Control system for mobile NOx SCR applications

A system for metering an external reductant to a reducing catalyst in an SCR system applied to a vehicle powered by an internal combustion engine comprising:

• a) means for sensing operating conditions of the vehicle and engine to generate, by calculation and/or measurement, an actual NOx signal indicative of the actual quantity of NOx emissions emitted by the engine, an exhaust gas temperature signal indicative of the actual temperature of the exhaust gas and a space velocity signal indicative of the actual space velocity of the exhaust gas;
• b) means for filtering said actual NOx emission signal by an NOx time constant to produce a calculated NOx signal different than said actual NOx signal when said NOx signal is changing;
• c) means for filtering said exhaust gas temperature signal by a catalyst time constant to produce a functional catalyst temperature signal different than said exhaust gas temperature when said space velocity signal is changing;
• d) means for factoring said functional catalyst temperature signal and said space velocity signal to generate an NSR signal indicative of a normalized stoichiometric ratio of reductant to NOx emissions;
• and,
• e) means for metering the reductant to said reducing catalyst as a function of said calculated NOx signal and said NSR signal to produce a metering signal controlling a metering device for the external reductant.

A method for controlling dosage of an external reductant supplied to an SCR system including a reducing catalyst in a mobile application having an IC engine to account for transient NOx emissions produced by the engine, said method comprising the steps of:

• a) determining the actual NOx emissions produced by the engine to generate an NOx actual signal;
• b) filtering the NOx actual signal when the reducing catalyst is within a set temperature change to produce a variable delay in the NOx actual signal;
• and
• c) metering the reductant in real time at the value of the delayed NOx actual signal.