Exhaust gas aftertreatment system and method for exhaust gas aftertreatment in an internal combustion engine

An exhaust gas aftertreatment system for an internal combustion engine comprising:

• an exhaust system in which a three-way catalytic converter that is situated close to the engine and, downstream from the three-way catalytic converter that is situated close to the engine, a second catalytic converter, and a particulate filter are arranged in a direction in which an exhaust gas of the internal combustion engine flows through an exhaust gas channel of the exhaust system, and
• a fuel injector arranged on the exhaust gas channel and configured so as to inject fuel into the exhaust gas channel downstream from the three-way catalytic converter that is situated close to the engine and upstream from a feed point and the second catalytic converter,
• wherein the exhaust system comprises a secondary air system having an air pump and an air valve with which a regulated volume of secondary air can be introduced via the feed point and blown into the exhaust gas channel downstream from the three-way catalytic converter that is situated close to the engine, downstream of the fuel injector, and upstream from the second catalytic converter, and
• wherein three lambda sensors are arranged in the exhaust system, whereby a first lambda sensor is arranged upstream from the three-way catalytic converter that is situated close to the engine, whereby a second lambda sensor is arranged downstream from the three-way catalytic converter that is situated close to the engine and upstream from the fuel injector as well as from the feed point of the secondary air system, and whereby a third lambda sensor is arranged downstream from the fuel injector and downstream from the feed point of the secondary air system and upstream from the second catalytic converter.