Exhaust gas purification device for an internal combustion engine

An exhaust gas purification device for an internal combustion engine comprising:

• an NOx occluding and reducing catalyst disposed in an exhaust gas passage of the internal combustion engine to absorb NOx in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in is larger than a stoichiometric air-fuel ratio and to release and reduce the absorbed NOx when the air-fuel ratio of the exhaust gas flowing in becomes smaller than the stoichiometric air-fuel ratio, said NOx occluding and reducing catalyst exhibiting a decrease in the capability of absorbing, releasing and reducing the NOx as it adsorbs or absorbs contaminants in the exhaust gas;
• a holding amount estimation means for estimating the amount of said contaminants adsorbed or absorbed by said NOx occluding and reducing catalyst;
• a heating means for releasing said contaminants from the NOx occluding and reducing catalyst by heating said NOx occluding and reducing catalyst when the amount of said contaminants increases to be in excess of a predetermined judging value and when the operating condition of the engine turns into a predetermined heating-conducting condition;
• and
• a heating-conducting condition-setting means for setting said heating-conducting condition depending upon the history of the operating conditions of the engine.

An exhaust gas purification device for an internal combustion engine comprising:

• an NOx occluding and reducing catalyst disposed in an exhaust gas passage of the internal combustion engine to absorb NOx in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in is larger than a stoichiometric air-fuel ratio and to release and reduce the absorbed NOx when the air-fuel ratio of the exhaust gas flowing in becomes smaller than the stoichiometric air-fuel ratio, said NOx occluding and reducing catalyst exhibiting a decrease in the capability of absorbing, releasing and reducing the NOx as it adsorbs or absorbs contaminants from the exhaust gas;
• a holding amount estimation means for estimating the amount of said contaminants adsorbed or absorbed by said NOx occluding and reducing catalyst;
• a heating means for releasing said contaminants from the NOx occluding and reducing catalyst by heating said NOx occluding and reducing catalyst when the amount of said contaminants increases in excess of a predetermined judging value and when the operating condition of the engine turns into a predetermined heating-conducting condition;
• and
• a heating-conducting condition-setting means for setting said heating-conducting condition depending upon the properties of the fuel of the engine.

An exhaust gas purification device for an internal combustion engine comprising:

• an NOx occluding and reducing catalyst disposed in an exhaust gas passage of the internal combustion engine to absorb NOx in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in is larger than a stoichiometric air-fuel ratio and to release and reduce the absorbed NOx when the air-fuel ratio of the exhaust gas flowing in becomes smaller than the stoichiometric air-fuel ratio, said NOx occluding and reducing catalyst exhibiting a decrease in the capability of absorbing, releasing and reducing the NOx as it adsorbs or absorbs contaminants in the exhaust gas;
• a holding amount estimation means for estimating the amount of said contaminants adsorbed or absorbed by said NOx occluding and reducing catalyst;
• a heating means for releasing said contaminants from the NOx occluding and reducing catalyst by heating said NOx occluding and reducing catalyst when the amount of said contaminants increases in excess of a predetermined judging value and when the operating condition of the engine turns into a predetermined heating-conducting condition;
• and
• a heating-conducting condition-setting means for setting said heating-conducting condition depending upon the temperature of the cooling water of the engine.

An exhaust gas purification device for an internal combustion engine comprising:

• an NOx occluding and reducing catalyst disposed in an exhaust gas passage of the internal combustion engine to absorb NOx in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in is larger than a stoichiometric air-fuel ratio and to release and reduce the absorbed NOx when the air-fuel ratio of the exhaust gas flowing in becomes smaller than the stoichiometric air-fuel ratio, said NOx occluding and reducing catalyst exhibiting a decrease in the capability of absorbing, releasing and reducing the NOx as it adsorbs or absorbs contaminants in the exhaust gas;
• a holding amount estimation means for estimating the amount of said contaminants adsorbed or absorbed by said NOx occluding and reducing catalyst;
• a recovering means which maintains said NOx occluding and reducing catalyst within a predetermined high-temperature range for a predetermined recovering period when the holding amount of said contaminants estimated by said holding amount estimation means has reached a predetermined value, and controls the air-fuel ratio of the exhaust gas flowing into said NOx occluding and reducing catalyst to assume a recovering air-fuel ratio at which said contaminants are released;
• a recovering degree evaluation means for evaluating the degree of recovery of the capability of absorbing, releasing and reducing NOx by reduction of said NOx occluding and reducing catalyst accomplished by said recovering means;
• and
• a first changing means for changing the total amount of the reducing substances in the exhaust gas flowing into said NOx occluding and reducing catalyst during the recovering period of the next time depending upon the degree of recovery evaluated by said recovering degree evaluation means.

An exhaust gas purification device for an internal combustion engine comprising:

• an NOx occluding and reducing catalyst disposed in an exhaust gas passage of the internal combustion engine to absorb NOx in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in is larger than a stoichiometric air-fuel ratio and to release and reduce the absorbed NOx when the air-fuel ratio of the exhaust gas flowing in becomes smaller than the stoichiometric air-fuel ratio, said NOx occluding and reducing catalyst exhibiting a decrease in the capability of absorbing, releasing and reducing the NOx as it adsorbs or absorbs contaminants in the exhaust gas;
• a holding amount estimation means for estimating the amount of said contaminants held by being adsorbed or absorbed by said NOx occluding and reducing catalyst;
• a recovering means which maintains said NOx occluding and reducing catalyst within a predetermined high-temperature range for a predetermined recovering period when the holding amount of said contaminants estimated by said holding amount estimation means has reached a predetermined value, and controls the air-fuel ratio of the exhaust gas flowing into said NOx occluding and reducing catalyst to assume a recovering air-fuel ratio at which said contaminants are released;
• an estimation means for estimating the concentration of precursors of said contaminants in the fuel;
• and
• a second changing means for changing the total amount of the reducing substances flowing into said NOx occluding and reducing catalyst during said recovering period depending upon the concentration of said precursors estimated by said estimation means.