Method and system for controlling injection of a reducing agent into an exhaust gas stream

The invention provides a method and system for controlling injection of a reducing agent into an exhaust gas stream. The aftertreatment (AT) system for an exhaust gas stream of an internal combustionengine may comprise a selective catalytic reduction (SCR) device, a particulate filter (PF) device, a reducing agent injection system configured to inject a reducing agent into the exhaust gas streamat a location upstream of the SCR device. A reducing agent injection rate control system may be embedded in an engine control module and may be configured to calculate and output a reducing agent injection rate signal and to apply the injection rate signal to the injection system to control the amount of reducing agent injected into the exhaust gas stream. Calculation of the reducing agent injection rate signal may involve applying a dynamic weighting factor to predetermined minimum and maximum allowable injection rates to obtain a weighted injection rate based upon operating parameters of theexhaust gas stream and/or