Patent ID: 8731804

Claim:
A hydrogen detecting method comprising: obtaining a low oxygen concentration response period that is a response period from a time a target air-fuel ratio is switched from lean to rich to a time an output of a sensor detecting an oxygen concentration of an exhaust as is reflected by the switching with a feedback control stopped, the feedback control controlling the target air-fuel ratio of the exhaust gas on a basis of a detection result of the sensor such that an air-fuel ratio of the exhaust gas comes close to a theoretical air-fuel ratio; obtaining a high oxygen concentration response period that is a response period from a time the target air-fuel ratio is switched from rich to lean to a time an output of the sensor is reflected by the switching with the feedback control stopped; detecting an information according to a hydrogen concentration level on a basis of the high and low oxygen concentration response periods; and deciding that there is a variation between cylinders, when the hydrogen concentration level detected by the detecting is greater than or equal to a given value.