Misfire Detection Index Distinguishing the Difference of the Engine Angular Acceleration Between Two Specified Teeth of the Sensor Wheel

This study proposes the slope of the engine speed trend line (Slope_ESTL) as a new misfire detection index for a four-cylinder engine, not limited to four-cylinder engines. Slope_ESTL is defined as angular acceleration between the first and the last teeth of each cylinder in the cycle. Slope_ESTL is flat and near 0 when the cylinder is normally combusted. A misfire leads to an abrupt decrease under the threshold. While it is affected by post oscillation just after misfires, there is enough margin between Slope_ESTL of the misfired cylinder and post-oscillated Slope_ESTL. The mean misfire detection and detection fault rates of the Slope_ESTL were over 97% and under 1% in this study, making it a good misfire detection index. However, most of the first misfired cylinder on dual cylinder misfire can seldom be detected as a misfire at the high engine speed over 5000 rpm in the single cylinder misfire pattern. This is caused by the inertia force of the crankshaft system and is a demerit for the misfire detection index. It is one of the two RPM slopes used to calculate the Gap and ΔGap slopes proposed by the author. Slope_ESTL can be used with Gap and ΔGap slopes, because they have their specific characteristics as misfire detection indices and their combination logic should be studied more. Furthermore, Slope_ESTL can be affected by the machining tolerance of the teeth in the sensor wheel, torsional vibration, and non-uniformity in the stroke operation of the piston. However, it uses the tooth time measured using the existing crankshaft position sensor; an additional sensor is not required, which makes it economical.