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1 We have developed an in–vehicle detection system that can directly monitor the combustion conditions of individual cylinders by detecting the ions produced near to the combustion flame surface as an electric current and applying the derived data to engine management. This system consists of existing ignition plugs used as ion probes, ignition coils with additional electronic parts for the detection, and a detection module which processes the ionic current signals, and yields various information to inform the engine control system of combustion conditions. This detection system can discriminate between misfires and normal combustion over a wide operation range of an engine, and detect the knocking level by cylinder.

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.