Methods and system for exhaust gas recirculation estimation via an exhaust oxygen sensor

Patent metadata

Field	Value
Publication number	US-9920699-B1
Application number	US-201615298016-A
Country	US
Kind code	B1
Filing date	Oct 19, 2016
Priority date	Oct 19, 2016
Publication date	Mar 20, 2018
Grant date	Mar 20, 2018

Abstract

Methods and systems are provided for estimating an amount of exhaust gas recirculation (EGR) from an exhaust passage into an intake passage of an engine system by operating an exhaust oxygen sensor in a variable voltage (VVs) mode. In one example, a method includes during operation of an exhaust oxygen sensor in the VVs mode where a reference voltage of the exhaust oxygen sensor is adjusted from a lower, first voltage to a higher, second voltage, adjusting engine operation based on the EGR amount estimated based on an output of the exhaust oxygen sensor and a learned correction factor based on the second voltage. In this way, the exhaust oxygen sensor may be used to correct for variations arising due to changing fuel composition and ambient humidity and further used to estimate the amount of EGR being recirculated in the system, thereby enhancing engine fueling and EGR control.

First claim

The invention claimed is:

1. A method, comprising:
during operation of an exhaust oxygen sensor in a variable voltage mode where a reference voltage of the exhaust oxygen sensor is adjusted from a lower, first voltage to a higher, second voltage, adjusting engine operation based on an exhaust gas recirculation (EGR) amount estimated based on an output of the exhaust oxygen sensor and a learned correction factor based on the second voltage.

2. The method of claim 1 , wherein the learned correction factor includes an estimated fuel ethanol content and further comprising estimating the fuel ethanol content based on an output of the exhaust oxygen sensor during operation of the exhaust oxygen sensor in the variable voltage mode during a steady-state engine operation condition when EGR is off and not circulating from an exhaust passage to an intake passage.

3. The method of claim 2 , wherein the steady-state engine operation condition includes an engine idle condition.

4. The method of claim 1 , wherein the learned correction factor further includes an ambient humidity.

5. The method of claim 4 , further comprising estimating the ambient humidity based on an output of the exhaust oxygen sensor while operating in the variable voltage mode during an engine non-fueling condition and based on a dry air pumping current output of the exhaust oxygen sensor.

6. The method of claim 5 , further comprising estimating the dry air pumping current output based on an output of the exhaust oxygen sensor while operating the exhaust oxygen sensor in the variable voltage mode during one or more of an engine start, after a number of travel miles, after a duration of engine operation, after a number of engine cycles, and the engine non-fueling condition.

7. The method of claim 5 , wherein the engine non-fueling condition includes a deceleration fuel shut off.

8. The method of claim 1 , wherein the output of the exhaust oxygen sensor which the EGR amount estimate is based on, is obtained while EGR is flowing from an exhaust passage to an intake passage, where the exhaust oxygen sensor is disposed in the exhaust passage.

9. The method of claim 8 , further comprising determining a total water concentration in exhaust based on the output of the exhaust oxygen sensor and determining a water concentration in exhaust due to humidity and a fuel ethanol content based on the learned correction factor and estimating the EGR amount by subtracting the water concentration in exhaust due to humidity and fuel ethanol content from the total water concentration.

10. A method for an engine, comprising:
determining an amount of exhaust gas recirculation (EGR) flowing in the engine based on a first output of an exhaust oxygen sensor during operation in a variable voltage mode, where a reference voltage of the exhaust oxygen sensor is adjusted from a lower, first voltage to a higher, second voltage, with EGR flowing and a second output of the exhaust oxygen sensor during operation in the variable voltage mode without EGR flowing; and
adjusting engine operation based on the determined amount of EGR.

11. The method of claim 10 , further comprising estimating a fuel ethanol content based on the second output of the exhaust oxygen sensor during a steady-state engine operating condition and inferring a first water concentration in engine exhaust gases based on the estimated fuel ethanol content.

12. The method of claim 11 , further comprising estimating ambient humidity based on a third output of the exhaust oxygen sensor while operating in the variable voltage mode during an engine non-fueling condition and based on a dry air pumping current output of the exhaust oxygen sensor, the dry air pumping current estimated during one or more of an engine start, after a number of travel miles, after a duration of engine operation, after a number of engine cycles, and the engine non-fueling condition.

13. The method of claim 12 , further comprising inferring a second water concentration in the exhaust based on the estimated ambient humidity.

14. The method of claim 13 , further comprising determining the amount of EGR flowing in the engine by subtracting each of the first water concentration and the second water concentration from a total water concentration in the exhaust, the total water concentration determined based on the first output of the exhaust oxygen sensor.

15. The method of claim 10 , further comprising, operating the exhaust oxygen sensor at only the first voltage, in a non-variable voltage mode, in response to a request to determine an air-fuel ratio of the engine, and adjusting engine operation based on an estimated air-fuel ratio, the estimated air-fuel ratio determined based on an output of the exhaust oxygen sensor operating in the non-variable voltage mode.

16. A system for an engine, comprising:
an exhaust gas recirculation (EGR) system including an EGR passage coupling an exhaust passage with an intake passage, the EGR passage including an EGR valve;
an exhaust oxygen sensor configured to operate in a variable voltage mode, where a reference voltage of the exhaust oxygen sensor is adjusted from a lower, first voltage to a higher, second voltage, and coupled to the exhaust passage; and
a controller including computer readable instructions for:
operating the exhaust oxygen sensor in the variable voltage mode while the EGR valve is closed to generate a first output;
opening the EGR valve to circulate EGR and operating the exhaust oxygen sensor in the variable voltage mode to generate a second output; and
adjusting engine operation based on an estimated amount of EGR, the estimated amount of EGR determined based on a difference between the second output and the first output.

17. The system of claim 16 , wherein the controller includes further instructions for generating each of the first output and the second output during an engine idle condition.

18. The system of claim 16 , wherein the controller includes further instructions for:
operating the exhaust oxygen sensor in the variable voltage mode during an engine non-fueling condition and generating a third output of the exhaust oxygen sensor; and
estimating ambient humidity based on the third output of the exhaust oxygen sensor and further based on a dry air pumping current output of the exhaust oxygen sensor.

19. The system of claim 18 , wherein the controller includes further instructions for estimating the amount of EGR flowing in the engine based on a difference between the second output and each of the first and third outputs.

20. The system of claim 18 , wherein the controller includes further instructions for estimating the dry air pumping current based on ratio between a first pumping current generated when the exhaust oxygen sensor is operated at the first voltage, and a second pumping current of the exhaust oxygen sensor generated when the exhaust oxygen sensor is operated at the second voltage.

Assignees

• Ford Global Tech Llc

Inventors

• Mcquillen Michael
• Surnilla Gopichandra
• Makled Daniel A
• Soltis Richard E

Classifications

• F02D41/0072 Primary

  Estimating, calculating or determining the EGR rate, amount or flow (sensors in EGR systems F02M26/45) · CPC title

• F02M26/46

  for determining the characteristics of gases, e.g. composition · CPC title

• F02D41/1454 Primary

  the characteristics being an oxygen content or concentration or the air-fuel ratio · CPC title

• F02D2041/1472

  the characteristics being a humidity or water content of the exhaust gases · CPC title

• F01N11/00

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