Patent ID: 7178328

Claim:
A reductant dosing control system, for use in an SCR system of a motor vehicle, comprising: an input receiving a NOx feedback signal from an NOx sensor provided to said SCR system; a base dosing module calculating a quantity of required reductant to inject in front of a SCR catalyst of said SCR system based on the NOx feedback signal, wherein the SCR catalyst has ammonia storage properties; an intermittent dosing module calculating the quantity of reductant on an intermittent basis by using a base lookup excess urea quantity and a base on time and calculating an off time based on the required quantity of reductant; and an output signaling a reductant metering mechanism to periodically inject excess reductant based on the required quantity of reductant, including signaling the reductant metering mechanism to intermittently inject reductant according to the base on time, the off time, and the quantity of reductant by turning a bit on and off according to the base on time and the off time and multiplying the bit by the quantity of reductant; wherein a period of injection controlled by the base on time has a predetermined length, while a rate of injection controlled by a set point and a duration of no injection controlled by the off time are variable.