Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-03-21
2001-05-22
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S285000, C060S295000, C060S301000
Reexamination Certificate
active
06233923
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an exhaust emission control device of an internal combustion engine.
BACKGROUND OF THE INVENTION
Fuel economy improves if an internal combustion engine is run at a lean air-fuel ratio, but during lean running, the NOx in the exhaust gas increases. Therefore, a NOx storage catalyst is used as exhaust catalyst for an engine which performs lean air-fuel ratio running.
The NOx storage catalyst traps and stores NOx contained in the exhaust gas when the engine is running at a lean air-fuel ratio. When the engine is run at a rich or stoichiometric air-fuel ratio, the stored NOx is reduced by components in the exhaust gas such as HC (hydrocarbons) and CO.
However, SOx (sulfur oxides) in the exhaust gas are also trapped and stored by this NOx storage catalyst. Therefore, the ability of the NOx storage catalyst to trap NOx falls if the amount of stored SOx increases (SOx poisoning).
In Tokkai Hei 10-54274 published by the Japanese Patent Office in 1998, when the amount of SOx stored in the NOx storage catalyst increases and NOx trapping performance declines, a misfire is caused at a lean air-fuel ratio for a predetermined time, and unburnt fuel is supplied to the NOx storage catalyst. By burning this unburnt fuel on the catalyst or by retarding ignition time to increase the exhaust gas temperature, the catalyst temperature is increased, and the stored SOx is thereby discharged.
SUMMARY OF THE INVENTION
Even in an engine which runs at a lean air-fuel ratio, the engine is usually operated at a stoichiometric air-fuel ratio outside a predetermined region, so a three-way catalyst must be provided in addition to the NOx storage catalyst.
The most common method of diagnosing the deterioration of the three-way catalyst is to measure its oxygen storage performance. The oxygen storage performance is for example determined by measuring the change of air-fuel ratio downstream of the three-way catalyst when the air-fuel ratio of the exhaust flowing into the three-way catalyst is made to periodically fluctuate between rich and lean around the stoichiometric air-fuel ratio. For this reason, deterioration diagnosis of the three-way catalyst is performed while running at the stoichiometric air-fuel ratio.
However, if the range in which lean air-fuel ratio running is performed is set wide in order to improve fuel economy, the range in which deterioration diagnosis of the three-way catalyst is possible will become narrow, and opportunities to make a diagnosis will decrease.
Moreover, as the amounts of unburnt fuel and oxygen in the exhaust gas are increased and exhaust gas temperature is raised while performing SOx discharge control, a precise deterioration diagnosis cannot be made and this also reduces diagnostic opportunities.
It is therefore an object of this invention to permit a precise deterioration diagnosis of a three-way catalyst, even when diagnostic opportunities have decreased due to lean air-fuel ratio running or SOx discharge control.
In order to achieve above object, this invention provides an exhaust emission control device of an engine, comprising an exhaust pipe, a front three-way catalyst provided in the exhaust pipe, a rear catalyst provided downstream of the front three-way catalyst which traps or reduces NOx according to an air-fuel ratio of the inflowing exhaust gas, a sensor which detects the air-fuel ratio of the exhaust gas downstream of the front three-way catalyst, a sensor which detects the running state of the engine, and a microprocessor. The microprocessor is programmed to determine whether or not conditions are satisfied for discharging SOx stored in the rear catalyst, perform SOx discharge control of the rear catalyst when conditions are satisfied for discharging SOx and the running state of the engine is within an SOx discharge running region, cause the air-fuel ratio of the engine to fluctuate periodically between rich and lean around the stoichiometric air-fuel ratio when the running state of the engine is in a catalyst diagnosis region whereof part overlaps with the SOx discharge running region, perform a primary diagnosis of whether or not the front three-way catalyst has deteriorated based on the air-fuel ratio of the exhaust gas downstream of the front three-way catalyst detected in a first period each time the first period elapses when the engine is running in the diagnosis region, and perform a secondary diagnosis of whether or not the front three-way catalyst has deteriorated based on the air-fuel ratio of the exhaust gas downstream of the front catalyst detected in a second period longer than the first period each time the second period elapses when the engine is running in the diagnosis region. The microprocessor is further programmed to prohibit the primary diagnosis and second diagnosis when SOx discharge control is performed, and prohibit SOx discharge control when it is diagnosed that the front three-way catalyst has deteriorated in the primary diagnosis.
According to an aspect of this invention, this invention provides an exhaust emission control device of an engine, comprising an exhaust pipe, a three-way catalyst provided in the exhaust pipe which traps or reduces NOx according to an air-fuel ratio of the inflowing exhaust gas, a sensor which detects the air-fuel ratio of the exhaust gas downstream of the three-way catalyst, a sensor which detects the running state of the engine, and a microprocessor. The microprocessor is programmed to determine whether or not conditions are satisfied for discharging SOx stored in the three-way catalyst, perform SOx discharge control of the three-way catalyst when conditions are satisfied for discharging SOx and the running state of the engine is within a SOx discharge running region, cause the air-fuel ratio of the engine to fluctuate periodically between rich and lean around the stoichiometric air-fuel ratio when the running state of the engine is in a catalyst diagnosis region whereof part overlaps with the SOx discharge running region, perform a primary diagnosis of whether or not the three-way catalyst has deteriorated based on the air-fuel ratio of the exhaust gas downstream of the three-way catalyst detected in a first period each time the first period elapses when the engine is running in the diagnosis region, and perform a secondary diagnosis of whether or not the three-way catalyst has deteriorated based on the air-fuel ratio of the exhaust gas downstream of the three-way catalyst detected in a second period longer than the first period each time the second period elapses when the engine is running in the diagnosis region. The microprocessor is further programmed to prohibit the primary diagnosis and secondary diagnosis when SOx discharge control is performed, and prohibit SOx discharge control when it is diagnosed that the three-way catalyst has deteriorated in the primary diagnosis.
According to another aspect of this invention, this invention provides an exhaust emission control device of an engine, comprising an exhaust pipe, a three-way catalyst provided in the exhaust pipe, a sensor which detects the air-fuel ratio of the exhaust gas downstream of the three-way catalyst, a sensor which detects the running state of the engine, and a microprocessor. The microprocessor is programmed to control the air-fuel ratio of the engine to a lean value when the running state of the engine is in a lean air-fuel ratio running region, cause the air-fuel ratio of the engine to fluctuate periodically between rich and lean around the stoichiometric air-fuel ratio when the running state of the engine is in a catalyst diagnosis region and lean air-fuel ratio control is not being performed, perform a primary diagnosis of whether or not the three-way catalyst has deteriorated based on the air-fuel ratio of the exhaust gas downstream of the three-way catalyst detected in a first period each time the first period elapses when the engine is running in the diagnosis region, and perform a secondary diagnosis of whether or not the three-way catalyst has deteriorated based on
Itou Hidetoshi
Nishizawa Kimiyoshi
Takahashi Hideaki
Denion Thomas
Foley & Lardner
Nissan Motor Co,. Ltd.
Tran Diem
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