Functioning turbos for many years have used full-floating bushing-type bearings to achieve the 100k+ rpm required for higher than 2psia Boost pressures - pressurized engine oil enters the cartridge and splits into two galleries, one to each floating bearing bore - oil exits from the bushings and shaft into a central open mezzanine-type gallery - each bushing has at least two oil passages, most having 4, bored from outer to inner diameter - the floating bushing rotates @ ~1/2 shaft speed on a film of oil in the cartridge bore - the gas-turbine driven compressor drive-shaft rotates @ speed on the rotating film of oil inside the bushing - this action totally reduces oil pressure in the cartridge bore to almost nil, as the lubricating oil is thrashed into dense foam by the highly spinning bearings and shaft - thus, the steeply-angled oil-drain return-line is sized ~1" to accomodate the resultant foam, which gravity-drains from the central mezzanine area in the cartridge back down into the sump - engine oil pressure in top-side, gravity return out bottom-side - thus the importance of cartridge mounting orientation
Therein, the bushings rotate at ~50000rpm wrt the cartridge, the shaft rotates at ~50000rpm wrt the bushing, which is ~100000rpm wrt the cartridge - that method allowed the proliferation of inexpensive, functional, reliable turbochargers
Turbo compressor seals for Diesel service are labyrinthine\centrifugal, as Boost pressure prevents leaks, and Diesel engines do not develop significant vacuum levels in the intake system which would pull the oil past the shaft - the turbine seals are also labyrinthine\centrifugal, as Exhaust Gas Pressure prevents oil leaks - the turbine end also has a piston-ring type seal to prevent hot sooty exhaust gas under pressure from leaking in and carbonizing the lube oil, and the soot from contaminating the oil - reason the turbine shaft spins easy when hot, not so easy when cold, is partly because the oil film is denser when cool, providing increased resistance to shaft rotation - also, the shaft and bushings have gravity-settled on the bottom of their respective bores, which increases resistance to rotation
Some modern-tech turbos have returned to ball-bearing technology - early attempts were disastrous failures, as some were sealed\self-lubricated, said bearings soon self-destructing due to centrifugal forces slinging the lube out of the bearing races - others, lubed by pressurized engine oil, also failed where the oil was saturated with both filterable and unfilterable combustion byproducts, in addition to the primitive methods of crankcase ventilation, usually a vented brillo-filled cap on a valve-cover with an open-ended blow-by tube hanging down under the vehicle in the road-draft - that caused the wide black stain down the middle of all hiways, byways, and roadways in those eldritch times - also resulted in high silicates content in the sump oil supply - ball bearings are extremely allergic to silicates and other contaminate particles
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