Patent ID: 6327849
Filing Date: 2001-12-11
Classification: F01N,F02D,F02M,Y02T

Abstract:
An exhaust gas purifying apparatus for the exhaust system of an internal combustion engine, comprising:nitrogen oxide purifying means for absorbing the nitrogen oxide in exhaust gases in a lean exhaust-gas condition during which the oxygen concentration of the exhaust gas is comparatively high;deterioration detection means for detecting the deterioration of the nitrogen oxide purifying means;air-fuel ratio variation means for, when the deterioration of the nitrogen oxide purifying means is detected by the deterioration detection means, varying, during an interval that is set equal to or shorter than a predetermined time, the air-fuel ratio for the air-fuel mixture supplied to the internal combustion engine, and to thus provide an air-fuel ratio that is leaner or richer than a stoichiometric air-fuel ratio;operating state identification means for determining whether one of the air-fuel ratio variation means and a contamination removal process is implemented, wherein the air-fuel ratio variation means does not occur if one of a speed of an apparatus containing the internal combustion engine, an engine revolution rate and an absolute air intake-pipe internal pressure, is not respectively higher than a predetermined amount; anddeterioration recovery means for, when an elevated temperature attained at the nitrogen oxide purifying means exceeds a deterioration recovery temperature following activation of the air-fuel ratio variation means, performing deterioration recovery by maintaining for an adequate period of time a richer air-fuel ratio than the stoichiometric air-fuel ratio.