JP2008051003A - Multi-cylinder engine air-fuel ratio control device - Google Patents

Abstract

An object of the present invention is to realize an air-fuel ratio control apparatus for a multi-cylinder engine capable of specifying a cylinder in which an air-fuel ratio deviation occurs.
Therefore, an air-fuel ratio control apparatus for a multi-cylinder engine including a catalyst, an upstream air-fuel ratio detection means, and a downstream air-fuel ratio detection means includes a crank angle detection means, a cylinder identification means, and a flow rate detection means. Cylinder imbalance identification means for identifying a cylinder causing an air-fuel ratio imbalance among multiple cylinders using a calculated value based on the value of the downstream air-fuel ratio detection means and the flow rate of the flow rate detection means When the cylinder imbalance identifying means recognizes that there is an imbalanced cylinder, the cylinder identifying means measures the time taken to pass a specific process of each cylinder, and the measured time is subjected to frequency analysis. Thus, there is provided an imbalance cylinder specifying means for specifying the cylinder in which the air-fuel ratio is imbalanced.
[Selection] Figure 1

Description

  The present invention relates to an air-fuel ratio control apparatus for a multi-cylinder engine, and more particularly to an air-fuel ratio control apparatus for a multi-cylinder engine that can identify a cylinder in which an air-fuel ratio deviation occurs.

In an air-fuel ratio control device of an engine mounted on a vehicle, for example, a multi-cylinder engine, an upstream air-fuel ratio is detected in order to detect the air-fuel ratio of exhaust gas discharged from the multi-cylinder engine upstream and downstream of the catalyst. Detection means (also referred to as “front air-fuel ratio (A / F) sensor”) and downstream air-fuel ratio detection means (also referred to as “rear oxygen (O 2) sensor”) are provided.
When the upstream air-fuel ratio detecting means, the catalyst, and the downstream air-fuel ratio detecting means are activated, the fuel injection amount with respect to the intake air amount is corrected and controlled based on the load state of the multi-cylinder engine and the air-fuel ratio is set downstream. Based on the side air-fuel ratio detecting means, feedback control to the target air-fuel ratio, that is, rear O2 feedback (F / B) control is enabled.

Japanese Patent Laid-Open No. 2002-201984 JP 2002-332895 A JP 2002-371906 A JP 2006009674 A

By the way, in the conventional multi-cylinder engine air-fuel ratio control apparatus, the detection method for the cylinder-by-cylinder air-fuel ratio imbalance diagnosis necessary for satisfying US regulations is extremely difficult.
In other words, the detection method requirement is
It is defined that the air-fuel ratio deviation of one cylinder or more that becomes the exhaust gas regulation value * 1.5 = failure.
As a result, there is an infinite number of combinations of “one-cylinder or more air-fuel ratio deviation that becomes the exhaust gas regulation value * 1.5”, and it is impossible to actually set a test and / or failure detection threshold (threshold value). There is an inconvenience.
In particular, when detecting a specific cylinder, if both banks such as a V-type engine fail at the same time, there is an inconvenience that it becomes impossible to specify the cylinder.

  The object of the present invention is to make it possible to take an effective measure for identifying a cylinder in which an air-fuel ratio shift has occurred and to eliminate the air-fuel ratio shift, and to provide OBDII regulations (“exhaust gas OBD” for sale in the North American market. It is also referred to as “regulation.”) To realize an air-fuel ratio control apparatus for a multi-cylinder engine that can satisfy the requirements.

  In view of this, the present invention eliminates the above-mentioned disadvantages by providing an upstream air-fuel ratio detection means and a downstream air-fuel ratio that can detect the air-fuel ratio of the exhaust gas discharged from the multi-cylinder engine on the upstream side and downstream side of the catalyst. An air-fuel ratio control apparatus for a multi-cylinder engine having a detecting means is provided with a crank angle detecting means for detecting a crank angle. The crank angle detecting means includes a cylinder identifying means for identifying a cylinder and passes through the catalyst. Provided with a flow rate detecting means for detecting the flow rate of the exhaust gas, and using a calculated value calculated based on a value detected by the downstream air-fuel ratio detecting means and a passing flow rate detected by the flow rate detecting means. Cylinder imbalance identifying means for identifying whether or not there is a cylinder causing an air-fuel ratio imbalance among the cylinders. When the cylinder identification means recognizes that there is a cylinder, the cylinder identification means measures the time required to pass through a specific process of each cylinder, and performs frequency analysis of the measured time to provide a cylinder in which the air-fuel ratio is imbalanced. An imbalance cylinder specifying means for specifying is provided.

As described above in detail, according to the present invention, upstream air-fuel ratio detection means and downstream air-fuel ratio detection capable of detecting the air-fuel ratio of the exhaust gas discharged from the multi-cylinder engine are provided upstream and downstream of the catalyst. And an air-fuel ratio control apparatus for a multi-cylinder engine, comprising crank angle detection means for detecting a crank angle, cylinder identification means for identifying the cylinder by the crank angle detection means, and exhaust gas passing through the catalyst Provided with a flow rate detection means for detecting a flow rate, and using the calculated value calculated based on the value detected by the downstream air-fuel ratio detection means and the passing flow rate detected by the flow rate detection means, Cylinder imbalance identifying means for identifying whether there is a cylinder causing an imbalance in the fuel ratio is recognized, and it is recognized that there is an imbalanced cylinder by the cylinder imbalance identifying means. In this case, an imbalance cylinder identifying means for measuring a time for passing a specific process of each cylinder by the cylinder identifying means and identifying a cylinder in which the air-fuel ratio is imbalanced by frequency analysis of the measured time. I have.
Accordingly, it is possible to specify a cylinder in which an “air-fuel ratio shift” occurs that deviates greatly from the exhaust gas regulation value only in a specific cylinder.
As a result, it is possible to identify the cylinder in which the air-fuel ratio shift has occurred, and therefore it is possible to take an effective measure for eliminating the air-fuel ratio shift.

  As a result of the invention as described above, when it is recognized that there is an imbalanced cylinder by the cylinder imbalance identifying means, the cylinder identifying means measures the time taken to pass a specific process of each cylinder and measures Frequency is analyzed, and the cylinder in which the air-fuel ratio is imbalanced by the imbalance cylinder specifying means, that is, the cylinder in which the “air-fuel ratio deviation” that greatly deviates from the exhaust gas regulation value occurs only in the specific cylinder is specified. This makes it possible to take effective measures to eliminate the deviation.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

1 to 5 show an embodiment of the present invention.
In FIG. 2, reference numeral 1 denotes an air-fuel ratio control apparatus for a multi-cylinder engine.
This air-fuel ratio control apparatus 1 is an upstream air-fuel ratio detection means that can detect the air-fuel ratio of exhaust gas discharged from a multi-cylinder engine upstream of a catalyst (not shown), for example, a front A / F sensor ("LAF Sensor"). 2), and downstream air-fuel ratio detecting means, for example, a rear O2 sensor 3, is provided on the downstream side of the catalyst.
Further, the air-fuel ratio control apparatus 1 includes a water temperature sensor 4 capable of detecting the cooling water temperature, an intake air temperature sensor 5 capable of detecting the intake air temperature, and a cam angle sensor 6 capable of detecting the cam angle, as shown in FIG. And a crank angle detecting means capable of detecting the crank angle, for example, a crank angle sensor 7 with a pulse rotor.

Further, the air-fuel ratio control apparatus 1 includes a control unit 8.
The control unit 8 is also described as rear O2 sensor feedback control means (also referred to as “rear O2 sensor F / B control means”) 9 and target air-fuel ratio calculation means (“target A / F calculation means”). .) 10, front A / F sensor feedback control means (also referred to as “front A / F sensor F / B control means”) 11, and injector injection time calculation means 12.
The rear O2 sensor feedback control means 9 inputs a detection signal from the rear O2 sensor 3 which is a downstream air-fuel ratio detection means, and corrects and controls the fuel injection amount relative to the intake air amount based on the load state of the multi-cylinder engine. In addition, feedback control of the air-fuel ratio to the target air-fuel ratio based on the rear O2 sensor 3 which is downstream air-fuel ratio detection means, that is, rear O2 feedback control is enabled.
The target air-fuel ratio calculating means 10 has a function of communicating with the rear O2 sensor feedback control means 9 and calculating the target air-fuel ratio.
Further, the front A / F sensor feedback control means 11 communicates with the front A / F sensor 2 and the target air-fuel ratio calculation means 10 to enable feedback control of the front A / F sensor 2.
Furthermore, the injector injection time calculation means 12 has a function of communicating with the front A / F sensor feedback control means 11 and calculating a fuel injection time from an injector (not shown).

  The control unit 8 of the air-fuel ratio control apparatus 1 includes a cylinder identifying unit 13 for identifying a cylinder by a crank angle sensor 7 with a pulse rotor serving as a crank angle detecting unit, and a flow rate for detecting the flow rate of exhaust gas passing through the catalyst. A detecting means 14, a calculated value calculated based on a value detected by the rear O2 sensor 3, which is the downstream air-fuel ratio detecting means, and a passing flow rate (“catalyst passing flow rate” detected by the flow rate detecting means 14. Or a “catalyst passing gas flow rate”), and cylinder imbalance identifying means 15 for identifying whether there is a cylinder causing an air-fuel ratio imbalance among the multiple cylinders. When the balance identifying means 15 recognizes that there is an imbalanced cylinder, the cylinder identifying means 13 measures the time for passing through a specific process of each cylinder. And, a imbalance cylinder specifying means 16 for specifying a cylinder that imbalance of air-fuel ratio by the measured time to frequency analysis.

More specifically, the control unit 8 of the air-fuel ratio control apparatus 1 is a multi-cylinder engine having the front A / F sensor 2, the rear O2 sensor 3, the cam angle sensor 6, and the crank angle sensor 7 with a pulse rotor. It specifies the imbalance associated with individual cylinders of a multi-cylinder engine.
That is, the difference between the target voltage and the actual voltage of the rear O2 sensor 3 during the period corresponding to the engine speed condition, the load condition, and the linear air-fuel ratio condition is calculated, and PI control (integral operation for proportional operation) is calculated from the difference. The calculated value, which is a correction value of the rear O2 sensor 3, is calculated by the control (see FIG. 3B).
Further, the calculated value which is the correction value of the rear O2 sensor 3 and the passing flow rate detected by the flow rate detecting means 14 are calculated, and this product corresponds to the linear air-fuel ratio condition as shown in FIG. Accumulate during the running period.
As shown in FIG. 3 (d), when the accumulated value exceeds the threshold value and is held for X seconds, the cylinder imbalance identifying means 15 causes an air-fuel ratio imbalance among the multiple cylinders. Recognize that there is.

In addition, when the cylinder imbalance identifying means 15 recognizes that there is an imbalanced cylinder, a lean side rear O2 correction fuel diagnosis abnormality always occurs, so the cam angle is exceeded after the lean side threshold is exceeded. The cylinder is specified by the imbalance cylinder specifying means 16 by utilizing the fact that the cylinder is identified by the sensor 6 and the crank angle sensor 7 with a pulse rotor.
That is, as shown in FIG. 4, the crank angle sensor 7 with a pulse rotor measures the time required to pass through the compression process, which is a specific process of each cylinder at the time of two crank angles when idling, for each cylinder N times.
The measured time is subjected to frequency analysis (parameterization by Fourier transform), and the relative strength of the components between the cylinders is compared, whereby the cylinder can be specified.

Here, frequency analysis will be described.
In a typical frequency analysis method, a Fourier transform is used to examine the frequency of a time invariant signal.
This Fourier transform can convert a time axis signal into a frequency axis signal.
For example, it is possible to specify the frequency by Fourier-transforming a sin wave having an unknown frequency, such as the time of the compression process, which is a specific process of each cylinder this time.
In addition, when an imbalance occurs between cylinders, the time width of the compression process during idling will be shifted only by that cylinder, but it is difficult to make a relative comparison without converting it as it is. It is difficult to distinguish between abnormal and normal.
Therefore, by using frequency analysis, as shown in FIG. 5, a signal in a specific band is extracted to distinguish between a normal time and an abnormal time.
In particular, when detecting an abnormality in a single cylinder, a relative comparison in the frequency band corresponding to two rotations of the crank angle is a point. When detecting an abnormality in two cylinders of the opposite cylinder such as a V6 engine, 1 Comparison in the frequency band for rotation is the point.
In addition to this, there is a distinction from vehicle vibration, but this time, since the imbalance detection of a single cylinder is performed, the description is omitted.

  Next, the operation will be described along the control flowchart of the air-fuel ratio control device 1 of the multi-cylinder engine of FIG.

  First, the control flowchart of the multi-cylinder engine air-fuel ratio control apparatus 1 will be described. The cylinder imbalance identifying means 15 detects the cylinder imbalance until the items (102) to (107) for processing and judgment are described. Items (108) to (112) are portions for specifying the cylinders that are imbalanced by the imbalance cylinder specifying means 16.

When the control program of the air-fuel ratio control device 1 of the multi-cylinder engine is started (101), the process proceeds to a determination (102) as to whether or not an imbalance detection diagnostic condition is satisfied.
At this time, in the determination (102), it is necessary to satisfy all of the following five items which are diagnostic conditions for imbalance detection.
(1) Is rear O2 sensor feedback control established?
(2) Is it not in fuel enrichment state?
(3) Is the difference between the target air-fuel ratio and the actual air-fuel ratio within a predetermined range?
(4) Is the engine load and the intake air amount within certain ranges?
(5) Whether the front A / F sensor 2, the rear O2 sensor 3, the water temperature sensor 4, the intake air temperature sensor 5, the cam angle sensor 6, and the crank angle sensor 7 with a pulse rotor have not failed.

In the determination of whether or not the above-described imbalance detection diagnostic conditions are satisfied (102), any one of the five imbalance detection diagnosis conditions is not satisfied, that is, the determination (102) is NO. In this case, the determination (102) is repeated until the determination (102) becomes YES.
If all of the imbalance detection diagnostic conditions having five items are satisfied, that is, if the determination (102) is YES, the routine proceeds to determination (103) as to whether or not the rear O2 correction is within a predetermined range. .

In the determination (103) of whether or not the rear O2 correction is within a predetermined range, if the determination (103) is YES, the calculated value that is the correction value of the rear O2 sensor 3 and the flow rate detection means 14 are determined. The process shifts to a process (104) for resetting the product of the flow rate detected by step (104) and the process returns to the determination (102) as to whether or not the above-described imbalance detection diagnostic conditions are satisfied.
If the determination (103) is NO, the product of the calculated value, which is the correction value of the rear O2 sensor 3, and the passing flow rate detected by the flow rate detecting means 14 is calculated, and the index is calculated. The process proceeds to (105), and then the process proceeds to a determination (106) as to whether or not the integration index exceeds a certain threshold value and is held for X seconds.

If the determination (106) is NO in the determination (106) as to whether or not the integrated index exceeds a certain threshold value and is held for X seconds, whether or not the above-described imbalance detection diagnostic condition is satisfied. Return to the determination (102).
If the determination (106) is YES, the cylinder imbalance abnormality is detected, that is, the cylinder imbalance identifying means 15 recognizes that there is an air-fuel ratio imbalance among the multiple cylinders. The processing shifts to (107).

After this cylinder imbalance abnormality detection, that is, the process (107) for recognizing that there is an air-fuel ratio imbalance among the multiple cylinders by the cylinder imbalance identifying means 15, the imbalance cylinder identification is performed. The process proceeds to determination (108) of whether or not all the diagnostic conditions are satisfied.
At this time, in the determination (108), it is necessary to satisfy all of the following four items that are diagnostic conditions for specifying the imbalance cylinder.
(1) Is the idle condition satisfied?
(2) Is the complete warm-up condition satisfied?
(3) Is the rotational speed condition satisfied?
(4) Is the intake air flow rate condition satisfied?

Then, in determining whether or not the above-described imbalance cylinder specifying diagnostic condition is satisfied (108), any one of the four imbalance cylinder specifying diagnostic conditions is not satisfied, that is, determining (108). If NO is NO, the determination (108) is repeated until the determination (108) becomes YES.
If all of the diagnostic conditions for specifying the imbalance cylinder having four items are satisfied, that is, if the determination (108) is YES, the idle ignition correction is stopped and the ignition timing is fixed, and the ISC (“idle speed control”) The process proceeds to the determination (109) of whether or not the rotation speed feedback is stopped.

In the determination (109) of whether or not the idling ignition correction is stopped, the ignition timing is fixed, and the rotation speed feedback of the ISC (also referred to as “idle speed control”) is stopped, the determination (109) is NO. In this case, the determination (109) is repeatedly performed until the determination (109) becomes YES.
Further, when the determination (109) is YES, the processing (110) of measuring the time to pass through the compression process, which is a specific process of each cylinder (also referred to as “WINDOW time”) N times for each cylinder. Then, the process proceeds to determination (111) by frequency analysis.

At this time, the determination by frequency analysis (111) is performed by frequency analysis of the time measured by the imbalance cylinder specifying means 16, and whether the specific cylinder exceeds a predetermined threshold by relative comparison of the component intensities between the cylinders. It is to judge whether or not.
When the determination (111) is NO, the process returns to the determination (108) as to whether or not the above-described imbalance cylinder specifying diagnostic conditions are satisfied.
If the determination (111) is YES, the process proceeds to a process (112) for specifying the cylinder causing the inter-cylinder imbalance. Move to end (113).
As described above, it is possible to satisfy the exhaust gas OBD regulation and to ensure the “cylinder-by-cylinder air-fuel ratio imbalance diagnosis detection method”.

As a result, the front A / F sensor 2 which is an upstream air-fuel ratio detecting means capable of detecting the air-fuel ratio of the exhaust gas discharged from the multi-cylinder engine and the downstream air-fuel ratio detecting means are provided upstream and downstream of the catalyst. In an air-fuel ratio control apparatus 1 for a multi-cylinder engine provided with a certain rear O2 sensor 3, the air-fuel ratio control apparatus 1 includes a crank angle sensor 7 with a pulse rotor that is a crank angle detection means, a cylinder identification means 13, and a flow rate detection means. 14, and using the calculated value calculated based on the value detected by the rear O2 sensor 3, which is the downstream air-fuel ratio detecting means, and the passing flow rate detected by the flow rate detecting means 14, Cylinder imbalance identifying means 15 is provided for identifying whether there is a cylinder causing an air-fuel ratio imbalance among the cylinders. When it is recognized that there is a balanced cylinder, the cylinder identification means 13 measures the time required to pass through a specific process of each cylinder, and performs frequency analysis of the measured time to imbalance the air-fuel ratio. An imbalance cylinder specifying means 16 for specifying the cylinder being operated is provided.
Accordingly, it is possible to specify a cylinder in which an “air-fuel ratio shift” occurs that deviates greatly from the exhaust gas regulation value only in a specific cylinder.
As a result, it is possible to identify the cylinder in which the air-fuel ratio shift has occurred, and therefore it is possible to take an effective measure for eliminating the air-fuel ratio shift.

In addition, a specific process of each cylinder is a compression process.
Therefore, by making the specific process of each cylinder a compression process, the detection accuracy by the crank angle sensor with pulse rotor 7 serving as the crank angle detection means and the specific process of each cylinder by the cylinder identification means 13 are passed. It can contribute to the improvement of time measurement accuracy.

3 is a flowchart for control of an air-fuel ratio control apparatus for a multi-cylinder engine showing an embodiment of the present invention. 1 is a system diagram of an air-fuel ratio control apparatus for a multi-cylinder engine. (A) is a time chart showing a rear O2 sensor output, (b) is a time chart showing a rear O2 sensor correction value (difference between actual voltage and target), c) is a time chart showing the catalyst passing gas flow rate (from MFA), and (d) is a time chart showing correction value * catalyst passing gas flow rate. It is a time chart which shows the output state of the cam angle sensor and crank angle sensor of the air-fuel ratio control apparatus of a multicylinder engine. It is a figure explaining general frequency analysis from the relation between frequency intensity and frequency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air-fuel ratio control apparatus of multi-cylinder engine 2 Front A / F sensor 3 Rear O2 sensor 4 Water temperature sensor 5 Intake temperature sensor 6 Cam angle sensor 7 Crank angle sensor with pulse rotor 8 Control unit 9 Rear O2 sensor feedback control means 10 Target sky Fuel ratio calculation means 11 Front A / F sensor feedback control means 12 Injector injection time calculation means 13 Cylinder identification means 14 Flow rate detection means 15 Cylinder imbalance identification means 16 Imbalance cylinder identification means

Claims (2)

  An air-fuel ratio control device for a multi-cylinder engine comprising upstream and downstream air-fuel ratio detection means and downstream air-fuel ratio detection means capable of detecting the air-fuel ratio of exhaust gas discharged from the multi-cylinder engine on the upstream side and downstream side of the catalyst A crank angle detecting means for detecting a crank angle, a cylinder identifying means for identifying a cylinder by the crank angle detecting means, a flow rate detecting means for detecting a flow rate of exhaust gas passing through the catalyst, Cylinder in which the air-fuel ratio is imbalanced among the multiple cylinders using the calculated value calculated based on the value detected by the downstream air-fuel ratio detecting means and the passing flow rate detected by the flow rate detecting means A cylinder imbalance identifying means for identifying whether there is a cylinder, and when the cylinder imbalance identifying means recognizes that there is an imbalanced cylinder, the cylinder identification An imbalance cylinder identifying means is provided for measuring a time required to pass a specific process of each cylinder by a stage and identifying a cylinder in which the air-fuel ratio is imbalanced by frequency analysis of the measured time. An air-fuel ratio control device for a multi-cylinder engine.   The air-fuel ratio control apparatus for a multi-cylinder engine according to claim 1, wherein the specific process of each cylinder is a compression process.

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