Exhaust gas purification device of an engine
First Claim
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1. An exhaust gas purification device of an engine having an exhaust passage, said device comprising:
- a NOx absorbent arranged in the exhaust passage and absorbing NOx when an air-fuel ratio of exhaust gas flowing into said NOx absorbent is lean, said NOx absorbent releasing absorbed NOx when the concentration of oxygen in the exhaust gas flowing into said NOx absorbent is lowered;
determining means for determining whether an engine operating region belongs to a first engine operating region in which an air-fuel ratio of an air-fuel mixture fed into the engine should be made approximately the stoichiometric air-fuel ratio or a second engine operating region in which the amount of fuel fed into the engine is reduced below the amount of fuel which is necessary to make said air-fuel ratio of the air-fuel mixture the stoichiometric air-fuel ratio; and
an air-fuel ratio control means for controlling said air-fuel ratio of the air-fuel mixture to make said air-fuel ratio of the air-fuel mixture approximately the stoichiometric air-fuel ratio after temporarily making said air-fuel ratio of the air-fuel mixture rich when the engine operating region is changed over from said second engine operating region to said first engine operating region.
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Abstract
An engine comprising an exhaust passage having therein a NOx absorbent which absorbs the NOx when the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is lean and releases the absorbed NOx when the air-fuel ratio of the exhaust gas flowing into the NOx absorbent becomes the stoichiometric air-fuel ratio or rich. When the air-fuel ratio of the air-fuel mixture should be changed over from lean to the stoichiometric air-fuel ratio, the air-fuel ratio of the air-fuel mixture is temporarily made rich and is then made the stoichiometric air-fuel ratio.
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10 Claims
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1. An exhaust gas purification device of an engine having an exhaust passage, said device comprising:
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a NOx absorbent arranged in the exhaust passage and absorbing NOx when an air-fuel ratio of exhaust gas flowing into said NOx absorbent is lean, said NOx absorbent releasing absorbed NOx when the concentration of oxygen in the exhaust gas flowing into said NOx absorbent is lowered; determining means for determining whether an engine operating region belongs to a first engine operating region in which an air-fuel ratio of an air-fuel mixture fed into the engine should be made approximately the stoichiometric air-fuel ratio or a second engine operating region in which the amount of fuel fed into the engine is reduced below the amount of fuel which is necessary to make said air-fuel ratio of the air-fuel mixture the stoichiometric air-fuel ratio; and an air-fuel ratio control means for controlling said air-fuel ratio of the air-fuel mixture to make said air-fuel ratio of the air-fuel mixture approximately the stoichiometric air-fuel ratio after temporarily making said air-fuel ratio of the air-fuel mixture rich when the engine operating region is changed over from said second engine operating region to said first engine operating region. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification