Method and apparatus for determining deterioration of three-way catalysts in double air-fuel ratio sensor system

Claim 1

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a rich air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 2

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a rich air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 3

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a lean air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 4

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a lean air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 5

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a rich air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a first time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; determining whether or not said engine is switched from the stoichiometric air-fuel ratio driving state to a lean air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a second time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; and determining whether or not a sum of said first time and said second time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when the sum of said first time and said second time is shorter than said predetermined time.

Claim 6

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a rich air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a first time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; determining whether or not said engine is switched from the stoichiometric air-fuel ratio driving state to a lean air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a second time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; and determining whether or not a sum of said first time and said second time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when the sum of said first time and said second time is shorter than said predetermined time.

Claim 7

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a lean air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a rich air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a time from a timing when said engine is switched from the lean air-fuel ratio to the stoichiometric air-fuel ratio driving state or the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 8

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a lean air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a rich air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a time from a timing when said engine is switched from the lean air-fuel ratio to the stoichiometric air-fuel ratio driving state or the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 9

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a rich air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a lean air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a time from a timing when said engine is switched from the rich air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 10

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a rich air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a lean air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a time from a timing when said engine is switched from the rich air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 11

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a lean air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a rich air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a first time from a timing when said engine is switched from the lean air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; determining whether or not said engine is switched from the rich air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or a lean air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a second time from a timing when said engine is switched from the rich air-fuel ratio driving state or the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; and determining whether or not a sum of said first time and said second time is shorter than a predetermine time, thereby determining that said three-way catalyst converter is deteriorated when the sum of said first time and said second time is shorter than said predetermined time.

Claim 12

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is switched from a lean air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a rich air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a first time from a timing when said engine is switched from the lean air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; determining whether or not said engine is switched from the rich air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or a lean air-fuel ratio driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a second time from a timing when said engine is switched from the rich air-fuel ratio driving state or the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; and determining whether or not a sum of said first time and said second time is shorter than a predetermine time, thereby determining that said three-way catalyst converter is deteriorated when the sum of said first time and said second time is shorter than said predetermined time.

Claim 13

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is in a predetermined driving state; forcibly making the air-fuel ratio of said engine rich and thereafter forcibly making the air-fuel ratio of said engine lean, when said engine is in said predetermined driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a time from a timing when the air-fuel ratio of said engine is forcibly switched from the rich state to the lean state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 14

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is in a predetermined driving state; forcibly making the air-fuel ratio of said engine rich and thereafter forcibly making the air-fuel ratio of said engine lean, when said engine is in said predetermined driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a time from a timing when the air-fuel ratio of said engine is forcibly switched from the rich state to the lean state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 15

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is in a predetermined driving state; forcibly making the air-fuel ratio of said engine lean and thereafter forcibly making the air-fuel ratio of said engine rich, when said engine is in said predetermined driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a time from a timing when the air-fuel ratio of said engine is forcibly switched from the lean state to the rich state to a timing when the output of said downstream air-fuel ratio sensor is switched from lean state to the rich state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 16

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is in a predetermined driving state; forcibly making the air-fuel ratio of said engine lean and thereafter forcibly making the air-fuel ratio of said engine rich, when said engine is in said predetermined driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a time from a timing when the air-fuel ratio of said engine is forcibly switched from the lean state to the rich state to a timing when the output of said downstream air-fuel ratio sensor is switched from lean state to the rich state; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated when said time is shorter than said predetermined time.

Claim 17

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is in a predetermined driving state; forcibly making the air-fuel ratio of said engine rich and thereafter forcibly making the air-fuel ratio of said engine lean, when said engine is in said predetermined driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a first time from a timing when the air-fuel ratio of said engine is forcibly switched from the rich state to the lean state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; forcibly making the air-fuel ratio of said engine lean and thereafter forcibly making the air-fuel ratio of said engine rich, when said engine is in said predetermined driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a second time from a timing when the air-fuel ratio of said engine is forcibly switched from the lean state to the rich state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; and determining whether or not a sum of said first time and said second time is shorter than a predetermined time; thereby determining that said three-way catalyst converter is deteriorated when the sum of said first time and said second time is shorter than said predetermined time.

Claim 18

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: determining whether or not said engine is in a predetermined driving state; forcibly making the air-fuel ratio of said engine rich and thereafter forcibly making the air-fuel ratio of said engine lean, when said engine is in said predetermined driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; counting a first time from a timing when the air-fuel ratio of said engine is forcibly switched from the rich state to the lean state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; forcibly making the air-fuel ratio of said engine lean and thereafter forcibly making the air-fuel ratio of said engine rich, when said engine is in said predetermined driving state; determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; counting a second time from a timing when the air-fuel ratio of said engine is forcibly switched from the lean state to the rich state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; and determining whether or not a sum of said first time and said second time is shorter than a predetermined time; thereby determining that said three-way catalyst converter is deteriorated when the sum of said first time and said second time is shorter than said predetermined time.

Claim 19

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having upstream and downstream air-fuel ratio sensors disposed upstream and downstream, respectively, of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: estimating a full O 2 storage amount in said three-way catalyst converter; and determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount; calculating a first air-fuel ratio correction amount in accordance with the output of said upstream air-fuel ratio sensor; and calculating a second air-fuel ratio correction amount in accordance with the output of said downstream air-fuel ratio sensor, thereby adjusting said actual air-fuel ratio in accordance with said first and second air-fuel ratio correction amounts.

Claim 20

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having upstream and downstream air-fuel ratio sensors disposed upstream and downstream, respectively, of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: estimating a full O 2 storage amount in said three-way catalyst converter; and determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount; calculating a first air-fuel ratio correction amount in accordance with the output of said upstream air-fuel ratio sensor; and calculating a second air-fuel ratio correction amount in accordance with the output of said downstream air-fuel ratio sensor, thereby adjusting said actual air-fuel ratio in accordance with said first and second air-fuel ratio correction amounts.

Claim 21

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having upstream and downstream air-fuel ratio sensors disposed upstream and downstream, respectively, of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: estimating a full O 2 storage amount in said three-way catalyst converter; and determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount; calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream air-fuel ratio sensor; and calculating an air-fuel ratio correction amount in accordance with the output of said upstream air-fuel ratio sensor and said air-fuel ratio feedback control parameter, thereby adjusting said actual air-fuel ratio in accordance with said air-fuel ratio correction amount.

Claim 22

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having upstream and downstream air-fuel ratio sensors disposed upstream and downstream, respectively, of said three-way catalyst converter, for detecting a specific component in the exhaust gas, comprising the steps of: estimating a full O 2 storage amount in said three-way catalyst converter; and determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount; calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream air-fuel ratio sensor; and calculating an air-fuel ratio correction amount in accordance with the output of said upstream air-fuel ratio sensor and said air-fuel ratio feedback control parameter, thereby adjusting said actual air-fuel ratio in accordance with said air-fuel ratio correction amount.

Claim 27

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a rich air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; and means for counting a time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state, said time corresponding to said estimated full O 2 storage amount.

Claim 28

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a rich air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; and means for counting a time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state, said time corresponding to said estimated full O 2 storage amount.

Claim 29

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a lean air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; and means for counting a time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state, said time corresponding to said estimated full O 2 storage amount.

Claim 30

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a lean air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; and means for counting a time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state, said time corresponding to said estimated full O 2 storage amount.

Claim 31

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a lean air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; and means for counting a first time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state, means for determining whether or not said engine is switched from stoichiometric air-fuel ratio driving state to a lean air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; and means for counting a second time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state, a sum of said first time and said second time corresponding to said estimated full O 2 storage amount.

Claim 32

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a stoichiometric air-fuel ratio driving state to a lean air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; and means for counting a first time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state, means for determining whether or not said engine is switched from stoichiometric air-fuel ratio driving state to a lean air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; and means for counting a second time from a timing when said engine is switched from the stoichiometric air-fuel ratio driving state to the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state, a sum of said first time and said second time corresponding to said estimated full O 2 storage amount.

Claim 33

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a lean air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a rich air-fuel ratio driving state; means for counting a time from a timing when said engine is switched from the lean air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state side to the rich state, said time corresponding to said estimated full O 2 storage amount.

Claim 34

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a lean air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a rich air-fuel ratio driving state; means for counting a time from a timing when said engine is switched from the lean air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state side to the rich state, said time corresponding to said estimated full O 2 storage amount.

Claim 35

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a rich air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a lean air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel sensor is switched from a rich state to a lean state; and means for counting a time from a timing when said engine is switched from the rich air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or the lean air-fuel ratio driving state to a timing when the output of said downstream-side air-fuel ratio sensor is switched from the rich state to the lean state, said time corresponding to said estimated full O 2 storage amount.

Claim 36

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a rich air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a lean air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel sensor is switched from a rich state to a lean state; and means for counting a time from a timing when said engine is switched from the rich air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or the lean air-fuel ratio driving state to a timing when the output of said downstream-side air-fuel ratio sensor is switched from the rich state to the lean state, said time corresponding to said estimated full O 2 storage amount.

Claim 37

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a lean air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a rich air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; means for counting a first time from a timing when said engine is switched from the lean air-fuel ratio driving sate to the stoichiometric air-fuel ratio driving state or the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; means for determining whether or not said engine is switched from the rich air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or a lean air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; and means for counting a second time from a timing when said engine is switched from the rich air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state, a sum of said first time and said second time corresponding to said estimated full O 2 storage amount.

Claim 38

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is switched from a lean air-fuel ratio driving state to a stoichiometric air-fuel ratio driving state or a rich air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; means for counting a first time from a timing when said engine is switched from the lean air-fuel ratio driving sate to the stoichiometric air-fuel ratio driving state or the rich air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; means for determining whether or not said engine is switched from the rich air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or a lean air-fuel ratio driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; and means for counting a second time from a timing when said engine is switched from the rich air-fuel ratio driving state to the stoichiometric air-fuel ratio driving state or the lean air-fuel ratio driving state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state, a sum of said first time and said second time corresponding to said estimated full O 2 storage amount.

Claim 39

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is in a predetermined driving state; means for forcibly making the air-fuel ratio of said engine rich and thereafter forcibly making the air-fuel ratio of said engine lean, when said engine is in said predetermined driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; means for counting a time from a timing when the air-fuel ratio of said engine is forcibly switched from the rich state to the lean state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich side to the lean side, and said time corresponding to said estimated full O 2 storage amount.

Claim 40

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is in a predetermined driving state; means for forcibly making the air-fuel ratio of said engine rich and thereafter forcibly making the air-fuel ratio of said engine lean, when said engine is in said predetermined driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; means for counting a time from a timing when the air-fuel ratio of said engine is forcibly switched from the rich state to the lean state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich side to the lean side, and said time corresponding to said estimated full O 2 storage amount.

Claim 41

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is in a predetermined driving state; means for forcibly making the air-fuel ratio of said engine lean and thereafter forcibly making the air-fuel ratio of said engine rich, when said engine is in said predetermined driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; and means for counting a time from a timing when the air-fuel ratio of said engine is forcibly switched from the lean state to the rich state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state, said time corresponding to said estimated full O 2 storage amount.

Claim 42

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is in a predetermined driving state; means for forcibly making the air-fuel ratio of said engine lean and thereafter forcibly making the air-fuel ratio of said engine rich, when said engine is in said predetermined driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; and means for counting a time from a timing when the air-fuel ratio of said engine is forcibly switched from the lean state to the rich state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state, said time corresponding to said estimated full O 2 storage amount.

Claim 43

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is a predetermined driving state; means for forcibly making the air-fuel ratio of said engine rich and thereafter forcibly making the air-fuel ratio of said engine lean, when said engine is in said predetermined driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; means for counting a first time from a timing when the air-fuel ratio of said engine is forcibly switched from the rich state to the lean state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; means for forcibly making air-fuel ratio of said engine lean and thereafter forcibly making the air-fuel ratio of said engine rich, when said engine is in said predetermined driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; and means for counting a second time from a timing when the air-fuel ratio of said engine is forcibly switched from the lean state to the rich state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; a sum of said first time and said second time corresponding to said estimated full O 2 storage amount.

Claim 44

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having a downstream air-fuel ratio sensor disposed downstream of said catalyst converter, for detecting a specific component in the exhaust gas, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, wherein said full O 2 storage amount estimating means comprises: means for determining whether or not said engine is a predetermined driving state; means for forcibly making the air-fuel ratio of said engine rich and thereafter forcibly making the air-fuel ratio of said engine lean, when said engine is in said predetermined driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a rich state to a lean state; means for counting a first time from a timing when the air-fuel ratio of said engine is forcibly switched from the rich state to the lean state to a timing when the output of said downstream air-fuel ratio sensor is switched from the rich state to the lean state; means for forcibly making air-fuel ratio of said engine lean and thereafter forcibly making the air-fuel ratio of said engine rich, when said engine is in said predetermined driving state; means for determining whether or not the output of said downstream air-fuel ratio sensor is switched from a lean state to a rich state; and means for counting a second time from a timing when the air-fuel ratio of said engine is forcibly switched from the lean state to the rich state to a timing when the output of said downstream air-fuel ratio sensor is switched from the lean state to the rich state; a sum of said first time and said second time corresponding to said estimated full O 2 storage amount.

Claim 45

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having upstream and downstream air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter, for detecting a specific component in the exhaust gas, thereby adjusting an actual air-fuel ratio in accordance with the outputs of said upstream and downstream air-fuel ratio sensors, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, means for calculating a first air-fuel ratio correction amount in accordance with the output of said upstream air-fuel ratio sensor; and means for calculating a second air-fuel ratio correction amount in accordance with the output of said downstream air-fuel ratio sensor, thereby adjusting said actual air-fuel ratio in accordance with said first and second air-fuel ratio correction amounts.

Claim 46

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having upstream and downstream air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter, for detecting a specific component in the exhaust gas, thereby adjusting an actual air-fuel ratio in accordance with the outputs of said upstream and downstream air-fuel ratio sensors, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, means for calculating a first air-fuel ratio correction amount in accordance with the output of said upstream air-fuel ratio sensor; and means for calculating a second air-fuel ratio correction amount in accordance with the output of said downstream air-fuel ratio sensor, thereby adjusting said actual air-fuel ratio in accordance with said first and second air-fuel ratio correction amounts.

Claim 47

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having upstream and downstream air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter, for detecting a specific component in the exhaust gas, thereby adjusting an actual air-fuel ratio in accordance with the outputs of said upstream and downstream air-fuel ratio sensors, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, means for calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream air-fuel ratio sensor; and means for calculating an air-fuel ratio correction amount in accordance with the output of said upstream air-fuel ratio sensor and said air-fuel ratio feedback control parameter, thereby adjusting said actual air-fuel ratio in accordance with said air-fuel ratio correction amount.

Claim 48

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having upstream and downstream air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter, for detecting a specific component in the exhaust gas, thereby adjusting an actual air-fuel ratio in accordance with the outputs of said upstream and downstream air-fuel ratio sensors, comprising: means for estimating a full O 2 storage amount in said three-way catalyst converter; and means for determining whether or not said estimated full O 2 storage amount is smaller than a predetermined amount, thereby determining that said three-way catalyst converter is deteriorated, when said estimated full O 2 storage is smaller than said predetermined amount, means for calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream air-fuel ratio sensor; and means for calculating an air-fuel ratio correction amount in accordance with the output of said upstream air-fuel ratio sensor and said air-fuel ratio feedback control parameter, thereby adjusting said actual air-fuel ratio in accordance with said air-fuel ratio correction amount.

Claim 53

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: detecting a first state wherein the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio when an engine is in a driving state for the stoichiometric air-fuel ratio or a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; detecting a second state wherein said engine is in a driving state for a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio and the first air-fuel ratio signal of said downstream-side air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 54

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: detecting a first state wherein the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio when an engine is in a driving state for the stoichiometric air-fuel ratio or a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; detecting a second state wherein said engine is in a driving state for a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio and the first air-fuel ratio signal of said downstream-side air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 55

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: detecting a first state wherein the second air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio when an engine is in a driving state for the stoichiometric air-fuel ratio or a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; detecting a second state wherein said engine is in a driving state for a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; counting a time from a timing when said second state is detected after said first state is detected, to a timing when both of the first and second air-fuel ratio signals of said upstream and downstream air-fuel ratio sensors indicate a rich state with respect to the stoichiometric air-fuel ratio; thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 56

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: detecting a first state wherein the second air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio when an engine is in a driving state for the stoichiometric air-fuel ratio or a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; detecting a second state wherein said engine is in a driving state for a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; counting a time from a timing when said second state is detected after said first state is detected, to a timing when both of the first and second air-fuel ratio signals of said upstream and downstream air-fuel ratio sensors indicate a rich state with respect to the stoichiometric air-fuel ratio; thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 57

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: detecting a first state wherein the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio when an engine is in a driving state for the stoichiometric air-fuel ratio or a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; detecting a second state wherein said engine is in a driving state for a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; and counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 58

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: detecting a first state wherein the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio when an engine is in a driving state for the stoichiometric air-fuel ratio or a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; detecting a second state wherein said engine is in a driving state for a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; and counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 60

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter, and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: detecting a first state wherein the second air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio when the engine is in a driving state for the stoichiometric air-fuel ratio or a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; detecting a second state wherein said engine is in a driving state for a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio and the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; and counting a time from a timing when said second state is detected after said first state is detected, to a timing when both of the first and second the air-fuel ratio signals of said upstream and downstream air-fuel ratio sensors indicate a lean state with respect to the stoichiometric air-fuel ratio; thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 61

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter, and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: detecting a first state wherein the second air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio when the engine is in a driving state for the stoichiometric air-fuel ratio or a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; detecting a second state wherein said engine is in a driving state for a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio and the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; and counting a time from a timing when said second state is detected after said first state is detected, to a timing when both of the first and second the air-fuel ratio signals of said upstream and downstream air-fuel ratio sensors indicate a lean state with respect to the stoichiometric air-fuel ratio; thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 63

A method of determining state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: detecting a first state wherein said engine is in a fuel cut-off state for a time longer than a first predetermined time; detecting a second state wherein said engine is in a driving state for the stoichiometric air-fuel ratio; and counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than a second predetermined time.

Claim 64

A method of determining state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: detecting a first state wherein said engine is in a fuel cut-off state for a time longer than a first predetermined time; detecting a second state wherein said engine is in a driving state for the stoichiometric air-fuel ratio; and counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than a second predetermined time.

Claim 66

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter, and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; calculating a mean value of the air-fuel ratio correction amount; making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio for a definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by reducing the air-fuel ratio correction amount based upon the mean value thereof, after said definite time has passed; counting a time from a time when the controlled air-fuel ratio is switched from the rich state side to the lean state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than said predetermined time.

Claim 67

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter, and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; calculating a mean value of the air-fuel ratio correction amount; making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio for a definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by reducing the air-fuel ratio correction amount based upon the mean value thereof, after said definite time has passed; counting a time from a time when the controlled air-fuel ratio is switched from the rich state side to the lean state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than said predetermined time.

Claim 68

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter, and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; calculating a mean value of the air-fuel ratio correction amount; making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio for a definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio by increasing the air-fuel ratio correction amount based upon the mean value thereof, after said definite time has passed; counting a time from a time when the controlled air-fuel ratio is switched from the lean state side to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than said predetermined time.

Claim 69

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter, and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; calculating a mean value of the air-fuel ratio correction amount; making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio for a definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio by increasing the air-fuel ratio correction amount based upon the mean value thereof, after said definite time has passed; counting a time from a time when the controlled air-fuel ratio is switched from the lean state side to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; and determining whether or not said time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated, when said time is shorter than said predetermined time.

Claim 70

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter, and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; calculating a mean value of the air-fuel ratio correction amount; making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio for a first definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by increasing the air-fuel ratio correction amount based upon the mean value thereof, for a second definite time after said first definite time has passed; making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio by increasing the air-fuel ratio correction based upon the mean thereof, after said second time has passed; counting a first time from a time when the controlled air-fuel ratio is switched from the rich state to the lean state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; counting a second time from a time when the controlled air-fuel ratio is switched from the lean state to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; and determining whether or not a sum of said first time and said second time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated, when said sum is shorter than said predetermined time.

Claim 71

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter, and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; calculating a mean value of the air-fuel ratio correction amount; making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio for a first definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by increasing the air-fuel ratio correction amount based upon the mean value thereof, for a second definite time after said first definite time has passed; making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio by increasing the air-fuel ratio correction based upon the mean thereof, after said second time has passed; counting a first time from a time when the controlled air-fuel ratio is switched from the rich state to the lean state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; counting a second time from a time when the controlled air-fuel ratio is switched from the lean state to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; and determining whether or not a sum of said first time and said second time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated, when said sum is shorter than said predetermined time.

Claim 72

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter, and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; calculating a mean value of the air-fuel ratio correction amount; making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio for a first definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; making the controlled air-fuel ratio rich with by increasing the air-fuel ratio correction amount based upon the mean value thereof, for a second definite time after said first definite time has passed; making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by reducing the air-fuel ratio correction based upon the mean thereof, after said second time has passed; counting a first time from a time when the controlled air-fuel ratio is switched from the lean state to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; counting a second time from a time when the controlled air-fuel ratio is switched from the rich state to the lean state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; and determining whether or not a sum of said first time and said second time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated, when said sum is shorter than said predetermined time.

Claim 73

A method of determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine having an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter, and having a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter, comprising the steps of: calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; calculating a mean value of the air-fuel ratio correction amount; making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio for a first definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; making the controlled air-fuel ratio rich with by increasing the air-fuel ratio correction amount based upon the mean value thereof, for a second definite time after said first definite time has passed; making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by reducing the air-fuel ratio correction based upon the mean thereof, after said second time has passed; counting a first time from a time when the controlled air-fuel ratio is switched from the lean state to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; counting a second time from a time when the controlled air-fuel ratio is switched from the rich state to the lean state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; and determining whether or not a sum of said first time and said second time is shorter than a predetermined time, thereby determining that said three-way catalyst converter is deteriorated, when said sum is shorter than said predetermined time.

Claim 74

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an air-fuel ratio sensor ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for detecting a first state wherein the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio when an engine is in a driving state for the stoichiometric air-fuel ratio or a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for detecting a second state wherein said engine is in a driving state for a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio and the first air-fuel ratio signal of said downstream-side air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; means for counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; and means for determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 75

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an air-fuel ratio sensor ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for detecting a first state wherein the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio when an engine is in a driving state for the stoichiometric air-fuel ratio or a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for detecting a second state wherein said engine is in a driving state for a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio and the first air-fuel ratio signal of said downstream-side air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; means for counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; and means for determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 76

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an upstream air-fuel ratio sensor ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for detecting a first state wherein the second air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio when the engine is in a driving state for the stoichiometric air-fuel ratio or a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for detecting a second state wherein said engine is in a driving state for a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for counting a time from a timing when said second state is detected after said first state is detected, to a timing when both of the first and second air-fuel ratio signals of said upstream and downstream air-fuel ratio sensors indicate a rich state with respect to the stoichiometric air-fuel ratio; and means for determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 77

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an upstream air-fuel ratio sensor ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for detecting a first state wherein the second air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio when the engine is in a driving state for the stoichiometric air-fuel ratio or a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for detecting a second state wherein said engine is in a driving state for a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for counting a time from a timing when said second state is detected after said first state is detected, to a timing when both of the first and second air-fuel ratio signals of said upstream and downstream air-fuel ratio sensors indicate a rich state with respect to the stoichiometric air-fuel ratio; and means for determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 78

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an air-fuel ratio sensor ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for detecting a first state wherein the air-fuel ratio signal of said air-fuel ratio signal of said air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio when engine is in a driving state for the stoichiometric air-fuel ratio or a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for detecting a second state wherein said engine is in a driving state for a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; and means for determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 79

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an air-fuel ratio sensor ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for detecting a first state wherein the air-fuel ratio signal of said air-fuel ratio signal of said air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio when engine is in a driving state for the stoichiometric air-fuel ratio or a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for detecting a second state wherein said engine is in a driving state for a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; and means for determining that said three-way catalyst converter is deteriorated, when said time is shorter than a predetermined time.

Claim 81

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for detecting a first state wherein the second air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio when the engine is in a driving state for the stoichiometric air-fuel ratio or a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for detecting a second state that said engine is in a driving state for a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio and the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; means for counting a time from a timing when said second state is detected after said first state is detected, to a timing when both of the first and second air-fuel ratio signals of said upstream and downstream air-fuel ratio sensors indicate a lean state with respect to the stoichiometric air-fuel ratio; and means for determining that said three-way catalyst converter is deteriorated, when said time is shorter than predetermined time.

Claim 82

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for detecting a first state wherein the second air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio when the engine is in a driving state for the stoichiometric air-fuel ratio or a rich air-fuel ratio with respect to the stoichiometric air-fuel ratio; means for detecting a second state that said engine is in a driving state for a lean air-fuel ratio with respect to the stoichiometric air-fuel ratio and the air-fuel ratio signal of said air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; means for counting a time from a timing when said second state is detected after said first state is detected, to a timing when both of the first and second air-fuel ratio signals of said upstream and downstream air-fuel ratio sensors indicate a lean state with respect to the stoichiometric air-fuel ratio; and means for determining that said three-way catalyst converter is deteriorated, when said time is shorter than predetermined time.

Claim 84

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; means for detecting a first state wherein said engine is in a fuel cut-off state for a time longer than a first predetermined time; means for detecting a second state wherein said engine is in a driving state for the stoichiometric air-fuel ratio; means for counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; and means for determining that said three-way catalyst converter is deteriorated, when said time is shorter than a second predetermined time.

Claim 85

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate an air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; means for detecting a first state wherein said engine is in a fuel cut-off state for a time longer than a first predetermined time; means for detecting a second state wherein said engine is in a driving state for the stoichiometric air-fuel ratio; means for counting a time from a timing when said second state is detected after said first state is detected, to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; and means for determining that said three-way catalyst converter is deteriorated, when said time is shorter than a second predetermined time.

Claim 87

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; means for adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; means for calculating a mean value of the air-fuel ratio correction amount; means for making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio for a definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; means for making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by reducing the air-fuel ratio correction amount based upon the mean value thereof, after said definite time has passed; means for counting a time from a time when the controlled air-fuel ratio is switched from the rich state to the lean state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; means for determining whether or not said time is shorter than predetermined time, and means determining that said three-way catalyst converter is deteriorated, when said time is shorter than said predetermined time.

Claim 88

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; means for adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; means for calculating a mean value of the air-fuel ratio correction amount; means for making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio for a definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; means for making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by reducing the air-fuel ratio correction amount based upon the mean value thereof, after said definite time has passed; means for counting a time from a time when the controlled air-fuel ratio is switched from the rich state to the lean state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; means for determining whether or not said time is shorter than predetermined time, and means determining that said three-way catalyst converter is deteriorated, when said time is shorter than said predetermined time.

Claim 89

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; means for adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; means for calculating a mean value of the air-fuel ratio correction amount; means for making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio for a definite time by reducing the air-fuel ratio correction amount based upon the mean value thereof; means for making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio by increasing the air-fuel ratio correction amount based upon the mean value thereof, after said definite time has passed; means for counting a time from a time when the controlled air-fuel ratio is switched from the lean state to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; means for determining whether or not said time is shorter than predetermined time, and means determining that said three-way catalyst converter is deteriorated, when said time is shorter than said predetermined time.

Claim 90

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; means for adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; means for calculating a mean value of the air-fuel ratio correction amount; means for making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio for a definite time by reducing the air-fuel ratio correction amount based upon the mean value thereof; means for making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio by increasing the air-fuel ratio correction amount based upon the mean value thereof, after said definite time has passed; means for counting a time from a time when the controlled air-fuel ratio is switched from the lean state to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; means for determining whether or not said time is shorter than predetermined time, and means determining that said three-way catalyst converter is deteriorated, when said time is shorter than said predetermined time.

Claim 91

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; means for adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; means for calculating a mean value of the air-fuel ratio correction amount; means for making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio for a first definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; means for making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by reducing the air-fuel ratio correction amount based upon the mean value thereof, for a second definite time after said first definite time has passed; means for making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio by increasing the air-fuel ratio correction based upon the mean thereof, after said second time has passed; means for counting a first time from a time when the controlled air-fuel ratio is switched from the rich state to the lean state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; means for counting a second time from a time when the controlled air-fuel ratio is switched from the lean state to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; means for determining whether or not a sum of said first time and said second time is shorter than a predetermined time, and means for determining that said three-way catalyst converter is deteriorated, when said sum is shorter than said predetermined time.

Claim 92

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: an upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; means for adjusting an actual air-fuel ratio in accordance with the air-fuel ratio correction amount; means for calculating a mean value of the air-fuel ratio correction amount; means for making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio for a first definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; means for making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by reducing the air-fuel ratio correction amount based upon the mean value thereof, for a second definite time after said first definite time has passed; means for making the controlled air-fuel ratio rich with respect to the stoichiometric air-fuel ratio by increasing the air-fuel ratio correction based upon the mean thereof, after said second time has passed; means for counting a first time from a time when the controlled air-fuel ratio is switched from the rich state to the lean state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; means for counting a second time from a time when the controlled air-fuel ratio is switched from the lean state to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; means for determining whether or not a sum of said first time and said second time is shorter than a predetermined time, and means for determining that said three-way catalyst converter is deteriorated, when said sum is shorter than said predetermined time.

Claim 93

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: a upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; means for adjusting an actual air-fuel ratio is accordance with the air-fuel ratio correction amount; means for calculating a mean value of the air-fuel ratio correction amount; means for making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio for a first definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; means for making the controlled air-fuel ratio rich by increasing the air-fuel ratio correction amount based upon the mean value thereof, for a second definite time after said first definite time has passed; means for making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by reducing the air-fuel ratio correction amount based upon the mean thereof, after said second time has passed; means for counting a first time from a time when the controlled air-fuel ratio is switched from the lean state to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; means for counting a second time from a time when the controlled air-fuel ratio is switched from the rich side to the lean side to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; means for determining whether or not a sum of said first time and said second time is shorter than a predetermined time, and means for determining that said three-way catalyst converter is deteriorated, when said sum is shorter than said predetermined time.

Claim 94

An apparatus for determining a state of deterioration of a three-way catalyst converter for removing pollutants in the exhaust gas of an internal combustion engine comprising: a upstream air-fuel ratio sensor disposed upstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a first air-fuel ratio signal indicating the air-fuel ratio upstream of said three-way catalyst converter; a downstream air-fuel ratio sensor disposed downstream of said three-way catalyst converter, for detecting a specific component in the exhaust gas to generate a second air-fuel ratio signal indicating the air-fuel ratio downstream of said three-way catalyst converter; means for calculating an air-fuel ratio correction amount in accordance with the air-fuel ratio signal of said upstream air-fuel ratio sensor so that the controlled air-fuel ratio is brought close to the stoichiometric air-fuel ratio; means for adjusting an actual air-fuel ratio is accordance with the air-fuel ratio correction amount; means for calculating a mean value of the air-fuel ratio correction amount; means for making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio for a first definite time by increasing the air-fuel ratio correction amount based upon the mean value thereof; means for making the controlled air-fuel ratio rich by increasing the air-fuel ratio correction amount based upon the mean value thereof, for a second definite time after said first definite time has passed; means for making the controlled air-fuel ratio lean with respect to the stoichiometric air-fuel ratio by reducing the air-fuel ratio correction amount based upon the mean thereof, after said second time has passed; means for counting a first time from a time when the controlled air-fuel ratio is switched from the lean state to the rich state to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a rich state with respect to the stoichiometric air-fuel ratio; means for counting a second time from a time when the controlled air-fuel ratio is switched from the rich side to the lean side to a timing when the air-fuel ratio signal of said downstream air-fuel ratio sensor indicates a lean state with respect to the stoichiometric air-fuel ratio; means for determining whether or not a sum of said first time and said second time is shorter than a predetermined time, and means for determining that said three-way catalyst converter is deteriorated, when said sum is shorter than said predetermined time.