Internal combustion engine and method for controlling the internal combustion engine

An internal combustion engine, comprising:

• an exhaust gas recirculation control valve disposed in an exhaust gas recirculation passage through which an exhaust gas discharged from a combustion chamber is recirculated into an intake passage of the engine;
• a catalyst disposed in the exhaust gas recirculation passage, the catalyst being operable to purify recirculated exhaust gas passing through the exhaust gas recirculation passage;
• and
• a throttle valve disposed in the intake passage;
• wherein an amount of soot produced gradually increases and reaches a peak as an amount of the recirculated exhaust gas supplied to the combustion chamber increases, and, when the amount of the recirculated exhaust gas supplied to the combustion chamber further increases, a temperature of fuel and surrounding gas at the time of combustion in the combustion chamber becomes lower than temperatures that permit production of soot, the internal combustion engine being capable of operating in a combustion mode in which the amount of the recirculated exhaust gas supplied to the combustion chamber is larger than that of the recirculated exhaust gas with which the amount of soot produced reaches a peak, and almost no soot is produced;
• the internal combustion engine further comprising:
• a controller that reduces an opening amount of the exhaust gas recirculation control valve and reduces an opening amount of the throttle valve when the air-fuel ratio is shifted to a rich side of the stoichiometric ratio while the engine is operating in the combustion mode in which almost no soot is produced, as compared with when the air-fuel ratio is not shifted to the rich side of the stoichiometric ratio.