JP2013238111A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device of an internal combustion engine capable of improving responsiveness of air-fuel ratio feedback control, in a scavenging region.SOLUTION: An air-fuel ratio sensor is provided in an exhaust passage. When an engine operating condition is not in a scavenging region in which the inside of a cylinder is scavenged, a fuel injection amount of each cylinder is corrected on the basis of a difference between an air-fuel ratio corresponding to an averaging output value obtained by applying averaging processing to an instantaneous value sequentially output from the air-fuel ratio sensor and a target air-fuel ratio so that an actual air-fuel ratio matches the target air-fuel ratio. When the engine operating condition is in the scavenging region, a fuel injection amount of each cylinder is corrected by a corrected injection amount calculated on the basis of a difference between the air-fuel ratio corresponding to the instantaneous value and the target air-fuel ratio so that the actual air-fuel ratio matches the target air-fuel ratio.

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control apparatus for an internal combustion engine suitable for executing control of an internal combustion engine mounted on a vehicle.

  Conventionally, as disclosed in Patent Document 1, for example, an internal combustion engine having air-fuel ratio sensors upstream and downstream of a catalyst disposed in an exhaust passage is known. Patent Document 1 discloses that air-fuel ratio feedback control is performed by an upstream air-fuel ratio sensor and that control constants used for the air-fuel ratio feedback control are corrected based on the downstream air-fuel ratio sensor output. Yes. The applicant has recognized the following documents including the above-mentioned documents as related to the present invention.

JP-A-9-88683 JP 2008-175201 A JP 2006-183553 A JP 2006-194112 A

  In general, it is desirable to attach an air-fuel ratio sensor to the exhaust manifold from the viewpoint of inter-cylinder imbalance detection and sensor warm-up. In the conventional air-fuel ratio feedback control, the output value (instantaneous value) of the air-fuel ratio sensor is subjected to a smoothing process in order to suppress the hunting of the air-fuel ratio correction against the rough air-fuel ratio. There is. The fuel injection amount can be corrected by calculating the corrected injection amount from the difference between the air-fuel ratio corresponding to the smoothed output value subjected to the annealing process and the target air-fuel ratio and reflecting this.

  By the way, in the scavenging area where the inside of the cylinder is scavenged, the specified amount of fuel is injected in a state where the amount of fresh air blown into the exhaust passage and the amount of air in the cylinder is insufficient by the amount of blow-through. The rich gas produced by the engine alternately hits the air-fuel ratio sensor. As a result, the output value (instantaneous value) of the air-fuel ratio sensor greatly repeats rich / lean. In such a scavenging region, if the corrected injection amount based on the above-described smoothing process is used for the air-fuel ratio feedback control, there is a concern that the time when the corrected injection amount is reflected is greatly delayed from the calculation delay. As a result, the responsiveness of the air-fuel ratio feedback control is deteriorated, and as a result, the emission may be deteriorated.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an air-fuel ratio control device for an internal combustion engine that can improve the responsiveness of air-fuel ratio feedback control in a scavenging region. To do.

In order to achieve the above object, a first invention is an air-fuel ratio control apparatus for an internal combustion engine comprising an air-fuel ratio sensor in an exhaust passage,
When the engine operating state is not in the scavenging region where the inside of the cylinder is scavenged, the smoothed output is applied to the instantaneous value sequentially output from the air-fuel ratio sensor so that the actual air-fuel ratio matches the target air-fuel ratio Non-scavenging region air-fuel ratio control means for correcting the fuel injection amount of each cylinder based on the difference between the air-fuel ratio corresponding to the value and the target air-fuel ratio;
When the engine operating state is in the scavenging region, the corrected injection amount calculated based on the difference between the air-fuel ratio corresponding to the instantaneous value and the target air-fuel ratio so that the actual air-fuel ratio matches the target air-fuel ratio And scavenging region air-fuel ratio control means for correcting the fuel injection amount of each cylinder.

The second invention is the first invention, wherein
The scavenging area air-fuel ratio control means includes:
Correction by the corrected injection amount with respect to the fuel injection amount when the engine operating state is in the scavenging region is started from the fuel injection amount of the cylinder whose fuel injection amount is determined immediately after the calculation of the corrected injection amount. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein:

The third invention is the first or second invention, wherein
The scavenging area air-fuel ratio control means includes:
If the air-fuel ratio corresponding to the instantaneous value is leaner than the set air-fuel ratio when the engine operating state is in the scavenging region, the exhaust stroke is detected in the cylinder that becomes the exhaust stroke immediately after the calculation of the corrected injection amount is completed. 3. An air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein an amount of fuel corresponding to the corrected injection amount is injected at a timing when the fuel injected into the exhaust passage is discharged.

  According to the present invention, it is possible to improve the responsiveness of the air-fuel ratio feedback control and to suppress the deterioration of the emission in the scavenging region where the delay of correction greatly affects the emission.

It is a conceptual block diagram for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure for demonstrating the fluctuation | variation of the air fuel ratio of the gas discharged | emitted by the exhaust passage in a scavenge area | region. It is a figure for demonstrating the air fuel ratio feedback control in a non-scavenge area | region. It is a figure for demonstrating the problem at the time of performing the air fuel ratio feedback control using the smoothed output value in a scavenge area | region. FIG. 6 is a diagram for explaining a control example when a state occurs in which the overall air-fuel ratio of gas discharged from the internal combustion engine in the scavenging region becomes rich in the system of the first embodiment. FIG. 6 is a diagram for describing a control example when a state occurs in which the overall air-fuel ratio of gas discharged from the internal combustion engine becomes lean in the scavenging region in the system of the first embodiment. 4 is a flowchart of a control routine executed by an ECU 50 in the system according to the first embodiment. FIG. 10 is a diagram for describing an example of characteristic control in the system of the second embodiment. 7 is a flowchart of a control routine executed by an ECU 50 in the system according to the second embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
FIG. 1 is a conceptual configuration diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes a spark ignition type internal combustion engine (hereinafter also simply referred to as an engine) 10. The internal combustion engine 10 is mounted on a vehicle or the like and used as a power source. Although the internal combustion engine 10 shown in FIG. 1 is an in-line four-cylinder type, in the present invention, the number of cylinders and the cylinder arrangement are not limited thereto. For convenience, in the following description, the first to fourth cylinders are denoted as # 1 to # 4, respectively.

  Connected to the internal combustion engine 10 are an intake passage 12 for taking air into the cylinder and an exhaust passage 14 for discharging exhaust gas from the cylinder. In the vicinity of the inlet of the intake passage 12, an air flow meter 16 that outputs a signal corresponding to the flow rate of air sucked into the intake passage 12 is provided. A compressor 18 a of the supercharger 18 is disposed downstream of the air flow meter 16. The supercharger 18 includes a turbine 18b that is integrally connected to the compressor 18a and that is operated by exhaust energy of exhaust gas. The compressor 18a is rotationally driven by the exhaust energy of the exhaust gas input to the turbine 18b.

  An intercooler 20 that cools the air compressed by the compressor 18a is disposed in the intake passage 12 on the downstream side of the compressor 18a. An electronically controlled throttle valve 22 for adjusting the amount of air flowing through the intake passage 12 is disposed downstream of the intercooler 20. A surge tank 24 for equalizing the amount of air supplied to each cylinder is provided downstream of the throttle valve 22. An intake port 26 is provided downstream of the surge tank 24 for each cylinder. The surge tank 24 and the intake port 26 constitute a part of the intake passage 12.

  In the vicinity of the intake port 26, a port injector 28 for injecting fuel into the intake port 26 toward the cylinder (combustion chamber) is attached. An intake valve 29 that opens and closes between the cylinder and the intake passage 12 is provided at the downstream end of the intake passage 12. An in-cylinder injector 30 for directly injecting fuel into the cylinder and an ignition plug 32 for igniting the air-fuel mixture are attached in the cylinder.

  An exhaust valve 34 that opens and closes between the cylinder and the exhaust passage 14 is provided at the upstream end of the exhaust passage 14. An exhaust manifold 35 that constitutes a part of the exhaust passage 14 is provided downstream of the exhaust valve 34 of each cylinder. The exhaust manifold 35 joins downstream. An air-fuel ratio sensor 36 that outputs a signal corresponding to the air-fuel ratio of the passing gas is provided in the vicinity of the joining portion of the exhaust manifold 35. In the exhaust passage 14 after merging, a turbine 18b that is rotated by the energy of the exhaust gas is disposed. A catalyst 37 for purifying harmful components in the exhaust gas is provided downstream of the turbine 18b. For example, a three-way catalyst is used as the catalyst 37.

  The system of this embodiment further includes an ECU (Electronic Control Unit) 50. ECU50 is comprised by the arithmetic processing apparatus provided with the memory circuit containing ROM, RAM, etc., for example. On the input side of the ECU 50, in addition to the air flow meter 16 and the air-fuel ratio sensor 36 described above, the crank angle sensor 52 for detecting the crank angle and the engine speed, and the pressure in the surge tank 24 (hereinafter referred to as surge tank pressure). .) Is connected to various sensors for detecting the operating state of the internal combustion engine 10, such as an intake pressure sensor 54.

  On the output side of the ECU 50, the internal combustion engine 10 such as the throttle valve 22, the port injector 28, the in-cylinder injector 30, the ignition plug 32, and the variable valve timing device (hereinafter referred to as VVT (Variable Valve Timing)) 56. Various actuators for controlling the operation state are connected. The VVT 56 can change the valve timing of at least one of the intake valve 29 and the exhaust valve 34.

  The ECU 50 controls the operating state of the internal combustion engine 10 by driving various actuators according to a predetermined program based on various sensor outputs. For example, the crank angle and the engine speed are calculated based on the output of the crank angle sensor 52, and the intake air amount is calculated based on the output of the air flow meter 16. Further, the engine load (load factor) is calculated based on the intake air amount, the engine speed, the intake pressure, and the like. A basic fuel injection amount (for example, a basic amount for setting the exhaust air-fuel ratio to the target air-fuel ratio) according to the engine operating state is acquired from a map including parameters relating to the intake air amount, the load, and the like. Based on the basic fuel injection amount, the fuel injection amounts of the port injector 28 and the in-cylinder injector 30 are calculated. The fuel injection timing and ignition timing are determined based on the crank angle. When these times arrive, the injectors 28 and 30 and the spark plug 32 are driven. Thereby, the air-fuel mixture is combusted in the cylinder, and the internal combustion engine 10 can be operated.

(Regarding fluctuations in the air-fuel ratio in the scavenge region)
FIG. 2 is a diagram for explaining fluctuations in the air-fuel ratio of the gas discharged to the exhaust passage 14 in the scavenging region. Here, the scavenging region is a supercharging region and a valve overlap region, and is an operation region in which the surge tank pressure is higher than the exhaust pressure and a valve overlap amount that can scavenge the inside of the cylinder by the VVT 56 is set. .

  FIG. 2A is a diagram showing the intake stroke during the valve overlap period. When the valve overlap amount capable of scavenging the inside of the cylinder is set by the VVT 56, a part of the fresh air is blown through the exhaust passage 14. Therefore, the air-fuel ratio of the gas that reaches the air-fuel ratio sensor 36 becomes lean. Therefore, the air-fuel ratio corresponding to the instantaneous value of the air-fuel ratio sensor 36 becomes lean.

  FIG. 2B is a diagram illustrating the intake stroke after the valve overlap period has elapsed. At this time, the combustion chamber is in a state where air is insufficient by the amount of air blown through in (A). Therefore, when the fuel injection amount based on the basic fuel injection amount is injected from the in-cylinder injector 30, the air-fuel ratio of the in-cylinder gas becomes rich.

  (C) of FIG. 2 is a diagram showing an exhaust stroke after (B). Since the air-fuel ratio of the cylinder interior gas is rich, the air-fuel ratio of the gas discharged to the exhaust passage is also rich. Therefore, the air-fuel ratio corresponding to the instantaneous value of the air-fuel ratio sensor 36 becomes rich.

  As shown in FIGS. 2A to 2C, in the scavenging region, even if the overall air-fuel ratio of the gas discharged from the engine 10 is the target air-fuel ratio, it corresponds to the output value of the air-fuel ratio sensor 36. As for the air-fuel ratio, rich and lean are repeated.

[Characteristic Control in Embodiment 1]
In view of such a change in the air-fuel ratio in the scavenging region, in the first embodiment of the present invention, regarding the air-fuel ratio control, different processes are executed in the scavenging region and the non-scavenging region other than the scavenging region. The system of the present embodiment has an air-fuel ratio feedback control function that corrects the fuel injection amount so that the actual air-fuel ratio matches the target air-fuel ratio. The air-fuel ratio feedback control function corresponds to the output value detected by the air-fuel ratio sensor 36 separately from the routine for obtaining the basic fuel injection amount according to the engine operating state from a map including parameters relating to the intake air amount and load. A routine for calculating a corrected injection amount based on a difference between the air-fuel ratio and the target air-fuel ratio; Once the corrected injection amount is calculated, this corrected injection amount is reflected in the basic fuel injection amount according to the current engine operating state until the next fuel injection amount / injection timing is determined, and the basic fuel injection amount is corrected. Is done.

(Air-fuel ratio feedback control in non-scavenging range)
In the non-scavenging region, in order to prevent hunting for air-fuel ratio correction, an output value (hereinafter referred to as a smoothed output value) obtained by subjecting a group of instantaneous values sequentially output from the air-fuel ratio sensor 36 to a smoothing process. The corrected injection amount is calculated based on the difference between the air-fuel ratio that is used and the smoothed output value and the target air-fuel ratio. The basic fuel injection amount is corrected by the corrected injection amount. In the non-scavenging region, the fuel injection amounts of all cylinders are uniformly corrected.

  FIG. 3 is a diagram for explaining air-fuel ratio feedback control in the non-scavenging region. 3, 60 represents the change in the air-fuel ratio corresponding to the smoothed output value, and 62 represents the change in the air-fuel ratio corresponding to the instantaneous output value (instantaneous value). After the air-fuel ratio sensor 36 suddenly outputs an instantaneous value corresponding to the air-fuel ratio richer than the target air-fuel ratio at time t1, the smoothed output value is calculated with a delay. Therefore, when the smoothed output value is used, reflection of the corrected injection amount is delayed. However, in the non-scavenging region, only the combustion gas hits the air-fuel ratio sensor 36, so the air-fuel ratio corresponding to the smoothed output value changes in the vicinity of the target air-fuel ratio. For this reason, the air-fuel ratio does not greatly deviate from the target air-fuel ratio, and the influence on emissions is small. According to such air-fuel ratio feedback control, the actual air-fuel ratio can be matched with the target air-fuel ratio while suppressing hunting for air-fuel ratio correction using the smoothed output value in the non-scavenging region.

(Air-fuel ratio feedback control in scavenging region)
On the other hand, when the air-fuel ratio feedback control using the smoothed output value is executed in the scavenge region as in the non-scavenge region, the following problem occurs.

  FIG. 4 is a diagram for explaining a problem in the case where the smoothed output value is used for air-fuel ratio feedback control in the scavenging region. 4, 64 represents the change in the air-fuel ratio corresponding to the smoothed output value, 66 represents the change in the air-fuel ratio corresponding to the instantaneous output value (instantaneous value), and # 1 to # 4 represent the blown-out cylinders. Yes. In the scavenging region, with respect to the instantaneous value detected at time t1, the air-fuel ratio deviates further to the rich side from the state where the air-fuel ratio corresponding to the sensor output originally deviates from the target air-fuel ratio. When the smoothed output value is used for air-fuel ratio feedback control, the correction injection amount is reflected slowly because of the smoothing process. Furthermore, since correction is performed uniformly for all cylinders, the air-fuel ratio correction itself takes time.

  Unlike the non-scavenge region, the scavenge region is far away from the target air-fuel ratio, and the correction delay greatly affects the emission. Therefore, it is desired to improve the responsiveness of the air-fuel ratio feedback control and to reduce the emission at an early stage.

  Therefore, in the system of the present embodiment, in the scavenging region, correction is made based on the difference between the air-fuel ratio corresponding to the instantaneous value of the air-fuel ratio sensor 36 and the target air-fuel ratio so that the actual air-fuel ratio matches the target air-fuel ratio. The injection amount is calculated. Then, the basic fuel injection amount of a cylinder (hereinafter, also simply referred to as “next cylinder” or “second cylinder”) whose fuel injection amount is determined immediately after the calculation of the corrected injection amount is corrected by this corrected injection amount. It was decided. According to this, the corrected injection amount can be reflected earlier than using the smoothed output value. As a result, it becomes possible to improve the responsiveness of the air-fuel ratio feedback control and to reduce the emission at an early stage.

(Specific example of air-fuel ratio feedback control in the scavenge region)
More specifically, an example of air-fuel ratio feedback control in the scavenge region will be described with reference to FIGS. FIG. 5 is a diagram for explaining a control example when a state occurs in which the overall air-fuel ratio of the gas discharged from the engine 10 becomes rich in the scavenging region. In FIG. 5, 68 represents the change in the air-fuel ratio corresponding to the smoothed output value, 70 represents the change in the air-fuel ratio corresponding to the instantaneous output value (instantaneous value), and # 1 to # 4 represent the blow-off cylinders. Yes.

  As described above, in the exhaust stroke of the blow-off cylinder, the rich air-fuel ratio combustion gas originally deviating from the target air-fuel ratio hits the air-fuel ratio sensor 36. At time t1, the instantaneous value corresponding to the rich-side air-fuel ratio further. Is output. Therefore, a corrected injection amount corresponding to the decrease is calculated based on the instantaneous value, and this corrected injection amount is used as the basic fuel of cylinder # 4 (that is, the cylinder whose fuel injection amount is determined immediately after the calculation of the corrected injection amount). Reflecting the injection amount, the basic fuel injection amount is corrected to decrease. For example, the fuel injection amount by the in-cylinder injector 30 of the cylinder # 4 is reduced. According to this, the corrected injection amount is reflected earlier than in the case of performing the annealing process, and the responsiveness of the air-fuel ratio feedback control is enhanced. Further, by correcting only the fuel injection amount of the next cylinder, the time until the actual air-fuel ratio converges to the target air-fuel ratio is shortened as compared with the case where correction is performed uniformly for all cylinders.

  In the example of FIG. 5, when the smoothed output value is used, it takes time until time t4. However, when the instantaneous value is used, the correction is completed at time t3 earlier than time t4, and the actual air-fuel ratio is obtained. Converges to the target air-fuel ratio. Since the air-fuel ratio control can be completed within the cycle, the deterioration of emissions can be minimized.

  FIG. 6 is a diagram for describing a control example when a state occurs in which the overall air-fuel ratio of the gas discharged from the engine 10 becomes lean in the scavenging region. In FIG. 6, 72 represents the change in the air-fuel ratio corresponding to the smoothed output value, 74 represents the change in the air-fuel ratio corresponding to the instantaneous output value (instantaneous value), and # 1 to # 4 represent the blow-by cylinders. Yes.

  As described above, in the valve overlap period of the blow-off cylinder, the lean air-fuel ratio originally deviating from the target air-fuel ratio hits the air-fuel ratio sensor 36, and at time t1, it further corresponds to the lean-side air-fuel ratio. Instantaneous value is output. Therefore, a corrected injection amount corresponding to the increased amount is calculated according to the instantaneous value, and this corrected injection amount is used as the basic fuel for the next cylinder # 3 (that is, the cylinder whose fuel injection amount is determined immediately after the calculation of the corrected injection amount). Reflecting the injection amount, the basic fuel injection amount is corrected to be increased. For example, the fuel injection amount by the in-cylinder injector 30 of the next cylinder # 3 is increased. According to this, the corrected injection amount is reflected earlier than in the case of performing the annealing process, and the responsiveness of the air-fuel ratio feedback control is enhanced. Further, by correcting only the fuel injection amount of the next cylinder, the time until the actual air-fuel ratio converges to the target air-fuel ratio is shortened as compared with the case where correction is performed uniformly for all cylinders.

  In the example of FIG. 6, when the instantaneous value is used, the correction is completed at time t2 earlier than when the smoothed output value is used, and the actual air-fuel ratio converges to the target air-fuel ratio. Since the air-fuel ratio control can be completed within the cycle, the deterioration of emissions can be minimized.

  FIG. 7 is a flowchart of a control routine executed by the ECU 50 in order to realize the above-described operation. In the routine shown in FIG. 7, first, the ECU 50 determines whether or not the valve overlap amount is larger than a predetermined value (step S100). As the predetermined value, a valve overlap amount capable of scavenging the cylinder is set. The ECU 50 calculates the actual overlap amount from the phase of the VVT 56 and compares it with a predetermined value. When the valve overlap amount is less than or equal to the predetermined value, the process of this routine is terminated, and the above-described air-fuel ratio feedback control in the non-scavenge region is executed.

  On the other hand, when the valve overlap amount is larger than the predetermined value, the ECU 50 next determines whether or not the surge tank pressure is higher than the exhaust pressure (step S110). For example, the determination condition is satisfied in the supercharging region. If the determination condition is not satisfied, the processing of this routine is terminated, and the above-described air-fuel ratio feedback control in the non-scavenge region is executed.

  On the other hand, when the determination condition is satisfied, it is determined that the portion of the intake air is in the scavenge region where the air is blown through the cylinder (step S120), and the air-fuel ratio feedback control in the scavenge region described above is performed in the subsequent steps. Executed.

  First, the ECU 50 determines whether or not the air-fuel ratio corresponding to the raw voltage (instantaneous value) of the air-fuel ratio sensor 36 when part of the intake air is blown through is richer or leaner than the set air-fuel ratio ( Step S130). This set air-fuel ratio is a lean-side set air-fuel ratio obtained by adding, to the target air-fuel ratio, the amount that becomes lean when part of fresh air blows through the exhaust passage 14 during the valve overlap period at the beginning of the intake stroke. In the stroke, the rich side set air-fuel ratio is obtained by subtracting from the target air-fuel ratio the amount that becomes rich due to the amount of air in the cylinder being insufficient by the amount of blow-through. The median value of the two set air-fuel ratios is a target air-fuel ratio (for example, the theoretical air-fuel ratio). For example, when the air-fuel ratio corresponding to the instantaneous value of the air-fuel ratio sensor deviates from the set air-fuel ratio of the stroke, it can be determined that the air-fuel ratio needs to be corrected. In this case, a correction injection amount necessary for returning the actual air-fuel ratio to the target air-fuel ratio is calculated (step S140).

  After calculating the corrected injection amount, the basic fuel injection amount of the cylinder (next cylinder) in which the fuel injection amount is determined immediately after completion of the calculation of the corrected injection amount is corrected by this corrected injection amount (step S150). For example, fuel injection based on the corrected fuel injection amount is performed from the in-cylinder injector 30 in the intake stroke.

  As described above, according to the routine shown in FIG. 7, the corrected injection amount can be reflected earlier by using the instantaneous value in the scavenging region as compared with the case of using the smoothing process. Therefore, in the scavenging region where the delay in correction greatly affects the emission, the responsiveness of the air-fuel ratio feedback control can be improved and the emission can be reduced.

  In the first embodiment described above, the air-fuel ratio sensor 36 corresponds to the “air-fuel ratio sensor” in the first invention, and the air-fuel ratio feedback control in the non-scavenge area described above corresponds to the “non-scavenge area in the first invention. The above-mentioned air-fuel ratio feedback control in the scavenge region corresponds to the “scavenge region air-fuel ratio control unit” in the first and second inventions. Further, here, the “scavenge region air-fuel ratio control means” in the second aspect of the present invention is realized by the ECU 50 executing the processing of steps S130 to S150.

Embodiment 2. FIG.
[System Configuration of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. The system of the present embodiment can be realized by causing the ECU 50 to execute a routine of FIG. 9 described later in the configuration shown in FIG.

  In the first embodiment described above, with reference to FIGS. 6 and 7, when an instantaneous value corresponding to an air-fuel ratio leaner than the set air-fuel ratio is output during the valve overlap period in the initial stage of the intake stroke in the scavenging region, The case where the correction injection amount is calculated using the instantaneous value and the basic fuel injection amount of the next cylinder is increased and corrected has been described. However, even when the corrected injection amount is calculated using the instantaneous value, there may be a case where the calculation of the corrected injection amount is not in time for the latest determination of the fuel injection amount / injection timing. In such a case, if the determination timing of the fuel injection amount / injection timing of the next cylinder is waited, the corrected injection amount is reflected in the basic fuel injection amount as described in the first embodiment. It is desirable if the actual air-fuel ratio can be matched with the target air-fuel ratio.

[Characteristic Control in Embodiment 2]
Therefore, in the system of the present embodiment, when the air-fuel ratio corresponding to the instantaneous value is leaner than the set air-fuel ratio when the engine operating state is in the scavenging region, the exhaust stroke is calculated immediately after the calculation of the corrected injection amount is completed. In this cylinder, the amount of fuel corresponding to the corrected injection amount is injected at the timing when the fuel injected during the exhaust stroke is discharged to the exhaust passage 14. That is, prior to the correction injection amount reflection timing in the air-fuel ratio feedback control in the scavenging region described in the first embodiment, an amount of fuel corresponding to the correction injection amount is injected.

  FIG. 8 is a diagram for describing an example of characteristic control in the second embodiment. In FIG. 8, 76 represents the change in the air-fuel ratio corresponding to the smoothed output value, 78 represents the change in the air-fuel ratio corresponding to the instantaneous output value (instantaneous value), and # 1 to # 4 represent the blow-off cylinders. Yes.

  As described above, in the valve overlap period of the blow-off cylinder, when fresh air originally deviating from the target air-fuel ratio hits the air-fuel ratio sensor 36, an instantaneous value corresponding to the lean-side air-fuel ratio is further output at time t1. ing. In the second embodiment, a corrected injection amount corresponding to the increased amount is calculated according to the instantaneous value, and an amount of fuel corresponding to the corrected injection amount is injected in a cylinder that becomes an exhaust stroke immediately after the completion of the calculation. In the example of FIG. 8, the cylinder (next cylinder) for which the fuel injection amount is determined immediately after completion of the calculation of the correction injection amount is # 4. However, for the # 4 cylinder, the correction injection amount is not waited for. An amount of fuel corresponding to is injected. In addition, when the fuel is injected from the in-cylinder injector 30, the injection timing is injected at an arbitrary timing during the exhaust stroke, and when the fuel is injected from the port injector 28, the injection is performed at least at the timing of the valve overlap period. .

  FIG. 9 is a flowchart of a control routine executed by the ECU 50 in order to realize the above-described function. This routine is the same as the routine shown in FIG. 7 except that the process of step S130 is replaced with step S230 and the process of step S150 is replaced with step S250. In FIG. 9, the same steps as those shown in FIG. 7 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 9, in step S230, the ECU 50 determines that the air-fuel ratio corresponding to the raw voltage (instantaneous value) of the air-fuel ratio sensor 36 when part of the intake air is blown is leaner than the set air-fuel ratio. It is determined whether or not there is (step S230). The set air-fuel ratio is a lean-side set air-fuel ratio obtained by adding, to the target air-fuel ratio, the amount that becomes lean when a part of fresh air blows into the exhaust passage 14 during the valve overlap period at the beginning of the intake stroke. In this case, the median value of the two set air-fuel ratios, which are rich side set air-fuel ratios obtained by subtracting the amount that becomes rich due to the shortage of air amount in the cylinder by the amount of blow-through, is the target air-fuel ratio (for example, Theoretical air / fuel ratio).

  After the correction injection amount is calculated in step S140, an amount of fuel corresponding to the correction injection amount is injected in the cylinder that becomes the exhaust stroke immediately after the completion of the calculation (step S250). Since the injection timing is as described above, the description is omitted.

  As described above, according to the routine shown in FIG. 9, when the air-fuel ratio of the gas blown through in the scavenge region is leaner than the set air-fuel ratio, the air-fuel ratio feedback control in the scavenge region described in the first embodiment is performed. An amount of fuel corresponding to the corrected injection amount can be injected prior to the correction injection amount reflecting timing. Therefore, it becomes possible to make the actual air-fuel ratio coincide with the target air-fuel ratio earlier. As a result, emission can be reduced.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Intake passage 14 Exhaust passage 16 Air flow meter 18, 18a, 18b Supercharger, compressor, turbine 22 Throttle valve 24 Surge tank 26 Intake port 28 Port injector 29 Intake valve 30 In-cylinder injector 34 Exhaust valve 35 Exhaust manifold 36 Air-fuel ratio sensor 37 Catalyst 50 ECU (Electronic Control Unit)
52 Crank Angle Sensor 54 Intake Pressure Sensor 56 VVT (Variable Valve Timing)

Claims (3)

In an air-fuel ratio control apparatus for an internal combustion engine provided with an air-fuel ratio sensor in an exhaust passage,
When the engine operating state is not in the scavenging region where the inside of the cylinder is scavenged, the smoothed output is applied to the instantaneous value sequentially output from the air-fuel ratio sensor so that the actual air-fuel ratio matches the target air-fuel ratio Non-scavenging region air-fuel ratio control means for correcting the fuel injection amount of each cylinder based on the difference between the air-fuel ratio corresponding to the value and the target air-fuel ratio;
When the engine operating state is in the scavenging region, the corrected injection amount calculated based on the difference between the air-fuel ratio corresponding to the instantaneous value and the target air-fuel ratio so that the actual air-fuel ratio matches the target air-fuel ratio An air-fuel ratio control apparatus for an internal combustion engine, comprising: scavenging region air-fuel ratio control means for correcting the fuel injection amount of each cylinder by The scavenging area air-fuel ratio control means includes:
Correction by the corrected injection amount with respect to the fuel injection amount when the engine operating state is in the scavenging region is started from the fuel injection amount of the cylinder whose fuel injection amount is determined immediately after the calculation of the corrected injection amount. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein: The scavenging area air-fuel ratio control means includes:
If the air-fuel ratio corresponding to the instantaneous value is leaner than the set air-fuel ratio when the engine operating state is in the scavenging region, the exhaust stroke in the cylinder that becomes the exhaust stroke immediately after the calculation of the corrected injection amount is completed. 3. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein an amount of fuel corresponding to the corrected injection amount is injected at a timing when the fuel injected into the exhaust passage is discharged into the exhaust passage.

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