| With the execution of the policy"lower energy consumption and reduce pollutants discharge"and"to build a harmonious society", the vehicle NVH performance has been paid more attention. Powertrain is the main excitation source of the vibration and noise, especially for the traditional internal combustion engine, every cylinder's gas force leads to broad frequency scope of powertrain excitation, at the same time, multiple action of every cylinder in a engine work cycle and imbalance etc will invite high excitation force in a certain frequencies, if the structure of connection between the engine and transmission is unreasonable, resonance will occur while the powertain works, then the whole vehicle's NVH performance should be worse, and there will be potential crack in flywheel housing and rear part of the engine block, all of this lower the reliability performance of the whole vehicle. So in the development of the powertrain, the study on forecast of the powertrain's elastic modal and verification of the latest production's modal performance is very necessary.This thesis reach the target through the study on FE model building and modal analysis, elastic modal test and powertrain ODS analysis. The FE model could be built by tetrahedron and hexahedron, HyperMesh software satisfy the requirement of preprocess, but in reality, 3D data of transmission inner part is not available, in this part, the thesis focus on how to solve the model building problem by concentrated mass and satisfy the calculation precision.Aim to identify accurately the modal of the powertrain, it is important to set the boundary condition properly to avoid the influence to test result, and satisfy the free to free condition in calculation, the thesis use the LSCF method to do the modal test according to the damping and modal character of the powertrain.The thesis adopt the ODS analysis to verify that powertrain modal frequency is reasonable or not, generally, the lowest frequency of overall bending modes and torsional modes should be higher 20% than the engine main excitation frequency, but the connection stiffness could not be increasing infinitely in reality, so this thesis use ODS to do the response analysis, consider the relationship between the excitation force, damping, modal frequency and real response, take both the modes and response into account to guarantee the production quality by possible structure design.This thesis based on real engineering problem, not only study the CAE and test theory, but also pay more attention on practical using of study fruit, theory and production bonds closely, realize the study on the powertrain's elastic modes forecast, modal identification, performance acceptance, got the good effect, improve the production quality. |
