IPC분류정보
국가/구분 |
United States(US) Patent
등록
|
국제특허분류(IPC7판) |
|
출원번호 |
US-0682730
(2003-10-10)
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우선권정보 |
JP-0305879 (2002-10-21) |
발명자
/ 주소 |
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출원인 / 주소 |
- Toyota Jidosha Kabushiki Kaisha
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대리인 / 주소 |
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인용정보 |
피인용 횟수 :
16 인용 특허 :
8 |
초록
▼
An exhaust emission control system for an internal combustion engine is provided which includes a NOx storage/reduction catalyst disposed in an exhaust passage of the engine, and a NOx sensor positioned in the exhaust passage downstream of the catalyst. A controller of the system performs a rich-spi
An exhaust emission control system for an internal combustion engine is provided which includes a NOx storage/reduction catalyst disposed in an exhaust passage of the engine, and a NOx sensor positioned in the exhaust passage downstream of the catalyst. A controller of the system performs a rich-spike operation to temporarily operate the engine at a rich air/fuel ratio each time a NOx storage state of the catalyst satisfies a predetermined rich-spike condition during a lean-burn operation. When the degree of degradation of the catalyst is determined by comparing the output of the NOx sensor with a predetermined evaluation value, the rich-spike condition is changed so that the amount of NOx stored in the catalyst at the time of a start of the rich-spike operation during a degradation determination period is made larger than that reached during a period other than the determination period.
대표청구항
▼
1. An exhaust emission control system for an internal combustion engine, comprising:a NOx storage/reduction catalyst disposed in an exhaust passage of the internal combustion engine, the NOx storage/reduction catalyst selectively storing NOx contained in exhaust gas flowing into the catalyst, throug
1. An exhaust emission control system for an internal combustion engine, comprising:a NOx storage/reduction catalyst disposed in an exhaust passage of the internal combustion engine, the NOx storage/reduction catalyst selectively storing NOx contained in exhaust gas flowing into the catalyst, through adsorption, absorption, or both of adsorption and absorption, when an air/fuel ratio of the exhaust gas is lean, and reducing and removing the stored NOx by using reducing components in the exhaust gas when the air/fuel ratio of the exhaust gas becomes equal to a stoichiometric air/fuel ratio or a rich air/fuel ratio; a NOx sensor positioned in the exhaust passage downstream of the NOx storage/reduction catalyst, the NOx sensor being operable to detect a NOx concentration in the exhaust gas; and a controller that: performs a rich-spike operation to temporarily operate the engine at a rich air/fuel ratio each time a NOx storage state of the NOx storage/reduction catalyst satisfies a predetermined rich-spike condition during an operation of the engine at a lean air/fuel ratio, so as to supply exhaust gas having a rich air/fuel ratio to the NOx storage/reduction catalyst for reduction and removal of the NOx stored in the NOx storage/reduction catalyst; determines a degree of degradation of the NOx storage/reduction catalyst by comparing an output value of the NOx sensor obtained in a predetermined determination period during the operation of the engine at a lean air/fuel ratio, with a predetermined evaluation value; and changes the rich-spike condition so that an amount of NOx stored in the NOx storage/reduction catalyst at the time of a start of the rich-spike operation during the determination period is made larger than the amount of NOx stored in the catalyst at the time of the start of the rich-spike operation during a period other than the determination period. 2. The exhaust emission control system according to claim 1, wherein the controller delays the start of the rich-spike operation during the determination period so as to increase the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the determination period, to be larger than the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the period other than the determination period.3. The exhaust emission control system according to claim 1, wherein:the controller uses the amount of NOx stored in the NOx storage/reduction catalyst as the NOx storage state of the NOx storage/reduction catalyst, and uses a condition that the amount of NOx stored in the catalyst reaches a predetermined reference storage amount as the predetermined rich-spike operation; and the controller sets the reference storage amount during the determination period to a larger value than the reference storage amount set during the period other than the determination period, so as to increase the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the determination period, to be larger than the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the period other than the determination period. 4. The exhaust emission control system according to claim 1, wherein:the controller uses an elapsed time measured from the time of completion of the last rich-spike operation as the NOx storage state of the NOx storage/reduction catalyst, and uses a condition that the elapsed time reaches a predetermined reference time as the predetermined rich-spike condition; and the controller sets the reference time during the determination period to be longer than the reference time set during the period other than the determination period, so as to increase the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the determination period, to be larger than the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the period other than the determination period. 5. An exhaust emission control method for an internal combustion engine, comprising the steps of:providing a NOx storage/reduction catalyst in an exhaust passage of the internal combustion engine, the NOx storage/reduction catalyst selectively storing NOx contained in exhaust gas flowing into the catalyst, through adsorption, absorption, or both of adsorption and absorption, when an air/fuel ratio of the exhaust gas is lean, and reduces and removes the stored NOx by using reducing components in the exhaust gas when the air/fuel ratio of the exhaust gas becomes equal to a stoichiometric air/fuel ratio or a rich air/fuel ratio; positioning a NOx sensor in the exhaust passage downstream of the NOx storage/reduction catalyst, the NOx sensor being operable to detect a NOx concentration in the exhaust gas; performing a rich-spike operation to temporarily operate the engine at a rich air/fuel ratio each time a NOx storage state of the NOx storage/reduction catalyst satisfies a predetermined rich-spike condition during an operation of the engine at a lean air/fuel ratio, so as to supply exhaust gas having a rich air/fuel ratio to the NOx storage/reduction catalyst for reduction and removal of the NOx stored in the NOx storage/reduction catalyst; determining a degree of degradation of the NOx storage/reduction catalyst by comparing an output value of the NOx sensor obtained in a predetermined determination period during the operation of the engine at a lean air/fuel ratio, with a predetermined evaluation value; and changing the rich-spike condition so that an amount of NOx stored in the NOx storage/reduction catalyst at the time of a start of the rich-spike operation during the determination period is made larger than the amount of NOx stored in the catalyst at the time of the start of the rich-spike operation during a period other than the determination period. 6. The exhaust emission control method according to claim 5, wherein the start of the rich-spike operation is delayed during the determination period so that the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the determination period is increased to be larger than the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the period other than the determination period.7. The exhaust emission control method according to claim 5, wherein:the amount of NOx stored in the NOx storage/reduction catalyst is used as the NOx storage state of the NOx storage/reduction catalyst, and a condition that the amount of NOx stored in the catalyst reaches a predetermined reference storage amount is used as the predetermined rich-spike operation; and the reference storage amount is set during the determination period to a larger value than the reference storage amount set during the period other than the determination period, so that the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the determination period is increased to be larger than the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the period other than the determination period. 8. The exhaust emission control method according to claim 5, wherein:an elapsed time measured from the time of completion of the last rich-spike operation is used as the NOx storage state of the NOx storage/reduction catalyst, and a condition that the elapsed time reaches a predetermined reference time is used as the predetermined rich-spike condition; and the reference time is set during the determination period to be longer than the reference time set during the period other than the determination period, so that the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the determination period is increased to be larger than the amount of NOx stored in the NOx storage/reduction catalyst at the time of the start of the rich-spike operation during the period other than the determination period.
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