The Effect of Oil Debris in Turbocharger Journal Bearings on Subsynchronous NVH

Instances have occurred where the outer surface of turbocharger fully floating journal bearing bushings have exhibited damage from oil debris resulting in constant tone noise and subsequent warranty claims. This paper studies the effect of oil debris in Turbocharger journal bearings on Subsynchronous NVH. A CFD model is built to study the behavior of oil debris particles with different sizes. It is found that the dominant centrifugal forces prevent larger particles from reaching the inner film while smaller particles travel more easily to the inner film. It is also found that the turbine side is more likely to become damaged from debris than the compressor side bearing due to higher temperatures. A tribology analysis shows that oil debris particles in the outer film will reduce the speed ratio, while oil debris particles in inner film will increase the speed ratio. The tribology analysis also predicts the effects of oil debris on bearing stiffness and damping. These stiffness and damping effects are incorporated into a rotordynamics simulation to predict the influence on Subsynchronous NVH. Shaft tip displacements and bearing forces are predicted as a relationship to oil debris particles collected in the inner or outer film. It is found that the peak dynamic reaction forces at the bearings can increase two fold as compared to undamaged bushings and clean oil films. The predicted frequency of these Subsynchronous forces matches well with measured data taken from vehicles exhibiting offending constant tone noises whose bearing bushings were found heavily damaged from oil debris.