Air-fuel ratio control system for internal combustion engine

Claim 2

An air-fuel ratio control system for an internal combustion engine having a catalytic converter disposed in an exhaust gas passageway of the engine, said system comprising: means for detecting an air-fuel ratio of an air-fuel mixture supplied to the engine, by sensing a component of exhaust gas in the exhaust gas passageway downstream of the catalytic converter, said air-fuel ratio detecting means including no more than a single air-fuel ratio sensor, wherein said single air-fuel ratio sensor is disposed in the exhaust gas passageway downstream of the catalytic converter to detect an air-fuel ratio in the exhaust passageway downstream of the catalytic converter; means for setting an air-fuel ratio correction amount in accordance with said detected air-fuel ratio, to control said air-fuel ratio toward a target air-fuel ratio, said air-fuel ratio correction amount having a period and an amplitude in variation; means for setting a cycle correction amount in accordance with an engine operating condition, at least one of said period and said amplitude of said air-fuel ratio correction amount being changeable in accordance with said cycle correction amount, said cycle correction amount being set such that said amplitude of said air-fuel ratio correction amount is large at a low engine coolant temperature as compared with that at a high engine coolant temperature higher than said low engine coolant temperature; means for setting a fuel supply amount in accordance with said air-fuel ratio correction amount and said cycle correction amount; means for supplying a fuel into the engine; and means for controlling an amount of the fuel to be supplied from said fuel supply means, in accordance with said fuel supply amount.

Claim 3

An air-fuel ratio control system as claimed in claim 1, wherein said cycle correction amount is set such that said period of said air-fuel ratio correction amount is changeable in accordance with the engine operating condition, wherein said period decreases as an engine load increases.

Claim 4

An air-fuel control system as claimed in claim 1, wherein said cycle correction amount is set such that said period of said air-fuel ratio correction amount is changeable in accordance with an amount of intake air, wherein said period decreases as an amount of intake air increases.

Claim 5

An air-fuel control system as claimed in claim 1, wherein said cycle correction amount is set such that a time width (TL1) of each wave in variation and said period (TL2) of said air-fuel ratio correction amount are in a relationship of TL1=TL2/2=t1/Qa where t1 is a constant value; and Qa is an amount of intake air.

Claim 6

An air-fuel control system as claimed in claim 1, wherein said cycle correction amount is set such that said amplitude of said air-fuel ratio correction decreases as an engine speed increases.

Claim 7

An air-fuel control system as claimed in claim 1, wherein said cycle correction amount is set such that said amplitude of said air-fuel ratio correction amount increases as an engine load increases.

Claim 8

An air-fuel control system as claimed in claim 1, wherein said cycle correction amount is set such that said amplitude of said air-fuel ratio correction amount is constant regardless of an engine speed at a low engine load lower than a predetermined value, and decreases as the engine speed increases at an engine load higher than the predetermined value.

Claim 9

An air-fuel ratio control system as claimed in claim 1, wherein said air-fuel ratio sensor is an oxygen sensor disposed in the exhaust gas passageway downstream of the catalytic converter, said oxygen sensor being adapted to detect the concentration of oxygen in the exhaust gas.

Claim 10

An air-fuel control system as claimed in claim 1, wherein the catalytic converter is a three-way catalytic converter.

Claim 11

An air-fuel ratio control system as claimed in claim 1, wherein said air-fuel ratio correction amount setting means includes means for controlling said air-fuel ratio toward a stoichiometric air-fuel ratio.

Claim 12

An air-fuel control system as claimed in claim 8, wherein said air-fuel ratio setting means includes means for setting a control constant in accordance with an output of said oxygen concentration, said control constant being changeable with time.

Claim 13

An air-fuel control system as claimed in claim 11, wherein said cycle correction amount setting means includes means for outputting a cycle correction pulse signal having a predetermined pulse interval, and means for outputting a signal representative of a constant corresponding to said amplitude, said constant being determined in accordance with an engine operating condition.

Claim 14

An air-fuel control system as claimed in claim 12, wherein said fuel supply amount setting means includes means for setting an air-fuel ratio correction coefficient in accordance with said control constant and at least one of said predetermined pulse interval and pulse width, said fuel supply amount being set in accordance with said air-fuel ratio correction coefficient.

Claim 15

An air-fuel ratio control system as claimed in claim 13, wherein said fuel supply amount setting means includes means for changing said air-fuel ratio correction coefficient in accordance with at least one of said predetermined pulse interval and pulse width of said cycle correction pulse signal.

Claim 16

An air-fuel ratio control system for an internal combustion engine having a catalytic converter disposed in an exhaust gas passageway of the engine, said system comprising: means for detecting an air-fuel ratio of an air-fuel mixture supplied to the engine, by sensing a component of exhaust gas in the exhaust gas passageway downstream of the catalytic converter, said air-fuel ratio detecting means including no more than a single air-fuel ratio sensor, wherein said single air-fuel ratio sensor is disposed in the exhaust gas passageway downstream of the catalytic converter to detect an air-fuel ratio in the exhaust passageway downstream of the catalytic converter; means for setting an air-fuel ratio correction amount in accordance with said detected air-fuel ratio, to control said air-fuel ratio toward a target air-fuel ratio, said air-fuel ratio correction amount having a period and an amplitude in variation; means for setting a cycle correction amount in accordance with an engine operating condition, at least one of said period and said amplitude of said air-fuel ratio correction amount being changeable in accordance with said cycle correction amount, said cycle correction amount being set such that said amplitude of said air-fuel ratio correction amount is constant regardless of an engine speed at a low engine load lower than a predetermined value, and decreases as the engine speed increases at an engine load higher than the predetermined value; means for setting a fuel supply amount in accordance with said air-fuel ratio correction amount and said cycle correction amount; means for supplying a fuel into the engine; and means for controlling an amount of the fuel to be supplied from said fuel supply means, in accordance with said fuel supply amount.

Claim 17

An air-fuel ratio control system for an internal combustion engine having a catalytic converter disposed in an exhaust gas passageway of the engine, said system comprising: means for detecting an air-fuel ratio of an air-fuel mixture supplied to the engine, by sensing a component of exhaust gas in the exhaust gas passageway downstream of the catalytic converter, said air-fuel ratio detecting means including no more than a single air-fuel ratio sensor, wherein said single air-fuel ratio sensor is disposed in the exhaust gas passageway downstream of the catalytic converter to detect an air-fuel ratio in the exhaust passageway downstream of the catalytic converter; means for setting an air-fuel ratio correction amount in accordance with said detected air-fuel ratio, to control said air-fuel ratio toward a target air-fuel ratio, said air-fuel ratio correction amount having a period and an amplitude in variation; means for setting a cycle correction amount in accordance with an engine operating condition, at least one of said period and said amplitude of said air-fuel ratio correction amount being changeable in accordance with said cycle correction amount, said cycle correction amount being set such that said amplitude of said air-fuel ratio correction amount is constant regardless of an engine speed at a low engine load lower than a predetermined value, and decreases as the engine speed increases at an engine load higher than the predetermined value; means for setting a fuel supply amount in accordance with said air-fuel ratio correction amount and said cycle correction amount; means for supplying a fuel into the engine; and means for controlling an amount of the fuel to be supplied from said fuel supply means, in accordance with said fuel supply amount.

Claim 18

An air-fuel ratio control system for an internal combustion engine having a catalytic converter disposed in an exhaust gas passageway of the engine, said system comprising: means for detecting an air-fuel ratio of an air-fuel mixture supplied to the engine, by sensing a component of exhaust gas in the exhaust gas passageway downstream of the catalytic converter, said air-fuel ratio detecting means including no more than a single air-fuel ratio sensor, wherein said single air-fuel ratio sensor is disposed in the exhaust gas passageway downstream of the catalytic converter to detect an air-fuel ratio in the exhaust passageway downstream of the catalytic converter; means for setting an air-fuel ratio correction amount in accordance with said detected air-fuel ratio, to control said air-fuel ratio toward a target air-fuel ratio, said air-fuel ratio correction amount having a period and an amplitude in variation; means for setting a cycle correction amount in accordance with an engine operating condition, at least one of said period and said amplitude of said air-fuel ratio correction amount being changeable in accordance with said cycle correction amount, said cycle correction amount is set such that (a) said amplitude of said air-fuel ratio correction amount is large at a low engine coolant temperature as compared with that at a high engine coolant temperature higher than said low engine coolant temperature, and (b) said amplitude of said air-fuel ratio correction amount is constant regardless of an engine speed at a low engine load lower than a predetermined value, and decreases as the engine speed increases at an engine load higher than the predetermined value; means for setting a fuel supply amount in accordance with said air-fuel ratio correction amount and said cycle correction amount; means for supplying a fuel into the engine; and means for controlling an amount of the fuel to be supplied from said fuel supply means, in accordance with said fuel supply amount.

Claim 19

An air-fuel ratio control system for an internal combustion engine having a catalytic converter disposed in an exhaust gas passageway of the engine, said system comprising: means for detecting an air-fuel ratio of an air-fuel mixture supplied to the engine, by sensing a component of exhaust gas in the exhaust gas passageway downstream of the catalytic converter, said air-fuel ratio detecting means including no more than a single air-fuel ratio sensor, wherein said single air-fuel ratio sensor is disposed in the exhaust gas passageway downstream of the catalytic converter to detect an air-fuel ratio in the exhaust passageway downstream of the catalytic converter; means for setting an air-fuel ratio correction amount in accordance with said detected air-fuel ratio, to control said air-fuel ratio toward a target air-fuel ratio, said air-fuel ratio correction amount having a period and an amplitude in variation; means for setting a cycle correction amount in accordance with an engine operating condition, at least one of said period and said amplitude of said air-fuel ratio correction amount being changeable in accordance with said cycle correction amount, said cycle correction amount is set such that (a) said amplitude of said air-fuel ratio correction amount is large at a low engine coolant temperature as compared with that at a high engine coolant temperature higher than said low engine coolant temperature, and (b) said amplitude of said air-fuel ratio correction amount is constant regardless of an engine speed at a low engine load lower than a predetermined value, and decreases as the engine speed increases at an engine load higher than the predetermined value; means for setting a fuel supply amount in accordance with said air-fuel ratio correction amount and said cycle correction amount; means for supplying a fuel into the engine; and means for controlling an amount of the fuel to be supplied from said fuel supply means, in accordance with said fuel supply amount.