Air-fuel ratio detecting apparatus of engine and method thereof

1. An air-fuel ratio detecting apparatus of an engine for detecting an air-fuel ratio of a combustion mixture in the engine, said apparatus comprising:

an oxygen concentration detector generating a detection signal according to oxygen concentration in an engine exhaust gas, said detection signal being abruptly changed upon said air-fuel ratio reaching a stoichiometric air-fuel ratio;

a temperature detector generating a detection signal according to a temperature of said oxygen concentration detector; and

an air-fuel ratio calculator receiving the detection signal from said oxygen concentration detector and the detection signal from said temperature detector, to calculate the air-fuel ratio based on these detection signals,

wherein said air-fuel ratio calculator converts the detection signal from said oxygen concentration detector to a value having a characteristic linear to the air-fuel ratio in an air-fuel ratio area containing therein the stoichiometric air-fuel ratio, to calculate the air-fuel ratio based on the value after conversion, and

modifies said conversion characteristic of the detection signal in the air-fuel ratio area containing therein said stoichiometric air-fuel ratio according to the temperature of said oxygen concentration detector.

2. An air-fuel ratio detecting apparatus of an engine according to claim 1 ,

wherein said temperature detector detects an internal resistance of an element of said oxygen concentration detector.

3. An air-fuel ratio detecting apparatus of an engine according to claim 1 ,

wherein said air-fuel ratio detector converts the detection signal from said oxygen concentration detector based on a predetermined transformation, and

modifies coefficients of said transformation according to the temperature of said oxygen concentration detector.

4. An air-fuel ratio detecting apparatus of an engine according to claim 1 ,

wherein said oxygen concentration detector generates an electromotive force based on a difference between the oxygen concentration in the engine exhaust gas and oxygen concentration in the atmosphere.

5. An air-fuel ratio detecting apparatus of an engine according to claim 1 ,

wherein said oxygen concentration detector generates an electromotive force based on a difference between the oxygen concentration in the engine exhaust gas and oxygen concentration in the atmosphere, and

said air-fuel ratio calculator is constituted to convert an electromotive force Es of said oxygen concentration detector to a value LD having a characteristic linear to the air-fuel ratio, based on the following equations;

LD=Aα−βb Exp ( A− 0.5)/(0.5+ A ) −2 +50

in which A=Exp (1−Es)/(0.04+Es)

b=constant,

to modify said coefficients α and β according to the temperature of said oxygen concentration detector.

6. An air-fuel ratio detecting apparatus of an engine according to claim 5 ,

wherein said temperature detector detects an internal resistance Ri of an element of said oxygen concentration detector, and

said air-fuel ratio calculator calculates said coefficients α and β provided that;

α=150/a (Ri+150),

β=150/c (0.4Ri+150), and

a, c constants.

7. An air-fuel ratio detecting apparatus of an engine according to claim 1 ,

wherein said oxygen concentration detector generates an electromotive force based on a difference between the oxygen concentration in the engine exhaust gas and oxygen concentration in the atmosphere, and

said temperature detector superimposes a voltage for measuring an internal resistance on said electromotive force, to calculate the internal resistance based on the voltage at this time.

8. An air-fuel ratio detecting apparatus of an engine for detecting an air-fuel ratio of a combustion mixture in the engine, said apparatus comprising:

oxygen concentration detecting means for generating a detection signal according to oxygen concentration in an engine exhaust gas, said detection signal being abruptly changed upon said air-fuel ratio reaching a stoichiometric air-fuel ratio;

temperature detecting means for detecting a temperature of said oxygen concentration detecting means;

converting means for converting the detection signal from said oxygen concentration detecting means to a value having a characteristic linear to the air-fuel ratio in an air-fuel ratio area containing therein the stoichiometric air-fuel ratio;

air-fuel ratio calculating means for calculating the air-fuel ratio based on the value converted by said converting means; and

conversion characteristic modifying means for modifying a conversion characteristic of the detection signal by said converting means in the air-fuel ratio area containing therein said stoichiometric air-fuel ratio according to the temperature of said oxygen concentration detecting means.

9. An air-fuel ratio detecting method of an engine, for detecting an air-fuel ratio of a combustion mixture in the engine using an oxygen concentration detector generating a detection signal according to oxygen concentration in an engine exhaust gas, said detection signal being abruptly changed upon said air-fuel ratio reaching a stoichiometric air-fuel ratio, said method comprising the steps of:

converting the detection signal of said oxygen concentration detector to a value having a characteristic linear to an air-fuel ratio in an air-fuel ratio area containing therein the stoichiometric air-fuel ratio;

calculating the air-fuel ratio based on said converted value;

detecting a temperature of said oxygen concentration detector; and

modifying a conversion characteristic of said detection signal in the air-fuel ratio area containing therein the stoichiometric air-fuel ratio according to the temperature of said oxygen concentration detector.

10. An air-fuel ratio detecting method of an engine according to claim 9 , wherein said step of detecting a temperature comprises detecting an internal resistance of an element of said oxygen concentration detector.

11. An air-fuel ratio detecting method of an engine according to claim 9 ,

wherein said step of converting a detecting signal comprises a step of converting the detection signal from said oxygen concentration detector based on a predetermined transformation, and

said step of modifying a conversion characteristic comprises a step of modifying coefficients of said transformation according to the temperature of said oxygen concentration detector.

12. An air-fuel ratio detecting method of an engine according to claim 9 ,

wherein said oxygen concentration detector generates an electromotive force based on a difference between the oxygen concentration in the engine exhaust gas and oxygen concentration in the atmosphere.

13. An air-fuel ratio detecting method of an engine according to claim 9 ,

wherein said oxygen concentration detector generates an electromotive force Es based on a difference between the oxygen concentration in the engine exhaust gas and oxygen concentration in the atmosphere,

said step of converting a detection signal comprises a step of converting said electromotive force Es to a value LD having a characteristic linear to the air-fuel ratio, based on the following equations;

LD=Aα−βb Exp( A− 0.5)/(0.5 +A ) −2 +50

in which A=Exp (1−Es)/(0.04+Es)

b=constant, and

said step of modifying a conversion characteristic comprises a step of modifying said coefficients α and β according to the temperature of said oxygen concentration detector.

14. An air-fuel ratio detecting method of an engine according to claim 13 ,

wherein said step of detecting a temperature comprises a step of detecting an internal resistance Ri of an element of said oxygen concentration detector, and

said step of modifying a conversion characteristic comprises a step of calculating said coefficients α and β provided that;

α=150/a (Ri+150),

β=150/c (0.4Ri+150), and

a, c=constants.

15. An air-fuel ratio detecting method of an engine according to claim 9 ,

wherein said oxygen concentration detector generates an electromotive force based on a difference between the oxygen concentration in the engine exhaust gas and oxygen concentration in the atmosphere, and

said step of detecting a temperature comprises a step of superimposing a voltage for measuring an internal resistance on said electromotive force, and calculating the internal resistance based on the voltage at this time.

16. An air-fuel ratio detecting apparatus of an engine for detecting an air-fuel ratio of a combustion mixture in the engine, said apparatus comprising:

an oxygen concentration detector generating an electromotive force Es based on a difference between the oxygen concentration in the engine exhaust gas and oxygen concentration in the atmosphere;

a temperature detector generating a detection signal according to a temperature of said oxygen concentration detector; and

an air-fuel ratio calculator receiving the detection signal from said oxygen concentration detector and the detection signal from said temperature detector, to calculate the air-fuel ratio based on these detection signals,

wherein said air-fuel ratio calculator converts the electromotive force Es of said oxygen concentration detector to a value LD having a characteristic linear to the air-fuel ratio, based on the following equations;

LD=Aα−βb Exp( A− 0.5)/(0.5 +A ) −2 +50

where A=Exp (I−Es)/(0.04+Es), and

b=constant,

to modify said coefficients α and β according to the temperature of said oxygen concentration detector, and to calculate the air-fuel ratio based on said value LD.

17. An air-fuel ratio detecting apparatus of an engine according to claim 16 ,

wherein said temperature detector detects an internal resistance Ri of an element of said oxygen concentration detector, and

said air-fuel ratio calculator calculates said coefficients α and β such that;

α=150/a (Ri+150),

β=150/c (0.4Ri+150), and

a, c=constants.

18. An air-fuel ratio detecting method of an engine, for detecting an air-fuel ratio of a combustion mixture in the engine using an oxygen concentration detector generating an electromotive force Es based on a difference between the oxygen concentration in the engine exhaust gas and oxygen concentration in the atmosphere, said method comprising the steps of:

converting the electromotive force Es of said oxygen concentration detector to a value LD having a characteristic linear to the air-fuel ratio, based on the following equations;

LD=Aα−βb Exp( A− 0.5)/(0.5 +A ) −2 +50

where A=Exp (I−Es)/(0.04+Es), and

b=constant,

detecting a temperature of said oxygen concentration detector;

modifying said coefficients α and β according to the temperature of said oxygen concentration detector; and

calculating the air-fuel ratio based on said value LD.

19. An air-fuel ratio detecting method of an engine according to claim 18 , wherein said step of detecting a temperature comprises a step of detecting an internal resistance Ri of an element of said oxygen concentration detector, and

wherein said step of modifying a conversion characteristic comprises a step of calculating said coefficients α and β such that;

α=150/a (Ri+150),

β=150/c (0.4Ri+150), and

a, c=constants.