Modal Analysis And Structure Improvement Of Body-in-White

The body is the key to the passenger vehicle assembly,white body modal analysis can not only examine the overall body structure characteristics,but also can guide engineers to improve the body structure and conduct the response analysis.In this paper,the white body of a passenger vehicle under research is treated as the research object.Due to the unreasonable design of the white body,there exist defects in its structural characteristics.Because the first order torsional modal frequency of the body couples with the idle speed frequency,the rear seat noise is too loud to be accepted by the subjective evaluation,even leading to the rumbling problem.The problems above are analyzed by the modal analysis method in the paper,through which the following conclusions are obtained:(1)A finite element model of the white body including 494785 nodes and 485891 unit grids is established,the quality of which has passed the company's internal modeling standard.The computational modal analysis of the model is conducted to get the first six order elastic modal.The natural frequency of the second order modal corresponding to the first-order torsion vibration mode is 30.71 Hz,which is quite low.The result of the white body experiment shows that the correlation coefficients of the frequency response function are greater than 0.9,proving the high reliability of the experiment.The models of experiment and simulation are compared,the maximum error of natural frequencies is 4.4% and the models of all orders match well,verifying the accuracy of the finite element model.(2)According to the simulation and experiment results,the structural dynamic performance is evaluated.It is concluded that the first order torsional modal frequency of the body possibly couples with the idle speed frequency.By conducting the modal analysis experiment of the transverse girder of the trimmed body,it is verified that the frequency of the first order torsional modal decrease from 32.39 Hz to 26.1 Hz after installing the inner decoration parts on the trimmed body,coupling with the firing frequency of the engine at the idle speed of 750±10 r/min,which is the main reason for the large noise at the idle condition.(3)By conducting the sensitivity analysis of the first order torsional model frequency to the elastic modal of the bone pieces,the improving positions is confirmed to be the four joints of A column.Three improvement measures are decided,specifically,both the corner radius and plate thickness of the junction between A column and ceiling are increased,moreover the welding spots are increased.As a result,the first order torsional modal frequency increases from the original 32.39 Hz to 37.1 Hz,the inner ear noise value of the rear right seat reduces 3dB(A),which all meet the enterprise target and reach the same level with the benchmarking car.Based on the above content,from the modeling of the white body to the body structure improvement,a relatively complete research method is formed.Since the subject starting from the practical situation of vehicle body development,the research provides a certain reference for the improvement of the body structure dynamic performance.