Patent ID: 8623305

Claim:
A method for controlling an injection device for feeding an ammonia-releasing reducing agent into an exhaust-gas purification system of an internal combustion engine to reduce nitrogen oxide emissions, the exhaust-gas purification system comprising an SCR catalytic converter with n cells which are arranged in series in an exhaust-gas throughflow direction and in which ammonia is stored, the method comprising: determining a desired degree of ammonia loading at an exhaust-gas inlet temperature T 0 and determining an ammonia partial pressure in an exhaust gas directly upstream of the SCR catalytic converter; determining an actual degree of ammonia loading of the SCR catalytic converter by adding each individual degree of ammonia loading of each cell i of all of the n cells of the SCR catalytic converter, the individual degree of ammonia loading of each cell i determined as a function of a temperature T i of the cell i and of an ammonia outlet partial pressure of a neighboring cell i−1 which is directly adjacent in an upstream direction; determining a difference between the actual degree of ammonia loading and the desired degree of ammonia loading; if the actual degree of ammonia loading is less than the desired degree of ammonia loading, increasing an amount of injected ammonia; and if the actual degree of ammonia loading exceeds the desired degree of ammonia loading, reducing the amount of injected ammonia.