Control device for an internal combustion engine

Abstract

The present application aims to suppress useless update of a sub-feedback learning value caused by execution of active control of air-fuel ratio. A control device of an internal combustion engine is capable of executing air-fuel ratio sub-feedback control, sub-feedback learning control, and active control of air-fuel ratio. In the sub-feedback learning control, the control device executes rich adhesion update processing that updates the sub-feedback learning value so that the post-update target air-fuel ratio becomes an air-fuel ratio more biased toward the lean side than the pre-update target air-fuel ratio, in the case where a rich adhesion condition indicating a state in which lean burn failure has not been detected continuously after switching of the target air-fuel ratio from a rich air-fuel ratio to a lean air-fuel ratio based on the air-fuel ratio sub-feedback control is satisfied. In the active control of air-fuel ratio, the control device forcibly performs switching of the target air-fuel ratio between a lean air-fuel ratio and a rich air-fuel ratio. The control device prohibits execution of the rich adhesion update processing during execution of the active control of air-fuel ratio.

Description

Technical Field

[0001] This invention relates to a control device for an internal combustion engine. Background Technology

[0002] Patent Document 1 describes a system comprising an internal combustion engine. The internal combustion engine includes a cylinder, an exhaust passage, an exhaust purification catalyst, an upstream air-fuel ratio sensor, and a downstream air-fuel ratio sensor. Exhaust gas discharged from the cylinder flows through the exhaust passage. The exhaust purification catalyst has oxygen storage capacity. The upstream air-fuel ratio sensor detects the air-fuel ratio of the exhaust gas in the portion of the exhaust passage located upstream of the exhaust purification catalyst. The downstream air-fuel ratio sensor detects the air-fuel ratio of the exhaust gas in the portion of the exhaust passage located downstream of the exhaust purification catalyst.

[0003] The system in Patent Document 1 includes a control device that controls an internal combustion engine. The control device performs air-fuel ratio main feedback control. Specifically, the control device adjusts the fuel injection quantity based on the detection value of the upstream air-fuel ratio sensor so that the air-fuel ratio of the mixture burned in the cylinder becomes the target air-fuel ratio.

[0004] The control device performs sub-feedback control of the air-fuel ratio. Specifically, when the downstream air-fuel ratio sensor detects a lean-burn failure in the exhaust gas purification catalyst, the control device switches the target air-fuel ratio from a lean air-fuel ratio (more lean than the stoichiometric air-fuel ratio) to a rich air-fuel ratio (more rich than the stoichiometric air-fuel ratio). Conversely, when the downstream air-fuel ratio sensor detects a rich-burn failure in the exhaust gas purification catalyst, the control device switches the target air-fuel ratio from a rich air-fuel ratio (more rich than the stoichiometric air-fuel ratio) to a lean air-fuel ratio (more lean than the stoichiometric air-fuel ratio).

[0005] The control device performs sub-feedback learning control. This sub-feedback learning control is used to update the sub-feedback learning value, which is a correction value for the target air-fuel ratio. Specifically, the control device determines whether a rich-fuel attachment condition is met, which means that no lean-fuel failure has been detected continuously after the target air-fuel ratio is switched from a rich air-fuel ratio to a lean air-fuel ratio based on the air-fuel ratio sub-feedback control. Furthermore, the control device performs a rich-fuel attachment update process, which, if the rich-fuel attachment condition is determined to be met, updates the sub-feedback learning value so that the updated target air-fuel ratio is more lean-biased than the original. Also, the control device determines whether a lean-fuel attachment condition is met, which means that no rich-fuel failure has been detected continuously after the target air-fuel ratio is switched from a lean air-fuel ratio to a rich air-fuel ratio based on the air-fuel ratio sub-feedback control. Furthermore, the control device performs a lean-fuel attachment update process, which, if the lean-fuel attachment condition is determined to be met, updates the sub-feedback learning value so that the updated target air-fuel ratio is more lean-biased than the original.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-023621 Summary of the Invention

[0007] In the system shown in Patent Document 1, the control device sometimes performs active air-fuel ratio control, which forces a switch between a lean air-fuel ratio and a rich air-fuel ratio for a target air-fuel ratio. In such a system, for example, when the control device sets the target air-fuel ratio to a lean air-fuel ratio via air-fuel ratio sub-feedback control, the control device sometimes forces a switch to a rich air-fuel ratio via active air-fuel ratio control. In this case, after the switch from a rich air-fuel ratio to a lean air-fuel ratio based on the air-fuel ratio sub-feedback control, a state where lean-fuel failure is not detected can easily persist. As a result, the sub-feedback learning value may be unnecessarily updated by performing a rich-fuel attachment update process. Furthermore, similarly, even when the target air-fuel ratio is forcibly switched to a lean air-fuel ratio via active air-fuel ratio control, the sub-feedback learning value may still be unnecessarily updated by performing a lean-fuel attachment update process.

[0008] A control device for an internal combustion engine to solve the above-mentioned problems includes: an exhaust gas purification catalyst located in the exhaust passage and having oxygen storage capacity; an upstream air-fuel ratio sensor located upstream of the exhaust gas purification catalyst in the exhaust passage; and a downstream air-fuel ratio sensor located downstream of the exhaust gas purification catalyst in the exhaust passage. The control device is capable of performing: air-fuel ratio main feedback control, which adjusts the fuel injection quantity based on the detection value of the upstream air-fuel ratio sensor to make the air-fuel ratio of the mixture burned in the cylinder a target air-fuel ratio; The system includes: a fuel ratio sub-feedback control, which switches the target air-fuel ratio from a lean air-fuel ratio (more lean than the stoichiometric air-fuel ratio) to a rich air-fuel ratio (more rich than the stoichiometric air-fuel ratio) when the exhaust gas purification catalyst is detected by the downstream air-fuel ratio sensor; and a sub-feedback learning control, which updates the sub-feedback learning value as a correction value for the target air-fuel ratio; and an active air-fuel ratio control, which, when the exhaust gas purification catalyst is detected by the downstream air-fuel ratio sensor, switches the target air-fuel ratio from the rich air-fuel ratio to the lean air-fuel ratio. Under specific conditions predetermined based on the different conditions of the rich-fuel failure and the lean-fuel failure, a forced switch between the target air-fuel ratio and the rich-fuel ratio is performed. The sub-feedback learning control includes: a rich-fuel attachment update process, which updates the sub-feedback learning value when a predetermined rich-fuel attachment condition is met, representing a state in which the lean-fuel failure is not detected continuously after the switch from the rich-fuel ratio to the lean-fuel ratio based on the air-fuel ratio sub-feedback control. This update ensures that the target air-fuel ratio is updated to a more suitable value. The fuel ratio becomes a lean-biased air-fuel ratio compared to before the update; and a lean-fuel attachment update process is performed, which updates the sub-feedback learning value to make the updated target air-fuel ratio more lean-biased than before the update, provided that a predetermined lean-fuel attachment condition is met, which represents a state in which the rich-fuel failure is not detected continuously after the target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio based on the air-fuel ratio sub-feedback control, so that the updated target air-fuel ratio becomes a rich-fuel ratio compared to before the update. During the execution of the active air-fuel ratio control, the rich-fuel attachment update process and the lean-fuel attachment update process are prohibited.

[0009] Invention Effects

[0010] Based on the above structure, unnecessary updates to the sub-feedback learning values ​​caused by the rich-fuel attachment update process and lean-fuel attachment update process resulting from the execution of active air-fuel ratio control can be suppressed. Attached Figure Description

[0011] Figure 1 It is a schematic diagram of the vehicle's structure.

[0012] Figure 2 (a) ~ Figure 2(e) is a timing diagram representing the actions of the typical update process of sub-control and learning control.

[0013] Figure 3 (a) ~ Figure 3 (e) is a timing diagram representing the actions of the lean-burn attachment update process of sub-control and learning control.

[0014] Figure 4 This is a flowchart representing the switching control.

[0015] Figure 5 (a) ~ Figure 5 (h) is a sequence diagram representing the actions of active control. Detailed Implementation

[0016] <General Structure of the Vehicle>

[0017] The following is based on Figures 1-5 An embodiment of the present invention will be described. First, the general structure of the vehicle 100 will be described.

[0018] like Figure 1 As shown, the vehicle 100 is equipped with a spark-ignition internal combustion engine 10. The internal combustion engine 10 includes multiple cylinders 11, a crankshaft 12, an intake passage 21, a throttle valve 22, and multiple fuel injection valves 23. Furthermore, the internal combustion engine 10 includes multiple ignition devices 24, an exhaust passage 26, a first three-way catalytic converter 27, and a second three-way catalytic converter 28.

[0019] Cylinder 11 is a space for burning the fuel-air mixture. The internal combustion engine 10 has four cylinders 11. Furthermore, a crankshaft 12 is connected to a piston (not shown) located within each cylinder 11. The crankshaft 12 rotates due to the combustion of the fuel-air mixture in the cylinder 11. In this embodiment, gasoline is used as an example of the fuel.

[0020] The intake passage 21 is connected to the cylinder 11. The intake passage 21 has four branches, including a portion at its downstream end. Each branch is connected to a cylinder 11. The intake passage 21 introduces intake air from outside the internal combustion engine 10 into each cylinder 11. Additionally, an intake valve (not shown) is located at the connection point between the intake passage 21 and each cylinder 11. The intake valve opens and closes the connection point between the intake passage 21 and the cylinder 11. The throttle valve 22 is located upstream of the branch portion of the intake passage 21. The throttle valve 22 adjusts the amount of air flowing through the intake passage 21.

[0021] Fuel injection valve 23 is located near the downstream end of intake passage 21. Internal combustion engine 10 has four fuel injection valves 23 corresponding to four cylinders 11. The fuel injection valves 23 inject fuel supplied from a fuel tank (not shown) into intake passage 21. As a result, fuel from the fuel injection valves 23 is supplied to the cylinders 11. Ignition devices 24 are located in the cylinders 11. Internal combustion engine 10 has four ignition devices 24 corresponding to the four cylinders 11. Ignition devices 24 ignite the fuel-intake air mixture via spark discharge.

[0022] Exhaust passage 26 is connected to cylinder 11. Exhaust passage 26 has four branches, including a portion at its upstream end. Each branch is connected to a cylinder 11. Exhaust passage 26 discharges exhaust gas from each cylinder 11 to the outside of the internal combustion engine 10. Additionally, an exhaust valve (not shown) is located at the connection point between exhaust passage 26 and each cylinder 11. The exhaust valve opens and closes the connection point between exhaust passage 26 and cylinder 11.

[0023] The first three-way catalytic converter 27 is located downstream of a branch in the exhaust passage 26. The first three-way catalytic converter 27 purifies the exhaust gas flowing through the exhaust passage 26. Specifically, the first three-way catalytic converter 27 has the function of purifying hydrocarbons, carbon monoxide, and nitrogen oxides contained in the exhaust gas. Furthermore, the first three-way catalytic converter 27 has the function of storing oxygen contained in the exhaust gas, i.e., oxygen storage capacity. Therefore, for example, when the air-fuel ratio of the exhaust gas flowing into the first three-way catalytic converter 27 is higher than the stoichiometric air-fuel ratio (AFS), by storing oxygen through the first three-way catalytic converter 27, the air-fuel ratio of the exhaust gas flowing out of the first three-way catalytic converter 27 becomes close to the stoichiometric air-fuel ratio (AFS). On the other hand, for example, when the air-fuel ratio of the exhaust gas flowing into the first three-way catalytic converter 27 is lower than the stoichiometric air-fuel ratio (AFS), by releasing oxygen through the first three-way catalytic converter 27, the air-fuel ratio of the exhaust gas flowing out of the first three-way catalytic converter 27 becomes close to the stoichiometric air-fuel ratio (AFS). Here, the air-fuel ratio is the ratio obtained by dividing the mass of air by the mass of fuel. Therefore, the more air relative to fuel, the higher the air-fuel ratio, i.e., the fuel becomes lean. On the other hand, the less air relative to fuel, the lower the air-fuel ratio, i.e., the fuel becomes rich. In this embodiment, the first three-way catalyst 27 is an example of an exhaust gas purification catalyst.

[0024] The second three-way catalyst 28 is located downstream of the first three-way catalyst 27 in the exhaust passage 26. The second three-way catalyst 28 purifies the exhaust gas flowing through the exhaust passage 26. Specifically, the second three-way catalyst 28 has the function of purifying hydrocarbons, carbon monoxide, and nitrogen oxides contained in the exhaust gas. Furthermore, the second three-way catalyst 28 has the function of storing oxygen contained in the exhaust gas, i.e., oxygen storage capacity.

[0025] The vehicle 100 is equipped with an air flow meter 81, a coolant temperature sensor 82, an intake air temperature sensor 83, and a crankshaft angle sensor 84. Furthermore, the vehicle 100 is equipped with a throttle input sensor 85, a vehicle speed sensor 86, an upstream air-fuel ratio sensor 87, and a downstream air-fuel ratio sensor 88.

[0026] Air flow meter 81 detects the amount of intake air flowing through intake passage 21 per unit time, i.e., intake air volume GA. Coolant temperature sensor 82 detects the temperature of the coolant flowing through various parts of the internal combustion engine 10, i.e., coolant temperature THW. Intake air temperature sensor 83 detects the temperature of the intake air flowing through intake passage 21, i.e., intake air temperature THA. Crankshaft angle sensor 84 detects the crankshaft angle SC, which is the rotational position of crankshaft 12. Throttle operation amount sensor 85 detects the throttle operation amount ACC, which is the amount of throttle pedal operation by the driver. Vehicle speed sensor 86 detects the vehicle speed SP, which is the speed of the vehicle 100.

[0027] The upstream air-fuel ratio sensor 87 is located downstream of a branch in the exhaust passage 26 and upstream of the first three-way catalyst 27. The upstream air-fuel ratio sensor 87 detects the air-fuel ratio of the exhaust gas upstream of the first three-way catalyst 27 within the exhaust passage 26, i.e., the upstream air-fuel ratio AF1. Furthermore, when the internal combustion engine 10 is driven, exhaust gas from all four cylinders 11 flows continuously into the exhaust passage 26, therefore the upstream air-fuel ratio AF1 becomes a value close to the average of the air-fuel ratios in the four cylinders 11. The downstream air-fuel ratio sensor 88 is located downstream of the first three-way catalyst 27 in the exhaust passage 26 and upstream of the second three-way catalyst 28. The downstream air-fuel ratio sensor 88 detects the air-fuel ratio of the exhaust gas downstream of the first three-way catalyst 27 within the exhaust passage 26, i.e., the downstream air-fuel ratio AF2.

[0028] Vehicle 100 is equipped with a control device 90. The control device 90 acquires a signal indicating the intake air volume GA from an air flow meter 81. The control device 90 acquires a signal indicating the coolant temperature THW from a coolant temperature sensor 82. The control device 90 acquires a signal indicating the intake air temperature THA from an intake air temperature sensor 83. The control device 90 acquires a signal indicating the crankshaft angle SC from a crankshaft angle sensor 84. The control device 90 acquires a signal indicating the throttle input ACC from a throttle input sensor 85. The control device 90 acquires a signal indicating the vehicle speed SP from a vehicle speed sensor 86. The control device 90 acquires a signal indicating the upstream air-fuel ratio AF1 from an upstream air-fuel ratio sensor 87. The control device 90 acquires a signal indicating the downstream air-fuel ratio AF2 from a downstream air-fuel ratio sensor 88.

[0029] The control device 90 includes an execution device 91 and a storage device 92. An example of the execution device 91 is a CPU. The storage device 92 includes a read-only ROM, a read-and-write volatile RAM, and a read-and-write non-volatile storage device. The storage device 92 pre-stores a control program 92A as one of various programs. The execution device 91 performs the various processes described later by executing the control program 92A.

[0030] The control unit 90 calculates the vehicle's required driving force, which is the driving force requested by the vehicle 100 for driving, based on the throttle input (ACC) and vehicle speed (SP). The control unit 90 controls the internal combustion engine 10 based on the vehicle's required driving force. Specifically, the control unit 90 controls the opening of the throttle valve 22, the amount of fuel injected from the fuel injection valve 23, and the ignition timing of the ignition device 24 by outputting control signals to the internal combustion engine 10.

[0031] The control device 90 calculates the internal combustion engine speed NE, which is the rotational speed of the crankshaft 12 per unit time, based on the crankshaft angle SC. Furthermore, the control device 90 calculates the catalyst temperature TSC, which is the temperature of the first three-way catalyst 27, based on the driving conditions of the internal combustion engine 10, such as the intake air filling efficiency or the internal combustion engine speed NE. Additionally, the intake air filling efficiency is a value obtained by dividing the mass of intake air actually introduced from the intake passage 21 into the cylinder 11 by the mass of intake air that can be introduced into the cylinder 11 under standard atmospheric conditions.

[0032] <Main Control>

[0033] Next, the main control performed by the control device 90 will be described. In the main control, the control device 90 adjusts the fuel injection quantity from the fuel injection valve 23 based on the upstream air-fuel ratio AF1, so that the air-fuel ratio of the mixture burned in the cylinder 11 becomes the target air-fuel ratio AFT. Furthermore, the target air-fuel ratio AFT is the target value of the air-fuel ratio. In this embodiment, the main control is equivalent to air-fuel ratio main feedback control.

[0034] <Sub-control>

[0035] Next, the sub-control performed by the control device 90 will be explained. This sub-control is equivalent to air-fuel ratio sub-feedback control. In this sub-control, when the downstream air-fuel ratio sensor 88 detects a lean-burn failure in the first three-way catalytic converter 27, the control device 90 switches the target air-fuel ratio AFT from lean air-fuel ratio AFL to rich air-fuel ratio AFR. In this embodiment, the control device 90 determines that a lean-burn failure in the first three-way catalytic converter 27 has been detected by the downstream air-fuel ratio sensor 88 when the downstream air-fuel ratio AF2 is above a predetermined lean value DL. Here, the lean value DL is an air-fuel ratio that is only a certain value higher than the stoichiometric air-fuel ratio AFS. An example of the stoichiometric air-fuel ratio AFS is "14.7". Another example of the lean value DL is "14.8". Furthermore, the lean air-fuel ratio AFL is the lean side of the stoichiometric air-fuel ratio AFS. And the rich air-fuel ratio AFR is the rich side of the stoichiometric air-fuel ratio AFS.

[0036] Furthermore, in the sub-control, when the downstream air-fuel ratio sensor 88 detects a fuel-rich failure in the first three-way catalytic converter 27, the control device 90 switches the target air-fuel ratio AFT from a rich air-fuel ratio AFR to a lean air-fuel ratio AFL. In this embodiment, the control device 90 determines that a fuel-rich failure in the first three-way catalytic converter 27 has been detected by the downstream air-fuel ratio sensor 88 when the downstream air-fuel ratio AF2 is below a predetermined rich value DR. Here, the rich value DR is an air-fuel ratio that is only a certain value lower than the stoichiometric air-fuel ratio AFS. An example of the rich value DR is "14.6".

[0037] <Routine Update Processing for Learning Control>

[0038] Next, the normal update process of the learning control performed by the control device 90 will be described. This learning control is a control used to update the learning value LV, which is a correction value for the target air-fuel ratio (AFT). Here, the learning value LV is equivalent to a sub-feedback learning value. Furthermore, the learning control is equivalent to sub-feedback learning control.

[0039] The learning control includes a routine update process. In this routine update process, the control device 90 calculates a presumed oxygen storage amount DA, which is a presumed value of the oxygen stored in the first three-way catalyst 27 during the period from the target air-fuel ratio AFT to the lean air-fuel ratio AFL, until lean-fuel failure is detected. Specifically, the control device 90 calculates the amount of oxygen stored in the first three-way catalyst 27 per unit time based on the upstream air-fuel ratio AF1. Furthermore, the control device 90 calculates the presumed oxygen storage amount DA by accumulating the amount of oxygen stored per unit time.

[0040] Furthermore, in the normal update process, the control device 90 calculates the estimated deoxygenation amount DB of the first three-way catalytic converter 27 as an estimated value of the amount of oxygen removed during the period from the sub-control-based switch to the target air-fuel ratio AFT (AFR) until the detection of fuel-rich failure. Specifically, the control device 90 calculates the amount of oxygen removed per unit time in the first three-way catalytic converter 27 based on the upstream air-fuel ratio AF1. Moreover, the control device 90 calculates the estimated deoxygenation amount DB by accumulating the amount of oxygen removed per unit time.

[0041] Furthermore, in the normal update process, the control device 90 updates the learning value LV based on the difference between the estimated storage amount DA and the estimated depletion amount DB. As a prerequisite, for example, if the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is the true value, in other words, the actual air-fuel ratio, then the estimated storage amount DA and the estimated depletion amount DB are the same. Conversely, for example, if the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is more biased towards the rich side than the true value, then the estimated storage amount DA is less than the estimated depletion amount DB. On the other hand, for example, if the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is more biased towards the lean side than the true value, then the estimated storage amount DA is greater than the estimated depletion amount DB. Therefore, for example, if the estimated storage amount DA is less than the estimated depletion amount DB, the control device 90 updates the learning value LV based on the difference between the estimated storage amount DA and the estimated depletion amount DB, so that the updated target air-fuel ratio AFT is more biased towards the rich side than before the update. In this embodiment, when the estimated storage amount DA is less than the estimated depletion amount DB, the learning value LV decreases. On the other hand, for example, when the estimated storage amount DA is greater than the estimated depletion amount DB, the control device 90 updates the learning value LV based on the difference between the estimated storage amount DA and the estimated depletion amount DB, so that the updated target air-fuel ratio AFT is more lean-biased than the original air-fuel ratio. In this embodiment, when the estimated storage amount DA is greater than the estimated depletion amount DB, the learning value LV increases.

[0042] <Regarding the routine update processing of sub-controls and learning controls>

[0043] exist Figure 2 In the example shown, assuming a time point before time t11, the control device 90 sets the target air-fuel ratio AFT to a rich air-fuel ratio AFR. Furthermore, assuming the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is the true value, in other words, the actual air-fuel ratio. In this case, as... Figure 2 As shown by the solid line in (a), at time points before t11, the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is only slightly lower than the theoretical air-fuel ratio AFS. Furthermore, as... Figure 2As shown in (c), the actual stored OSA decreases before time t11. Furthermore, the actual stored OSA is the amount of oxygen actually stored in the first ternary catalyst 27. Thus, as the actual stored OSA decreases, oxygen is less likely to be released from the first ternary catalyst 27 when the actual stored OSA approaches its lower limit.

[0044] Then, as Figure 2 As shown in (b), at time t11, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes below the rich-fuel ratio DR. In this case, the control device 90 determines that the first three-way catalyst 27 has experienced a rich-fuel failure as detected by the downstream air-fuel ratio sensor 88. Furthermore, the control device 90 switches the target air-fuel ratio AFT from rich-fuel ratio AFR to lean-fuel ratio AFL. Then, as... Figure 2 As shown by the solid line in (a), at time t11, the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is only slightly higher than the theoretical air-fuel ratio AFS. Moreover, as... Figure 2 As shown in (c), after time t11, the actual storage amount of OSA increases. Thus, when the actual storage amount of OSA approaches its upper limit, oxygen is not easily stored by the first ternary catalyst 27.

[0045] Then, as Figure 2 As shown in (b), at time t12, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes above the lean specified value DL. In this case, the control device 90 determines that the first three-way catalyst 27 has experienced a lean-burn failure as detected by the downstream air-fuel ratio sensor 88. Furthermore, the control device 90 switches the target air-fuel ratio AFT from lean air-fuel ratio AFL to rich air-fuel ratio AFR. Then, as... Figure 2 As shown by the solid line in (a), at time t12, the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is only slightly lower than the theoretical air-fuel ratio AFS. Moreover, as... Figure 2 As shown in (c), after time t12, the actual storage amount of OSA decreases.

[0046] Then, as Figure 2 As shown in (b), at time t13, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes below the rich-fuel ratio DR. In this case, the control device 90 determines that the first three-way catalyst 27 has experienced a rich-fuel failure as detected by the downstream air-fuel ratio sensor 88. Furthermore, the control device 90 switches the target air-fuel ratio AFT from rich-fuel ratio AFR to lean-fuel ratio AFL. Then, the control device 90 repeatedly executes the processing from time t11 to time t13.

[0047] In contrast, for example, suppose the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is more biased towards the rich side than the true value. In this case, such as Figure 2 As shown by the dashed line in (a), the actual air-fuel ratio at the location of the upstream air-fuel ratio sensor 87 is a value that is more lean-towards than the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87. Therefore, as Figure 2 As shown in (d), the estimated storage amount DA from time t11 to time t12 is less than the estimated detachment amount DB from time t12 to time t13. The result is as follows: Figure 2 As shown in (e), at time t13, the control device 90 updates the learning value LV based on the difference between the estimated storage amount DA and the estimated depletion amount DB, so that the updated target air-fuel ratio AFT is more biased towards the rich side than before the update. Furthermore, Figure 2 In (d), the oxygen excess / deficient amount (OED) is an indicator used to represent the estimated storage amount (DA) and the estimated depletion amount (DB). In this embodiment, the control device 90 resets the oxygen excess / deficient amount (OED) to zero if it detects one or more of the rich fuel failure and lean fuel failure.

[0048] <Learning-Controlled Fuel-Rich Adhesion Renewal Process>

[0049] Next, the fuel-rich fuel attachment update process performed by the control device 90 will be described. The learning control includes the fuel-rich fuel attachment update process. This process updates the learning value LV when the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is more lean than the actual value, and this deviation is large. In other words, the fuel-rich fuel attachment update process updates the learning value LV when the actual air-fuel ratio is significantly more lean than the upstream air-fuel ratio AF1. Specifically, the control device 90 determines whether a predetermined fuel-rich fuel attachment condition is met after a target air-fuel ratio AFT is switched from a rich air-fuel ratio AFR to a lean air-fuel ratio AFL based on sub-control. Furthermore, if the fuel-rich fuel attachment condition is met, the control device 90 updates the learning value LV so that the updated target air-fuel ratio AFT is more lean than the previous one. In this embodiment, the learning value LV increases in the above-described case.

[0050] Here, the rich-fuel adhesion condition refers to the condition that no lean-fuel failure is detected continuously after the target air-fuel ratio (AFT) is switched. In this embodiment, the control device 90 determines that the rich-fuel adhesion condition is met when the cumulative intake air volume (GAA), which is the cumulative amount of intake air volume (GA), is a predetermined cumulative amount (GZ) or higher. Furthermore, the control device 90 resets the cumulative intake air volume (GAA) to zero if one or more of the following conditions (A-1) to (A-4) are met.

[0051] Requirement (A-1): Switch the target air-fuel ratio (AFT) from a rich air-fuel ratio (AFR) to a lean air-fuel ratio (AFL) via sub-control.

[0052] Requirement (A-2): Switch the target air-fuel ratio (AFT) from lean air-fuel ratio (AFL) to rich air-fuel ratio (AFR) via sub-control.

[0053] Requirement (A-3): Fuel-rich adhesion renewal treatment was performed.

[0054] Requirement (A-4): The lean-burn attachment renewal process described later has been performed.

[0055] Therefore, in this embodiment, the cumulative intake air volume GAA is equivalent to the cumulative intake air volume after the target air-fuel ratio AFT is switched from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL based on sub-control.

[0056] <Low-burning Adhesion Renewal Treatment Based on Learning>

[0057] Next, the lean-burn attachment update process performed by the control device 90 will be described. The learning control includes the lean-burn attachment update process. This process updates the learning value LV when the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is more lean than the actual value, and this deviation is large. In other words, the lean-burn attachment update process updates the learning value LV when the actual air-fuel ratio is significantly leaner than the upstream air-fuel ratio AF1. Specifically, the control device 90 determines whether a predetermined lean-burn attachment condition is met after a target air-fuel ratio AFT is switched from a lean air-fuel ratio AFL to a rich air-fuel ratio AFR based on sub-control. Furthermore, if the lean-burn attachment condition is met, the control device 90 updates the learning value LV so that the updated target air-fuel ratio AFT is more lean than the previous target air-fuel ratio. In this embodiment, the learning value LV is smaller in the above-described case.

[0058] Here, the lean-burn adhesion condition refers to the condition that no rich-burn failure is detected continuously after the target air-fuel ratio (AFT) is switched. In this embodiment, the control device 90 determines that the lean-burn adhesion condition is met when the cumulative intake air volume (GAA), which is the cumulative amount of intake air, is a predetermined cumulative amount (GZ) or higher. As described above, the control device 90 resets the cumulative intake air volume (GAA) to zero when one or more of the conditions (A-1) to (A-4) are met. Therefore, in this embodiment, the cumulative intake air volume (GAA) is equivalent to the cumulative intake air volume after the target air-fuel ratio (AFT) is switched from the lean air-fuel ratio (AFL) to the rich air-fuel ratio (AFR) based on sub-control.

[0059] <Regarding the actions for lean-burn attachment renewal in sub-control and learning control>

[0060] exist Figure 3 In the example shown, assuming that at a time point before time t21, the control device 90 sets the target air-fuel ratio AFT to a lean air-fuel ratio AFL. Furthermore, for example, assuming that the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is more biased towards the rich side than the true value, and that this deviation is large. That is, as... Figure 3 As shown by the dashed line in (a), the actual air-fuel ratio at the location of the upstream air-fuel ratio sensor 87 is a value that is significantly more lean than the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87.

[0061] Then, as Figure 3 As shown in (b), suppose that at time t21, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes a lean value DL or higher. In this case, the control device 90 determines that the first three-way catalyst 27 has experienced a lean-burn failure as detected by the downstream air-fuel ratio sensor 88. Furthermore, the control device 90 switches the target air-fuel ratio AFT from lean air-fuel ratio AFL to rich air-fuel ratio AFR.

[0062] As mentioned above, the actual air-fuel ratio at the location of the upstream air-fuel ratio sensor 87 is a value that is significantly more lean than the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87. Therefore, as Figure 3 As shown in (c), after time t21, the actual storage amount of OSA is not easily reduced.

[0063] Then, as Figure 3 As shown in (d), at time t22, the cumulative intake air volume GAA reaches or exceeds a predetermined cumulative volume GZ. In this case, the control device 90 determines that the predetermined lean-burn adhesion condition is met after the target air-fuel ratio AFT is switched from lean air-fuel ratio AFL to rich air-fuel ratio AFR based on sub-control. Moreover, as Figure 3 As shown in (e), at time t22, the control device 90 updates the learned value LV so that the updated target air-fuel ratio AFT is more biased towards the rich side than before the update. In addition, in this case, the control device 90 resets the intake cumulative quantity GAA to zero.

[0064] Then, as Figure 3 As shown in (d), similarly to time t22, at time t23, the cumulative intake air volume GAA also becomes a predetermined cumulative volume GZ or higher. Therefore, as Figure 3 As shown in (e), at time t23, the control device 90 updates the learned value LV so that the updated target air-fuel ratio AFT is more biased towards the rich side than before the update. In addition, in this case, the control device 90 resets the intake cumulative quantity GAA to zero.

[0065] Then, as Figure 3 As shown in (b), at time t24, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes below the rich-fuel ratio DR. In this case, the control device 90 determines that the first three-way catalyst 27 has experienced a rich-fuel failure as detected by the downstream air-fuel ratio sensor 88. Furthermore, the control device 90 switches the target air-fuel ratio AFT from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL.

[0066] <Switching control of execution content related to learning control>

[0067] Next, refer to Figure 4 The switching control will be explained below. This switching control is used to switch the execution content of the learning control. In this embodiment, the control device 90 starts the switching control according to a predetermined control cycle, taking the operation of the internal combustion engine 10 as a necessary condition.

[0068] like Figure 4 As shown, when the control device 90 starts switching control, it executes the process in step S11. In step S11, the control device 90 determines whether it is in the period of executing active control (described later). In step S11, if the control device 90 determines that it is in the period of executing active control (S11: Yes), the control device 90 causes the process to proceed to step S21.

[0069] In step S21, the control device 90 prohibits the execution of both rich-fuel attachment renewal processing and lean-fuel attachment renewal processing. However, the control device 90 does not prohibit the execution of normal renewal processing. After step S21, the control device 90 terminates this switching control.

[0070] On the other hand, in step S11 above, if the control device 90 determines that it is not in the period of active control (S11: No), the control device 90 causes the process to proceed to step S22.

[0071] In step S22, the control device 90 allows the execution of both rich-fuel adhesion renewal processing and lean-fuel adhesion renewal processing. That is, in this case, the control device 90 can perform normal renewal processing, rich-fuel adhesion renewal processing, and lean-fuel adhesion renewal processing. After step S22, the control device 90 terminates this switching control.

[0072] <Active Control>

[0073] Next, the active control performed by the control device 90 will be explained. This active control is a control that forcibly switches between a lean air-fuel ratio (AFL) and a rich air-fuel ratio (AFR) target air-fuel ratio (AFT) when certain predetermined conditions are met. That is, active control is equivalent to active air-fuel ratio control. In this embodiment, the control device 90 determines that the specific conditions are met when all of the following conditions (B-1) and conditions (B-2) are met.

[0074] Requirement (B-1): The catalyst temperature TSC is above the predetermined specified temperature TZ.

[0075] Requirement (B-2): Active control was not performed during the operation of the internal combustion engine 10.

[0076] Here, temperature TZ is predetermined as the temperature at which the degree of activation of the first ternary catalyst 27 can be determined. Therefore, under specific conditions, the first ternary catalyst 27 is in a state where its oxygen storage capacity can be fully utilized. Furthermore, these specific conditions are different from those used to detect rich-burn and lean-burn failures.

[0077] Active control includes a first process, a second process, and a determination process. Specifically, after determining that a specific condition is met, the control device 90 executes a first process to set the target air-fuel ratio (AFT) to a rich air-fuel ratio (AFR). Then, if a rich air-fuel ratio failure is detected during the execution of the first process, the control device 90 executes a second process to set the target air-fuel ratio (AFT) to a lean air-fuel ratio (AFL). Furthermore, the control device 90 executes a determination process. In the determination process, the control device 90 calculates a calculated storage amount (DAZ) as the calculated oxygen storage capacity of the first three-way catalyst 27 from the rich air-fuel ratio failure during the execution of the first process to the detection of a lean air-fuel ratio failure in the second process. Furthermore, based on the calculated storage amount (DAZ), the control device 90 determines whether the oxygen storage capacity has decreased. For example, if the calculated storage amount (DAZ) is below a predetermined reference value, the control device 90 determines that the oxygen storage capacity is decreasing. Additionally, the control device 90 calculates the calculated storage amount (DAZ) as follows. The control device 90 calculates the amount of oxygen stored per unit time in the first three-way catalyst 27 based on the upstream air-fuel ratio AF1. Furthermore, the control device 90 calculates the calculated storage amount DAZ by accumulating the amount of oxygen stored per unit time.

[0078] <Regarding Active Control Actions>

[0079] exist Figure 5 In the example shown, such as Figure 5 As shown in (d), suppose that at a time point before t33, the catalyst temperature TSC is lower than a predetermined temperature TZ. Therefore, as Figure 5 As shown in (e), at time points before t33, the control device 90 did not perform active control. Furthermore, as... Figure 5 As shown in (c), suppose that at time t31, the control device 90 switches the target air-fuel ratio AFT from lean air-fuel ratio AFL to rich air-fuel ratio AFR via sub-control. In this case, as Figure 5 As shown in (f), after time t31, the actual storage amount of OSA decreases.

[0080] Then, as Figure 5 As shown in (b), at time t32, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes below the rich-fuel ratio DR. In this case, the control device 90 determines that the first three-way catalyst 27 has experienced a rich-fuel failure as detected by the downstream air-fuel ratio sensor 88. Furthermore, the control device 90 switches the target air-fuel ratio AFT from the rich-fuel ratio AFR to the lean-fuel ratio AFL via sub-control. As a result, as Figure 5 As shown in (f), after time t32, the actual storage capacity OSA increases. Furthermore, as... Figure 5 As shown in (g), after time t32, the cumulative intake air volume (GAA) increases. Additionally, as... Figure 5 As shown in (g), at time t32, the intake cumulative amount GAA is reset to zero.

[0081] Then, as Figure 5 As shown in (d), at time t33, the catalyst temperature TSC becomes above a predetermined temperature TZ. In this case, the control device 90 determines that a specific condition has been met. Moreover, as... Figure 5 As shown in (e), after time t33, the control device 90 performs active control. Specifically, at time t33, after determining that a specific condition is met, the control device 90 performs the first process of setting the target air-fuel ratio (AFT) to the rich air-fuel ratio (AFR). The result is as follows: Figure 5 As shown in (f), after time t33, the actual stored OSA decreases. Furthermore, at time t33, since none of the above requirements (A-1) to (A-4) are met, the control device 90 does not reset the intake accumulated amount GAA to zero. Therefore, as... Figure 5 As shown in (g), after time t33, the cumulative intake air volume GAA continues to increase.

[0082] Then, as Figure 5 As shown in (b), at time t34, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes below the rich-fuel ratio DR. In this case, the control device 90 determines that the rich-fuel ratio of the first three-way catalyst 27 has failed to be detected by the downstream air-fuel ratio sensor 88. Furthermore, the control device 90 performs a second process. That is, if the control device 90 detects a rich-fuel ratio failure during the execution of the first process, it performs a second process of setting the target air-fuel ratio AFT to a lean air-fuel ratio AFL. Then, as... Figure 5 As shown in (f), the actual storage capacity OSA increases after time t34.

[0083] Then, as Figure 5As shown in (b), at time t36, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes a lean specified value DL or higher. In this case, the control device 90 determines that a lean-burn failure of the first three-way catalytic converter 27 has been detected by the downstream air-fuel ratio sensor 88. Furthermore, the control device 90 performs a determination process. That is, the control device 90 calculates a calculated storage amount DAZ as a calculated value of the oxygen storage capacity of the first three-way catalytic converter 27 during the period from the rich-burn failure during the execution of the first process to the detection of the lean-burn failure in the second process. Then, based on the calculated storage amount DAZ, the control device 90 determines whether the oxygen storage capacity has decreased. In addition, at time t36, the control device 90 switches the target air-fuel ratio AFT from lean air-fuel ratio AFL to rich air-fuel ratio AFR through sub-control.

[0084] <The function of this implementation method>

[0085] For example, suppose that the control device 90 does not prohibit the rich-fuel attachment renewal process and the lean-fuel attachment renewal process during the active control period from time t33 to time t36. In this case, such as Figure 5 As shown in (g), at time t35, after time t34 and before time t36, the cumulative intake air quantity GAA reaches or exceeds a predetermined cumulative quantity GZ. Then, the control device 90 determines that the predetermined rich fuel adhesion condition is met after the target air-fuel ratio AFT is switched from a rich air-fuel ratio AFR to a lean air-fuel ratio AFL based on sub-control. Then, as... Figure 5 As shown by the double-dotted line in (h), at time t35, the control device 90 updates the learned value LV so that the updated target air-fuel ratio AFT is more lean-biased than the previous one. In other words, as... Figure 5 As shown in (a), although the actual air-fuel ratio AF1 is not significantly more lean than the upstream side, the control device 90 will still update the learning value LV so that the updated target air-fuel ratio AFT is more lean than the original air-fuel ratio.

[0086] <Effects of this implementation method>

[0087] (1) In this embodiment, the control device 90 prohibits the execution of rich-fuel attachment renewal processing and lean-fuel attachment renewal processing during active control. This suppresses the useless updating of the learning value LV caused by the rich-fuel attachment renewal processing and lean-fuel attachment renewal processing performed during active control. Furthermore, suppressing the useless updating of the learning value LV in this way also suppresses the deterioration of exhaust emissions from the internal combustion engine 10 caused by useless updating.

[0088] (2) As described above, for example, if the period from the switch to the target air-fuel ratio AFT based on the sub-control to the lean air-fuel ratio AFL due to the execution of active control until the lean-fuel failure is detected becomes longer, the intake gas accumulation GAA is likely to increase. On the other hand, the values ​​of the estimated storage amount DA and the estimated depletion amount DB in the normally updated processing due to the execution of active control are less likely to change.

[0089] Regarding this, during active control, the control device 90 prohibits the execution of rich-fuel attachment update processing and lean-fuel attachment update processing, but does not prohibit the execution of normal update processing. Therefore, even during active control, the learning value LV can be appropriately updated based on the estimated storage amount DA and the estimated detachment amount DB through normal update processing.

[0090] (3) In active control, after determining that a specific condition is met, the control device 90 executes a first process to set the target air-fuel ratio AFT to a rich air-fuel ratio AFR. Then, if a rich-fuel failure is detected during the execution of the first process, the control device 90 executes a second process to set the target air-fuel ratio AFT to a lean air-fuel ratio AFL. Furthermore, the control device 90 performs a determination process. That is, the control device 90 calculates a calculated storage amount DAZ, which is a calculated value of the oxygen storage capacity of the first three-way catalyst 27 during the period from the rich-fuel failure during the execution of the first process to the detection of a lean-fuel failure in the second process. Furthermore, the control device 90 determines whether the oxygen storage capacity has decreased based on the calculated storage amount DAZ. Thus, it is possible to determine whether the oxygen storage capacity has decreased based on the calculated storage amount DAZ from the rich-fuel failure to the lean-fuel failure. In other words, it is possible to determine whether the performance of the first three-way catalyst 27 has decreased based on the calculated storage amount DAZ.

[0091] (4) For example, even if the period following the switch from the target air-fuel ratio AFR to the lean air-fuel ratio AFL based on the sub-control is the same, the amount of oxygen in the first three-way catalyst 27 will vary depending on the amount of exhaust gas flowing through the exhaust passage 26 per unit time. Therefore, in the learning control, it is assumed that if the focus is only on the period following the switch from the target air-fuel ratio AFR to the lean air-fuel ratio AFL based on the sub-control, the ease with which the rich air-fuel condition is satisfied can be easily changed.

[0092] Regarding this, the control device 90 determines that the rich-fuel adhesion condition is met when the cumulative intake air volume GAA after the sub-control switches from the target air-fuel ratio AFT from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL is at least a predetermined cumulative volume GZ. Furthermore, the control device 90 determines that the lean-fuel adhesion condition is met when the cumulative intake air volume GAA after the sub-control switches from the target air-fuel ratio AFT from the lean air-fuel ratio AFL to the rich air-fuel ratio AFR is at least a predetermined cumulative volume GZ. Therefore, it is possible to suppress changes in the ease of meeting the rich-fuel adhesion condition, etc., based on the amount of exhaust gas flowing through the exhaust passage 26 per unit time.

[0093] <Example of Change>

[0094] This embodiment can be modified as follows. This embodiment and the following modifications can be combined with each other within the scope of technical inconsistency.

[0095] • In the above implementation method, the switching control can be changed.

[0096] For example, in step S21, in addition to prohibiting the execution of fuel-rich attachment renewal processing and fuel-lean attachment renewal processing, the control device 90 can also prohibit the execution of normal renewal processing.

[0097] • In the above implementation, the learning control can be modified.

[0098] For example, if the learning control includes both rich-fuel attachment renewal processing and lean-fuel attachment renewal processing, then the learning control may not include the normal renewal processing. In other words, the control device 90 may only be able to execute the rich-fuel attachment renewal processing and lean-fuel attachment renewal processing in the learning control.

[0099] For example, the fuel-rich adhesion conditions can be changed. Specifically, if the period following the switch from a target air-fuel ratio (AFR) to a lean air-fuel ratio (AFL) based on sub-control is longer than a predetermined period, the control device 90 can determine that the fuel-rich adhesion conditions are met. Furthermore, for example, if the change in the amount of exhaust gas flowing through the exhaust passage 26 per unit time is relatively small, the change described above will not cause any problem.

[0100] For example, the lean-burn conditions can be changed. Specifically, if the period following the switch from a lean air-fuel ratio (AFL) to a target air-fuel ratio (AFR) based on sub-control is longer than a predetermined period, the control device 90 can determine that the lean-burn conditions are met. Furthermore, if the change in the amount of exhaust gas flowing through the exhaust passage 26 per unit time is relatively small, the change described above will not be problematic.

[0101] • In the above implementation method, the active control can be changed.

[0102] For example, the contents of the first process, the second process, and the determination process in the active control can be changed. As a specific example, the first process can have the following structure: First, after determining that a specific condition is met, the control device 90 executes the first process, setting the target air-fuel ratio AFT to a lean air-fuel ratio AFL. Next, if a lean-burn failure is detected during the execution of the first process, the control device 90 executes the second process, setting the target air-fuel ratio AFT to a rich air-fuel ratio AFR. Furthermore, the control device 90 executes the determination process. In the determination process, the control device 90 calculates a calculated deoxygenation amount DBZ, which is a calculated value of the amount of oxygen removed from the first three-way catalyst 27 during the period from the lean-burn failure during the execution of the first process to the detection of a rich-burn failure in the second process. Furthermore, based on the calculated deoxygenation amount DBZ, the control device 90 determines whether the oxygen storage capacity has decreased. Additionally, as an example, if the calculated deoxygenation amount DBZ is below a predetermined reference value, the control device 90 determines that the oxygen storage capacity has decreased. Based on this structure, it is possible to determine whether the oxygen storage capacity has decreased based on the calculated separation amount DBZ from lean-burn failure to rich-burn failure. In other words, it is possible to determine whether the performance of the first ternary catalyst 27 has decreased based on the calculated separation amount DBZ.

[0103] • In the above embodiments, the structure of vehicle 100 can be changed.

[0104] For example, the structure of the control device 90 can be modified. Specifically, the control device 90 can be configured as a circuit including one or more processors that perform various processes according to a computer program (software). Alternatively, the control device 90 can also be configured as a circuit including one or more dedicated hardware circuits, such as application-specific integrated circuits (ASICs), or combinations thereof, that perform at least a portion of the various processes. The processor includes a CPU and memories such as RAM and ROM. Program code or instructions configured for execution by the CPU are stored in the memory. Memory, or computer-readable medium, includes any medium that can be accessed by a general-purpose or special-purpose computer.

[0105] Symbol Explanation

[0106] 10-Internal combustion engine, 11-Cylinder, 12-Crankshaft, 21-Intake passage, 22-Throttle valve, 23-Fuel injection valve, 24-Ignition device, 26-Exhaust passage, 27-First three-way catalytic converter, 28-Second three-way catalytic converter, 81-Air flow meter, 82-Water temperature sensor, 83-Intake air temperature sensor, 84-Crankshaft angle sensor, 85-Throttle input sensor, 86-Vehicle speed sensor, 87-Upstream air-fuel ratio sensor, 88-Downstream air-fuel ratio sensor, 90-Control device, 91-Actuator, 92-Storage device, 92A-Control program, 100-Vehicle.

Claims

1. A control device for an internal combustion engine, characterized in that, have: An exhaust gas purification catalyst is located in the exhaust passage and has oxygen storage capacity; an upstream air-fuel ratio sensor is located upstream of the exhaust gas purification catalyst in the exhaust passage; and a downstream air-fuel ratio sensor is located downstream of the exhaust gas purification catalyst in the exhaust passage. The control device of the internal combustion engine is capable of performing: Air-fuel ratio main feedback control adjusts the fuel injection quantity based on the detection value of the upstream air-fuel ratio sensor so that the air-fuel ratio of the mixture burned in the cylinder becomes the target air-fuel ratio. The air-fuel ratio feedback control switches the target air-fuel ratio from a lean air-fuel ratio (more lean than the stoichiometric air-fuel ratio) to a rich air-fuel ratio (more rich than the stoichiometric air-fuel ratio) when the downstream air-fuel ratio sensor detects a lean-burn failure of the exhaust purification catalyst; and switches the target air-fuel ratio from the rich air-fuel ratio to the lean air-fuel ratio when the downstream air-fuel ratio sensor detects a rich-burn failure of the exhaust purification catalyst. Subfeedback learning control updates the subfeedback learning value as a correction value for the target air-fuel ratio; and Active air-fuel ratio control, which, when specific conditions predetermined and different from those for detecting rich-fuel failure and lean-fuel failure are met, forces a switch between the target air-fuel ratio and the rich-fuel ratio. The sub-feedback learning control includes: The rich-fuel attachment update process updates the sub-feedback learning value when a predetermined rich-fuel attachment condition is met, representing a state where no lean-fuel failure is detected after a switch from the rich air-fuel ratio to the lean air-fuel ratio based on the air-fuel ratio sub-feedback control. This update ensures that the updated target air-fuel ratio is more lean-biased than the previous one. The lean-burn attachment update process updates the sub-feedback learning value when a predetermined lean-burn attachment condition is met, which represents a state in which no rich-burn failure is detected after the target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio based on the air-fuel ratio sub-feedback control. This update makes the target air-fuel ratio more biased towards the rich side than before the update. During the execution of the active air-fuel ratio control, the rich fuel attachment renewal process and the lean fuel attachment renewal process are prohibited.

2. The control device for an internal combustion engine according to claim 1, characterized in that, The sub-feedback learning control includes: The typical update process involves calculating, based on the detection values ​​from the upstream air-fuel ratio sensor, the oxygen storage capacity of the exhaust gas purification catalyst during the period from the switch from the target air-fuel ratio based on the air-fuel ratio sub-feedback control to the lean air-fuel ratio until the detection of lean-fuel failure, and the oxygen removal capacity of the exhaust gas purification catalyst during the period from the switch from the target air-fuel ratio based on the air-fuel ratio sub-feedback control to the rich air-fuel ratio until the detection of rich-fuel failure. The sub-feedback learning value is then updated based on the difference between the oxygen storage capacity and the oxygen removal capacity. During the active air-fuel ratio control, the rich-fuel attachment update process and the lean-fuel attachment update process are prohibited, while the normal update process is not prohibited.

3. The control device for an internal combustion engine according to claim 1, characterized in that, The active air-fuel ratio control includes: The first process sets the target air-fuel ratio to the rich air-fuel ratio after the specific conditions are met. The second process, which, if the rich-fuel failure is detected during the execution of the first process, sets the target air-fuel ratio to the lean-fuel ratio; and The determination process is based on the oxygen storage capacity of the exhaust gas purification catalyst during the period from the rich-fuel failure during the execution of the first process to the detection of the lean-fuel failure in the second process, to determine whether the oxygen storage capacity has decreased.

4. The control device for an internal combustion engine according to claim 1, characterized in that, The active air-fuel ratio control includes: The first process sets the target air-fuel ratio to the lean air-fuel ratio after the specific conditions are met. The second process, which, if the lean-burn failure is detected during the execution of the first process, sets the target air-fuel ratio to the rich air-fuel ratio; and The determination process is based on the amount of oxygen removed by the exhaust gas purification catalyst during the period from the lean-burn failure during the execution of the first process to the detection of the rich-burn failure in the second process, to determine whether the oxygen storage capacity has decreased.

5. The control device for an internal combustion engine according to claim 1 or 2, characterized in that, In the sub-feedback learning control, the cumulative amount of intake air after the target air-fuel ratio switch from the rich air-fuel ratio to the lean air-fuel ratio based on the air-fuel ratio sub-feedback control is used to determine whether the rich fuel adhesion condition is met. The lean-burn adhesion condition is determined based on the cumulative amount of intake air after the target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio based on the air-fuel ratio sub-feedback control.

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