Power Losses Identification on Turbocharger Hydrodynamic Bearing Systems: Test and Prediction

Abstract

Design of automotive engines, with increasing focus on downsizing, high performance and low fuel emissions, provides several challenges to turbocharging technology and design. The development of a low friction rotor-bearing system is fundamental to effectively differentiate in the current environment. The exhaust gas energy from the turbine is transmitted through the bearing system to the compressor stage, and then to the engine. A lower bearing system friction allows more power to be transmitted to the compressor. This paper deals with experimental and analytical investigations for rotor-bearing system (RBS) power losses. A powerful test facility and associated experimental approach, based on the temperature drop of the gas flowing through the turbine stage, have been developed. The uncertainty due to instrumentation and process is identified as lower than 12%. The power loss related to the radial bearing is calculated analytically using the laminar Couette model; the power loss due to the axial bearing is calculated by the integration of the 2D Reynolds equation. The additional power loss between the slender shaft and inner bearing surface is calculated using a turbulent Couette model. The power loss due to the seals is not taken into account. Extensive testing in steady state condition has been completed on the test bench. Two different bearing designs with axial grooves have been tested. The influence of oil on the bearing loss has been identified by testing at two oil inlet temperatures (30 °C and 100 °C) and two oil inlet pressures (2 bars and 4 bars). The measurement and prediction of power losses are in good agreement.