Improvements on Ring Pack Performance by Using PVD Coating

摘要

Technologies focusing fuel consumption and CO_2 reduction are being discussed for all car makers worldwide. For the South America it is not different and government initiatives like Inovar-Auto are being released in order to enable these solutions for the Brazilian engines. After the introduction of the flex fuel technology, Brazilian passenger car engines are starting to be exposed to other technical challenges, as the increasing of the specific power output (downsizing trend) in order to attend the legislation requirements. The consequence of that is the miniaturization of the components, followed by a more aggressive thermal-mechanical working condition, as well as the reduction of the mechanical losses. Within this environment, it is expected from the piston ring pack to cope with its functionality, to have a stable performance during its service life and extended durability. CrN-PVD is a coating largely applied to European and Japanese applications, due to its excellent tribological properties, i.e. reduced friction, higher scuffing resistance and higher wear resistance. However, regarding the Brazilian flex fuel engines, which present some special characteristics, CrN-PVD needs to have a special tuning on its recipe in order to provide suitable toughness. This paper will show the current scenario of this technology in the South American market and comparative results among CrN-PVD against the usual ring materials technologies. Attention is required on flex fuel engines and the ring pack performance regarding scuffing, wear and spalling. Particularly for oil control rings it will be presented the friction reduction potential through the application of PVD coating and the design improvements that it enables. This way, the reduction on mechanical losses would come from both material and design in order to contribute on CO_2 reduction. Different engine and rig tests are presented to support the conclusions of this paper.