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The authors have utilized a modified engine with a transparent glass cylinder for motoring equipment. The effect of the top ring which has a special joint (triangle step joint) on the lubricating oil flow was examined. The results indicate that the lubricating oil flow is considerably reduced by utilizing the top ring with a special joint (triangle step joint) as compared to a standard joint (straight joint). We have also found that if the modified engine is operated with attention to the pressure difference between intake manifold and crankcase, or the positions of the piston ring gaps, the lubricating oil flow is reduced by utilizing a two piston ring set (where a top ring and an oil ring are set on a piston) with the top ring having a special joint and without the second ring as compared to a three piston ring set (where a top ring, a second ring and an oil ring are set on a piston) with the top ring having a standard joint and with the second ring.

The piston ring design using low tangential force to reduce friction loss has become a general trend in engine development - especially in passenger car engine - in recent years. This trend emphasizes the importance of stable sealing function that does not require much tangential force. Thus, it is important to grasp the correct pressure distribution between the ring and the cylinder. Reliable and accurate calculation to understand the pressure distribution has been an issue for many years among the engineers. In this report, we propose a new calculation method based on the piston ring contour in a free condition. Generally, the piston ring contour is calculated to achieve its correspondence to a given pressure distribution. By analyzing inversely, the pressure distribution is calculated when a ring contour is given. But as is well known, the solution is often unstable in inverse analyses. We introduced the idea of the method of least squares to avoid this problem.

Reducing engine noise of passenger cars has always been a great concern to engine manufacturers. Of late, increasing attention has been paid to the noise developed during the idling operation of engines. There are various noises that can be produced in and around engines. In conducting an analysis of engine noise, the authors focused on the noise produced during the idling of gasoline engines that employ a 3-piece piston ring. The 3-piece oil ring has been identified as a source of noise depending on the ring geometry and design employed. The noise is often made near the top and bottom dead centers with peak amplitude around frequencies of 2 to 3 kHz. The noise varies with the tension of the 3-piece oil ring and the peripheral form of the side rail. It is more likely to take place when the peripheral sliding surface of the side rail, in contact with the cylinder bore, is of a high unit pressure design.

The gas nitrided stainless steel pistoring (referred to as the gas nitrided ring in the following) was placed in mass production in 1983 to improve the durability of small diesel engines and leaded gasoline engines. Since their introduction, gas nitrided rings with their stable performance have replaced many chromium-plated rings with low durability and thermal-sprayed rings with weak coating strength. As a result of their superior wear resistance, the application of gas nitrided rings has expanded to a variety of engines1). After a steady increase in production over the past 10 years, gas nitrided rings account for more than 20 percent of the total piston ring production at our plant today. Gas nitriding contributed significantly to the change of the base piston ring material from cast iron to steel in Japan. During this period, however, requirements for piston rings have grown more sophisticated as a result of improvements in engines.

Engine manufactures are continuing to develop new engine designs that provide higher power output, lower fuel consumption and lower engine weight. In order to achieve significant engine weight reduction, the light weight cylinder block structure employs dry cylinder liners rather than wet cylinder liners. The cast iron dry liner structure is utilized because of the superior wear and scuff resistance of the cast iron. Thin wall dry cast iron liners are being employed in both gasoline and diesel engines. Dry cylinder liners with wall thickness of 1.5mm are in production for Japanese automotive diesel engines. In the case of the dry thin wall cast iron liners, two(2) design configurations are employed: Loose-fit type having a specified clearance between the outer liner surface and the cylinder bore surface. Press-in type having an interference fit between the outer surface of liner and the cylinder bore surface.

Using a modified engine with a transparent glass cylinder for motoring equipment, the effects of the structure in the vicinity of the oil ring groove drain back slots of the inside of the piston, the end clearance size of the oil ring side rail gaps and the shape of the top ring gap on the lubricating oil flow were examined. The results indicate that the amount of undesirable oil flow was reduced by utilizing a piston with the covers installed under the drain back slots on the inside of the piston, the side rails with the optimized upper and lower side rail gap size and the top ring with a special joint (triangle step joint) as compared to a standard piston and standard piston rings. Furthermore, the amount of undesirable oil flow was considerably reduced by utilizing the combination of the modified piston and rings.