Challenges Involved in Piston Top Ring Designs for Modern SI Engines

Abstract

Driven by energy conservation and environment protection, modern SI engines are required to have higher and higher power density. Consequently, engines and engine components are becoming tighter and lighter, and engines are more 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 paper is intended to give an overview of the problems associated with top ring performance in modern SI engines, the mechanisms behind these problems, and possible solutions. The analysis is based on engine test data and computer models. Major topics covered in this paper include (1) top ring flutter and collapse, and their influence on blow-by; (2) top ring reverse flutter and its influence on oil consumption; (3) contact between top ring and its groove, and its potential influence on ring/groove wear and micro-welding; (4) top ring/liner lubrication and its influence on ring face friction, wear, and scuffing.