Air-fuel ratio control system for internal combustion engines.

摘要

An air-fuel ratio control system for an internal combustion engine (1) includes a LAF sensor (16) and an O2 sensor (17) arranged in an exhaust pipe at respective locations upstream and downstream of a catalytic converter (15). A desired air-fuel ratio coefficent (KCMD) used in calculating an amount of fuel (TOUT) supplied to the engine (1) is calculated based on operating conditions of the engine, and corrected by an amount ( DELTA KCMB) based on output (VO2) from the O2 sensor (17). The air-fuel ratio of a mixture supplied to the engine is feedback-controlled to a stoichiometric air-fuel ratio based on the corrected desired air-fuel ratio coefficient (KCMDM). When the output (VO2) from the O2 sensor (17) falls within a predetermined range (VL-VH), the desired air-fuel ratio coefficient (KCMDM) is not corrected, but held at an immediately preceding value thereof. <IMAGE>