Air-fuel ratio control system for internal combustion engines

• US 5,732,689 A
• Filed: 02/23/1996
• Issued: 03/31/1998
• Est. Priority Date: 02/24/1995
• Status: Expired due to Term

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Akazaki, Shusuke, Ohno, Hiroshi, Hasegawa, Yusuke, Saiki, Koichi, Takasuka, Yoshitaka, Noda, Yukio
• Primary Examiner(s): Dolinar, Andrew M.
• Application Number:
  US08/606,382
• Time in Patent Office: 767 Days
• Field of Search: 123/673, 123/688, 123/691, 123/694-696
• US Class Current: 123/673
• CPC Class Codes: F02B 2275/18 DOHC [Double overhead camshaft]
• CPC Class Codes: F02D 41/008 Controlling each cylinder individually
• 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 41/2454 Learning of the air-fuel ratio control
• CPC Class Codes: F02D 41/2474 Characteristics of sensors
• CPC Class Codes: F02D 41/2477 characterised by the method used for learning

Abstract

An air-fuel ratio control system for an internal combustion engine has an air-fuel ratio sensor arranged in an exhaust passage of the engine for detecting an air-fuel ratio of exhaust gases emitted from a plurality of cylinders. An output from the air-fuel ratio sensor is sampled whenever the engine rotates through a predetermined crank angle, and sampled values of the output from the air-fuel ratio sensor are sequentially stored. An output characteristic of the air-fuel ratio sensor is detected. One of the sampled values of the output from the air-fuel ratio sensor is selected at least depending on the output characteristic of the air-fuel ratio sensor. An air-fuel ratio of a mixture supplied to each of the cylinders is estimated, separately from other ones of the cylinders, based on selected ones of the sampled values of the output from the air-fuel ratio sensor and a model representative of a behavior of the exhaust passage. The air-fuel ratio of the mixture supplied to the each of the cylinders is controlled in a feedback manner responsive to the estimated air-fuel ratio of the mixture such that the estimated air-fuel ratio of the mixture supplied to the each of the cylinders is converged to a desired air-fuel ratio.

Claims

1. An air-fuel ratio control system for an internal combustion engine having a plurality of cylinders, and an exhaust passage connected to said plurality of cylinders, comprising:

air-fuel ratio-detecting means arranged in said exhaust passage, for detecting an air-fuel ratio of exhaust gases emitted from said cylinders;

sampling means for sampling an output from said air-fuel ratio-detecting means whenever said engine rotates through a predetermined crank angle, and for sequentially storing sampled values of said output from said air-fuel ratio-detecting means;

output characteristic-detecting means for detecting an output characteristic of said air-fuel ratio-detecting means;

selecting means for selecting one of said sampled values of said output from said air-fuel ratio-detecting means at least depending on said output characteristic of said air-fuel ratio-detecting means detected by said output characteristic-detecting means;

cylinder-by-cylinder air-fuel ratio-estimating means for estimating an air-fuel ratio of a mixture supplied to each of said cylinders, separately from other ones of said cylinders, based on selected ones of said sampled values of said output from said air-fuel ratio-detecting means and a model representative of a behavior of said exhaust passage; and

cylinder-by-cylinder feedback control means for controlling said air-fuel ratio of said mixture supplied to said each of said cylinders in a feedback manner responsive to the estimated air-fuel ratio of said mixture such that the estimated air-fuel ratio of said mixture supplied to said each of said cylinders is converged to a desired air-fuel ratio.

2. An air-fuel ratio control system according to claim 1, including operating condition-detecting means for detecting operating conditions of said engine, and wherein said selecting means selects said one of said sampled values depending on said operating conditions of said engine detected by said operating condition-detecting means.

3. An air-fuel ratio control system according to claim 2, wherein said output characteristic-detecting means detects a response characteristic of said air-fuel ratio-detecting means as said output characteristic thereof, said selecting means selecting, as said one of said sampled values, a sampled value which was sampled at a later timing as a degree of deterioration of said response characteristic of said air-fuel ratio-detecting means increases.

4. An air-fuel ratio control system according to claim 2, wherein said selecting means includes timing-determining means for determining a timing for selecting said one of said sampled values sampled and stored, and timing correction amount-calculating means for calculating a timing correction amount for changing said timing depending on said output characteristic of said air-fuel ratio-detecting means.

5. An air-fuel ratio control system according to claim 4, wherein said output characteristic-detecting means detects a response characteristic of said air-fuel ratio-detecting means, said timing correction amount-calculating means calculating said timing correction amount such that said timing is changed to a later timing as a degree of deterioration of said response characteristic of said air-fuel ratio-detecting means increases.

6. An air-fuel ratio control system according to claim 4, including learned value-calculating means for calculating a learned value of said timing correction amount, storing means for storing said learned value of said timing correction amount, and timing-correcting means for correcting said timing by the stored learned value of said timing correction amount.

7. An air-fuel ratio control system according to claim 1, wherein said output characteristic-detecting means detects, as said output characteristic of said air-fuel ratio-detecting means, deterioration of a response characteristic of said air-fuel ratio-detecting means, based on a repetition period of inversion of said air-fuel ratio with respect to a stoichiometric air-fuel ratio detected by said air-fuel ratio-detecting means, which is obtained when said air-fuel ratio detected by said air-fuel ratio-detecting means is feedback-controlled to said stoichiometric air-fuel ratio.

8. An air-fuel ratio control system according to claim 1, wherein said output characteristic-detecting means detects, as said output characteristic of said air-fuel ratio-detecting means, deterioration of a response characteristic of said air-fuel ratio-detecting means, based on a time period elapsed from a time point of interruption of fuel supply to said engine to a time point at which said air-fuel ratio detected by said air-fuel ratio-detecting means becomes equal to a predetermined value.

9. An air-fuel ratio control system according to claim 1, wherein said cylinder-by-cylinder air-fuel ratio-estimating means includes observer means for observing an internal operative state of said exhaust passage by means of said model representative of said behavior of said exhaust passage, and for estimating said air-fuel ratio of said mixture supplied to said each of said cylinders, based on said output from said air-fuel ratio-detecting means.

10. In an air-fuel ratio control system for an internal combustion engine having a plurality of cylinders, and an exhaust passage connected to said plurality of cylinders, said air-fuel ratio control system including air-fuel ratio-detecting means arranged in said exhaust passage, for detecting an air-fuel ratio of exhaust gases emitted from said cylinders, cylinder-by-cylinder air-fuel ratio-estimating means for estimating an air-fuel ratio of a mixture supplied to each of said cylinders, separately from other ones of said cylinders, based on an output from said air-fuel ratio-detecting means and a model representative of a behavior of said exhaust passage, and cylinder-by-cylinder feedback control means for controlling said air-fuel ratio of said mixture supplied to said each of said cylinders in a feedback manner responsive to the estimated air-fuel ratio of said mixture such that the estimated value of said air-fuel ratio of said mixture supplied to said each of said cylinders is converged to a desired air-fuel ratio,

the improvement comprising:

stoichiometric output deterioration-detecting means for detecting stoichiometric output deterioration of said air-fuel ratio-detecting means such that said output from said air-fuel ratio-detecting means, corresponding to a stoichiometric air-fuel ratio, deviates from a proper value by an amount exceeding a predetermined amount; and

inhibiting means for inhibiting operation of said cylinder-by-cylinder feedback control means when said stoichiometric output deterioration of said air-fuel ratio-detecting means is detected by said stoichiometric output deterioration-detecting means.

11. An air-fuel ratio control system according to claim 10, including second air-fuel ratio-detecting means having an output characteristic that an output from said second air-fuel ratio-detecting means sharply changes as said air-fuel ratio of exhaust gases changes across a narrow range including said stoichiometric air-fuel ratio, said stoichiometric output deterioration-detecting means having desired air-fuel ratio-changing means responsive to said output from said second air-fuel ratio-detecting means, for progressively changing said desired air-fuel ratio with respect to said stoichiometric air-fuel ratio, average air-fuel ratio value-calculating means for calculating an average value of values of said air-fuel ratio detected by said first-mentioned air-fuel ratio-detecting means of time points of inversion of said output of said second air-fuel ratio-detecting means caused by said progressive change of said desired air-fuel ratio;

and determining means for determining that said first-mentioned air-fuel ratio-detecting means suffers from said stoichiometric output deterioration when a difference between said average value of said values of said air-fuel ratio detected by said first-mentioned air-fuel ratio-detecting means and said stoichiometric air-fuel ratio exceeds a predetermined value.

12. An air-fuel ratio control system according to claim 10, including second air-fuel ratio-detecting means having an output characteristic that an output from said second air-fuel ratio-detecting means sharply changes as said air-fuel ratio of exhaust gases changes across a narrow range including said stoichiometric air-fuel ratio, said stoichiometric output deterioration-detecting means having determining means for determining that said first-mentioned air-fuel ratio-detecting means suffers from said stoichiometric output deterioration when an average value of a correction amount set based on said output from said second air-fuel ratio-detecting means for correcting said desired air-fuel ratio exceeds a predetermined value.

13. An air-fuel ratio control system according to claim 10, wherein said cylinder-by-cylinder air-fuel ratio-estimating means includes observer means for observing an internal operative state of said exhaust passage by means of said model representative of said behavior of said exhaust passage, and for estimating said air-fuel ratio of said mixture supplied to said each of said cylinders, based on said output from said air-fuel ratio-detecting means.

14. In an air-fuel ratio control system for an internal combustion engine having a plurality of cylinders, and an exhaust passage connected to said plurality of cylinders, said air-fuel ratio control system including air-fuel ratio-detecting means arranged in said exhaust passage and being capable of detecting at least leaner values of an air-fuel ratio of exhaust gases emitted from said cylinders than a stoichiometric air-fuel ratio, cylinder-by-cylinder air-fuel ratio-estimating means for estimating an air-fuel ratio of a mixture supplied to each of said cylinders, separately from other ones of said cylinders, based on an output from said air-fuel ratio-detecting means and a model representative of a behavior of said exhaust passage, and cylinder-by-cylinder feedback control means for controlling said air-fuel ratio of said mixture supplied to said each of said cylinders in a feedback manner responsive to the estimated air-fuel ratio of said mixture such that the estimated value of said air-fuel ratio of said mixture supplied to said each of said cylinders is converged to a desired air-fuel ratio,

the improvement comprising:

lean output deterioration-detecting means for detecting lean output deterioration of said air-fuel ratio-detecting means that said output from said air-fuel ratio-detecting means corresponding to a predetermined value leaner than said stoichiometric air-fuel ratio deviates from a proper value by an amount exceeding a predetermined amount,

said cylinder-by-cylinder feedback control means setting said desired air-fuel ratio to a value equal to or close to said stoichiometric air-fuel ratio when said lean output deterioration of said air-fuel ratio-detecting means is detected by said lean output deterioration-detecting means.

15. An air-fuel ratio control system according to claim 14, wherein said lean output deterioration-detecting means determines that said air-fuel ratio-detecting means suffers form said lean output deterioration when said output from said air-fuel ratio-detecting means continuously falls outside a predetermined range after a predetermined time period has elapsed from a time point of interruption of fuel supply to said engine.

16. An air-fuel ratio control system according to claim 15, including permitting means responsive to interruption of fuel supply to said engine, for permitting said lean output deterioration-detecting means to detect said lean output deterioration of said air-fuel ratio-detecting means when said engine is operating in a lean control region in which said air-fuel ratio of said mixture is controlled to a leaner value than said stoichiometric air-fuel ratio.

17. An air-fuel ratio control system according to claim 14, wherein said cylinder-by-cylinder air-fuel ratio-estimating means includes observer means for observing an internal operative state of said exhaust passage by means of said model representative of said behavior of said exhaust passage, and for estimating said air-fuel ratio of said mixture supplied to said each of said cylinders, based on said output from said air-fuel ratio-detecting means.

18. In an air-fuel ratio control system for an internal combustion engine having a plurality of cylinders, and an exhaust passage connected to said plurality of cylinders, said air-fuel ratio control system including air-fuel ratio-detecting means arranged in said exhaust passage, for detecting an air-fuel ratio of exhaust gases emitted from said cylinders, cylinder-by-cylinder air-fuel ratio-estimating means for estimating an air-fuel ratio of a mixture supplied to said each of said cylinders, separately from other ones of said cylinders, based on an output from said air-fuel ratio-detecting means and a model representative of a behavior of said exhaust passage, and cylinder-by-cylinder feedback control means for controlling said air-fuel ratio of said mixture supplied to said each of said cylinders in a feedback manner by the use of at least one of a proportional control term, an integral control term, and a differential control term, which are calculated based on the estimated air-fuel ratio of said mixture supplied to said each of said cylinders, such that the estimated value of said air-fuel ratio of said mixture supplied to said each of said cylinders is converged to a desired air-fuel ratio,

the improvement comprising:

response deterioration-detecting means for detecting deterioration of a response characteristic of said air-fuel ratio-detecting means,

said cylinder-by-cylinder feedback control means for controlling the air-fuel ratio of said mixture supplied to said each of said cylinders in said feedback manner by changing said at least one of said proportional term, said integral term, and said differential term to a smaller value when said deterioration of said response characteristic of said air-fuel ratio-detecting means is detected by said response deterioration-detecting means.

19. An air-fuel ratio control system according to claim 18, wherein said response deterioration-detecting means detects said deterioration of said response characteristic of said air-fuel ratio-detecting means based on a repetition period of inversion of said air-fuel ratio with respect to a stoichiometric air-fuel ratio detected by said air-fuel ratio-detecting means, which is obtained when said air-fuel ratio detected by said air-fuel ratio-detecting means is feedback-controlled to said stoichiometric air-fuel ratio.

20. An air-fuel ratio control system according to claim 18, wherein said response deterioration-detecting means detects said deterioration of said response characteristic of said air-fuel ratio-detecting means, based on a time period elapsed from a time point of interruption of fuel supply to said engine to a time point at which said air-fuel ratio detected by said air-fuel ratio-detecting means becomes equal to a predetermined value.

21. An air-fuel ratio control system according to claim 18, wherein said cylinder-by-cylinder air-fuel ratio-estimating means includes observer means for observing an internal operative state of said exhaust passage by means of said model representative of said behavior of said exhaust passage, and for estimating said air-fuel ratio of said mixture supplied to said each of said cylinders, based on said output from said air-fuel ratio-detecting means.