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This paper describes a measurement method using laser induced fluorescence we have developed for simple simultaneous measurements of piston ring oil film thickness at plural points for internal combustion engines. The findings obtained by the measurements of oil film thickness on both thrust and anti-thrust sides of the piston for a mono-cylinder compact diesel engine using this new measurement method are also discussed in this paper. One of main findings is that the oil film thickness of each ring on both sides differs markedly in terms of the absolute value and the stroke- to-stroke variation. It is found that this difference in oil film thickness is caused by the difference in the amount of lubricating oil supplied to the oil ring, and the effect is greater than that of engine speed or load.

Automobile engines have undergone continuous improvements over the years in terms of higher output, lower pollutant emission, and lower fuel consumption. With recent steep rise in crude oil price, consumer interest in fuel economy of automobiles has increased. With such interest, lowering fuel consumption appears to be the issue that currently needs to be tackled. The piston ring and piston friction were measured with floating liner, we confirmed that wear of piston ring running surface influenced friction. It was confirmed by this study that main cause of break in is decrease in liner surface roughness and piston ring OD wear. Additionally, this paper indicated that friction decreased by preventing piston ring OD wear in the process of break in.

Three exhaust emissions, hydrocarbons, carbon monoxide and oxides of nitrogen, from the automotive spark-ignition engines are presently subject to regulatory control. Of these harmful pollutants, NOx emissions are the hardest to control under current status of emission control technology. Accordingly, exhaust gas recirculation (EGR) has been receiving continued efforts as one of promising NOx control. This paper reports the effects of EGR on the mechanism of NOx reduction and engine fuel economy, on the basis of research made in the following areas: (1). NOx formation in a combustion vessel. (2). Studies on EGR effects in a single-cylinder engine. (3). Effects of EGR on NOx and HC emissions and fuel economy.

By observation through a glass window, the effect of side surface sealing ability of piston ring on the increase of oil consumption for light load and at medium engine speed range was confirmed. In each engine stroke, effects of ring motion on oil consumption were predicted by simulation and the flow of oil around piston ring was observed during actual firing engine operation through a visualization window with a test engine. Importance of the side surface sealing ability of piston ring on oil consumption and effect of small width top ring with positive twist for second ring collapse were reconfirmed.

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.

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.

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.

The relationship between piston ring and out side of diameter (hereon referred to as OD) wear of ring has not been fully analyzed. In this study, the relationship between the ring OD wear and ring friction force during the break-in period, where ring OD wear occurs in a short period of time, was analyzed. After 20 hours of firing test, Friction mean effective Pressure (hereon referred to as FMEP) of nitrided ring having OD wear was 1.6kPa higher than that of Physical Vapor Deposition (hereon referred to as PVD) ring having little amount of wear (hereon referred to as “no OD wear”). In addition, lubricating condition of piston system during break-in period was also analyzed in this study. When plateau-honing cylinder was used, the FMEP showed an increasing trend over a 20-hour period of firing test. The cause of this increasing trend is the deterioration of lubricating condition of the piston skirt.

As vehicle emission regulations become increasingly rigorous, the automotive industry is accelerating the development of electrified vehicle platforms such as Battery Electric Vehicles (BEV) and Plug-in Hybrid Electric Vehicles (PHEV). Since the available waste heat from these vehicles is limited, additional heat sources such as electric heaters are needed for cabin heating operation. The use of a heat pump system is one of the solutions to improve EV driving range at cold ambient conditions. In this study, an efficient gas-injection heat pump system has been developed, which achieves high cabin heating performance at low ambient temperature and dehumidification operation without the assistance of electric heaters in ’17 model year Prius Prime.

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.

A recent increase in detergent additives to gasoline has resulted in an increase in the accumulation of deposits inside the engine's combustion chamber (this type of deposit will be hereinafter referred to as “CCD”;Combustion Chamber Deposit). Along with this tendency, authors have observed an engine noise generated during warm up, which may be attributable to the CCD accumulation. It was reported that the engine noise was identified as carbon knocking caused when the piston and cylinder head physically come in contact because of these CCDs(1X2) This paper deals with another noise generated by the CCD trapped between the piston ring and piston ring groove.

To reduce the oil consumption in diesel engines, the combination of top ring gap clearance (C1) and second ring gap clearance (C2) (ring gap balance) was applied. The effect of the ring gap balance on piston ring axial motion and second land pressure was observed and factors to control oil consumption were analyzed. The authors obtained a technique to reduce oil consumption by decreasing second land pressure and thus making second ring liable to lift off. Blow up gas was significantly concerned about oil consumption of blow-by gas.

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.

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.

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.

It is well known that lubricating oil consumption (LOC) is much affected by the cylinder bore deformation occurring within internal combustion engines. There are few analytical reports, however, of this relationship within internal combustion engines in operation. This study was aimed at clarifying the relationship between cylinder bore deformation and LOC, using a conventional in-line four-cylinder gasoline engine. The rotary piston method developed by the author et al. was used to measure the cylinder bore deformation of the engine’s cylinder #3 and cylinder #4. In addition, the sulfur tracer method was applied to measure LOC of each cylinder. LOC was also measured by changing ring tension with a view to taking up for discussion how piston ring conforms to cylinder, and how such conformability affects LOC. Their measured results were such that the cylinder bore deformation was small in the low engine load area and large in the high engine load area.