Double air-fuel ratio sensor system in internal combustion engine

Claim 3

A method as set forth in claim 1, further comprising a step of activating an alarm when said downstream-side air-fuel ratio sensor is in an abnormal state.

Claim 4

A method as set forth in claim 1, wherein said downstream-side air-fuel ratio sensor state determining step comprises a step of determining whether or not the output of said downstream-side air-fuel sensor crosses over a predetermined voltage, thereby determining that said downstream-side air-fuel ratio sensor is in a normal state after the output of said downstream-side air-fuel ratio sensor crosses over said predetermined voltage and wherein said predetermined voltage is set at an intermediate level between said second reference voltage of said downstream-side air-fuel ratio sensor and a nonactive output level thereof; and wherein said downstream-side air-fuel state determining step further comprises the steps of calculating a time duration for which said downstream-side air-fuel ratio sensor is in an abnormal state; determining whether or not the calculated time duration is longer than a predetermined time duration; and changing said predetermined voltage when the calculated time duration is longer than said predetermined time duration.

Claim 5

A method as set forth in claim 1, further comprising a step of holding said air-fuel ratio feedback control parameter immediately before said downstream-side air-fuel ratio sensor is switched from a normal state to an abnormal state.

Claim 6

A method as set forth in claim 4, wherein said air-fuel ratio adjusting step adjusts the actual air-fuel ratio in accordance with said air-fuel ratio feedback correction amount and said held air-fuel ratio feedback control parameter, when said downstream-side air-fuel ratio sensor is in an abnormal state.

Claim 7

A method as set forth in claim 1, further comprising a step of holding said air-fuel ratio feedback control parameter at a definite value when said downstream-side air-fuel ratio sensor is in an abnormal state.

Claim 8

A method as set forth in claim 6, wherein said air-fuel ratio adjusting step adjusts the actual air-fuel ratio in accordance with said air-fuel ratio feedback correction amount and said held air-fuel ratio feedback control parameter, when said downstream-side air-fuel ratio sensor is in an abnormal state.

Claim 9

A method as set forth in claim 1, further comprising a step of forcibly changing the actual air-fuel ratio when said downstream-side air-fuel ratio sensor is in an abnormal state.

Claim 10

A method as set forth in claim 8, further comprising a step of pulling down the output of said downstream-side air-fuel ratio sensor via a resistor thereby generating a lean signal during a nonactive mode, said air-fuel ratio forcible-change step changing the actual air-fuel ratio on the rich side.

Claim 11

A method as set forth in claim 9, further comprising a step of determining whether or not said engine is in an acceleration state, said air-fuel ratio forcible-change step changing the actual air-fuel ratio on the rich side, only when said engine is in an acceleration state.

Claim 12

A method as set forth in claim 8, further comprising a step of pulling up the output of said downstream-side air-fuel ratio sensor via a resistor thereby generating a rich signal during a nonactive mode, said air-fuel ratio forcible-change step changing the actual air-fuel ratio on the lean side.

Claim 13

A method as set forth in claim 1, further comprising the steps of: pulling down the output of said downstream-side air-fuel ratio sensor via a resistor; determining whether or not a fuel enrichment state of said engine continues for a predetermined time period; said downstream-side air-fuel ratio sensor state .[.predetermining.]. .Iadd.determining .Iaddend.step comprising a step of determining whether or not the output of said downstream-side air-fuel ratio sensor indicates a lean signal, thereby determining that said downstream-side air-fuel ratio sensor is in an abnormal state when the output of said downstream-side air-fuel ratio sensor indicates a lean signal.

Claim 14

A method as set forth in claim 1, wherein said air-fuel correction amount calculating step comprises the steps of: gradually decreasing said air-fuel ratio correction amount when the output of said upstream-side air-fuel ratio sensor is on the rich side with respect to said first predetermined reference voltage; gradually increasing said air-fuel ratio correction amount when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said first predetermined reference voltage; remarkably decreasing said air-fuel ratio correction amount when the output of said upstream-side air-fuel ratio sensor is switched from the lean side to the rich side; and remarkably increasing said air-fuel ratio correction amount when the output of said upstream-side air-fuel ratio sensor is switched from the rich side to the lean side.

Claim 15

A method as set forth in claim 1, further comprising a step of delaying the result of the comparison of said upstream-side air-fuel ratio sensor with said first predetermined reference voltage.

Claim 16

A method as set forth in claim 1, further comprising a step of delaying the result of the comparison of said downstream-side air-fuel ratio sensor with said second predetermined reference voltage.

Claim 17

A method as set forth in claim 14, wherein said air-fuel ratio feedback control parameter is determined by a rich delay time period in said delaying step for delaying the result of the comparison of said upstream-side air-fuel ratio sensor switched from the lean side to the rich side and a lean delay time period in said delaying step for delaying the result of the comparison of said upstream-side air-fuel ratio sensor switched from the rich side to the lean side.

Claim 18

A method as set forth in claim 16, wherein said air-fuel ratio feedback control parameter calculating step comprises the steps of: increasing said lean delay time period when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and decreasing said lean delay time period when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 19

A method as set forth in claim 16, wherein said air-fuel ratio feedback control parameter calculating step comprises the steps of: decreasing said rich delay time period when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and increasing said rich delay time period when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 20

A method as set forth in claim 16, wherein said air-fuel ratio feedback control parameter calculating step comprises the steps of: increasing said lean delay time period and decreasing said rich delay time period when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and decreasing said lean delay time period and increasing said rich delay time period when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 21

A method as set forth in claim 13, wherein said air-fuel ratio feedback control parameter is determined by a lean skip amount in said remarkable-decrease step and a rich skip amount in said remarkable-increase step.

Claim 22

A method as set forth in claim 20, wherein said air-fuel ratio feedback control parameter calculating step comprises the steps of: increasing said lean skip amount when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and decreasing said lean skip amount when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 23

A method as set forth in claim 20, wherein said air-fuel ratio feedback control parameter calculating step comprises the steps of: decreasing said rich skip amount when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and increasing said rich skip amount when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined value.

Claim 24

A method as set forth in claim 20, wherein said air-fuel ratio feedback control parameter calculating step comprises the steps of: increasing said lean skip amount and decreasing said rich skip amount when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and decreasing said lean skip amount and increasing said rich skip amount when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined value.

Claim 25

A method as set forth in claim 20, wherein said air-fuel ratio feedback control parameter is determined by the decreasing speed of said gradual-decrease step and the increasing speed of said gradual-increase step.

Claim 26

A method as set forth in claim 24, wherein said air-fuel ratio feedback control parameter calculating step comprises the steps of: increasing the decreasing speed of said gradual-decrease step when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and decreasing the decreasing speed of said gradual-decrease step when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 27

A method as set forth in claim 24, wherein said air-fuel ratio feedback control parameter calculating step comprises the steps of: decreasing the increasing speed of said gradual-increase step when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and increasing the increasing speed of said gradual-increase step when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 28

A method as set forth in claim 24, wherein said air-fuel ratio feedback control parameter calculating step comprises the steps of: increasing the decreasing speed of said gradual-decrease step and decreasing the increasing speed of said gradual-increase step when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and decreasing the decreasing speed of said gradual-decrease step and increasing the increasing speed of said gradual-increase step when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 29

A method as set forth in claim 1, wherein said upstream-side air-fuel ratio sensor is mounted on a water-cooled cylinder head portion of said engine.

Claim 30

A method as set forth in claim 1, wherein said downstream-side air-fuel ratio sensor is of a semiconductor type which is mounted within a catalyst converter on a downstream-side of said catalyst means.

Claim 31

A method as set forth in claim 29, wherein said semiconductor type air-fuel ratio sensor is mounted in the center of said catalyst converter.

Claim 34

A method as set forth in claim 31, wherein .Iadd.said downstream-side air-fuel ratio sensor having a flow-out type signal processing circuit, .Iaddend.said downstream-side air-fuel ratio sensor state determining step comprises the steps of: determining whether or not said upstream-side air-fuel ratio is rich in accordance with the output of said upstream-side air-fuel ratio sensor; determining whether or not said downstream-side air-fuel ratio sensor outputs a lean signal; counting a duration for which said downstream-side air-fuel ratio sensor outputs a lean signal when said upstream-side air-fuel ratio is rich; and determining whether or not the duration is longer than a predetermined term, thereby determining that said downstream-side air-fuel ratio sensor is in an abnormal state when the duration is longer than said predetermined term.

Claim 35

A method as set forth in claim 32, further comprising a step of releasing the operation of said prohibiting step when the output of said downstream-side air-fuel ratio sensor indicates a rich signal during an active mode.

Claim 36

A method as set forth in claim 32, wherein said determining step for determining whether said upstream-side air-fuel ratio is rich comprises the steps of calculating an average value or blunt value of the output of said upstream-side air-fuel ratio sensor; and determining whether or not the average value or blunt value of the output of said upstream-side air-fuel ratio sensor is larger than a predetermined value, thereby determining a rich signal during an active mode for said upstream-side air-fuel ratio sensor, when the average value or blunt value of the output of said upstream-side air-fuel ratio sensor is larger than said predetermined value.

Claim 37

A method as set forth in claim 31, wherein .Iadd.said downstream-side air-fuel sensor having a flow-in type signal processing circuit, .Iaddend.said downstream-side air-fuel ratio sensor state determining step comprises the steps of: determining whether or not said upstream-side air-fuel ratio is .[.rich.]. .Iadd.lean .Iaddend.in accordance with the output of said upstream-side air-fuel ratio sensor; determining whether or not said downstream-side air-fuel ratio sensor outputs a .[.lean.]. .Iadd.rich .Iaddend.signal; counting a duration for which said downstream-side air-fuel ratio sensor outputs a .[.lean.]. .Iadd.rich .Iaddend.signal when said upstream-side air-fuel ratio is .[.rich.]. .Iadd.lean.Iaddend.; and determining whether or not said duration is longer than a predetermined term, thereby determining that said downstream-side air-fuel ratio sensor is in an abnormal state when said duration is longer than said predetermined term.

Claim 38

A method as set forth in claim 35, further comprising a step of releasing the operation of said prohibiting step when the output of said downstream-side air-fuel ratio sensor indicates a lean signal during an active mode.

Claim 39

A method as set forth in claim 35, wherein said determining step for determining whether said upstream-side air-fuel ratio is lean comprises the steps of calculating an average value or blunt value of the output of said upstream-side air-fuel ratio sensor; and determining whether or not the average value or blunt value of the output of said upstream-side air-fuel ratio sensor is smaller than a predetermined value, thereby determining a lean signal during an active mode for said upstream-side air-fuel ratio sensor, when the average value or blunt value of the output of said upstream-side air-fuel ratio sensor is smaller than said predetermined value.

Claim 42

A method as set forth in claim 38, wherein said predetermined value is dependent upon the speed of said engine.

Claim 61

A method as set forth in claim 48, wherein said predetermined time period is dependent upon the load of said engine.

Claim 62

A method as set forth in claim 48, wherein said predetermined value is dependent upon the load of said engine.

Claim 73

An apparatus as set forth in claim 55, further comprising means for activating an alarm when said downstream-side air-fuel ratio sensor is in an abnormal state.

Claim 74

An apparatus as set forth in claim 55, wherein said downstream-side air fuel sensor state determining means comprises means for determining whether or not the output of said downstream-side air-fuel ratio sensor crosses over a predetermined voltage, thereby determining whether said downstream-side air-fuel ratio sensor is in a normal state after the output of said downstream-side air-fuel ratio sensor crosses over said predetermined voltage; wherein said predetermined voltage is set at an intermediate level between said second reference voltage of said downstream-side air-fuel ratio sensor and a nonactive output level thereof; and wherein said downstream side air-fuel ratio state determining means further comprises: means for calculating a time duration when said downstream-side air-fuel ratio sensor is in an abnormal state; means for determining whether or not the calculated time duration is longer than a predetermined time duration; and means for changing said predetermined voltage when the calculated time is longer than said predetermined time duration.

Claim 75

An apparatus as set forth in claim 55, further comprising means for holding said air-fuel ratio feedback control parameter immediately before said downstream-side air-fuel ratio sensor is switched from a normal state to an abnormal state.

Claim 76

An apparatus as set forth in claim 58, wherein said air-fuel ratio adjusting means adjusts the actual air-fuel ratio in accordance with said air-fuel ratio feedback correction amount and said held air-fuel ratio feedback control parameter, when said downstream-side air-fuel ratio sensor is in an abnormal state.

Claim 77

An apparatus as set forth in claim 55, further comprising means for holding said air-fuel ratio feedback control parameter at a definite value when said downstream-side air-fuel ratio sensor is in an abnormal state.

Claim 78

An apparatus as set forth in claim 60, wherein said air-fuel ratio adjusting means adjusts the actual air-fuel ratio in accordance with said air-fuel ratio feedback correction amount and said held air-fuel ratio feedback control parameter, when said downstream-side air-fuel ratio sensor is in an abnormal state.

Claim 79

An apparatus as set forth in claim 55, further comprising means for forcibly changing the actual air-fuel ratio when said downstream-side air-fuel ratio sensor is in an abnormal state.

Claim 80

An apparatus as set forth in claim 62, further comprising means for pulling down the output of said downstream-side air-fuel ratio sensor via a resistor thereby generating a lean signal during a nonactive mode, said air-fuel ratio forcible-change means changing the actual air-fuel ratio on the rich side.

Claim 81

An apparatus as set forth in claim 63, further comprising means for determining whether or not said engine is in an acceleration state, said air-fuel ratio forcible-change means changing the actual air-fuel ratio on the rich side, only when said engine is in an acceleration state.

Claim 82

An apparatus as set forth in claim 62, further comprising means for pulling up the output of said downstream-side air-fuel ratio sensor via a resistor thereby generating a rich signal during a nonactive mode, said air-fuel ratio forcible-change means changing the actual air-fuel ratio on the lean side.

Claim 83

An apparatus as set forth in claim 55, further comprising: means for pulling down the output of said downstream-side air-fuel ratio sensor via a resistor; means for determining whether or not a fuel enrichment state of said engine continues for a predetermined time period; said downstream-side air-fuel ratio sensor state determining means comprising means for determining whether or not the output of said downstream-side air-fuel ratio sensor indicates a lean signal, thereby determining that said downstream-side air-fuel ratio sensor is in an abnormal state when the output of said downstream-side air-fuel ratio sensor indicates a lean signal.

Claim 84

An apparatus as set forth in claim 55, wherein said air-fuel correction amount calculating means comprises: means for gradually decreasing said air-fuel ratio correction amount when the output of said upstream-side air-fuel ratio sensor is on the rich side with respect to said first predetermined reference voltage; means for gradually increasing said air-fuel ratio correction amount when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said first predetermined reference voltage; means for remarkably decreasing said air-fuel ratio correction amount when the output of said upsteam-side air-fuel ratio sensor is switched from the lean side to the rich side; and means for remarkably increasing said air-fuel ratio correction amount when the output of said upstream-side air-fuel ratio sensor is switched from the rich side to the lean side.

Claim 85

An apparatus as set forth in claim 55, further comprising means for delaying the result of the comparison of said upstream-side air-fuel ratio sensor with said first predetermined reference voltage.

Claim 86

An apparatus as set forth in claim 55, further comprising means for delaying the result of the comparison of said downstream-side air-fuel ratio sensor with said second predetermined reference voltage.

Claim 87

An apparatus as set forth in claim 68, wherein said air-fuel ratio feedback control parameter is determined by a rich delay time period in said delaying means for delaying the result of the comparison of said upsteam-side air-fuel ratio sensor switched from the lean side to the rich side and a lean delay time period in said delaying means for delaying the result of the comparison of said upstream-side air-fuel ratio sensor switched from the rich side to the lean side.

Claim 88

An apparatus as set forth in claim 70, wherein said air-fuel ratio feedback control parameter calculating means comprises: means for increasing said lean delay time period when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and means for decreasing said lean delay time period when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 89

An apparatus as set forth in claim 70, wherein said air-fuel ratio feedback control parameter calculating means comprises: means for decreasing said rich delay time period when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and means for increasing said rich delay time period when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 90

An apparatus as set forth in claim 70, wherein said air-fuel ratio feedback control parameter calculating means comprises: means for increasing said lean delay time period and decreasing said rich delay time period when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and means for decreasing said lean delay time period and increasing said rich delay time period when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 91

An apparatus as set forth in claim 67, wherein said air-fuel ratio feedback control parameter is determined by a lean skip amount in said remarkable-decrease means and a rich skip amount in said remarkable-increase means.

Claim 92

An apparatus as set forth in claim 74, wherein said air-fuel ratio feedback control parameter calculating means comprises: means for increasing said lean skip amount when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and means for decreasing said lean skip amount when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 93

An apparatus as set forth in claim 74, wherein said air-fuel ratio feedback control parameter calculating means comprises: means for decreasing said rich skip amount when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and means for increasing said rich skip amount when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined voltage.

Claim 94

An apparatus as set forth in claim 74, wherein said air-fuel ratio feedback control parameter calculating means comprises: means for increasing said lean skip amount and decreasing said rich skip amount when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and means for decreasing said lean skip amount and increasing said rich skip amount when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined voltage.

Claim 95

An apparatus as set forth in claim 74, wherein said air-fuel ratio feedback control parameter is determined by the decreasing speed of said gradually-decreasing means and the increasing speed of said gradually-increasing means.

Claim 96

An apparatus as set forth in claim 78, wherein said air-fuel ratio feedback control parameter calculating means comprises: means for increasing the decreasing speed of said gradually-decreasing means when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and means for decreasing the decreasing speed of said gradually-decreasing means when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 97

An apparatus as set forth in claim 78, wherein said air-fuel ratio feedback control parameter calculating means comprises: means for decreasing the increasing speed of said gradual-increase means when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and means for increasing the increasing speed of said gradual-increase means when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 98

An apparatus as set forth in claim 78, wherein said air-fuel ratio feedback control parameter calculating means comprises: means for increasing the decreasing speed of said gradual-decrease means and decreasing the increasing speed of said gradual-increase means when the output of said downstream-side air-fuel ratio sensor is on the rich side with respect to said second predetermined reference voltage; and means for decreasing the decreasing speed of said gradual-decrease means and increasing the increasing speed of said gradual-increase means when the output of said downstream-side air-fuel ratio sensor is on the lean side with respect to said second predetermined reference voltage.

Claim 99

An apparatus as set forth in claim 55, wherein said upstream-side air-fuel ratio sensor is mounted on a water-cooled cylinder head portion of said engine.

Claim 100

An apparatus as set forth in claim 55, wherein said downstream-side air-fuel ratio sensor is of a semi-conductor type which is mounted within a catalyst converter on a downstream-side of said catalyst means.

Claim 101

An apparatus as set forth in claim 83, wherein said semiconductor type air-fuel ratio sensor is mounted in the center of said catalyst converter.

Claim 104

An apparatus as set forth in claim 85, wherein .Iadd.said downstream-side air-fuel ratio sensor having a flow-out type signal processing circuit, and .Iaddend.said means for determining said downstream-side air-fuel ratio sensor state comprises: means for determining whether or not said upstream-side air-fuel ratio is rich in accordance with the output of said upstream-side air-fuel ratio sensor; means for determining whether or not said downstream-side air-fuel ratio sensor outputs a lean signal; means for counting a duration for which said downstream-side air-fuel ratio sensor outputs a lean signal when said upstream-side air-fuel ratio is rich; and means for determining whether or not the duration is longer than a predetermined term, thereby determining that said downstream-side air-fuel ratio sensor is in an abnormal state when the duration is longer than said predetermined term.

Claim 105

An apparatus as set forth in claim 86, further comprising means for releasing the operation of said prohibiting means when the output of said downstream-side air-fuel ratio sensor indicates a rich signal during an active mode.

Claim 106

An apparatus as set forth in claim 86, wherein said means for determining whether said upstream-side air-fuel ratio is rich comprises: means for calculating an average value or blunt value of the output of said upstream-side air-fuel ratio sensor; and means for determining whether or not the average value or blunt value of the output of said upstream-side air-fuel ratio sensor is larger than a predetermined value. thereby determining a rich signal during an active mode for said upstream-side air-fuel ratio sensor, when the average value or blunt value of the output of said upstream-side air-fuel ratio sensor is larger than said predetermined value.

Claim 107

An apparatus as set forth in claim 85, wherein .Iadd.said downstream-side air-fuel ratio sensor having a flow-in type signal processing circuit, and .Iaddend.said means for determining said downstream-side air-fuel ratio sensor state comprises: means for determining whether or not said upstream-side air-fuel ratio is .[.rich.]. .Iadd.lean .Iaddend.in accordance with the output of said upstream-side air-fuel ratio sensor; means for determining whether or not said downstream-side air-fuel ratio sensor outputs a .[.lean.]. .Iadd.rich .Iaddend.signal; means for counting a duration for which said downstream-side air-fuel ratio sensor outputs a .[.lean.]. .Iadd.rich .Iaddend.signal when said upstream-side air-fuel ratio is .[.rich.]. .Iadd.lean; .Iaddend.and means for determining whether or not said duration is longer than a predetermined term, thereby determining that said downstream-side air-fuel ratio sensor is in an abnormal state when said duration is longer than said predetermined term.

Claim 108

An apparatus as set forth in claim 89, further comprising means for releasing the operation of said prohibiting means when the output of said downstream-side air-fuel ratio sensor indicates a lean signal during an active mode.

Claim 109

An apparatus as set forth in claim 89, wherein said means for determining whether said upstream side air-fuel ratio is lean comprises; means for calculating an average value or blunt value of the output of said upstream-side air-fuel ratio sensor; and means for determining whether or not the average value or blunt value of the output of said upstream-side air-fuel ratio sensor is smaller than a predetermined value, thereby determining a lean signal during an active mode for said upstream-side air-fuel ratio sensor, when the average value or blunt value of the output of said upstream-side air-fuel ratio sensor is smaller than said predetermined value.

Claim 112

An apparatus as set forth in claim 92, wherein said predetermined value is dependent upon the speed of said engine.

Claim 131

An apparatus as set forth in claim 102, wherein said predetermined time period is dependent upon a load of said engine.

Claim 132

An apparatus as set forth in claim 102, wherein said predetermined value is dependent upon a load of said engine.

Claim 143

A method for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in an exhaust gas, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting a concentration of a specific component the exhaust gas, comprising the steps of: comparing an output of said upstream-side air-fuel ratio sensor with a first predetermined reference voltage; calculating an air-fuel ratio feedback correction amount in accordance with the comparison result of the output of said upstream-side air-fuel ratio sensor with said first predetermined reference voltage; comparing an output of said downstream-side air-fuel ratio sensor with a second predetermined reference voltage; calculating, in accordance with the comparison result of the output of said downstream-side air-fuel ratio sensor, at least one air-fuel ratio feedback control parameter of delay time periods for which the comparison result of the output of said upstream side air-fuel ratio sensor is delayed, skip amounts by which said air-fuel ratio feedback correction amount is skipped at a switching of the comparison result of said upstream-side air-fuel ratio sensor, and integration amounts by which said air-fuel ratio feedback correction amount as gradually changed in accordance with the comparison result of the output of said upstream-side air-fuel ratio sensor; adjusting the actual air-fuel ratio in accordance with said air-fuel ratio feedback correction amount and said air-fuel ratio feedback control parameter; and determining whether or not said catalyst converter has deteriorated, wherein said catalyst converter deterioration determining step comprises the steps of: calculating a period of the amount of said downstream-side air-fuel ratio sensor; and determining whether or not the period of the output of said downstream-side air-fuel ratio sensor is smaller than a predetermined period, thereby determining that said catalyst converter has deteriorated when the period of the output of said downstream-side air-fuel ratio sensor is smaller than said predetermined period. .Iaddend. .Iadd.111. A method as set forth in claim 110, wherein said catalyst converter deterioration determining step further comprises the steps of: calculating an amplitude of the output of the downstream-side air-fuel ratio sensor; and determining whether or not the amplitude of the output of said downstream-side air-fuel ratio sensor is larger than a predetermined amplitude, thereby determining that said catalyst converter has deteriorated when the period of the output of said downstream-side air-fuel ratio sensor is smaller than said predetermined period and the amplitude of the output of said downstream-side air-fuel ratio is larger than said predetermined

Claim 144

amplitude. .Iaddend. .Iadd.112. A method for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in an exhaust gas, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting a concentration of a specific component in the exhaust gas, comprising the steps of: comparing an output of said upstream-side air-fuel ratio sensor with a first predetermined reference voltage; calculating an air-fuel ratio feedback correction amount in accordance with the comparison results of the output of said upstream-side air-fuel ratio sensor with said first predetermined reference voltage; comparing an output of said downstream-side air-fuel ratio sensor with a second predetermined reference voltage; calculating, in accordance with the comparison result of the output of said downstream-side air-fuel ratio sensor, at least one air-fuel ratio feedback control parameter of delay time periods for which the comparison result of the output of said upstream-side air-fuel ratio sensor is delayed, skip amounts by which said air-fuel ratio feedback correction amount is skipped at a switching of the comparison result of said upstream-side air-fuel ratio sensor, and integration amounts by which said air-fuel ratio feedback correction amount is gradually changed in accordance with the comparison result of the output of said upstream-side air-fuel ratio sensor; adjusting the actual air-fuel ratio in accordance with said air-fuel ratio feedback correction amount and said air-fuel ratio feedback control parameter; and determining whether or not said catalyst converter has deteriorated, wherein said catalyst converter deterioration determining step comprises the steps of: calculating a period of the output of said upstream-side air-fuel ratio sensor; calculating a period of the output of said downstream-side air-fuel ratio sensor; calculating a ratio of the period of the output of said upstream-side air-fuel ratio sensor to that of said downstream-side air-fuel ratio sensor; and determining whether or not the calculated ratio is larger than a predetermined ratio, thereby determining that said catalyst converter has deteriorated when the

Claim 145

amplitude. .Iaddend. .Iadd.112. A method for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in an exhaust gas, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting a concentration of a specific component in the exhaust gas, comprising the steps of: comparing an output of said upstream-side air-fuel ratio sensor with a first predetermined reference voltage; calculating an air-fuel ratio feedback correction amount in accordance with the comparison results of the output of said upstream-side air-fuel ratio sensor with said first predetermined reference voltage; comparing an output of said downstream-side air-fuel ratio sensor with a second predetermined reference voltage; calculating, in accordance with the comparison result of the output of said downstream-side air-fuel ratio sensor, at least one air-fuel ratio feedback control parameter of delay time periods for which the comparison result of the output of said upstream-side air-fuel ratio sensor is delayed, skip amounts by which said air-fuel ratio feedback correction amount is skipped at a switching of the comparison result of said upstream-side air-fuel ratio sensor, and integration amounts by which said air-fuel ratio feedback correction amount is gradually changed in accordance with the comparison result of the output of said upstream-side air-fuel ratio sensor; adjusting the actual air-fuel ratio in accordance with said air-fuel ratio feedback correction amount and said air-fuel ratio feedback control parameter; and determining whether or not said catalyst converter has deteriorated, wherein said catalyst converter deterioration determining step comprises the steps of: calculating a period of the output of said upstream-side air-fuel ratio sensor; calculating a period of the output of said downstream-side air-fuel ratio sensor; calculating a ratio of the period of the output of said upstream-side air-fuel ratio sensor to that of said downstream-side air-fuel ratio sensor; and determining whether or not the calculated ratio is larger than a predetermined ratio, thereby determining that said catalyst converter has deteriorated when the

Claim 146

ratio is larger than said predetermined ratio. .Iaddend. .Iadd.113. A method as set forth in claim 112, wherein said catalyst converter deterioration determining step further comprises the steps of: calculating an amplitude of the output of the downstream-side air-fuel ratio sensor; and determining whether or not the amplitude of the output of said downstream-side air-fuel ratio sensor is larger than a predetermined amplitude, thereby determining that said catalyst converter has deteriorated when the calculated ratio is larger than said predetermined ratio and the period of the output of said downstream-side air-fuel ratio sensor is smaller than said predetermined period and the amplitude of the output of said downstream-side air-fuel ratio is larger than said predetermined ratio. .Iaddend. .Iadd.114. An apparatus for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in an exhaust gas, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting a concentration of a specific component in the exhaust gas, comprising: means for comparing an output of said upstream-side air-fuel ratio sensor with a first predetermined reference voltage; means for calculating an air-fuel ratio feedback correction amount in accordance with the comparison result of the output of said upstream-side air-fuel ratio sensor with said first predetermined reference voltage; means for comparing an output of said downstream-side air-fuel ratio sensor with a second predetermined reference voltage; means for calculating, in accordance with the comparison result of the output of said downstream-side air-fuel ratio sensor, at least one air-fuel ratio feedback control parameter of delay time periods for which the comparison result of the output of said upstream-side air-fuel ratio sensor is delayed, skip amounts by which said air-fuel ratio feedback correction amount is skipped at a switching of the comparison result of said upstream-side air-fuel ratio sensor, and integration amounts by which said air-fuel ratio feedback correction amount is gradually changed in accordance with the comparison result of the output of said upstream-side air-fuel ratio sensor; means for adjusting the actual air-fuel ratio in accordance with said air-fuel ratio feedback correction amount and said air-fuel ratio feedback control parameter; means for determining whether or not said catalyst converter has deteriorated; and means for prohibiting the calculation of said air-fuel ratio feedback control parameter when said catalyst converter has deteriorated. .Iaddend. .Iadd.115. An apparatus for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in an exhaust gas, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting a concentration of a specific component the exhaust gas, comprising: means for comparing an output of said upstream-side air-fuel ratio sensor with a first predetermined reference value; means for calculating an air-fuel ratio feedback correction amount in accordance with the comparison result of the output of said upstream-side air-fuel ratio sensor with said first predetermined reference voltage; means for comparing an output of said downstream-side air-fuel ratio sensor with a second predetermined reference voltage; means for calculating, in accordance with the comparison result of the output of said downstream-side air-fuel ratio sensor, at least one air-fuel ratio feedback control parameter of delay time periods for which the comparison result of the output of said upstream side air-fuel ratio sensor is delayed, skip amounts by which said air-fuel ratio feedback correction amount is skipped at a switching of the comparison result of said upstream-side air-fuel ratio sensor, and integration amounts by which said air-fuel ratio feedback correction amount is gradually changed in accordance with the comparison result of the output of said upstream-side air-fuel ratio sensor; means for adjusting the actual air-fuel ratio in accordance with said air-fuel ratio feedback correction amount and said air-fuel ratio feedback control parameter; and means for determining whether or not said catalyst converter has deteriorated, wherein said means for determining whether or not said catalyst converter has deteriorated comprises: means for calculating a period of the output of said downstream-side air-fuel ratio sensor; and means for determining whether or not the period of the output of said downstream-side air-fuel ratio sensor is smaller than a predetermined period, thereby determining that said catalyst converter has deteriorated when the period of the output of said downstream-side air-fuel ratio sensor is smaller than said predetermined period. .Iaddend. .Iadd.116. An apparatus as set forth in claim 115, wherein said means for determining whether or not said catalyst converter has deteriorated further comprises: means for calculating an amplitude of the output of the downstream-side air-fuel ratio sensor; and means for determining whether or not the amplitude of the output of said downstream-side air-fuel ratio sensor is larger than a predetermined amplitude, thereby determining that said catalyst converter has deteriorated when the period of the output of said downstream-side air-fuel ratio sensor is smaller than said predetermined period and the amplitude of the output of said downstream-side air-fuel ratio is larger than said predetermined amplitude. .Iaddend. .Iadd.117. An apparatus for controlling an air-fuel ratio in an internal combustion engine having a catalyst converter for removing pollutants in an exhaust gas, and upstream-side and downstream-side air-fuel ratio sensors disposed upstream and downstream, respectively, of said catalyst converter for detecting a concentration of a specific component in the exhaust gas, comprising: means for comparing an output of said upstream-side air-fuel ratio sensor with a first predetermined reference voltage; means for calculating an air-fuel ratio feed-back correction amount in accordance with the comparison results of the output of said upstream-side air-fuel ratio sensor with said first predetermined reference voltage; means for comparing an output of said downstream-side air-fuel ratio sensor with a second predetermined reference voltage; means for calculating, in accordance with the comparison result of the output of said downstream-side air-fuel ratio sensor, at least one air-fuel ratio feedback control parameter of delay time periods for which the comparison result of the output of said upstream-side air-fuel ratio sensor is delayed, skip amounts by which said air-fuel ratio feedback correction amount is skipped at a switching of the comparison result of said upstream-side air-fuel ratio sensor, and integration amounts by which said air-fuel ratio feedback correction amount is gradually changed in accordance with the comparison result of the output of said upstream-side air-fuel ratio sensor; means for adjusting the actual air-fuel ratio in accordance with said air-fuel ratio feedback correction amount and said air-fuel ratio feedback control parameter; and wherein said means for determining whether or not said catalyst converter has deteriorated, means for determining whether or not said catalyst converter has deteriorated comprises: means for calculating a period of the output of said upstream-side air-fuel ratio sensor; means for calculating a period of the output of said downstream-side air-fuel ratio sensor; means for calculating a ratio of the period of the output of said upstream-side air-fuel ratio sensor to that of said downstream-side air-fuel ratio sensor; and means for determining whether or not the calculated ratio is larger than a predetermined ratio, thereby determining that said catalyst converter has deteriorated when the ratio is larger than said predetermined ratio. .Iaddend. .Iadd.118. An apparatus as set forth in claim 117, wherein said means for determining whether or not said catalyst converter has deteriorated further comprises: means for calculating an amplitude of the output of the downstream-side air-fuel ratio sensor; and means for determining whether or not the amplitude of the output of said downstream-side air-fuel ratio sensor is larger than a predetermined amplitude, thereby determining that said catalyst converter has deteriorated when the calculated ratio is larger than said predetermined ratio and the period of the output of said downstream-side air-fuel ratio sensor is smaller than said predetermined period and the amplitude of the output of said downstream-side air-fuel ratio is larger than said predetermined ratio. .Iaddend.