Catalyst degradation determination apparatus and method

A catalyst degradation determination apparatus comprising:

• an exhaust-purifying catalyst arranged in an exhaust passage;
• upstream air by fuel ratio detection means provided at an upstream position, for detecting the air by fuel ratio;
• downstream air by fuel ratio detection means provided at a downstream position, for detecting the air by fuel ratio;
• engine condition detection means for detecting the driving condition of an engine;
• degradation determination condition judgment means for judging a predetermined degradation determination condition of the exhaust-purifying catalyst, based on the driving condition of the engine;
• catalyst degradation judgment means for judging the degradation of the exhaust-purifying catalyst when the predetermined degradation determination conditions are satisfied, based on a ratio by each condition value of output values of the upstream air by fuel ratio detection means and the downstream air by fuel ratio detection means during a predetermined period;
• and
• holding means for holding the condition values of output values of the upstream air by fuel ratio detection means and the downstream air by fuel ratio detection means when the predetermined degradation determination conditions are not satisfied during the judgment of the catalyst degradation during the predetermined period;
• wherein said catalyst degradation judgment means judges the degradation of the exhaust-purifying catalyst based on the condition values when the predetermined degradation determination conditions are again satisfied during a predetermined period after the predetermined degradation determination conditions are not satisfied.

A catalyst degradation determination apparatus, comprising:

• an exhaust-purifying catalyst arranged to an exhaust passage;
• an upstream oxygen sensor provided at an upstream position for detecting air by fuel ratio;
• a downstream oxygen sensor provided at a downstream position for detecting the air by fuel ratio;
• an engine condition detection sensor for detecting a driving condition of an engine;
• a controller for judging a predetermined degradation determination condition of the exhaust-purifying catalyst based on the driving condition of the engine, and for judging the degradation of the exhaust-purifying catalyst when the predetermined degradation determination conditions are satisfied, based on a ratio by each condition value of output values of the upstream oxygen sensor and the downstream oxygen sensor during a predetermined period;
• wherein said controller holds the condition values of output values of the upstream oxygen sensor and the downstream oxygen sensor when the predetermined degradation determination conditions are not satisfied during the judgment of the catalyst degradation during the predetermined period, and judges the degradation of the exhaust-purifying catalyst based on the condition values when the predetermined degradation determination conditions are again satisfied after an activated status of the exhaust-purifying catalyst are judged continuously while holding the condition values.

A catalyst degradation determination apparatus, comprising:

• an exhaust-purifying catalyst arranged to an exhaust passage;
• an upstream oxygen sensor provided at an upstream position for detecting air by fuel ratio;
• a downstream oxygen sensor provided at a downstream position for detecting the air by fuel ratio;
• an engine condition detection sensor for detecting a driving condition of an engine;
• a controller for judging a predetermined degradation determination condition of the exhaust-purifying catalyst, based on the driving condition of the engine, and for judging the degradation of the exhaust-purifying catalyst when the predetermined degradation determination conditions are satisfied, based on a ratio by each condition value of output values of the upstream oxygen sensor and the downstream oxygen sensor during a predetermined period;
• wherein said controller holds the condition values of output values of the upstream oxygen sensor and the downstream oxygen sensor when the predetermined degradation determination conditions are not satisfied during the judgment of the catalyst degradation during the predetermined period, and judges the degradation of the exhaust-purifying catalyst based on the condition values when the predetermined degradation determination conditions are again satisfied during a predetermined period after the predetermined degradation determination conditions are not satisfied.

A catalyst degradation determination method employing A/F ratio sensors respectively provided at an upstream position and a downstream position of an exhaust-purifying catalyst, integrating output values from said respective A/F ratio sensors when predetermined degradation determination conditions are satisfied, and detecting degradation of said exhaust-purifying catalyst by comparing the respective integrated values, comprising:

• a holding step of holding integrated values when the predetermined degradation determination conditions are not satisfied during integration of the output values from said respective A/F ratio sensors;
• an integration step of re-starting the integration of the output values with the integrated values held at said holding step when the predetermined degradation determination conditions are satisfied again;
• and
• a clearing step of clearing the integrated values held at said holding step if a predetermined period has elapsed since the predetermined degradation determination conditions were not satisfied.