Method of controlling air-fuel ratio in internal combustion engine

Claim 1

In a control system for controlling an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine, the system comprising a sensor for sensing an absolute intake negative pressure of said internal combustion engine, negative pressure switch means for detecting that a difference between the atmospheric pressure and said absolute intake negative pressure has attained a predetermined value, means for detecting a revolution number of said engine, a sensor for sensing a quantity of oxygen in the exhaust gas of said engine, means for controlling a fuel supply to said engine, and a data processing unit including a central processing unit and a read-only memory for executing arithmetic operation in order to control the air-fuel ratio in dependence upon output data derived from said sensors and detecting means, a method of controlling said control system in such a manner that the exhaust gas components are kept within a permissible range even in an accelerating operation at places of high altitude where an oxygen content in air is decreased, the method comprising the steps of: (a) detecting the atmospheric pressure and the corresponding altitude by said absolute intake negative pressure sensor in dependence upon said negative pressure switch means detecting, that a difference between the atmospheric pressure and said absolute intake negative pressure has attained a predetermined value; (b) arithmetically determining a fuel supply quantity which maintaines the exhaust gas components within the permissible range at the accelerating operation at the altitude detected in the detecting step; and (c) applying said arithmetically determined fuel supply quantity to said fuel supply control means.