JP4144275B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly, to a control device that sets a guard value for an air-fuel ratio based on a rotational speed fluctuation amount of the internal combustion engine.
[0002]
[Prior art]
Conventionally, in order to control the combustion air-fuel ratio of the internal combustion engine at the target air-fuel ratio, the fuel injection amount is controlled based on the deviation between the sensor output value for detecting the air-fuel ratio and the target air-fuel ratio, and the air-fuel ratio is reduced. A technique for performing accurate air-fuel ratio control by following a target air-fuel ratio is widely known. In such a control, as a sensor for detecting the air-fuel ratio of combustion, an O2 sensor that outputs the air-fuel ratio according to the oxygen concentration or an A / F sensor that linearly outputs the air-fuel ratio according to the oxygen concentration is usually used. Are known.
[0003]
[Problems to be solved by the invention]
However, the air-fuel ratio feedback control for accurately controlling the air-fuel ratio is a control that does not hold unless a sensor that detects the air-fuel ratio outputs a correct value. That is, when the sensor for detecting the air-fuel ratio temporarily outputs an incorrect value for the air-fuel ratio output value, the fuel injection amount is corrected based on the deviation between the incorrect output value and the target air-fuel ratio. In addition, for example, when the actual air-fuel ratio is close to the theoretical air-fuel ratio, but the sensor output value is large and rich, the feedback correction coefficient is set to a correction value for reducing the fuel injection amount, and the actual air-fuel ratio Will be greatly lean. Similarly, when the sensor output value shows a large lean value, the feedback correction coefficient is set to a correction value that increases the fuel injection amount, and the actual air-fuel ratio becomes greatly rich.
[0004]
In any case, since the sensor output value shows a value different from the actual air-fuel ratio, there is a possibility that the air-fuel ratio is greatly deviated from the target air-fuel ratio.
[0005]
The present invention has been made in view of the above-described problems, and an internal combustion engine capable of suppressing the actual air-fuel ratio from deviating from the target air-fuel ratio even when the sensor output value is significantly different from the actual air-fuel ratio. An object is to provide an air-fuel ratio control device for an engine.
[0006]
[Means for Solving the Problems]
Therefore, as in the first aspect of the invention, the fuel injection amount is determined based on the air-fuel ratio sensor output value that is disposed in the exhaust passage of the internal combustion engine and detects the exhaust gas component in the exhaust passage, and the target air-fuel ratio. In an air-fuel ratio control apparatus for an internal combustion engine that calculates a feedback correction coefficient for feedback control, a guard value for the feedback correction coefficient is set based on the rotational fluctuation of the internal combustion engine.
[0007]
As a result, when the actual air-fuel ratio deviates from the target rotational speed, when a rotational speed fluctuation occurs, the present invention sets a guard value for the feedback correction coefficient based on the rotational fluctuation, so the fuel injection amount is largely corrected. It is possible to prevent the actual air-fuel ratio from deviating from the target air-fuel ratio.
[0008]
Also, Claim 1 In the invention, the lean side guard value for the feedback correction coefficient for correcting the fuel injection amount to the decreasing side and / or the rich side guard side for the feedback correction coefficient for correcting the fuel injection amount to the increasing side are used as the guard value described above. Prepare.
[0009]
As a result, the actual air-fuel ratio is prevented from deviating from the target air-fuel ratio even when the air-fuel ratio sensor output value outputs an incorrect output value to the rich side or when an incorrect output value is output to the lean side. be able to.
[0010]
Also , Claims 1 Invention Then When the rotational speed fluctuation is larger than the predetermined value, the guard value setting means makes the deviation of the rich side guard value and / or the lean side guard value with respect to the reference value of the feedback correction coefficient small according to the rotational speed fluctuation. Set.
[0011]
Thereby, when the rotation speed fluctuation becomes large, the rich side guard value and / or the lean side guard value for the feedback correction coefficient are set small. At this time, for example, even when the output of the air-fuel ratio sensor outputs an output value on the rich side compared to the actual air-fuel ratio, if the rotational fluctuation becomes large, the feedback correction coefficient for correcting the fuel injection amount Since the guard value is set small, the feedback correction coefficient is not set to a value exceeding the guard value. That is, since the fuel injection amount is prevented from being corrected to be greatly reduced, the actual air-fuel ratio is suppressed from deviating from the target air-fuel ratio.
[0012]
Similarly, the claims 2 As in the invention of claim 1, the guard value setting means has a rotational speed variation. 1 When the value is smaller than the predetermined value, the rich side guard value and / or the lean side guard value are set so that the deviation of the feedback correction coefficient from the reference value gradually increases.
[0013]
As described above, when the rotational speed fluctuation is small, it is preferable to set the guard value for the feedback correction coefficient to be gradually increased.
[0014]
Embodiment
<First Embodiment>
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram showing an engine control apparatus according to the present embodiment.
[0015]
In FIG. 1, an engine 1 is a spark ignition type four-cycle multi-cylinder internal combustion engine, and an intake pipe 2 and an exhaust pipe 3 are connected to an intake port and an exhaust port, respectively. The intake pipe 2 is provided with a throttle valve 4 that is linked to an accelerator pedal (not shown) and an air flow meter 5 for detecting the amount of intake air. The opening degree of the throttle valve 4 is detected by a throttle sensor 20, and the sensor 20 also detects the fully closed state of the throttle.
[0016]
A piston 7 that reciprocates in the vertical direction in the figure is disposed in a cylinder 6 that constitutes a cylinder of the engine 1, and the piston 7 is connected to a crankshaft (not shown) via a connecting rod 8. A combustion chamber 10 defined by a cylinder 6 and a cylinder head 9 is formed above the piston 7. The combustion chamber 10 communicates with the intake pipe 2 and the exhaust pipe 3 through an intake valve 11 and an exhaust valve 12. Yes. The cylinder 6 (water jacket) is provided with a water temperature sensor 17 for detecting the temperature of the engine cooling water.
[0017]
Two catalytic converters 13 and 14 are disposed in the exhaust pipe 3, and these catalytic converters 13 and 14 are formed of a three-way catalyst for purifying three components such as HC, CO, and NOx in the exhaust gas. The upstream catalytic converter 13 has a smaller capacity than the downstream catalytic converter 14, and has a role as a so-called start catalyst in which warm-up immediately after engine startup is relatively fast. The upstream catalytic converter 13 is provided at a position about 300 mm from the end face of the engine exhaust port.
[0018]
A laminated A / F sensor 15 including a limit current type laminated air-fuel ratio sensor is provided on the upstream side of the catalytic converter 13, and the laminated A / F sensor 15 has an oxygen concentration in exhaust gas (or one in unburned gas). A wide-range and linear air-fuel ratio signal is output in proportion to the concentration of carbon oxide). Further, on the downstream side of the catalytic converter 14, an O2 sensor 16 that outputs different voltage signals on the rich side and the lean side with respect to the stoichiometric air-fuel ratio (stoichiometric) is provided. In the present embodiment, air-fuel ratio feedback control is performed based on the output of the laminated A / F sensor 15 and the target air-fuel ratio. The feedback control may be a conventionally known control. For example, a feedback correction coefficient for correcting the fuel injection amount is calculated according to the deviation between the sensor output value of the actual air-fuel ratio and the target air-fuel ratio. Further, the upstream target air-fuel ratio of the catalytic converter 14 may be corrected based on the output value of the O2 sensor disposed on the downstream side of the catalytic converter 14.
[0019]
The electromagnetically driven injector 18 is supplied with high-pressure fuel from a fuel supply system (not shown), and the injector 18 injects and supplies fuel to the engine intake port when energized. In the present embodiment, a multi-point injection (MPI) system having one injector 18 for each branch pipe of the intake manifold is configured. A spark plug 19 disposed in the cylinder head 9 is ignited by a high voltage for ignition supplied from an igniter (not shown).
[0020]
In this case, fresh air supplied from upstream of the intake pipe and fuel injected by the injector 18 are mixed at the engine intake port, and the mixture flows into the combustion chamber 10 as the intake valve 11 opens. The fuel that has flowed into the combustion chamber 10 is ignited by an ignition spark from the spark plug 19 and is used for combustion.
[0021]
An intake side camshaft 21 for opening and closing the intake valve 11 at a predetermined timing and an exhaust side camshaft 22 for opening and closing the exhaust valve 12 at a predetermined timing are connected to the crankshaft via a timing belt (not shown) or the like. Drive coupled. The intake side camshaft 21 is provided with a hydraulically driven intake side variable valve timing mechanism 23, and the exhaust side camshaft 22 is similarly provided with a hydraulically driven exhaust side variable valve timing mechanism 24.
[0022]
The intake-side and exhaust-side variable valve timing mechanisms 23, 24 are phase-adjustable variable valve timing mechanisms for adjusting the relative rotation phases between the intake-side and exhaust-side camshafts 21, 22 and the crankshaft, respectively. The operation is adjusted according to hydraulic control by a solenoid valve (not shown). That is, the intake side and exhaust side camshafts 21, 22 rotate to the retard side or advance side with respect to the crankshaft according to the control amount of the intake side and exhaust side variable valve timing mechanisms 23, 24, In accordance with the operation, the opening / closing timing of the intake and exhaust valves 11, 12 shifts to the retard side or the advance side.
[0023]
The intake side camshaft 21 is provided with an intake side cam position sensor 25 for detecting the rotational position of the camshaft 21, and the exhaust side camshaft 22 is provided for detecting the rotational position of the camshaft 22. An exhaust side cam position sensor 26 is provided.
[0024]
The electronic control unit (ECU) 30 is mainly configured by a microcomputer including a CPU 31, a ROM 32, a RAM 33, a backup RAM 34, and the like. The ECU 30 receives detection signals from the air flow meter 5, the A / F sensor 15, the O2 sensor 16, the water temperature sensor 17, the throttle sensor 20, and the cam position sensors 25 and 26, and intake air based on the detection signals. The engine operating state such as the amount Qa, the air-fuel ratio (A / F) upstream and downstream of the catalyst, the engine water temperature Tw, the throttle opening, and the cam position is detected. In addition, the ECU 30 includes a reference position sensor 27 that outputs a pulse signal every 720 ° CA and a rotation angle sensor 28 that outputs a pulse signal every finer crank angle (for example, every 30 ° CA). The ECU 30 is connected and detects the reference crank position (G signal) and the engine speed Ne by inputting the pulse signals from the sensors 27 and 28.
[0025]
The ECU 30 controls the fuel injection by the injector 18, the ignition timing by the spark plug 19, and the intake / exhaust valves 11 and 12 by the variable valve timing mechanisms 23 and 24 based on the various engine operating states detected as described above. Implement opening / closing timing control.
[0026]
The guard processing program for the feedback correction coefficient according to the present invention implemented in the above configuration will be described in detail with reference to FIGS. 2 to 6 and FIG. First, the air-fuel ratio feedback program will be briefly described with reference to the flowchart of FIG. First, in step S301, it is determined whether a feedback condition is satisfied. This feedback condition is, for example, such a condition that the A / F sensor 15 is not in an accelerating / decelerating operation state (fuel cut, fuel increase correction, etc.) as an active state or a transient operation state. As a condition for executing the feedback control, the process proceeds to step S302 only when all of the above conditions are satisfied. If this condition is not satisfied, the process proceeds to step S309, the feedback correction coefficient FAF is set to 1, and this routine is terminated.
[0027]
On the other hand, in step S302, the engine speed Ne, the intake pipe pressure Pm, the engine coolant temperature Thw, and the like are detected as operating conditions of the internal combustion engine. In step S303, the target air-fuel ratio is calculated based on the above operating conditions. Next, in step S304, the actual air-fuel ratio in the exhaust pipe 3 is detected by the A / F sensor 15.
[0028]
In step S305, an air-fuel ratio feedback correction coefficient FAF for controlling the air-fuel ratio is calculated based on the deviation between the target air-fuel ratio calculated in step S303 and the actual air-fuel ratio detected in step S304. In step S306, the feedback correction coefficient is compared with guards (FAFgardL, FAFgardR) for the feedback correction coefficient FAF described later.
[0029]
If the feedback correction coefficient FAF is within the guard area FAFgardL <FAF <FAFgardR, the routine ends with the feedback correction coefficient FAF being set based on the target air-fuel ratio and the actual air-fuel ratio.
[0030]
On the other hand, if it is determined in step S306 that the feedback correction coefficient FAF is smaller than a guard value FAFgardL which will be described later, the process proceeds to step S307, where the feedback correction coefficient FAF is set to FAFgardL, and this routine ends. On the other hand, when the feedback correction coefficient FAF is larger than a guard value FAFgardR described later in step S306, the process proceeds to step S308, where the guard value FAFgardR is set in the feedback correction coefficient FAF, and this routine is ended.
[0031]
The flowchart of FIG. 2 is the main program of the present invention. First, in step S100, it is determined whether or not an execution condition is satisfied. Here, the execution condition is a condition under which feedback control is established. For example, a condition that the acceleration / deceleration operation state (fuel cut, fuel increase correction, etc.) is not set as the active state of the A / F sensor 15 or the transient operation state. It is. As a condition for executing the feedback control, the process proceeds to step S110 only when all the above conditions are satisfied. On the other hand, if even one condition for executing the feedback control is not satisfied, this routine is terminated as it is.
[0032]
When the execution condition is satisfied and the process proceeds to step S110, a fluctuation amount of the rotational speed (hereinafter referred to as a roughness detection value) is obtained by calculation based on the engine rotational speed of the internal combustion engine. This calculation is performed by the roughness detection value calculation program shown in the flowchart of FIG. In this program, for example, the rotation phase of a crankshaft of an engine (not shown) is started every 30 ° CA, and roughness detection value calculation is executed. When this program is started, first, in step S101, the rotational angular velocity ω (n) is calculated for each crankshaft angle 30 ° CA of the internal combustion engine and stored in the RAM 33. Here, the calculation of the rotational angular velocity ω (n) is performed by, for example, counting the time required for 30 ° CA to elapse with a timer, and calculating the rotational angular velocity ω (n) as the rotational angle per second based on the count value. Calculate.
[0033]
In step S102, the previous rotation angular velocity ω (n-4) and the previous rotation angular velocity ω (n) stored in the RAM 33 are called, and the process proceeds to step S103. In step S103, the average rotational angular velocity value Δωave (= (ω (n−4) −ω (n)) / 4) is calculated. In step S104, a deviation Δω (= ω (n−1) −ω (n)) between the previous rotational speed and the current rotational speed is calculated, and the process proceeds to step S105. In step S105, the roughness detection value Δωgard (= Δωave−Δω) is calculated based on Δωave calculated in step S103 and Δω calculated in step S104.
[0034]
The roughness detection value Δωgard will be described with reference to the time chart shown in FIG. The rotational angular velocity deviation Δω (n) every 180 ° CA is indicated by ○ in the figure, and the average angular velocity deviation Δωave is indicated by Δ in the figure. The roughness detection value is a value obtained by subtracting the rotational angular velocity deviation Δω between 180 ° CA from this average angular velocity deviation Δωave, and when this value deviates greatly from the reference value (Δωave), it indicates that the fluctuation amount of the engine is large. When the value is small from the reference value (Δωave), it indicates that the engine fluctuation amount is small. Further, the fluctuation on the side where the rotational speed falls is calculated as a negative value as the roughness detection value Δωgard, while the fluctuation on the side where the rotation speed protrudes is calculated as a positive value as the roughness detection value Δωgard.
[0035]
As described above, when the roughness detection value Δωgard is calculated by the roughness detection value calculation program, the process returns to step S120 of the main routine of FIG. 2 again. Based on the roughness detection value Δωgard, a guard correction value RVCgard (n) for the air-fuel ratio guard value is calculated. The guard correction value RVCgard (n) is calculated using the map shown in FIG. According to the map of FIG. 5, the guard value (FAFgardL, FAFgardR) with respect to the feedback correction coefficient FAF value is set to the reference value of the feedback correction coefficient FAF value (FAFgardL, FAFgardR) as the roughness detection value Δωgard increases (the drop in rotational speed increases). For example, a correction value (solid line in FIG. 5) that is smaller than 1) is set.
[0036]
Next, in step S130, it is determined whether or not the correction value RVCgard (n) is equal to or less than a predetermined value COEF1. Here, when it is determined that the value is smaller than the predetermined value COEF1, that is, when the roughness detection value Δωgard (n) indicates that the fluctuation amount (sag) of the engine rotation speed is large, the process proceeds to step S140, and the guard against the feedback correction value is performed. The guard correction value RVCgard (n) calculated in step S120 is input to the final correction value LRVCgard (n) for the value, and the process proceeds to step S160.
[0037]
On the other hand, if the correction value RVCgard (n) is greater than the predetermined value COEF1, the process proceeds to step S150 if the roughness detection value Δωgard (n) indicates that the engine rotational speed fluctuation amount (sag) is small. In step S150, a predetermined value COEF2 for gradually increasing the guard value for the feedback correction value is set as the final correction value LRVCgard (n), and the process proceeds to step S160.
[0038]
In step S160, the guard value FAFgardL (n) for the feedback correction value on the lean side as the guard value for the feedback correction value FAF is the last correction set in step S140 or step S150 to the previous guard value FAFgardL (n). It is obtained by subtracting the value LRVCgard (n). Similarly, the guard value FAFgardR (n) for the feedback correction value on the rich side is obtained by adding the final correction value LVCgard (n) to the previous guard value FFgardR (n).
[0039]
FIG. 6 shows a case where the guard values FAFgardL (n) and FAFgardR (n) for the feedback correction values obtained as described above are used for air-fuel ratio control when the output value of the A / F sensor 15 is incorrect. This will be described using a time chart. In this time chart, an example in which the sub feedback control of the rear O2 sensor is not performed will be described.
[0040]
First, FIG. 6A shows the output value of the A / F sensor 15. The output value of the A / F sensor 15 outputs the same A / F output value as the actual air-fuel ratio up to point A in the figure, and the points A to B in the figure are indicated by dotted lines in the figure. Thus, an A / F output value different from the actual air-fuel ratio is output. (After the point B in the figure, the A / F output value is omitted.) When the output value of the A / F sensor 15 is incorrect in this way, the feedback correction coefficient FAF of the prior art is A in the figure. Up to the point, as normal feedback control, when the output value of the A / F sensor 15 switches between lean and rich, the FAF value skip control is performed, and the output value of the A / F sensor 15 is rich or lean output. In this case, integral control of the FAF value is performed. In this way, the air-fuel ratio is controlled to the target air-fuel ratio (theoretical air-fuel ratio). Here, when the output value of the A / F sensor 15 becomes large and rich after the point A in the figure, the feedback control tries to make the rich air-fuel ratio follow the target air-fuel ratio (theoretical air-fuel ratio) and perform fuel injection. In order to correct the amount by decreasing, the FAF value is decreased. Then, it is set to a guard value (fixed value: conventional) of the air-fuel ratio feedback correction coefficient FAF in the shaded area in the figure. For this reason, the fuel injection amount is greatly reduced and corrected by correcting the FAF value, and the actual air-fuel ratio becomes greatly lean.
[0041]
Further, when the output value of the A / F sensor 15 returns to a normal value at point B in the figure, a lean air-fuel ratio is output, so the FAF value is largely skipped and the fuel injection amount is reduced. It is controlled to a value that greatly corrects the increase. As described above, in the prior art, the fuel injection amount is greatly changed, so that the actual air-fuel ratio may be greatly disturbed as shown by the one-dot chain line in FIG. Therefore, in the present embodiment, as shown in FIG. 6B, the roughness detection value Δωgard is obtained from the roughness detection value calculation routine of FIG. 3, and based on the roughness detection value Δωgard, as shown in FIG. Is set to the final correction value RVCgard for the guard of the FAF value. The final correction value RVCgard is corrected so that the guard value for the FAF value becomes smaller than the reference value (for example, 1) of the feedback correction coefficient FAF value as the roughness detection value Δωgard is larger.
[0042]
That is, when the actual air-fuel ratio deviates greatly from the target air-fuel ratio (theoretical air-fuel ratio), if the FAF value is corrected so that the fuel injection amount is greatly reduced, the actual air-fuel ratio becomes lean and the roughness detection value Δωgard increases. However, in the present embodiment, when the roughness detection value Δωgard is larger than the reference value (for example, 1), the FAF guard values (FAFgardL, FAFgardR) are fed back when the final correction value RVCgard is set. Correction is performed so that the deviation of the correction coefficient FAF value from the reference value (for example, 1) becomes small. When the roughness detection value Δωgard is small, the guard value (FAFgardL, FAFgardR) of the FAF value is gradually corrected so that the deviation from the reference value (for example, 1) of the feedback correction coefficient FAF value becomes large.
[0043]
As described above, since the guard value for the feedback correction coefficient FAF value is corrected according to the roughness detection value Δωgard, the FAF value for erroneously correcting the fuel injection amount is set to the guard FAFgardL as shown in FIG. Is done. When the FAF value is set to the guard value FAFgardL, it is possible to prevent the fuel injection amount from being largely corrected to decrease. Therefore, as shown in FIG. 6A, the actual air-fuel ratio becomes large and the target air-fuel ratio (theoretical air-fuel ratio) It is prevented from coming off greatly. Further, even when the output value of the A / F sensor 15 deviates significantly from the actual air-fuel ratio, according to the present embodiment, the guard values (FAFgardL, FAFgardR) are set according to the rotational speed fluctuation. Since the correction is performed, it is suppressed that the feedback correction coefficient FAF value is erroneously corrected to increase the fuel injection amount, and the actual air-fuel ratio is suppressed from greatly deviating from the target air-fuel ratio (theoretical air-fuel ratio).
[0044]
As described above, in this embodiment, even if the output value of the A / F sensor 15 deviates significantly from the actual air-fuel ratio, the guard values (FAFgardL, FAFgardR) are corrected based on the roughness detection value Δωgard, so that feedback correction is performed. The coefficient FAF value is suppressed from erroneously correcting the fuel injection amount, and therefore, the actual air-fuel ratio is suppressed from greatly deviating from the target air-fuel ratio.
[0045]
In the present embodiment, the deviation between the guard value (FAFgardL, FAFgardR) and the reference value 1 is set to be small only when the roughness detection value is large, particularly when the rotational fluctuation amount is reduced. However, when either a sag or a protrusion is detected as the rotational speed variation based on the roughness detection value Δωgard, the deviation between the guard values (FAFgardL, FAFgardR) and the reference value 1 may be set to be small. However, both the depression and the protrusion may be used as the rotational speed fluctuation.
[0046]
In the present embodiment, the rotation speed variation detecting means corresponds to the flowchart of FIG. 3, and the guard value setting means corresponds to the flowchart of FIG.
[0047]
<Second Embodiment>
In the first embodiment, the guard values (FAFgardL, FAFgardR) for the feedback correction coefficient FAF value are set by the correction value calculated according to the roughness detection value Δωgard shown in FIG. In the present embodiment, a method of setting guard values (FAFgardL, FAFgardR) for the feedback correction coefficient FAF value is performed by a different method described below. In the following, for the guard value (FAFgardL, FAFgardR) calculation program shown in the flowchart of FIG. 7, the same processing steps as those in the flowchart of FIG. 2 used in the first embodiment are denoted by the same reference numerals, Different parts will be described.
[0048]
First, in the flowchart of FIG. 7, in step S100, it is determined whether or not the execution condition is satisfied. On the other hand, if it is established, the processing after step S110 is performed. In the process of step S110, the roughness detection value Δωgard is calculated as the variation amount of the engine rotation speed of the internal combustion engine as in the first embodiment. In step S200, a value obtained by subtracting the predetermined value COEF3 from the roughness detection value Δωgard is calculated. The roughness detection value Δωgard is a negative value when the rotational speed Ne drops. In the present embodiment, in order to correct the guard values (FAFgardL, FAFgardR) against the drop in the rotational speed Ne, the value obtained by subtracting the predetermined value COEF3 (negative value) from the roughness detection value Δωgard in step S210 is negative. If it is a value, the process proceeds to step S220.
[0049]
In step S220, the guard correction value RVCgard (n) corresponding to (Δωgard−COEF3) is calculated using the map of FIG. According to this map, as (Δωgard−COEF3) is larger, a larger correction value RVCgard (n) is set, and the process proceeds to step S240. In step S240, the final correction value LRVCgard (n) for correcting the guard values (FAFgardL, FAFgardR) for the feedback correction coefficient FAF value is set, and the process proceeds to step S160. On the other hand, if it is determined in step S210 that (Δωgard−COEF3) is a positive value, in step S230, the guard values (FAFgardL, FAFgardR) are gradually increased, that is, the reference value of the FAF value ( For example, the predetermined coefficient COEF4 is set to the final correction amount LRVCgard (n) so that the deviation with respect to 1) becomes large, and the process proceeds to step S160.
[0050]
In step S160, based on the final correction value LRVCgard (n) set in step S230 or step S240, the guard value (FAFgardL, FAFgardR) for the feedback correction coefficient FAF value is set as in the first embodiment. . As described above, even in the present embodiment, similarly to the first embodiment, even if the output value of the A / F sensor 15 deviates greatly from the actual air-fuel ratio, the guard value is based on the roughness detection value Δωgard. Since (FAFgardL, FAFgardR) is corrected, the feedback correction coefficient FAF value is prevented from erroneously correcting the fuel injection amount, and therefore, the actual air-fuel ratio is suppressed from greatly deviating from the target air-fuel ratio.
[0051]
In the present embodiment, the guard value setting means corresponds to the flowchart of FIG. 7 and functions.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of the present invention.
FIG. 2 is a guard value calculation program for the feedback correction coefficient FAF value according to the first embodiment of the present invention.
FIG. 3 is a program for calculating a roughness detection value according to the present invention.
FIG. 4 is a timing chart for calculating a roughness detection value based on an engine rotation angular velocity ω (n).
FIG. 5 is a diagram showing characteristics of a roughness detection value Δωgard and a correction value RVCgard according to the first embodiment of the present invention.
FIG. 6 is a timing chart showing the prior art and the present invention when the output of the A / F sensor is richer than the actual air-fuel ratio.
FIG. 7 is a guard value calculation program for the feedback correction coefficient FAF value according to the second embodiment of the present invention.
FIG. 8 is a diagram showing characteristics of a roughness detection value Δωgard and a correction value RVCgard according to the second embodiment of the present invention.
FIG. 9 is a program for air-fuel ratio feedback control in the first embodiment of the present invention;
[Explanation of symbols]
1 ... Engine as an internal combustion engine,
2 ... Intake pipe,
3 ... exhaust pipe,
19 ... Spark plug,
11 ... Intake valve,
12 ... exhaust valve,
18 ... Injector,
19 ... Spark plug,
20 ... Throttle sensor,
27: Reference position sensor,
28 ... Rotation angle sensor,
30. ECU.

Claims (2)

An air-fuel ratio sensor output value that is disposed in the exhaust passage of the internal combustion engine and detects an exhaust gas component in the exhaust passage and a feedback correction coefficient for feedback-controlling the fuel injection amount based on the target air-fuel ratio are calculated. In an air-fuel ratio control apparatus for an internal combustion engine,
A rotational speed fluctuation detecting means for detecting a rotational speed fluctuation of the internal combustion engine;
Guard value setting means for setting a guard value for the feedback correction coefficient based on the rotation fluctuation of the internal combustion engine detected by the rotation speed fluctuation detection means ;
The guard value setting means includes a lean guard value for the feedback correction coefficient for correcting the fuel injection amount to the decrease side, and / or a rich side guard value for the feedback correction coefficient for correcting the fuel injection amount to the increase side. And
When the rotation speed fluctuation is larger than a predetermined value by the rotation speed fluctuation detection means, the guard value setting means sets the rich side guard value and / or the lean side guard value set by the guard value setting means, An air-fuel ratio control apparatus for an internal combustion engine, wherein a deviation from a reference value of the feedback correction coefficient is set to be small according to the rotational speed fluctuation . The guard value setting means, when the rotation speed fluctuation detected by the rotation speed fluctuation detection means is smaller than the predetermined value, the rich side guard value and / or the lean side set by the guard value setting means. the guard value, the air-fuel ratio control apparatus for an internal combustion engine according to claim 1, characterized in that deviation with respect to a reference value of the feedback correction coefficient is set so as to gradually increase.

Images