The Exhaust System Of The Cold End Dynamic Characteristics Analysis

Exhaust System is motivated by each connecting part,and meanwhile affects each part’s vibration.Its dynamic property which is playing an important part on improving the NVH feature is more and more widely concerned.This study is dedicated to researching and improving the system’s dynamic property.The research methods include combining engineering practice objects;optimizing exhaust system’s hanger position and match of flexible couplings with finite element and dynamics software;analyzing motion envelope.Firstly,the study optimized the exhaust system’s hanger position.It conducted the exhaust system’s three dimensional mathematical model provided by customers,established a proper structural finite element model on which a free numerical modal analysis and experimental modal analysis are carried,in order to verify the reasonability of the model.Then it determined the potential position of the hanger by using the method of traditional and improved ADDOFD（average driving degrees of freedom displacement）.Plus,it confirmed with hanger transmission.Based on the previous research,along with the consideration of spatial layout,system strength,and technological requirements,the exact position of the hanger is finally determined.The final position reduced the system’s vibration,avoided the resonance between the engine and frame.Secondly,this study conducted a study on the match of flexible couplings.It established a finite element model for the flexible couplings’ bellows.Then it analyzed the model’s axial stiffness and bending stiffness,studied its relationship between the length and transmissibility of bellows.Result shows that the stiffness of the two directions is a constant.The longer length,the smaller stiffness,and they are nonlinear.The longer length,the smaller transmissibility,and they are impacted by the structural frequency.Taking an overall consideration of spatial arrangement and price,we set 18 wave crests（2 preliminary waves and16 dominant waves）as the final bellow length.At last,this study analyzed the exhaust system’s motion envelope.By importing complete neutral file of finite element modal,establishing exhaust system’s dynamical model,verifying the model reasonability with static balance check method,analyzing motion characteristics,this study finally determined the moving envelope surface.Compared the moving envelope surface with car floor boundary condition,it shows that the least distance for P₁,P₂,P₃,P-4 is 18.94 mm,33.80 mm,23.91 mm,18.46 mm respectively.Nevertheless,P-1,P-3,and P-4 cannot meet the requirement of minimal distance less than 30 mm.Thus,the floor is modified to meet the distance requirement.Through the improvement of these 3 aspects,the exhaust system’s performance basically meets the enterprise’s requirement.Meanwhile,it has reference value on the design and research of the system.