Oxygen sensor element blackening detection

Patent metadata

Field	Value
Publication number	US-10078033-B2
Application number	US-201615002199-A
Country	US
Kind code	B2
Filing date	Jan 20, 2016
Priority date	Jan 20, 2016
Publication date	Sep 18, 2018
Grant date	Sep 18, 2018

Abstract

The present description relates generally to methods and systems for detecting thermal aging and blackening in oxygen sensors. Thermal aging and blackening effects may be differentiated based on a monitored change in impedance in each of a pump cell and a Nernst cell of the oxygen sensor following application of an alternating voltage. In response to detection of thermal aging and/or blackening in the oxygen sensor corrective measures may be taken to ensure accurate oxygen estimation using the sensor.

First claim

The invention claimed is:

1. A method for an engine comprising:
differentiating between thermal aging and blackening of an oxygen sensor element based on a monitored change in impedance of each of a pump cell and a Nernst cell of the oxygen sensor element following application of a voltage, wherein the differentiating includes:
indicating thermal aging in response to the monitored change in impedance of each of the pump cell and the Nernst cell being higher than a threshold value; and
indicating blackening in response to the monitored change in impedance of the pump cell being higher than the threshold value while the monitored change in impedance of the Nernst cell is lower than the threshold value; and
lowering one or more operating parameters of the oxygen sensor element in response to the indication of blackening, wherein the operating parameters include one or more of a reference voltage and a voltage ramp rate, and, in response to the indication of thermal aging, adjusting a compensation factor for oxygen estimation.

2. The method of claim 1 , wherein the voltage is an alternating voltage.

3. The method of claim 1 , wherein differentiating based on a monitored change includes differentiating based on the monitored change following a current application of the voltage relative to the monitored change in impedance of each of the pump cell and the Nernst cell following a previous application of the voltage.

4. The method of claim 1 , wherein the threshold value is one of a constant value and a value based on the impedance following a previous application of the voltage.

5. The method of claim 1 , wherein indicating blackening further includes indicating a level of blackening based on the change in impedance of the pump cell following a previous application of the voltage.

6. A method for an engine comprising:
periodically applying an alternating voltage to each of a pump cell and a Nernst cell of an oxygen sensor;
generating a frequency scan for each of the pump cell and the Nernst cell including a change in impedance upon the application of the alternating voltage;
indicating blackening based on an end point of the frequency scan for each of the pump cell and the Nernst cell.

7. The method of claim 6 , wherein periodically applying the alternating voltage includes applying the alternating voltage once every drive cycle, after a threshold distance of travel, or after a threshold period of time elapsed since a previous application.

8. The method of claim 6 , wherein the frequency scan includes applying the alternating voltage to each of the pump cell and the Nernst cell while keeping a peak voltage constant;
gradually changing a frequency of the alternating voltage;
measuring a pumping current following the application of the alternating voltage; and
calculating an impedance of each of the pump cell and the Nernst cell based on the applied alternating voltage and the measured pumping current.

9. The method of claim 6 , wherein the frequency scan includes a first frequency scan of the pump cell following the application of the alternating voltage and a second frequency scan of the Nernst cell following the application of the alternating voltage.

10. The method of claim 9 , further comprising indicating thermal aging based on an end point impedance of each of the first and second frequency scans being lower than a first and a second threshold impedance, respectively, and indicating blackening based on the end point impedance of the first frequency scan being lower than the first threshold impedance and the end point impedance of the second frequency scan being equal to the second threshold impedance.

11. The method of claim 10 , wherein the first and second threshold impedances are based on the end point of each of the first and second frequency scans following a previous application of the alternating voltage to each of the pump cell and the Nernst cell.

12. The method of claim 11 , further comprising, in response to the indication of thermal aging, adjusting a compensation factor for oxygen estimation, and, in response to the indication of blackening, lowering operating parameters including a reference voltage and a voltage ramp rate of the oxygen sensor.

13. A method for an engine comprising:
differentiating between thermal aging and blackening of an oxygen sensor element based on a monitored change in impedance of each of a pump cell and a Nernst cell of the oxygen sensor element following application of a voltage, wherein the differentiating includes differentiating based on an end point impedance of a frequency scan generated following application of the voltage to the pump cell, and indicating blackening of the oxygen sensor based on the end point impedance being lower than a threshold impedance.

14. The method of claim 13 , wherein the threshold impedance is based on the end point impedance of the frequency scan following a previous application of the voltage to the pump cell.

Assignees

• Ford Global Tech Llc

Inventors

• Mcquillen Michael
• Surnilla Gopichandra
• Soltis Richard E
• Makled Daniel A
• Virga John Joseph

Classifications

• G01N27/4175

  Calibrating or checking the analyser · CPC title

• F02D41/1495 Primary

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• G01M15/104 Primary

  using oxygen or lambda-sensors (testing catalytic converters F01N3/18, F01N11/007) · CPC title

• Y02T10/40

  Engine management systems · CPC title

• F02D41/222 Primary

  relating to the failure of sensors or parameter detection devices · CPC title