Apparatus and method for controlling air-to-fuel ratio for an internal combustion engine

摘要

A gas sensor of constant-current type is used to detect a gas component in exhaust gases from an internal combustion engine so as to perform feedback control of air/fuel ratio of an air-fuel mixture supplied to the engine. In order to detect an air/fuel ratio which is richer than a stoichiometric value, a voltage applied to the gas sensor is set to a high value so that the gas sensor does not exhibit a constant-current characteristic. In the case it is desired to detect an air/fuel ratio which is either richer or leaner than the stoichiometric value, the voltage may be changed between the high value and a lower value at which the gas sensor exhibits a constant-current characteristic. Engine parameters are detected to determine whether the engine requires a rich mixture or a lean mixture, and the voltage may be changed as the result of such determination. An output current of the gas sensor is detected to ascertain air/fuel ratio so that air/fuel ratio is controlled to a desired value suitable for engine operating condition.