Design And Experimental Study Of An Oil Free Turbocharger

Gas foil bearings(GFBs) are self-acting compliant-surface hydrodynamic bearings that use ambient air(or any process gas) as their working fluid or lubricant. With this type of bearing, turbochargers can become oil free, thus getting rid of the speed limitation and power loss imposed by oil lubrication, eliminating oil leakage entirely and reducing the complexity of the whole system. However, there is little research focusing on the manufacture, performance test and application of GFBs in China. In this dissertation, GFBs are tried to be applied to a turbocharger, design principles and performance test procedure of oil free turbo machi nery are tried to be estabilshed. The main contents of this dissertation are as follows:A certain type of turbocharger was chosen to replace its floating ring bearings by GFBs. Modification of the rotor system, bearing housing and turbine housing has been done to accomplish bearing replacement.Both the journal foil bearings and thrust foil bearings were carefully designed and their performances were predicted. Besides, the rotordynamic performance of the whole rotor system was also predicted. Calculation results show that the load capacity of designed foil bearings is fairly enough and the critical speeds of the rotor system are out of the operating speed range of turbocharger. A rap test was done to measure the natural frequencies of the rotor system.Based on previous experience on journal foil bearings, the manufacturing method of thrust foil bearings were established. Two journal foil bearings and two thrust foil bearings have been manufactured and a layer of solid lubricant has been coated on the surface of top foils.Test rigs were built for journal foil bearings and thrust foil bearings separately to test their performance. Experimental results show that journal foil bearings lift off at the speed of 11,000 rpm with a small temperature rise during the whole test process. Load-deflection curve of the foils of thrust foil bearings show a nonlinear stiffness. Besides, some hysteresis can also be seen.A prototype of oil free turbocharger is built. After 3 tests, both journal foil bearings are found damaged, while thrust foil bearings are as good as before. Test results show that the temperature of top foil is a reliable signal that can tell whether the foil bearings work well, and the designed thrust foil bearing has enough load capacity to withstand the axial load during the whole operation process of the turbocharger. Finally, the possible causes that damage the journal foil bearings are discussed.