Thrust Bearing in Large Medium Speed Diesel Engine Turbochargers:
(a) Why a Thrust Bearing is Needed:
A thrust bearing is a crucial component within a large medium-speed diesel engine turbocharger for managing axial forces acting on the shaft. Here’s why it’s necessary:
- Opposing Axial Forces: During operation, the turbine and compressor blades in the turbocharger generate opposing axial forces along the shaft.
- Turbine: The exhaust gas pushing on the turbine blades creates a force trying to push the shaft towards the exhaust side.
- Compressor: The compressed air pushing on the compressor blades creates a force trying to push the shaft in the opposite direction.
- Axial Force Management: The thrust bearing absorbs these opposing axial forces, ensuring the shaft remains properly positioned within the housing. This prevents excessive axial movement that could lead to:
- Inefficient Operation: Misalignment due to uncontrolled axial movement could hinder proper operation of the turbine and compressor wheels.
- Increased Friction Losses: Excessive axial movement might cause the shaft to rub against the housing, increasing friction and reducing efficiency.
- Potential Damage: Uncontrolled axial movement could lead to contact and wear between the shaft and housing, potentially damaging the turbocharger.
(b) Where the Thrust Bearing is Fitted:
The thrust bearing is typically located on the compressor side of the turbocharger shaft within the housing. This placement allows it to effectively counter the axial force generated by the turbine on the opposite end. The exact location may vary slightly depending on the specific turbocharger design.
(c) How the Thrust Bearing is Lubricated:
The thrust bearing relies on the engine’s pressurized lubrication system for proper operation:
- Engine Oil Supply: Engine oil is continuously circulated through dedicated passages within the turbocharger housing.
- Oil Reaches Bearing: Channels within the housing deliver oil to the thrust bearing surfaces.
- Hydrodynamic Lubrication: The pressurized oil creates a thin film between the bearing surfaces, separating the shaft from the housing. This film minimizes friction and allows for smooth, low-friction rotation of the shaft while absorbing the axial forces.
- Oil Return: Used oil from the thrust bearing drains back to the engine’s crankcase through a return line, where it re-enters the lubrication system for filtration and further cooling.
Maintaining a healthy engine oil system with clean oil and proper oil pressure is crucial for optimal lubrication of the thrust bearing and overall turbocharger health.