Conceptual Design And NVH Simulation Analysis Of The Structure For Electric Vehicle Body

The problems of traditional fuel vehicle are becoming more and more prominent.The research and popularization of electric vehicle has attracted worldwide attention.Developing pure electric vehicle(PEV)is an important part of “Made in China 2025” plan,and also an important development direction for China’s automotive industry to break through to high-end.The pure electric vehicle is not only very different from the traditional fuel vehicle in power system and energy storage device,but also there is great difference in its body structure form.Following the body structure of traditional fuel vehicle,the vehicle body lightweight and mechanical performance requirements such as body stiffness can not be best satisfied.Therefore,new requirements should be put forward to the design of electric vehicle body.The study of dynamic stiffness chain based on the vibration performance,is of great significance to the forward conceptual design of vehicle body and comfort of the car.This thesis was aimed at the conceptual design phase of the vehicle body.Researched the forward conceptual design process of vehicle body and a simplified geometric model of vehicle body was established by class A surface and the scheme of vehicle general layout.The location of the 22 main cross-sections was determined.Based on the beam element theory and transfer matrix method,the dynamic stiffness chain model of the vehicle body in Modal coordinate system was obtained,then taking the main cross-section property parameters as the design variables and the relationship between the main cross-section property parameters and the natural frequency of the vehicle body was established.Body lightweight was taken as the objective function,and the vehicle body static stiffness and the first order natural frequency were taken as constraints for optimization,and using genetic algorithms to solve it for the main cross-section properties.The feasibility of the design method of the dynamic stiffness chain was verified by comparing the results of static stiffness simulation and modal analysis with the approximate benchmark car.The attachment points of vehicle body are important channels for external excitation to transfer through the body to inside of the vehicle.The dynamic stiffness of the attachment points is an important parameter to reflect the sensitivity of the vehicle body,and is also the important object for the dynamic performance inspection of the vehicle body local structure.On the basis of establishing the 3D model of vehicle body frame using CAD software,this thesis preprocessed vehicle body frame model by Hypermesh,and used MSC.Nastran(SOL 111)solver to analyze the frequency response of the vehicle body attachment points,and the dynamic stiffness analysis results of the vehicle body attachment points were obtained.The simulation results were compared with the dynamic stiffness target values and the dynamic stiffness test results of the vehicle body attachment points,and the dynamic stiffness characteristics at the vehicle body attachment points were investigated.The study of the thesis not only considered the overall stiffness performance and the first order natural frequency of the vehicle body skeleton structure,but also took into account the local dynamic stiffness characteristics near by the vehicle body attachment points.The overall and local structure,static and dynamic properties of the vehicle body were comprehensively investigated with stiffness performance as the guidance.which provides a reference for the forward development of the pure electric vehicle body in the conceptual design stage.