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Although various factors affecting oil consumption of an internal combustion engine can be considered, a technique to predict the amount of oil consumed within a cylinder that passes across a running surface of a ring was developed in this study. In order to predict the effect of cylinder deformation on oil consumption, a simple and easy technique to calculate the oil film thickness in deformed cylinder was proposed. For this technique, the piston ring was assumed to be a straight beam, and the beam bends with ring tension, gas pressure, and oil film pressure. From the calculated oil film thickness, amount of oil passing across the running surface of the TOP ring and into the combustion chamber was calculated. The calculated results were then compared to the oil film thickness of the ring and oil consumption measured during engine operation, and their validity was confirmed.

Surface scuffing related to gas nitrided piston rings is attracting more attention as the effective cylinder pressure is increased in the recent years. However, the mechanism behind scuffing induced in long-term operations remained unknown. This study focuses on clarifying the mechanism behind scuffing related to gas nitrided piston rings. In addition, application of a thin composite plated surface film containing dispersed particles is proposed as an effective measure for preventing surface scuffing during long-term operations. Furthermore, factors enabling maintenance of high scuffing resistance on the ring surface after the thin plated composite film wears off and the underlying nitrided surface is exposed were analyzed. The dominant factor was discovered to be the difference in the resulting sliding surface profile, after initial wear, between a ring surface with composite plating and a ring surface with only gas nitriding treatment.

To obtain low friction engine through piston ring design, a set of two piston rings (two-ring set), one compression ring and one oil ring, has been recently developed. To reduce the number of compression rings from two to one, double angle step joint was employed for the shape of top ring gap, and taper face was introduced to O.D. surface shape. Major subjects of two-ring set were to reduce the oil consumption, to increase the durability, and to get the reliability of double angle step joint. The authors obtained the two piston ring design and the reliability of double angle step joint by rig tests and engine tests.

Today preservation of the global environment is an international challenge, and air pollution has attracted more concern than ever. Especially, pollution due to exhaust emission from automobiles is a serious matter, and among others, the improvement of exhaust emission is urgent. For this purpose, regulations have been tightened on exhaust emission such as particulate control and NOx control. Thus, it is essential for oil consumption of diesel engines to reduce oil consumption and employ Exhaust Gas Recirculation (EGR), and piston rings are the important key to solve these problems. This paper clarifies the effect of top rings, among piston rings, on oil consumption through engine tests and theoretical calculation of oil film thickness, and suggests techniques to reduce oil consumption.

Friction and scuff resistance of ceramic coatings (K-ramic and ion plating) for rings was studied by using a basic wear test machine. Ceramic coatings have been recently remarked for their high heat and wear resistances. Friction force under firing condition was also measured by Furuhama's movable liner method to evaluate piston ring coatings. Ceramic coatings showed lower friction force than the conventional coatings of chromium plate and molybdenum spray coat. A durability test was also conducted to evaluate the wear resistance. Ion plating has the lowest friction with excellent wear resistance, and accordingly is a promising surface treatment for piston rings.

The Furuhama's movable liner method (1)*, (2) for measuring piston friction force under firing condition has been improved. The new device can avoid the influence of gas pressure of movable liner and also the lateral deformation from the piston slap impulse force. The modified measurement device is illustrated, and then effect by test conditions - cylinder wall temperature, engine speed, and load - on piston friction force is evaluated resulting in similar conclusions to those which obtained by Furuhama et al. (3). Changing the number of piston rings, specifications of both TOP and OIL rings are discussed in terms of decreasing friction force. In the case of TOP ring, the narrower the ring width, the lower the friction force. As for its surface treatment, the gas nitriding treatment was most favorable. As for OIL ring, its tension gives more effect on friction force than its sliding width does.