The paper presents the development of a methodology for detecting the misfire event using the time-frequency analysis of the instantaneous engine speed signal. The diagnosis of this type of malfunctioning operating condition is enforced by OBD requirements over the whole operating range of the engine, and many different approaches have been developed in the past in order to solve this problem.
The novel approach presented here is based on the observation that the misfire causes an impulsive lack of torque acting on the engine crankshaft, and thus it causes the excitation of damped torsional vibrations at frequencies characteristic of the system under study. In order to enlighten the presence of this torsional vibration (and therefore detect the misfire event), information contained in the instantaneous crankshaft speed fluctuations have been processed in the time-frequency domain. A misfire detection parameter has then been defined showing a good capability of diagnosing the misfire occurrence.
The procedure has been setup and validated running a supercharged 2 liter V6 SI engine in an engine test cell; in-cylinder pressure signals have been acquired together with the instantaneous engine speed, in order to verify the capability of the methodology.