Selective catalytic reduction steady state ammonia slip detection with positive perturbation

Patent metadata

Field	Value
Publication number	US-10344654-B2
Application number	US-201715699210-A
Country	US
Kind code	B2
Filing date	Sep 8, 2017
Priority date	Sep 8, 2017
Publication date	Jul 9, 2019
Grant date	Jul 9, 2019

Abstract

Described herein is a method for detecting steady state ammonia slip for a motor vehicle having an internal combustion engine and an emissions control system. The emissions control system includes a selective catalytic reduction (SCR) device, a NOx sensor, and a controller. The controller executes a method for ammonia slip detection that includes determining if the SCR device is at steady state, comparing a NOx measurement from the NOx sensor with a predicted NOx value. If the NOx measurement exceeds the predicted NOx value by a threshold, perturbing a reductant injection, the perturbation having a selected magnitude and a selected duration. The method also includes measuring a NOx value resulting from the perturbation and computing a gradient thereof relative to the measured NOx, and ascertaining if a gradient of the NOx resulting from the perturbation exceeds a threshold and identifying a reductant slip condition if so.

First claim

What is claimed is:

1. An emissions control system for treating exhaust gas in a motor vehicle including an internal combustion engine, the emissions control system comprising:
a selective catalytic reduction (SCR) Device;
a NOx sensor; and
a controller that is configured to perform reductant slip detection by:
determining if the SCR device is in a steady state operating condition with a steady state reductant injection;
comparing a steady state NOx measurement from the NOx sensor with a predicted steady state NOx value; and
in response to a magnitude of the steady state NOx measurement exceeding the predicted steady state NOx value by a first threshold value:
perturbing the reductant injection corresponding to the steady state; the perturbation of the reductant injection having a selected magnitude and a selected duration;
measuring a NOx value resulting from the perturbation of the reductant injection and computing a gradient in the NOx value resulting from the perturbation of the reductant injection relative to the NOx value measured at steady state;
determining if the reductant consumed by the SCR device resultant from the perturbation exceeds a second selected threshold; and
ascertaining if a gradient of the NOx resulting from the perturbing exceeds a third selected threshold and identifying a reductant slip condition if so, otherwise, identifying a poor efficiency operating condition for the internal combustion engine.

2. The emissions control system of claim 1 , further including a temperature sensor and another NOx sensor.

3. The emissions control system of claim 2 , wherein the another NOx sensor is upstream of the SCR device and wherein the determining includes computing a gradient of a temperature of the SCR device and a gradient of the NOx measured by the another NOx sensor.

4. The emissions control system of claim 3 , wherein the determining further includes identifying the SCR devices as at steady state if the gradient of a temperature of the SCR device is less than a third selected threshold value and a gradient of the NOx measured by the another NOx sensor is less than a fourth selected threshold value.

5. The emissions control system of claim 1 , wherein the predicted NOx value is based on a chemical model of the SCR device.

6. The emissions control system of claim 1 , wherein the NOx sensor is located downstream from the SCR device.

7. The emissions control system of claim 1 , wherein at least one of the selected magnitude and selected duration of the perturbing of the reductant injection is based on at least one of a magnitude of the steady state reductant injection, an exhaust flow and a temperature.

8. The emissions control system of claim 1 , further including the controller adapting a reductant dosing rate of the SCR device according to the ascertaining to achieve a desired NH 3 storage.

9. An exhaust system for treating exhaust gas emitted by an internal combustion engine, configured to perform a selective catalytic reduction (SCR) of exhaust gas, the exhaust system comprising:
a controller configured to perform ammonia slip detection by:
determining if an SCR device is in a steady state operating condition with a steady state reductant injection;
comparing a steady state NOx measurement from the NOx sensor with a predicted steady state NOx value; and
in response to a magnitude of the steady state NOx measurement exceeding the predicted steady state NOx value by a first threshold value:
perturbing a reductant injection corresponding to the steady state; the perturbation of the reductant injection having a selected magnitude and a selected duration;
measuring a NOx value resulting from the perturbation of the reductant injection and computing a gradient in the NOx value resulting from the perturbation of the reductant injection relative to the NOx value measured at steady state;
determining if the reductant consumed by the SCR device resulting from the perturbing exceeds a second selected threshold; and
ascertaining if a gradient of the NOx resulting from the perturbing exceeds a third selected threshold and identifying a reductant slip condition if so, otherwise, identifying a poor efficiency operating condition for the internal combustion engine.

10. The exhaust system of claim 9 , further including a temperature sensor and another NOx sensor.

11. The exhaust system of claim 10 , wherein the another NOx sensor is upstream of the SCR device and wherein the determining includes computing a gradient of a temperature of the SCR device and a gradient of the NOx measured by the another NOx sensor.

12. The exhaust system of claim 11 , wherein the determining further includes identifying the SCR devices as at steady state if the gradient of a temperature of the SCR device is less than a third selected threshold value and a gradient of the NOx measured by the another NOx sensor is less than a fourth selected threshold value.

13. The exhaust system of claim 9 , wherein the predicted NOx value is based on a chemical model of the SCR.

14. The exhaust system of claim 9 , wherein at least one of the selected magnitude and selected duration of the perturbation of the reductant injection is based on at least one of a magnitude of the steady state reductant injection, an exhaust flow and a temperature.

15. The exhaust system of claim 9 , further including the controller adapting a reductant dosing rate of the SCR device according to the ascertaining to achieve a desired NH 3 storage.

16. A computer-implemented method for controlling a selective catalytic reduction (SCR) device of an exhaust system of an internal combustion engine, the method comprising:
determining if the SCR device is in a steady state operating condition with a steady state reductant injection;
comparing a steady state NOx measurement from a NOx sensor with a predicted steady state NOx value; and
in response to a magnitude of the steady state NOx measurement exceeding the predicted steady state NOx value by a first threshold value:
perturbing the reductant injection corresponding the steady state; the perturbation of the reductant injection having a selected magnitude and a selected duration;
measuring a NOx value resulting from the perturbation of the reductant injection and computing a gradient in the NOx value resulting from the perturbation of the reductant injection relative to the NOx value measured at steady state;
determining if the reductant consumed by the SCR device resultant from the perturbing exceeds a second selected threshold; and
ascertaining if a gradient of the NOx resultant from the perturbing exceeds a third selected threshold and identifying a reductant slip condition if so, otherwise, identifying a poor efficiency operating condition for the internal combustion engine.

17. The method of claim 16 , wherein the determining includes computing a gradient of a temperature of the SCR device and a gradient of the NOx measured by another NOx sensor, the another NOx sensor being located upstream of the SCR device.

18. The method of claim 16 , wherein the determining further includes identifying the SCR devices as at steady state if the gradient of a temperature of the SCR device is less than a third selected threshold value and a gradient of the NOx measured by the another NOx sensor is less than a fourth selected threshold value.

19. The method of claim 16 , wherein at least one of the selected magnitude and selected duration of the perturbation of the reductant injection is based on at least one of a magnitude of the st

Assignees

• Gm Global Tech Operations Llc

Inventors

• Lauritano Luca
• Guerrero Cruz Luis Daniel

Classifications

• F01N3/0842

  Nitrogen oxides · CPC title

• F01N3/208 Primary

  Control of selective catalytic reduction [SCR], e.g. by adjusting the dosing of reducing agent · CPC title

• C01C1/18

  Nitrates of ammonium · CPC title

• F01N3/2073

  Means for generating a reducing substance from the exhaust gases · CPC title

• C01B21/20

  Nitrogen oxides; Oxyacids of nitrogen; Salts thereof · CPC title