Misfire detection system based on the measurement of crankshaft angular velocity

Misfire detection systems are becoming increasingly important in automotive market due to recent environmental issues (Euro rules). An early misfire diagnosis also allows to prevent damages to the exhaust emission system and consequent costs for the user. Today few low cost methods exists in order to precisely detect single misfires in real time, the majority in fact require the use of expensive sensors (e.g. pressure sensors) or dedicated circuits (e.g. ionization current sensing). This work describes a method and electronic system capable of detecting misfires with good accuracy, using parameters such as the speed sensor signal, already available in commercial engines. The proposed method is exclusively based on the real time analysis of the crankshaft angular velocity and its variations. This is possible since each misfire event generates an abrupt perturbation of the crankshaft angular velocity, that can be detected using an appropriate signal processing algorithm.