duct and runs under a linear lambda regulation in a forced activation a default value is set around a stoichiometric lambda set value as the anticipatory control for the lambda regulation in this case a shift of the mixture alternately to the lean and the rich is given in the lean shift the three way catalytic converter that has oxygen storage properties is filled with oxygen whereas it is emptied again in the rich shift this filling and emptying process depends on the difference between the default value and the stoichiometric set value in the phases i e on the amplitude of the forced activation as well as the duration of the shift the amount of oxygen by means of which the three way catalytic converter is filled and extracted depends on the amount of air that is fed into the internal combustion engine during combustion the oxygen mass fed into a lean phase takes place according to the following equation mo2 0 23 u00b7 u222b i 0 i tm u2062 1 1 lam u00b7 m u2062 u2062 l u2062 u2062 u2146 t in which case ml represents the air mass and dlam the lambda change i e the amplitude of the forced activation this equation is also designated as the oxygen mass.