Method of evaluating deteriorated state of catalytic converter for purifying exhaust gas

• US 6,427,438 B1
• Filed: 11/09/2000
• Issued: 08/06/2002
• Est. Priority Date: 11/12/1999
• Status: Expired due to Fees

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Yasui, Yuji, Oshima, Yoshikazu
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): NGUYEN, TU MINH
• Application Number:
  US09/708,707
• Time in Patent Office: 635 Days
• Field of Search: 602/74, 602/76, 602/77, 602/85, 738/613.1, 731/181, 123/674, 701/109, 701/103
• US Class Current: 60/277
• CPC Class Codes: F01N 11/00 Monitoring or diagnostic devices for exhaust-gas treatment apparatus , e.g. for catalytic activity safety, indicating or supervising devices for internal combustion engines F02B77/08; testing of machines G01M13/00
• CPC Class Codes: F01N 2550/02 Catalytic activity of catalytic converters
• CPC Class Codes: F01N 2560/023 for measuring or detecting HC
• CPC Class Codes: F02D 2041/143 the control loop including a non-linear model or compensator
• CPC Class Codes: F02D 41/1401 characterised by the control or regulation method F02D41/1473, F02D41/1477 take precedence
• CPC Class Codes: F02D 41/1441 Plural sensors
• CPC Class Codes: F02D 41/1456 with sensor output signal being linear or quasi-linear with the concentration of oxygen
• CPC Class Codes: F02D 41/146 the characteristics being an NOx content or concentration
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

The characteristics of an output of an exhaust gas sensor with respect to an air-fuel ratio of an engine are expressed according to a quadratic function, and the parameters of the quadratic function are sequentially identified according to a sequential identifying algorithm using data of the output of the exhaust gas sensor and data of an output of an air-fuel sensor which detects the air-fuel ratio of the engine. Deterioration evaluating parameters whose values change as the deterioration of a catalytic converter processes are sequentially determined from the identified values of the parameters of the quadratic function, and the deteriorated state of the catalytic converter is evaluated based on the determined deterioration evaluating parameters.

Claims

1. A method of evaluating a deteriorated state of a catalytic converter which is disposed in an exhaust passage of an internal combustion engine for purifying an exhaust gas flowing through the exhaust passage, using data of the output of an exhaust gas sensor which is disposed downstream of the catalytic converter for detecting the concentration of a particular component of the exhaust gas purified by the catalytic converter while the internal combustion engine is in operation, comprising the steps of:

identifying the values of parameters contained in a nonlinear function for expressing the correlating characteristics of the concentration of the particular component, which is detected by said exhaust gas sensor and has a minimum and a maximum value with respect to an air-fuel ratio of the exhaust gas upstream of said catalytic converter, using data of the air-fuel ratio of the exhaust gas upstream of said catalytic converter and the data of the output of said exhaust gas sensor; and

evaluating the deteriorated state of the catalytic converter based on the identified values of the parameters.

2. A method of evaluating a deteriorated state of a catalytic converter which is disposed in an exhaust passage of an internal combustion engine for purifying an exhaust gas flowing through the exhaust passage, using data of the output of an exhaust gas sensor which is disposed downstream of the catalytic converter for detecting the concentration of a particular component of the exhaust gas purified by the catalytic converter while the internal combustion engine is in operation, comprising the steps of:

identifying the values of parameters contained in a nonlinear function of a predetermined type for expressing the correlating characteristics of the concentration of the particular component detected by said exhaust gas sensor with respect to an air-fuel ratio of the exhaust gas upstream of said catalytic converter, using data of the air-fuel ratio of the exhaust gas upstream of said catalytic converter and the data of the output of said exhaust gas sensor;

evaluating the deteriorated state of the catalytic converter based on the identified values of the parameters; and

wherein said step of identifying the values of parameters comprises the step of identifying the value of at least one of the parameters while limiting the value of said at least one of the parameters to a value satisfying a predetermined condition.

3. A method of evaluating a deteriorated state of a catalytic converter which is disposed in an exhaust passage of an internal combustion engine for purifying an exhaust gas flowing through the exhaust passage, using data of the output of an exhaust gas sensor which is disposed downstream of the catalytic converter for detecting the concentration of a particular component of the exhaust gas purified by the catalytic converter while the internal combustion engine is in operation, comprising the steps of:

identifying the values of parameters contained in a nonlinear function of a predetermined type for expressing the correlating characteristics of the concentration of the particular component detected by said exhaust gas sensor with respect to an air-fuel ratio of the exhaust gas upstream of said catalytic converter, using data of the air-fuel ratio of the exhaust gas upstream of said catalytic converter and the data of the output of said exhaust gas sensor;

evaluating the deteriorated state of the catalytic converter based on the identified values of the parameters;

sequentially identifying the values of the parameters of said nonlinear function according to a sequential identifying algorithm; and

wherein said step of identifying the values of parameters comprises the step of identifying the value of at least one of the parameters while limiting the value of said at least one of the parameters to a value satisfying a predetermined condition.

4. A method according to claim 3, wherein the data of the air-fuel ratio of the exhaust gas upstream of said catalytic converter, which is used to identify the values of parameters contained in the nonlinear function, comprises data representing the difference between the air-fuel ratio of the exhaust gas and a predetermined reference value.

5. A method according to claim 3, wherein said nonlinear function comprises a quadratic function, and said step of identifying the values of parameters comprises the steps of:

regarding a coefficient of a term of maximum degree of said quadratic function as said at least one of the parameters which is to be limited; and

identifying the value of said coefficient while limiting the value of said coefficient in order for the concentration of said particular component represented by the function value of said quadratic function to have a minimum value.

6. A method according to claim 3, wherein an air-fuel ratio sensor is disposed upstream of the catalytic converter for detecting an air-fuel ratio of the exhaust gas upstream of the catalytic converter, and said step of identifying the values of parameters comprises the step of:

using the air-fuel ratio detected by said air-fuel ratio sensor as the air-fuel ratio of the exhaust gas upstream of the catalytic converter.

7. A method according to claim 6, further comprising the steps of:

determining the value of an air-fuel ratio which minimizes the concentration of said particular component represented by a function value of said nonlinear function with the values of the parameters thereof being identified, using the identified values of the parameters of the nonlinear function, and obtaining the determined value of the air-fuel ratio as a target air-fuel ratio of the exhaust gas upstream of the catalytic converter; and

manipulating the air-fuel ratio of an air-fuel mixture combusted by said internal combustion engine according to a feedback control process to converge the air-fuel ratio detected by said air-fuel ratio sensor to said target air-fuel ratio.

8. A method according to claim 3, wherein said step of evaluating the deteriorated state of the catalytic converter comprises the steps of:

determining the value of an evaluating parameter defined, using the parameters of said nonlinear function, as representing a change depending on the progress of deterioration of said catalytic converter, from the identified values of the parameters of said nonlinear function; and

evaluating the deteriorated state of the catalytic converter based on the value of the evaluating parameter.

9. A method according to claim 8, wherein said evaluating parameter comprises an evaluating parameter which changes as a graph of said nonlinear function with the identified values of the parameters is shifted into a leaner air-fuel ratio range as the deterioration of said catalytic converter processes.

10. A method according to claim 9, wherein said evaluating parameter comprises the value of an air-fuel ratio which minimizes the concentration of said particular component represented by a function value of said nonlinear function.

11. A method according to claim 8, wherein said evaluating parameter comprises an evaluating parameter which changes as a graph of said nonlinear function with the identified values of the parameters is shifted in a direction to increase the concentration of said particular component represented by a function value of said nonlinear function as the deterioration of said catalytic converter processes.

12. A method according to claim 11, wherein said evaluating parameter comprises an extremal value of the function value of the nonlinear function which corresponds to a minimum value of the concentration of said particular component represented by the function value of said nonlinear function.

13. A method according to claim 8, wherein said evaluating parameter comprises an evaluating parameter which changes as the gradient of a graph of said nonlinear function increases in an air-fuel ratio range which is leaner or richer than the value of an air-fuel ratio which minimizes the concentration of said particular component represented by a function value of said nonlinear function with the identified values of said parameters, as deterioration of said catalytic converter processes.

14. A method according to claim 13, wherein said evaluating parameter comprises a function value of said nonlinear function at the value of an air-fuel ratio which is changed a predetermined quantity from the value of an air-fuel ratio which minimizes the concentration of said particular component represented by the function value of said nonlinear function.

15. A method according to claim 8, wherein said evaluating parameter comprises a plurality of evaluating parameters, and said step of evaluating the deteriorated state of the catalytic converter comprises the step of:

combining evaluations of the deteriorated state of the catalytic converter based on said plurality of evaluating parameters to evaluate the deteriorated state of the catalytic converter.