Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2002-06-04
2004-08-03
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C701S109000
Reexamination Certificate
active
06769422
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for computing an air-fuel ratio control signal based on an output signal from an oxygen sensor that detects oxygen concentration in exhaust gas, for example, in an engine for a vehicle.
RELATED ART OF THE INVENTION
Heretofore, there has been known an air-fuel ratio control apparatus provided with an oxygen sensor from which output signal is changed in response to oxygen concentration in exhaust gas, for computing an air-fuel ratio control signal based on the oxygen sensor.
In an air-fuel ratio control apparatus disclosed in Japanese Unexamined Patent Publication No. 7-127505, an output signal from the oxygen sensor is converted into data of air-fuel ratio to obtain an actual air-fuel ratio, and an air-fuel ratio control signal is feedback controlled based on a deviation (error amount) between the actual air-fuel ratio and a stoichiometric air-fuel ratio being a target air-fuel ratio.
However, in such an oxygen sensor, while an output is abruptly changed in the vicinity of the stoichiometric air-fuel ratio, in a region apart from the stoichiometric air-fuel ratio, a change in sensor output relative to a change in air-fuel ratio becomes less since a change in oxygen concentration is small. Therefore, conversion accuracy into air-fuel ratio data is largely degraded even in a small variation of sensor output.
Consequently, in a rich or lean region where the air-fuel ratio is largely deviated from the stoichiometric air-fuel ratio, the error amount of air-fuel ratio is misjudged, resulting in a possibility that air-fuel ratio control performance shall be largely degraded.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the above problems, and has an object to provide an apparatus and a method for controlling an air-fuel ratio of engine that can stably converge the air-fuel ratio to a stoichiometric air-fuel ratio by an air-fuel ratio feedback control using an oxygen sensor and also can ensure stability of air-fuel ratio control even if the air-fuel ratio is largely deviated from the stoichiometric air-fuel ratio.
To achieve the above object, the present invention is constructed such that, when an output signal from an oxygen sensor is within a predetermined range including a value equivalent to a stoichiometric air-fuel ratio, the output signal is converted into air-fuel ratio data, to compute an air-fuel ratio control signal based on a deviation between the air-fuel ratio data and a target air-fuel ratio, while when the output signal from the oxygen sensor is outside the predetermined range, it is judged whether an actual air-fuel ratio is richer or leaner than the target air-fuel ratio based on the output signal, to compute the air-fuel ratio control signal based on the judgment result.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.
REFERENCES:
patent: 4917067 (1990-04-01), Yoshida
patent: 4922429 (1990-05-01), Nakajima et al.
patent: 5363831 (1994-11-01), Tomisawa et al.
patent: 5394856 (1995-03-01), Furuya
patent: 5435290 (1995-07-01), Gopp et al.
patent: 5778866 (1998-07-01), Uchikawa
patent: 6481427 (2002-11-01), Javaherian
patent: 198 60 463 (2000-07-01), None
patent: 7-127505 (1995-05-01), None
patent: 11-326266 (1999-11-01), None
Ali Hyder
Argenbright Tony M.
Foley & Lardner LLP
Unisia Jecs Corporation
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