Patent ID: 8652410

Claim:
A method for controlling a selective catalytic reduction system, the catalytic reduction system being for an internal combustion engine, which method exploits a predetermined set of trigger events and a predetermined set point for NOx concentration downstream from a catalyst element, the method comprising the steps of: a) waiting for a trigger event, b) at the occurrence of a trigger event, starting a NOx concentration measurement downstream from the catalyst element, c) determining the difference between the measured concentration and the set point, d) in the event of the difference being negative, decreasing the dosing of the reducing agent with an amount dependent on the difference and moving back to the first step, e) in the event of the difference being positive, increasing the dosing of the reducing agent with an amount dependent on the difference, f) waiting a predetermined amount of time for the stabilization of the system, g) starting a new NOx concentration measurement and comparing the NOx concentration to the result of the previous measurement, h) in the event of the measured value being below the previous measured value, maintaining the same dosing of the reducing agent and moving back to the first step, and i) in the event of the measured value being above the previous measured value, decreasing the dosing of the reducing agent with an amount greater than the increase after the previous measurement and moving back to the first step.