Control system for internal combustion engine

A control system for an internal combustion engine, the control system comprising:

• an EGR system that has an EGR passage connected at its one end to an exhaust system of the internal combustion engine, and at its other end to an intake system of the internal combustion engine, and that introduces a part of an exhaust gas flowing through the exhaust system into the intake system through the EGR passage as an EGR gas;
• an NOx selective reduction catalyst that is arranged in the exhaust system;
• an ammonia derived compound addition device configured to add an ammonia derived compound, which is a reducing agent, into the exhaust gas, and arranged in the exhaust system at an upstream side of the NOx selective reduction catalyst in such a position as to enable at least a part of the ammonia derived compound thus added to arrive at a connection portion of the EGR passage;
• and
• at least one controller configured to suppress an inflow of the ammonia derived compound added by the ammonia derived compound addition device into the EGR passage, the controller further configured to suppress the inflow of the ammonia derived compound added by the ammonia derived compound addition device into the EGR passage at a time when the EGR gas is introduced into the intake system by way of the EGR passage, by making an amount of addition of the ammonia derived compound by the ammonia derived compound addition device smaller in comparison with a case when the introduction of the EGR gas into the intake system is stopped.