Method and device for detecting misfires in a controlled-ignition internal combustion engine

A device for detecting misfires in a controlled-ignition internal combustion engine, for implementation of a method having steps of:

• a) formulating, for a combustion/expansion phase in each corresponding cylinder of the engine, a signal representative of a value of a gas torque (Cg) produced in the corresponding cylinder by a corresponding combustion, b) measuring a rotational speed (N) of the engine and formulating a signal representative of the rotational speed for at least an inlet phase which preceded the combustion/expansion phase in the corresponding cylinder, c) measuring a parameter representative of a unitary filling of the corresponding cylinder and formulating a signal representative of the unitary filling for at least the inlet phase which preceded the combustion/expansion phase during a same engine cycle in the corresponding cylinder, d) entering the signals representative of the speed (N) and of the unitary filling as addresses in a reference theoretical gas torque map, and deducing from the torque map a signal representative of a reference torque (Cref), e) i) assigning to at least one of the signals representative of the value of the gas torque (Cg) and of the reference torque (Cref) a respective multiplicative correction factor (KM) associated with the corresponding cylinder so as to obtain proportional signals which are proportional to the value of the gas torque (Cg) and to the reference torque (Cref) respectively, and, ii) assigning to at least one of the proportional signals, an additive correction factor (KA) when the engine is running in a transient mode, and deducing therefrom a signal representative of an expected theoretical torque (Cpr) on a basis of the signal which is proportional to the reference torque (Cref), and a signal representative of a calculated gas torque (Cgc) on a basis of the signal which is proportional to the value of the gas torque (Cg), and f) calculating a ratio of the signal representative of the expected theoretical torque (Cpr) to the signal representative of the calculated gas torque (Cgc), and deeming there to be a misfire when this ratio is higher than a given ratio threshold (S2);
• said device comprising:
• at least one sensor for sensing a rotational speed of the engine, and for delivering a speed signal (N),
• at least one sensor for sensing a parameter representative of a unitary filling of the cylinders of the engine, and for delivering a signal representative of this parameter,
• a torque calculating means for calculating the gas torque (Cg) based on the engine speed signal (N),
• a memory means for storing the gas torque maps and the thresholds,
• a calculation means for calculating and for storing values of the reference torque (Cref), of the expected torque (Cpr), of the calculated gas torque (Cgc), of the multiplicative and additive correction factors (KM, KA), and of the Cpr/Cgc ratio, and
• a comparison means for comparing the stored values with thresholds (S1, S2, S3, S4, S5) in order to determine the presence of misfires.