Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-08-30
2002-10-15
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S285000, C060S297000
Reexamination Certificate
active
06463734
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust emission control device of an internal combustion engine, in which a three way catalyst and a catalyst with an NOx absorbing function are disposed in an exhaust gas passage.
2. Description of Related Art
In recent years, a lean burn internal combustion engine which improves fuel economy by running the internal combustion engine at a lean air-fuel ratio has been put to practical use. If the lean bum internal combustion engine is run at the lean air-fuel ratio, a three way catalyst cannot sufficiently purify NOx (nitrogenous substance) in exhaust gas due to its purifying characteristic. To address this problem, an exhaust emission control catalyst device provided with an absorption-type NOx catalyst, which absorbs NOx in exhaust gas while the engine is run at the lean air-fuel ratio and emits and reduces the absorbed NOx while the engine is run at a stoichiometrical air-fuel ratio or a rich air-fuel ratio, has been adopted recently.
The absorption-type NOx catalyst has the characteristics of absorbing NOx in exhaust gas as nitrate (or acid oxide) in an atmosphere with excessive oxygen of exhaust gas, and emitting the absorbed NOx in an atmosphere mainly with excessive carbon monoxide of exhaust gas and reducing the NOx into nitrogen (N2) (carbonate is produced at the same time).
In the internal combustion engine, the three way catalyst is provided at the upstream of an exhaust passage in order to control the exhaust of a large amount of uncombusted HC generated when the engine is cold-started. The three way catalyst, however, ordinarily carries a noble metal (e.g., platinum and rhodium), and the noble metal is oxidized to deteriorate the catalyst performance (heat deterioration) when the exhaust gas becomes a lean atmosphere with a high temperature. Therefore, for the exhaust emission control device in which the catalyst with a three way function is disposed in the exhaust passage, Japanese Patent Provisional Publication No. 5-59935 has proposed an air-fuel ratio control for preventing the heat deterioration by making the exhaust air-fuel ratio stoichiometrical if the catalyst is exposed to a predetermined high temperature in oxide atmosphere.
In the lean burn internal combustion engine, the three way catalyst and the NOx absorption-type catalyst are provided in the exhaust passage. The three way catalyst and the absorption-type NOx catalyst have different deterioration characteristics such as heat deterioration characteristic. For this reason, a technique for effectively controlling the deterioration by using both the three way catalyst and the NOx absorption-type catalyst has not yet been established.
More specifically, the three way catalyst and the NOx absorption-type catalyst differ in their heat-resisting temperatures. Controlling the deterioration of one catalyst may proceed the deterioration of other catalyst. More specifically, the three way catalyst is oxidized and deteriorated when it is exposed to a high temperature and the exhaust gas becomes the lean atmosphere. To address this problem, it is necessary to control the air-fuel ratio in such a manner as to make the exhaust air-fuel ratio stoichiometrical when the three way catalyst is exposed to a high temperature in the oxide atmosphere. The heat-resisting temperature of the absorption-type NOx catalyst, however, is lower than that of the three way catalyst. Thus, if the absorption-type NOx catalyst is exposed to a high temperature and the exhaust gas becomes a stoichiometric atmosphere to reduce CO and THC (the generic name for hydrocarbon substance), absorbing material thereof never becomes carbonate or nitrite (or acid oxide) and is destabilized. Therefore, the absorbing material cannot absorb the NOx by combining with a carrier (deterioration).
Particularly if the flow rate of exhaust gas is high, the oxidization of the three way catalyst advances the deterioration, and if the flow rate of exhaust gas is low, there is a shortage of CO, THC and the like to thereby advance the deterioration of the absorption-type NOx catalyst.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an exhaust emission control device of an internal combustion engine, which can prevent the deterioration such as heat deterioration of the three way catalyst and the absorption-type NOx catalyst to thereby prevent the deterioration of an exhaust gas characteristic and the increase in cost.
The above object can be accomplished by providing an exhaust emission control device of an internal combustion engine, which purifies exhaust gas exhausted from the internal combustion engine; the exhaust emission control device comprising: a catalyst device composed of a three way catalyst for purifying harmful substance in the exhaust gas when an exhaust air-fuel ratio is substantially stoichiometrical and an NOx catalyst having a function of absorbing NOx in the exhaust gas when the air-fuel ratio is closer to a lean air-fuel ratio than to the stoichiometrical air-fuel ratio, the catalyst device being provided in an exhaust passage of the internal combustion engine; catalyst deterioration determination means for determining deterioration state of the catalyst device, the deterioration resulting from at least temperature; and control means for deteriorating exhaust gas components flowing into the catalyst device much more than exhaust gas components flowing into the catalyst device when an air-fuel ratio of a mixture supplied to the internal combustion engine is substantially stoichiometrical, if the catalyst deterioration determination means determines that the catalyst device is in a predetermined deterioration state.
The deterioration of an NOx absorbing function of the NOx catalyst results from at least the destabilization of absorbing material in the NOx catalyst, which is caused by the increase in the temperature. Thus, if the catalyst deterioration determination means determines that the catalyst device is in the predetermined deterioration state, the exhaust gas components flowing into the catalyst device are deteriorated much more than the exhaust gas components flowing into the catalyst device when the air-fuel ratio of the mixture supplied to the internal combustion engine is substantially stoichiometrical. Therefore, CO, H2, NOx, O2, THC and the like are supplied to the absorbing material to thereby stabilize the absorbing material as carbonate, nitrite or acid oxide. This prevents the heat deterioration, extends a heat-resisting life of the catalyst device, and prevents the deterioration of an exhaust gas characteristic and an increase in expense.
In one preferred mode of the present invention, the exhaust emission control device of the internal combustion engine further comprises: catalyst temperature sensing means for sensing or estimating a temperature of the catalyst device; and wherein the catalyst deterioration determination means determines that the catalyst device is in a predetermined deterioration state if a catalyst temperature sensed or estimated by the catalyst temperature sensing means is in excess of a heat-resisting temperature of the catalyst device.
In one preferred mode of the present invention, the exhaust emission control device of the internal combustion engine further comprises: catalyst temperature sensing means for sensing or estimating a temperature of the NOx catalyst; and wherein the catalyst deterioration determination means determines that the catalyst device is in a predetermined deterioration state if a temperature of the NOx catalyst sensed or estimated by the catalyst temperature sensing means is in excess of a heat-resisting temperature of the NOx catalyst.
In one preferred mode of the present invention, the control means prohibits the air-fuel ratio of the mixture supplied to the internal combustion engine from being substantially stoichiometrical in order to deteriorate the exhaust gas components.
In one preferred mode of the present invention, the exhaust emission control
Kawashima Kazuhito
Nakayama Osamu
Tamura Yasuki
Watanabe Tetsuya
Denion Thomas
Mitsubishi Jidosha Kogyo Kabushiki Kaisha
Rossi & Associates
Tran Binh
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