Patent ID: 6311482
Filing Date: 2001-11-06
Classification: B60K,B60W,F01N,F02D,Y02T,Y10S

Abstract:
An air-fuel ratio control apparatus for internal combustion engines comprising:upstream and downstream catalysts mounted on an upstream and downstream sides of an exhaust passage of an internal combustion engine for exhaust gas purification;fuel injection means for injection of a quantity of fuel into a cylinder of the engine in accordance with an engine operating condition; andair-fuel ratio change means for changing lean and rich magnitude of an exhaust air-fuel ratio by alternately increasing and decreasing the magnitude for correcting the quantity of fuel injection;wherein the air-fuel ratio change means performs lean/rich changeover of the exhaust air-fuel ratio at an internal including a period during which the lean and rich components in the exhaust gas react with the upstream catalyst and a period thereafter during which an unreacted exhaust gas passes through the upstream catalyst;a first control of the lean/rich changeover of the exhaust air-fuel ratio is carried out at a relatively short interval at which an unreacted exhaust gas does not pass through the upstream catalyst when the upstream and downstream catalysts are both in an interactive condition; anda second control of the lean/rich changeover of the exhaust air-fuel ratio is carried out at a relatively long interval at which the unreacted exhaust gas passes through the upstream catalyst when only the downstream catalyst is in an inactive condition.