Device for purifying exhaust gases from internal combustion engine

Abstract

In a device for purifying the exhaust gases discharged from an internal combustion engine of the type having a secondary air supply pipe for charging the secondary air from an air source such as an air pump into an exhaust pipe upstream of an exhaust gas reactor or the like, a three-way valve is inserted in the supply pipe in such a manner that the three-way valve may be displaced between a first position at which the air source and the exhaust pipe are communicated with each other and a second position at which the communication between them is interrupted and the secondary air is relieved or returned to the air source bypassing the exhaust pipe; an air-fuel ratio sensor is inserted into the exhaust pipe downstream of the opening of the secondary air supply pipe into the exhaust pipe; and means for controlling the three-way valve is provided so that when the air-fuel ratio detected by the sensor is lower than a reference or optimum ratio at which the best performance of the reactor is expected the three-way valve is caused to move to the first position, whereas when the sensed air-fuel ratio exceeds the reference ratio, the three-way valve is caused to move to the second position, whereby the air-fuel ratio may be controlled with a higher degree of accuracy.