Vibration Isolation Performance Analysis And Optimization For Powertrain Mounting System

As a complicated vibration system, the vibration isolation performance of powertrain mounting system directly affects vehicle NVH peroperties. The vibration isolation performance of powertrain mounting system can be influenced by many factors, such as the mount dynamic character, the modal characteristic of mounting system, the dynamic behavior of powertrain auxiliary system, the dynamic stiffness of body skeleton and mount bracket, and so on.The mechanical property of rubber mount is between the mechanical property of perfect elastic material and perfect viscosity material, so it is depicted by the Kelvin-voigt complex stiffness model. Powertrain mounting system is not a ideal rigid body with elastic mounting system, but its analysis model can be built according to the classical vibration isolation theory, then on this basis, the influence of the body elasticity should be taken into account. Specific to actual engineering problem, the vibration acceleration of a midibus powertrain mounting system is tested. The vibration isolation performance is analysed based on the test result, and the analysis result shows that the vibration isolation performance is not so well.The modal characteristic of mounting system and the dynamic stiffness of body are analysised and optimized to improve the vibration isolation performance of the powertrain mounting system.Modal analysis includes experimental modal analysis and numerical modal analysis. The experimental modal analysis of the powertrain mounting system at the state of vehicle is carried out in LMS.test lab software. The dynamic parameters of the powertrain mounting system are tested, the dynamic mode is built and the numerical modal analysis is carried out. The modal analysis indicates the phenomenon that the powertrain first order vertical bending mode couple with engine idle incentive and the rigid mode of the powertrain mounting system does not have a suitable match.Contraposing the fact that the powertrain first order vertical bending mode couple with engine idle incentive, observing whether the powertrain mounting system vibration isolation performance is change when adjusting the powertrain first order vertical bending mode frequency through the method that adding mass to the powertrain. The experiment shows that adjusting the powertrain first order vertical bending mode frequency can improve the mounting system vibration isolation performance. According to the numerical modal analysis result, an optimization method for powertrain mounting system is put forward, with some design variables such as mount stiffness, installation position and angel, several constraints of normal frequencies, and an objective of maximizing the main vibration energy weighted sum.The influence of the mounting attaching point dynamic stiffness of BIW to the vibration isolation performance of the powertrain mounting system is deduced by means of four-end parameters method. The dynamic stiffness of BIW mounting attaching points were calculated, the rear frame was also optimized based on the dynamic stiffness calculating result. By comparing the test result of the vibration isolation performance before and after optimization, the feasibility and validity of the way that enhancing the dynamic stiffness of BIW attaching points to improve the vibration isolation performance of the mounting system are conformed.