Development and Testing of Air Foil Bearing System for an Automotive Exhaust Gas Turbocharger

Abstract

Lubricated bearings are usually used to support and guide the shafts in gas turbines, exhaust gas turbochargers and other turbomachines. The lubricant is also used for cooling the hot parts such as the turbine side of the rotor. The high temperature condition effects a contamination of the compressed air by evaporating the lubricant. In special applications an oil-free operation has to be guaranteed. In other applications an oil lubricated bearing system prevents an immediate engine stop. The use of air foil bearings eliminates the disadvantages of the oil lubricated bearings. An air foil bearing works self-adjusting the necessary gap which depends on relative speed of the rotor and the stator surfaces and on the viscosity of the lubricating fluid. A low rotor speed requires a small bearing gap, whereas the gap must be enlarged for high speed at constant viscosity of the lubricant. An air foil bearing works contact-free in a wide speed range even at small rotation speed depending on design. On an experimental basis an air foil bearing system was developed and tested for a standard automotive exhaust gas turbocharger. The developed bearings need no infrastructure for supplying with lubricant and its cooling and filtering. The air foil bearings was calculated and designed based on the estimated bearing loads. For the manufacturing of the radial wave springs a procedure was developed. A test facility was set up for the experiments. The modified rotor works at the standard rotation speed of 80000 rpm. The bearings support and guide the shaft contact-free (without wear) in a range of a few thousands of revolutions per minute up to the standard rotation speed.