車輛排氣結構減振研究

Abstract

排氣系統為附掛在車輛底盤上的次結構，很容易被簡化處理，若處理不慎可能引起共振或振動能量集中於局部而導致結構噪音或掛架斷裂，甚至有局部拍擊的現象，降低行車品質。本文提出一套車輛排氣結構系統的動態特性分析與設計參數調整自動化的「結構動態分析為基礎的設計最佳化」運算程序。 首先建立排氣管有限元素分析模型，接著以敲擊試驗，運用系統識別確定排氣管結構的模態參數，以此為依據修正有限元素模型的未確定參數。 其次將實車量測到的主機排氣口段加速度資料，換算成位移頻譜作為主機排氣口的外力頻譜，利用ANSYS諧和分析算出頻率反應函數，兩者結合計算排氣結構系統動態反應頻譜。 最後應用最佳化方法，以尋找排氣系統的吊掛結構材料參數與掛吊位置的變更方式，以降低排氣管吊點反力頻譜峰值，達到最低振動量的目標，排除排氣系統振動傳遞到車體的結構噪音問題。

The exhaust structure system is the sub-system hung under the vehicle chassis. This sub-system may be considered rashly as a simple structure. If the structure system is arrayed unreasonably, the structure resonance or the concentration of vibration energy on local area will accrue, which will induce structure noise or damage of mountings components. Farther more the structure components may pound together and the ridding quality will be reduced. This paper proposed a dynamic analysis based optimization procedure to reduce the vibration level of the vehicle exhaust structure system. At first, the FEM model with initial parameters is established, and then this parameter will be modified in accordance with the modal parameters which are identified form vibration test. Secondly, the acceleration of the exhaust pipe on air vent section will be measured in car running test, and then converted into displacement spectrum used as input exciting spectrum. The frequency response functions of exhaust structure are determined by harmonic analysis using ANSYS. And then the dynamic response spectrum can be calculated. Finally, the equivalent elastic modulus and the location of the suspension rubber can be optimized to achieve the minimum reaction forces of suspension rubber. So that the noise and vibration in the body transmitted from the exhaust system should be reduced to a minimum level.