Combustion state detection apparatus for internal combustion engine

A combustion state detection apparatus for an internal combustion engine, comprising:

• operation state detection means for detecting an operation state of the internal combustion engine;
• an ignition coil that has a primary winding and a secondary winding, and generates a high voltage in the secondary winding when a primary current flowing through the primary winding is shut off;
• an ignition plug that is connected to the secondary winding, and generates a spark discharge for firing an air-fuel mixture in a combustion chamber of the internal combustion engine when the high voltage generated in the secondary winding is applied to the ignition plug;
• a switching element that is connected to the primary winding, and conducts and shuts off the primary current;
• switching control means for creating an ignition signal that switches between conduction and shutoff of the primary current based on the operation state, and for controlling driving of the switching element in accordance with the ignition signal;
• ion current detection means for detecting, as an ion current, ions generated in combustion of the air-fuel mixture by the spark discharge;
• and
• abnormal combustion detection means for determining that abnormal combustion has occurred in the combustion chamber in a case where one of a crank angle of a crankshaft at a point of time when the ion current exceeds a predetermined current value and a crank angle at a point of time when the ion current that exceeds the predetermined current value reaches a peak value thereof is on a spark-advance side compared with a crank angle for determining abnormality,
• wherein the switching control means ends the spark discharge at a predetermined timing while the spark discharge is in progress after the primary current is shut off and the spark discharge is generated.