This study presents an experimental analysis of a turbocharger with semi-floating ring bearings, focusing on hysteresis in subsynchronous vibrations. Four automotive oils (SAE 0W-20, SAE 0W-30, SAE 5W-30, SAE 5W-40) were tested across six oil inlet temperatures from 20 °C to 120 °C during ramp-up and ramp-down cycles to examine the effects of lubricant viscosity and temperature on rotor dynamics. Hysteresis and bifurcation points were observed at distinct rotational speeds in both directions, with subsynchronous components providing insights into rotor–lubrication interactions. This study applies the concept of hysteresis loop width for turbocharger rotors, highlighting its nonlinear dependence on oil temperature, an unexpected and unexplained phenomenon. Additionally, the results suggest that vibration sensors could provide real-time feedback on oil supply conditions, offering potential enhancements for turbochargers and other rotating machinery.

This study presents an experimental analysis of a turbocharger equipped with a semi-floating bearing system, with a particular focus on the bifurcation phenomenon within the subsynchronous vibration spectrum. A predefined design of experiments (DoE) methodology was employed to determine the measurement domains to be analyzed, where the primary input parameters included the lubricant supply temperature and pressure values. The bifurcation phenomenon in relation to the physical parameters of the system is observed via vibration and displacement sensors in two directions, enabling the collection of subsynchronous frequency data for further insights into the influence of lubricant parameters on the rotor system. While the nonlinear effect of oil temperature is well studied in the literature. However, the combined effect of oil supply temperature and pressure was not yet examined, which was the focus of the present study. This paper aims to investigate its coupled effects on the bifurcation phenomenon associated with both lubricant temperature and pressure. The occurrence of the introduced phenomenon is further examined to enhance the understanding of the uncharted behavior of turbocharger rotors and other rotor-bearing-based machinery.

This study presents an experimental analysis of a turbocharger equipped with a semi-floating bearing system, with a particular focus on the bifurcation phenomenon within the subsynchronous vibration spectrum. A predefined Design of Experiments (DoE) methodology was employed to determine the measurement domains to be analyzed, where the primary input parameters included the lubricant supply temperature and pressure values. The bifurcation phenomenon in relation to the physical parameters of the system are observed via vibration and displacement sensors in two, enabling the collection of subsynchronous frequency data for further insights into the influence of lubricant parameters on the rotor system. While the nonlinear effect of oil temperature is well studied in the literature. However the combined effect of oil supply temperature and pressure was not yet examined. This paper aims to investigate its coupled effects on the bifurcation phenomenon associated with both lubricant temperature and pressure. The occurrence of the introduced phenomenon is further examined to enhance the understanding of uncharted behavior of turbocharger rotors and other rotor-bearing-based machinery.

Lubricants significantly influence the performance and durability of internal combustion engines (ICEs), yet fresh oils seldom represent in-service conditions. To replicate realistic end-of-life scenarios, lubricants were artificially degraded in sufficient quantities for experimental investigation. This study introduces a methodology to evaluate the impact of altered lubricants on turbocharger dynamics under controlled laboratory conditions. A comparative analysis was performed on turbochargers operating with fresh and aged oils of varying compositions to establish correlations between lubricant properties and vibrational response. Particular attention was given to sub-synchronous phenomena and their implications for rotordynamic stability. Variations in damping and stiffness were assessed under constant pressure and temperature to support mathematical modeling of lubricant degradation and viscosity evolution. Experiments were conducted on a cold turbocharger test bench equipped with acceleration, speed, and displacement sensors, while a mobile oil control unit ensured precise regulation of inlet oil pressure and temperature.