Exhaust emission control device for engine
AssigneeNissan Motor Co., Ltd.
InventorsMikio Tsuzuki, Ritsuo Sato, Kimiyoshi Nishizawa
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Abstract
A three-way catalyst (9) which has an oxygen storage capacity is disposed in an exhaust passage (3) and HC adsorbent-catalysts (10, 11) which can adsorb and oxidize HC are disposed further downstream. If release of HC from the HC adsorbent-catalysts is determined, the lean level of an air-fuel ratio is increased temporarily after HC release is commenced. Thereafter the air-fuel ratio is controlled to a lower lean level which corresponds to an HC concentration during release. In this way, after lean control is commenced, the three-way catalyst is saturated in a short time and oxygen is sent to the HC adsorbent-catalysts (10, 11) and released HC is oxidized.
Claims10
An emission control device for an engine comprising:
- a catalyst disposed in an exhaust passage, the catalyst storing oxygen;
- a hydrocarbon adsorbent-catalyst disposed in the exhaust passage at a location downstream of the catalyst;
- and
- a control unit that controls an air-fuel ratio of the engine, wherein the control unit is programmed.
- to determine release of hydrocarbons from the hydrocarbon adsorbent-catalyst based on the hydrocarbon adsorbent-catalyst temperature
- to control the air-fuel ratio to a first lean air-fuel ratio when the hydrocarbon adsorbent-catalyst starts to release hydrocarbons, and
- to control an air-fuel ratio to a second lean air-fuel ratio after controlling to the first lean air-fuel ratio during hydrocarbon release by the hydrocarbon adsorbent-catalyst;
- the first lean air-fuel ratio being leaner than the second lean air-fuel ratio.
An emission control device for an engine comprising:
- a catalyst disposed in an exhaust passage, the catalyst storing oxygen;
- a hydrocarbon adsorbent-catalyst disposed in the exhaust passage at a location downstream of the catalyst;
- and
- means for determining relase of hydrocarbons from the hydrocarbon adsorbent-catalyst based on the hydrocarbon adsorbent-catalyst temperature;
- means for controlling the air-fuel ratio to a first lean air-fuel ratio when the hydrocarbon adsorbent-catalyst starts to release hydrocarbons;
- and
- means for controlling an air-fuel ratio to a second lean air-fuel ratio after controlling to the first lean air-fuel ratio during hydrocarbon release by the hydrocarbon adsorbent-catalyst;
- the first lean air-fuel ratio being leaner than the second lean air-fuel ratio.
An emission control device for an engine comprising:
- a catalyst disposed in an exhaust passage, the catalyst storing oxygen;
- a first hydrocarbon adsorbent-catalyst disposed in the exhaust passage at a location downstream of the catalyst, the first hydrocarbon adsorbent-catalyst storing oxgen;
- a second hydrocarbon adsorbent-catalyst disposed in the exhaust passage at a location downstream of the first hydrocarbon adsorbent catalyst;
- and
- a control unit that controls an air-fuel ratio of the engine, wherein the control unit is programmed
- to determine release of hydrocarbons from the first and second hydrocarbon adsorbent-catalyst based on the respective hydrocarbon adsorbent-catalyst temperatures.
- to control the air-fuel ratio to a first lean air-fuel ratio according to remaining oxygen storage capacity of the catalyst when the first hydrocarbon adsorbent-catalyst starts to release hydrocarbons, and to control an air-fuel ratio to a second lean air-fuel ratio after controlling to the first lean air-fuel ratio during hydrocarbon release by the first hydrocarbon adsorbent-catalyst;
- the first lean air-fuel ratio being leaner than the second lean air-fuel ratio and
- to control the air-fuel ratio to a third lean air-fuel ratio according to remaining oxygen storage capacity of the catalyst and the first hydrocarbon adsorbent-catalyst when the second hydrocarbon adsorbent-catalyst starts to release hydrocarbons, and to control an air-fuel ratio to a fourth lean air-fuel ratio after controlling to the third lean air-fuel ratio during hydrocarbon release by the second hydrocarbon adsorbent-catalyst;
- the third lean air-fuel ratio being leaner than the fourth lean air-fuel ratio.
Dependencies are inferred from the claim text.