Apparatus and method for controlling internal combustion engine

A vehicle, comprising:

• an engine having a combustion chamber, in which air-fuel mixture is drawn;
• an intake passage connected to the combustion chamber;
• a fuel tank for storing fuel;
• a canister that adsorbs fuel vapor generated in the fuel tank;
• a purge line connecting the canister to the intake passage;
• a purge control valve located in the purge line, wherein, when the purge control valve is opened, gas containing fuel vapor is purged as purge gas from the canister to the intake passage through the purge line by intake negative pressure generated in the intake passage;
• an air-fuel ratio sensor for detecting the air-fuel ratio of the air-fuel mixture;
• an air flow rate sensor for detecting the flow rate of air flowing through the intake passage;
• and
• an electronic control unit, wherein, according to a deviation of a detected air-fuel ratio relative to a target air-fuel ratio, the electronic control unit renews a vapor concentration value representing the concentration of fuel vapor contained in the purge gas by a predetermined renew amount at a time, wherein the electronic control unit sets the amount of fuel supplied to the combustion chamber according to the renewed vapor concentration value such that the detected air-fuel ratio seeks the target air-fuel ratio,
• wherein the electronic control unit computes the ratio of an air flow rate detected by the air flow rate sensor to a predetermined maximum air flow rate, and sets the computed ratio as an engine load ratio, and wherein the electronic control unit sets a smaller value of the renew amount for a greater value of the engine load ratio.

A method for controlling the air-fuel ratio of air-fuel mixture drawn into a combustion chamber of an engine, wherein an intake passage of the engine is connected to a canister, wherein the canister adsorbs fuel vapor generated in a fuel tank, wherein gas containing fuel vapor is purged as purge gas from the canister to the intake passage through a purge control device by intake negative pressure generated in the intake passage, the method comprising:

• detecting the air-fuel ratio of the air-fuel mixture;
• renewing a vapor concentration value representing the concentration of fuel vapor contained in the purge gas by a predetermined renew amount at a time according to a deviation of a detected air-fuel ratio relative to a target air-fuel ratio;
• setting the amount of fuel supplied to the combustion chamber according to the renewed vapor concentration value such that the detected air-fuel ratio seeks the target air-fuel ratio;
• and
• setting a smaller value of the renew amount for a greater value of the load on the engine.