Patent ID: 8201394

Claim:
An apparatus for reducing NO x emissions in an engine exhaust gas stream of an engine system, comprising: a NO x reduction target module configured to determine a NO x reduction requirement, the NO x reduction requirement comprising an amount of NO x in the exhaust gas stream to be reduced on a selective catalytic reduction (SCR) catalyst; a tailpipe NO x module configured to determine a sensed amount of NO x exiting the engine system and a predicted amount of NO x exciting the engine system, the predicted amount of NO x exiting the engine system being based at least partially on an analytical model; a signal correction algorithm module configured to determine a corrected amount of NO x exiting the engine system based at least partially on the sensed amount of NO x exiting the engine system and an ammonia correction factor, wherein the ammonia correction factor is adjustable by dithering, and wherein dithering comprises comparing the sensed amount of NO x exiting the engine system with the predicted amount of NO x exiting the engine system adjusting the ammonia correction factor accordingly; a feedback ammonia target module configured to determine a feedback ammonia addition requirement, the feedback ammonia addition requirement comprising an amount of ammonia added to the exhaust gas stream to achieve the NO x reduction requirement, wherein the feedback ammonia addition requirement is based at least partially on the corrected amount of NO x exiting the engine system; and a reductant target module configured to determine a reductant injection requirement, the reductant injection requirement comprising an amount of reductant added to the exhaust gas stream to achieve the feedback ammonia addition requirement.