| Exhaust system is one of the important parts of vehicles with internal-combustion engines, and it is widely used for cleaning up burned gases and reducing exhaust noise. It works under severe conditions, which bears not only the excitations of engine vibration and road loads, but also the corrosive effects of exhaust gas and road wastewater. Its structure design affects its performance on emission and noise reduction. During the development of an automotive exhaust system, we used the Computer Aid Engineering(CAE) technology to analyze and improve the structure strength of the exhaust system.Based on the shell element and supplemented by the solid element and one-dimension element, a finite element(FE) model of the exhaust system was established. The accuracy of the FE model was verified by comparing the simulation modal frequency and modal shape with experimental data.The Average Driving DOF Displacement(ADDOFD) values of all the exhaust system element was calculated by Patran software, and the hanger location was determined considering the spatial layout, which was further verified by the static analysis. To reduce the force of the No.5 hanger under the gravity of the exhaust system, we changed the hangers? arrangement direction. According to the simulation, the force of No.5 hanger was decreased from 52.3N to 45.9N and the status of hanger?s force was improved. In addition, the stress under 4g acceleration and hanger modal frequency meet the engineering requirements.The constraint modal analysis of exhaust system was performed and it was further validated by experiments. The results demonstrated that, under the idle state(engine excitation frequency [24-25.7Hz]) and the economic speed(engine excitation frequency 80Hz), the main frequency of X-direction vibration from road loads is 12.84 Hz, the Y-direction 3.19 Hz, and the Z-direction 8-10 Hz, respectively, all of the excitations did not coupled with the natural frequency of exhaust system. Modal transient dynamic analysis was carried out using FEA with loading from Road Load Data Acquisition to calculate the stress curve of the exhaust system under ?resonance?(or ?no resonance?) conditions. The results revealed that it is necessary to consider the effects of vibration frequency from proving ground event on fatigue life analysis.The analysis model of local structure was established by considering the characteristics of durability test device. Local structure fatigue durability analysis was simulated and the results of damage calculation of every model are obtained. The fatigue life of the rear muffler inlet was increased from 79.8 thousands cycles to 440 thousands cycles by adding a supporter. The structure strength of local parts was verified by experiments. The simulation analysis can effectively predict the crack location and the fatigue life of simulation is relatively reliable by comparing the results of simulation with those of tests. |
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