Power plants – Internal combustion engine with treatment or handling of... – Methods
Utility Patent
1999-02-12
2001-01-02
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S277000, C060S301000, C060S276000, C073S118040
Utility Patent
active
06167695
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to method and system for diagnosing deterioration of a catalytic converter of an internal combustion engine, and more specifically to a nitrogen oxide (NOx) catalyst employed in an exhaust gas passage of the engine.
BACKGROUND OF THE INVENTION
There is known a NOx catalyst that is arranged in an exhaust gas passage of an internal combustion engine and adapted to absorb nitrogen oxides (NOx) present in exhaust gas emitted from the engine when the engine is operated in a lean air/fuel (A/F) ratio (excess oxygen), i.e., the lean-burn operation, and discharge the NOx absorbed therein when the engine is operated in a rich A/F ratio (excess fuel). Namely, when an amount of the NOx absorbed in the NOx catalyst reaches a predetermined large value, the engine is temporarily operated for controlling the A/F ratio less than a stoichiometric or theoretical A/F ratio, namely, controlling to a rich side with respect to the stoichiometric A/F ratio. Such the control of the A/F ratio to the rich side is hereinafter referred to as rich spike control of A/F ratio. As a result of the rich spike control of A/F ratio, amounts of hydrocarbons (HC) present as unburned component in the exhaust gas from the engine and carbon monoxide increase and an amount of oxygen present in the exhaust gas decreases. The NOx catalyst discharges the NOx absorbed therein in response to the decrease of oxygen. Then, the NOx discharged is reacted with hydrocarbons (HC) present as unburned component in the exhaust gas and reduced to nitrogen. Thus, the NOx can be removed from the exhaust gas emitted from the engine. Such kind of the NOx catalyst is disclosed in U.S. Pat. No. 5,473,887 issued Dec. 12, 1995 which is incorporated herein by reference.
When the NOx absorbency of such the NOx catalyst is deteriorated, the timing of the rich spike control of A/F ratio is offset or the amount of the unburned HC supplied by the rich spike control of A/F ratio far exceeds that required for reducing the NOx discharged from the catalyst. This is undesirable from the viewpoint of emission control. Therefore, it is required to accurately determine deterioration of the catalyst.
Japanese Patent Application First Publication No. 7-208151 discloses a NOx catalyst deterioration determining device for an internal combustion engine. The device is adapted for determining deterioration of a NOx catalyst in an exhaust system by measuring the time elapsed from a moment the entire amount of the NOx absorbed in the NOx catalyst is discharged therefrom after the rich spike control to a moment the amount of the NOx absorbed reaches a predetermined large value, and comparing the time measured with a reference value to thereby determine that the NOx catalyst is deteriorated if the time measured is less than the reference value.
Japanese Patent Application First Publication No. 8-232644 discloses a NOx catalyst deterioration determining device for an internal combustion engine. The device is adapted for determining deterioration of a NOx catalyst in an exhaust system by measuring a rate of change in the A/F ratio downstream of the NOx catalyst that occurs when the rich spike control of A/F ratio is carried out after the NOx absorbed in the NOx catalyst reaches saturation.
SUMMARY OF THE INVENTION
In the device described in the former conventional art, it is not taken into consideration that a rate of change in concentration of the NOx in the exhaust gas flowing into the catalyst varies depending on the engine operation conditions. Therefore, it seems uncertain that the time measured accurately corresponds to the amount of the NOx absorbed in the catalyst. Assuming that the engine runs in a specific operating range, it is possible to accurately measure the time. However, it is a rare case that the engine operation is kept in the specific range until the absorbed NOx varies from zero to the predetermined large value. Therefore, the determination of the deterioration of the catalyst can be conducted merely at a considerably low frequency.
Meanwhile, it will be possible to determine the deterioration of the NOx catalyst by estimating a rate of change in amount of the NOx absorbed in the catalyst per unit time on the basis of the engine operation condition, calculating a sum of the estimated values of the rate of change to obtain a saturation amount of the NOx absorbed, and comparing the saturation amount of the NOx absorbed with a predetermined reference value. However, the calculated saturation amount of the absorbed NOx contains an error that is accumulation of errors in initially estimated change rates from actual change rates over the entire period of time during which the calculation is made, so that the determination of deterioration of the NOx catalyst cannot be conducted with sufficient accuracy.
In the device described in the latter conventional art, it is required that the NOx catalyst is completely saturated with the NOx before conducting the determination of deterioration of the NOx catalyst. This leads to an undesirable emission condition in which the NOx in the exhaust gas from the engine is permitted to pass through the saturated NOx catalyst without being absorbed therein.
It is an object of the present invention to provide catalyst-deterioration diagnosis capable of determining deterioration of a catalyst in an exhaust system of an internal combustion engine with high accuracy and with a simple arrangement.
According to one aspect of the present invention, there is provided a system for diagnosing deterioration of a nitrogen oxide catalyst coupled to an internal combustion engine, said catalyst being capable of absorbing nitrogen oxides present in exhaust gas emitted from the engine during lean-burn operation and releasing the nitrogen oxides absorbed when an air/fuel ratio is less than a stoichiometric air/fuel ratio, comprising:
a nitrogen oxide sensor arranged downstream of the nitrogen oxide catalyst to detect concentration of the nitrogen oxides in the exhaust gas passing through the nitrogen oxide catalyst and generate a signal indicative of the detected concentration of the nitrogen oxides; and
a controller operative, in response to said signal generated from said nitrogen oxide sensor, to calculate a rate of change in the detected concentration of the nitrogen oxides over a predetermined period of time after the air/fuel ratio becomes less than the stoichiometric air/fuel ratio, compare said rate of change in the detected concentration of the nitrogen oxides with a predetermined reference value and determine, in response to the comparison result, that the nitrogen oxide catalyst is deteriorated.
According to further aspect of the present invention, there is provided a system for diagnosing deterioration of a nitrogen oxide catalyst coupled to an internal combustion engine, said catalyst being capable of absorbing nitrogen oxides present in exhaust gas emitted from the engine during lean-burn operation and releasing the nitrogen oxides absorbed when an air/fuel ratio is less than a stoichiometric air/fuel ratio, comprising:
a nitrogen oxide sensor arranged downstream of the nitrogen oxide catalyst to detect concentration of the nitrogen oxides in the exhaust gas passing through the nitrogen oxide catalyst and generate a signal indicative of the detected concentration of the nitrogen oxides; and
a controller operative, in response to said signal generated from said nitrogen oxide sensor, to calculate rates of change in the detected concentration of the nitrogen oxides a plurality of times over a predetermined period of time after the air/fuel ratio becomes less than the stoichiometric air/fuel ratio, compare a representative value derived from the calculated rates of change in the detected concentration of the nitrogen oxides with a predetermined reference value and determine, in response to the comparison result, that the nitrogen oxide catalyst is deteriorated.
According to still further aspect of the present invention, there is provided a method of diagnosing deterioration of a nitr
Ishihara Kouji
Itou Hidetoshi
Itou Yasuyuki
Denion Thomas
Foley & Lardner
Nissan Motor Co,. Ltd.
Trieu Thai-Ba
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