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Abstract

The invention relates to a method for operating an internal combustion engine (1), in particular having compression ignition, comprising at least one SCR catalytic converter (5) in the exhaust gas system (3) and an exhaust gas recirculation valve (8), wherein the exhaust gas recirculation amount and/or the position of the exhaust gas recirculation valve (8) is controlled in accordance with the NOx concentration upstream of the SCR catalytic converter (5) in such a way that a NOx concentration (NOx_I1) measured by at least one first NOx sensor (6) upstream of the SCR catalytic converter (5) corresponds to a specified NOx concentration target value (NOx_s). In order to be able to adhere to legally required NOx emission limits with little complexity regardless of signs of aging, the NOx concentration in the exhaust gas is also measured downstream of the SCR catalytic converter (5) by means of at least one second NOx sensor (7) and is compared with the NOx concentration (NOx_I1) of the first NOx sensor (6) upstream of the SCR catalytic converter (5) and an efficiency value (K_nox) of the SCR catalytic converter (5) for the NOx conversion is determined from a comparison of the measured NOx values (NOx_I1, NOx_I2), wherein the NOx concentration target value (NOx,) upstream of the SCR catalytic converter (5) is modified if the determined efficiency value (K_nox) deviates from a specified target efficiency value (K_noxs).

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First Claim