Exhaust gas purification device for an internal combustion engine
First Claim
1. An exhaust gas purification device for an internal combustion engine, comprising:
- a NOX occluding and reducing catalyst disposed in an exhaust gas passage of an internal combustion engine, the catalyst absorbing NOX in exhaust gas when an inflowinq air-fuel ratio of exhaust gas flowing into the catalyst is lean and releasing and reducing previously absorbed NOX when the inflowinq air-fuel ratio is one of a stoichiometric air-fuel ratio and a rich air-fuel ratio;
an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst and detecting an outflowing air-fuel ratio of exhaust gas flowing out of the catalyst;
air-fuel ratio control means for switching the inflowing air-fuel ratio from a rich air-fuel ratio to a lean air-fuel ratio; and
evaluating means for evaluating an ability of the catalyst based on length of time during which the outflowing air-fuel ratio is maintained at a stoichiometric air-fuel ratio after the inflowing air fuel ratio is switched by the air-fuel ratio control means.
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Accused Products
Abstract
In an exhaust gas purification device for an internal combustion engine, a NOX occluding and reducing catalyst is disposed in the exhaust gas passage of an engine. The NOX occluding and reducing catalyst absorbs NOX in the exhaust gas when the air-fuel ratio of the exhaust gas is at a lean air-fuel ratio and releases and reduces NOX when the air-fuel ratio of the exhaust gas is at a rich air-fuel ratio. The air-fuel ratio of the exhaust gas flowing out from the catalyst is detected by an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst. When the air-fuel ratio of the exhaust gas flowing into the catalyst is changed from a rich air-fuel ratio to a lean air-fuel ratio, the air-fuel ratio of the exhaust gas flowing out from the catalyst stays at a stoichiometric air-fuel ratio before it changes to a lean air-fuel ratio. The length of the period in which the air-fuel ratio of the exhaust gas flowing out from the catalyst stays at a stoichiometric air-fuel ratio corresponds to the magnitude of the ability of the NOX occluding and reducing catalyst as a reducing catalyst. Thus, by measuring the length of the stoichiometric air-fuel ratio period of the exhaust gas flowing out from the NOX occluding and reducing catalyst, the ability of the NOX occluding and reducing catalyst as a reducing catalyst can be precisely evaluated.
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Citations
6 Claims
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1. An exhaust gas purification device for an internal combustion engine, comprising:
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a NOX occluding and reducing catalyst disposed in an exhaust gas passage of an internal combustion engine, the catalyst absorbing NOX in exhaust gas when an inflowinq air-fuel ratio of exhaust gas flowing into the catalyst is lean and releasing and reducing previously absorbed NOX when the inflowinq air-fuel ratio is one of a stoichiometric air-fuel ratio and a rich air-fuel ratio; an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst and detecting an outflowing air-fuel ratio of exhaust gas flowing out of the catalyst; air-fuel ratio control means for switching the inflowing air-fuel ratio from a rich air-fuel ratio to a lean air-fuel ratio; and evaluating means for evaluating an ability of the catalyst based on length of time during which the outflowing air-fuel ratio is maintained at a stoichiometric air-fuel ratio after the inflowing air fuel ratio is switched by the air-fuel ratio control means. - View Dependent Claims (2)
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3. An exhaust gas purification device for an engine, comprising:
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a NOX occluding and reducing catalyst disposed in an exhaust gas passage of an internal combustion engine, the catalyst absorbing NOX in exhaust gas when an inflowing air-fuel ratio of exhaust gas flowing into the catalyst is lean and releasing and reducing previously absorbed NOX when the inflowing air-fuel ratio is one of a stoichiometric air-fuel ratio and a rich air-fuel ratio; an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst and detecting an outflowing air-fuel ratio of exhaust gas flowing out of the catalyst; air-fuel ratio control means for changing the inflowing air-fuel ratio from a lean air-fuel ratio to a rich air-fuel ratio and, after maintaining the inflowing air-fuel ratio rich for a predetermined period, changing the inflowing air-fuel ratio to a lean air-fuel ratio; and evaluating means for evaluating an ability of the catalyst based on changes in the outflowing air-fuel ratio when the inflowing air fuel ratio is changed from a rich air-fuel ratio to a lean air-fuel ratio. - View Dependent Claims (4)
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5. An exhaust gas purification device for an engine, comprising:
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a NOX occluding and reducing catalyst disposed in an exhaust gas passage of an internal combustion engine, the catalyst absorbing NOX in exhaust gas when an inflowing air-fuel ratio of exhaust gas flowing into the catalyst is lean and releasing and reducing previously absorbed NOX when the inflowing air-fuel ratio is one of a stoichiometric air-fuel ratio and a rich air-fuel ratio; an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst and detecting an outflowing air-fuel ratio of exhaust gas flowing out of the catalyst; air-fuel ratio control means for changing the inflowing air-fuel ratio from a rich air-fuel ratio to a predetermined lean air-fuel ratio; and evaluating means for evaluating an ability of the catalyst based on an amount of deviation of the outflowing air-fuel ratio from the predetermined lean air-fuel ratio after the air-fuel ratio of the inflowing air fuel ratio is changed to the predetermined lean air-fuel ratio by the air-fuel ratio control means. - View Dependent Claims (6)
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Specification