Hangers Location’s Design And Structural Optimization Of The Vehicle Exhaust System

Facing the increasingly stringent environmental requirements，the role of the vehicleexhaust system，which affects the quality of the vehicle，is gradually being valued by thepeople. The vehicle exhaust system not only to ensure it could discharge the combustionexhaust gas of the engine smoothly，but also could have a chemical reaction to the exhaustgas，which will translate combustion exhaust gas into some colorless，odorless and harmlessgas，which is harmless to human and the environment. At the same time，since the engine willgenerate vibration and noise when the engine burns the fuel, so the exhaust system shouldalso can reduce the translation of vibration energy to the vehicle body，which will achieve thepurpose of reducing vibration and noise.During the running process of the automobile, exhaust system’s energy of vibration willbe delivered to the body through the hangers, which will induce the vibration and noise to thecab. By the modal analysis theory of multi degree of freedom system, the exhaust system’svibration energy transmitted to the body can be effectively controlled by the reasonabledesign of hangers location. Modal analysis and Finite Element Technology, two cornerstonesto the structural dynamics analysis, were combined to design the hangers location of exhaustsystem. First, the exhaust system’s finite element simulation modal was built, a modalexperiment was performed and the modal parameters were distinguished by LMS test lab’sPolyMax. The modal’s feasibility was tested by the value of MAC(Modal AssuranceCriterion)between the computational free modal and experimental free modal; Next, themodal analysis method was employed to design hangers location of the exhaust system, andthe rationality of the hangers location was verified through modal, static and dynamicsimulation analysis. Use the finite element simulation model of the exhaust system to designthe hangers location, which will greatly reduce the number of tests and research costs, shortenthe development cycle, and improve the NVH performance of vehicle.The vehicle exhaust system’s simulation modal was built by computational fluiddynamics (CFD), and the modal’s feasibility was tested by bench test. In order to decrease the back-pressure and increase the power performance and fuel economy, the structure of theexhaust system was optimized. According to bench test and the analysis result of CFD, itcould get every part’s contribution to the back-pressure and know about the reasons of theback-pressure. The main muffler and two-stage catalytic converter of the exhaust systemwas optimized, and the flow field characteristics before and after optimization was analyzedin detail. After optimizing, the back-pressure decreased by about25%, and the maximumback-pressure was reduced from74.8MPa to53.2MPa. At the same time, the power of theengine at rated conditions increased by about15%, and the biggest drop of the fuelconsumption was about16%.Domestic and foreign design of the vehicle exhaust system is always to reduce exhaustbackpressure point suspension for automotive exhaust systems are mostly concentrated intheory, be used to guide the project and the article is not a lot of practical application, makingthe theoretical research and practical application phase "out of touch." In view of this, thispaper designed exhaust system hanging position and reduce exhaust back pressure, improveengine ride comfort, power and economy as the goal to bench test and finite elementnumerical simulation as a method, discussed automobile exhaust system suspension pointselection and optimization of the process, the application of the actual project has some valuefor references.