Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2003-11-07
2004-09-21
Kwon, John T. (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S479000, C701S109000, C073S118040
Reexamination Certificate
active
06792928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a degradation determining system and method for an exhaust gas sensor and an engine control unit, which determine degradation of the exhaust gas sensor based on an output from the exhaust gas sensor, the exhaust gas sensor outputting a signal indicative of the amount of a predetermined component contained in exhaust gases emitted from an internal combustion engine into an exhaust passage thereof.
2. Description of the Related Art
Conventionally, a degradation determining system of the aforementioned kind has been disclosed e.g. in the publication of Japanese Patent No. 2978960 (seventh column at page 4 to fifteenth column at page 8, and FIG. 3 and FIGS. 7 to 10). This degradation determining system determines degradation of an air-fuel ratio sensor that outputs a signal indicative of a sensed concentration of oxygen contained in the exhaust gases. The degradation of the air-fuel ratio sensor is determined during feedback control of the air-fuel ratio of a mixture supplied to the engine, which is provided in response to an output from the air-fuel ratio sensor. More specifically, when the output from the air-fuel ratio sensor assumes, for example, a richer value than a threshold value equivalent to a stoichiometric air-fuel ratio, an air-fuel ratio correction coefficient for controlling the air-fuel ratio of the mixture is decremented each time by a predetermined value, whereby the air-fuel ratio of the mixture is progressively changed in the leaning direction. Then, after a time point the output from the air-fuel ratio sensor crosses the above threshold value in the leaning direction, the control of the air-fuel ratio is held at the resulting state until a predetermined time period elapses. Upon the lapse of the predetermined time period, the air-fuel ratio correction coefficient starts to be incremented each time by a predetermined value, whereby the air-fuel ratio is changed in the enriching direction. Then, after a time point the output from the air-fuel ratio sensor crosses the above threshold value in the enriching direction, the state of control of the air-fuel ratio is held at the resulting state until a predetermined time period elapses. The above air-fuel ratio control for changing the air-fuel ratio in the leaning direction and then in the enriching direction is repeatedly carried out to see if the cycle of changes in the output from the air-fuel ratio sensor during provision of the above-described air-fuel ratio control is equal to or larger than a predetermined reference value, and when the cycle is equal to or larger than the predetermined reference value, it is determined that the air-fuel ratio sensor is degraded.
However, according to the above conventional degradation determining system, the air-fuel ratio is progressively increased and decreased, and therefore, during execution of the degradation determining process, if the opening degree of the throttle valve is changed due to an unintended slight change in the degree of depression of an accelerator pedal by the driver, the fuel injection amount is increased or decreased in response thereto to cause changes in the air-fuel ratio. This changes the cycle of changes in the output from the air-fuel ratio sensor. Further, there is a case in which even with the same fuel injection amount, the actual air-fuel ratio can vary due to variation in adhesion properties of fuel. In such a case as well, the output from the air-fuel ratio sensor undergoes changes in the cycle. If noise caused by such unexpected changes in the air-fuel ratio during provision of the above-described control of the air-fuel ratio is mixed into the output from the air-fuel ratio sensor, there is a fear that the accuracy of the determination of degradation of the air-fuel ratio sensor is lowered.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a degradation determining system and method for an exhaust gas sensor and an engine control unit, which are capable of determining degradation of the exhaust gas sensor, while suppressing influence of noise caused by unexpected changes in the air-fuel ratio of a mixture on the output from the exhaust gas sensor during provision of control of the air-fuel ratio, thereby enhancing the accuracy of the determination of degradation of the exhaust gas sensor.
To attain the above object, in a first aspect of the present invention, there is provided a degradation determining system for an exhaust gas sensor, for determining degradation of the exhaust gas sensor based on an output from the exhaust gas sensor, the exhaust gas sensor outputting a signal indicative of an amount of a predetermined component contained in exhaust gases emitted from an internal combustion engine into an exhaust passage thereof,
the degradation determining system comprising:
determining input-generating means for generating a determining input for determining degradation of the exhaust gas sensor;
modulation output-generating means for generating a modulation output by modulating the generated determining input, using any one of a &Dgr;&Sgr; modulation algorithm, a &Sgr;&Dgr; modulation algorithm, and a &Dgr; modulation algorithm;
control means for controlling an amount of fuel to be injected into the engine, according to the generated modulation output; and
degradation determining means for determining degradation of the exhaust gas sensor based on the output from the exhaust gas sensor delivered when the amount of fuel to be injected is controlled by the control means.
With the arrangement of the degradation determining system according to the first aspect of the present invention, a determining input for determining degradation of the exhaust gas sensor is modulated using any one of the &Dgr;&Sgr; modulation algorithm, the &Sgr;&Dgr; modulation algorithm, and the &Dgr; modulation algorithm, thereby generating a modulation output. The amount of fuel to be injected into the engine (fuel injection amount) is controlled according to the generated modulation output, and at the same time degradation of the exhaust gas sensor is determined based on the output from the exhaust gas sensor delivered when the fuel injection amount is controlled by the control means. The above-mentioned three modulation algorithms output a signal indicative of a value of +1 or a value of −1, and therefore, by setting the gain of the modulation output to an appropriate value, the fuel injection amount can be varied with a relatively large amplitude. This makes it possible to vary the fuel injection amount with a larger amplitude than a range of changes in the fuel injection amount causing the unexpected changes in the air-fuel ratio described hereinabove. This makes it possible to make the unexpected changes in the air-fuel ratio obscure or lost in changes in the air-fuel ratio the range of which is controlled by the above-described control of the fuel injection amount. As a result, it is possible to suppress adverse influence of noise caused by the unexpected changes in the air-fuel ratio on the output from the exhaust gas sensor. Further, since the degradation of the exhaust gas sensor is determined based on the output from the exhaust gas sensor delivered in a state where the adverse influence of noise caused by the unexpected changes in the air-fuel ratio on the output from the exhaust gas sensor is suppressed as described above, it is possible to enhance the accuracy of the determination of degradation of the sensor.
Preferably, the degradation determining system further comprises a bandpass filter for filtering the output from the exhaust gas sensor input thereto, such that components of the output from the exhaust gas sensor corresponding to a predetermined frequency band including a frequency of the determining input are allowed to pass therethrough, and the degradation determining means determines degradation of the exhaust gas sensor based on the output of the exhaust gas sensor, the output having been filtered by the bandpass filter.
Wit
Ishikawa Yosuke
Minowa Shintaro
Yasui Yuji
Honda Motor Co. Ltd.
Kwon John T.
Squire Sanders & Dempsey L.L.P.
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