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This paper presents a further investigation into the effect of more-expansion cycle in a spark-ignition engine. On the basis of the results obtained in the previous studies, several combinations of late-closing (L.C.) of intake valve and expansion ratios were tested using a single-cylinder production engine. A large volume of intake capacity was put into the intake manifold to simulate multi-cylinder engines. With a large intake capacity, L.C. can decrease the pumping loss and thus increase the mechanical efficiency. Increasing the expansion ratio from 11 to 23.9 with L.C. application can produce about 11% improvement of thermal efficiency which was suggested to be caused by the increased cycle efficiency. The decrease of compression ratio from 11 to 5.5 gives little effect on the thermal efficiency if the expansion ratio could be kept constant.

The objective of the present study is to clarify the effect of early-closing of an intake-valve on the engine performance in a spark-ignition engine. For the first step of the study, under natural aspirating condition, four sets of expansion ratio pistons of 11, 16, 20 and 22 were prepared for two kinds of camshaft, one is, original and the other is geometrically half early-closing.. The obtained performance data and the indicator pressure records were analyzed. It was shown that up to 7 % of improvement in the thermal efficiency can be realized over a wide range of operating condition. This is considered to be mainly caused by the effect of the increased-expansion cycle. The increased-expansion effect can be estimated to be about 1.4 which almost corresponds to the geometrical inlet-valve closure timing. However, this value is not consistent with the measured volumetric efficiency which was almost half the value associated with original timing.

Variable-valve-actuation mechanism is considered to be one of the most suitable solutions to realize the compatibility between higher power output and performances in the practical speed range. A new variable-valve-actuation mechanism named “Shuttle Cam” was designed and studied. In this mechanism which was applied to a conventional motorcycle engine with rocker arms and gear-train-driven valve system, the cam gears move along the idler gear. And cam shafts simultaneously slide along the rocker-arm slipper surfaces which are concentric with the idler gear. Consequently valve lift varies continuously in accordance with the alteration in the rocker-arm lever ratio and the cam phasing changes simultaneously in accordance with the cam gear rotation. Result of the experiments has confirmed that the mechanism functions accurately even at high speeds up to 10,000 rpm and some improvements were achieved in power output, fuel consumption, idling quality, and exhaust-noise level.

In the previous reports (SAE PAPER 880268, 900223), a relationship between dimensional specifications and total engine loss (Pmf) measured by motoring method under certain conditions was established by analyzing 300 different types of mass-produced engines of which engine speed for maximum power output (Nepsmax) was obtained between 8,000 and 16,000 rpm, and thereby an empirical formula was proposed (Pmf). In this paper, it is proved that brake mean effective pressure (Pme) can be estimated by using the empirical formula for Pmf and modified indicated mean effective pressure (Pmi*) obtained from analyzing various types of motorcycle engines consisting of different cylinder configurations, valve sizes and numbers. At first, the relationship between the characteristic values of engine and Nepsmax is described, and methods to obtain higher power output by increasing engine speed are also discussed.

For the prediction of frictional mean effective pressure (Pmf), the experimental data of over 300 engines, including super high speed engines whose maximum revolutional speeds were up to 16000 rpm, were analyzed. It was found that Pmf is nearly proportional to a non-dimensional number given by piston stroke (S), mean equivalent crank diameter (Dcm) and cylinder bore (B). Its proportional constant consists of an engine speed dependent term and a constant term. We focused on the influence of pumping loss on the first term and made a tribological study on the second term. As a result of this research, regardless of cylinder configuration or maximum engine speed, Pmf can be estimated at the stage of engine designing.

Many papers are written on the frictional loss of each component in an engine, such as piston, crankshaft or bearings, but few papers describe on the total engine friction in detail. In this paper, the total engine friction is analyzed using the engine friction data of 145 HONDA mass produced motorcycle in-line engines, including single-, 2- and 4-cylinder configurations measured by the motoring method. Consequently, it is shown that the total engine friction, that is the frictional mean effective pressure (Pmf), is mainly influenced by the following dimensions; cylinder bore, piston stroke, crank pin and journal diameters. Thus the empirical equation for the total engine friction is derived, and it becomes thereby possible to reduce the total engine friction as well as to estimate it.

In this paper, the fuel consumpion and exhaust gas emission characteristics of a newly developed 1.5ℓ CVCC engine are compared with those of a conventional engine, the pressure and temperature of combustion gas in each cylinder are measured on real time in order to clarify the differences between these characteristics, arid combustion analyses are made on the basis thereof. Basically, this CVCC engine differs little from original CVCC engines, in which, however, the auxiliary combustion chamber is located closer to the center of the main combustion chamber than in original ones and torch opening is modified to be of the multi-opening type so that the torch flame spreads all over the main combustion chamber.

Through continued research on the combustion system of the stratified charge engine, we have found a new combustion system (named Branched Conduit system) which is able to further reduce exhaust emissions, HC and NOx, in particular with no adverse effect on fuel consumption under the wide range of engine operating conditions. In this paper, we describe the construction of new combustion system and its characteristics including fuel consumption and exhaust emissions. In addition, the combustion process with or without the branched conduits is examined by the time-resolved measurements of gas pressure and temperature obtained in the main combustion chamber, and observed with high-speed colored photography.

In the CVCC engine, the air-fuel mixture formation in the auxiliary and main combustion chambers immediately prior to ignition is dependent on its geometrical and operating factors. Varying of such factors, as stated in SAE Papers (1) (2), leads to considerable changes in the engine's characteristics, namely, its fuel consumption and the exhaust emissions. In this paper, we have obtained the combustion gas pressure and temperature diagrams of both main and auxiliary combustion chambers of a 1.5 litre, 4 cylinder CVCC engine and analyzed the diagrams by using the Mixture Formation Model, in order to study the characteristics of the generation of the exhaust emissions. As a result we found that the pattern of the pressure and temperature diagrams vary according to the air-fuel mixture formation and that the generation of emissions is in fact governed by the maximum combustion gas pressure and temperature, but the general tendency can also be shown by the temperature - time area ratio.

In this paper, the experimental results concerning the effect of the geometrical and operating factors of the CVCC engine on NOx emission, taking into consideration the fuel economy, are described with respect to a specific engine configuration, and they are compared with the results calculated by means of the mixture formation model. Furthermore the relationship between the NOx emission level and specific fuel consumption has been explained, and then it has been shown that the controlled combustion obtained with the CVCC engine is very effective for eliminating fuel economy penalty and reducing emissions.

This paper summarizes some of the technical considerations upon which Honda's CVCC system is based, relating to reduction of pollutants in automobile engine exhaust gases. The CVCC engine employs a stratified charge to produce stable combustion of an overall lean mixture. A unique mixture is formed immediately before ignition to reduce three pollutants (CO, HC, and NOx) simultaneously, as well as to improve fuel economy. This mixture is produced by contolling fuel mixtures supplied to the engine and by geometrical combustion chamber design features. An evaluation model conceived by Honda to evaluate emissions and fuel economy during the driving cycle mode is explained, and a comparison of estimated values obtained from the evaluation model with those obtained under actual driving test conditions is made.

Honda has produced high-speed, high-performance, 4-stroke cycle gasoline engines by applying advanced technology gained through the design and development of motorcycles and automobiles for Grand Prix racing. Some of Honda's racing engines attained performance as high as 260 bhp/liter or nearly 4.3 bhp/cu in. at speeds of up to 25,000 rpm. This paper describes our technical approach for optimizing combustion efficiency, volumetric efficiency, and mechanical efficiency-the keys to high-speed, high-performance engines.

In the small displacement, high-speed, high-performance spark ignition engines being developed by Honda, the difficulties in reducing exhaust emissions without seriously impairing inherent engine characteristics are different from those encountered with the large displacement engines generally used in American cars. This paper reports on some of research in the following areas: 1. Development of a control device to minimize exhaust emissions during the frequent accelerations and decelerations in normal driving conditions. 2. Application of the air injection reactor system in small displacement engines. 3. The effect of “squish action” in a hemispherical combustion chamber on exhaust emissions. Through research and development, many of the difficulties were overcome and satisfactory results have been obtained in exhaust emission control under certain limited operating conditions.