Method for adapting an amount of reductant for controlling the nitrogen oxide pollution of gases in a motor exhaust line

A process for adapting an amount of reducing agent for a removal of nitrogen oxides from gases in an exhaust line of a heat engine of a motor vehicle, the removal of nitrogen oxides being carried out by a system according to a selective catalytic reduction by injection of the amount of reducing agent into the exhaust line, the amount of reducing agent injected being predetermined by a nominal control pre-established on characteristics of the system and motorization of the motor vehicle by establishing a control model that estimates an efficiency of conversion of the nitrogen oxides by the system, the nominal control being corrected while the motor vehicle is operating by an adaptive control that takes into account an amount of nitrogen oxides measured before and after the system by upstream and downstream nitrogen oxide sensors respectively, the adaptive control including an adaptive correction which is carried out when the amount of nitrogen oxides downstream of the system is outside of a predetermined correction range, the process comprising:

• aligning the amounts of nitrogen oxides measured by the upstream and downstream nitrogen oxide sensors toward a largest amount of nitrogen oxides measured by one of the upstream and downstream nitrogen oxide sensors with a readjusted calibration of the other sensor of the upstream and downstream nitrogen oxide sensors that has measured a lowest amount of nitrogen oxides as a function of the largest amount, the aligning of the nitrogen oxides measured by the upstream and downstream nitrogen oxide sensors taking place when no injection of reducing agent into the exhaust line is effective and with a catalyst of the system emptied of a store of ammonia within the system;
• aligning the reduction of the nitrogen oxides estimated by the control model with the reduction of the nitrogen oxides measured by the upstream and downstream sensors by a difference between amounts of nitrogen oxides upstream and downstream during a substoichiometric injection of reducing agent without creation of the store of ammonia within the catalyst of the system, the aligning the reduction of the nitrogen oxides taking place via a first correction of the amount of reducing agent injected, after the aligning of the nitrogen oxides measured by the upstream and downstream nitrogen oxide sensors;
• and
• aligning an efficiency of retaining nitrogen oxides measured by the control model with an efficiency of retaining nitrogen oxides estimated by the sensors after the aligning of the nitrogen oxides measured by the upstream and downstream nitrogen oxide sensors and after the aligning the reduction of the nitrogen oxides, the aligning the efficiency of the retaining nitrogen oxides taking place via a second correction of the amount of reducing agent injected as the adaptive correction.