Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-03-16
2001-07-24
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S295000, C060S301000
Reexamination Certificate
active
06263666
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an exhaust emission control device of an internal combustion engine.
BACKGROUND OF THE INVENTION
A NOx storage catalyst which traps NOx (nitrogen oxides) in exhaust gas is used in the exhaust emission control device of an internal combustion engine.
The NOx storage catalyst traps and stores NOx in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean. When the engine is run at a rich or stoichiometric air fuel ratio, the stored NOx is reduced by components such as HC and CO in the exhaust gas.
However, SOx (sulfur oxide) is trapped by this NOx storage catalyst, too, and is stored. Therefore, the ability to trap NOx of an NOx storage catalyst falls when the amount of stored SOx increases (SOx poisonings).
In this regard, the exhaust emission control device disclosed in Tokkai Hei 7-217474 published by the Japanese Patent office in 1995 discloses a method wherein the SOx amount stored in the NOx storage catalyst provided in an exhaust pipe is estimated, and when the estimated SOx storage amount exceeds a permitted value, the exhaust gas flowing into the NOx storage catalyst is lean or at the stoichiometric air fuel ratio and catalyst temperature is higher than a predetermined temperature, the air-fuel ratio of the exhaust gas flowing into the catalyst is temporarily made rich, and stored SOx is discharged.
SUMMARY OF THE INVENTION
In the aforesaid device when the SOx storage amount is above a permitted value and catalyst temperature is lower than the predetermined temperature, the ignition timing is delayed to raise the catalyst temperature. However, when the catalyst temperature does not reach the predetermined temperature even if the ignition timing is delayed, retardation of ignition timing is stopped and lean air-fuel ratio operation is resumed.
Therefore, the vehicle may run at a lean air fuel ratio although the SOx storage amount in the NOx storage catalyst exceeds the permitted value and the NOx trapping capacity is low. The amount of NOx which passes through the NOx storage catalyst without being trapped then increases, and exhaust emissions increase.
In addition, in tee aforesaid device, no consideration was given to permanent deterioration of the NOx catalyst such as heat deterioration which leads to decrease of NOx trapping capacity as in the case when the SOx storage amount increased. Therefore, SOx discharge control is performed when the catalyst has permanently deteriorated and NOx trapping capacity does not return even if SOx discharge control is performed. This is detrimental to fuel economy.
It is therefore an object of the present invention to prevent increase of exhaust emissions and impairment of fuel economy when the NOx trapping capacity of an NOx storage catalyst decreases due to SOx poisoning or permanent deterioration, in an exhaust emission control device which performs discharge control of SOx stored in the NOx storage catalyst.
In order to achieve above object, this invention provides an exhaust emission control device for an engine comprising an exhaust pipe, a catalyst provided in the exhaust pipe which traps and stores NOx in exhaust gas and reduces the stored NOx according to an air-fuel ratio of the exhaust gas flowing into the catalyst, and a microprocessor programmed to determine whether or not conditions for discharging SOx stored in the catalyst are satisfied, raise the temperature of the catalyst to discharge SOx when SOx discharge conditions are satisfied and the running conditions of the engine are in a predetermined SOx discharge running region, and prohibit lean air fuel ratio running of the engine from when SOx discharge conditions are satisfied to when SOx discharge is complete.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.
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Ishizuka Yasuji
Kubo Kengo
Nishizawa Kimiyoshi
Denion Thomas
Foley & Lardner
Nissan Motor Co,. Ltd.
Tran Diem
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