System for controlling the urea supply to SCR catalysts
First Claim
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1. 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.
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Abstract
A reductant dosing control system, for use in a Selective Catalytic Reduction (SCR) system of a motor vehicle includes an input receiving a NOx feedback signal from an NOx sensor provided to the SCR system. A base dosing module calculates a required quantity of reductant to inject in front of a SCR catalyst of the SCR system based on the NOx feedback signal. The SCR catalyst has ammonia storage properties. An output signals a reductant metering mechanism to periodically or continuously inject excess reductant based on the required quantity of reductant.
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Citations
16 Claims
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1. A reductant dosing control system, for use in an SCR system of a motor vehicle, comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A reductant dosing control method, for use in an SCR system of a motor vehicle, comprising:
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receiving a NOx feedback signal from an NOx sensor provided to said SCR system; calculating a required quantity of 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; and periodically supplying an excess amount of reductant based on the required quantity of reductant; calculating the quantity of reductant on an intermittent basis, including using a base lookup excess urea quantity and a base on time and calculating an off time based on the quantity of reductant; and intermittently injecting reductant according to the base on time, the off time, and the quantity of reductant, including 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. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A selective catalytic reduction system for use in a motor vehicle, comprising:
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a Zeolite based catalyst resident in an exhaust system receptive of NOx exhaust exiting a diesel engine; a supply of reductant; a reductant dosing mechanism adapted to inject reductant into the exhaust system before the catalyst according to a variable reductant dosing setpoint; an NOx feedback sensor supplying a NOx feedback signal indicating an amount of NOx exhaust exiting the diesel engine; and a reductant dosing control system adapted to calculate a required quantity of reductant to inject in front of the Zeolite based SCR catalyst based on the NOx feedback signal, to modify the quantity of reductant based on sensory signals from engine mass airflow sensors of said diesel engine and temperature sensors of the enclosure, and to communicate a reductant set point to said reductant dosing mechanism based on the required quantity of reductant, wherein said reductant dosing control system is adapted to control said reductant dosing mechanism to intermittently inject excess reductant into the exhaust system before the catalyst for periods of time separated by durations of no injection, wherein at least one of the periods of time and the durations are calculated based on the required quantity of reductant, and wherein said reductant dosing control system is adapted to compare the required quantity of reductant to a reductant quantity associated with constant operation of said dosing mechanism at a minimum setpoint. - View Dependent Claims (14, 15, 16)
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Specification