Dynamic Analysis Of Turbocharger Rotor System Of Floating Ring Bearing

The turbocharger rotor system with floating ring bearing is a core component and a system that is prone to failure.Its performance will have a direct impact on the turbocharger's operating efficiency,rotational performance and service life.During the operation of the floating ring bearing turbocharger,due to the randomness of the load environment and the complexity of the operating conditions,the factors affecting the stability of the rotor system are diverse,and the airflow exciting is one of the factors causing the rotor to be unstable.The turbocharger airflow exciting force is mainly derived from the sealing structure and the tip clearance airflow exciting force.Due to the high speed of the turbocharger rotor system and the light load,it is greatly affected by the airflow exciting force.Therefore,it is important to study the dynamic characteristics of the floating ring bearing turbocharger rotor system and the influence of airflow excitation on the stability of the rotor system.The main research contents and results of this paper are as follows:Firstly,according to the structural characteristics of the floating ring bearing,the dynamic model of the floating ring bearing is constructed.The dynamic eccentricity,power loss and journaling trajectory of the bearing are analyzed respectively.The Reynolds equation of the inner and outer oil film of the floating ring bearing is solved.The stiffness and damping coefficient of the inner and outer oil films were calculated,and the influence of the eccentricity and the aspect ratio of the floating ring bearing on the oil film pressure distribution was studied.The results show that with the increase of the rotational speed,the eccentricity of the journal and the eccentricity of the floating ring are gradually reduced and tend to be fixed,with an automatic centering tendency;a smaller eccentricity can be selected in the design of the floating ring bearing.The aspect ratio is to increase the end discharge flow to reduce the temperature rise of the lubricating oil,reduce the nonlinear characteristics of the oil film,and improve the running stability of the bearing.Secondly,the finite element dynamics model of the turbocharger rotor system is established.The rotor static deformation and load analysis,critical speed and mode,unbalanced response and nonlinear transient response analysis are carried out.The results show that the rotor system is greatly affected by the unbalanced mass.In order to ensure the stability of the supercharger,the critical speed should have sufficient safety margin with the rotor operating speed.With the increase of the speed,the rotor system has a linear period.Sexual motion becomes limit cycle motion.When the high speed is reached,the motion trajectory becomes complicated,and the multi-frequency vibration component can grow rapidly in a short time,which affects the stability of the rotor system.Finally,taking a certain type of floating ring bearing turbocharger for vehicles as the research object,the airflow exciting forces of sealing structure and blade tip clearance were calculated according to Alford and Black model.The finite element models considering and without considering airflow exciting forces were built.The simulation calculations of the two models were carried out,namely the critical speed,steady state response and transient response of the turbocharger rotor system.Through the comparative analysis of the two models,the results show that the airflow exciting force produces a tangential force that pushes the rotor forward whirl,resulting in an increase in the rotor system amplitude and a decrease in rotor stability.The turbulence generated by the airflow increases the rotational speed of the rotor,and the airflow exciting force of the tip clearance has a great influence on the stability of the rotor system.The research content of this paper can provide theoretical basis and technical support for turbocharger dynamics design,manufacturing,vibration control and fault diagnosis,which has important practical significance for improving the reliability and service life of turbocharger.