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Decrease of engine lubricating oil consumption is necessary to reduce environmental impact. Usually oil consumption is estimated experimentally at the engine development stage, and it is expensive in terms of both time and cost. Therefore it is essential to develop its calculation method. The purposes of this study are clarifying the mechanism of engine lubricating oil consumption and developing the calculation method for the estimation of oil consumption. In this report, oil film on the piston skirt, which affected on oil volume supplied to the oil ring, was observed. Furthermore the effect of piston skirt design on oil consumption was investigated. Findings showed that the splashed oil on the cylinder liner had much effect on the oil film on the piston skirt hence oil consumption. It was suggested that the splashed oil on the cylinder liner affected on supply oil volume and it should be considered in the calculation of oil consumption.

Clarifying the mechanism of the oil consumption of engines is necessary for developing its estimation method. Oil moves upwards on the piston to the combustion chamber through ring sliding surfaces, ring backs and ring gaps. The mechanisms of oil upwards transport through the ring gaps are hardly analyzed. In this report, oil pressure just under the oil ring was successfully measured by newly developed method to clarify the oil transport mechanism at the ring gap. It was showed that the generated oil pressure pushed up the oil at the ring gap.

The necessity of the reduction of the lubricating oil consumption of diesel engines has been increasing its importance to reduce the negative effect of exhausted oil on after treatment devices for exhausted gas. The final purpose of the studies is clarifying the mechanism of the oil consumption and developing the method of its estimation. For the basic study, the mechanism of oil film generation on the piston skirt could be explained by hydrodynamic lubrication in our first and second reports [1, 2]. In this paper, the piston skirt was calculated using the measured piston motion to clarify the effect of the piston motion to the piston skirt oil film behavior.

Reduction of oil consumption of engines is required to avoid a negative effect on engine after treatment devices. Engines are required fuel economy for reduction of carbon-dioxide emission, and it is known that reduction of piston frictions is effective on fuel economy. However friction reduction of pistons sometimes causes an increase in engine oil consumption. Therefore reduction of engine oil consumption becomes important subject recently. The ultimate goal of this study is developing the estimation method of oil consumption, and the mechanism of oil upward transport at oil ring gap was investigated in this paper. Oil pressure under the oil ring lower rail was measured by newly developed apparatus. It was found that the piston slap motion and piston up and down motion affected oil pressure rise under the oil ring and oil was spouted through ring-gap by the pressure. The effect of the piston design on the oil pressure generation was also investigated.

Roller-Tappets have been adopted on the valve train systems of OHV type diesel engines, due to their low friction losses. When a roller-tappet is actuated by the cam, it moves upwards and downwards in the guide with a slight skew motion. This motion affects the life of cam and tappets. The purpose of this study was, therefore, to establish the skew estimation method. The skew motion was measured under the engine motoring condition, and its calculation based on the assumed mechanism was carried out. The calculated skew motion showed good agreement with the measured.

The requirements for emission control, lower fuel consumption and higher engine output have changed the engine valve train system to 4-valve/cylinder and higher cam lift designs, and these changes make the cam/tappet lubrication conditions more severe than before. Under such a working condition, there is a high possibility that cam/tappet surface damages such as scuffing, pitting and wear may occur. Among the damages, the wear of cam/tappet is the most difficult to predict since the wear mechanism still remains unclear. To understand the lubrication condition and therefore, the wear mechanism at the cam/tappet contact, friction was measured with a newly developed apparatus. Measurement results showed that the lubrication condition between cam and tappet is predominantly in the mixed and boundary lubrication conditions.