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While the restriction on exhaust emission as an environmental measure has been reinforced more than ever, the demands for high power for engines are escalating. The technology corresponding to these demands in the engine management system for motorcycles is being developed under such a situation. With the changing from carburetors system to electronic fuel injection system, various devices are installed; it can be said that technology for engine management system control has advanced remarkably these days. As for the microcomputer within the ECU that controls the system, microcomputer installed in ignition units had only 8 bits and the capacity of ROM was about 16 kB in 1990, but the microcomputer installed in fuel injection units is so efficient that it has 32 bits and the capacity of ROM is increased up to 256 kB in 2004.

An in-vehicle detecting system, which directly monitors the combustion condition in each cylinder by detecting the ionic current generated in the vicinity of combustion flame surface in the internal combustion engine, has been developed for engine control. This system comprises the existing ignition plug employed as an ion probe, an additional ignition coil added with electronic components for the detection, and a detection module to process the ionic current and to provide the engine management system with various information indicating the combustion condition. This system allows the judgment of misfire or normal combustion in the overall engine driving conditions and the detection of knocking level in each cylinder. Furthermore, the development is now under way for practically driving the engine drive with leaner mixture, namely, the control of air fuel ratio in each cylinder through the information based on this ionic current indicating the combustion condition.

An in-vehicle detecting apparatus has been developed which detects an ion current to monitor the combustion condition of each cylinder of the spark ignition internal combustion engine. This apparatus uses the spark plug electrode as an ion probe, and applies, as bias power, a very low ignition energy accumulated in the ignition coil. Thus it has the feature of requiring no particular modification on the engine side except a minor revision of the ignition system and addition of a detection module. This paper presents the construction and operation of this detection apparatus; in-engine evaluation and consideration on misfire and knocking level detecting performance; and consideration on effects of various factors on ion current values detected. In addition, data on the possibility of detecting an air-fuel ratio is reported.