Air-fuel ratio adjusting system for internal combustion engines

Claim 1

In an air-fuel ratio adjusting system for an internal combustion engine including: means communicated with an intake manifold of an internal combustion engine for producing and supplying to said engine air-fuel mixture; a throttle valve disposed in said means for controlling the amount of said air-fuel mixture; a bypass passage communicated with said intake manifold downstream of said throttle valve for supplying additional air therethrough; a bypass valve operatively disposed in said bypass passage for controlling the opening area of said passage through which said additional air flows, whereby the amount of said additional air is controlled by said bypass valve; an air-fuel ratio sensor disposed in an exhaust manifold of said engine for sensing the air-fuel ratio of the air-fuel mixture fed to said engine; driving means operatively connected to said bypass valve for driving the same in a valve opening or closing direction; and a control unit electrically connected to said air-fuel ratio sensor and driving means for actuating said driving means in accordance with the output from said air-fuel ratio sensor in order to adjust the air-fuel ratio of the mixture to be fed to said engine, the improvement comprising: a maximum opening detecting circuit electrically connected to said control unit for limiting a maximum opening of said bypass valve to a predetermined value depending on at least one of operating conditions of said engine, whereby effective operation for adjusting the air-fuel ratio can be obtained.