System for controlling the urea supply to SCR catalysts

• US 7,178,328 B2
• Filed: 12/20/2004
• Issued: 02/20/2007
• Est. Priority Date: 12/20/2004
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Solbrig, Charles E.
• Primary Examiner(s): Denion; Thomas
• Assistant Examiner(s): EDWARDS, LOREN C
• Application Number:
  US11/017,363
• Publication Number:
  US 20060130458A1
• Time in Patent Office: 792 Days
• Field of Search: 602/82, 602/86, 602/87, 602/99, 603/01
• US Class Current: 60/286
• CPC Class Codes: B01D 53/90 Injecting reactants
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 13/008 Mounting or arrangement of exhaust sensors in or on exhaust apparatus sensor arrangements for engine control F02D41/1439
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 13/0097 the purifying devices are arranged in a single housing
• CPC Class Codes: F01N 2340/02 characterised by the distance of the apparatus to the engine, or the distance between two exhaust treating apparatuses
• CPC Class Codes: F01N 2560/026 for measuring or detecting NOx
• CPC Class Codes: F01N 2560/06 the means being a temperature sensor
• CPC Class Codes: F01N 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2610/146 Control thereof, e.g. control of injectors or injection valves
• CPC Class Codes: F01N 2900/08 said parameters being related to the engine
• CPC Class Codes: F01N 3/035 with catalytic reactors , e.g. catalysed diesel particulate filters
• CPC Class Codes: F01N 3/103 Oxidation catalysts for HC and CO only
• CPC Class Codes: F01N 3/106 Auxiliary oxidation catalysts
• CPC Class Codes: F01N 3/206 Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents F01N3/2066 takes precedence
• CPC Class Codes: F01N 3/208 Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

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.

Claims

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.

2. The system of claim 1, further comprising an enable logic module making a determination whether a reductant dosing system of said SCR system is capable of supplying the quantity of reductant under present circumstances, and selectively communicating a set point dosing quantity reflecting the quantity of reductant to the reductant dosing system based on results of the determination.

3. The system of claim 1, wherein said input receives sensory signals from engine mass airflow sensors of said motor vehicle and temperature sensors of said SCR system, the system further comprising a dosing modification module calculating modifiers based on the sensory signals to tailor the quantity of reductant to physical conditions of the engine and catalyst, including temperature and space velocity, and modifying the quantity of reductant for engine and catalyst operating conditions according to the modifiers.

4. The system of claim 1, further comprising an NOx flow rate determination module converting a PPM signal from the NOx sensor to a mass per time NOx flow rate signal using air flow rate, fuel flow rate, and NOx molecular weight, wherein said base dosing module is adapted to calculate a stoichiometric dosing amount of urea for a 32.5% urea/water solution, including calculating the dosing amount from the NOx flow rate using a urea to ammonia decomposition property and molecular weights of Urea and NOx, to correct the stoichiometric dosing amount for additional dilution with water, and to filter the amount to reduce noise, thereby determining a set point dosing quantity.

5. The system of claim 1, further comprising a concentration calculations module estimating NO/NO2 fraction based on oxidation catalyst (DOC) properties.

6. The system of claim 1, further comprising a concentration calculations module calculating NH₃/NOx molar ratios.

7. A reductant dosing control method, for use in an SCR system of a motor vehicle, comprising:

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.

8. The method of claim 7, further comprising:

making a determination whether a reductant dosing system of said SCR system is capable of supplying the quantity of reductant under present circumstances;

selectively communicating a set point dosing quantity reflecting the quantity of reductant to the reductant dosing system based on results of the determination.

9. The method of claim 7, further comprising:

receiving sensory signals from engine mass airflow sensors of said motor vehicle and temperature sensors of said SCR system;

calculating modifiers based on the sensory signals to tailor the quantity of reductant to physical conditions of the engine and catalyst, including temperature and space velocity; and

modifying the quantity of reductant for engine and catalyst operating conditions according to the modifiers.

10. The method of claim 7, further comprising:

converting a PPM signal from the NOx sensor to a mass per time NOx flow rate signal using air flow rate, fuel flow rate, and NOx molecular weight;

calculating a stoichiometric dosing amount of urea for a 32.5% urea/water solution, including calculating the dosing amount from the NOx flow rate using a urea to ammonia decomposition property and molecular weights of Urea and NOx; and

correcting the stoichiometric dosing amount for additional dilution with water, and filtering the amount to reduce noise, thereby determining a set point dosing quantity.

11. The method of claim 7, further comprising estimating NO/NO2 fraction based on oxidation catalyst (DOC) properties.

12. The method of claim 7, further comprising calculating NH₃/NOx molar ratios.

13. A selective catalytic reduction system for use in a motor vehicle, comprising:

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.

14. The system of claim 13, wherein said reductant dosing control system is adapted to estimate NO/NO2 fraction, and to calculate NH₃/NOx molar ratios.

15. The system of claim 14, wherein said reductant dosing control system is adapted to convert a PPM signal from the NOx sensor to a mass per time NOx flow rate signal using air flow rate, fuel flow rate, and NOx molecular weight, calculate a stoichiometric dosing amount of urea for a 32.5% urea/water solution, including calculating the dosing amount from the NOx flow rate using a urea to ammonia decomposition property and molecular weights of Urea and NOx, correct the stoichiometric dosing amount for additional dilution with water, and filter the amount to reduce noise, thereby determining a base set point dosing quantity.

16. The system of claim 13, wherein a base on time is employed for the period, and the set point and the duration are periodically calculated as a function of quantity of reductant.