The Research On The Design Of Vehicle Mounting Systems Based On Uncertainty Analysis

With the development of society and the improvement of automotive technologies,vehicles are well received by more and more consumers. When consumers buy or drive a car,their reception is influenced by the ride comfort directly. In order to enhance automotives’ride comfort, the technology of vehicle NVH is the essential way. The vehicle mountingsystem is a key elastic vibration isolation system in cars, which is significant to vehicle’ssafety and ride comfort. Therefore, more and more vehicle engineers pay attention to theresearch and design of vehicle engine mounting systems.In order to take consideration of the parameter’s uncertainties, this thesis present tworobust design methods which aim to improve the isolation performance of vehicle enginemounting systems. The presented methods are the combination of robust design and themulti-objective optimization, and the model of uncertain parameters is based on stochasticmodeland interval analysis model in the theory of uncertainty. What’s more, based on the tworobust design methods, MATLAB is used to establish the software platform which is able toanalyze and optimize the vibration isolation performance of vehicle mounting systems, and itwill be conveniently applied in engineering field.The main works are listed as follows(1) After constructing the six degrees of freedom dynamic model of a vehicle enginemounting system, the modal parameters of a vehicle engine mounting system which are thebasis of follow-up dynamic calculation are obtained. In order to optimize the dynamiccharacteristics of a vehicle engine mounting system, the dynamic reaction force is introducedinto the objective functions and the modal parameters are taken as constraint conditions.(2) By applying the stochastic model in uncertainty theory to model the uncertainty ofmounting stiffness, this thesis presents a robust design method for vehicle engine mountingsystems, which is the combination of robust design and multi-objective optimization. In thepresented method, the uncertainty of mounting stiffness is considered in design and assumedto obey normal distribution. The robust function of dynamic reaction is obtained byLHS(Latin Hypercube Sampling) and is taken as a cost function in the vector of the objectivefunctions. Taking the decoupling rate and the minimum of the dynamic reaction force as theoptimization goal, the Genetic Algorithm (GA) is applied to conduct global optimization andall the Pareto optimal solutions could be found out. The optimal and robust solution can befinally obtained by the robust evaluation. (3) Based on the theory of interval analysis, a robust optimization design method forengine mounting systems with uncertain parameters is proposed in this thesis. The proposedmethod is the combination of robust design and multi-objective design. A robust optimizationmodel is established based on the interval mathematical model. In the optimization model, theobjective function includes the minimum of the dynamic reaction force and the fluctuationrange of the dynamic reaction force. The allocation of the natural frequencies is the constraintand the optimization variables are mountings stiffness. The variables of interval parametersinclude the fluctuation ranges of mountings stiffness and the installation location ofsuspension components. An application example of the optimal design of a car’s enginemounting system is presented, which shows that the isolation performance and its robustnessare improved simultaneously and the goals of robust design are achieved.(4) The software platform is founded through MATLAB and the platform could analyzeand optimize the vibration isolation performance of vehicle mounting systems. When theparameter’s uncertainty is taken into consideration, the design of a vehicle engine mountingsystem is a significantly complex work and a lot of the work is simply repeating, so theplatform will be conveniently applied in engineering field. The platform has a strong practicalvalue and its function includes characteristics analysis, statics analysis, dynamic analysis,sensitivity analysis, robust design and so on.This thesis presents the robust design flow of vehicle engine mounting systems based onthe vibration theory, uncertainty analysis theory, FEM(Finite Element Method) as well asrobust design and multi-objective optimization. Based on the presented methods, the softwareplatform of the robust design of vehicle engine mounting systems is founded throughMATLAB and it has a strong practical value.