Polymeric Engine Bearings for Hybrid and Start Stop Applications 2012-01-1966
The implementation of legislations to ban the usage of lead as an alloying element in internal combustion engines and incrementally reducing emission output is having a fundamental impact on the design and function of half bearings. It has been witnessed that bearing operating environments are becoming more aggressive as there is a trend for manufactures to adopt various technologies and strategies such as start stop / hybrid systems, downsizing and low viscosity oils in an effort to improve fuel consumption and reduce emission output. Engine bearings normally operate under hydrodynamic lubrication, however the consequence of implementing such technologies, is that the bearings have to operate under mixed or boundary lubrication for increased durations without compromising the bearing system durability. It is considered that the commercial vehicle sector will additionally start to adopt these technologies and strategies in an effort to achieve the specified targets. To attend to this difficult aggressive operating environment MAHLE have developed a proprietary lead free polymer overlay. The foundation of the coating is a high strength, temperature and chemically resistant polymer matrix. An addition of solid lubricant, metallic fillers, adhesive promoters and specific curing regime generates the desired properties. Rig and engine test results demonstrate excellent wear and fatigue resistance performance compared to conventional uncoated bearing materials. The overlay is suitable to be applied to aluminum and copper based substrates which enables it to be utilized for a wide range of applications. The purpose of this paper is to highlight the impact on the bearing operating environment and present a lead free polymeric solution to improve the system robustness and integrity.