bending mode and torsion mode frequencies of exhaust system must be avoided 3 Hz with the second-order idling excitation frequency of engine and the first bending frequency of body.Firstly,the exhaust system model is analyzed by simulation method,and then the results are compared with the experimental results to determine the reliability of the simulation results,while ensuring that the first-order lateral bending mode,the first-order vertical bending mode and the first-order torsion mode meet the pre-determined target values.Finally,the dynamic force of the exhaust system hanging ear is calculated,and the dynamic reaction force of the side hook is extracted.The calculation results show that the scheme meets the target of the reaction force.Aiming at the acoustic performance of the exhaust system of the target vehicle,the acoustic performance target of the exhaust system is introduced,and the control flow of the acoustic performance of the exhaust system is introduced in detail.In the first stage,the internal structure of the front muffler and the rear muffler is optimized according to the exhaust noise of the exhaust system of a certain type of vehicle.Adjust the position of the second baffle of the front muffler to increase the volume of the resonant cavity.The rear muffler reduces the through-hole ratio of the partition,adds encapsulated sound-absorbing cotton to the exhaust core tube,and perforates the air core tube of the first chamber.The experimental results show that the overall and the second,fourth and sixth order noise of the optimized scheme are improved obviously.In the second stage,due to the change of the prototype car,the idle condition has a certain power requirement for GMC motor,and the parameters such as the wavelength of exhaust noise change,which exceeds the noise elimination range of the current exhaust silencing device,resulting in greater noise after idle engine.The final scheme is determined by test.