The NVH Performance Optimization Of Exhaust System Under Engine Excitation

With the continuous improvement of vehicle technology,people's demand for vehicle's vibration performance is also increasing.The vibration of vehicle mainly comes from the flow of engine,pavement and air.But for engine idling and vehicle running at low,the main source of the vibration is the engine.Therefore,under common working conditions,the vibration induced by engine excitation is very important.However,there are many vibration ways to pass the engine to the driver.So we need to find out which path is the main route of vibration transmission,and then optimize the components and subsystems of the path.A finite element model of the interior part of a passenger car is built in this article.The excitation spectrum of engine is extracted from the analyzed experimental data of engine cylinder pressure,and the frequency spectrum of engine excitation is obtained.Then,the vibration transmission path of the trim body is analyzed,and several routes of vibration transmission caused by the excitation of the engine are obtained.Finally,the route which has great contribution is optimized to reduce the amount of vibration transmission on this route.In this paper,the main vibration transmission routes obtained by finite element analysis are: The engine passes the vibration to the exhaust system,then the vibration of the exhaust system passes through the lifting lug to the floor of the car,and then passes through the vehicle floor to the seat.After finding the main vibration transmission route,vibration performance optimization for exhaust system is carried out.First,the vibration transfer function analysis of the trim body of vehicle is carried out,and the vibration level of the driver seat under the unit excitation of the engine is determined before optimization.Then,the position of the hook is optimized according to the hanging position of the exhaust system on the body.The position of the small vibration in the exhaust pipe is found by the average driving free displacement method,and the layout of the hook is arranged in this position to reduce vibration conduction to the vehicle.Finally,through static analysis,it is confirmed that the state of exhaust system under static suspension is satisfied with the requirement after the hook is optimized.Finally,the vibration transfer function analysis of the car body is carried out,and the vibration condition before and after optimization is compared,and the final optimization conclusion are obtained as follows:The original hook position is not at the best location of the vibration performance.After the optimization of the hook position,the vibration peak of the driver's seat is reduced by 30% at the idle speed of the engine.Through the simulation and optimization of the actual problem of the vehicle,the engineering cost and time cost was greatly reduced.This method is applied not only to solve the problems in actual engineering quickly,but also to provide references for the forward development and design of vehicle.