Lubrication on Demand: A Novel Polymeric Bearing Coating with Oil-Filled Microcapsules

Modern High-Speed Diesel (HSD) engines place increasing demands on engine components. Specifically, for connecting rod bearings there is a requirement to endure increased peak cylinder pressures and the resulting loads transmitted through the connecting rods to the crankshaft. In addition to these high loads, the operating environment for bearings is becoming more aggressive. Reductions in oil film thickness combined with the move towards lower viscosity oils means that the seizure and wear resistance of the bearings play a crucial role in modern engine development. In order to attend to these demands, MAHLE has developed a novel high-performance polymer coating containing lubricant-filled microcapsules. The Microcapsules are designed to rupture during nascent scuff and high wear events and consequently release the contained lubricant ‘on demand’. This introduces additional lubrication when required to prevent seizure. A clear tendency for the novel polymer coating to provide improved recovery after scuffing events was measured, allowing for continuing safe operation of the bearings and thus reducing the seizure risk. Testing shows that microcapsules improved the recovery rate after seizure events to 66% whereas conventional polymer overlays show a recovery rate of 25%. As an additional benefit, the microcapsulefilled polymer coatings provide a wear improvement of more than 20% compared to current polymer bearing coatings. Simultaneously, they maintain the exceptional fatigue performance expected of polymer overlay coatings. The present paper reviews the development of the novel polymeric overlay with lubricant-filled microcapsules and details rig test as well as engine test results.