Air-fuel ratio control system

In a system for controlling the air-fuel ratio for an internal combustion engine having an induction passage leading to the engine, an exhaust passage from the engine, a throttle valve in the induction passage, detecting means for detecting the concentration of a constituent of exhaust gases passing through said exhaust passage, air-fuel mixture supply means for supplying air-fuel mixture to the induction passage, electromagnetic valve means for correcting the air-fuel ratio of the air-fuel mixture supplied by said air-fuel mixture supply means, comparator means for comparing the output signal of said detecting means with a predetermined value, integrating circuit means having an integrating circuit for integrating the output of said comparator means, and driving circuit means for driving said electromagnetic valve means in dependency upon the output signal of said integrating circuit means, the improvement comprising

• a throttle valve switch,
• a first means operatively connecting said throttle valve switch to said throttle valve for actuating said throttle valve switch in dependency on the position of said throttle valve,
• a vacuum switch,
• a second means communicating with said induction passage so as to be operated by the vacuum pressure in said induction passage for actuating said vacuum switch when said throttle valve is opened to a predetermined degree,
• switching circuit means for changing the circuit constant of said integrating circuit, and
• decision circuit means responsive to operations of said throttle valve switch and said vacuum switch for actuating said switching circuit means, so that said circuit constant is changed in a steady state of the engine compared with idling operation.