Patent Application
20100077728
The present invention relates to engine control, and more particularly to engine emission control using air-fuel imbalance detection.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines compress and ignite a mixture of air and fuel in a cylinder to produce power. An imbalance in the air-fuel mixture may produce excessive emissions in exhaust gases exiting the cylinders. An oxygen concentration sensor may measure oxygen concentration levels in the exhaust gas. By measuring the oxygen concentration in the exhaust gas, the air-fuel mixture may be adjusted to improve combustion efficiency and reduce excessive emissions.
Accordingly, the present disclosure provides a control system comprising an oxygen sensor that generates an oxygen signal based on an oxygen concentration level in an exhaust gas of an engine, a filtering module that determines a filtered signal based on the oxygen signal, and an air-fuel imbalance detection module that detects an air-fuel imbalance in the engine based on the oxygen signal and the filtered signal. In addition, the present disclosure provides a method comprising generating an oxygen signal based on an oxygen concentration level in an exhaust gas of an engine, determining a filtered signal based on the oxygen signal, and detecting an air-fuel imbalance in the engine based on the oxygen signal and the filtered signal.
Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.
The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure.
As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.
Referring now to
The inlet and outlet O2 sensors 24, 26 generate signals based on the O2 content of the exhaust gas. The signals are communicated to the control module 16. The control module 16 determines the A/F ratio based on the signals. The control module 16 communicates with a fuel system 28, which regulates fuel flow to the engine 12. In this manner, the control module 16 adjusts and regulates the A/F ratio to the engine 12.
The inlet and outlet O2 sensors 24, 26 are typically narrow range switching sensors. It is appreciated, however, that the inlet and outlet O2 sensors 24, 26 are not limited to narrow range type switching sensors. Voltage output signals that are generated by the O2 sensors 24, 26 are based on the O2 content of the exhaust passing the O2 sensors relative to stoichiometry. The signals transition between lean and rich in an A/F ratio range that brackets the stoichiometric A/F ratio. The O2 sensor signal that is generated by the inlet O2 sensor 24 switches back and forth between rich and lean values.
The control module 16 regulates the fuel flow based on the O2 sensor signals. For example, if the inlet O2 sensor signal indicates a lean condition, the control module 16 increases fuel flow to the engine 12. Conversely, if the inlet O2 sensor signal indicates a rich condition, the control module 16 decreases fuel flow to the engine 12. The amount of fuel is determined based on fuel offset gains, which are determined based on the sensor signals.
An air-fuel imbalance in the engine 12 causes fast switching of the O2 sensor 24, yielding a high frequency O2 sensor signal. The amount of air flowing through the intake manifold 18 and the rotational speed of the engine 12 may cause undesired exhaust gas separation. Depending on sensitivity level of the O2 sensor 24, exhaust gas separation may cause O2 sensor signal noise and false diagnosis of an air-fuel imbalance. The air-fuel imbalance detection system and method of the present disclosure has a sufficient signal-to-noise (S/N) ratio to prevent false diagnosis of an air-fuel imbalance.
The air-fuel imbalance detection system and method of the present disclosure detects an air-fuel imbalance in the engine 12 based on an O2 sensor signal. More specifically, the air-fuel imbalance detection system and method filters the O2 sensor signal and detects an air-fuel imbalance based on the unfiltered O2 sensor signal and the filtered O2 sensor signal. The air-fuel imbalance detection system and method employs a filter that removes any high-frequency imbalance from the unfiltered O2 sensor signal such that the unfiltered and filtered O2 sensor signals may be used to identify an air-fuel imbalance. A sufficient S/N ratio is achieved through a filter that removes any high-frequency imbalance but does not remove noise due to sensitivity of the O2 sensor 24.
The control module 16 detects an air-fuel imbalance according to the principles of an air-fuel imbalance detection system and method of the present disclosure. When the engine 12 is running, the control module 16 filters the O2 sensor signal using a zero-phase, low-pass digital filter to obtain the filtered O2 sensor signal. The control module 16 calculates a difference between the O2 sensor signal and the filtered O2 sensor signal and calculates a variance based on the difference to yield an index that indicates an air-fuel imbalance level. When the index exceeds a predetermined threshold, the control module 16 detects an air-fuel imbalance.
Referring now to
The air-fuel imbalance detection module 202 receives the unfiltered O2 sensor signal from the pre-catalyst O2 sensor 24 and the filtered O2 sensor signal from the filtering module 200. The air-fuel imbalance detection module 202 calculates a difference between the unfiltered and filtered O2 sensor signals and determines a variance of the difference. More specifically, the air-fuel imbalance detection module 202 sets the variance equal to the square of the difference between the unfiltered and filtered O2 sensor signals.
The air-fuel imbalance detection module 202 determines an index of an air-fuel imbalance level based on the variance. More specifically, the air-fuel imbalance detection module 202 may set the index equal to the variance. Alternatively, the air-fuel imbalance detection module 202 may filter the variance and set the index equal to the filtered variance to avoid false detection of an air-fuel imbalance due to variations in an unfiltered index. The air-fuel imbalance detection module 202 determines whether the index exceeds a predetermined threshold. When the index exceeds the predetermined threshold, the air-fuel imbalance detection module 202 detects an air-fuel imbalance and generates a service indicator signal.
Referring now to
In step 304, control determines a difference between the unfiltered and filtered O2 sensor signals. In step 306, control determines an index of an air-fuel imbalance level based on a variance or square of the difference. More specifically, control may set the index equal to the variance. Alternatively, control may filter the variance and set the index equal to the filtered variance to avoid false detection of an air-fuel imbalance due to variations in an unfiltered index.
In step 308, control determines whether the index of the air-fuel imbalance level exceeds a predetermined air-fuel imbalance level threshold. When the index exceeds the threshold, control detects an air-fuel imbalance in step 310. For robustness (i.e., avoidance of false air-fuel imbalance detection), control may detect the air-fuel imbalance when the index exceeds the threshold for a predetermined time period. Control may set a service indicator, such as a diagnostic trouble code (DTC), when an air-fuel imbalance is detected. Since O2 sensors typically measure O2 content of exhaust gas exiting a single bank of cylinders, control may set independent service indicators for each bank.
Referring now to
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In the graph on the right, the y-axis represents a variance of the residual between the unfiltered and filtered O2 sensor signals and the x-axis represents the number of samples from the O2 sensor signal monitored to detect an air-fuel imbalance. The graph on the right compares a passing variance (i.e., does not indicate an air-fuel imbalance) and a failing variance (i.e., indicates an air-fuel imbalance). The passing variance remains relatively constant compared to the failing variance, and the magnitude of the passing variance is significantly lower than the magnitude of the failing variance.
Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.
