Vibration Isolation Performance Analysis And Parameter Optimization Of A Commercial Vehicle Powertrain Mounting System

As a direct link to isolate the transmission of engine vibration to the vehicle,the vibration isolation performance of the powertrain mounting system has a significant impact on the vibration and noise level in the vehicle.The current simulation evaluation of the vibration isolation performance of the mounting system is mostly based on the modal distribution of the system and its decoupling,which does not correspond well with the vibration isolation rate,a common evaluation index in the test.In addition,the disturbance of the design stiffness brought by the manufacture and installation of the mount also affects the vibration isolation performance of the mounting system in real vehicles.Therefore,in order to improve the NVH performance of the whole vehicle,it is necessary to establish a simulation model that can better evaluate the vibration isolation performance of the mounting system,and to reasonably match the parameters of the mounting system to improve its vibration isolation performance and its robustness,so as to reduce the transmission of vibration to the vehicle.In this paper,a 6×4 heavy truck is studied in cooperation with a domestic commercial vehicle company.The vibration isolation performance of the powertrain mounting system of this model is analyzed in terms of the dynamic frame stiffness and the robustness optimization of the stiffness parameters is carried out.The purpose of this study is to improve the NVH performance of the vehicle based on a better simulation of the idle vibration isolation rate of the mounting system,and to reduce the adverse effects of manufacturing and installation uncertainties on the vibration isolation performance.The specific work involved in this paper is mainly in the following areas.1.Theoretical analysis and research related to powertrain mounting system.From a single-cylinder engine,the engine excitation force is analyzed,and then the theoretical expressions of the excitation force vector and the main excitation frequency of the multicylinder engine are given.At the same time,the method of obtaining the parameters required for modeling and simulation of powertrain mounting system is studied,and the basic vibration isolation theory of multi-degree-of-freedom system is derived and analyzed from the vibration differential equation.2.The modal and vibration isolation performance test of the powertrain mounting system.The rigid body modal test of the mounting system was conducted in the vehicle state using the shaker,and the vibration isolation rate of the vehicle engine at idle speed and at constant speed was measured,and the vibration noise level in the vehicle and the modal test results were combined to find that the mounting system has a large deficiency in vibration isolation performance and needs to be re-matched and optimized.3.Six-degree-of-freedom modeling analysis of the powertrain mounting system.A simplified six-degree-of-freedom model of the powertrain mounting system was derived and established using Lagrange’s equation.The dynamics simulation model was used to analyze the inherent characteristics and decoupling calculations,and then the reliability of the model for subsequent vibration isolation simulation and optimization was verified by combining the modal test results.4.Construction of a simulation model of vibration isolation rate of powertrain mounting system considering frame dynamic stiffness.According to the established six-degree-offreedom dynamic model,the identification formula of the equivalent excitation force of the center of mass with the active side vibration of the mounting point as the main input condition is deduced by transformation in the frequency domain.The iterative solution method for the vibration acceleration of the active and passive sides of the mounting point is also given.The IPI（dynamic stiffness at origin）test is performed on the passive side frame of the powertrain mounting point by the hammer method to obtain the frequency response function data.Combined with the identified equivalent excitation force,the idle vibration isolation rate of the mount is simulated and compared with the measured vibration isolation rate.The results show that this method has sufficient simulation accuracy and can be used to predict the vibration isolation rate of the powertrain mounting system after optimization.5.Discuss the influence of vertical characteristics of powertrain mounting system on vehicle ride comfort.A four-degree-of-freedom vertical dynamic simulation model including the cab,powertrain,sprung mass and unsprung mass of the front axle is established for the prototype vehicle.Under the random excitation of the road surface,the influence of the vertical offset frequency and damping lag angle of the powertrain mounting system on the ride comfort index of the vehicle is analyzed.6.Robust optimization of stiffness parameters of powertrain mounting system.Using the method of experimental optimization design,the stiffness sensitivity analysis is carried out on the key directional indicators of the mounting system to determine the variation range of the design variables.Considering the decoupling rate,static compression,modal frequency distribution,system dynamic reaction and other objectives of the mounting system,the stiffness deterministic optimization of the layout schemes of large and small span mounting systems is carried out based on NSGA-II multi-objective genetic algorithm,and the robustness optimization based on 6σ method is carried out to improve the robustness of vibration isolation performance.The results of the robustness optimization of the mounting system are brought into the simulation model of the vibration isolation rate for simulation calculation to verify the effectiveness of the mounting system robustness optimization design on the improvement of the mount idle vibration isolation rate.