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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.

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.

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.