Key to this positioning is the oil filling the clearances between the center housing bore, bearings, and shaft. This oil filled clearance is vital to a turbocharger's efficiency and longevity. The Oil Flow Schematic in Figure 10 describes how oil delivered from the engine's lubrication system is directed by ports and grooves to the journal bearings. Oil flows through the holes in the bearings to lubricate and cool the bearings, bores and shaft journals. Oil is also directed from the inlet port to the thrust bearing or through a passage in the backplate to the thrust bearing.
Oil drains from the center housing by gravity.
Seal systems separate the center housing from both the turbine and compressor stage. The seals restrict the oil from entering the compressor and turbine areas and reduce the flow of gases from those areas into the center housing. Various retaining rings and bolts secure or hold in place the rotating components. Thrust components maintain axial integrity. A shaft nut or threaded wheel is used to join the compressor wheel and the turbine wheel.