Robustness Optimization Of Powertrain Mounting System Based On Inverse Substructure Method

Due to the energy shortage and the call for energy saving and emission reduction,the three-cylinder engine has the advantages of low fuel consumption and small size.Many domestic automakers have begun to develop and use the three-cylinder engine.The powertrain is connected to the body through mounting system,and the vibration isolation performance of the mounting system is closely related to the NVH performance of the vehicle.Moreover,the excitation frequency of the three-cylinder engine is many and dense,so a reasonable mounting system design scheme is very important.The traditional design of mounting system only starts from the mount element itself.When establishing a multi-degree-of-freedom model,more parameters need to be obtained.The operation is cumbersome and the accuracy is low.The feasibility of the transmission path analysis is high,but the power source is removed during the operation for the purpose of decoupling,which is low efficiency.Therefore,this paper proposes a transfer path analysis method based on the inverse substructure,which combines the inverse substructure method with OPAX parameterized modeling to overcome the drawbacks of removing the excitation source in the previous TPA analysis process.In the subsequent optimization process,the uncertainty of the parameters is taken into account,and the design variables and parameter variables are described through the probability interval model,and the suspension system is designed robustly.First,the theoretical knowledge of the transfer path is explained,and the traditional TPA,fast TPA,multi-level TPA and OPAX are introduced.It focuses on the analysis of OPAX theory and parametric modeling steps,and derives the parametric formulas for the elastic elements of the single-free model and the multi-bandwidth model.Then the inverse sub-structure analysis method is derived,and the substructure frequency response function of the single-coupling degree of freedom system and the multicoupling degree of freedom system and the dynamic stiffness of the connecting element at the coupling are derived theoretically.Combining the inverse substructure method with OPAX parametric modeling,proposes a transfer path analysis method based on inverse substructure,and introduces its analysis process.Then,taking a passenger car equipped with a three-cylinder engine as the target vehicle,an OPAX analysis model of the vehicle structure vibration was established,and the experimental requirements and experimental equipment were briefly described.In the vehicle idling condition and speed-up condition,the vibration level of the vehicle is evaluated and analyzed through spectrum analysis and order tracking technology.Data collection of engine signals,input points and response points is carried out,and OPAX parameterized model is established through a single free model.Based on the inverse substructure method,the substructure level frequency response function is obtained through the system level frequency response function,and compared with the frequency response function obtained by the direct method test to verify the accuracy of the frequency response function calculation.The calculated sub-structure frequency response function is combined with the established OPAX parameterized model to identify the load.Finally,the contribution is calculated,and the number of main contribution paths is counted to determine the critical path,which points out the direction for the subsequent optimization design.In the process of optimizing the mounting system,the benchmark car and the target vehicle are selected for benchmarking test to determine the NVH problem of the target vehicle.Aiming at the multiobjective problem of the system,the determination of the objective function,the selection of design variables and the selection of constraint conditions are introduced in detail.Finally,the system is optimized by the non-dominated genetic algorithm,and the decoupling rate and support before and after optimization are compared.The reaction force and the response in the vehicle can be known,and multiobjective optimization can meet the design requirements.Next,the robustness analysis method is introduced,and the probability-interval model is introduced to describe the uncertainty of the variables.The 6 Sigma robust optimization method is used to optimize the design,and the reliability of the two design schemes is compared to verify the reliability of the robustness design of the mounting system is higher than multi-objective optimization.Finally,the required robustness optimization plan is verified on the actual vehicle,and the sample of mount is made from the calculated stiffness parameters,and the idle speed condition and the third gear acceleration condition are selected for research.From the test analyzes the optimization effect of the mounting system and compares it with the benchmark car.The result shows that the optimization of the mounting system is beneficial to improve the NVH characteristics.