Patent ID: 7836864

Claim:
An internal-combustion-engine combustion condition detection apparatus comprising: an ignition means that makes an ignition plug ignite a fuel-air mixture taken into a combustion chamber; an ignition control means that generates a control signal for controlling operation of the ignition means; an ion-current detection means that detects an ion current that occurs when the fuel-air mixture combusts; an ion current detection range setting means that sets a detection range for an ion current to be detected by the ion-current detection means; a preignition detection means that detects preignition or a precursor phenomenon of preignition, based on an ion current detected within a detection range set by the ion current detection range setting means; a leakage current detection range setting means that sets a detection range for a leakage current caused by an ignition-plug smolder; and a leakage current determination means that determines whether or not an ignition-plug smolder exists, based on a current detected, within a detection range set by the leakage current detection range setting means, by the ion-current detection means, wherein the ignition control means includes a non-combustion-stroke ignition control means that makes the ignition plug perform ignition during a fuel-air mixture non-combustion stroke, and wherein the leakage-current detection range set by the leakage current detection range setting means is set within the non-combustion stroke, wherein the preignition detection means includes a preignition detection threshold value setting means that sets a threshold value for detecting preignition or a precursor phenomenon of preignition within a detection range set by the ion current detection range setting means, based on a current detected, in a detection range set by the leakage current detection range setting means, by the ion-current detection means.