Apparatus for detecting deterioration of a three-way catalytic converter for an engine

An apparatus for detecting deterioration of a catalytic converter disposed in an exhaust passage of an internal combustion engine comprising:

• an upstream air-fuel ratio sensor disposed in the exhaust passage at the upstream side of said catalytic converter for outputting a signal corresponding to the air-fuel ratio of the exhaust gas at the upstream side of said catalytic converter;
• a downstream air-fuel ratio sensor disposed in the exhaust passage at the downstream side of said catalytic converter for outputting a signal corresponding to the air-fuel ratio of the exhaust gas at the downstream side of said catalytic converter;
• an air-fuel ratio feedback control means for calculating an air-fuel ratio correction factor for correcting the amount of fuel supplied to the engine at least in accordance with said upstream air-fuel ratio sensor and an air-fuel ratio leaning factor for compensating for age deterioration of devices related to a fuel supply system;
• a deterioration detecting means for detecting a deterioration of the converter at least in accordance with the output of said downstream air-fuel ratio sensor;
• an oxygen balance estimating means for estimating a balance between the oxygen absorbing power and the oxygen releasing power in accordance with the integral of the difference between the air-fuel ratio correction factor and the air-fuel ratio leaning factor calculated by said air-fuel ratio feedback control means;
• and
• a detection inhibiting means for inhibiting the detection of the deterioration with said deterioration detecting means when the balance estimated by said oxygen balance estimating means deviates from at least one fixed threshold.

A method for detecting deterioration of a three-way catalytic converter disposed in an exhaust passage of an internal combustion engine with an upstream air-fuel ratio sensor disposed in the exhaust passage at the upstream side of said catalytic converter for outputting a signal corresponding to the air-fuel ratio of the exhaust gas at the upstream side of said catalytic converter and a downstream air-fuel ratio sensor disposed in the exhaust passage at the downstream side of said catalytic converter for outputting a signal corresponding to the air-fuel ratio of the exhaust gas at the downstream side of said catalytic converter comprising the steps of;

• an air-fuel ratio feedback control step for controlling the amount of fuel supplied to the engine at least in accordance with the output of the upstream air-fuel ratio sensor;
• a deterioration detecting step for detecting deterioration of the converter at least in accordance with the output of the downstream air-fuel ratio sensor;
• an oxygen balance estimating step for estimating a balance between the oxygen absorbing power and the oxygen releasing power;
• and
• a detection inhibiting step for inhibiting the detection of the deterioration degree at said deterioration detecting step when the balance estimated at said oxygen balance estimating step deviates from at least one fixed threshold.

A method for detecting deterioration of a three-way catalytic converter disposed in an exhaust passage of an internal combustion engine with an upstream air-fuel ratio sensor disposed in the exhaust passage at the upstream side of said catalytic converter for outputting a signal substantially proportional to the air-fuel ratio of the exhaust gas at the upstream side of said catalytic converter and a downstream air-fuel ratio sensor disposed in the exhaust passage at the downstream side of said catalytic converter for outputting a signal corresponding to the air-fuel ratio of the exhaust gas at the downstream side of said catalytic converter comprising the steps of;

• an air-fuel ratio feedback control step for calculating an air-fuel ratio correction factor for correcting the amount of fuel supplied to the engine at least in accordance with the output of the upstream air-fuel ratio sensor and an air-fuel ratio leaning factor for compensating for age deterioration of devices related to a fuel supply system;
• a deterioration detecting step for detecting a deterioration degree of the converter at least in accordance with the output of the downstream air-fuel ratio sensor;
• an oxygen balance estimating step for estimating a balance in accordance with the integral of the difference between the air-fuel ratio correction factor and the air-fuel ratio leaning factor calculated at said air-fuel ratio feedback control step;
• and
• a detection inhibiting step for inhibiting the detection of the deterioration at said deterioration detecting step when the balance estimated at said oxygen balance estimating step deviates from at least one fixed threshold.