Method of detecting element resistance of gas concentration sensor

Abstract

A method that detects an air-fuel ratio in each cylinder of an internal combustion engine by properly setting a cycle of detecting an element resistance of an A/F oxygen concentration sensor. Although an actual A/F signal is at the stoichiometric ratio in each cylinder at exhaust timing cycle in a practical engine rotational speed range, the ratio is largely deviated to the rich side in the #1 cylinder. The first element resistance detection timing cycle coincides with generation timing of the actual A/F signal, so that the A/F signal cannot be detected. When the element resistance detection timing cycle is preset so as to be longer than the exhaust timing cycle, the second actual A/F signal detection timing for the #1 cylinder does not coincide with the element resistance detection timing. Consequently, the actual A/F signal of the #1 cylinder can be detected as an A/F signal by the A/F sensor.