Power plants – Internal combustion engine with treatment or handling of... – Methods
Patent
1992-05-01
1993-10-12
Hart, Douglas
Power plants
Internal combustion engine with treatment or handling of...
Methods
60276, 60285, 123674, 123691, F01N 320
Patent
active
052514374
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air/fuel ratio control for an internal combustion engine. More particularly, the invention relates to a method and system for feedback control of an air/fuel ratio with high precision, on the basis of detected values of two air/fuel ratio sensors.
2. Description of the Related Art
A typical air/fuel ratio control system for an internal combustion engine, in the prior art, is disclosed in Japanese Unexamined Patent Publication No. 60-240840.
In brief, the system disclosed in the above-identified publication detects an intake air flow rate Q and an engine speed N, calculates a basic fuel supply amount Tp (=K.multidot.Q/N; K is constant) corresponding to an amount of air introduced into an engine cylinder, corrects the basic fuel supply amount Tp with correction factors, such as engine temperature and so forth, further performs a feedback correction using an air/fuel ratio correction coefficient (air/fuel ratio correction amount) set by a signal from an air/fuel ratio sensor (oxygen sensor), which detects air/fuel ratio of a mixture by detecting oxygen concentration in an exhaust gas, and performs a correction based on a battery voltage and so forth to thus set a final fuel supply amount TI.
Then, by outputting a drive pulse signal having a pulse width corresponding to the set fuel supply amount TI, to a fuel injection valve, a predetermined amount of fuel is injected to the engine.
The air/fuel ratio feedback correction based on the signal from the air/fuel ratio sensor is performed so as to control the air/fuel ratio to be near a target air/fuel ratio (stoichiometric air/fuel ratio). This is because an emission control catalyst device (catalytic converter) disposed in an exhaust system for oxidation of CO and HC (hydrocarbon) in the exhaust gas and for reducing NOx is set to operate with an optimal converting efficiency (purification efficiency) at the exhaust gas condition corresponding to combustion of the stoichiometric air/fuel ratio mixture.
The air/fuel ratio sensor is provided to swiftly vary a generated electromotive force (output voltage) in the vicinity of the stoichiometric air/fuel ratio. Therefore, by comparing the output voltage V.sub.0 with a reference voltage (threshold level) corresponding to the stoichiometric air/fuel ratio, a judgement can be made whether the air/fuel ratio of the mixture is rich or lean. For example, when the air/fuel ratio is lean (rich), the relatively large proportional component P of the air/fuel ratio feedback correction coefficient .alpha., which is to be multiplied by the basic fuel supply amount Tp, is increased (decreased) at the initial cycle after switching the air/fuel ratio to lean (rich), and is subsequently increased (decreased) by a given integral component I at every cycle to control the air/fuel ratio to be near the target air/fuel ratio (stoichiometric air/fuel ratio). It should be noted that there are some air/fuel ratio control systems which neglect the proportional component and set the air/fuel ratio feedback correction coefficient .alpha. by an integration control.
In the above-mentioned normal air/fuel ratio feedback control system, the air/fuel ratio sensor is located at the convergent section of the exhaust manifold close to the combustion chamber, to obtain higher response characteristics with a single air/fuel ratio sensor, but since the exhaust gas temperature at this portion is high, it affects the air/fuel ratio sensor to thus cause a variation of the sensor characteristics due to thermal influence or fatigue. Furthermore, the mixture of the exhaust gas from each engine cylinder is insufficient and makes it difficult to detect an average air/fuel ratio over all of the engine cylinders, and thus makes the precision of the detection of the air/fuel ratio low. This necessarily causes a degradation of the precision of the air/fuel ratio control.
In view of the above, there has been provided a system providing an additional air/fuel ratio sensor downstre
REFERENCES:
patent: 4715344 (1987-12-01), Tomisawa
patent: 4796425 (1989-01-01), Nagai et al.
patent: 4800857 (1989-01-01), Tomisawa
patent: 5077970 (1992-01-01), Hamburg
Hart Douglas
Japan Electronic Control Systems Co. Ltd.
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