Exhaust gas recirculation and aftertreatment control

A method of controlling an engine assembly comprising:

• an internal combustion engine having:
• a combustion chamber with a combustion chamber inlet for supplying air to the combustion chamber and a combustion chamber outlet for releasing exhaust gas from the combustion chamber;
• an exhaust channel arrangement configured to receive exhaust from the combustion chamber outlet and to supply exhaust to a first exhaust channel and a second exhaust channel;
• an exhaust aftertreatment apparatus configured to receive exhaust from the first exhaust channel;
• and
• an exhaust gas recirculation circuit configured to receive exhaust gas from the second exhaust channel and to supply exhaust gas to the combustion chamber inlet for supplying recirculated exhaust gas to the combustion chamber, wherein the exhaust gas recirculation circuit comprises an exhaust gas recirculation valve for regulating flow of exhaust through the exhaust gas recirculation circuit;
• wherein the method comprises:
• determining a desired proportion of exhaust gas to be directed to the exhaust gas recirculation circuit;
• determining, based on the proportion of exhaust gas to be directed to the exhaust gas recirculation circuit, a baseline value for an extent to which to open the exhaust gas recirculation valve for a clean aftertreatment apparatus;
• determining an age of the exhaust aftertreatment apparatus;
• determining an inferred aftertreatment flow restriction value based on a pressure drop across the exhaust aftertreatment apparatus and the age of the exhaust aftertreatment apparatus;
• determining a compensation function based on the inferred aftertreatment flow restriction value;
• and
• controlling an extent to which the exhaust gas recirculation valve is open based on the baseline value modified by the compensation function in order to maintain the desired proportion of exhaust gas to be directed to the exhaust gas recirculation circuit.