Abstract

Oil-engine lubricated turbochargers (TCs) operate at high temperature and must withstand large temperature gradients that produce severe thermo-mechanical stresses in the TC mechanical components. Thus, an insight into the thermal energy flows and an effective thermal management are paramount to ensure reliable TC operation. The paper analyzes the transport of energy and heat flows in semi-floating ring bearings (SFRBs) for automotive TCs with integrated heat and fluid flow models for both (turbine and compressor sides) radial bearings and thrust bearings to produce a complete thermo-hydrodynamic analysis predictive tool. The model couples the energy transport equations and the lubrication Reynolds equations in the inner and outer films of a SFRB and the adjacent thrust films to a three-dimensional heat conduction in the floating ring and along with thermal soaking into the casing. Cold lubricant, supplied at a specific temperature and pressure, flows to fill the films of the radial bearings, and then the thrust bearings. The lubricated bearings, radial and axial, support shaft loads, static and dynamic, and produce drag power losses. The streams of lubricant warm up as they take away a sizable portion of the heat flow from the hot shaft plus that due to viscous shear drag. Another fraction of thermal energy flow sinks into the floating ring which presents a distinct temperature field varying along the radial, circumferential and axial directions. The improvements in the energy transport and heat flow modeling of a SFRB system will produce significant savings in TC performance.

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