Challenges involved in piston top ring designs for modern SI engines

Driven by energy conservation and environment protection, modern SI engines are required to have higher and higher power density. Consequently, engine s and engine components are becoming tighter and lighter; and engines are m ore often operated at elevated speed and component temperature. Piston and piston ring designs thus face constant challenge to provide proper control of blow-by, oil consumption, friction, wear, and oil consumption. This pape r is intended to give art overview of the problems associated with top ring performance in modern SI engines, the mechanisms behind these problems, an d possible solutions. The analysis is based on engine test data and compute r models. Major topics covered in this paper include (1) top ring flutter a nd collapse, and their influence on blow-by; (2) top ring reverse flutter a nd its influence on oil consumption; (3) contact between top ring and its g roove, and its potential influence on ring/groove, wear and micro-welding; (4) top ring/liner lubrication and its influence on ring face friction, wea r, and scuffing.