Characteristic Analysis And Optimization On Exhaust System’s Structure Vibration

Exhaust system is always one of the important parts of vehicle which could clear the emissions and deduce the vibration. Its performance affects the evaluation index of the whole vehicle, such as vibration, noise and emissions of waste gas and so on. In the aspect of NVH performance, it is necessary to pay attention to the matching of the exhaust system and the whole vehicle. It is difficult to use the traditional vibration theory to study the exhaust system that is the multi-degrees freedoms and nonlinear system.In this thesis, some kind of exhaust system is used as the research objection. By the method of shell element, the finite elements model is established. Firstly the numerical modal analysis is done, to verify the accuracy of the numerical model, and then the modal experiment is done to compare their conclusions. The absolute difference between experimental frequency value and simulation frequency value is controlled within 6Hz.The main modal shapes of the experiment and simulation are mainly consistent, so this step can verify the accuracy of the model and the correctness of the solution. After that, the statics analysis is done. The result shows that the spread of statics load is not in uniformity. The dynamics research divided into three aspects: Frequency response of hangers’ constraint reaction forces; the hooks’ dynamic stiffness analysis; the rubber hangers’ transmissibility. The results is as below: The five hangers’ statics load is non-uniform; Under low frequency section(around 20Hz).the peak value of dynamic constraint reaction forces is large and the forces are non-uniform; The dynamic stiffness of hooks are too low under low frequency and fluctuate greatly, the rubber hangers’ transmissibility is comparatively low. The vibration isolation system can basically meet the design requirements but the performance is not excellent, it needs to be optimized.Looking upon the existing problems, it is necessary to do the optimization on exhaust system’s vibration isolation performance. Firstly, the method called dots of synthesis modal is used to optimize the hanger position of the former model initially, after calculation and arrangements, it leads to lower vibration and more uniform. Except that, the new design is done to the rubber hanger itself. Problems existing in the structure of hanger have been solved by the optimization:1.There is no absolute restriction.2.The stiffness section which can be chosen is narrow. The newly design hanger has the metal frame so that it can restrict the great transform and the stiffness section is greater than the former one. The action is useful to the problem solving that the dynamic stiffness is comparatively small. Then, the performance comparison between the former one and the new one is done, it is showed that the new one leads to less static displacement and has the better transmissibility characteristics.At last, the corrugated pipe and the hangers’ stiffnesses are chosen to be the design variables which are aimed to calculate the best matching solutions. Orthogonal experiment and multi-goals optimizations are used to set up the exhaust system’s optimization model, the calculations are done in sequence upon the statics and dynamics. The results show that the combination of each hanger’s best stiffness and the corrugated pipe’s stiffness has achieved better performance. In statics aspect, the optimized statics displacements are all lower than 3mm, the new hangers’ statics load are less uniform than the former one, with the standard deviation rising from 3.98 to 4.12.In dynamics aspect, the greatest dynamic restriction force has reduced by 13.76 N, hangers’ restricted forces are more uniform, its standard deviation reduces from6.01 to 5.34.The flow which is set up in this thesis is realizable. In the initial time, the hook locations’ optimization can be done with the suspension design. Changing the stiffness of corrugated pipe and rubber hanger is easy for the designer to do the optimization. The automatic optimization software Isight makes the flow more efficiency.