First and second air feeding means to regulate a/f ratio wherein second air feed requires two signals for actuation

An exhaust gas purifying device in an internal combustion engine having at least one cylinder, comprising:

• an intake and an exhaust passage of said engine;
• means for producing a rich air-fuel mixture in said intake passage;
• a catalytic converter containing a three way catalyzer therein and disposed in said exhaust passage;
• first detecting means for detecting the concentration of oxygen containing in the exhaust gas flowing in the exhaust passage located upstream of said catalytic converter, said first detecting means issuing a first output signal indicative of the concentration of oxygen;
• means for regulating the air-fuel ratio of said rich air-fuel mixture so that said air-fuel ratio conforms to the stoichiometric air-fuel ratio in response to said first output signal of said first detecting means;
• second detecting means for detecting the concentration of oxygen contained in the exhaust gas flowing in the exhaust passage located downstream of said catalytic converter, said second detecting means issuing a second output signal indicative of the concentration of oxygen;
• third detecting means for detecting the accelerating, decelerating, and gear-shifting operations of the engine and for issuing a third output signal indicative of said operations, and means for feeding secondary air into the exhaust gas flowing in the exhaust passage located upstream of said catalytic converter so that the ratio of air consisting of said secondary air and air contained in the mixture introduced into the cylinder of the engine to the fuel contained in the mixture introduced into the cylinder of the engine is made equal to the stoichiometric air-fuel ratio in response to both said second and third output signals of said second and third detecting means at the time of acceleration, deceleration and gear-shifting.