Study of Turbocharger Fully Floating Hydrodynamic Bearing Oil Whirl Behavior—Test and Prediction

Automotive engines are facing increased design focus toward downsizing, higher performance and lower emissions, in the process challenging turbocharger technology to their limits. The exhaust-driven turbine energy must transmit to the compressor stage with minimal losses through the bearing system. In general, two types of bearings are used in turbocharger applications, namely semi-floating rotary bearings (SFRB) and fully floating rotary bearing (RFRB) system. In the latter, bearing is suspended in the lubricant, and by virtue of its rotational speed, brings down the angular speed of the fluid in the clearances between the shaft and the bearings. The ring rotates in the range from 0.25 to 0.4 times the shaft speed, and as a result has a positive effect on lubricant drag. On the other hand, this bearing system now has two spinning oil films and has to sustain the dual self-excited oil whirl vibrations in the inner and outer clearances that have a reciprocal influence on each other. The final evaluation calls for application specific validation either on the respective engine or vehicle system, as the system peripherals could resonate at the same frequencies and amplify these waves. This work describes the oil whirl-related sub-synchronous investigations of the RFRB on turbochargers. A brief theoretical explanation followed by numerical rotor dynamic simulations on two bearing designs using AVL Excite simulation tool is discussed, and thus, obtained results are later validated through tests at the turbocharger sub-system-level evaluations on gas stand.