Misfire detection device for an internal combustion engine

Claim 1

A misfire detection device for an internal combustion engine having an ignition coil and a plurality of cylinders, each of said cylinders having a respective ignition plug, said misfire detection device comprising: an ionic current detection means to detect an ionic current which is caused by combustion and occurs at the respective ignition plug of at least one of said plurality of cylinders and to generate an output signal which represents said detected ionic current, said ionic current detection means comprising a capacitor to be charged by a current flowing through a secondary winding of said ignition coil, wherein said ionic current caused by combustion flows through said capacitor and a resistor of said ionic current detection means; a gate means to mask said output signal generated from said ionic current detection means only during an ignition sparking time period; a comparing means to compare said masked output signal passed through said gate means with a predetermined level and to provide a comparison output signal; a misfire detection means to detect the presence or the absence of a misfire and a misfired cylinder based on the comparison output signal; and fuel supply controlling means to control supply of fuel to said misfired cylinder in response to an output of said misfire detection means.