Dynamic Misfire Threshold Determination Based On Zone-Level and Buffer-Level Adaptations for Internal Combustion Engines

Misfire is generally defined as be no or partial combustion during the power stroke of internal combustion engine. Because a misfired engine will dramatically increase the exhaust emission and potentially cause permanent damage to the catalytic converters, California Air Resources Board (CARB), as well as most of other countries’ on-board diagnostic regulations mandates the detection of misfire. Currently almost all the OEMs utilize crankshaft position sensors as the main input to their misfire detection algorithm. The detailed detection approaches vary among different manufacturers. For example, some chooses the crankshaft angular velocity calculated from the raw output of the crankshaft positon sensor as the measurement to distinguish misfires from normal firing events, while others use crankshaft angular acceleration or the associated torque index derived from the crankshaft position sensor readings as the measurement of misfire detection. Regardless which measurement is chosen, an optimized threshold setting that clearly separates misfiring and normal firing cylinder events is desired. Traditionally, the threshold setting is determined during pre-launch calibration process with test data obtained from development vehicles. The threshold for each speed-load zone is typically a fixed value by looking up of a 3D calibration table. Such threshold setting approach, however, faces more and more challenges from the application of new engine technologies, because the crankshaft position sensor outputs could gradually change over the vehicle’s life cycle, and could even change swiftly under stable engine speed and load conditions due to the application of certain new technologies. A fixed misfire threshold setting will yield false detections and result in regulation compliance concerns as well as unsatisfactory of the customers. To address this issue, this article propose a unique approach to dynamically determine the misfire threshold with zone-level adaptation to adjust thresholds for vehicle life-cycle changes and buffer-level adaption to address the needs to quickly adjust misfire thresholds in the same speed-load zone.