Air-fuel ratio control apparatus and method for internal combustion engine

An air-fuel ratio control method for an internal combustion engine, wherein the engine includes a first injection valve, which is one of a port injection valve that injects fuel into an intake passage and a direct injection valve that injects fuel into a combustion chamber, and a second injection valve, which is the other, the air-fuel ratio control method comprising:

• setting a base injection amount, which is an open-loop operation amount for controlling an air-fuel ratio to a target value;
• calculating a feedback operation amount for controlling a detection value of the air-fuel ratio to the target value;
• performing, to supply fuel to the combustion chamber of the engine, at least one of an operation of the first injection valve based on the base injection amount that has been corrected using the feedback operation amount and a first learning value, and an operation of the second injection valve based on the base injection amount that has been corrected using the feedback operation amount and a second learning value;
• updating the first learning value based on the feedback operation amount when only the first injection valve is being operated;
• when the first learning value is being updated, determining that the first learning value has converged on condition that a correction ratio of the base injection amount, which is obtained using the feedback operation amount, is less than or equal to a predetermined ratio;
• and
• when the first injection valve and the second injection valve are both being operated
• updating the second learning value based on the feedback operation amount on condition that the first learning value is determined to have converged and an injection distribution ratio, which is a ratio of an injection amount of the second injection valve to a total injection amount of the first injection valve and the second injection valve, is greater than or equal to a specified value, and
• refraining from updating the second learning value when the injection distribution ratio is less than the specified value.

An air-fuel ratio control apparatus for an internal combustion engine, wherein the engine includes a first injection valve, which is one of a port injection valve that injects fuel into an intake passage and a direct injection valve that injects fuel into a combustion chamber, and a second injection valve, which is the other, the air-fuel ratio control apparatus comprising circuitry that is configured to

• set a base injection amount, which is an open-loop operation amount for controlling an air-fuel ratio to a target value;
• calculate a feedback operation amount for controlling a detection value of the air-fuel ratio to the target value;
• perform, to supply fuel to the combustion chamber of the engine, at least one of an operation of the first injection valve based on the base injection amount that has been corrected using the feedback operation amount and a first learning value, and an operation of the second injection valve based on the base injection amount that has been corrected using the feedback operation amount and a second learning value;
• update the first learning value based on the feedback operation amount when operating only the first injection valve;
• when updating the first learning value, determine that the first learning value has converged on condition that a correction ratio of the base injection amount, which is obtained using the feedback operation amount, is less than or equal to a predetermined ratio;
• and
• update the second learning value based on the feedback operation amount when operating both the first injection valve and the second injection valve, wherein the circuitry is configured to
• update the second learning value on condition that the first learning value is determined to have converged and an injection distribution ratio, which is a ratio of an injection amount of the second injection valve to a total injection amount of the first injection valve and the second injection valve, is greater than or equal to a specified value, and
• refrain from updating the second learning value when the injection distribution ratio is less than the specified value.