Turbo Oil Clearance

The oil film clearance of a turbocharger refers to the small radial or axial space between the rotating shaft (turbine shaft/compressor shaft) and the bearings supporting it (such as floating bearings, ball bearings, or hydraulic bearings) within the turbocharger. This clearance is filled with lubricating oil (engine oil) during turbocharger operation, forming an oil film, hence the term ‘oil film clearances.’

The core function of the oil film clearance
The existence of the oil film clearance is one of the key design features enabling the turbocharger to operate efficiently and stably, with its core functions including:

1 : Lubrication and Friction Reduction
The turbocharger’s rotor (the turbine and compressor wheels are mounted on the same shaft) must rotate at extremely high speeds (typically 100,000 to 300,000 RPM). The engine oil in the oil film clearance forms a continuous oil film between the shaft and bearing surfaces, converting direct metal-to-metal friction into internal friction within the oil film, significantly reducing wear and heat generation.

2 : Load-bearing and stability
The high-speed rotating rotor generates centrifugal force and vibration. The oil film produces an upward supporting force through the fluid dynamic pressure effect (fluid dynamic pressure bearing principle), balancing the radial load on the rotor (such as centrifugal force). Simultaneously, the axial oil film restricts the axial movement of the rotor (such as the axial force exerted by high-temperature gases on the turbine end), ensuring smooth operation of the rotor.

3 : Heat Dissipation
During operation, the turbine end of the turbocharger comes into contact with high-temperature exhaust gases (up to 900°C or higher), transferring a significant amount of heat to the rotor. The bearing area requires effective heat dissipation. The circulating engine oil within the oil film removes heat, which is then cooled by the oil cooler to prevent bearing failure due to high temperatures.

4 : Damping and Noise Reduction
The elasticity of the oil film absorbs minor vibrations and impacts during rotor operation, reducing mechanical noise and extending bearing life.