不同模型计算动力总成刚体模态方法
Calculation of Natural Frequencies for a Powertrain Using Different Models

首先,建立了由动力总成、车身和非簧载质量组成的13自由度整车模型，推导了整车模型的运动微分方程; 然后,分别建立了车身3自由度模型、动力总成6自由度模型、车身和非簧载质量组成的7自由度平顺性分析模型及动力总成和车身组成的9自由度平顺性分析模型，给出了各简化模型的运动微分方程; 最后,分别利用上述不同自由度的模型计算并对比分析了动力总成的固有频率和能量分布、车身和非簧载质量的固有频率。计算结果表明，动力总成6自由度模型计算的动力总成固有频率与其实际频率存在差异；计算车身固有频率时需考虑动力总成的质量和转动惯量；各模型计算的非簧载质量固有频率基本一致；13自由度模型计算的动力总成、车身和非簧载质量的固有频率更加准确, 对整车振动与噪声研究具有很大的参考价值。
A 13 degrees of freedom (DOFs) model was established that includes a powertrain mounting system (PMS), a body, and four unsprung masses. In the model, the mounts in the PMS and the tires were simplified as stiffness and damping elements. The degrees for the powertrain, body and unsprung mass were 6, 3 and 4, respectively. Some widely used models were specific cases of the presented model of 13 DOFs, such as the 6 DOFs model (powertrain′s 6DOFs) for the design calculation of a PMS, the 7 DOFs model (body′s 3 DOFs and unsprung mass′s 4 DOFs) and the 9 DOFs model (powertrain′s 6 DOFs and body′s 3 DOFs) for ride analyses of a vehicle. The natural frequencies and modal energies for the powertrain in a PMS were calculated, and the results were compared and analyzed using different models. A difference in the calculated frequency and energy of the powertrain in the bounce direction was demonstrated using the mode with 6 DOFs compared to other models with 9 and 13 DOFs. The model with 6 DOFs was simple and required fewer input parameters for calculations, so it is used widely in the initial design stage of a car. The models with 7 DOFs can be used in the calculation of natural frequencies and mode energies for the body and unsprung mass.