Power plants – Internal combustion engine with treatment or handling of... – Methods
Patent
1991-12-12
1992-10-27
Wolfe, Willis R.
Power plants
Internal combustion engine with treatment or handling of...
Methods
60276, 60285, 123691, F02D 4114
Patent
active
051579200
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of and an apparatus for controlling the air-fuel ratio of an internal combustion engine, and particularly to a method of and an apparatus for detecting the air-fuel ratio of an intake air-fuel mixture to an internal combustion engine of a vehicle according to the concentration of a component contained in the exhaust on the upstream and downstream sides of the exhaust purifying catalytic converter disposed in an exhaust system of the engine, and carrying out air-fuel ratio feedback control for attaining a target air-fuel ratio according to the detected air-fuel ratio.
BACKGROUND ART
A three-way catalytic converter for purifying an exhaust is disposed in the exhaust system of an engine. For catalytic converter to maintain good converting efficiency, it is usual to carry out feedback control by having an intake air-fuel mixture to the engine maintain a theoretical air-fuel ratio.
The air-fuel ratio feedback control employs an oxygen sensor (an air-fuel ratio sensor) for detecting an air-fuel ratio according to the concentration of oxygen contained in the exhaust. To ensure good response from the oxygen sensor, the oxygen sensor is disposed at, for example, a collecting portion of an exhaust manifold in the vicinity of a combustion chamber. The oxygen 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 (a target air-fuel ratio). According to the rich or lean determination, the feedback control adjusts the supply of fuel to the engine.
Since the oxygen sensor is disposed close to the combustion chamber in the exhaust system, the oxygen sensor is exposed to a high-temperature exhaust, which may thermally deteriorate the characteristics of the sensor. When the oxygen sensor is located at the collecting portion of the exhaust manifold, where the exhaust from respective cylinders are not yet sufficiently mixed together, the oxygen sensor hardly detects a mean air-fuel ratio of all cylinders. This may cause a fluctuation in the air-fuel ratio detecting accuracy. Although detective response is secured by placing the oxygen sensor in the vicinity of the combustion chamber, the air-fuel ratio feedback control employing the oxygen sensor alone cannot stabilize an air-fuel ratio control accuracy.
To solve this problem, it has been proposed to arrange another oxygen sensor on the downstream side of the catalytic converter in addition to the one disposed on the upstream side thereof, and carry out the air-fuel ratio feedback control according to values detected by the two oxygen sensors (Japanese Unexamined Patent Publication No. 58-48756).
Although the downstream oxygen sensor has poor response due to an O.sub.2 storage effect of the three-way catalytic converter (causing an output delay in the sensor because excessive oxygen remains when an actual air-fuel ratio is lean with respect to a theoretical air-fuel ratio and residual oxygen remains when the actual air-fuel ratio is rich), it can stably detect an air-fuel ratio at which the CO, HC and NOx converting efficiency of the three-way catalytic converter is best. The downstream oxygen sensor, therefore, can achieve accurate and stabilized detection by compensating for the deterioration of the upstream oxygen sensor.
Values detected by the two oxygen sensors may be independently used to carry out air-fuel ratio feedback control. Alternatively, a control quantity for air-fuel ratio feedback control carried out according to a value detected by the upstream oxygen sensor may be corrected such that an air-fuel ratio detected by the downstream oxygen sensor approaches a target air-fuel ratio. Namely, the upstream oxygen sensor ensures the response of air-fuel ratio control, while the downstream oxygen sensor secures control accuracy of the air-fuel ratio control, thereby precisely carrying out the air-fuel ratio feedback control.
According to th
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patent: 4712373 (1987-12-01), Nagai et al.
patent: 4745741 (1988-05-01), Masui et al.
patent: 4761950 (1988-08-01), Nagai et al.
patent: 4779414 (1988-10-01), Nagai et al.
patent: 4796425 (1989-01-01), Nagai et al.
Japan Electronic Control Systems Co. Ltd.
Wolfe Willis R.
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