Systems and methods for running a NOx self-diagnostic test

Patent metadata

Field	Value
Publication number	US-9670817-B2
Application number	US-201514739834-A
Country	US
Kind code	B2
Filing date	Jun 15, 2015
Priority date	Jun 15, 2015
Publication date	Jun 6, 2017
Grant date	Jun 6, 2017

Abstract

Methods and systems are provided for detecting NOx sensor degradation based on results from a NOx sensor self-diagnostic (SD) test. In one example, a method may comprise: determining that a nitrogen oxide (NOx) sensor is degraded if outputs received from the sensor via a CAN bus during a self-diagnostic test are outside a threshold range. Additionally, only outputs received from the sensor during a self-diagnostic (SD) test performed after a first completed SD test after a key-off event, where the outputs are generated under conditions where a temperature at the sensor is less than a threshold, and an oxygen concentration is within a threshold range may be used to determine if the sensor is degraded.

First claim

The invention claimed is:

1. A method comprising:
with an electronic controller communicating with a nitrogen oxide (NOx) sensor, determining that the NOx sensor measuring engine exhaust gas is degraded based on outputs received from the sensor during a self-diagnostic (SD) test performed after a first completed SD test after an ignition off event, only when the outputs are generated under conditions where the controller determines that a temperature at the sensor is less than a threshold, and an oxygen concentration is within a threshold range; and
generating a warning via a vehicle display responsive to the determination that the sensor is degraded.

2. The method recited in claim 1 , wherein the determining that the NOx sensor is degraded is based further on outputs received from the sensor, only if the outputs are generated under conditions where a NOx concentration is less than a threshold.

3. The method recited in claim 1 , wherein the ignition off event comprises terminating a combustion cycle in an engine based on input from a vehicle operator via an input device.

4. The method recited in claim 1 , wherein the outputs received from the NOx sensor are received via a CAN bus from a NOx control module, where the NOx control module is in electrical communication with the NOx sensor.

5. The method recited in claim 1 , wherein a NOx concentration and the oxygen concentration are estimated based on outputs from the NOx sensor during the SD test.

6. The method recited in claim 1 , wherein the temperature at the sensor is based on outputs from a temperature sensor positioned in line with the NOx sensor relative to a flow of exhaust gasses past the NOx sensor.

7. The method recited in claim 1 , further comprising determining that the NOx sensor is degraded in response to the received outputs of the SD test being outside a threshold range.

8. The method recited in claim 6 , where the threshold range is determined based on the positioning of the NOx sensor relative to a selective catalytic reduction (SCR) catalyst.

9. The method recited in claim 1 , wherein the outputs received from the NOx sensor are SD tests results corresponding to the SD test, and where the SD test results are a ratio between one or more pumping currents output by the NOx sensor and stored values.

10. The method recited in claim 1 , further comprising alerting a vehicle driver in response to determining that the NOx sensor is degraded.

11. The method recited in claim 1 , wherein a completed SD test comprises running the NOx sensor in both a first mode and a second mode, the second mode before the first mode, wherein the first mode comprises adjusting the oxygen concentration in a cavity of the NOx sensor to a first level and measuring a concentration of NOx in the cavity, and wherein the second mode comprises adjusting the oxygen concentration in the cavity of the NOx sensor to a second level and not measuring a concentration of NOx in the cavity.

12. A method comprising:
excluding a first completed self-diagnostic (SD) test result of a NOx sensor measuring exhaust gas after an engine ignition off event;
excluding second and subsequent test results from a completed SD test if one or more of an exhaust gas temperature is greater than a threshold, and an oxygen concentration of the exhaust gas is outside a threshold range;
otherwise not excluding second and subsequent test results from a completed SD test;
determining that the sensor is degraded only when the non-excluded test results are different from a reference value by more than a threshold; and
generating a warning via a display responsive to determining that the sensor is degraded.

13. The method of claim 12 , further comprising determining that an SD test is completed based on outputs from a NOx control module via a CAN bus, where the NOx control module is in electrical communication with the NOx sensor.

14. The method of claim 12 , wherein the exhaust gas temperature is a temperature of exhaust gasses flowing past the NOx sensor during the SD test, and where the temperature is estimated based on outputs from a temperature sensor positioned adjacent to the NOx sensor.

15. The method of claim 12 , wherein the oxygen concentration of the exhaust gas is estimated based on outputs from the NOx sensor during the SD test.

16. The method of claim 12 , further comprising applying a correction factor to the test results based on a mean NOx concentration of the exhaust gas, where the mean NOx concentration is calculated based on a NOx concentration of the exhaust gas estimated over a duration, the duration being a portion of the SD test.

17. The method of claim 12 , further comprising supplying power to the NOx sensor from a glow plug control module, after the engine ignition off event.

18. The method of claim 12 , further comprising receiving outputs from the NOx sensor via a NOx control module, where the outputs comprise one or more of a status of an SD test, where the status of the SD test indicates if the SD test is completed, an SD test result, the oxygen concentration, and a NOx concentration.

19. A system comprising:
a first NOx sensor positioned in an engine exhaust system upstream of a selective catalytic reduction (SCR) catalyst;
a second NOx sensor positioned downstream of the SCR;
a first temperature sensor aligned with the first NOx sensor relative to an exhaust gas flow in the exhaust system for measuring a temperature of exhaust gasses flowing past the first NOx sensor;
a second temperature sensor aligned with the second NOx sensor relative to the exhaust gas flow in the exhaust system for measuring a temperature of exhaust gasses flowing past the second NOx sensor; and
a controller in electrical communication with the first and second NOx sensors via a CAN bus, the controller having computer-readable instructions for:
determining that one or more of the first NOx sensor and second NOx sensor is degraded based on outputs from the first NOx and temperature sensors, and the second NOx and temperature sensors, respectively, where the outputs are generated during a self-diagnostic test after a vehicle ignition key-off, and generating a warning via a vehicle display responsive to the determination that the sensor is degraded.

20. The system recited in claim 19 , wherein the controller further includes computer-readable instructions for a test result, test status, and one or more NOx concentrations and oxygen concentrations of exhaust gasses sampled by the NOx sensors to be estimated based on the outputs received from the first and second NOx sensors, and computer-readable instructions for estimating a temperature of exhaust gasses based on outputs received from the temperature sensors.

Assignees

• Ford Global Tech Llc

Inventors

• Yoo In Kwang
• Van Nieuwstadt Michiel J
• Meyer Garth Michael

Classifications

• F01N3/2066 Primary

  Selective catalytic reduction [SCR] · CPC title

• F01N2550/05

  Systems for adding substances into exhaust · CPC title

• F01N2900/08

  said parameters being related to the engine · CPC title

• F01N11/00 Primary

  Monitoring or diagnostic devices for exhaust-gas treatment apparatus · CPC title

• F01N2570/14

  Nitrogen oxides · CPC title