Abstract
Abstract
Misfiring in spark-ignition engines can cause immediate damage to the catalyst and increase emissions since it brings unburned fuel and oxygen into the catalyst, resulting in an increase in temperature owing to subsequent combustion. Therefore, misfirings must be detected, as specified in the on-board diagnostics (OBD) regulations. One of the common methods of misfire detection is to detect the fluctuation in angular velocity of the crankshaft, which can be misdetected under conditions of high speed and low load and under conditions of rough road driving. An alternative method of misfire detection is suggested here, which utilizes the signal fluctuation of a wide-range oxygen sensor installed at the confluence point in the exhaust manifold. To understand the fluctuation in the wide-range oxygen sensor signal caused by a misfiring, the fluctuation in oxygen concentration in an exhaust manifold was estimated by measuring the hydrocarbon concentration. The effect of the transient response of a wide-range oxygen sensor on misfire detection performance was also investigated. It was found that differentiation of the sensor signal gives the criteria for misfire detection. The misfiring can be detected by monitoring the amplitude of the fluctuation in the differentiated signal, and the misfired cylinder can be identified by monitoring the phase delay between the peak point of the differentiated signal and a reference signal. This scheme has been shown to detect the misfiring condition reliably and to identify the misfiring cylinder up to an engine speed of 5000 r/min.
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