A new concept of misfire detection using a wide-range oxygen sensor in a spark-ignition engine

Misfiring in spark-ignition engines can cause immediate damage to the catal yst and increase emissions since it brings unburned fuel and oxygen into th e catalyst, resulting in an increase in temperature owing to subsequent com bustion. Therefore, misfirings must be detected, as specified in the on-boa rd diagnostics (OBD) regulations. One of the common methods of misfire dete ction is to detect the fluctuation in angular velocity of the crankshaft, w hich can be misdetected under conditions of high speed and low load and und er conditions of rough road driving. An alternative method of misfire detec tion is suggested here, which utilizes the signal fluctuation of a wide-ran ge oxygen sensor installed at the confluence point in the exhaust manifold. To understand the fluctuation in the wide-range oxygen sensor signal cause d by a misfiring, the fluctuation in oxygen concentration in an exhaust man ifold was estimated by measuring the hydrocarbon concentration. The effect of the transient response of a wide-range oxygen sensor on misfire detectio n performance was also investigated. It was found that differentiation of t he sensor signal gives the criteria for misfire detection. The misfiring ca n be detected by monitoring the amplitude of the fluctuation in the differe ntiated signal, and the misfired cylinder can be identified by monitoring t he phase delay between the peak point of the differentiated signal and a re ference signal. This scheme has been shown to detect the misfiring conditio n reliably and to identify the misfiring cylinder up to an engine speed of 5000 r/min.