Air-fuel ratio control system for internal combustion engines

• US 6,003,308 A
• Filed: 10/29/1997
• Issued: 12/21/1999
• Est. Priority Date: 10/29/1996
• 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: Miyatake, Naoko, Watanabe, Katsushi, Tsutsumi, Kojiro, Ukai, Asao
• Primary Examiner(s): ARGENBRIGHT, TONY MICHAEL
• Application Number:
  US08/959,980
• Time in Patent Office: 783 Days
• Field of Search: 60/274, 60/276, 60/277, 60/285
• US Class Current: 60/276
• CPC Class Codes: F01N 11/002 the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust apparatus
• CPC Class Codes: F01N 11/007 the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
• CPC Class Codes: F01N 2550/02 Catalytic activity of catalytic converters
• CPC Class Codes: F01N 2900/0422 measuring the elapsed time
• 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 41/1479 Using a comparator with variable reference
• CPC Class Codes: F02D 41/2458 with an additional dither signal
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An air-fuel ratio control system for an internal combustion engine has an exhaust gas-purifying device arranged in the exhaust system of the engine. An oxygen concentration sensor is arranged either in the exhaust system at a location downstream of the exhaust gas-purifying device or in the exhaust gas-purifying device, and an ECU periodically changes the air-fuel ratio of a mixture supplied to the engine alternately to a rich side and to a lean side with respect to a stoichiometric air-fuel ratio. The purification capacity of the exhaust gas-purifying device is determined based on an output from the oxygen concentration sensor. The repetition period of the periodical changing of the air-fuel ratio is shortened as the determined purification capacity is deteriorated.

Claims

1. In an air-fuel ratio control system for an internal combustion engine having an exhaust system, and exhaust gas-purifying means arranged in said exhaust system, including an oxygen concentration sensor arranged either in said exhaust system at a location downstream of said exhaust gas-purifying means or in said exhaust gas-purifying means, and air-fuel ratio perturbation means for periodically changing an air-fuel ratio of a mixture supplied to said engine alternately to a rich side and to a lean side with respect to a stoichiometric air-fuel ratio,

the improvement comprising:

purification capacity-determining means for determining purification capacity of said exhaust gas-purifying means, based on output from said oxygen concentration sensor; and

repetition period-changing means for shortening a repetition period of said periodical changing of said air-fuel ratio by said air-fuel ratio perturbation means as said purification capacity determined by said purification capacity-determining means is deteriorated.

2. An air-fuel ratio control system as claimed in claim 1, including an air-fuel ratio sensor arranged in said exhaust system at a location upstream of said exhaust gas-purifying means, for outputting a signal proportional to concentration of oxygen present in exhaust gases emitted from said engine, and feedback control means for carrying out feedback control of said air-fuel ratio of said mixture supplied to said engine in response to an output from said air-fuel ratio sensor such that said air-fuel ratio becomes equal to a desired air-fuel ratio, and wherein said air-fuel ratio perturbation means periodically changes said desired air-fuel ratio.

3. An air-fuel ratio control system as claimed in claim 1, wherein said purification capacity-determining means determines said purification capacity of said exhaust gas-purifying means, based on a time period elapsed from a time point said air-fuel ratio is deflected from said rich side to said lean side with respect to said stoichiometric air-fuel ratio, or vise versa, to a time point said output from said oxygen concentration sensor actually changes.

4. An air-fuel ratio control system as claimed in claim 1, wherein said repetition period-changing means prolongs at least one of a rich-side duration over which said air-fuel ratio is continuously deflected to said rich side by said air-fuel ratio perturbation means and a lean-side duration over which said air-fuel ratio is continuously deflected to said lean side by said air-fuel ratio perturbation means when a rich-side duration correction coefficient for correcting said rich-side duration and a lean-side duration correction coefficient for correcting said lean-side duration both exceed a predetermined value, said repetition period-changing means shortening at least one of said rich-side duration and said lean-side duration when said rich-side duration correction coefficient and said lean-side duration correction coefficient are both below said predetermined value.

5. An air-fuel ratio control system as claimed in claim 4, including learning means for calculating a learned value of said rich-side duration correction coefficient and said lean-side duration correction coefficient, said learned value being increased or decreased depending upon a relationship between said rich-side and lean-side duration correction coefficients and a predetermined non-corrective value.

6. An air-fuel ratio control system as claimed in claim 4, wherein said learned value is used as an initial value of said rich-side duration correction coefficient and said lean-side duration correction coefficient.

7. In an air-fuel ratio control system for an internal combustion engine having an exhaust system, and exhaust gas-purifying means arranged in said exhaust system, including an oxygen concentration sensor arranged either in said exhaust system at a location downstream of said exhaust gas-purifying means or in said exhaust gas-purifying means, and air-fuel ratio perturbation means for periodically changing an air-fuel ratio of a mixture supplied to said engine alternately to a rich side and to a lean side with respect to a stoichiometric air-fuel ratio,

the improvement comprising:

purification capacity-determining means for determining purification capacity of said exhaust gas-purifying means, based on an output from said oxygen concentration sensor; and

repetition period-changing means for shortening a repetition period of said periodical changing of said air-fuel ratio by said air-fuel ratio perturbation means as said purification capacity determined by said purification capacity-determining means is deteriorated, wherein said repetition period-changing means prolongs at least one of a rich-side duration over which said air-fuel ratio is continuously deflected to said rich side by said air-fuel ratio perturbation means and a lean-side duration over which said air-fuel ratio is continuously deflected to said lean side by said air-fuel ratio perturbation means when a rich-side duration correction coefficient for correcting said rich-side duration and a lean-side duration correction coefficient for correcting said lean-side duration both exceed a predetermined value, said repetition period-changing means shortening at least one of said rich-side duration and said lean-side duration when said rich-side duration correction coefficient and said lean-side duration correction coefficient are both below said predetermined value.

8. An air-fuel ratio control system as claimed in claim 7, including learning means for calculating a learned value of said rich-side duration correction coefficient and said lean-side duration correction coefficient, said learned value being increased or decreased depending upon a relationship between said rich-side and lean-side duration correction coefficients and a predetermined non-corrective value.

9. An air-fuel ratio control system as claimed in claim 8, wherein said learned value is used as an initial value of said rich-side duration correction coefficient and said lean-side duration correction coefficient.

10. In an air-fuel ratio control system for an internal combustion engine having an exhaust system, and exhaust gas-purifying means arranged in said exhaust system, including an oxygen concentration sensor arranged either in said exhaust system at a location downstream of said exhaust gas-purifying means or in said exhaust gas-purifying means, and air-fuel ratio perturbation means for periodically changing an air-fuel ratio of a mixture supplied to said engine alternately to a rich side and to a lean side with respect to a stoichiometric air-fuel ratio,

the improvement comprising:

purification capacity-determining means for determining purification capacity of said exhaust gas-purifying means, based on an output from said oxygen concentration sensor; and

repetition period-changing means for shortening a repetition period of said periodical changing of said air-fuel ratio by said air-fuel ratio perturbation means based upon a degree of deterioration of said purification capacity which is determined by said purification capacity-determining means.