Mapping Temperatures on Turbocharger Bearing Cartridge Assemblies Using Thermal History Paints

In this study, temperatures were mapped on four off turbocharger bearing cartridges, each subject to four different gas-stand tests using Thermal History Paints (THPs). The temperature maps were used to inform initial axial end play settings (and resulting mounted end play) for proper turbocharger performance. THPs are ceramic-derived sensor coatings doped with a lanthanide ion, giving the THP luminescent properties. Exposure to temperatures permanently alters the THP’s luminescent properties. Therefore, by optically probing the THP across the painted bearing cartridge surfaces to trigger its luminescence, historic maximum exposure temperatures maps were evaluated. Each gas stand test was devised to test each cartridge to the most severe temperature conditions the turbocharger was expected to be exposed to, including one with a heat-soak without water cooling. The tests lasted at least 15 minutes to ensure the cartridge assemblies were fully heat-soaked. THP measurements were taken across pre-determined surfaces of the inner rings and outer ring of all cartridge assemblies. The THP measurement point pitch was 1 mm, providing a unique insight into the historic thermal maps across the cartridge surfaces. The THP temperature mapping had excellent coverage across each cartridge assembly surface. Some THP detachment occurred, especially on the edges of the inner and outer rings and close to the bearing racers. The THP was especially manufactured for this project to measure lower temperatures (< 200 °C), but this was at the expense of THP durability and adherence. As expected from the thermal profile of a turbocharger, the turbine-side inner ring was the hottest for all cartridge assemblies. The compressor side inner ring, and outer ring were the coolest. Notably, the outer ring temperature gradient was low, providing confidence in the overall cooling conditions of the cartridge assemblies. The end play of the turbocharger is driven more by the thermal expansion of the outer ring rather than the inner ring. As such, knowledge that it remains cool throughout the test helps inform setting the most appropriate axial end-play clearance.