Double air-fuel ratio sensor system having improved response characteristics

Claim 1

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream, respectively, of said catalyst converter for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: adjusting an actual air-fuel ratio in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors; detecting a coolant temperature of said engine prohibing the adjustment of said actual air-fuel ratio by the output of said downstream-side air-fuel ratio sensor in accordance with the detected coolant temperature, wherein said adjustment prohibiting step comprises the steps of: determining whether or not said engine is started; calculating a reference duration in accordance with the coolant temperature detected immediately after said engine is started or after a predetermined time period has passed after said engine is started; calculating a duration after said engine is started; and determining whether or not said duration is smaller than said reference duration, thereby prohibiting the adjustment of said actual air-fuel ratio sensor when said duration is smaller than said reference duration; detecting a deterioration degree of said downstream-side air-fuel ratio sensor; and correcting said reference duration in accordance with said deterioration degree.

Claim 2

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream, respectively, of said catalyst converter for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: adjusting an actual air-fuel ratio in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors; detecting a coolant temperature of said engine prohibing the adjustment of said actual air-fuel ratio by the output of said downstream-side air-fuel ratio sensor in accordance with the detected coolant temperature, wherein said adjustment prohibiting step comprises the steps of: determining whether or not said engine is started; calculating a reference duration in accordance with the coolant temperature detected immediately after said engine is started or after a predetermined time period has passed after said engine is started; calculating a duration after said engine is started; and determining whether or not said duration is smaller than said reference duration, thereby prohibiting the adjustment of said actual air-fuel ratio sensor when said duration is smaller than said reference duration; detecting a deterioration degree of said downstream-side air-fuel ratio sensor; and correcting said reference duration in accordance with said deterioration degree.

Claim 5

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting the concentration of a specific component in the exhaust gas, comprising: means for adjusting an actual air-fuel ratio in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors; means for detecting a coolant temperature of said engine; means for prohibiting the adjustment of said actual air-fuel ratio by the output of said downstream-side air-fuel ratio sensor in accordance with the detected coolant temperature, wherein said adjustment probihiting means comprises: means for determining whether or not said engine is started; means for calculating a reference duration in accordance with the coolant temperature detected immediately after said engine is started or after a predetermined time period has passed after said engine is started; means for calculating a duration after said engine is started; and means for determining whether or not said duration is smaller than said reference duration, thereby prohibiting the adjustment of said actual air-fuel ratio by the output of said downstream-side air fuel ratio sensor when said duration is smaller than said reference duration; means for detecting a deterioration degree of said downstream-side air-fuel ratio sensor; and means for correcting said reference duration in accordance with said deterioration degree.

Claim 6

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting the concentration of a specific component in the exhaust gas, comprising: means for adjusting an actual air-fuel ratio in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors; means for detecting a coolant temperature of said engine; means for prohibiting the adjustment of said actual air-fuel ratio by the output of said downstream-side air-fuel ratio sensor in accordance with the detected coolant temperature, wherein said adjustment probihiting means comprises: means for determining whether or not said engine is started; means for calculating a reference duration in accordance with the coolant temperature detected immediately after said engine is started or after a predetermined time period has passed after said engine is started; means for calculating a duration after said engine is started; and means for determining whether or not said duration is smaller than said reference duration, thereby prohibiting the adjustment of said actual air-fuel ratio by the output of said downstream-side air fuel ratio sensor when said duration is smaller than said reference duration; means for detecting a deterioration degree of said downstream-side air-fuel ratio sensor; and means for correcting said reference duration in accordance with said deterioration degree.

Claim 9

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: determining whether or not said upstream-side air-fuel ratio sensor is in an activation state; detecting a coolant temperature of said engine; determining whether or not said downstream-side air-fuel ratio sensor is in an activation state in accordance with the detected coolant temperature; carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio sensors are both in the activation state.

Claim 10

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: determining whether or not said upstream-side air-fuel ratio sensor is in an activation state; detecting a coolant temperature of said engine; determining whether or not said downstream-side air-fuel ratio sensor is in an activation state in accordance with the detected coolant temperature; carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio sensors are both in the activation state.

Claim 11

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: determining whether or not said upstream-side air-fuel ratio sensor is in a activation state by determining whether or not the output of said upstream-side air-fuel ratio sensor is once changed between the rich side and the lean side; detecting a coolant temperature of said engine; determining whether or not said downstream-side air-fuel ratio sensor is in an activation state in accordance with the detected coolant temperature; carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio sensors are both in the activation state.

Claim 12

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: determining whether or not said upstream-side air-fuel ratio sensor is in a activation state by determining whether or not the output of said upstream-side air-fuel ratio sensor is once changed between the rich side and the lean side; detecting a coolant temperature of said engine; determining whether or not said downstream-side air-fuel ratio sensor is in an activation state in accordance with the detected coolant temperature; carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio sensors are both in the activation state.

Claim 13

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensor, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: detecting a coolant temperature of said engine; determining whether or not the detected coolant temperature is higher than a first predetermined value; determining whether or not the detected temperature is higher than a second predetermined value; carrying out an air-fuel ratio feedback control operation in accordance with the output of said upstream-side air-fuel ratio sensor according to when the coolant temperature is higher than said first predetermined value and the output of said upstream-side air-fuel ratio sensor is once changed between the rich side and the lean side; and carrying out an air-fuel ratio feedback control operation in accordance with the output of said downstream-side air-fuel ratio sensor according to when the coolant temperature is higher than said second predetermined value.

Claim 14

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensor, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: detecting a coolant temperature of said engine; determining whether or not the detected coolant temperature is higher than a first predetermined value; determining whether or not the detected temperature is higher than a second predetermined value; carrying out an air-fuel ratio feedback control operation in accordance with the output of said upstream-side air-fuel ratio sensor according to when the coolant temperature is higher than said first predetermined value and the output of said upstream-side air-fuel ratio sensor is once changed between the rich side and the lean side; and carrying out an air-fuel ratio feedback control operation in accordance with the output of said downstream-side air-fuel ratio sensor according to when the coolant temperature is higher than said second predetermined value.

Claim 15

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, comprising the steps of; determining whether or not said upstream-side air-fuel ratio sensor is in an activation state; determining whether or not said engine is being started; detecting a coolant temperature of said engine when said engine is being started or immediately thereafter; calculating a reference duration in accordance with the detected coolant temperature, said reference duration being needed for said downstream-side air-fuel ratio sensor to be activated; calculating a reference duration in accordance with the detected coolant temperature, said reference duration being needed for said downstream-side air-fuel ratio sensor to be activated; calculating a duration after said engine is started; determining whether or not said duration is smaller than said reference duration; carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said duration is smaller than said reference duration; and carrying out an air-fuel feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side air-fuel ratio sensor is in the activation state and said duration is not smaller than said reference duration.

Claim 16

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, comprising the steps of; determining whether or not said upstream-side air-fuel ratio sensor is in an activation state; determining whether or not said engine is being started; detecting a coolant temperature of said engine when said engine is being started or immediately thereafter; calculating a reference duration in accordance with the detected coolant temperature, said reference duration being needed for said downstream-side air-fuel ratio sensor to be activated; calculating a reference duration in accordance with the detected coolant temperature, said reference duration being needed for said downstream-side air-fuel ratio sensor to be activated; calculating a duration after said engine is started; determining whether or not said duration is smaller than said reference duration; carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said duration is smaller than said reference duration; and carrying out an air-fuel feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side air-fuel ratio sensor is in the activation state and said duration is not smaller than said reference duration.

Claim 23

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: determining whether or not said upstream-side air-fuel ratio sensor is in an activation state; detecting a coolant temperature of said engine; determining whether said engine is started at a low temperature state of said engine or at a high temperature state of said engine; determining whether or not said downstream-side air-fuel ratio sensor is in an activation state by whether or not the output of said downstream-side air-fuel ratio sensor is once changed between the rich side and the lean side, when said engine is started at the high temperature state; determining whether or not said downstream-side air-fuel rataio sensor is in the activation state by whether or not the coolant temperature is higher than a predetermined value, when said engine is started at the low temperature state; carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio senosrs are both in the activation state.

Claim 24

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: determining whether or not said upstream-side air-fuel ratio sensor is in an activation state; detecting a coolant temperature of said engine; determining whether said engine is started at a low temperature state of said engine or at a high temperature state of said engine; determining whether or not said downstream-side air-fuel ratio sensor is in an activation state by whether or not the output of said downstream-side air-fuel ratio sensor is once changed between the rich side and the lean side, when said engine is started at the high temperature state; determining whether or not said downstream-side air-fuel rataio sensor is in the activation state by whether or not the coolant temperature is higher than a predetermined value, when said engine is started at the low temperature state; carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio senosrs are both in the activation state.

Claim 26

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, said apparatus comprising: means for determining whether or not said upstream-side air-fuel ratio sensor is in an activation state; means for detecting a coolant temperature of said engine; means for determining whether or not said downstream-side air-fuel ratio sensor is in an activation state in accordance with the detected coolant temperature; means for carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and means for carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio sensors are both in the activation state.

Claim 27

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, said apparatus comprising: means for determining whether or not said upstream-side air-fuel ratio sensor is in an activation state; means for detecting a coolant temperature of said engine; means for determining whether or not said downstream-side air-fuel ratio sensor is in an activation state in accordance with the detected coolant temperature; means for carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and means for carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio sensors are both in the activation state.

Claim 28

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, said apparatus comprising: means for determining whether said upstream-side air-fuel ratio sensor is in a activation state by determining whether the output of said upstream-side air-fuel ratio sensor is once changed between the rich and the lean side; means for detecting a coolant temperature of said engine; means for determining whether said downstream-side air-fuel ratio sensor is in an activation state in accordance with the detected coolant temperature; means for carrying out an air-fuel ratio feedback control opertion in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and means for carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio sensors are both in the activation state.

Claim 29

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, said apparatus comprising: means for determining whether said upstream-side air-fuel ratio sensor is in a activation state by determining whether the output of said upstream-side air-fuel ratio sensor is once changed between the rich and the lean side; means for detecting a coolant temperature of said engine; means for determining whether said downstream-side air-fuel ratio sensor is in an activation state in accordance with the detected coolant temperature; means for carrying out an air-fuel ratio feedback control opertion in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and means for carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio sensors are both in the activation state.

Claim 30

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, said apparatus comprising: means for detecting a coolant temperature of said engine; means for determining whether the detected coolant temperature is higher than a first predetermined value; means for determining whether the detected temperature is higher than a second predetermined value; means for carrying out an air-fuel ratio feedback control operation in accordance with the output of said upstream-side air-fuel ratio sensor according to when the coolant temperature is higher than said first predetermined value and the output of said upstream-side air-fuel ratio sensor is once changed between the rich side and the lean side; and means for carrying out an air-fuel ratio feedback control operation in accordance with the output of said downstream-side air-fuel ratio sensor according to when the coolant temperature is higher than said second predetermined value.

Claim 31

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, said apparatus comprising: means for detecting a coolant temperature of said engine; means for determining whether the detected coolant temperature is higher than a first predetermined value; means for determining whether the detected temperature is higher than a second predetermined value; means for carrying out an air-fuel ratio feedback control operation in accordance with the output of said upstream-side air-fuel ratio sensor according to when the coolant temperature is higher than said first predetermined value and the output of said upstream-side air-fuel ratio sensor is once changed between the rich side and the lean side; and means for carrying out an air-fuel ratio feedback control operation in accordance with the output of said downstream-side air-fuel ratio sensor according to when the coolant temperature is higher than said second predetermined value.

Claim 32

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalayst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, said apparatus comprising: means for determining whether said upstream-side air-fuel ratio sensor is in an activation state; means for determining whether or not said engine is being started; means for detecting a coolant temperature of said engine when said engine is being started or immediately thereafter; means for calculating a reference duration in accordance with the detected coolant temperature, said reference duration being needed for said downstream-side air-fuel ratio sensor to be activated; means for calculating a reference duration in accordance with the detected coolant temperature, said reference duration being needed for said downstream-side air-fuel ratio sensor to be activated; means for calculating a duration after said engine is started; means for determining whether said duration is smaller than said reference duration; means for carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said duration is smaller than said reference duration; and means for carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side air-fuel ratio sensor is in the activation state and said duration is not smaller than said reference duration.

Claim 33

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalayst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, said apparatus comprising: means for determining whether said upstream-side air-fuel ratio sensor is in an activation state; means for determining whether or not said engine is being started; means for detecting a coolant temperature of said engine when said engine is being started or immediately thereafter; means for calculating a reference duration in accordance with the detected coolant temperature, said reference duration being needed for said downstream-side air-fuel ratio sensor to be activated; means for calculating a reference duration in accordance with the detected coolant temperature, said reference duration being needed for said downstream-side air-fuel ratio sensor to be activated; means for calculating a duration after said engine is started; means for determining whether said duration is smaller than said reference duration; means for carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said duration is smaller than said reference duration; and means for carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side air-fuel ratio sensor is in the activation state and said duration is not smaller than said reference duration.

Claim 40

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing polutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, said apparatus comprising: means for determining whether said upstream-side air-fuel ratio sensor is in an activation state; means for detecting a coolant temperature of said engine; means for determining whether said engine is started at a lower temperature state of said engine or at a high temperature state of said engine; means for determining whether said downstream-side air-fuel ratio sensor is in an activation state by whether the output of said downstream-side air-fuel ratio sensor is once changed between the rich side and the lean side, when said engine is started at the high temperature state; means for determining whether said downstream-side air-fuel ratio sensor is in the activation state by whether the coolant temperature is higher than a predetermined value, when said engine is started at the low temperature state; means for carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and means for carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio sensors are both in the activation state.

Claim 41

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing polutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors, disposed upstream and downstream, respectively, of said catalyst converter, for detecting the concentration of a specific component in the exhaust gas, said apparatus comprising: means for determining whether said upstream-side air-fuel ratio sensor is in an activation state; means for detecting a coolant temperature of said engine; means for determining whether said engine is started at a lower temperature state of said engine or at a high temperature state of said engine; means for determining whether said downstream-side air-fuel ratio sensor is in an activation state by whether the output of said downstream-side air-fuel ratio sensor is once changed between the rich side and the lean side, when said engine is started at the high temperature state; means for determining whether said downstream-side air-fuel ratio sensor is in the activation state by whether the coolant temperature is higher than a predetermined value, when said engine is started at the low temperature state; means for carrying out an air-fuel ratio feedback control operation in accordance with only the output of said upstream-side air-fuel ratio sensor when said upstream-side air-fuel ratio sensor is in the activation state and said downstream-side air-fuel ratio sensor is not in the activation state; and means for carrying out an air-fuel ratio feedback control operation in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors when said upstream-side and downstream-side air-fuel ratio sensors are both in the activation state.

Claim 43

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: adjusting an actual air-fuel ratio in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors; detecting a coolant temperature of said engine; and prohibiting the adjustment of said actual air-fuel ratio by the output of said downstream-side air-fuel ratio sensor in accordance with the detected coolant temperature; wherein said air-fuel ratio adjusting step comprises the steps of: calculating an air-fuel ratio feedback control parameter in accordance with the output of the said downstream-side air-fuel ratio sensor; calculating an air-fuel ratio correction amount in accordance with the output of said downstream-side air-fuel ratio sensor and said air-fuel ratio feedback control parameter; and adjusting the actual air-fuel ratio in accordance with said air-fuel ratio correction amount; and wherein said air-fuel ratio feedback control parameter is determined by a lean skip amount by which said air-fuel ratio correction amount is skipped down when the output of said downstream-side air-fuel ratio sensor is switched from the lean side to the rich side and a rich skip amount of by which said air-fuel ratio correction amount is skipped up when the output of said downstream-side air-fuel ratio sensor is switched from the rich side to the lean side.

Claim 44

A method for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting the concentration of a specific component in the exhaust gas, comprising the steps of: adjusting an actual air-fuel ratio in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors; detecting a coolant temperature of said engine; and prohibiting the adjustment of said actual air-fuel ratio by the output of said downstream-side air-fuel ratio sensor in accordance with the detected coolant temperature; wherein said air-fuel ratio adjusting step comprises the steps of: calculating an air-fuel ratio feedback control parameter in accordance with the output of the said downstream-side air-fuel ratio sensor; calculating an air-fuel ratio correction amount in accordance with the output of said downstream-side air-fuel ratio sensor and said air-fuel ratio feedback control parameter; and adjusting the actual air-fuel ratio in accordance with said air-fuel ratio correction amount; and wherein said air-fuel ratio feedback control parameter is determined by a lean skip amount by which said air-fuel ratio correction amount is skipped down when the output of said downstream-side air-fuel ratio sensor is switched from the lean side to the rich side and a rich skip amount of by which said air-fuel ratio correction amount is skipped up when the output of said downstream-side air-fuel ratio sensor is switched from the rich side to the lean side.

Claim 48

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting the concentration of a specific component in the exhaust gas comprising: means for adjusting an actual air-fuel ratio in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors; means for detecting a coolant temperature of said engine; and means for prohibiting the adjustment of said actual air-fuel ratio by the output of said downstream-side air-fuel ratio sensor in accordance with the detected coolant temperature; wherein said means for adjusting said air-fuel ratio comprises: means for calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream-side air-fuel ratio sensor; means for calculating an air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor and said air-fuel ratio feedback control parameter; and means for adjusting the actual air-fuel ratio in accordance with said air-fuel ratio correction amount; wherein said air-fuel ratio feedback control parameter is determined by a lean skip amount by which said air-fuel ratio correction amount is skipped down when the output of said downstream-side air-fuel ratio sensor is switched from the lean side to the rich side and a rich skip amount by which said air-fuel ratio correction amount is skipped up when the output of said downstream-side air-fuel sensor is switched from the rich side to the lean side.

Claim 49

An apparatus for controlling the air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in the exhaust gas thereof, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting the concentration of a specific component in the exhaust gas comprising: means for adjusting an actual air-fuel ratio in accordance with the outputs of said upstream-side and downstream-side air-fuel ratio sensors; means for detecting a coolant temperature of said engine; and means for prohibiting the adjustment of said actual air-fuel ratio by the output of said downstream-side air-fuel ratio sensor in accordance with the detected coolant temperature; wherein said means for adjusting said air-fuel ratio comprises: means for calculating an air-fuel ratio feedback control parameter in accordance with the output of said downstream-side air-fuel ratio sensor; means for calculating an air-fuel ratio correction amount in accordance with the output of said upstream-side air-fuel ratio sensor and said air-fuel ratio feedback control parameter; and means for adjusting the actual air-fuel ratio in accordance with said air-fuel ratio correction amount; wherein said air-fuel ratio feedback control parameter is determined by a lean skip amount by which said air-fuel ratio correction amount is skipped down when the output of said downstream-side air-fuel ratio sensor is switched from the lean side to the rich side and a rich skip amount by which said air-fuel ratio correction amount is skipped up when the output of said downstream-side air-fuel sensor is switched from the rich side to the lean side.