Radial bearing system
With a sleeve bearing, the shaft turns without friction on an oil film in the sleeve bearing bushing. For the turbocharger, the oil supply comes from the engine oil circuit. The bearing system is designed such that brass floating bushings, rotating at about half shaft speed, are situated between the stationary centre housing and the rotating shaft. This allows these high speed bearings to be adapted such that there is no metal contact between shaft and bearings at any of the operating points. Besides the lubricating function, the oil film in the bearing clearances also has a damping function, which contributes to the stability of the shaft and turbine wheel assembly. The hydrodynamic load-carrying capacity and the bearing damping characteristics are optimised by the clearances. The lubricating oil thickness for the inner clearances is therefore selected with respect to the bearing strength, whereas the outer clearances are designed with regard to the bearing damping. The bearing clearances are only a few hundredths of a millimetre.
The one-piece bearing system is a special form of a sleeve bearing system. The shaft turns within a stationary bushing, which is oil scavenged from the outside. The outer bearing clearance can be designed specifically for the bearing damping, as no rotation takes place.