GAIN/AMPLITUDE DIAGNOSTICS OF NOx SENSORS

• US 20120303206A1
• Filed: 05/26/2011
• Published: 11/29/2012
• Est. Priority Date: 05/26/2011
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust)
• Inventors: Rajagopalan, Sai S.V., Wang, Yue-Yun, Feldmann, Scott T.
• Granted Patent: US 8,694,197 B2
• Time in Patent Office: Days
• US Class Current: 701/30.8
• CPC Class Codes: F02D 41/146 the characteristics being an NOx content or concentration
• CPC Class Codes: F02D 41/222 relating to the failure of sensors or parameter detection devices
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A method that includes in-vehicle systems and practices for determining whether a NOx sensor in an exhaust stream is performing properly. The method uses the gain and/or the offset of the NOx sensor to determine its accuracy.

Claims

1. A method of diagnosing vehicle NOx sensor faults, comprising the steps of:

(a) recording the output received from an NOx sensor relative to an amount of fuel consumption over a period of time;

(b) calculating the mean of the NOx sensor output relative to fuel consumption recorded over the period of time;

(c) repeating steps (a) and (b) at least once;

(d) performing a least-squares estimation (LSE) for more than one calculated mean based on an expected NOx sensor output;

(e) generating a NOx sensor gain based on the LSE; and

(f) determining whether the NOx sensor gain is above or below predetermined a threshold.

2. The method of claim 1, wherein step (a) further comprises establishing a data sampling rate, a period of time during which to record, or both.

3. The method of claim 1, further comprising the step of determining if one or more initial conditions have been satisfied.

4. The method of claim 3, further comprising the step of determining if the one or more initial conditions have been satisfied for more than a predetermined amount of time.

5. The method of claim 3, wherein the initial conditions further comprise determining that an exhaust gas recirculating (EGR) valve is closed and that the rate of fuel flow to a vehicle engine is above a predetermined rate.

6. The method of claim 1, wherein step (b) further comprises normalizing the recorded data based on one or more vehicle operation metrics.

7. The method of claim 1, further comprising the step of storing the expected output from a healthy NOx sensor as a lookup table in memory at the vehicle.

8. The method of claim 1, wherein performing the LSE further comprises fitting a linear equation to a plurality of calculated means based on expected output from a healthy NOx sensor.

9. The method of claim 8, wherein the linear equation is used to determine the NOx sensor gain, a NOx sensor offset, or both.

10. The method of claim 8, wherein the slope of the linear equation represents the gain of the NOx sensor.

11. The method of claim 9, wherein the y-intercept of the linear equation represents the NOx sensor offset.

12. A method of diagnosing vehicle NOx sensor faults, comprising the steps of:

(a) determining if one or more predetermined initial conditions exist that relate to vehicle operation;

(b) recording output from a NOx sensor when the initial conditions exist;

(c) calculating the mean of the recorded output;

(d) repeating step (b) and step (c) more than once to generate a plurality of means;

(e) performing a least squares estimate (LSE) on the plurality of means based on expected NOx output data values included in a lookup table;

(f) comparing the output of the LSE with a maximum gain or a minimum gain for a healthy NOx sensor; and

(g) determining if the output of the LSE is greater than or less than the data values included in the lookup table.

13. The method of claim 12, wherein the initial conditions further comprise determining that an exhaust gas recirculating (EGR) valve is closed and that the rate of fuel flow to a vehicle engine is above a predetermined rate.

14. The method of claim 12, wherein performing the LSE further comprises fitting a linear equation to the plurality of calculated means based on expected output from a healthy NOx sensor.

15. The method of claim 14, wherein the linear equation is used to determine the NOx sensor gain, a NOx sensor offset, or both.

16. The method of claim 14, wherein the slope of the linear equation represents the gain of the NOx sensor.

17. The method of claim 15, wherein the y-intercept of the linear equation represents the NOx sensor offset.

18. A method of diagnosing vehicle NOx faults, comprising the steps of:

(a) determining that an exhaust gas recirculating (EGR) valve is closed and that the fuel flow to a vehicle engine is above a predetermined threshold;

(b) recording the output from an NOx sensor over a predetermined amount period of time while the EGR valve is closed and fuel flow is above the predetermined threshold;

(c) calculating the mean value of the recorded output;

(d) performing step (b) and step (c) a plurality of times thereby generating a plurality of mean values;

(e) calculating a least squares estimate (LSE) of the plurality of mean values with respect to expected output from a healthy NOx sensor;

(f) using the LSE to determine if an offset exists; and

(g) monitoring output from the NOx sensor to determine if the output rises above the high-gain threshold or falls below the low gain threshold.

19. The method of claim 18, wherein calculating the LSE further comprises fitting a linear equation to a plurality of calculated mean values based on expected output from a healthy NOx sensor.

20. The method of claim 19, wherein the linear equation is used to determine the NOx sensor gain, an NOx sensor offset, or both.