Effects of semi-floating ring bearing outer clearance on the subsynchronous oscillation of turbocharger rotor

Abstract

Semi-floating ring bearing(SFRB) is developed to control the vibration of turbocharger rotor. The outer clearance of SFRB affects the magnitude and frequency of nonlinear whirl motion, which is significant for the design of turbocharger. In order to explore the effects of outer clearance, a transient finite element analysis program for rotor and oil film bearing is built and validated by a published experimental case. The nonlinear dynamic behaviors of rotor-SFRB system are simulated. According to the simulation results, two representative subsynchronous oscillations excited by the two bearings respectively are discovered. As the outer clearance of SFRB increases from 24 μm to 60 μm, the low-frequency subsynchronous oscillation experiences three steps, including a strong start, a gradual recession and a combination with the other one. At the same time, the high-frequency subsynchronous oscillation starts to appear gradually, then strengthens, and finally combines. If gravity and unbalance are neglected, the combination will start starts from high rotor speed and extents to low rotor speed, just like a "zipper". It is found from the quantitative analysis that when the outer clearance increases, the vibration amplitude experiences large value firstly, then reduction, and suddenly increasing after combination. A useful design principle of SFRB outer clearance for minimum vibration amplitude is proposed: the outer clearance value should be chosen to keep the frequency of two subsynchronous oscillations clearly separated and their amplitudes close.

Literature Research on Experimental Investigations of Automotive Turbocharger Rotordynamics

“…The equivalent simplified rotor model was divided into 25 one-dimensional elements with 26 nodes. The blue section on the figure represents the aluminium alloy compressor impeller [21]. Figure 10.…”

“…Figure 10. Simplified model of the rotor of [21] The basic rotordynamic equation, which helps to specify the correct model, is the following:…”

“…Figure 11. Bearing model of [21] For a comprehensive model, the oil film model also had to be deduced. The pressure distribution in a fluid film bearing can be described by the Reynolds equation.…”

“…The research presented in this section was published in the Chinese Journal of Mechanical Engineering written by Liang Feng, Zhou Ming, and Xu Quanyong, in the School of Aerospace Engineering, Tsinghua University, Beijing in 2016 [21].…”

“…The high-frequency subsynchronous oscillations start to evolve gradually first, then their amplitudes increase, and finally the vibration modes combine. The increasing outer clearance causes a "zipper" effect to these oscillations, which means that the subsynchrons vibrations start to combine at lower speeds if the outer clearance increases [21,22,23].…”