Method for controlling air-fuel ratio for internal combustion engine and apparatus therefor

Claim 3

A method of controlling the air-fuel ratio of an air-fuel mixture according to claim 1 wherein the step of detecting an engine acceleration includes the steps of detecting an amplitude of an absolute intake pressure of an intake passage downstream of a throttle valve to calculate a variation of the absolute intake pressure between successive detected absolute intake pressures which in turn is compared with a reference value to determine whether said second additional operational condition exists wherein an acceleration of the engine is commencing.

Claim 6

A method of controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine according to claim 3 further comprising the steps of: detecting a concentration of a predetermined component of an exhaust gas to generate an air-fuel ratio signal, wherein said engine is provided with a fuel injector and said step of determining the air-fuel ratio includes the steps of: calculating a basic fuel injection time corresponding to a fuel injection rate of the fuel injector in accordance with an engine speed and the engine load; correcting, depending on the engine operating state, the basic fuel injection time duration so that it becomes less than the basic fuel injection time duration, thereby attaining a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio and wherein a result of correction is feedback controlled to be substantially at the stoichiometric air-fuel ratio.

Claim 7

A method of controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine according to claim 4 wherein said step of correcting the basic fuel injection includes the steps of: calculating a lean correction coefficient FLEAN for lean control mode and a feedback correction coefficient FAF for feedback control mode, said lean correction coefficient FLEAN being determined to be less than 1.0 in the lean control mode and be 1.0 in the feedback control mode, said feedback correction coefficient FAF being determined in such a manner than when the air-fuel ratio signal represents the lean air-fuel ratio in the feedback control mode, the feedback correction coefficient FAF is greater than 1.0 and when the air-fuel ratio signal represents the rich air-fuel ratio in the feedback control mode, the feedback correction coefficient FAF is less than 1.0, and the feedback correction coefficient FAF is 1.0 is the lean control mode.

Claim 8

Apparatus for controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine comprising: (a) means for detecting and determining that the engine is operating under a first operational state wherein conditions exist where a cooling water temperature is greater than a predetermined cooling water temperature, an engine load is less than a predetermined engine load and a vehicle speed is greater than a first operational condition of a predetermined vehicle speed; (b) means for detecting said vehicle speed and determining if an additional first operational condition exists wherein said vehicle speed is less than a second predetermined vehicle speed wherein said second predetermined vehicle speed is greater than said first predetermined vehicle speed; (c) means for detecting an engine acceleration and determining if a second additional operational condition exists wherein an acceleration of the engine is commencing; and (d) means for determining said air-fuel ratio such that when at least said first operational state exists, the air-fuel ratio is adjusted to the lean side of stoichiometric, and if both first and second additional operational conditions exist, the air-fuel ratio is adjusted towards substantially stoichiometric.

Claim 9

Apparatus for controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine comprising: (a) means for detecting and determining that the engine is operating under a first operational state wherein conditions exist where a cooling water temperature is greater than a predetermined cooling water temperature, an engine load is less than a predetermined engine load and a vehicle speed is greater than a first operational condition of a predetermined vehicle speed; (b) means for detecting said vehicle speed and determining if an additional first operational condition exists wherein said vehicle speed is less than a second predetermined vehicle speed wherein said second predetermined vehicle speed is greater than said first predetermined vehicle speed; (c) means for detecting an engine acceleration and determining if a second additional operational condition exists wherein an acceleration of the engine is commencing; and (d) means for determining said air-fuel ratio such that when at least said first operational state exists, the air-fuel ratio is adjusted to the lean side of stoichiometric, and if both first and second additional operational conditions exist, the air-fuel ratio is adjusted towards substantially stoichiometric.

Claim 10

Apparatus for controlling the air-fuel ratio of an air-fuel mixture according to claim 6 wherein said means for detecting an engine acceleration includes means for detecting an amplitude of an absolute intake pressure of an intake passage downstream of a throttle valve, means for calculating a variation of the absolute intake pressure between successive detected absolute intake pressures, and means for comparing said variation with a reference value to determine whether said second additional operational condition exists wherein an acceleration of the engine is commencing.

Claim 11

Apparatus for controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine comprising: (a) means for detecting and determining that the engine is operating under a first operational state wherein conditions exist where a cooling water temperature is greater than a predetermined cooling water temperature, an engine load is less than a predetermined engine load and a vehicle speed is greater than a first operational condition of a predetermined vehicle speed; (b) means for detecting said vehicle speed and determining if an additional first operational condition exists wherein said vehicle speed is less than a second predetermined vehicle speed wherein said second predetermined vehicle speed is greater than said first predetermined vehicle speed; (c) means for measuring a time period starting from a time at which a fully closed throttle valve is opened; (d) means for comparing the measured time period with a predetermined time period to determine whether the predetermined time period has lapsed; and (e) means for determining said air-fuel ratio such that when at least said first operational state exists, the air-fuel ratio is adjusted to the lean side of stoichiometric, and that if it is detected that the predetermined period of time has not lapsed and said additional first operational condition exists while the first operational state exists, the air-fuel ratio is adjusted towards substantially stoichiometric.

Claim 12

Apparatus for controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine comprising: (a) means for detecting and determining that the engine is operating under a first operational state wherein conditions exist where a cooling water temperature is greater than a predetermined cooling water temperature, an engine load is less than a predetermined engine load and a vehicle speed is greater than a first operational condition of a predetermined vehicle speed; (b) means for detecting said vehicle speed and determining if an additional first operational condition exists wherein said vehicle speed is less than a second predetermined vehicle speed wherein said second predetermined vehicle speed is greater than said first predetermined vehicle speed; (c) means for measuring a time period starting from a time at which a fully closed throttle valve is opened; (d) means for comparing the measured time period with a predetermined time period to determine whether the predetermined time period has lapsed; and (e) means for determining said air-fuel ratio such that when at least said first operational state exists, the air-fuel ratio is adjusted to the lean side of stoichiometric, and that if it is detected that the predetermined period of time has not lapsed and said additional first operational condition exists while the first operational state exists, the air-fuel ratio is adjusted towards substantially stoichiometric.

Claim 13

Apparatus for controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine according to claim 8 further comprising: means for detecting a concentration of a predetermined component of an exhaust gas to generate an air-fuel ratio signal, wherein said engine is provided with a fuel injector and said means for determining the air-fuel ratio includes: means for calculating a basic fuel injection time corresponding to a fuel injection rate of said fuel injector in accordance with an engine speed and the engine load; means for correcting, depending on the engine operational state, the basic fuel injection time duration so that it becomes less than the basic fuel injection time duration, thereby attaining a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio and means responsive to the result of the correction for feedback controlling the air-fuel ratio to be substantially at the stoichiometric air-fuel ratio.

Claim 14

Apparatus for controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine according to claim 9 wherein said means for correcting the basic fuel injection includes: means for calculating a lean correction coefficient FLEAN for lean control mode and a feedback correction coefficient FAF for feedback control mode, said lean correction coefficient FLEAN being determined to be less than 1.0 in the lean control mode and be 1.0 in the feedback control mode, said feedback correction coefficient FAF being determined in such a manner that when the air-fuel ratio signal represents the lean air-fuel ratio in the feedback control mode, the feedback correction coefficient FAF is greater than 1.0 and when the air-fuel ratio signal represents the rich air-fuel ratio in the feedback control mode, the feedback correction coefficient FAF is less than 1.0, and the feedback correction coefficient FAF is 1.0 is the lean control mode.