Method for controlling air fuel ratio of an internal combustion engine

Claim 1

A system for controlling an air-fuel ratio of an internal combustion engine having an apparatus for controlling an amount of fuel vapor purged into said engine from a canister which adsorbs said fuel vapor from a fuel tank, the system comprising: detecting means for detecting an engine operating condition; calculating means for calculating a basic fuel injection amount according to said engine operating condition; setting means responsive to said engine operating condition for setting a feedback coefficient; learning means responsive to said feedback coefficient and said operating condition for learning an air-fuel ratio learning value; deciding means responsive to said basic fuel injection amount and said air-fuel ratio learning value for deciding upon a decided fuel injection amount; judging means responsive to said engine operating condition for judging whether or not the engine is in a steady running condition; changing means for changing said amount of fuel vapor purged from the canister at a predetermined rate when said engine is running in said steady running condition; determining means for determining how said feedback coefficient varies when said amount of fuel vapor purged from the canister is changed at said predetermined rate and providing a variation value indicative thereof; computing means responsive to said variation value of said feedback coefficient as determined by said determining means for computing a purge correction value; rewriting means for rewriting said air-fuel ratio learning value according to said purge correction value so as to have a rewritten air-fuel ratio learning value when said engine is stopped; and memory means for memorizing the rewritten air-fuel ratio learning value such that the rewritten air-fuel ratio learning value is available after the engine is stopped for providing an improved air-fuel ratio upon a restarting of the engine.

Claim 2

A system for controlling an air-fuel ratio of an internal combustion engine having an apparatus for controlling an amount of fuel vapor purged into said engine from a canister which adsorbs said fuel vapor from a fuel tank, the system comprising: detecting means for detecting an engine operating condition; calculating means for calculating a basic fuel injection amount according to said engine operating condition; setting means responsive to said engine operating condition for setting a feedback coefficient; learning means responsive to said feedback coefficient and said operating condition for learning an air-fuel ratio learning value; deciding means responsive to said basic fuel injection amount and said air-fuel ratio learning value for deciding upon a decided fuel injection amount; judging means responsive to said engine operating condition for judging whether or not the engine is in a steady running condition; changing means for changing said amount of fuel vapor purged from the canister at a predetermined rate when said engine is running in said steady running condition; determining means for determining how said feedback coefficient varies when said amount of fuel vapor purged from the canister is changed at said predetermined rate and providing a variation value indicative thereof; computing means responsive to said variation value of said feedback coefficient as determined by said determining means for computing a purge correction value; rewriting means for rewriting said air-fuel ratio learning value according to said purge correction value so as to have a rewritten air-fuel ratio learning value when said engine is stopped; and memory means for memorizing the rewritten air-fuel ratio learning value such that the rewritten air-fuel ratio learning value is available after the engine is stopped for providing an improved air-fuel ratio upon a restarting of the engine.

Claim 4

A method for controlling an air-fuel ratio of an internal combustion engine having an injector, a canister for absorbing fuel vapor from a fuel tank, a fuel injection control system for controlling an amount of fuel to be injected from said injector based on an air-fuel ratio feedback correction value determined by an air-fuel ratio feedback correction system in response to a signal from an oxygen sensor equipped at an exhaust portion of said engine, and on a learning value determined by a learning value determination system for use in compensating for drift of said air-fuel ratio feedback correction value, and a purge control system for controlling a fuel vapor purge quantity purged from said canister to an intake of said engine based on an operating condition of said engine, the method comprising: prohibiting learning of said learning value for a predetermined time period; changing said fuel vapor purge quantity at a predetermined rate during said predetermined time period; detecting how said air-fuel ratio feedback correction value varies while said fuel vapor purge quantity is changed at said predetermined rate and obtaining a variation value indicative thereof; calculating a deviation of said learning value caused by said changing of said fuel vapor purge quantity based upon said variation value; correcting said learning value based upon said deviation so as to have a corrected learning value when said engine is turned off; and storing the corrected learning value such that the corrected learning value is available after said engine is turned off for providing an improved air-fuel ratio upon a restarting of said engine.

Claim 5

A method for controlling an air-fuel ratio of an internal combustion engine having an injector, a canister for absorbing fuel vapor from a fuel tank, a fuel injection control system for controlling an amount of fuel to be injected from said injector based on an air-fuel ratio feedback correction value determined by an air-fuel ratio feedback correction system in response to a signal from an oxygen sensor equipped at an exhaust portion of said engine, and on a learning value determined by a learning value determination system for use in compensating for drift of said air-fuel ratio feedback correction value, and a purge control system for controlling a fuel vapor purge quantity purged from said canister to an intake of said engine based on an operating condition of said engine, the method comprising: prohibiting learning of said learning value for a predetermined time period; changing said fuel vapor purge quantity at a predetermined rate during said predetermined time period; detecting how said air-fuel ratio feedback correction value varies while said fuel vapor purge quantity is changed at said predetermined rate and obtaining a variation value indicative thereof; calculating a deviation of said learning value caused by said changing of said fuel vapor purge quantity based upon said variation value; correcting said learning value based upon said deviation so as to have a corrected learning value when said engine is turned off; and storing the corrected learning value such that the corrected learning value is available after said engine is turned off for providing an improved air-fuel ratio upon a restarting of said engine.

Claim 11

A system for controlling an air-fuel ratio of an internal combustion engine having an injector, a canister for absorbing fuel vapor from a fuel tank, an air-fuel ratio feedback correction system for determining an air flow ratio feedback correction value, a learning value determination system for determining a learning value for compensation for drift of said air-fuel ratio feedback correction value, a fuel injection control system for controlling an amount of fuel to be injected from said injector based on said air-fuel ratio feedback correction value, in response to a signal from an oxygen sensor equipped with an exhaust portion of said engine, and on said learning value, and a purge control system for controlling a quantity of fuel vapor to be purged from said canister to an intake of said engine based on operating conditions for said engine, the system comprising: prohibiting means for prohibiting learning of said learning value for a predetermined time period; changing means for changing said fuel vapor purge quantity at a predetermined rate during said predetermined time period; detecting means for detecting how said air-fuel ratio feedback correction value varies while said fuel vapor purge quantity is changed at said predetermined rate and providing a variation value indicative thereof; calculating means for calculating a deviation of said learning value caused by said changing of said fuel vapor purge amount based upon said variation value; correcting means for correcting said learning value based upon said deviation so as to have a corrected learning value when said engine is turned off; and storing the corrected learning value such that the corrected learning value is available after said engine is turned off for providing an improved air-fuel ratio upon a restarting of the engine.

Claim 12

A system for controlling an air-fuel ratio of an internal combustion engine having an injector, a canister for absorbing fuel vapor from a fuel tank, an air-fuel ratio feedback correction system for determining an air flow ratio feedback correction value, a learning value determination system for determining a learning value for compensation for drift of said air-fuel ratio feedback correction value, a fuel injection control system for controlling an amount of fuel to be injected from said injector based on said air-fuel ratio feedback correction value, in response to a signal from an oxygen sensor equipped with an exhaust portion of said engine, and on said learning value, and a purge control system for controlling a quantity of fuel vapor to be purged from said canister to an intake of said engine based on operating conditions for said engine, the system comprising: prohibiting means for prohibiting learning of said learning value for a predetermined time period; changing means for changing said fuel vapor purge quantity at a predetermined rate during said predetermined time period; detecting means for detecting how said air-fuel ratio feedback correction value varies while said fuel vapor purge quantity is changed at said predetermined rate and providing a variation value indicative thereof; calculating means for calculating a deviation of said learning value caused by said changing of said fuel vapor purge amount based upon said variation value; correcting means for correcting said learning value based upon said deviation so as to have a corrected learning value when said engine is turned off; and storing the corrected learning value such that the corrected learning value is available after said engine is turned off for providing an improved air-fuel ratio upon a restarting of the engine.