Air/fuel ratio control system for internal combustion engines, having atmospheric pressure compensating function

摘要

An air/fuel ratio control system for use with an internal combustion engine. The system is provided with an electrical circuit which operatively connects an O2 sensor with fuel quantity adjusting means in a manner effecting feedback control of the air/fuel ratio of a mixture produced by the fuel adjusting means and being supplied to the engine in response to the output signal of the O2 sensor. The electrical circuit includes means operable during open loop control of the air/fuel ratio under a particular engine operating condition, for controlling the fuel quantity adjusting means so as to obtain a mixture having a predetermined air/fuel ratio appropriate for the particular engine operating condition, irrespective of the O2 sensor output signal, and means for correcting the above predetermined ratio in response to atmospheric pressure. The electrical circuit further comprises fail safe means for detecting a malfunction in the atmospheric pressure sensor. The fail safe means is operable upon detection of such a malfunction to perform suitable fail safe functions including prevention of the mixture air/fuel ratio from being controlled to an inappropriate value even during the occurrence of the malfunction.