Characteristic Analysis And Optimization Design Of Miro-car Powertrain Mounting System

Engine is one of the main vibration excitation source in car, it has great influence on the car’s ride comfort and vibration performance. The rational design of automotive powertrain mounting system can significantly reduce the vibration transmission between powertrain and vehicle body, which can not only improve the riding comfort of the car, but also can prolong the life of the engine and its components. In this paper, use a mini-car as research object and analysis its vibration isolation.Firstly, According to the powertrain mounting system principle of isolation and excitation analysis, calculate the powertrain mounting system natural frequency arrangement.simplify the powertrain mounting system, analysis the vehicle frame excitation from road and engine under the simplified model. The analysis show that only the he frequency ratio between engine excitation frequency and natural frequency of mounting system is greater than can the system isolation vibration transmission, the vibration isolation performance of the system change little when the frequency ratio is greater than5. Analysis the combustion excitation frequency、 crankshaft imbalance mass excitation frequency, the inertia force excitation frequency and vibration excitation characteristics of engine, determine the engine excitation frequency range. According to the analysis that the mounting system natural frequency range is limited between5～17.68Hz when the engine in the idle condition.Secondly, establish powertrain mounting system analysis model to calculate its inherent properties and design powertrain mounting system inherent characteristic calculation software. Establish a six degree of freedom model of powertrain mounting system, by using Lagrange equation derive powertrain mounting system vibration kinetic energy, potential energy and dissipated energy equation; obtain powertrain center location, mass, moment of inertia, product of inertia parameter through the experiment, and setup mount three-spindle stiffness values, select the mounting system for three horizontal layout.According to the arrangement of the mounting system and powertrain parameters to calculate the natural frequency and mode shapes of the mounting system, by using of the energy decoupling method to decouple the system and design calculation software in MATLAB. The calculation results show that the system in2、4、5、6modal coupling rate is higher, the z and θx direction witch have greatest effect on vibration have the low decoupling rate, and the sixth modal natural frequency is beyond the range of frequency constraints and need to optimize the design of the model.Finally, optimize the mounting system decoupling rate. Taking isotropic stiffness of mounting system as design variables, decoupling rate as the objective function, rational range of natural frequency and range of stiffness as constraint. Using multi-objective function fgoalattain in MATLAB optimize the model. The optimization results show that the six natural frequency of the powertrain mounting system layout in the constraints range frequency of2.5～17.68Hz. After optimization, the decoupling rate in each direction of mounting system reaches80%or more, especially the decoupling rate in z direction improved from79.85%to96.32%, the decoupling rate in θx direction increased from61.79%to91.22%, meet the various constraint conditions.