Exhaust gas emission control device for e.g. four-cylinder petrol engine, has variation controlling device that operates based on cycle and amplitude that are determined to increase oxygen and carbon mono-oxide concentrations

摘要

The device has a catalytic converter arranged in an exhaust gas path (16). A feedback control device implements a feed back control to approximate an actual air/fuel ratio to a target air/fuel ratio based on an output signal of an air/fuel ratio detection device (25). An air fuel ratio variation controlling device operates based on a cycle and an amplitude that are determined to increase oxygen and carbon mono-oxide concentrations in emissions at an input of the converter, during the operation of the control device.