Comparison of engine body NVH predicted by different bearing calculation models

Abstract: A highly strengthened engine is the mainstream of the engine industr's future development; however, with increasing performance enhancements of the engine, the engine NVH issues will become increasingly more serious. Engine NVH problems will seriously affect the durability and comfort of the vehicle, therefore the noise and vibration reduction work of strengthening the engines is receiving more and more attention. How to solve these problems has become an important responsibility of internal combustion engine workers. As we know, reasonable analysis and diagnosis becomes the key to controlling the engine vibration and noise, so numerical analysis methods become an important means. Since current analysis models cannot meet the design requirements for high reinforcing Engine, it is necessary to improve the current method to find more accurate engine harshness (NVH) performance prediction model. According to previous research, the dynamic characteristic of bearing became crucial to predict the engine NVH performance. In order to study the effects of different bearing calculation models on engine vibration and acoustic prediction, and taking a four cylinder diesel engine as an example, the engine multi-body dynamics models coupling with HD (hydro-dynamic, HD) bearing model, EHD (elastic hydro-dynamic, EHD) bearing model, and TEHD (thermal elastic hydro-dynamic, TEHD) bearing model were respectively proposed in this paper. The maximum oil film pressure and minimum film thickness of different calculation models were analyzed at the engine rated operating conditions, and the results showed that, relative to the TEHD bearing model, the deviations of minimum film thickness and the maximum oil film pressure of the HD bearing model were -68 % and 130 %, respectively, and the deviations of minimum film thickness and the maximum oil film pressure of the EHD bearing model were 84% and -9%, respectively. These results revealed that bearing thermodynamic properties could significantly affect the bearing lubrication performance, which could not be ignored in the bearing lubrication analysis. With multi-body dynamics calculation results as the boundary condition, the engine body NVH performance was predicted. In the meantime, the surface of the engine body vibration acceleration was measured on the bench test, and the engine body radiated noise was calculated by vibration velocity method. Following this, the experimental and calculated values of the engine noise and vibration were compared to validate the calculation models. The comparison showed that the maximum vibration errors of the HD model, EHD model, and TEHD model are 7 dB, 4.5 dB, and 4.2 dB, respectively, and the maximum acoustic errors of the HD model, EHD model, and TEHD model are 13 dB, 6.1 dB, and 3.8 dBA, respectively. The results of this study showed that the bearing thermodynamic properties will not only affect the lubrication performance results, but also significantly affect the engine NVH performance prediction. After considering the elastic deformation and thermal deformation of bearing, the engine dynamics calculation model has high calculation precision in the engine vibration and noise predictions. Although the method requires more computation time, it is one of the most accurate calculation models in the main bearing force and engine noise analysis field.