Misfire detector device for use in an internal combustion engine

A misfire detector device for use in internal combustion engine comprising:

• an ignition coil including a primary coil and a secondary coil;
• an electrical interrupter circuit which on-off actuates a primary current flowing through a primary circuit of the ignition coil to induce a spark plug voltage;
• a check diode or a series gap provided in a secondary circuit of the ignition coil so as to prevent a current flowing back to the ignition coil;
• a spark plug which is to be energized from the ignition coil, the spark plug having a center electrode, a front end of which is projected from an insulator, and an outer surface area of the projected front end of the center electrode being 25 mm.sup.2 or more;
• a voltage divider circuit which detects a divided voltage level of the spark plug voltage applied across electrodes of the spark plug;
• a spark plug voltage detector circuit which detects attenuation time period length of attenuation characteristics of a spark plug voltage waveform, from the voltage divider circuit presented subsequent to a predetermined time period after an end of a spark action of the spark plug;
• and
• a distinction circuit which determines on the basis of the attenuation time period length of the attenuation characteristics whether or not the spark ignites an air-fuel mixture injected in a cylinder of an internal combustion engine.

A misfire detector device for use in internal combustion engine comprising:

• an ignition coil;
• an interrupter circuit which on-off actuates a primary current flowing through a primary circuit of the ignition coil to induce a spark plug voltage;
• a spark plug which is to be energized from the ignition coil, the spark plug having a center electrode, a front end of which is projected from an insulator, and an outer surface area of the projected front end of the center electrode being 25 mm.sup.2 or more;
• a voltage charging circuit which induces an electromotive voltage in the secondary circuit of the ignition coil by energizing the primary circuit, and deenergizing it after a certain period of time at a predetermined time after an end of a spark action due to an inductive discharge of the spark plug and before a next spark plug voltage is induced that causes a spark action, when the engine runs at a low revolution with a low load;
• a voltage divider circuit which detects a divided voltage level of the spark plug voltage applied across electrodes of the spark plug;
• a spark plug voltage detector circuit which detects attenuation characteristics of a spark plug voltage waveform presented from the voltage divider circuit subsequent to a predetermined time period after an end of a first spark action and either during a second spark action of the spark plug or after an end of the first spark action when the engine runs at a high revolution, and detecting attenuation characteristics of a spark plug voltage waveform derived from the voltage charging circuit when the engine runs at a low revolution with a low load;
• and
• a distinction circuit which determines on the basis of the attenuation characteristics whether or not the spark ignites an air-fuel mixture injected in a cylinder of an internal combustion engine.