Fuel injection amount control apparatus for an internal combustion engine

A fuel injection amount control apparatus comprising:

• a multi-cylinder internal combustion engine;
• a three way catalyst which is disposed in an exhaust passage of said engine and at a position downstream of an exhaust gas aggregated portion into which exhaust gases discharged from a plurality of cylinders of said engine merge;
• an air-fuel ratio sensor, which is disposed in said exhaust passage and at a position between said exhaust gas aggregated portion and said catalyst, which includes an air-fuel ratio detection element, an exhaust-gas-side electrode layer and a reference-gas-side electrode layer that are formed so as to face to each other across said air-fuel ratio detection element, and a porous layer which covers said exhaust-gas-side electrode layer, and which outputs an output value corresponding to an amount of oxygen and an amount of unburnt substances that are contained in an exhaust gas that has reached said exhaust-gas-side electrode layer via said porous layer, said gas being included in an exhaust gas passing through said position at which said air-fuel ratio sensor is disposed;
• a plurality of fuel injection valves, each of which is configured so as to inject a fuel to be contained in a mixture supplied to each of combustion chambers of a plurality of said cylinders in an amount corresponding to an instructed fuel injection amount;
• and
• an electric controller configured to:
• obtain an actual detected air-fuel ratio based on an actual output value (Vabyfs) of said air-fuel ratio sensor;
• calculate said instructed fuel injection amount by performing, based on said actual detected air-fuel ratio, a feedback correction on said amount of said fuel injected from a plurality of said fuel injection valves in such a manner that said actual detected air-fuel ratio coincides with a target air-fuel ratio;
• and
• obtain an air-fuel ratio imbalance indicating value which becomes larger as a degree of a non-uniformity among a plurality of said cylinders of cylinder-by-cylinder air-fuel ratios, each of which is an air-fuel ratio of said mixture supplied to each of said combustion chambers of a plurality of said cylinders, becomes larger, wherein,
• said electric controller is configured to:
• obtain said actual detected air-fuel ratio by converting said actual output value (Vabyfs) of said air-fuel ratio sensor into an air-fuel ratio which becomes leaner as said obtained air-fuel ratio imbalance indicating value becomes larger;
• calculate a feedback correction term by multiplying a value correlated to a difference between said actual detected air-fuel ratio and said target air-fuel ratio by a predetermined gain:
• carry out said feedback correction using said feedback term;
• and
• set said gain to a larger value in a period after rich-lean inversion time point than a value in a period after lean-rich inversion time point,
• wherein said period after rich-lean inversion time point being a time period until a predetermined time elapses from a rich-lean inversion time point at which said actual detected air-fuel ratio has changed from an air-fuel ratio richer than a stoichiometric air-fuel ratio to an air-fuel ratio leaner than said stoichiometric air-fuel ratio, and said period after lean-rich inversion time point being a time period until a predetermined time elapses from a lean-rich inversion time point at which said actual detected air-fuel ratio has changed from an air-fuel ratio leaner than said stoichiometric air-fuel ratio to an air-fuel ratio richer than said stoichiometric air-fuel ratio.

A fuel injection amount control apparatus comprising:

• a multi-cylinder internal combustion engine;
• a three way catalyst which is disposed in an exhaust passage of said engine and at a position downstream of an exhaust gas aggregated portion into which exhaust gases discharged from a plurality of cylinders of said engine merge;
• an air-fuel ratio sensor, which is disposed in said exhaust passage and at a position between said exhaust gas aggregated portion and said catalyst, which includes an air-fuel ratio detection element, an exhaust-gas-side electrode layer and a reference-gas-side electrode layer that are formed so as to face to each other across said air-fuel ratio detection element, and a porous layer which covers said exhaust-gas-side electrode layer, and which outputs an output value (Voxs) corresponding to an amount of oxygen and an amount of unburnt substances that are contained in an exhaust gas that has reached said exhaust-gas-side electrode layer via said porous layer, said gas being included in an exhaust gas passing through said position at which said air-fuel ratio sensor is disposed;
• a plurality of fuel injection valves, each of which is configured so as to inject a fuel to be contained in a mixture supplied to each of combustion chambers of a plurality of said cylinders in an amount corresponding to an instructed fuel injection amount;
• and
• an electric controller configured to:
• calculate said instructed fuel injection amount by performing, based on an actual output value (Vabyfs) of said air-fuel ratio sensor, a feedback correction on said amount of said fuel injected from a plurality of said fuel injection valves in such a manner that said actual output of said air-fuel ratio sensor coincides with a target air-fuel value;
• obtain an air-fuel ratio imbalance indicating value which becomes larger as a degree of a non-uniformity among a plurality of said cylinders of cylinder-by-cylinder air-fuel ratios, each of which is an air-fuel ratio of said mixture supplied to each of said combustion chambers of a plurality of said cylinders, becomes larger, wherein,
• said electric controller is configured to:
• obtain a corrected output value by correcting said actual output value (Vabyfs) of said air-fuel ratio sensor to be a value in a leaner side as said air-fuel ratio imbalance indicating value becomes larger;
• perform said feedback correction based on said corrected output value;
• and
• obtain said air-fuel ratio imbalance indicating value using an actual output proportional value (k·Voxs) which is a value directly proportional to said actual output value (Vabyfs) of said air-fuel ratio sensor.