Engine cylinder deactivation is used to save engine pumping loss but raises oil consumption concerns for the deactivated cylinders. In this paper, general mechanisms of oil transport via piston rings are reviewed. The characteristic of oil transport and oil accumulation in a cylinder deactivation mode through the piston ring path are analyzed. Suggestions to reduce the oil transport to the combustion chamber in a deactivated cylinder are discussed.
In a deactivated cylinder, the amount of oil brought into the combustion chamber by the top ring up-scraping due to the ring/bore conformability difference between intake stroke and compression stroke is much less compared to a firing cylinder. However, compared to a firing cylinder, a deactivated cylinder has more oil entering the combustion chamber through the top ring end gap and ring groove as a result of the lower cylinder gas pressure, lower ring temperature and more frequent top ring axial movements. Suggestions are given to reduce the net upward oil transport in a deactivated cylinder, including reducing the ring/groove clearances and the sizes of the ring gaps and drain-holes, reducing cylinder bore distortion, designing structures of the piston-lands and the oil drain-holes to enhance downward oil flow and restrict upward oil flow, reducing or eliminating positive static twist of the top ring, and limiting the overall oil supply from the bottom of the piston.