Patent ID: 8387368

Claim:
A method for controlling a selective catalytic reduction catalyst in an exhaust line of an internal combustion engine, wherein a supply of a quantity of a gaseous ammonia reductant to the SCR catalyst uses a closed-loop SCR catalyst model coupled to an SCR-out NOx sensor that measures an SCR-out NOx emission value, said closed-loop SCR catalyst model further including a NOx conversion efficiency model, characterized in that said closed-loop SCR catalyst model uses a relationship linking the measured SCR-out NOx emission value to the NOx conversion efficiency and an NH 3 emission value, wherein at least one of an actual NH 3 emission value and an actual SCR-out NOx indicative value are computed based upon differentiation of said relationship, and wherein a drift in the NOx conversion efficiency model and a variation of the NH 3 emission are considered to occur on a longer time scale than a variation of nitrous oxides entering and exiting the SCR catalyst, wherein a modification of the supply of reductant depends on both the actual NH 3 emission value and the actual SCR-out NOx indicative value.