Engine development, driven by environmental considerations outlined in the different emission regulations, fuel economy and fuel availability in combination with economical boundary conditions, needs new approaches in bearing material and design. Since gas engines are gaining market share and firing pressures increase in Diesel engines in order to fulfill fuel economy a special focus has also been taken to tailor-made bearings for these applications.
This complex task has to consider lining compound material strength and stability under different conditions like oil condition and dilution. Thin overlays with long term wear resistance and mixed friction capabilities as well as robust design for extraordinary events like dirt shock loading or adaptations at the engine start are necessary. To fulfill all these requirements different tasks have to be considered:
1. Bearing lining and steel shell compound to fulfill assembly requirements to combine a safe bearing seat with anti-fretting and high strength with base tribological characteristics
2. Design and use of different layers to compensate weakness of the one layer with the strength of another layer
3. Incorporation of special running conditions and cost reduction approaches in the layer design like polymer coatings for start stop and shaft designs with rougher surface finishes
4. Bearing design incorporating special shapes to cope better with deflections and geometric deficiencies of a special engine design or application
In this publication existing and new lining compound approaches including lead free designs, a variety of different overlays from electroplated, polymer and sputtered ones are briefly described. Additionally it is explained how these layers are combined and how they work together to improve bearing performance. Testing of the bearing components and designs on bearing test rigs with new test conditions considering dirt shock and misalignment and their confirmation by engine running experiences are given for a gas engine and a high speed diesel engine applications.
A special outlook on how this approach can be extended to other applications for the sake of robustness, cost reduction or performance increase will summarize the paper.