Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2001-07-09
2002-12-31
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S704000, C123S443000
Reexamination Certificate
active
06499474
ABSTRACT:
This application is based on Application No. 2001-001638, filed in Japan on Jan. 9, 2001, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air/fuel ratio control apparatus for an internal combustion engine which can detect the air/fuel ratio of a mixture in each cylinder based on the output of an air/fuel ratio sensor installed on a collective portion of an exhaust system at which exhaust gases from a plurality of cylinders are merged with each other, and uniformly control the air/fuel ratios of all the cylinders to a target value, and in particular, it concerns with such an air/fuel ratio control apparatus for an internal combustion engine which is improved in the reliability in control by the use of relatively easy determination processing.
2. Description of the Related Art
In general, with an air/fuel ratio control apparatus for an internal combustion engine (hereinafter simply referred to as an engine), there has been known a method for controlling an air/fuel ratio of an air fuel mixture supplied to each cylinder of the engine in the following manner. That is, an air/fuel ratio sensor is installed on a collective portion of an exhaust system of the engine, and the control apparatus operates to take in an output (i.e., air/fuel ratio signal) of the air/fuel ratio sensor in synchronization with the timing at which exhaust gases from respective cylinders of the engine pass through the exhaust system collective portion, and correct the amounts of fuel to be injected into the respective cylinders in response to the air/fuel ratio signal from the air/fuel ratio sensor thereby to uniformly control the air/fuel ratios of the air fuel mixture supplied to the respective cylinders.
At this time, it is required to accurately detect the air/fuel ratio of an exhaust gas corresponding to each cylinder, but it is known that in actuality, the exhaust gases from a plurality of cylinders in a state of being mixed with one another pass through the exhaust system collective portion (i.e., air/fuel ratio sensor), so the air/fuel ratio detection information obtained from the air/fuel ratio sensor includes the influence of the air/fuel ratios in the respective cylinders, and hence it is difficult to accurately detect the air/fuel ratio in each cylinder.
In addition, since the extent of the influences of other cylinders on the detected value of the air/fuel ratio of a specific cylinder varies according to the engine operating state (e.g., the number of revolutions per unit time of the engine, the amount of intake air, etc.), it is even more difficult to accurately detect the air/fuel ratio corresponding to the specific cylinder.
Moreover, since the air/fuel ratio sensor has a time lag (i.e., so-called response delay) from the time when an exhaust gas has actually arrived there to the time when the air/fuel ratio of the exhaust gas detected by the sensor appears as a detection value, it is necessary to take such a response delay into consideration and thus it becomes very difficult to detect the air/fuel ratio corresponding to each cylinder in a reliable manner.
Therefore, it is difficult for the conventional apparatus to accurately detect the air/fuel ratio corresponding to a specific cylinder, thus making it impossible to achieve a high degree of air/fuel ratio control accuracy to any satisfactory extent.
To cope with such a problem, apparatuses were proposed in the past in Japanese patent Nos. 2689362 and 2717744, for example.
In the apparatuses described in the above-mentioned patents, there is constructed a mathematical model representing the behaviors of component elements such as the flow of exhaust gases to an exhaust system, an output response delay of an air/fuel ratio sensor, etc., based on which an observer is designed to estimate an air/fuel ratio in each cylinder, whereby the air/fuel ratios in the respective cylinders are made uniform.
In the case of using such a mathematical model, however, the arithmetic operations in a central processing unit (CPU) become complicated, resulting in an increased processing time and an increased software load. Moreover, since the behaviors of respective component elements of the apparatus are expressed by the mathematical expressions, the results of estimation carried out by the use of the mathematical model are liable to various influences such as a change in the operating state of the engine, variations in the manufacture of component elements, etc., and hence it is impossible to obtain a satisfactorily high degree of control accuracy.
On the other hand, it was also proposed that as disclosed in Japanese Patent Publication No. 4-8616 for instance, the output value of an air/fuel ratio sensor and the air/fuel ratios of respective cylinders can be correlated with each other easily by limiting the requirements for detecting the air/fuel ratios to an idling state of the engine alone, thereby achieving uniform control on the air/fuel ratios in the respective cylinders.
However, in the idling state of the engine, the combustion state is unstable so the engine rotation is liable to undergo great fluctuations, as a consequence of which there are a lot of factors deteriorating the accuracy in the detection of the air/fuel ratios, and there is a decreased amount of exhaust gases in that engine operation range, thus further worsening the response of the air/fuel ratio sensor.
Therefore, even if the air/fuel ratio is detected in the idling state, the width or magnitude of variations in the sensor output will become small and hence it is difficult to accurately detect the information on an air/fuel ratio corresponding to each cylinder after all.
FIG. 14
is an explanatory view illustrating a correction target cylinder determining operation performed by a conventional apparatus which adopts a method of detecting air/fuel ratios at respective prescribed crank angles, in which the abscissa represents reference crank angle positions (TDC) corresponding to the respective cylinders (#
1
through #
4
), and the ordinate represents a change in the output value of an air/fuel ratio sensor (air/fuel ratio A/F).
In
FIG. 14
, arrows of broken lines indicate the air/fuel ratio detection timing of the respective cylinders, and the output value (A/F) of the air/fuel ratio sensor is read at the respective prescribed crank angles.
Herein is shown the case where the air/fuel ratio in the cylinder #
3
is shifted or deviated to a rich air/fuel ratio side (hereinafter simply referred to as a rich side) as compared with those in the remaining cylinders.
According to such a method of detecting at the respective prescribed crank angles, there might be a fear that though the cylinder #
3
is to be determined as a cylinder corresponding to a rich side peak phase, the cylinder #
4
is mistakenly determined as a correction target cylinder, for example, in the case where the air/fuel ratio of the cylinder #
4
is shifted or deviated to the rich side more than that of the cylinder #
3
, as indicated by solid line arrows.
In the conventional air/fuel ratio control apparatus for an internal combustion engine as described above, in the case where a variety of behavior factors are taken into a mathematical model, the load on software increases, and the apparatus is subject to influences such as a change in the engine operating state, variations in the manufacture of component parts, etc., which are difficult to represent by means of mathematical expressions, thus making it impossible to achieve sufficient reliability.
Moreover, when the air/fuel ratio detection condition is limited to an idling state of an engine, there arise the following problems: namely, in the idling state in which the combustion state of the engine is unstable and the amount of exhaust gases is limited, the rotational speed of the engine varies greatly, thus deteriorating the detection accuracy, and the variable range of the air/fuel ratio sensor output is small, as a consequence of which it
Hisato Hiromichi
Katashiba Hideaki
Liu Li
Wachi Satoshi
Argenbright Tony M.
Huynh Hai
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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