Development of a Misfire Detection's Technique Based on an Engine's Torsional Model

The recent OBD requirements enforce the misfire's diagnosis and the isolation of the cylinder where the missing combustion took place. Most of the common-used techniques developed are based on the engine's angular speed, that is derived by the signal usually measured with an inductive or Hall-effect sensor already used for the engine's control. The presence of single or multiple misfires (several misfires within the same engine's cycle) induces torsional vibration in the powertrain, requiring specific filtering of the diagnostic signal to avoid false alarms. This paper presents some preliminary results, related to a 4 cylinder 1.2 liter engine mounted on an eddy-current brake test bench, obtained by a new diagnosis technique based on two speed sensors, placed near the toothed wheels used respectively for the engine and current brake's control. The signals coming from the two sensors, applied to an equation derived by a torsional model of the engine powertrain, allow to evaluate an index based on the difference between engine and brake's torque that highlights the misfire presence. It will be shown that this index does not require any particular calibration procedure. Experimental tests, in which single and multiple misfires are induced in several operating conditions, show clearly the algorithm's robustness in misfire detection, especially in multiple misfire tests, where the misfiring cylinders are exactly detected.