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This study deals with reduced-order modeling of intake air dynamics in single-cylinder four-stroke naturally-aspirated spark-ignited engines without surge tanks. It provides an approximate calculation method for embedded micro computers to estimate intake manifold pressures in real time. The calculation method is also applicable to multi-cylinder engines with individual throttle bodies since the engines can be equated with parallelization of the single-cylinder engines. In this paper, we illustrate the intake air dynamics, describe a method to estimate the intake manifold pressures, and show experimental results of the method.

Attempts have been made to develop an electronically controlled fuel injection system that is ideal for small motorcycles, cost-efficient, compact, and electric power-saving while maintaining accuracy. For reducing the number of sensors and cost, highly accurate methods have been developed for the measurement of intake air mass, detection of acceleration, distinction of engine stroke, and estimation of atmospheric pressure without using a throttle position sensor, cam timing sensor, and barometric sensor in such a manner as to carry out sampling with the intake manifold pressure of single-cylinder engines synchronizing with the crank angle. For compactness and electric power saving, an injector and in-tank fuel pump module have been developed for small motorcycles.

The specific output of 4-cycle engines are generally smaller than that of 2-cycle engines. Increasing engine speed is one method to improve the specific output, however, it contains some disadvantages in application. Hence, improvement in torque with the 4-cycle engine is desirable. Although torque could be improved by super-charging, it seems difficult to apply existing systems for small displacement engines due to problems of their size and cost. We have, therefore, newly developed a super-charging system named Advanced Crankcase Super Charge (hereinafter referred to as ACSC) using a crankcase as a supercharger. In this study, we made a 50cc single cylinder prototype engine with ACSC and carried out the engine unit tests and actual running tests on a scooter. From these tests, the torque that is twice as that of the naturally aspirated engine was obtained.