Internal combustion engine system (1) with: an
internal combustion engine (10); an electric
turbocharger (83) provided on an intake
pipe (11A) connected to the
internal combustion engine (10), wherein the electric
turbocharger (83) is configured to cause intake air to flow in the intake
pipe (11A); an
exhaust gas recirculation (EGR)
pipe (13) which is designed to return a portion of
exhaust gas flowing through an
exhaust pipe (12B) connected to the
internal combustion engine (10) to the intake pipe (11A); an
exhaust gas recirculation (EGR) valve (13A) which is configured to adjust the opening degree of the EGR pipe (13); an exhaust gas purifier (40) provided on the
exhaust pipe (12B) on a downstream side of a connection between the EGR pipe (13) and the
exhaust pipe (12B), wherein the exhaust gas purifier (40) is configured to adsorb specific components contained in the exhaust gas and to allow the adsorbed specific components to undergo an oxidation reaction using
ambient oxygen; and a
control unit (50) which is set up to detect operating states of the internal
combustion engine (10) and to control the electric
turbocharger (83) and the EGR valve (13A); wherein the
control unit (50) is implemented by at least one programmed processor, further configured to: to measure the temperature of the exhaust gas cleaner (40); to detect whether the running internal
combustion engine (10) has stopped; and to implement a deterioration prevention step after it has been detected that the running internal
combustion engine (10) has stopped; wherein: in the deterioration prevention step: the
control unit (50) estimates an
oxygen-free period based on a detected temperature of the exhaust gas purifier (40), which is detected by the control unit (50) after it has been detected that the internal combustion engine (10) has stopped, wherein the
oxygen-free period is a period of time during which the
oxygen surrounding the exhaust gas purifier (40) is insufficient for the oxidation reaction of the specific components; the control unit (50) instructs the EGR valve (13A) to open before the estimated oxygen-free period and instructs the electric turbocharger (83) to be driven to exchange the air surrounding the exhaust gas purifier (40) with
fresh air; and the control unit (50) finishes instructing the electric turbocharger (83) to be driven after the exchange with
fresh air is complete.