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This study has been aimed at the reduction of the intense piston skirt friction force that appears in the expansion stroke out of all piston friction forces generated in gasoline engines. The friction characteristics at the piston skirt have been analyzed according to the measured results at piston friction forces and the shapes of wears at the piston skirt in actual engine operations. It is found from the above that the majority of the side force working on each piston is supported by the oil film on the skirt, while only some of the side force is supported by the portion in metallic contact with the cylinder. It is also found through experiments that the metallic contact portion has a great effect on the friction force at the skirt. The effect of piston posture in expansion stroke on the friction force has been also analyzed based on the measured results of piston slap motions.

The aim of this research was to analyze the lubrication conditions of piston pin boss bearings used in the press-fit piston pins of automobile gasoline engines. An original pin boss friction measuring device was developed and used to successfully obtain measurements. It was revealed that the friction force peaks twice every cycle at high engine loads, and non-fluid lubrication characteristics are displayed. The friction forces for various differing piston pins and pin boss bearings were analyzed, and it was shown that reducing piston pin length or thickness to reduce piston weight, or reducing the pin boss bearing clearance to reduce noise worsen the friction characteristics and increase the possibility of abnormal bearing friction as well as seizure.

Proposed at Musashi I.T. Engine research Laboratory in order to realize a smaller size and lower friction piston was a new piston ring parkage, which consisted of one pressure ring and one narrow single-rail oil ring. The new package has tested for two different types of gasoline engines to examine its influences on blow-by, piston temperature, piston friction and oil consumption. Efforts have been also made to improve these characteristics of the package and have resulted in its promising prospects.

A thin film thermocouple with a high accuracy was developed by means of computer analysis, which allowed measurements of instantaneous temperatures and heat fluxes on combustion chamber walls. Conventional Al-alloy and ceramic plates were compared in terms of the heat loss at the upper surface of each piston during combustion, using a gasoline engine and a diesel engine in the series of experiments. It was found by the comparison that the ceramic plates subjected to higher temperatures had greater heat losses in both the gasoline and diesel engines contrary to the anticipation.

To reduce the friction loss, the size of compression height and the weight of piston in the automobile gasoline engines, two-ring-pistons instead of usually used three-ring-pistons have been developed at many manufacturers. In many designs of piston ring arrengement, up to now, the second ring has been used for oil control not for gas sealing. And the second ring loses the sealing effect at a high speed by the ring movement in the groove. Therefore, it is expected that the trouble caused by an increase of blow-by is not large. However, an increase in thermal load caused by a decrease of the piston cooling passage and also an increase of the lubricating oil consumption are considered to be crucial problems, especially in case of high output engines. With respect to these problems, some improvement are indicated on the basis of the experiments.

Measurement of piston frictional forces during engine operation is valuable for improved fuel economy engine design. The measurement, however, is not easy work because the frictional forces are small compared with the gas and inertia forces. Several years ago, at the Musashi Institute of Technology, frictional forces were measured with a movable bore with pressure balancing. Recently, the pressure balancing devices have been improved and adapted for small engines. The piston frictional forces in a small diesel engine and a gasoline engine have been measured with the new device. The characteristics of the friction forces and the comparison between engine sizes, gasoline and diesel engines have been clarified and the effect of multi-grade oil and friction modifiers have been tested.

According to results of a number of studies made in past concerning premixed hydrogen-air engines, the problems lay in the low output, backfire and NOx emission. In addition, the necessity to reduce the fuel tank weight and volume for automobile application existed. In order to meet these requirements, Musashi Institute of Technology in Tokyo developed a method as an ideal fuel system, by inserting a small-sized LH2-pump in a LH2-tank, forcing high pressure LH2 into a low temperature and high pressure gas hydrogen container of 1ℓ or so, and injecting cold GH2 of −30 to −50°C during the first half of the compression stroke of a two-stroke engine. In this manner, two passenger cars were tried, with a 3-cylinder and 0.55ℓ engine installed in one of them and a 3-cylinder and 1.1ℓ engine installed in the other. It was demonstrated through engine dynamometer tests and on-vehicle tests on a test course that above mentioned problems could be all solved.

Under high thermal load operation, engine oil consumption was monitored using the hydrogen fuel method. Burning was detected in the piston top-land clearance, and this may be a key to understanding the carbon adhesion mechanism on the piston top-land. The following results were obtained in this study: 1. Oil consumption is greatly affected by the evaporation of oil at temperatures higher than 160°C. 2. Burning is found in top-land clearances of hydrogen, gasoline, and large clearance diesel engines. However, only weak burning could be detected in diesel engines with tight-fitting crowns.

Piston rings have significant influences on the engine performance and tribology. The effect of such rings has a delicate relation with the axial motion in the groove. By simultaneously measuring the ring motion and the gas pressure between the rings in actual operations of automobile gasoline engines and diesel ones, the authors could observe undesirable motions none has ever expected. The motions gave the engines serious problems. One was the occurrence of ring scuffing when, in a gasoline engine operation, the top and second ring lifted off simultaneously before combustion T.D.C. The other was, in a supercharged diesel engine, the time which the top ring contacts on the upper groove surface is long, which resulted in an asymmetric temperature distribution in the ring and possibility of a great oil consumption.

An L-ring (a piston ring with an L-shaped cross section) has been used on some air-cooled two-stroke gasoline engines. Good performance has been obtained; the reason is unknown. The maximum power of these small engines (used mainly for small cars, motorcycles, outboard motors, snowmobiles, etc.) is limited by its thermal load endurance. So piston and cylinder become the most important factors to the engine's performance. L-ring effects are examined in the light of these temperature measurements.