Air-fuel ratio imbalance detection device for internal combustion engine

A non-transitory computer-readable medium storing instructions that, when executed by a controller, cause the controller to perform a method comprising:

• acquiring an output from an in-cylinder pressure sensor mounted on each of a plurality of cylinders of an internal combustion engine;
• calculating a combustion parameter including an amount of generated heat within the plurality of cylinders based on an output of the in-cylinder pressure sensor;
• providing control to enlean an air-fuel ratio for each of the plurality of cylinders by reducing a fuel injection amount so that the amount of generated heat calculated coincides with a predetermined amount of generated heat;
• and
• responsive to determining that the amount of generated heat coincides with the predetermined amount of generated heat, detecting an air-fuel ratio imbalance between the plurality of cylinders based on a reduction amount of fuel injection amount, the reduction amount being provided by control that is exercised for each of the plurality of cylinders by the injection amount controller;
• receiving output of an air-fuel ratio sensor disposed in an exhaust path into which exhaust gas from the plurality of cylinders is introduced;
• and
• calculating the predetermined amount of generated heat with which the amount of generated heat should coincide under the control based on a ratio and an average value, the ratio being between an air-fuel ratio value that is obtained based on the output of the air-fuel ratio sensor and a predetermined lean air-fuel ratio value, the average value being an average of the amount of generated heat for the plurality of cylinders.