The continuous focus on improving engine efficiency and fulfilling new emissions legislations in high speed large bore (HSLB) applications is demanding higher performance of cylinder power cell. Regarding piston rings, this can be translated into the need for increased wear and scuff resistance in conjunction with low friction. However, there is no room to jeopardize the engine performance in terms of lube oil control and combustion gas sealing (i.e. blow-by).
The reduction in ring friction is linked with three main factors: reduction of ring tangential load, reduction of ring axial width and use of low friction coefficient materials. To enable load and axial width reduction the use of a steel ring pack becomes almost mandatory. The structural strength of steel is needed in the narrower cross-section which at the same time requires good resistance to temperature and loads. For better wear resistance and lower friction coefficient the use of improved materials is important on all three rings in the pack. The improved performance of nitriding treatment and CrN PVD coatings will be presented.
Results indicate a potential ring friction reduction of more than 30% combined with wear improvements of up to 50% depending on the engine operation. Evaluations of rig and engine tests are presented supporting the technical case.