Emission control apparatus for engine and method for reducing emissions of engine
AssigneeDenso Corporation
InventorsJun Hasegawa, Kouichi Shimizu, Hisashi Iida
Life of this patent
Estimating the term…
Abstract
An emission control apparatus for an engine has a plurality of catalysts disposed in series in an exhaust passage. An HC absorbent catalyst is utilized for at least one of the catalysts. An ECU controls an A/F ratio in an upstream side of the HC absorbent catalyst at a target value. The target value is corrected to a leaner value when the HC absorbent catalyst is in a desorbing condition. The leaner value is leaner than the target value during the HC absorbent catalyst is in an absorbing condition or an activated condition. The leaner atmosphere provides sufficient of oxygen to purify desorbed HC from the HC absorbent catalyst itself.
Claims22
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.
A method for reducing emissions of an engine including 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 when the catalyst is in an absorbing condition and desorbing an absorbed HC when the catalyst is in a desorbing condition, the method comprising:
- providing a normal target value as a target air-fuel ratio;
- maintaining an upstream side air-fuel ratio of the HC absorbent catalyst at the normal target value when the HC absorbent catalyst is in the absorbing condition;
- providing a leaner target value as the target air-fuel ratio which is leaner than the normal target value;
- and
- maintaining the upstream side air-fuel ratio of the HC absorbent catalyst at the leaner target value when the HC absorbent catalyst is in the desorbing condition;
- wherein the upstream side air-fuel ratio of the HC absorbent catalyst is provided by exhaust gas just upstream the HC absorbent catalyst.
Dependencies are inferred from the claim text.