The invention relates to a misfire detection system for an internal combustion engine, particularly of the type equipped with a catalytic converter for cleaning the exhaust gas.
Generally, when the engine misfire occurs in a vehicle equipped with a catalytic converter, the resultant large quantity of unburned combustion components which are discharged through the exhaust greatly increases the reaction heat of the catalyst. Such excessive heat, if unchecked, leads to deterioration or breakdown of the catalyst and in some cases to a fire accident of the vehicle.
Such effects can be partially avoided by employing known techniques based on the principle that engine misfires of this type cause an increase in the catalyst bed temperature or the exhaust gas temperature. In such techniques, an electrical indication triggered upon the overheating of one of these parameters is employed either to interrupt the fuel and secondary air supplies to the engine or to effect a bypass of the exhaust gas from its normal route through the converter.
One disadvantage of prior art schemes of this type is that the excess temperature sensing facilities operate too late to effect efficient correction of the defect, since overheating of a large portion of the catalyst has already occurred. Moreover, even if the overheating of the bed or gas is detected in time, the inertial time lags of the correcting system may cause the latter to respond too late to prevent destruction of the catalyst by heat.