Study On Design And Optimization Of Nonlinear Stiffness For Powertrain Mount System

With the development of the economy,people have higher requirements for the comfort of cars.The powertrain is fixed on the frame by the mount system,and the function of mount system is to reduce the transmission of vibrations from the powertrain to the frame.A well-designed powertrain mount system has better vibration isolation performance,which can improve the NVH(Noise Vibration and Harshness)performance of the car.At present,the common method is to design the stiffness of the powertrain mount system according to linear variation law,but it can only meet the vibration isolation requirement when the car is driven with high gear on the smooth road.When the car is accelerated at full throttle with low gear or driven on bumpy road,the mount system is already in a nonlinear motion state,the mount system with linear stiffness cannot isolate vibration well.And when the stiffness of the mount system is optimized,the influence of the amplitude of the reaction force is less considered.Aiming at this situation,based on nonlinear mathematical model,the decoupling ratio of the mount system and the amplitude of the reaction force of the mount element were taken as the optimization goals,and the nonlinear stiffness of a truck mount system was optimal designed.The main contents are as follows:1.Based on the vibration characteristics of the powertrain mount system,a 6-DOF dynamic model of the mount system was established through appropriate simplification,and the lagrange equation of the mount system was derived.A nonlinear mathematical model with cubic polynomial of force and displacement was used to represent the dynamic characteristics of the powertrain mount system,and the nonlinear differential equation of the powertrain mount system was obtained.The source of powertrain excitation was analyzed and the initial parameters of powertrain were tested.2.According to the design criteria of nonlinear stiffness of the powertrain mount system,the mount stiffness was divided into linear section,transition section and hard limit section.The stiffness matrix expression of the mount element on each section was obtained through the design of displacement and inflection point of mount element.Based on MATLAB and ADAMS,the 6-DOF simulation models of the mount system were established respectively,and the simulation models were proved to be correct by comparing them.Integrating MATLAB software and ADAMS software on Isight platform,the decoupling ratio of the mount system and the amplitude of the reaction force of the mount element were taken as the optimization goals,the stiffness of the mount element on each section was optimized.The nonlinear stiffness design method of the mount system was proved to be correct by comparing and verifying the optimized results of the two simulation models.After the optimization,the decoupling ratio of each section of the mount system can reach more than 80%,especially the decoupling ratio along the Z-axis movement direction and the X-axis rotation direction can reach more than 85%,and the amplitude of the reaction force of the front mount element,the rear left mount element and the rear right mount element decreases more than 4.69%,35.69% and 21.96%,it can effectively reduce the transmission of vibration from the powertrain to the frame.3.In order to facilitate the designer to optimize the nonlinear stiffness of powertrain mount system,integrating MATLAB software and ADAMS software on Isight platform,an optimization platform for the nonlinear stiffness of the powertrain mount system was designed.The platform has the functions of mount system modeling,nonlinear stiffness design,and model analysis,it is possessed of high optimization accuracy,simple interface and easy operation.