Power plants – Internal combustion engine with treatment or handling of... – Methods
Patent
1991-12-12
1992-12-08
Hart, Douglas
Power plants
Internal combustion engine with treatment or handling of...
Methods
60276, 60285, 123688, F01N 220
Patent
active
051687003
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for controlling the air-fuel ratio of an internal combustion engine, and particularly to a method of and an apparatus for precisely carrying out an air-fuel ratio feedback control according to values detected by two air-fuel ratio sensors disposed upstream and downstream of an exhaust purifying catalytic converter, respectively.
BACKGROUND ART
A conventional apparatus for controlling the air-fuel ratio of an internal combustion engine is disclosed in, for example, Japanese Unexamined Patent Publication No. 1-134749.
This disclosure will be roughly explained. An intake air quantity Q to the engine and an engine rotational speed N are detected to calculate a basic fuel supply quantity Tp (=K.Q/N, with K as a constant) for an intake air quantity supplied to a cylinder, the basic fuel supply quantity Tp is corrected according to an engine temperature, etc., and a feedback correction is carried out with an air-fuel ratio feedback correction coefficient (an air-fuel ratio correction quantity). This coefficient is based on a signal provided by an air-fuel ratio sensor (an oxygen sensor) for detecting the air-fuel ratio of an air-fuel mixture according to an oxygen concentration is an exhaust. The corrected quantity is further corrected according to a battery voltage, etc., to finally set a fuel supply quantity Ti.
A driving pulse signal having a pulse width corresponding to the fuel supply quantity Ti is provided to a fuel injection valve at a predetermined timing, to inject a predetermined quantity of fuel to the engine.
The air-fuel ratio feedback correction carried out according to the signal from the air-fuel ratio sensor is used to obtain a target air-fuel ratio (a theoretical air-fuel ratio). This feedback correction is carried out in an exhaust system because the converting efficiency (purifying efficiency) of an exhaust purifying catalytic converter (a three-way catalytic converter) for purifying an exhaust by oxidizing CO and HC (hydrocarbon) and reducing NOx contained in the exhaust is set to effectively function with a combustion based on the theoretical air-fuel ratio.
An electromotive force (an output voltage) of the air-fuel ratio sensor suddenly changes around the theoretical air-fuel ratio, and thus the output voltage V0 of the air-fuel ratio sensor is compared with a reference voltage (a slice level) SL corresponding to the theoretical air-fuel ratio, to determine whether the present air-fuel ratio is rich or lean with respect to the theoretical air-fuel ratio. If the air-fuel ratio is lean (rich), an air-fuel ratio feedback correction coefficient ALPP by which the basic fuel supply quantity Tp is multiplied is increased (decreased) by a large proportional portion P at the first time of a change to the lean (rich) side, and thereafter, is gradually increased (decreased) by a predetermined integral portion I. Accordingly, the fuel supply quantity Ti is increased (decreased) to obtain the target air-fuel ratio (the theoretical air-fuel ratio). The proportional portion may be omitted, and the air-fuel ratio feedback correction coefficient ALPP may be integrally set.
In this conventional air-fuel ratio feedback control apparatus, one air-fuel ratio sensor is arranged at a collecting portion of an exhaust manifold adjacent to a combustion chamber, to improve the responsiveness of the sensor. Since the temperature of an exhaust at this location is high, the properties of the air-fuel ratio sensor are deteriorated by heat. Also at this location, exhausts from respective cylinders are not sufficiently mixed, and thus it is difficult to detect a mean air-fuel ratio of all cylinders. This may lower the accuracy of detecting and controlling the air-fuel ratio.
To solve these problems, it has been proposed to arrange another air-fuel ratio sensor downstream of the exhaust purifying catalytic converter and carry out an air-fuel ratio feedback control according to the two air-fuel ratio sensors (Japanese Unexamined Patent Publication No. 61-2378
REFERENCES:
patent: 4251990 (1981-02-01), Norimatsu et al.
patent: 5117631 (1992-06-01), Moser
Hart Douglas
Japan Electronic Control Systems Co. Ltd.
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