JP4894529B2 - Catalyst degradation detector - Google Patents

Description

  The present invention relates to a catalyst deterioration detection apparatus, and more particularly, to a catalyst deterioration detection apparatus that realizes highly robust catalyst deterioration detection control by coping with hydrogen and unburned HC that adversely affect an exhaust gas sensor.

  2. Description of the Related Art Conventionally, a technique for detecting deterioration of a catalyst disposed in an exhaust system of an internal combustion engine using an output of an exhaust gas sensor (for example, an oxygen sensor or an A / F sensor) that detects oxygen is known. FIG. 9 is a diagram schematically illustrating an example of a method for detecting deterioration of the catalyst. While the catalyst releases oxygen when the exhaust air-fuel ratio is rich, it has the property of storing oxygen when it is lean (oxygen storage capacity), and the catalyst uses this property to purify exhaust. It has been broken. However, since this oxygen storage capacity decreases with the deterioration of the catalyst, it is necessary to grasp the degree of deterioration of the catalyst in order to perform fuel injection within a range that can sufficiently purify the exhaust gas, for example.

この演算式は触媒に流入する酸素量のうち、触媒が吸蔵或いは放出する酸素量を算出するとともに、算出した酸素量を積算していくように構成されている。なお、この演算式では空燃比（ここでは制御Ａ／Ｆ−ストイキＡ／Ｆ）に燃料噴射量（ここでは単位時間当たりの燃料噴射量ｍｆｒ×燃料噴射時間Δｔ）を乗じることで空気量が求まることから、この空気量にさらに空気中の酸素濃度（ここでは０．２３）を乗じることで触媒が吸蔵或いは放出する酸素量を求めている。そしてこの酸素量は触媒が酸素を放出し切ったときを基準とすれば、図９に示す酸素吸蔵量として表すことができる。 On the other hand, the oxygen storage capacity can be grasped by the maximum oxygen storage amount, and the maximum oxygen storage amount can be obtained by using, for example, the arithmetic expression shown in FIG. 9 and the following.

This calculation formula is configured to calculate the amount of oxygen stored or released by the catalyst out of the amount of oxygen flowing into the catalyst, and to integrate the calculated amount of oxygen. In this equation, the air amount is obtained by multiplying the air-fuel ratio (here, control A / F-stoichiometric A / F) by the fuel injection amount (here, fuel injection amount mfr per unit time × fuel injection time Δt). Therefore, the amount of oxygen absorbed or released by the catalyst is obtained by further multiplying the amount of air by the oxygen concentration in the air (here, 0.23). This oxygen amount can be expressed as the oxygen storage amount shown in FIG. 9 on the basis that the catalyst has completely released oxygen.

  Therefore, based on the output of the oxygen sensor disposed downstream of the catalyst, when the output of the oxygen sensor is reversed, the predetermined fuel injection amount mfr and the fuel injection time are set so that the exhaust air-fuel ratio is also rich and reversed between leans. If the fuel injection control is performed at Δt and the control A / F is detected by the A / F sensor disposed upstream of the catalyst at this time, the maximum oxygen storage amount is calculated using the above formula. it can. Further, since there is a correlation as shown in FIG. 10 between the maximum oxygen storage amount and the degree of deterioration of the catalyst, if the maximum oxygen storage amount is obtained as described above, the deterioration of the catalyst based on the relationship shown in FIG. Can be determined and detected (hereinafter, control for detecting catalyst deterioration as described above is simply referred to as active deterioration detection control). For example, Patent Document 1 proposes a technique for detecting deterioration of the catalyst using the output of the exhaust gas sensor.

JP 2002-364428 A

  By the way, the exhaust gas contains hydrogen and unburned HC in addition to oxygen. Of hydrogen and unburned HC, methane and the like are more likely to diffuse gas than oxygen, and therefore reach the exhaust gas sensor electrode faster than oxygen. In this state, oxygen that should originally reach the electrode cannot 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 closer to the richer than the true exhaust air-fuel ratio. It will be detected. That is, hydrogen and methane act 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. Therefore, at this time, the maximum oxygen storage amount is accurately determined because the timing of the fuel injection control performed when the output of the oxygen sensor is reversed due to the deviation of the output characteristics of the exhaust gas sensor. As a result, there is a possibility that the catalyst deterioration detection accuracy is lowered.

  On the other hand, since hydrogen and unburned HC are easily generated when a rich air-fuel mixture burns, the amount of hydrogen and methane generated increases if the air-fuel mixture is poorly mixed. 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 airflow control valve, for example, it is controlled to be half open. FIG. 11 is a diagram illustrating an example of the opening / closing behavior of the airflow control valve. For example, as shown in FIG. 11, the airflow control valve is appropriately controlled from full open to half open for the purpose of improving combustion. When the airflow control valve is controlled in this way, the mixing property of the air-fuel mixture is improved when the airflow control valve is half-opened. On the other hand, depending on the open state of the airflow control valve (for example, fully open) The generation amount of hydrogen and unburned HC will be relatively increased. In this case, since hydrogen and methane easily act on the exhaust gas sensor, the catalyst deterioration detection accuracy may be reduced.

  On the other hand, in the three-way catalyst, hydrogen and unburned HC react with oxygen and combust, and therefore, hydrogen and unburned HC are generally greatly reduced on the downstream side 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. 12 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 there is no air-fuel ratio variation between cylinders and between the cylinders. It is a figure shown about. FIG. 12 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. The vertical axis indicating the hydrogen concentration is a log scale.

  From FIG. 12, the air-fuel ratio varies between cylinders both 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. 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. Moreover, it is thought that the tendency concerned is materialized similarly about unburned HC. It can be seen from FIG. 12 that when the air-fuel ratio varies between the cylinders, the hydrogen concentration in the exhaust gas increases and the possibility of adverse effects on the exhaust gas sensor increases, but indefinite disturbance such as the air-fuel ratio varies between the cylinders in this way. It can be said that it is effective to first perform catalyst deterioration detection control such as active deterioration detection control in response to hydrogen and unburned HC from the viewpoint of the generation source.

  Accordingly, the present invention has been made in view of the above problems, and it is possible to realize highly robust catalyst deterioration detection control by dealing with hydrogen and unburned HC that adversely affect the exhaust gas sensor at the generation stage. An object is to provide a detection device.

In order to solve the above problems, the present invention provides a combustion improvement means for improving the condition of combustion performed in the internal combustion engine, a catalyst for purifying exhaust gas, the oxygen in the exhaust gas at the upstream side of the catalyst in an internal combustion engine system including an exhaust gas sensor to be detected, the a catalyst deterioration detection device for performing the catalyst deterioration detection control of the output by utilizing for detecting deterioration of the catalyst exhaust gas sensors, the combustion improvement means The combustion state is improved by generating a swirling airflow in the combustion chamber of the internal combustion engine, and the combustion improving means generates a strong swirling airflow in the combustion chamber of the internal combustion engine so that the mixing property of the air-fuel mixture is high. In some cases, a deterioration detection control permission means for permitting execution of the catalyst deterioration detection control is provided. Here, if the degree of combustion improvement is high, hydrogen and unburned HC are combusted, so the amount of hydrogen and unburned HC discharged from the combustion chamber is also reduced. Further, in such a state, even if the air-fuel ratio of each cylinder varies, the amount of hydrogen and unburned HC discharged from the cylinder in which the air-fuel ratio becomes rich can be reduced. The present invention has been made in view of this point, and according to the present invention, highly robust catalyst deterioration detection control can be realized by dealing with hydrogen and unburned HC at the generation stage.

  The combustion improving means may be any means as long as it can improve the combustion state by improving the mixing property of the air-fuel mixture, for example, improving the combustion of a helical port formed to generate a swirl flow. It can also be understood as a means. In this case, in order to allow the execution of the catalyst deterioration detection control according to the degree of combustion improvement by the helical port, for example, based on the operating state of the internal combustion engine when a predetermined combustion improvement effect is obtained by the helical port, the catalyst deterioration detection control It is also included in the present invention to permit execution of the above.

  In the present invention, the combustion improving means may be an airflow control valve disposed in an intake passage of an intake system of the internal combustion engine in order to generate a swirling airflow in the combustion chamber of the internal combustion engine. Specifically, the combustion improving means is preferably an airflow control valve that exhibits a high combustion improving effect, for example.

  In the present invention, the deterioration detection control permission unit may permit the execution of the catalyst deterioration detection control based on an open state of the airflow control valve. Here, since the mixing property of the air-fuel mixture changes depending on the open state of the airflow control valve, when the combustion improving means is an airflow control valve, specifically, for example, the catalyst based on the open state of the airflow control valve. By permitting the execution of the deterioration detection control, the execution of the catalyst deterioration detection control can be permitted according to the degree of combustion improvement. The deterioration detection control permission means preferably permits the execution of the deterioration detection control when the airflow control valve is in a half-open state. 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 catalyst deterioration detection apparatus which can implement | achieve highly robust catalyst deterioration detection control can be provided by dealing with the hydrogen and unburned HC which have a bad influence on an exhaust gas sensor at the generation | occurrence | production 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 a catalyst deterioration detection apparatus according to this embodiment implemented 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 intake air, a throttle valve 13 for adjusting the flow rate of intake air, A surge tank 14 that temporarily stores intake air, an intake manifold 15 that distributes intake air to each cylinder of the internal combustion engine 50, and intake pipes that are appropriately disposed between them are configured.

  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.

  In the exhaust system 20, an A / F sensor 23 for linearly detecting the air-fuel ratio based on the oxygen concentration in the exhaust is upstream of the three-way catalyst 22, and the air-fuel ratio is based on the oxygen concentration in the exhaust from the stoichiometric air-fuel ratio. Also, oxygen sensors 24 for detecting whether the gas is rich or lean are disposed downstream of the three-way catalyst 22, respectively. In the present embodiment, the above-described configuration is used to perform the active deterioration detection control. However, the combination of exhaust gas sensors disposed upstream and downstream of the three-way catalyst 22 is not limited to this. An appropriate combination may be employed, such as arranging the A / F sensor 23 or the oxygen sensor 24 both upstream and downstream of the original catalyst 22. For example, the A / F sensor 23 or the oxygen sensor 24 may be provided only upstream or downstream of the three-way catalyst 22.

  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 three-way catalyst 22 significantly reduces hydrogen and unburned HC by reacting with oxygen, so the post-catalyst A / F sensor is relatively less susceptible to hydrogen and unburned HC (for example, methane). In contrast, the pre-catalyst A / F sensor is greatly influenced by hydrogen and unburned HC. 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 influenced by hydrogen and unburned HC than in the post-catalyst A / F sensor. Therefore, if the active deterioration detection control is executed in this state, the exhaust gas flowing into the three-way catalyst 22 becomes leaner because the control A / F is shifted to the lean side. As a result, NOx increases as an emission. The tendency that the pre-catalyst A / F sensor is adversely affected by hydrogen and unburned HC as described above 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. This tendency is the same for unburned HC. From these characteristics, even when the air-fuel ratio is the same (for example, the stoichiometric air-fuel ratio), the higher the mixing of the air-fuel mixture, the more hydrogen and unburned HC can be prevented from being generated by the combustion of the rich air-fuel mixture. It turns out that it is more preferable.

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, when hydrogen or methane is contained in the exhaust gas, the concentration of hydrogen or methane is higher in the vicinity of the exhaust-side electrode 24c than in the exhaust gas outside the oxygen sensor 24 due to the high diffusion rate. Get higher. Further, in the vicinity of the exhaust side electrode 24c, hydrogen or methane 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 and methane 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) (not shown), a ROM (Read Only Memory), a RAM (Random Access Memory) and the like (hereinafter simply referred to as a microcomputer), An output circuit is included. 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 internal combustion engine 50 control program, a fuel injection control program for performing fuel injection control, A catalyst deterioration detection control program for performing catalyst deterioration detection control is also stored. These programs may be configured as a part of the internal combustion engine 50 control program. In this embodiment, the catalyst deterioration detection control program is a program for performing active deterioration detection control. In this embodiment, the catalyst deterioration detection control program includes a deterioration detection control permission program that permits the execution of the catalyst deterioration detection control according to the degree of combustion improvement by the airflow control valve 58.

  Specifically, this deterioration detection control permission program is created so as to first determine whether or not a predetermined active deterioration detection control execution condition is satisfied for the active deterioration detection control. Further, the deterioration detection control 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. However, the present invention is not limited to this. For example, map data in which the opening degree of the airflow control valve 58 that provides a predetermined degree of combustion improvement is set according to the operating state (for example, the rotational speed NE and load) of the internal combustion engine or the intake air amount. It is also possible to make the opening degree of the airflow control valve 58 read from this map data as the predetermined opening degree condition based on the operating state of the internal combustion engine or the intake air amount.

  Further, the deterioration detection control permission program determines that the predetermined active deterioration detection control execution condition is satisfied, and permits execution of the active deterioration detection control when it is determined that the predetermined opening degree condition is satisfied. Thus, the execution of the active deterioration detection control is permitted when the open state of the airflow control valve 58 is half-open according to the open state of the airflow control valve 58. In this embodiment, the deterioration detection control permission means is realized by the microcomputer and the deterioration detection control permission program.

  Next, processing performed by the ECU 1 will be described in detail with reference to the flowchart shown in FIG. The ECU 1 executes the active deterioration detection control by executing the processing shown in the flowchart based on various programs such as the above-described internal combustion engine 50 control program stored in the ROM and the catalyst deterioration detection control program. Do this with permission. The CPU executes processing for determining whether or not the internal combustion engine 50 is being started (step S11). 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 active deterioration detection control execution condition is satisfied (step S12). The predetermined active deterioration detection control execution condition is, for example, that the A / F sensor 23 or the oxygen sensor 24 is activated.

  If it is negative determination, CPU will perform the process which stops active deterioration detection control (step S14), and will complete | finish a process after that. That is, when the active deterioration detection control has already been executed, the active deterioration detection control is stopped in step S14 when a negative determination is made in step S12. On the other hand, if it is affirmation determination, CPU will perform the process which determines whether predetermined opening degree conditions were satisfied (step S13). 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 S13, the process proceeds to step S14. On the other hand, if an affirmative determination is made in step S13, the CPU executes active deterioration detection control (step S15). That is, if the determination in step S13 is affirmative, execution of active deterioration detection control is permitted.

  FIG. 6 is a view 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. 6 shows that hydrogen and methane tend to increase as the air-fuel ratio becomes richer. Furthermore, it can be seen that hydrogen and methane 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. As a result, the active deterioration detection control can be executed in a state where the generation amounts of hydrogen and methane are reduced, so that high robustness can be ensured.

  FIG. 7 is a diagram schematically showing the component structure of unburned HC contained in the exhaust gas. In FIG. 7, the component structure of unburned HC contained in the exhaust gas immediately after the internal combustion engine 50 is shown for a case where combustion improvement is not performed (case A) and a case where combustion improvement is performed (case B). The component structure of individual HC contained in the fuel is also shown at the same time. Here, when the combustion improvement is performed, the combustion of the unburned HC is promoted, so that the component structure of the unburned HC contained in the exhaust gas also changes. At this time, it can be seen from FIG. 7 that the olefin-based unburned HC increases when the combustion improvement is performed (case B) compared to the case where the combustion improvement is not performed (case A). On the other hand, as shown in FIG. 8, the olefin-based unburned HC has a high reactivity with the three-way catalyst 22, so that the purification rate is also increased. As a result, when the combustion is improved, the exhaust gas is simultaneously purified. It can be seen that it is also promoted. At this time, the combustion of hydrogen and methane can be expected to be promoted by the three-way catalyst 22, so that when the combustion is improved, the adverse effect of hydrogen and methane on the oxygen sensor 24 is also expected to be reduced. it can. 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 and unburned HC that adversely affect 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 with a flowchart. 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 typically the component structure of unburned HC contained in exhaust gas. It is a figure which compares the purification rate of the three way catalyst 22 about the case where combustion improvement is performed, and the case where combustion improvement is not performed. It is a figure which shows typically an example of the method of detecting deterioration of a catalyst. It is a figure which shows typically the correlation of the maximum oxygen storage amount and the deterioration degree of a catalyst. 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 (3)

In an internal combustion engine system comprising a combustion improvement means for improving the condition of combustion performed in the internal combustion engine, a catalyst for purifying exhaust gas, an exhaust gas sensor for detecting oxygen in the exhaust gas at the upstream side of the catalyst A catalyst deterioration detection device that performs catalyst deterioration detection control for detecting deterioration of the catalyst using the output of the exhaust gas sensor,
The combustion improving means improves the state of combustion by generating a swirling airflow in the combustion chamber of the internal combustion engine,
A deterioration detection control permission means for permitting execution of the catalyst deterioration detection control when the combustion improvement means generates a strong swirling air flow in the combustion chamber of the internal combustion engine and the mixing property of the air-fuel mixture is high. A catalyst deterioration detection device.   2. The catalyst according to claim 1, wherein the combustion improving means is an airflow control valve disposed in an intake passage of an intake system of the internal combustion engine in order to generate a swirling airflow in the combustion chamber of the internal combustion engine. Deterioration detection device.   3. The catalyst deterioration detection apparatus according to claim 2, wherein the deterioration detection control permission unit permits the execution of the catalyst deterioration detection control based on an open state of the airflow control valve.

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