The Effect of Thermal Energy Transport on the Performance of (SEMI) Floating Ring Bearing Systems for Turbochargers

Abstract

The thesis studies the effect of thermal energy flows on the performance of an oil lubricated (semi) floating ring bearing used in a passenger vehicle turbocharger. The model of the inner and outer fluid film flows in the floating bearing fully considers the thermal energy flows in the bearing system with a source from the hot shaft and drag power dissipation in both films. Implementation of the finite element method and the control volume method gives the solution of the heat conduction equation for the ring and the thermal energy transport equations for both films, respectively.

The developed numerical tool (XLBRG_TH®) is validated by comparison of predictions for the inner film pressure and temperature distributions against archival test data for a journal bearing with two supply grooves. The tool is next used to analyze the performance characteristics of a (semi) floating ring bearing in a turbocharger application, as well as the effects of some physical and operating parameters on the performance.

The results show that the inner film flow carries the largest fraction of thermal energy produced by shear drag power losses and heat flowing from the hot shaft. Lower oil supply temperature results in a larger heat flowing from the shaft but slightly influences the drag power loss. Either higher supply pressure or a larger film clearance promotes flow rate through the film region and then raises the heat flow from the hot journal and the drag power loss. Since the thermal energy from the hot shaft into the film is overwhelming, a higher shaft temperature raises the peak and average temperatures of the inner film and thus causes the oil viscosity to increase which reduces the drag power loss. Either additional or larger axial grooves on the inner side of the FRB can increase the flow rate and increase the heat flow from shaft. However, the drag power loss decreases with a wider groove because of the reduction in film area but increase with a deeper groove for a larger oil viscosity.