Air-fuel ratio control system

• US 4,386,592 A
• Filed: 02/04/1981
• Issued: 06/07/1983
• Est. Priority Date: 02/06/1980
• Status: Expired due to Fees

• Current Assignee: FJUI Jukogyo Kabushiki Kaisha, Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd., Fuji Heavy Industries Limited (Subaru Corp.)
• Inventors: Matsui, Fujio, Ohgami, Masaaki
• Primary Examiner(s): Nelli, Raymond A.
• Application Number:
  US06/231,557
• Time in Patent Office: 853 Days
• Field of Search: 123/440, 123/438, 123/434, 123/443, 123/489, 60/276, 60/285
• US Class Current: 123/694
• CPC Class Codes: F02D 41/2458 with an additional dither signal

Abstract

An air-fuel ratio control system for an internal combustion engine having an intake passage, an exhaust passage, air-fuel mixture supply unit, on-off type electro-magnetic valve for correcting the air-fuel ratio of the air-fuel mixture supplied by the air-fuel mixture supply unit, a dither signal generating circuit for producing a periodical dither signal having a waveform, a shift control circuit for shifting the level of the center of the dither signal, a driving circuit for producing a driving output according to the dither signal, and detecting means for detecting the concentration of oxygen in exhaust gases passing through the exhaust passage. The system is provided with a memory circuit unit for memorizing a peak level of output of the detecting circuit and for producing an output according to the memorized peak level, first circuit being applied with outputs of the detector and of the memory circuit for detecting deviation of the dither signal detected by the detector. A decision circuit is responsive to outputs of the first circuit for producing an output representing direction and amount of the deviation of the detected dither signal from the stoichiometric air-fuel ratio, and a second circuit responsive to the decision circuit output for providing dependent thereon a shifting amount for shifting the dither signal via the shift control circuit such that the deviation of the dither signal is corrected to the stoichiometric air-fuel ratio.

Claims

1. In an air-fuel ratio control system for an internal combustion engine having an intake passage and an exhaust passage, air-fuel mixture supply means for supplying the air-fuel mixture to the engine, on-off type electromagnetic valve means for correcting the air-fuel ratio of the air-fuel mixture supplied by said air-fuel mixture supply means, the improvement comprising

dither signal generating circuit means for producing a periodical dither signal having a waveform,

a shift control circuit means for shifting the level of the center of said dither signal,

driving circuit means operatively connected to said shift control circuit means for producing a driving output according to said dither signal and for driving said on-off type electromagnetic valve means,

detecting means for detecting the concentration of oxygen in exhaust gases passing through said exhaust passage,

a memory circuit means for memorizing a peak level of output of said detecting means and for producing an output according to the memorized peak level,

first circuit means being applied with outputs of said detecting means and of said memory circuit means for detecting deviation of the dither signal detected by said detecting means,

decision circuit means responsive to outputs of said first circuit means for producing a decision output representing the direction and amount of deviation of the detected dither signal from a stoichiometric air-fuel ratio,

second circuit means responsive to said decision output of said decision circuit means for controlling said shift control circuit means dependent on said decision output of said circuit means in such a manner that the deviation of said dither signal is corrected to the stoichiometric air-fuel ratio.

2. The system as set forth in claim 1, wherein

said second circuit means is for producing an output signal for deciding direction and amount of the shifting of said dither signal by the shift control circuit means such that the deviation of said dither signal is corrected to the stoichiometric air-fuel ratio.

3. The system as set forth in claim 1, wherein

said first circuit means comprises a plurality of level detecting circuits.

4. The system as set forth in claim 3, wherein

each of said plurality of level detecting circuits constitutes means for detecting deviation of the dither signal detected by said detecting means with respect to a different detecting level with respect to said memorized peak level from the detecting level of the others of said plurality of level detecting circuits and for comparing said detected dither signal with said detecting level, respectively.

5. The system as set forth in claim 4, wherein

said decision circuit means is responsive to various combinations of the outputs of said level detecting circuits for producing said decision output respectively dependent on said various combinations of the outputs of said level detecting circuits representing the direction and amount of deviation of the detected dither signal from the stoichiometric air-fuel ratio.