Self-calibrating NO
A system for calibrating a response to an exhaust-stream NO x level in a motor vehicle is provided. The system comprises a NO x sensor that includes an electrode, a current from the electrode responsive to the exhaust-stream NO x level while a bias voltage is applied to the electrode. The system further comprises a controller configured to interrupt the bias voltage and to adjust a motor-vehicle response to the current based at least partly on an attained voltage of the electrode while the bias voltage is interrupted. Other embodiments provide a method of calibrating a NO x sensor response in terms of gain and offset parameters.
1. A method of calibrating a response to an exhaust-stream NO x level in a motor vehicle, the motor vehicle including a NO x sensor, the method comprising:
interrupting a bias voltage to an electrode of the NO x sensor, a current from the electrode responsive to the exhaust-stream NO x level absent said interrupting; and
adjusting a motor-vehicle response to the current based at least partly on an attained voltage of the electrode during said interrupting.
2. The method of claim 1 , wherein the motor-vehicle response to the current includes reducing a NO x emission in response to the current.
3. The method of claim 1 , wherein the motor-vehicle response to the current includes regenerating an exhaust-aftertreatment device in response to the current.
4. The method of claim 1 , wherein the motor-vehicle response to the current includes reducing an air-to-fuel ratio in a combustion chamber in response to the current.
5. The method of claim 1 , wherein a duration of said interrupting is responsive to the current.
6. The method of claim 5 , wherein the duration increases as the current decreases.
7. The method of claim 1 , further comprising sampling the attained voltage of the electrode repeatedly while the current is interrupted.
8. The method of claim 7 , further comprising fitting a plurality of voltage samples to a model, the plurality of voltage samples furnished by said sampling.
9. The method of claim 7 , further comprising averaging a plurality of voltage samples, the plurality of voltage samples furnished by said sampling.
10. The method of claim 7 , further comprising extrapolating from a plurality of voltage samples, the plurality of voltage samples furnished by said sampling.
11. The method of claim 1 , wherein interrupting the bias voltage comprises opening a switch, the method further comprising restoring the bias voltage by closing the switch.
12. The method of claim 1 further comprising delaying interruption of the bias voltage for a period following a cold start of the motor vehicle.
13. The method of claim 12 , wherein the period is responsive to the current.
14. The method of claim 1 further comprising delaying interruption of the bias voltage for a period following an exhaust-aftertreatment device regeneration in the motor vehicle.
15. The method of claim 1 , wherein said interrupting is enacted repeatedly, according to a schedule.
16. The method of claim 15 , wherein the schedule is responsive to an age of the NO x sensor.
17. The method of claim 15 , wherein the schedule is responsive to a property of the NO x sensor interrogated by a controller.
18. The method of claim 1 further comprising adjusting a gain of the NO x sensor based at least partly on the attained voltage of the electrode during said interrupting.
19. The method of claim 1 , further comprising adjusting an offset of the NO x sensor based at least partly on the attained voltage of the electrode during said interrupting.
20. A method of calibrating a response of a NO x sensor, the method comprising:
interrupting a bias voltage to an electrode of the NO x sensor, a current from the electrode responsive to an exhaust-stream NO x level absent said interrupting; and
adjusting a gain of the NO x sensor based at least partly on an attained voltage of the electrode during said interrupting.
21. The method of claim 20 , further comprising adjusting an offset of the NO x sensor based at least partly on the attained voltage of the electrode during said interrupting.
22. A method for calibrating a response to an exhaust-stream NO x level in a motor vehicle, the motor vehicle including a NO x sensor, the method comprising:
interrupting a bias voltage to an electrode of the NO x sensor, a current from the electrode responsive to the exhaust-stream NO x level absent said interrupting;
adjusting a gain of the NO x sensor based at least partly on an attained voltage of the electrode during said interrupting; and
adjusting a motor-vehicle response to the current based at least partly on the attained voltage of the electrode during said interrupting.