JP4904999B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

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 that realizes highly robust air-fuel ratio feedback control by dealing with hydrogen that adversely affects an exhaust gas sensor at the generation stage.

  Conventionally, an oxygen concentration in an exhaust gas is detected by an exhaust gas sensor such as an oxygen sensor or an A / F sensor disposed in an exhaust passage of an internal combustion engine, and an air-fuel ratio is set to a target air-fuel ratio (for example, based on the output of the exhaust gas sensor). 2. Description of the Related Art An air-fuel ratio control device that controls to a theoretical air-fuel ratio) is known. By the way, exhaust gas contains hydrogen in addition to oxygen. Since hydrogen diffuses more easily than oxygen, it reaches the exhaust gas sensor electrode faster than oxygen. Further, when this hydrogen and oxygen react at the electrode, the oxygen concentration in the vicinity of the electrode becomes lower than the balanced oxygen concentration of the exhaust existing around the exhaust gas sensor. The oxygen concentration balanced here is the oxygen concentration after the combustible component (hydrogen or the like) in the exhaust gas completely reacts with the oxygen in the exhaust gas, and corresponds to the true exhaust air-fuel ratio.

  In other words, the above state is a state where oxygen that should originally reach the electrode does not reach the electrode due to the influence of hydrogen. At this time, based on the output of the exhaust gas sensor, the exhaust air / fuel ratio is higher than the true exhaust air / fuel ratio. It will be detected close to rich. That is, hydrogen acts on the exhaust gas sensor so as to erroneously detect that the exhaust air / fuel ratio is richer than the true exhaust air / fuel ratio. As a result, when the target air-fuel ratio is controlled based on the output level of the exhaust gas sensor at this time, the exhaust air-fuel ratio corresponding to the output level is shifted to the lean side. Therefore, if feedback control is executed to control the air-fuel ratio to the stoichiometric air-fuel ratio in this state, the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio, so that the exhaust purification action of the three-way catalyst is reduced. There is a risk that the emission of this will increase significantly. In order to deal with hydrogen that adversely affects the exhaust gas sensor in this way, for example, in Patent Document 1, a hydrogen concentration calculation unit is provided, and the higher the hydrogen concentration, the higher the air concentration is controlled to the rich side, and the leaner the air-fuel ratio due to hydrogen. An air-fuel ratio control apparatus for an internal combustion engine that corrects the shift is proposed.

JP 11-247687 A

  By the way, since hydrogen is easily generated when a rich air-fuel mixture burns, the amount of hydrogen generated increases if the mixing property of the air-fuel mixture is poor. In contrast, when an airflow control valve for generating a swirling airflow such as a tumble flow or a swirl flow is provided in the intake passage in the combustion chamber, the mixing of the air-fuel mixture with a strong swirling airflow for the purpose of improving combustion, etc. In order to improve the air flow control valve, the air flow control valve is generally controlled to be half open. FIG. 8 is a diagram illustrating an example of the opening / closing behavior of the airflow control valve. For example, as shown in FIG. 8, the air flow control valve is appropriately controlled from full open to half open for the purpose of improving combustion. As described above, when the airflow control valve is controlled to be half open, the mixing property of the air-fuel mixture is improved. On the other hand, depending on the open state of the airflow control valve (for example, fully open), the mixing property of the air-fuel mixture is decreased and the relative mixing property In addition, the amount of hydrogen generated increases. In this case, since hydrogen easily acts on the exhaust gas sensor correspondingly, the air-fuel ratio detection accuracy may be reduced.

  In the three-way catalyst, hydrogen reacts with oxygen and burns, so that hydrogen is generally greatly reduced downstream of the three-way catalyst. However, when the air-fuel ratio varies between the cylinders of the internal combustion engine, hydrogen contained in the exhaust gas discharged from the cylinder in which the air-fuel ratio becomes rich is not only upstream of the three-way catalyst but also downstream of each cylinder. This also has an adverse effect on the exhaust gas sensor. FIG. 9 shows the hydrogen concentration of the exhaust gas discharged from the internal combustion engine and the hydrogen concentration of the exhaust gas discharged from the three-way catalyst when the air-fuel ratio does not vary between cylinders and the air-fuel ratio varies between cylinders. It is a figure shown about a certain case. FIG. 9 shows the hydrogen concentration when measured with an in-line four-cylinder internal combustion engine, and reproduces the case where the air-fuel ratio varies by making the air-fuel ratio of each cylinder rich, lean, lean, and rich in order. is doing.

  FIG. 9 shows that the air-fuel ratio varies between cylinders when the hydrogen concentration is discharged from the internal combustion engine (after the internal combustion engine) and when discharged from the three-way catalyst (after the three-way catalyst). You can see that it is higher. The vertical axis indicating the hydrogen concentration is a log scale. Here, especially when exhausted from the three-way catalyst, the hydrogen concentration is high because the amount of oxygen in the three-way catalyst is insufficient and the hydrogen exhausted from the cylinder whose air-fuel ratio has become rich is oxygen. It is thought that this is the result of not being able to react sufficiently.

  It can be seen from FIG. 9 that when the air-fuel ratio varies between cylinders, the hydrogen concentration in the exhaust gas increases and the risk of adverse effects on the exhaust gas sensor increases, but indefinite disturbance such as the air-fuel ratio varies between cylinders in this way. In addition to correcting the air-fuel ratio feedback control as in the proposed technique described above, it is effective to first implement the air-fuel ratio feedback control by dealing with hydrogen from the viewpoint of the generation source. You can say that.

  Therefore, the present invention has been made in view of the above problems, and by dealing with hydrogen that adversely affects the exhaust gas sensor at the generation stage, the air-fuel ratio of the internal combustion engine that can realize highly robust feedback control of the air-fuel ratio can be realized. An object is to provide a control device.

In order to solve the above problems, the present invention is an air-fuel ratio control apparatus for an internal combustion engine that controls an air-fuel ratio of an internal combustion engine in which an airflow control valve for generating a swirling airflow in a combustion chamber is disposed in an intake passage. Te, conditions for executing the feedback control of the predetermined air-fuel ratio is established, and open state of the airflow control valve is in a state mixing of increases of the air-fuel mixture to generate strong swirling airflow into the combustion chamber half open characterized in the state, and executes a feedback control of the air-fuel ratio, when the open valve state of the airflow control valve is not in the half open state, further comprising a feedback control execution means for stopping the execution of the feedback control of the air-fuel ratio And Here, as described above, the mixing property of the air-fuel mixture changes depending on the open state of the airflow control valve, and the airflow control valve is controlled to be in the valve opening state so that the mixing property of the air-fuel mixture becomes high for the purpose of improving combustion or the like. If so, the amount of hydrogen discharged from the combustion chamber is also reduced. Furthermore, since the mixing property of the air-fuel mixture is high in such a state, even if the air-fuel ratio of each cylinder varies, the amount of hydrogen discharged from the cylinder in which the air-fuel ratio becomes rich can be reduced. The present invention has been made in view of the above points, and according to the present invention, it is possible to cope with hydrogen at the generation stage and to realize highly robust air-fuel ratio feedback control.

The present invention further based on the open state of the airflow control valve may comprise a sub-feedback control the actual Gyote stage that perform sub-feedback control of the air-fuel ratio to correct the air-fuel ratio feedback control. Here, in feedback control of the air-fuel ratio, there is known a double sensor system that performs feedback control of the air-fuel ratio using exhaust gas sensors provided upstream and downstream of the three-way catalyst. In this double sensor system, an air-fuel ratio for correcting F / B control of an air-fuel ratio using an exhaust gas sensor provided upstream of the three-way catalyst using an exhaust gas sensor provided downstream of the three-way catalyst is used. Sub feedback control is performed. Even in the case of such a double sensor system, according to the present invention, the adverse effect of hydrogen on the exhaust gas sensor downstream of the three-way catalyst is reduced. Therefore, highly robust air-fuel ratio feedback control including air-fuel ratio sub-feedback control is performed. realizable. Incidentally, the feedback control the actual Gyote stage or sub-feedback control the actual Gyote stage is preferably open state of the airflow control valve permits the execution of the feedback control or the sub feedback control of the air-fuel ratio when the half open position. This is due to the fact that when the airflow control valve is opened halfway, a strong swirling airflow is generated in the combustion chamber, and the mixing property of the air-fuel mixture becomes high.

  ADVANTAGE OF THE INVENTION According to this invention, the air-fuel ratio control apparatus of the internal combustion engine which can implement | achieve highly robust air-fuel ratio feedback control can be provided by dealing with the hydrogen which has an adverse effect on the exhaust gas sensor at the generation stage.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram schematically showing an air-fuel ratio control apparatus for an internal combustion engine according to the present embodiment realized by an ECU (Electronic Control Unit) 1 together with an internal combustion engine system 100. The internal combustion engine system 100 includes an intake system 10, an exhaust system 20, a fuel injection system 30, and an internal combustion engine 50. The intake system 10 is configured to introduce air into the internal combustion engine 50, and includes an air cleaner 11 for filtering intake air, an air flow meter 12 for measuring the amount of air, a throttle valve 13 for adjusting the flow rate of intake air, And the intake manifold 15 that distributes intake air to the cylinders of the internal combustion engine 50, and intake pipes that are appropriately disposed between them.

  The exhaust system 20 includes an exhaust manifold 21, a three-way catalyst 22, a silencer (not shown), and an intake pipe appropriately disposed between these components. The exhaust manifold 21 is configured to join the exhaust from each cylinder, and the exhaust passage branched according to each cylinder is gathered into one exhaust passage on the downstream side. The three-way catalyst 22 is configured to purify exhaust gas, and performs oxidation of hydrocarbons HC and carbon monoxide CO and reduction of nitrogen oxides NOx. The three-way catalyst 22 can simultaneously purify the above three components only when the air-fuel ratio of the inflowing exhaust is within a very narrow range near the stoichiometric air-fuel ratio, so that the exhaust air-fuel ratio flowing into the three-way catalyst 22 can be reduced. Maintaining near the stoichiometric air-fuel ratio is important for reducing emissions. For this reason, the exhaust system 20 has an A / F sensor 23 for detecting the air-fuel ratio linearly based on the oxygen concentration in the exhaust, upstream of the three-way catalyst 22, and the air-fuel ratio is reduced to the theoretical sky based on the oxygen concentration in the exhaust. An oxygen sensor 24 for detecting whether the fuel is richer or leaner than the fuel ratio is provided downstream of the three-way catalyst 22.

  The combination of the exhaust gas sensors disposed upstream and downstream of the three-way catalyst 22 is not limited to this, and for example, the A / F sensor 23 or the oxygen sensor 24 is disposed both upstream and downstream of the three-way catalyst 22. Any suitable combination may be used. Further, instead of a double sensor system that performs air-fuel ratio feedback (hereinafter also simply referred to as F / B) control using exhaust gas sensors disposed upstream and downstream of the three-way catalyst 22, for example, the three-way catalyst 22 A single sensor system that performs F / B control of the air-fuel ratio using the A / F sensor 23 or the oxygen sensor 24 disposed only upstream may be applied. Further, when a three-way catalyst 22 is used as a main catalyst and a relatively small three-way catalyst is provided upstream of the three-way catalyst 22 as a start catalyst, an A / F is provided upstream of the three-way catalyst 22. Instead of providing the sensor 23, an A / F sensor 23 may be provided upstream of the start catalyst.

  Next, the A / F sensor 23 will be described in detail. FIG. 2 is a diagram showing the output characteristics of the A / F sensor 23. The horizontal axis represents the true exhaust air-fuel ratio by the exhaust gas analyzer, and the vertical axis represents the exhaust air-fuel ratio detected based on the output of the A / F sensor 23. Each shows. In FIG. 2, in order to compare the difference in output characteristics between the case where the exhaust gas sensor is disposed upstream of the three-way catalyst 22 and the case where the exhaust gas sensor is disposed downstream, In addition, output characteristics when the A / F sensor 23 is provided are also shown. In FIG. 2, the relationship between the true exhaust air / fuel ratio and the hydrogen concentration is shown corresponding to the output characteristics. A line L1 indicated by a broken line indicates a true exhaust air-fuel ratio. On the other hand, the line L2 indicates the exhaust air-fuel ratio detected based on the output of the upstream A / F sensor 23 (hereinafter referred to as the pre-catalyst A / F sensor), and the line L3 indicates the downstream A / F sensor. The exhaust air-fuel ratio detected based on the output of the F sensor 23 (hereinafter referred to as a post-catalyst A / F sensor) is shown.

  When these lines L1, L2 and L3 are compared at the same true exhaust air-fuel ratio with reference to the true exhaust air-fuel ratio on the horizontal axis, the lines L2 and L3 are both from the line L1 indicating the true exhaust air-fuel ratio. It turns out that it is also richer. Further, it can be seen that the line L2 is considerably richer than the line L3. This is because the hydrogen reacts with oxygen in the three-way catalyst 22 and greatly decreases, so the post-catalyst A / F sensor is relatively less susceptible to hydrogen, whereas the pre-catalyst A / F sensor is By being greatly affected by hydrogen. For this reason, the post-catalyst A / F sensor detects an exhaust air-fuel ratio that is relatively close to the true exhaust air-fuel ratio, whereas the pre-catalyst A / F sensor is considerably richer than the true exhaust air-fuel ratio. The exhaust air-fuel ratio will be detected.

  Next, when these lines L1, L2 and L3 are compared with the same detected exhaust air-fuel ratio on the basis of the detected exhaust air-fuel ratio on the vertical axis, the lines L2 and L3 both show the true exhaust air-fuel ratio. It turns out that it has shifted | deviated to the lean side rather than the line L1. It can also be seen that the degree of deviation is larger in the pre-catalyst A / F sensor that is greatly affected by hydrogen than in the post-catalyst A / F sensor. Therefore, if the F / B control is performed on the air-fuel ratio to the stoichiometric air-fuel ratio in this state, the air-fuel ratio becomes lean. The tendency that the pre-catalyst A / F sensor is more adversely affected by hydrogen is the same even when the pre-catalyst or post-catalyst A / F sensor is the oxygen sensor 24. On the other hand, the hydrogen concentration increases as the true exhaust air-fuel ratio decreases. That is, it can be seen that the richer the gas mixture, the greater the amount of hydrogen generated. From these characteristics, even when the air-fuel ratio is the same (for example, the stoichiometric air-fuel ratio), it is more preferable for the exhaust gas sensor that the mixing property of the air-fuel mixture is higher because hydrogen can be avoided from being generated due to combustion of the rich air-fuel mixture. Recognize.

Next, the oxygen sensor 24 will be described in detail. FIG. 3 is a diagram schematically showing a detection unit of the oxygen sensor 24. The detection part of the oxygen sensor 24 has a configuration in which, for example, an atmosphere side electrode 24b and an exhaust side electrode 24c made of two platinum electrodes are arranged on both sides of a solid electrolyte 24a such as zirconium oxide (ZrO ₂ ). In a state where the oxygen sensor 24 is disposed in the exhaust passage, the exhaust side electrode 24c comes into contact with the exhaust gas through the porous protective layer 24d, the catalyst layer 24e, and the trapping layer 24f, and the atmosphere side electrode 24b comes into contact with the atmosphere. To do. When gases having different oxygen concentrations come into contact with the electrodes 24b and 24c on both sides of the solid electrolyte 24a in this way, oxygen molecules in the atmosphere are ionized in the atmosphere-side electrode 24b on the high oxygen concentration side due to the difference in oxygen concentration between the electrodes. The oxygen ions move in the zirconium oxide toward the exhaust side electrode 24c on the low oxygen concentration side, and become oxygen molecules at the exhaust side electrode 24c. Thereby, an electromotive force corresponding to the amount of oxygen ions flowing in the zirconium oxide is generated between the atmosphere-side electrode 24b and the exhaust-side electrode 24c. In addition, since the amount of oxygen ions flowing per unit time changes according to the difference in oxygen concentration between the atmosphere and the exhaust, it is possible to obtain an output corresponding to the oxygen concentration in the exhaust by taking out the electromotive force as an output voltage. it can.

  FIG. 4 is a diagram showing the output characteristics of the oxygen sensor 24. The output of the oxygen sensor 24 exhibits a so-called Z characteristic that changes relatively rapidly in the vicinity of the theoretical air-fuel ratio. However, if the exhaust gas contains hydrogen, the hydrogen concentration is higher in the vicinity of the exhaust-side electrode 24c than the exhaust gas outside the oxygen sensor 24 due to the high hydrogen diffusion rate. Further, in the vicinity of the exhaust side electrode 24c, this hydrogen reacts with oxygen and acts to lower the oxygen concentration in the vicinity of the exhaust side electrode 24c than the external exhaust gas. Therefore, the oxygen sensor 24 does not generate a lean output unless the external exhaust air-fuel ratio becomes considerably lean.

  On the other hand, the oxygen sensor 24 includes a porous catalyst layer 24e made of a catalyst carrier such as alumina outside the protective layer 24d. The catalyst layer 24e carries catalyst components such as platinum (Pt) and rhodium (Rh). As a result, combustible components such as hydrogen in the exhaust gas react with oxygen in the exhaust gas in the catalyst layer 24e, and after being balanced, reach the exhaust-side electrode 24c through the protective layer 24d. For this reason, in the oxygen sensor not provided with the catalyst layer 24e, the output characteristic is as shown in the line L4 due to the influence of hydrogen, whereas in the oxygen sensor 24, the true exhaust air / fuel ratio as shown in the line L5 is better handled. Output characteristics can be obtained. It is also possible to provide an oxygen sensor that does not have the catalyst layer 24e instead of the oxygen sensor 24.

  A fuel injection system 30 shown in FIG. 1 is configured to supply and inject fuel, and includes a fuel injection valve 31, a fuel injection pump 32, a fuel tank 33, and the like. The fuel injection valve 31 is configured to inject fuel, and is opened at an appropriate injection timing and injects fuel under the control of the ECU 1. The fuel injection amount is adjusted by the length of the valve opening period until the fuel injection valve 31 is closed under the control of the ECU 1. The fuel injection pump 32 is configured to pressurize the fuel to generate an injection pressure, and adjusts the injection pressure to an appropriate injection pressure under the control of the ECU 1.

  The internal combustion engine 50 includes a cylinder block 51, a cylinder head 52, a piston 53, a spark plug 54, an intake valve 55, and an exhaust valve 56. The internal combustion engine 50 shown in the present embodiment is an inline 4-cylinder gasoline engine. However, the internal combustion engine 50 is not particularly limited as long as it is an internal combustion engine capable of implementing the present invention, and may have other appropriate cylinder arrangement structure and number of cylinders, for example. In FIG. 1, the main part of the internal combustion engine 50 is shown with respect to the cylinder 51a as a representative of each cylinder. However, in this embodiment, the other cylinders have the same structure. The cylinder block 51 is formed with a substantially cylindrical cylinder 51a. A piston 53 is accommodated in the cylinder 51a. A cylinder head 52 is fixed to the upper surface of the cylinder block 51. The combustion chamber 57 is formed as a space surrounded by the cylinder block 51, the cylinder head 52, and the piston 53.

  In addition to an intake port 52a for guiding intake air to the combustion chamber 57, the cylinder head 52 is formed with an exhaust port 52b for exhausting the combusted gas from the combustion chamber 57, and opens and closes the intake and exhaust ports 52a and 52b. For this purpose, intake and exhaust valves 55 and 56 are provided. The internal combustion engine 50 may have an intake / exhaust valve structure including an appropriate number of intake / exhaust valves 55 and 56 per cylinder. The spark plug 54 is disposed in the cylinder head 52 with an electrode protruding substantially in the center above the combustion chamber 57. The fuel injection valve 31 is disposed in the cylinder head 52 with a fuel injection hole protruding into the intake port 52a so as to perform so-called port injection. However, the arrangement of the fuel injection valve 31 is not limited to this, and may be an arrangement in which fuel can be directly injected into the cylinder, for example.

  An air flow control valve 58 for generating a tumble flow in the combustion chamber 57 is disposed in the intake port 52a. The airflow control valve 58 is configured to generate a tumble flow in the combustion chamber 57 by causing the intake air to drift in the intake port 52 a under the control of the ECU 1. A notch (not shown) having a predetermined opening area is formed on the front end side of the airflow control valve 58, and this notch increases the flow rate of intake air particularly when the airflow control valve 58 is fully closed. The airflow control valve 58 may be disposed in the intake passage formed by the intake manifold 15. Further, the air flow control valve 58 is not limited to the one that generates the tumble flow, and any reverse tumble may be used as long as it can generate a strong swirling air flow in the combustion chamber 57 in a predetermined valve open state and improve the mixing property of the air-fuel mixture. It is also possible to generate an oblique tumble flow formed by combining a flow, a swirl flow, a tumble flow and a swirl flow. In addition, the internal combustion engine 50 is provided with various sensors such as a crank angle sensor 71 for generating an output pulse proportional to the rotational speed Ne and a water temperature sensor 72 for detecting the water temperature of the internal combustion engine 50.

  The ECU 1 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output circuit, and the like (not shown). The ECU 1 is mainly configured to control the internal combustion engine 50. In the present embodiment, in addition to the fuel injection valve 31 and the fuel injection pump 32, an ignition plug 54 (more specifically, an igniter not shown) and an airflow control valve 58 are provided. (More specifically, an actuator for the airflow control valve 58 (not shown)) is also controlled. In addition to the fuel injection valve 31 and the like, various control objects are connected to the ECU 1 via a drive circuit (not shown). The ECU 1 is connected to various sensors such as an air flow meter 12, a crank angle sensor 71, a water temperature sensor 72, and an accelerator sensor 73 for detecting the amount of depression (accelerator opening) of an accelerator pedal (not shown). Has been.

  The ROM is configured to store a program in which various processes executed by the CPU are described. In this embodiment, in addition to the program for controlling the internal combustion engine 50, the ROM is used for controlling the fuel injection valve 31. A program, an air-fuel ratio F / B control program for F / B control of the air-fuel ratio using the A / F sensor 23, and an air-fuel ratio using the A / F sensor 23 using the oxygen sensor 24 For air-fuel ratio sub-F / B control for correcting the F / B control of the air-fuel ratio, and for air-fuel ratio learning control for learning the correction amount calculated by the air-fuel ratio F / B control or sub-F / B control Also stores programs. These programs may be configured as a part of the internal combustion engine 50 control program.

  In this embodiment, the air-fuel ratio F / B control program includes an F / B control execution permission program for permitting execution of the air-fuel ratio F / B control. Specifically, the F / B control execution permission program is created so as to first determine whether or not a predetermined air-fuel ratio F / B execution condition is satisfied. Furthermore, in this embodiment, the F / B control execution permission program is created so as to determine whether or not a predetermined opening condition is satisfied based on the open state of the airflow control valve 58. The predetermined opening condition is that the air flow control valve 58 is in an open state in which the open state can generate a strong tumble flow and improve the mixing property of the air-fuel mixture. The valve opening condition that satisfies this opening degree is set to half open. The F / B control execution permission program determines that the predetermined air-fuel ratio F / B execution condition is satisfied, and executes F / B control when it is determined that the predetermined opening degree condition is satisfied. Created to allow.

Similarly, in the present embodiment, the air-fuel ratio sub-F / B control program has a sub-F / B control execution permission program for executing the air-fuel ratio sub-F / B control. Specifically, the sub F / B control execution permission program is created so as to determine whether or not a predetermined air-fuel ratio sub F / B execution condition is satisfied. Further, in the present embodiment, the sub F / B control execution program determines whether or not a predetermined opening degree condition is established based on the open state of the airflow control valve 58 as in the F / B control execution program. Has been created. The sub F / B control execution program determines that the predetermined air-fuel ratio sub F / B execution condition is satisfied, and if it is determined that the predetermined opening degree condition is satisfied, the sub F / B control execution program Created to allow execution. The air-fuel ratio F / B control and sub F / B control executed after the conditions are satisfied may be appropriate. In the present embodiment, various detection means, determination means, control means, and the like are realized by a CPU, a ROM, a RAM (hereinafter simply referred to as a CPU, etc.), and a program for controlling the internal combustion engine 50. the F / B control execution permission program and by the F / B control real Gyote stage, the sub F / B control real Gyote stage are respectively realized by a CPU or the like and the sub F / B control execution permission program .

  Next, processing performed by the ECU 1 when performing the air-fuel ratio F / B control based on the open state of the airflow control valve 58 will be described in detail with reference to the flowcharts shown in FIGS. The ECU 1 is shown in the flowchart based on various programs such as the above-described internal combustion engine 50 control program, F / B control execution permission program, and sub F / B control execution permission program stored in the ROM by the CPU. The air-fuel ratio is F / B controlled by executing the process. The CPU executes a process for determining whether or not the internal combustion engine 50 is being started (step 11). If the determination is negative, no special process is required in this flowchart, and the process ends. On the other hand, if the determination is affirmative, the CPU executes a process of determining whether or not a predetermined air-fuel ratio F / B execution condition is satisfied (step 12). The predetermined air-fuel ratio F / B execution condition includes, for example, that the A / F sensor 23 is activated and that the internal combustion engine 50 has been warmed up (the water temperature THW detected by the water temperature sensor 72 is equal to or higher than a predetermined value). And a predetermined time has elapsed after returning from the fuel cut. If the determination is negative, the CPU executes a process of stopping the air-fuel ratio F / B control (step 14A), and then ends the process. That is, when the air-fuel ratio F / B control has already been executed, when a negative determination is made in step 12, the F / B control is stopped in step 14A.

  On the other hand, if the determination is affirmative, the CPU executes a process of determining whether or not a predetermined opening condition is satisfied (step 13). In this step, it is determined whether or not the airflow control valve 58 is half open. If a negative determination is made in step 13, the CPU executes the process shown in step 14A. On the other hand, if the determination in step 13 is affirmative, the CPU executes air-fuel ratio F / B control (step 15A). That is, if the determination in step 13 is affirmative, execution of the F / B control is permitted. FIG. 7 is a diagram showing the characteristics of exhaust gas when the internal combustion engine 50 is operated in a steady state when the airflow control valve 58 is fully open and when it is half open. FIG. 7 shows that carbon monoxide (CO) and hydrogen tend to increase as the air-fuel ratio becomes richer. Furthermore, it can be seen that carbon monoxide and hydrogen are reduced when the air flow control valve 58 is in a half-open state, compared to when it is fully open. This is probably because a strong tumble flow is generated in the combustion chamber 57 and the mixing property of the air-fuel mixture is improved, and as a result, the locally rich air-fuel mixture is reduced. Thereby, since the F / B control of the air-fuel ratio can be executed in a state where the amount of hydrogen generated is reduced, high robustness can be ensured.

  On the other hand, FIG. 6 is a flowchart showing a process performed by the ECU 1 when performing the air-fuel ratio sub F / B control based on the open state of the airflow control valve 58. The process shown in this flowchart is the same as the flowchart shown in FIG. 6 except that step 12a is added following the affirmative determination in step 12, and steps 14A and 15A are changed to steps 14B and 15B. It has become. For this reason, steps 12a, 14B and 15B will be described in detail with respect to this flowchart. In performing the sub-F / B control of the air-fuel ratio, following the affirmative determination in step 12, the CPU further executes a process of determining whether or not a predetermined air-fuel ratio sub-F / B execution condition is satisfied (step 12a). ). The predetermined air-fuel ratio sub-F / B execution condition is, for example, that the water temperature THW is equal to or higher than a predetermined value, fuel increase such as post-start increase, warm-up increase, power increase, and OTP increase for preventing catalyst overheating is being executed. And that the specified time has elapsed since the completion of such an increase, that the fuel cut is not being executed, and that the specified time has elapsed since the fuel cut has ended, the internal combustion engine 50 The output of the oxygen sensor 24 has been reversed at least once after the start of the engine (the lean output has changed to the rich output or vice versa, that is, it has been determined that the oxygen sensor 24 has been activated). .

  If a negative determination is made in step 12a, the CPU executes a process of stopping the sub-F / B control of the air-fuel ratio (step 14B). That is, if the air-fuel ratio sub-F / B control has already been executed, the air-fuel ratio sub-F / B control is stopped in step 14B if a negative determination is made in step 12a. As shown in the figure, when the negative determination is made at steps 12 and 13, the sub-F / B control of the air-fuel ratio is similarly stopped at step 14B. On the other hand, if the determination in step 12a is affirmative, the CPU executes the process shown in step 13. If the determination in step 13 is affirmative, the CPU executes air-fuel ratio sub F / B control (step 15B). That is, if the determination in step 13 is affirmative, execution of the sub F / B control is permitted. Thereby, the sub air-fuel ratio F / B control for correcting the air-fuel ratio F / B control in a state where the generation amount of hydrogen is reduced can also be executed. In the present embodiment, a learning control program is also created so that the learning control of the air-fuel ratio is performed when a predetermined opening degree condition is satisfied, so that the learning control is correctly performed as intended. Is called. As described above, it is possible to realize the ECU 1 capable of executing the highly robust air-fuel ratio F / B control by dealing with hydrogen that adversely affects the exhaust gas sensor at the generation stage.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

1 is a diagram schematically showing an ECU 1 together with an internal combustion engine system 100. FIG. It is a figure which shows the output characteristic of the A / F sensor. It is a figure which shows the detection part of the oxygen sensor 24 typically. It is a figure which shows the output characteristic of the oxygen sensor. It is a figure which shows the process performed by ECU1 in the flowchart in performing F / B control of an air fuel ratio based on the valve opening state of the airflow control valve 58. FIG. 6 is a flowchart illustrating a process performed by the ECU 1 when performing sub-F / B control of an air-fuel ratio based on an open state of an airflow control valve 58. It is a figure which shows the characteristic of exhaust gas when the internal combustion engine 50 carries out a steady operation about the case where the valve-opening state of the airflow control valve 58 is a full open, and the case of a half open. It is a figure which shows an example of the opening / closing behavior of an airflow control valve. Regarding the hydrogen concentration of exhaust gas discharged from an internal combustion engine and the hydrogen concentration of exhaust gas discharged from a three-way catalyst when there is no variation in air-fuel ratio between cylinders and when there is variation in air-fuel ratio between cylinders FIG.

Explanation of symbols

1 ECU
DESCRIPTION OF SYMBOLS 10 Intake system 20 Exhaust system 30 Fuel injection system 50 Internal combustion engine 100 Internal combustion engine system

Claims (2)

An air-fuel ratio control device for an internal combustion engine that controls an air-fuel ratio of an internal combustion engine in which an airflow control valve for generating a swirling airflow in a combustion chamber is disposed in an intake passage,
A semi-open state in which a predetermined air-fuel ratio feedback control execution condition is satisfied and the airflow control valve is open is a state in which a strong swirling airflow is generated in the combustion chamber and mixing of the air-fuel mixture becomes high Sometimes, feedback control for air-fuel ratio is executed, and feedback control execution means for stopping execution of the air-fuel ratio feedback control when the open state of the airflow control valve is not the half-open state is provided. An air-fuel ratio control apparatus for an internal combustion engine.   2. The internal combustion engine according to claim 1, further comprising sub-feedback control execution means for executing air-fuel ratio sub-feedback control for correcting air-fuel ratio feedback control based on an open state of the airflow control valve. Air-fuel ratio control device.

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