Air-fuel ratio feed back type fuel injection control system

Abstract

A fuel injection control system comprising an air-fuel ratio feedback control in combination with an electronically controlled fuel injection system. In this system, the concentration of oxygen contained in the engine exhaust gases is compared with a predetermined value in a comparator whereby whether the fuel injection quantity is to be corrected in a direction to increase it or in a direction to decrease it is determined in accordance with the output of the comparator, and the rate of change of the correction is controlled in accordance with a sum output produced by adding a detected value of engine rpms and a detected value of engine intake state. When the air-fuel control cannot operate properly, for example because of a low exhaust temperature or under deceleration conditions, a holding circuit is connected to the integrater output to maintain the integrated output at a value intermediate the fluctuating range thereof. The system has an excellent follow-up characteristic to respond to rapid changes in the operating conditions of an engine and it is capable of maintaining the air-fuel mixture ratio at a predetermined value.

We claim: 
     
       1. An air-fuel ratio feedback type fuel injection control system comprising a main feedback circuit and a holding means; said main feedback circuit including: an oxygen concentration sensor for detecting the concentration of oxygen contained in the exhaust gases of a vehicle internal combustion engine;   a comparator for comparing the output of said oxygen concentration sensor with a first predetermined value to generate an output;   an adder circuit for adding at least a first detected value representing an intake state in said engine and a second detected value of the number of revolutions of said engine and generating a sum output thereof;   an inverter connected to said adding circuit to generate an inverted output of said sum output;   a switching circuit connected to said comparator, said adder circuit and said inverter and responsive to the output of said comparator for selecting and generating either of said sum output and said inverted output as an output thereof;   an integrating circuit connected to said switching circuit for integrating the output of said switching circuit to generate an integrated output;   an electronically controlled fuel injection means connected to said integrating circuit and said engine and adapted for injecting a fuel amount corresponding to at least one of operating parameters of said engine, whereby fuel amount to be injected is corrected in accordance with the output of said integrating circuit; and   said holding means being connected to said integrating circuit and said fuel injection means, and maintaining said integrated output at a second predetermined value except upper and lower saturation values of said integrated output when the correction of the injection fuel amount by said main feedback circuit is terminated.   
     
     
       2. An air-fuel ratio feedback type fuel injection system according to claim 1, wherein said second predetermined value is set at a substantial midpoint of the fluctuating range of said integrated output. 
     
     
       3. A fuel injection control system including a computing section for computing an optimum amount of fuel to be injected in accordance with parameters concerning operational conditions of an internal combustion engine in a vehicle, and fuel supplying means for injecting the fuel into said internal combustion engine in response to an output of said computing section, said computing section comprising: a. a main feedback circuit including air-fuel ratio detecting means for measuring an air-fuel ratio of gas mixture by detecting at least one component of exhaust gases of an internal combustion engine; integration constant generating means for generating a positive integration constant and a negative integration constant; selecting means connected to said air-fuel ratio detecting means and said integration constant generating means for selecting, in response to the output of said air-fuel ratio detecting means, one of said positive and negative constants in accordance with the output of said air-fuel ratio detecting means; and an integrating circuit connected to said selecting means for integrating said one of said positive and negative constants selected by said selecting means to produce an integrated output, thereby correcting the fuel amount to be injected; and   b. holding means connected to said integrating circuit for maintaining the integrated output of said integrating circuit in said main feedback circuit at a predetermined value intermediate within a fluctuating range of said integrated output when there occurs in said internal combustion engine a condition that the correction function of the fuel amount by said integrating circuit in said main feedback circuit is terminated.   
     
     
       4. A fuel injection control system according to claim 3, wherein said holding means includes condition detecting means for detecting the occurrence of said condition in said internal combustion engine to produce a condition detected output, and an auxiliary feedback circuit connected to said condition detecting means and in response to said condition detected output for feeding said integrated output back to an input terminal of said main feedback circuit to thereby maintain said integrated output at said predetermined value intermediate with the fluctuating range of said integrated output. 
     
     
       5. A fuel injection control system according to claim 4, wherein said condition detecting means detects the occurrence of the condition in that said air-fuel ratio detecting means cannot operate normally. 
     
     
       6. A fuel injection control system according to claim 3, wherein said air-fuel ratio detecting means includes an oxygen concentration sensor for detecting the concentration of oxygen contained in the exhaust gases of said internal combustion engine. 
     
     
       7. A fuel injection control system according to claim 6, wherein said holding means maintains said integrated output delivered by said integrating circuit in said main feedback circuit at said predetermined value when the temperature of the exhaust gases of said engine is below an allowable temperature at which said oxygen concentration sensor begins to operate normally. 
     
     
       8. A fuel injection control system according to claim 7, wherein said holding means includes condition detecting means for detecting the occurrence of a condition that the temperature of the exhaust gases of said engine is below said allowable temperature to produce a condition detected output, and an auxiliary feedback circuit connected to said condition detecting means and in response to said condition detected output for feeding said integrated output back to an input terminal of said main feedback circuit to thereby maintain said integrated output at said second predetermined value intermediate within the fluctuating range of said integrated output. 
     
     
       9. A fuel injection control system according to claim 3, wherein said holding means includes condition detecting means for detecting the occurrence of the condition that the supply of the fuel is cut off during deceleration of the vehicle to produce a condition detected output, and an auxiliary feedback circuit connected to said condition detecting means and in response to said condition detected output for feeding said integrated output back to an input terminal of said main feedback circuit to thereby maintain said integrated output at said predetermined value intermediate within the fluctuating range of said integrated output. 
     
     
       10. A fuel injection control system according to claim 3, wherein said selecting means in said main feedback circuit includes a comparator connected to said air-fuel ratio detecting means for delivering a comparison output when the output of said air-fuel ratio detecting means attains the predetermined air-fuel ratio, an adder circuit for adding at least a first detected value representing an intake state in said engine and a second detected value representing the number of revolutions of said engine and delivering a sum output thereof, and a selection circuit connected to said integration constant generating means for alternatively selecting, in accordance with the comparison output of said comparator, either one of said plus and minus integration constants. .Iadd. 11. An air-fuel ratio feedback type fuel control system comprising a main feedback circuit and a holding means; said main feedback circuit including: an oxygen concentration sensor for detecting the concentration of oxygen contained in the exhaust gases of a vehicle internal combustion engine;   a comparator for comparing the output of said oxygen concentration sensor with a first predetermined value to generate an output;   an adder circuit for adding at least a first detected value representing an intake state in said engine and a second detected value of the number of revolutions of said engine and generating a sum output thereof;   an inverter connected to said adding circuit to generate an inverted output of said sum output;   a switching circuit connected to said comparator, said adder circuit and said inverter and responsive to the output of said comparator for selecting and generating either of said sum output and said inverted output as an output thereof;   an integrating circuit connected to said switching circuit for integrating the output of said switching circuit to generate an integrated output;   an electronically controlled fuel supply means connected to said integrating circuit and said engine and adapted for supplying a fuel amount corresponding to at least one of operating parameters of said engine, whereby fuel amount to be supplied is corrected in accordance with the output of said integrating circuit; and   said holding means being connected to said integrating circuit and said fuel supply means, and maintaining said integrated output at a second predetermined value except upper and lower saturation values of said integrated output when the correction of the fuel amount by said main feedback circuit is terminated. .Iaddend..Iadd. 12. An air-fuel ratio feedback type fuel system according to claim 11, wherein said second predetermined value is set at a substantial midpoint of the fluctuating range of said integrated output. .Iaddend..Iadd. 13. A fuel control system including a computing section for computing an optimum amount of fuel in accordance with parameters concerning operational conditions of an internal combustion engine in a vehicle, and fuel supplying means for supplying the fuel into said internal combustion engine in response to an output of said computing section, said computing section comprising:   a. a main feedback circuit including air-fuel detecting means for measuring an air-fuel ratio of gas mixture by detecting at least one component of exhaust gases of an internal combustion engine; integration constant generating means for generating a positive integration constant and a negative integration constant; selecting means connected to said air-fuel ratio detecting means and said integration constant generating means for selecting, in response to the output of said air-fuel ratio detecting means, one of said positive and negative constants in accordance with the output of said air-fuel ratio detecting means; and an integrating circuit connected to said selecting means for integrating said one of said positive and negative constants selected by said selecting means to produce an integrated output, thereby correcting the fuel amount to be supplied, and   b. holding means connected to said integrating circuit for maintaining the integrated output of said integrating circuit in said main feedback circuit at a predetermined value intermediate within a fluctuating range of said integrated output when there occurs in said internal combustion engine a condition that the correction function of the fuel amount by said integrating circuit in said main feedback circuit is terminated. .Iaddend..Iadd. 14. A fuel control system according to claim 13, wherein said holding means includes condition detecting means for detecting the occurrence of said condition in said internal combustion engine to produce a condition detected output, and an auxiliary feedback circuit connected to said condition detecting means and in response to said condition detected output for feeding said integrated output back to an input terminal of said main feedback circuit to thereby maintain said integrated output at said predetermined value intermediate with the fluctuating range of said integrated output. .Iaddend.  .Iadd. 15. A fuel control system according to claim 14, wherein said condition detecting means detects the occurrence of the condition in that said air-fuel ratio detecting means cannot operate normally. .Iaddend..Iadd. 16. A fuel control system according to claim 13, wherein said air-fuel ratio detecting means includes an oxygen concentration sensor for detecting the concentration of oxygen contained in the exhaust gases of said internal combustion engine. .Iaddend..Iadd. 17. A fuel control system according to claim 16, wherein said holding means maintains said integrated output delivered by said integrating circuit in said main feedback circuit at said predetermined value when the temperature of the exhaust gases of said engine is below an allowable temperature at which said oxygen concentration sensor begins to operate normally. .Iaddend..Iadd. 18. A fuel control system according to claim 17, wherein said holding means includes condition detecting means for detecting the occurrence of a condition that the temperature of the exhaust gases of said engine is below said allowable temperature to produce a condition detected output, and an auxiliary feedback circuit connected to said condition detecting means and in response to said condition detected output for feeding said integrated output back to an input terminal of said main feedback circuit to thereby maintain said integrated output at said second predetermined value intermediate within the fluctuating range of said integrated output. .Iaddend..Iadd. 19. A fuel control system according to claim 13, wherein said holding means includes condition detecting means for detecting the occurrence of the condition that the supply of the fuel is cut off during deceleration of the vehicle to produce a condition detected output, and an auxiliary feedback circuit connected to said condition detecting means and in response to said condition detected output for feeding said integrated output back to an input terminal of said main feedback circuit to thereby maintain said integrated output at said predetermined value intermediate within the fluctuating range of said integrated output. .Iaddend..Iadd. 20. A fuel control system according to claim 13, wherein said selecting means in said main feedback circuit includes a comparator connected to said air-fuel ratio detecting means for delivering a comparison output when the output of said air-fuel ratio detecting means attains the predetermined air-fuel ratio, an adder circuit for adding at least a first detected value representing an intake state in said engine and a second detected value representing the number of revolutions of said engine and delivering a sum output thereof, and a selection circuit connected to said integration constant generating means for alternatively selecting, in accordance with the comparison output of said comparator, either one of said plus and minus integration constants. .Iaddend. .Iadd. 21. In combination with an air-fuel mixture supply controller for controlling the air-to-fuel ratio of mixture which is supplied to an internal combustion engine in accordance with engine operating conditions, a feedback control system comprising:   oxygen sensor means for detecting the amount of oxygen in the exhaust gas produced from said engine,   means including an integrator for generating an integration output which selectively increases and decreases, said integration output being applied to said air-fuel mixture controller adapted to correct the air-to-fuel ratio of the mixture in response to the difference between said integration output and a predetermined constant value,   means connecting said oxygen sensor means to said selective integration generating means for selecting as between said increasing and decreasing integration output according to the detected amount of exhaust gas oxygen to cause correction of said air-to-fuel ratio,   condition detecting means for detecting at least one preselected engine operating condition where the air-to-fuel ratio is not required to be corrected in response to the output of said oxygen sensor; and   hold circuit means connected to be responsive to said condition detecting means for holding the integration output of said integrator at said predetermined constant value during said preselected operating condition, whereby correction of the air-to-fuel ratio is automatically made zero while correction of the air-to-fuel ratio is not required. .Iaddend..Iadd. 22. A feedback control system according to claim 21 wherein said predetermined constant value is set between the upper limit and the lower limit of the integration output of said integrator. .Iaddend.