Research On Vibration Isolation Of Automobile Exhaust System

As an important part of the car,exhaust system is one of the important factors that affect the performance of vehicle NVH.When the vehicle is running,the exhaust system is mainly subjected to vibration excitation from the powertrain and the road.especially the periodic vibration and shock of the engine is transmitted directly to the exhaust system and then transmitted to the vehicle body through the rubber lug,which will affect the comfort of the passenger in the car.Therefore,researching on the vibration isolation of the exhaust system are important for improving the NVH performance of the vehicle.The finite model of the exhaust system was established by using the HyperWorks software through simplifying the modeling of components of the exhaust system.The numerical simulation and experimental analysis of the free mode and the constraint mode of the exhaust system were carried out respectively.The results showed that in the free mode and the constraint mode,the frequency and vibration mode of numerical mode and experimental mode are well consistent.These testified that the finite element analysis model of the exhaust system is accurate and reasonable.Based on the free modal analysis,the weight of each order modal shape was calculated by analytic hierarchy process(AHP),the suspension position is re-designed on the basis of average driving degree of freedom(ADDOFD).Next static analysis,constraint modal analysis and frequency response analysis were carried on the exhaust system.The results showed that the load distribution of each hanger point is uniform and the deformation of the hanger was less than 3mm.The constraint mode frequency completely avoided the second order excitation frequency more the 3Hz corresponding to the engine idling and economic speed.the dynamic force delivered to vehicle body decreased obviously more than before.Then the real car experiment verified that exhaust hangers' location layout was reasonable.The key component parameters with great influence on the modal frequency and the dynamic transfer force of rubber hangers are obtained by the sensitivity analysis.And the dynamic transfer force of rubber hangers was optimized by orthogonal test design.The calculation results were processed by extreme analysis method,and the optimal combination of component parameters was obtained.After optimization,the dynamic transfer force of each hanger was reduced between 5N and 7.5N.On the basis of this,the hangers' stiffness was optimized,and the hangers' transfer force and static displacement were reduced and uniform distribution,which fully met the design requirements of the exhaust system.The hyperelastic constitutive model of rubber material was analyzed.The hyperelastic constitutive model of the rubber hanger material was obtained by the rubber material experiment.The structure of rubber hanger was analyzed,and the design method of rubber hanger based on orthogonal test was proposed.Rubber hangers were designed by this method and the results showed that this design method can quickly design the required rubber hangers.In this paper,the research on the vibration isolation of the exhaust system was valuable to engineering application and practices guidance.For the development of a new vehicle exhaust system,it is cost saving and helpful to cut down the period of design.