Analysis And Optimization Of A Car Front Subframe NVH Performance

As a product of economic and technological development,automobiles have become a popular means of transportation.At the same time,drivers' demands for cars are also increasing.NVH performance as an important indicator of vehicle quality,it is an important evaluation index of car comfort.The front subframe is an important part of the current chassis of a car.The engine and the swing arm are connected to the vehicle body through the subframe.Under the working state of the vehicle,it can block the random vibration load from the engine and the road surface and prevent the vibration from being directly introduced into the cab.Therefore,the front subframe has an important influence on the NVH performance of vehicles.In this paper,a vehicle front subframe is taken as the research object,and the related NVH characteristics of the subframe are analyzed.Aiming at the shortcomings of the subframe,the subframe is optimized and it is studied in conjunction with engineering practice.The main contents of this paper are as follows:(1)Finite element model of the subframe is carried out in Hyper Mesh.Then,the mode of the subframe and the dynamic stiffness of the key attachment points of the subframe are analyzed,and the restraint modal parameters of the subframe and the dynamic stiffness of the key attachment points of the subframe are obtained.Through the modal analysis and dynamic stiffness analysis,the shortage of the subframe is found out to avoid resonance when the car is running,so that the sound pressure inside the car increases,and the NVH performance deteriorates.(2)The multi-objective optimization of the subframe is accomplished by using Hyper Study.The analytical model is established in Hyper Study,the approximate sample fitting points are obtained by Hammersley experimental design,and the approximate model function based on sample points is established by Hyper Kriging method and then optimized by MOGA.Then,through the modal strain energy analysis,the partial structure of the subframe is improved,and the final optimization result is obtained.(3)Insert the improved subframe into the Trimmed Body.The NTF simulation analysis is carried out on the key attachment points(engine rear mounting point,left swing arm front installation point,right swing arm front installation point,left swing arm rear installation point,right swing arm rear mounting point),and the sound pressure characteristics of front and back rows of cab are obtained.(4)Using the Impact Testing module in LMS Test.Lab,the modal test was performed on the subframe under installation to obtain modal parameters,and at the same time,the finite element modal analysis was verified;then the NTF test was performed on the key attachment points of the subframe to verify the NTF simulation.(5)Through the Testing-Advanced test module in LMS Test.Lab,the car and the marked vehicle equipped with the same type of subframe are tested on DG POT,focusing on the vibration characteristics of key attachment points in the subframe under driving conditions.The test data of the vehicle are compared with the test data of the marked vehicle.