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A misfire index model-based method and system for detecting misfire in a reciprocating internal combustion engine having an engine cycle frequency in the frequency domain from crankshaft angular velocity. The misfire index model is a function of engine operating condition such as engine load and RPM

A misfire index model-based method and system for detecting misfire in a reciprocating internal combustion engine having an engine cycle frequency in the frequency domain from crankshaft angular velocity. The misfire index model is a function of engine operating condition such as engine load and RPM. Crankshaft angular position is sensed to develop an electrical signal which is a function of the crankshaft angular velocity. The electrical signal contains data which is sampled. The sampled data is transformed to an equivalent frequency domain spectrum including frequency components of the engine cycle frequency and harmonics thereof. A load signal such as mass airflow and an RPM signal are generated. The magnitudes and/or phases of the frequency components and the load and RPM signals are supplied to the misfire index model in an appropriately programmed computer to distinguish between a true misfire and normal cyclic variability which characterizes the combustion process.

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A method for detecting the misfire of a reciprocating internal combustion engine with a misfire index model which is a function of engine operating condition, the engine including a plurality of reciprocating components having an engine cycle frequency, at least one cylinder and a crankshaft, the me

A method for detecting the misfire of a reciprocating internal combustion engine with a misfire index model which is a function of engine operating condition, the engine including a plurality of reciprocating components having an engine cycle frequency, at least one cylinder and a crankshaft, the method comprising the steps of: generating an electrical signal as a function of crankshaft angular velocity, the electrical signal containing data; sampling the data synchronously with crankshaft angular position at a sampling rate to obtain sampled data; transforming the sampled data to an equivalent frequency domain spectrum, including frequency components having complex amplitudes at the engine cycle frequency and harmonics thereof; forming a misfire index based on the complex amplitudes; and applying a threshold algorithm to the misfire index, which threshold algorithm distinguishes between a true misfire and normal cyclic variability which characterizes the combustion process in each cylinder of the engine to thereby obtain a misfire signal, the step of applying including the step of applying the misfire index to the misfire index model to identify the misfire.