Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
1999-07-01
2002-01-08
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, C060S277000, C060S276000, C123S443000
Reexamination Certificate
active
06336320
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purification device for an internal combustion engine. More specifically, the invention relates to an exhaust gas purification device for an internal combustion engine equipped with an exhaust gas purifying catalyst having an O
2
storage capability.
2. Description of the Related Art
There has been known a technology for purifying three components, i.e., HC, CO and NOx contained in the exhaust gas by disposing an exhaust gas purifying catalyst such as a three-way catalyst having an O
2
storage capability in an exhaust gas passage of an engine that is operated at nearly the stoichiometric air-fuel ratio. The O
2
storage capability of the three-way catalyst stands for a function for absorbing and holding the oxygen component in the exhaust gas in the catalyst when the air-fuel ratio of the exhaust gas flowing into the catalyst is lean, and for releasing the absorbed oxygen when the air-fuel ratio of the exhaust gas flowing in is rich. As is well known, the three-way catalyst is capable of simultaneously purifying three components, i.e., HC, CO and NOx contained in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the catalyst lies within a narrow range near the stoichiometric air-fuel ratio, but is no longer capable of simultaneously purifying the above-mentioned three components when the air-fuel ratio of the exhaust gas is deviated from the above-mentioned range. When the O
2
storage capability is added to the three-way catalyst, on the other hand, the three-way catalyst absorbs an excess of oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in becomes more lean than the stoichiometric air-fuel ratio, and releases oxygen when the air-fuel ratio of the exhaust gas becomes rich, making it possible to maintain the atmosphere of the three-way catalyst at near the stoichiometric air-fuel ratio even when the air-fuel ratio of the exhaust gas flowing into the catalyst is deviated from the stoichiometric air-fuel ratio. Upon purifying the exhaust gas of the engine operated at an air-fuel ratio close to the stoichiometric air-fuel ratio by using the three-way catalyst having the O
2
storage capability, therefore, it becomes possible to favorably remove three components, i.e., HC, CO and NOx simultaneously.
There has further been known an NOx occluding and reducing catalyst which absorbs NOx (nitrogen oxides) in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in is lean, and releases NOx which it has absorbed when the oxygen concentration in the exhaust gas flowing in becomes low.
An exhaust gas purification device using the NOx occluding and reducing catalyst has been disclosed in, for example, Japanese Patent No. 2600492. According to the exhaust gas purification device of this patent, the NOx occluding and reducing catalyst is disposed in the exhaust passage of the engine which operates at a lean air-fuel ratio so as to absorb NOx contained in the exhaust gas when the engine is operating at a lean air-fuel ratio, and to release NOx which it has absorbed when the amount of NOx absorbed by the NOx occluding and reducing catalyst has increased by executing a rich-spike operation in which the engine is operated at the stoichiometric air-fuel ratio or at a rich air-fuel ratio for a short period of time, in order to purify the released NOx by the reduction. That is, when the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, the concentration of oxygen in the exhaust gas sharply decreases compared to that of the exhaust gas of a lean air-fuel ratio and the amounts of the unburned HC and CO components sharply increase in the exhaust gas. Therefore, when the engine operating air-fuel ratio is changed over to the stoichiometric air-fuel ratio or to the rich air-fuel ratio by the rich-spike operation, the air-fuel ratio of the exhaust gas flowing into the NOx occluding and reducing catalyst changes from the lean air-fuel ratio into the stoichiometric air-fuel ratio or the rich air-fuel ratio, and NOx are released from the NOx occluding and reducing catalyst due to a decrease in the oxygen concentration in the exhaust gas. As described above, further, the unburned HO and CO components are contained in relatively large amounts in the exhaust gas of the stoichiometric air-fuel ratio or the rich air-fuel ratio and, hence, NOx released from the NOx occluding and reducing catalyst are reduced upon reacting with the unburned HC and CO components in the exhaust gas.
Further, the exhaust gas purifying device disclosed in Japanese Patent No. 2600492 judges the amount of NOx occluded by the NOx occluding and reducing catalyst based on a value of an NOx counter which increases or decreases depending upon the operating conditions of the engine, and executes the rich-spike operation when the value of the NOx counter has reached a predetermined value, so that the NOx occluding and reducing catalyst will not be saturated with the NOx that are absorbed. The NOx counter of the above-mentioned patent estimates the occluded amount of NOx by increasing the value of the NOx counter at a predetermined interval by an amount of NOx absorbed by the catalyst in accordance with the operating conditions of the engine when the engine is operating at a lean air-fuel ratio, and by decreasing the value of the NOx counter at the predetermined interval by an amount of NOx released from the catalyst in accordance with the operating conditions of the engine when the engine is operating at a rich air-fuel ratio. That is, the amount of NOx emitted per a unit time from an engine that is operating at a lean air-fuel ratio is determined in accordance with the operating conditions of the engine (load on the engine, air-fuel ratio, flow rate of the exhaust gas, etc.), and the NOx occluding and reducing catalyst absorbs NOx of this amount per a unit time. Therefore, the amount of NOx occluded by the NOx occluding and reducing catalyst per unit time is proportional to the amount of NOx emitted from the engine per a unit time. According to the above-mentioned patent, the amount of NOx absorbed by the NOx occluding and reducing catalyst per a unit time during operating conditions of the engine is stored as an absorbed amount of NOx in advance, and the absorbed amount of NOx is calculated in accordance with the operating conditions of the engine at a predetermined interval when the engine is operating at a lean air-fuel ratio thereby to increase the value of the NOx counter. Similarly, furthermore, the amount of NOx released from the NOx occluding and reducing catalyst per a unit time when the engine is operating at a rich air-fuel ratio is determined in accordance with the operating conditions of the engine (air-fuel ratio, flow rate of the exhaust gas). According to the above-mentioned patent, therefore, the amount of NOx released from the NOx occluding and reducing catalyst per a unit time during the operating conditions of the engine is stored as a released amount of NOx, and the value of the NOx counter is decreased by the released amount of NOx at a predetermined interval when the engine is operated at a rich air-fuel ratio such as during the rich-spike operation.
According to the exhaust gas purification device disclosed in Japanese Patent No. 2600492, it is allowed to efficiently purify NOx when the engine is operating at a lean air-fuel ratio. However, a problem arises when a three-way catalyst having an O
2
storage capability is added as a start catalyst to the device of the above-mentioned Patent No. 2600492.
A principal object of the start catalyst is to remove HC and CO components released in large amounts from the engine during starting. The start catalyst must be disposed in an exhaust gas passage at a position as close as possible to the engine so that its temperature rises and reaches the activated temperature within a short period of time after the start of the engine. When added to the exhaust gas p
Suzuki Naoto
Tanahashi Toshio
Tanaka Hiroshi
Denion Thomas
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Trieu Thai-Ba
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