Patent ID: 6012282
Filing Date: 2000-01-11
Classification: B01D,F01N,F02D,G01N,Y02T

Abstract:
A method for controlling an engine exhaust gas system, comprising the steps of:detecting an air-fuel ratio of exhaust gas discharged from an internal engine by an oxygen sensor;controlling said exhaust gas to near the stoichiometric air-fuel ratio by a closed-loop control referring to a resultant signal; andleading said exhaust gas to a three-way catalyst to treat nitrogen oxide, hydrocarbon and carbon monoxide;measuring a nitrogen oxide concentration by a nitrogen oxide sensor provided downstream of said three-way catalyst;providing a comparison signal based on the result obtained by comparing the measured nitrogen oxide concentration with a predetermined value of nitrogen oxide; andcorrecting the air-fuel ratio by a closed loop control based on said comparison signal so as to keep the nitrogen oxide concentration at said predetermined value.