CONTROL METHOD AND CONTROL DEVICE FOR VEHICULAR INTERNAL COMBUSTION ENGINE

A vehicular internal combustion engine system includes an internal combustion engine and an electric intake air supply device. The internal combustion engine is shifted into a stoichiometric combustion mode, and a lean combustion mode. The electric intake air supply device is driven by an on-vehicle battery, and employed to contribute a part of intake air quantity at least under a specific operating condition when in the lean combustion mode. A control method includes: determining an electric energy of the electric intake air supply device that is required to maintain achievement of a target air fuel ratio of the lean combustion mode when in a lean combustion operation region; and causing a shift from the lean combustion mode into a stoichiometric combustion mode when the on-vehicle battery is in an insufficient state of charge with respect to the electric energy.