Simulating thermo-hydrodynamic lubrication of turbocharger journal bearing

Abstract

The adoption of turbochargers in engine downsizing is effective to lower the CO2 emissions by internal combustion engines. However, the journal bearings, which are used to provide lubrication to the turbocharger shaft, can rotate up to 150,000 rpm. Thus, the undesirable frictional losses from this bearing system could severely affect the engine minimum speed, where low-end torque can be achieved. Therefore, as a first approximation, the study assesses the tribological characteristics of a typical turbocharger journal bearing. A thermo-hydrodynamic mathematical model is developed to simulate the journal bearing that operates between 10,000 rpm and 120,000 rpm. The model solves for the lubricant fluid film formation along the journal bearing by coupling the 2-D modified Reynolds and the 2-D energy equation. The energy equation considers convection and conduction cooling along with compressive and viscous heating. Surface flash temperatures are solved by simulating the dissipation of heat generated at the interface between the lubricant and the bounding solid through conduction cooling. The mathematical model correlates well with the measured friction power of a typical automotive turbocharger, thus, providing a fundamental numerical platform to better assess turbocharger journal bearing frictional losses that are essential in selecting/formulating suitable lubricant for turbochargers.