Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
1999-06-15
2001-02-13
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S286000, C060S295000, C060S297000, C060S311000
Reexamination Certificate
active
06185933
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an emission control device provided with a catalyst which purifies exhaust gas emissions from an engine.
BACKGROUND OF THE INVENTION
In Japanese Patent Publication Tokkai-Hei-7-144119, a three-way catalyst and a hydrocarbon (hereafter HC) catalyst are disposed in series in an exhaust passage. The HC trap catalyst is disposed downstream of the three-way catalyst.
In a cold operating condition, that is to say, in a condition in which the three-way catalyst is not activated, HC discharge from the engine is trapped in the HC trap catalyst.
After the temperature of the HC trap catalyst reaches a release temperature, the HC trap catalyst begins releasting HC. Released HC is oxidized in the HC trap catalyst.
In Japanese Patent Publication Tokkai-Hei-6-81637 and Tokkai-Hei-5-10178, and HC trapper and a three-way catalyst are disposed in an exhaust passage. HC released from the HC trapper is oxidized in the three-way catalyst disposed downstream of the HC trapper.
While the HC trapper is releasing HC, a control unit for controlling the operation condition of the engine controls an air-fuel ratio to a lean air-fuel ratio so that the exhaust gas flowing into the three-way catalyst creates an oxidizing atmosphere.
In order to accuately control the lean air-fuel ratio with respect to the amount of released HC, in the device disclosed in Tokkai-Hei-6-81637, the control unit controls the lean level according to the duration of the HC release.
In the device disclosed in Tokkai-Hei-5-10178, an oxygen concentration sensor is disposed downstream of the three-way catalyst and the lean level is controlled according to the oxygen concentration that is detected by the sensor.
SUMMARY OF THE INVENTION
An emmission control device having a catalyst which is disposed in an exhaust passage near combustion chambers of an engine can reduce the amount of HC emissions, because the catalyst disposed near engine activates in short time after engine start.
In order to increase emission control performance, if it is necessary for the device to have both of a start-up catalyst which activates in short time after engine start and a HC adsorbent catalyst, the HC adsorbent catalyst must be disposed at downstream of the start-up catalyst. In this case, even if the air-fuel ratio is varied towards a lean air-fuel ratio together with the release of HC from the HC adsorbent catalyst, the oxygen storage capacity of the upstream three-way catalyst functions so that oxygen in the exhaust gas does not immediately reach the downstream HC adsorbent catalyst. Oxygen is stored by three-way catalyst. Therefore only after saturation by the oxygen which is stored in the three-way catalyst, that is to say, after a time delay, remaining oxygen reaches the HC adsorbent catalyst.
Thus HC released during this period is not oxidized by the HC adsorbent catalyst and is released directly into the atmosphere.
The present invention is proposed to solve the above problems and has the object of providing an emission control device which is adapted to commence oxidization of released HC in the shortest possible time after HC release has commenced in the HC adsorbent catalyst.
Another object of the present invention is to reduce the level and time of application of the lean air-fuel ratio to the necessary minimum to oxidize released HC and thus to minimize adverse effects on vehicle performance as a result of operating on a lean air-fuel ratio.
In order to achieve above objects the present invention provides an emission control device for an engine.
The engine comprises 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 air-fuel ration of the engine. The control unit is programmed to determine release of hydrocarbons from the hydrocarbon adsorbent-catalyst based on a 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.
The details as well as other features and advantages of the invention are set forth in the remainder of the specification and are shown in the accompanying drawings.
REFERENCES:
patent: 5315824 (1994-05-01), Takeshima
patent: 5355672 (1994-10-01), Adamczyk, Jr. et al.
patent: 5662869 (1997-09-01), Abe et al.
patent: 5778667 (1998-07-01), Kinugasa et al.
patent: 5887422 (1999-03-01), Abe et al.
patent: 6047544 (2000-04-01), Yamamoto et al.
patent: 5-10178 (1993-01-01), None
patent: 6-81637 (1994-03-01), None
patent: 7-144119 (1995-06-01), None
Nishizawa Kimiyoshi
Sato Ritsuo
Tsuzuki Mikio
Denion Thomas
Foley & Lardner
Nguyen Tu M.
Nissan Motor Co,. Ltd.
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