DIAGNOSTIC METHOD AND CONTROL APPARATUS FOR GAS SENSOR

• US 20080196489A1
• Filed: 02/19/2008
• Published: 08/21/2008
• Est. Priority Date: 02/21/2007
• Status: Active Grant

• Current Assignee: NGK Spark PLUG Company Limited
• Original Assignee: NGK Spark PLUG Company Limited, Suzuki Motor Corporation
• Inventors: Suzuki, Takahiro, Tanaka, Masahiro, Inagaki, Hiroshi, Fukagai, Reina, Hirata, Masaki, Ieda, Norikazu
• Granted Patent: US 7,636,624 B2
• Time in Patent Office: Days
• US Class Current: 73/114.72
• CPC Class Codes: F02D 41/123 the fuel injection being cut-off
• CPC Class Codes: F02D 41/1454 the characteristics being an oxygen content or concentration or the air-fuel ratio
• CPC Class Codes: F02D 41/1495 Detection of abnormalities in the air/fuel ratio feedback system
• CPC Class Codes: G01N 27/4175 Calibrating or checking the analyser

Abstract

A gas sensor diagnostic method (or apparatus) is arranged to periodically obtain sensor output values of a gas sensor such as an oxygen sensor for an internal combustion engine, and to determine local extreme values from the sensor output values obtained during a period of interruption of fuel supply to the engine. Moreover, the local extreme values are compared with a first predetermined threshold level. When the number of the local extreme values reaches a predetermined first number, a diagnosis is performed to determine whether the gas sensor is in an improper condition or not, in accordance with results of the comparison of the local extreme values with the first threshold level.

Claims

1. A gas sensor diagnostic method of diagnosing an improper condition of a gas sensor for producing a gas sensor output representing a concentration of a specified gas component in an exhaust gas mixture of an internal combustion engine, comprising:

a sensor output obtaining step of obtaining sensor output values of the gas sensor output at regular time intervals of a predetermined obtaining period;

an interruption detecting step of detecting a fuel supply interruption to the engine;

an extremum determining step of determining local extreme values each of which is an extremum in a series of sensor output values obtained consecutively by the sensor output obtaining step during a fuel supply interruption period during which the fuel supply interruption is detected by the interruption detecting step;

an extremum comparing step of comparing each of the local extreme values with a first predetermined threshold level; and

a diagnosing step of determining whether the gas sensor is in the improper condition or not, in accordance with results of the comparison of the local extreme values with the first threshold level when a number of the local extreme values obtained from the gas sensor output becomes equal to a predetermined first number.

2. The gas sensor diagnostic method as claimed in claim 1, wherein the local extreme values are determined from sensor output values obtained after the lapse of a predetermined time interval which is longer than the obtaining period, from detection of the fuel supply interruption.

3. The gas sensor diagnostic method as claimed in claim 1, wherein the extremum determining step includes an operation of checking a series of first, second and third sensor output values obtained consecutively by the sensor output obtaining step, and examining the second sensor output value obtained after the first sensor output value and before the third sensor output value, to determine whether the second output value is a local extreme value or not.

4. The gas sensor diagnostic method as claimed in claim 1, wherein the extremum comparing step includes an operation of counting a number of over extreme values each of which is a local extreme value greater than an upper limit set as the first threshold level, and the diagnosing step includes an operation of determining whether the gas sensor is in the improper condition or not, in accordance with the number of the over extreme values.

5. The gas sensor diagnostic method as claimed in claim 1, wherein the extremum comparing step includes an operation of counting a number of under extreme values each of which is a local extreme value smaller than a lower limit set as the first threshold level, and the diagnosing step includes an operation of determining whether the gas sensor is in the improper condition or not, in accordance with the number of the under extreme values.

6. The gas sensor diagnostic method as claimed in claim 1, wherein the diagnosing step includes an operation of determining whether the gas sensor is in the improper condition or not, by comparing, with a second threshold level, at least one sensor output value of the gas sensor output obtained after a number of non-extreme values reaches a second predetermined number, each of the non-extreme values being a sensor output value which is not judged to be a local extreme value.

7. The gas sensor diagnostic method as claimed in claim 1, wherein the diagnosing step includes an operation of determining whether the gas sensor is in the improper condition or not, by comparing, with a third threshold level, an average of sensor output values of the gas sensor output obtained after a number of non-extreme values reaches a second predetermined number, each of the non-extreme values being a sensor output value which is not judged to be a local extreme value.

8. The gas sensor diagnostic method as claimed in claim 1, wherein the diagnosing step includes an operation of determining whether the gas sensor is in the improper condition or not, by comparing, with a fourth threshold level, an average of extreme values when a number of non-extreme values reaches a second predetermined number, each of the non-extreme values being a sensor output value which is not judged to be a local extreme value.

9. A gas sensor control apparatus to diagnose an improper condition of a gas sensor for producing a gas sensor output representing a concentration of a specified gas component in an exhaust gas mixture of an internal combustion engine, comprising:

a sensor output obtaining section to obtain sensor output values of the gas sensor output at regular time intervals of a predetermined obtaining period;

an interruption detecting section to detect a fuel supply interruption to the engine;

an extremum determining section to determine local extreme values each of which is an extremum in a series of sensor output values obtained consecutively by the sensor output obtaining section during a fuel supply interruption period during which the fuel supply interruption is detected by the interruption detecting section;

an extremum comparing section to compare each of the local extreme values with a first predetermined threshold level; and

a diagnosing section to determine whether the gas sensor is in the improper condition or not, in accordance with results of the comparison of the local extreme values with the first threshold level when a number of the local extreme values obtained from the gas sensor output becomes equal to a predetermined first number.

10. The gas sensor control apparatus as claimed in claim 9, wherein the extremum determining section is configured to determine the local extreme values from sensor output values obtained after the lapse of a predetermined time interval which is longer than the obtaining period, from detection of the fuel supply interruption by the interruption detecting section.

11. The gas sensor control apparatus as claimed in claim 9, wherein the extremum determining section is configured to check a series of first, second and third sensor output values obtained consecutively by the sensor output obtaining section, and to examine the second sensor output value obtained after the first sensor output value and before the third sensor output value, to determine whether the second output value is a local extreme value or not.

12. The gas sensor control apparatus as claimed in claim 9, wherein the extremum comparing section is configured to count a number of over extreme values each of which is a local extreme value greater than an upper limit set as the first threshold level, and the diagnosing section is configured to determine whether the gas sensor is in the improper condition or not, in accordance with the number of the over extreme values.

13. The gas sensor control apparatus as claimed in claim 9, wherein the extremum comparing section is configured to count a number of under extreme values each of which is a local extremum value smaller than a lower limit set as the first threshold level, and the diagnosing section is configured to determine whether the gas sensor is in the improper condition or not, in accordance with the number of the under extreme values.

14. The gas sensor control apparatus as claimed in claim 9, wherein the extremum determining section is configured to count a number of non-extreme values each of which is a sensor output value which is not judged to be a local extreme value;

and the diagnosing section is configured to determine whether the gas sensor is in the improper condition or not, by comparing, with a second threshold level, at least one sensor output value of the gas sensor output obtained after the number of non-extreme values reaches a second predetermined number.

15. The gas sensor diagnostic apparatus as claimed in claim 9, wherein the extremum determining section is configured to count a. number of non-extreme values each of which is a sensor output value which is not judged to be a local extreme value;

and the diagnosing section is configured to determine whether the gas sensor is in the improper condition or not, by comparing, with a third threshold level, an average of sensor output values of the gas sensor output obtained after the number of non-extreme values reaches a second predetermined number.

16. The gas sensor diagnostic apparatus as claimed in claim 9, wherein the extremum determining section is configured to count a number of non-extreme values each of which is a sensor output value which is not judged to be a local extreme value;

and the diagnosing section is configured to determine whether the gas sensor is in the improper condition or not, by comparing, with a fourth threshold level, an average of extreme values when the number of non-extreme values reaches a second predetermined number.