A Passenger Car Exhaust System Dynamics Research

The exhaust system is an important part of a vehicle, mainly responsible for the exhaust emissions. It has received extensive attention in the aspect of noise reduction, exhaust gas, but the dynamics problem is not getting enough attention.The exhaust system is motivated by the road and engine vibration when the vehicle is running. On the one hand, these vibration excitation affect the fatigue life of the exhaust system, on the other hand, the vibration energy transmits to the vehicle body by hanging, leading to noise and vibration in the car, and finally impacts on NVH performance of the entire vehicle. Therefore, it is necessary to study the dynamics of the exhaust system.Modal analysis is a key to study the dynamics of exhaust system, and inherent properties of the system can be drawn through it. Generally, using the method of combination numerical analysis with experimental analysis to study the modal of exhaust system. The article built the finite element modeling of exhaust system by the software of HyperMesh, and used Optistrust solver to calculate the low-level exhaust system natural frequencies and modes, then compared the results obtained by the finite element method and experimental modal analysis to verify the accuracy of the finite element model. In addition, the article got the stiffness of the bellows using the sensitivity principle, and the exhaust system can be effective to avoid resonance with the engine under the economic speed or the idle when the length is1.2L.The hook theoretical position can be Located by the method of Average driving degree of freedom displacement (ADDOFD), which is the minimum position by the influence of vibration, and then based on the actual postion and underbody’s spatial structure of exhaust system to determine the final hook position. Based on the lug durability to identify its static stiffness Initially, then using orthogonal method to select the most suitable stiffness lugs in the case of meeting the lug durability and vibration isolation performance. Finally, according to the principles of the mechanical admittance admittance to calculate for the whole hanging device, and the values are all less than-20dB in three directions of each hanging device, meeting the design requirements of the admittance values and verifying the vibration isolation performance.