A S tu d y on M e a s u re m e n t of C o n fo rm a b ility of th e P iston O il R in g on th e C y lin d e r Bore U n d e r E ngin e O p e ra tin g C o n d itio n by L a s e r In d u ced F lu o re s c e n c e M e th o d U sin g O p tic a l F ib e rIt is known that a cylinder-bore shape affects engine oil consumption. This study aimed clarifying the conformability of an oil-ring under engine operating condition. Oil film thickness at the sliding surface of oil-ring rails was measured by laser induced fluores cence (LIF) method using optical fiber embedded in the oil-ring. Findings showed that the piston tilting motion affected oil film thickness. Furthermore, thicker oil film was found at the following rail than that at former rail. It suggested that oil was supplied to the following rail from not only the former ring sliding surface but also somewhere, for example, the oil ring groove.

Engine oil consumption must be reduced for lowering particulate matter, deterioration of engine after treatment devices and users running cost. A lot of factors affect engine oil consumption, and it is usually estimated experimentally on very latter stage of engine development. Therefore calculation method for oil consumption which can be used for engine design is required. Supply oil volume is necessary to calculate oil consumption. In this study, oil pressure distribution under the oil ring which affects supply oil volume was measured, and a hypothesis for generating oil pressure was discussed. Oil pressure was deviated from crank case pressure and a pressure rise under the oil ring was found in the latter half of the piston down strokes. The maximum pressure was measured at the center of the piston skirt under the oil ring. It was showed that oil pressure rise could be simulated considering distribution of oil film thickness on the cylinder wall.

An increase in lubricating oil consumption in an engine causes an increase in particulate matters in exhaust gases, poisoning the catalyst of after treatment devices, abnormal combustion in a turbo-changed gasoline engine and so on. Recent trend of low friction of a piston and piston ring tends to increase in lubricating oil consumption. Therefore reducing oil consumption is required strongly. It is known that oil pressure generated under the oil ring affects lubricating oil consumption. It is also known that the position of oil drain holes affects lubricating oil consumption. In this study, the effect of the position of oil drain holes on oil pressure under the oil ring and lubricating oil consumption was investigated. The oil pressure under the oil ring is measured using fiber optic pressure sensors and pressure generation mechanisms were investigated. Lubricating oil consumption was also measured using sulfur tracer method and the effects of oil drain holes against the oil pressure under the oil ring were evaluated. Four types of arrangement of oil drain holes were tested. The oil pressure variations under the oil ring in the circumferential direction was measured using a gasoline engine. An increase in oil pressure was found during down-stroke of the piston. The lowest oil pressure was found for the piston with four oil drain holes. Two holes nearby the front / rear end of the piston skirt showed relatively lower pressure. The measured results of oil consumption showed good agreement to measured oil pressure under the oil ring. It was found that oil pressure under the oil ring affected oil consumption, and oil drain holes set near the front / rear end of the piston skirt were effective for reducing oil consumption.

Engine oil consumption causes particulate matter, poisoning of catalysts, abnormal combustion like pre-ignition in a gasoline engine, and an increase in customer’s running cost. Oil consumption, therefore, must be reduced. It is well known that pressure at a piston second land sometimes becomes larger than the cylinder pressure in the latter half of the expansion stroke. Larger pressure at the second land causes an increase in engine oil consumption. For reducing the second land pressure, increasing volume of a piston second land is one of design schemes. Pressure at a piston second land is calculated in piston design stage. In the calculation, pressure at a piston third land is assumed as same as pressure at the crankcase. This study aimed the effect of volume of the third land of a piston on engine oil consumption. The third and the second lands pressure were measured using an optical fiber type pressure sensor. It was found that the third land pressure showed a quite different trend from the crankcase pressure. It was also found that the pressure balance between the second land and the third land affected engine oil consumption. It was suggested that the third land pressure should be considered in the calculation for lands pressure of a piston and further investigation on third land design for reducing engine oil consumption may be required.

It is hypothesized that the sliding surface structures improve the lubrication condition by forming an oil sump on the sliding surface, redistributing the oil, and trapping wear debris. For these reasons, the sliding surface structures have been used as a friction reduction method for a long time. However, how to optimize the sliding surface structure is still controversial. In this work, effects of microstructure laid on the cylinder liner of an internal combustion engine on twin-land oil control ring (TLOCR) and piston skirt lubrication condition were investigated by comparing friction between the conventional fine-honed liner (CFL) and the microstructured liner (MSL) which was made based on the CFL. As a result of the friction measurement using a floating liner engine, it was found that the microstructure improved lubrication condition by reducing hydrodynamic friction. On the other hand, the result showed there was a possibility that the microstructure deteriorated friction depending on the engine operating conditions.