Power plants – Internal combustion engine with treatment or handling of... – Methods
Patent
1991-12-31
1993-03-16
Hart, Douglas
Power plants
Internal combustion engine with treatment or handling of...
Methods
60276, 60285, 123674, 123691, F01N 320
Patent
active
051933390
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of and an apparatus for controlling the air-fuel ratio of an intake air-fuel mixture to an internal combustion engine of a vehicle to a target air-fuel ratio, and particular to a method of and apparatus for precisely controlling the air-fuel ratio according to feedback control carried out according to values detected by two air-fuel ratio sensors disposed on the upstream and downstream sides, respectively, of an exhaust purifying catalytic converter arranged in an exhaust system.
BACKGROUND ART
A three-way catalytic converter is disposed in an exhaust system of an engine to purify an exhaust gas. To provide the catalytic converter with converting efficiency, it is usual to carry out feedback control having the intake air-fuel mixture to the engine maintain a theoretical air-fuel ratio.
The air-fuel ratio feedback control employs an air-fuel ratio sensor (an oxygen sensor) for detecting an air-fuel ratio according to the concentration of oxygen contained in an exhaust gas. To ensure good response from the air-fuel ratio sensor, the sensor is disposed at, for example, a collecting portion of an exhaust manifold in the vicinity of a combustion chamber. The sensor detects the concentration of oxygen contained in the exhaust, and according to the detected concentration, it is determined whether an actual air-fuel ratio is rich or lean with respect to a theoretical air-fuel ratio. According to the rich or lean determination, the feedback control adjusts the supply of a fuel to the engine so that the actual air-fuel ratio will agree with the theoretical air-fuel ratio.
Since the air-fuel ratio sensor is disposed close to the combustion chamber in the exhaust system, the sensor is exposed to high-temperature exhaust, which may thermally deteriorate the characteristics of the sensor. When the oxygen sensor is disposed at the collecting portion of the exhaust manifold, where exhausts from respective cylinders are not sufficiently mixed together yet, the oxygen sensor does not accurately detect a mean air-fuel ratio of all cylinders. Accordingly, the conventional air-fuel ratio feedback control may ensure responsiveness but hardly achieves accurate stabilized air-fuel ratio control.
To solve this problem, it has been proposed to arrange another oxygen sensor on the down stream side of the catalytic converter in addition to the one disposed on the upstream side thereof, and carry out air-fuel ratio feedback control according to values detected by the two oxygen sensors (Japanese Unexamined Patent Publication No. 58-48756).
Although the downstream air-fuel ratio sensor is not advantageous in terms of responsiveness due to its distance from the combustion chamber, it is less affected by heat and toxic components of an exhaust gas on the downstream side of the catalytic converter, and therefore, it can detect a mean air-fuel ratio of all cylinders because it receives a well mixed exhaust. As a result, the downstream air-fuel ratio sensor provides more accurate and stabilized detections compared with those provided by the upstream air-fuel ratio sensor.
Values detected by the two air-fuel ratio sensors are used to set two different air-fuel ratio feedback correction coefficients, which may be combined together and used. Alternatively, a value detected by the downstream air-fuel ratio sensor is used to correct a control quantity (a proportional portion or an integral portion) applied to an air-fuel ratio feedback correction coefficient set by the upstream air-fuel ratio sensor, or correct a comparison voltage used for an output voltage of the upstream air-fuel ratio sensor, or correct a delay time occurring when using a detected result of the upstream air-fuel ratio sensor for actual control. In this way, fluctuations of the output characteristics of the upstream air-fuel ratio sensor are compensated for with the downstream air-fuel ratio sensor, to accurately achieve air-fuel ratio feedback control.
When using the two air-fuel ratio sensors (usually, oxygen sen
REFERENCES:
patent: 4901240 (1990-02-01), Schmidt
patent: 5077970 (1992-01-01), Hamburg
Hart Douglas
Japan Electronic Control Systems Co. Ltd.
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