Patent ID: 6601383
Filing Date: 2003-08-05
Classification: F01N,F02D,Y02T

Abstract:
An emission control apparatus for an engine comprising:at least two series disposed catalysts in an exhaust passage including a first catalyst and a second catalyst, at least one of the catalysts being a HC absorbent catalyst which includes a HC absorbent for absorbing HC in an exhaust gas in an absorbing condition and desorbing an absorbed HC in a desorbing condition; a first sensor which detects an air-fuel ratio or rich/lean of the exhaust gas at an upstream side of the first catalyst; a second sensor which detects an air-fuel ratio or rich/lean of the exhaust gas at an upstream side of the second catalyst; a third sensor which detects an air-fuel ratio or rich/lean of the exhaust gas at a downstream side of the second catalyst; and a controller which provides a main feedback loop which varies a fuel amount supplied to the engine so that the air-fuel ratio detected by the first sensor is maintained at a first target value, a first sub-feedback loop which varies the first target value so that the air-fuel ratio detected by the second sensor is maintained at a second target value, and a second sub-feedback loop which varies the second target value based on the air-fuel ratio detected by the third sensor, wherein the controller further comprises a setting device which provides at least one of the target values associated with the HC absorbent catalyst by one of the feedback loops, and the setting device sets the target value to a leaner value when the corresponding HC absorbent catalyst is in the desorbing condition.