Stiffness Characteristics Of Ball Bearing Turbocharger And Influence On The Rotor Dynamic Characteristics

In recent years, with the development of high strength and light weight on the turbocharger, the application of hybrid ceramic ball bearing with higher mechanical efficiency instead of the traditional floating bearing has become a developing direction. There is a big difference on the high-speed working state between the dynamic characteristics of the ball bearing rotor system and the floating bearing rotor system, so it is necessary to analyze the dynamic characteristics of the ball bearing rotor system of turbocharger. In this paper, the dynamic model of the ball bearing rotor system of turbocharger is established, the stiffness of the ball bearing turbocharger and the influence of the dynamic characteristics of the rotor system are studied, the main research contents are as followsFirst, the dynamic model of ball bearing rotor system of turbocharger which only considering the bearing stiffness is established, and the dynamic characteristics of the rotor are analyzed. The correctness of the model is verified by comparing with the experimental results. On the basis of this, the dynamic stiffness of sealing structure and the air flow are added, and the coupling model is established, the results show that: the calculated critical speed of the coupling model is closer to the test value; the difference of the transient response is very small; the peak of the amplitude of the steady state response and the acceleration are decreased, and the stability of the system is promoted.Then, because the bearing stiffness of the bearing rotor system has an important impact on the rotor dynamic characteristics, key research on bearing stiffness is done. The static method of hertz theory is applied to calculate the bearing stiffness considering the bearing load, and the calculated values are added into the coupling model to analyze the dynamic characteristics of the bearing. The results show that the computed values of two order critical speed is more close to the test value; the change of the amplitude of the transient response is small; the effect of the amplitude and acceleration of the system is very great. Further, the application of the pseudo dynamic method is used to calculate the nonlinear bearing stiffness curve with the change of speed. A nonlinear bearing stiffness coupling model is established, the results show that the difference of the critical speed between the nonlinear bearing stiffness coupling model and the experimental values are only 0.19% and 0.59%; the maximum amplitude of the transient response is obvious; in the steady state, the changing trend of the amplitude and acceleration is basically the same, and the variation range is large; in the steady state, the peak amplitude of the first order critical speed is shifted.Finally, a comprehensive analysis is carried out throughout the linear bearing stiffness coupling model, the linear bearing stiffness coupling model considering the bearing load and the nonlinear bearing stiffness coupling model. The results show that the critical values calculated by the nonlinear bearing stiffness coupling model are the most close to the experimental values. In the engineering calculation, if the steady state response is considered, the calculation of bearing stiffness can be calculated by using the Hertz theory. The simulation results have reference value and it saves time. If the transient response is considered, the simulation analysis of the dynamic nonlinear bearing stiffness can be carried out by using the method of pseudo dynamic response.