Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2000-05-04
2001-10-09
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S672000
Reexamination Certificate
active
06298839
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 11-129792 filed on May 11, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air-fuel ratio control apparatus and method for an internal combustion engine and, more particularly, to an air-fuel ratio control apparatus for an internal combustion engine that detects the air-fuel ratio of an air-fuel mixture supplied into the engine and performs the feedback control of the concentration of fuel in the mixture on the basis of the detected air-fuel ratio so that the air-fuel ratio becomes equal to the theoretical air-fuel ratio.
2. Description of the Related Art
A technology for controlling the air-fuel ratio of air-fuel mixture to the theoretical air-fuel ratio with high precision has been developed in relation to the emission control of an internal combustion engine using a catalyst. In this technology, a sensor, such as an oxygen sensor or the like, that is able to detect a physical quantity that indicates an air-fuel ratio is disposed in an exhaust passage of the internal combustion engine. The technology detects the air-fuel ratio based on components of exhaust gas by using the sensor, and reflects a result of the detection in an air-fuel ratio feedback adjustment coefficient. Based on the air-fuel ratio feedback adjustment coefficient and the amount of intake air, the technology calculates an amount of fuel to be injected. Thus, the amount of fuel supplied corresponding to the amount of intake air is adjusted by using an air-fuel ratio feedback adjustment coefficient so that air-fuel ratio control can be performed with good precision.
For example, if the air-fuel ratio based on components of exhaust gas is on a fuel-lean side of the theoretical air-fuel ratio, the value of the air-fuel ratio feedback adjustment coefficient becomes greater, and the amount of fuel supplied is increased. Therefore, the fuel concentration is adjusted to a higher side so that the air-fuel ratio is brought closer to the theoretical air-fuel ratio. If the air-fuel ratio based on components of exhaust gas is on a fuel-rich side of the theoretical air-fuel ratio, the value of the air-fuel ratio feedback adjustment coefficient becomes smaller, and the amount of fuel supplied is decreased. Therefore, the fuel concentration is adjusted to a lower side so that the air-fuel ratio is brought closer to the theoretical air-fuel ratio. In this manner, the air-fuel ratio is adjusted to the theoretical air-fuel ratio with good precision.
Another technology, disclosed in, for example, Japanese Patent Application Laid-Open No. HEI 4-203446, performs feedback control of the air-fuel ratio by increasing or decreasing the amount of intake air, instead of the air-fuel ratio feedback control that adjusts the amount of fuel supplied. This technology increases or decreases the amount of intake air based on the value of the air-fuel ratio feedback adjustment coefficient, so as to control the air-fuel ratio to the theoretical air-fuel ratio with good precision.
However, the above-described air-fuel ratio feedback control technologies have a problem of fluctuation of torque produced by the internal combustion engine.
In the air-fuel ratio control technology based on the adjustment of the amount of fuel supplied, a state in which the amount of fuel supplied is increased to shift the concentration of fuel in the air-fuel mixture from a low value to a high value, and a state in which the amount of fuel supplied is decreased to shift the concentration of fuel in the air-fuel mixture from a high value to a low value are alternated. The torque produced by the internal combustion engine varies to a relatively great extent between the two states. That is, the torque is smaller when decreasing the amount of fuel supplied than when increasing the amount of fuel supplied. Therefore, fluctuation of the torque produced by the internal combustion engine is caused by the air-fuel ratio feedback control.
In the air-fuel ratio control technology based on the adjustment of the amount of intake air, a state in which the amount of intake air is increased to shift the concentration of fuel in the air-fuel mixture from a high value to a low value, and a state in which the amount of intake air is decreased to shift the concentration of fuel in the mixture from a low value to a high value are alternated in order to bring the air-fuel ratio closer to the theoretical air-fuel ratio. In this case, too, the torque produced by the internal combustion engine decreases during the state of decreasing the amount of intake air. The torque difference between the two states is relatively great. Therefore, fluctuation of the torque produced by the internal combustion engine is caused by the air-fuel ratio feedback control, as in the technology based on the adjustment of the amount of fuel supplied.
Therefore, in either one of the air-fuel ratio feedback control technologies, the drivability becomes insufficient in some cases.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an air-fuel ratio control apparatus for an internal combustion engine that improves drivability by reducing the torque fluctuation caused by the air-fuel ratio feedback control in the internal combustion engine.
To achieve the above and other objects of the invention, an air-fuel ratio control apparatus for an internal combustion engine in accordance with a first aspect of the invention includes a detector that detects an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine, and a control system that controls a fuel concentration in the air-fuel mixture.
The control system increases the fuel concentration in the air-fuel mixture by a process of increasing an amount of fuel supplied, when the air-fuel ratio detected by the detector indicates a lower fuel concentration than a target air-fuel ratio. The control system decreases the fuel concentration in the air-fuel mixture by a process of increasing the amount of intake air, when the air-fuel ratio detected by the detector indicates a higher fuel concentration than the target air-fuel ratio.
Thus, the fuel concentration in the air-fuel mixture is increased by the fuel-increasing process, and is decreased by the intake air-increasing process. That is, the increasing and the decreasing of the fuel concentration in the air-fuel mixture are both performed by the processes of increasing physical quantities, although the processes use different physical quantities (the quantity of fuel and the quantity of intake air).
Therefore, the difference between the torque produced during the fuel concentration-increasing control (that is, the air-fuel ratio-decreasing control) and the torque produced during the fuel concentration-decreasing control (that is, the air-fuel ratio-increasing control) becomes smaller. Hence, the torque fluctuation caused by the air-fuel ratio control of the internal combustion engine can be reduced, and the drivability can be improved.
An air-fuel ratio control apparatus for an internal combustion engine in accordance with a second aspect of the invention includes a detector that detects an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine, and a control system that controls a fuel concentration in the air-fuel mixture.
The control system increases the fuel concentration in the air-fuel mixture by a process of decreasing an amount of intake air, when the air-fuel ratio detected by the detector indicates a lower fuel concentration than a target air-fuel ratio. The control system decreases the fuel concentration in the air-fuel mixture by a process of decreasing the amount of fuel supplied, when the air-fuel ratio detected by the detector indicates a higher fuel concentration than the target air-fuel ratio.
Thus, the fuel concentration in the air-fuel mixture is increased by the intake air-decreasing process, and i
Fujita Makoto
Kushi Naoto
Muto Harufumi
Argenbright Tony M.
Oliff & Berridge, P.L.C.
Toyota Jidosha & Kabushiki Kaisha
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