Control device for internal combustion engines

Abstract

This suppresses unnecessary updates of subfeedback learning values ​​caused by the execution of active air-fuel ratio control. [Solution] The control device for the internal combustion engine is capable of performing air-fuel ratio subfeedback control, subfeedback learning control, and air-fuel ratio active control. In subfeedback learning control, if the control device satisfies the rich-sticking condition, which indicates that a lean breakdown has not been detected after the target air-fuel ratio has been switched from a rich air-fuel ratio to a lean air-fuel ratio by air-fuel ratio subfeedback control, it executes a rich-sticking update process to update the subfeedback learning value so that after the update, the target air-fuel ratio is leaner than before the update. In air-fuel ratio active control, the control device forcibly switches the target air-fuel ratio between a lean air-fuel ratio and a rich air-fuel ratio. The control device prohibits the execution of the rich-sticking update process while air-fuel ratio active control is being performed (S21).

Description

Technical Field

[0001] The present invention relates to a control device for an internal combustion engine.

Background Art

[0002] The system of Patent Document 1 includes 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. The exhaust passage allows the exhaust discharged from the cylinder to flow. The exhaust purification catalyst has an oxygen storage capacity. The upstream air-fuel ratio sensor detects the air-fuel ratio of the exhaust in the upstream portion with respect to the exhaust purification catalyst in the exhaust passage. The downstream air-fuel ratio sensor detects the air-fuel ratio of the exhaust in the downstream portion with respect to the exhaust purification catalyst in the exhaust passage.

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

[0004] The control device executes air-fuel ratio sub feedback control. Specifically, when the control device detects a lean breakthrough of the exhaust purification catalyst by the downstream air-fuel ratio sensor, the control device switches the target air-fuel ratio from a lean air-fuel ratio on the lean side of the stoichiometric air-fuel ratio to a rich air-fuel ratio on the rich side of the stoichiometric air-fuel ratio. Further, when the control device detects a rich breakthrough of the exhaust purification catalyst by the downstream air-fuel ratio sensor, the control device switches the target air-fuel ratio from a rich air-fuel ratio on the rich side of the stoichiometric air-fuel ratio to a lean air-fuel ratio on the lean side of the stoichiometric air-fuel ratio.

[0005] The control unit performs subfeedback learning control. This subfeedback learning control is a control for updating the subfeedback learning value, which is a correction value for the target air-fuel ratio. Specifically, the control unit determines whether the rich-sticking condition is met, which indicates that no lean failure has been detected after the target air-fuel ratio switch from a rich air-fuel ratio to a lean air-fuel ratio by air-fuel ratio subfeedback control. If the control unit determines that the rich-sticking condition is met, it performs a rich-sticking update process to update the subfeedback learning value so that after the update, the target air-fuel ratio is leaner than before the update. The control unit also determines whether the lean-sticking condition is met, which indicates that no rich failure has been detected after the target air-fuel ratio switch from a lean air-fuel ratio to a rich air-fuel ratio by air-fuel ratio subfeedback control. If the control unit determines that the lean-sticking condition is met, it performs a lean-sticking update process to update the subfeedback learning value so that after the update, the target air-fuel ratio is richer than before the update. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-023621 [Overview of the project] [Problems that the invention aims to solve]

[0007] In a system like the one described in Patent Document 1, the control device may perform active air-fuel ratio control, which forcibly switches the target air-fuel ratio between a lean air-fuel ratio and a rich air-fuel ratio. In such a system, for example, when the control device has set the target air-fuel ratio to a lean air-fuel ratio using air-fuel ratio subfeedback control, the control device may forcibly switch the target air-fuel ratio to a rich air-fuel ratio using active air-fuel ratio control. In this case, it is likely that a state in which lean failure is not detected will continue after the target air-fuel ratio is switched from a rich air-fuel ratio to a lean air-fuel ratio by air-fuel ratio subfeedback control. As a result, the subfeedback learning value may be unnecessarily updated by the execution of the rich-setting update process. Similarly, when the target air-fuel ratio is forcibly switched to a lean air-fuel ratio by active air-fuel ratio control, the subfeedback learning value may be unnecessarily updated by the execution of the lean-setting update process. [Means for solving the problem]

[0008] A control device for an internal combustion engine to solve the above problems comprises: an exhaust gas purification catalyst having oxygen storage capacity located in the exhaust passage; 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, wherein the control device includes air-fuel ratio main feedback control that adjusts the fuel injection amount so that the air-fuel ratio of the mixture burned in the cylinder becomes a target air-fuel ratio based on the value detected by the upstream air-fuel ratio sensor, and the exhaust gas purification catalyst detected by the downstream air-fuel ratio sensor. Subfeedback control of the air-fuel ratio that switches the target air-fuel ratio from a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio to a rich air-fuel ratio richer than the stoichiometric air-fuel ratio when lean breakdown is detected, and switches the target air-fuel ratio from the rich air-fuel ratio to the lean air-fuel ratio when rich breakdown of the exhaust gas purification catalyst is detected by the downstream air-fuel ratio sensor; subfeedback learning control that updates the subfeedback learning value, which is a correction value for the target air-fuel ratio; and conditions that are predetermined to be different from the conditions for detecting rich breakdown and lean breakdown. The system is capable of performing air-fuel ratio active control, which forcibly switches the target air-fuel ratio between the lean air-fuel ratio and the rich air-fuel ratio when certain conditions are met, and the sub-feedback learning control is performed such that, after the switch from the rich air-fuel ratio to the lean air-fuel ratio by the air-fuel ratio sub-feedback control, a predetermined rich attachment condition is met, indicating that the state in which no lean breakdown is detected continues, the sub-feedback learning control is performed so that after the update the target air-fuel ratio becomes a leaner air-fuel ratio than before the update. The system includes a rich setting update process that updates a value, and a lean setting update process that updates the subfeedback learning value so that the target air-fuel ratio becomes richer than before the update after the update, when a predetermined lean setting condition is met, which indicates that the state in which no rich breakdown is detected continues after the target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio by the air-fuel ratio subfeedback control, wherein the execution of the rich setting update process and the lean setting update process is prohibited while the air-fuel ratio active control is being executed. [Effects of the Invention]

[0009] According to the above configuration, unnecessary updates of subfeedback learning values ​​due to rich-setting update processing and lean-setting update processing caused by the execution of active air-fuel ratio control can be suppressed. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of the vehicle's configuration. [Figure 2] Figures 2(a) to 2(e) are time charts showing the operation of the normal update process for sub-control and learning control. [Figure 3] Figures 3(a) to 3(e) are time charts showing the operation of the lean paste update process for sub-control and learning control. [Figure 4] Figure 4 is a flowchart showing the switching control. [Figure 5] Figures 5(a) to 5(h) are time charts showing the operation of the active control. [Modes for carrying out the invention]

[0011] <Outline of the vehicle configuration> An embodiment of the present invention will be described below with reference to Figures 1 to 5. First, the general configuration of the vehicle 100 will be described.

[0012] As shown in Figure 1, the vehicle 100 is equipped with a spark-ignition type internal combustion engine 10. The internal combustion engine 10 comprises multiple cylinders 11, a crankshaft 12, an intake passage 21, a throttle valve 22, and multiple fuel injectors 23. The internal combustion engine 10 also comprises multiple ignition devices 24, an exhaust passage 26, a first three-way catalytic converter 27, and a second three-way catalytic converter 28.

[0013] Cylinder 11 is a space for burning a mixture of fuel and intake air. The internal combustion engine 10 has four cylinders 11. The crankshaft 12 is connected to pistons (not shown) located in each cylinder 11. The crankshaft 12 rotates due to the combustion of the fuel-intake mixture in the cylinders 11. In this embodiment, an example of fuel is gasoline.

[0014] The intake passage 21 is connected to the cylinder 11. A portion of the intake passage 21, including its downstream end, branches into four. Each branched passage is connected to each cylinder 11. The intake passage 21 introduces intake air into each cylinder 11 from outside the internal combustion engine 10. 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 branched portion of the intake passage 21. The throttle valve 22 adjusts the amount of intake air flowing through the intake passage 21.

[0015] The fuel injectors 23 are located near the downstream end of the intake passage 21. The internal combustion engine 10 has four fuel injectors 23 corresponding to the four cylinders 11. The fuel injectors 23 inject fuel supplied from a fuel tank (not shown) into the intake passage 21. As a result, fuel from the fuel injectors 23 is supplied to the cylinders 11. The ignition devices 24 are located in the cylinders 11. The internal combustion engine 10 has four ignition devices 24 corresponding to the four cylinders 11. The ignition devices 24 ignite the fuel-intake mixture by spark discharge.

[0016] The exhaust passage 26 is connected to the cylinder 11. A portion of the exhaust passage 26, including its upstream end, branches into four. Each branched passage is connected to each cylinder 11. The exhaust passage 26 discharges exhaust gas from each cylinder 11 to the outside of the internal combustion engine 10. An exhaust valve (not shown) is located at the connection point between the exhaust passage 26 and each cylinder 11. The exhaust valve opens and closes the connection point between the exhaust passage 26 and the cylinder 11.

[0017] The first three-way catalyst 27 is located on the downstream side with respect to the branched portion of the exhaust passage 26. The first three-way catalyst 27 purifies the exhaust flowing through the exhaust passage 26. Specifically, the first three-way catalyst 27 has a function of purifying hydrocarbons, carbon monoxide, and nitrogen oxides contained in the exhaust. Further, the first three-way catalyst 27 has a function of storing oxygen contained in the exhaust, that is, oxygen storage capacity. Therefore, for example, when the air-fuel ratio of the exhaust flowing into the first three-way catalyst 27 is higher than the theoretical air-fuel ratio AFS, the first three-way catalyst 27 stores oxygen, so that the air-fuel ratio of the exhaust flowing out of the first three-way catalyst 27 becomes a value close to the theoretical air-fuel ratio AFS. On the other hand, for example, when the air-fuel ratio of the exhaust flowing into the first three-way catalyst 27 is lower than the theoretical air-fuel ratio AFS, the first three-way catalyst 27 releases oxygen, so that the air-fuel ratio of the exhaust flowing out of the first three-way catalyst 27 becomes a value close to the theoretical air-fuel ratio AFS. Here, the air-fuel ratio is a ratio obtained by dividing the mass of air by the mass of fuel. Therefore, the more air there is with respect to the fuel, the higher the air-fuel ratio, that is, the leaner the fuel state. On the other hand, the less air there is with respect to the fuel, the lower the air-fuel ratio, that is, the richer the fuel state. In the present embodiment, the first three-way catalyst 27 is an example of an exhaust purification catalyst.

[0018] The second three-way catalyst 28 is located on the downstream side with respect to the first three-way catalyst 27 in the exhaust passage 26. The second three-way catalyst 28 purifies the exhaust flowing through the exhaust passage 26. Specifically, the second three-way catalyst 28 has a function of purifying hydrocarbons, carbon monoxide, and nitrogen oxides contained in the exhaust. Further, the second three-way catalyst 28 has a function of storing oxygen contained in the exhaust, that is, oxygen storage capacity.

[0019] The vehicle 100 includes an air flow meter 81, a water temperature sensor 82, an intake air temperature sensor 83, and a crank angle sensor 84. Further, the vehicle 100 includes an accelerator operation amount sensor 85, a vehicle speed sensor 86, an upstream side air-fuel ratio sensor 87, and a downstream side air-fuel ratio sensor 88.

[0020] The air flow meter 81 detects the intake air amount GA, which is the amount of intake air flowing through the intake passage 21 per unit time. The water temperature sensor 82 detects the coolant water temperature THW, which is the temperature of the coolant water flowing through each part of the internal combustion engine 10. The intake air temperature sensor 83 detects the intake air temperature THA, which is the temperature of the intake air flowing through the intake passage 21. The crank angle sensor 84 detects the crank angle SC, which is the rotational position of the crankshaft 12. The accelerator operation amount sensor 85 detects the accelerator operation amount ACC, which is the operation amount of the accelerator pedal operated by the driver. The vehicle speed sensor 86 detects the vehicle speed SP, which is the speed of the vehicle 100.

[0021] The upstream side air-fuel ratio sensor 87 is located on the downstream side with respect to the branched portion and on the upstream side with respect to the first three-way catalyst 27 in the exhaust passage 26. The upstream side air-fuel ratio sensor 87 detects the upstream side air-fuel ratio AF1, which is the air-fuel ratio of the exhaust on the upstream side of the first three-way catalyst 27 in the exhaust passage 26. When the internal combustion engine 10 is running, the exhaust from the four cylinders 11 flows continuously into the exhaust passage 26, so the upstream side air-fuel ratio AF1 is close to the average value of the air-fuel ratios in the four cylinders 11. The downstream side air-fuel ratio sensor 88 is located on the downstream side with respect to the first three-way catalyst 27 and on the upstream side with respect to the second three-way catalyst 28 in the exhaust passage 26. The downstream side air-fuel ratio sensor 88 detects the downstream side air-fuel ratio AF2, which is the air-fuel ratio of the exhaust on the downstream side of the first three-way catalyst 27 in the exhaust passage 26.

[0022] Vehicle 100 is equipped with a control device 90. The control device 90 obtains a signal indicating the intake air volume GA from the airflow meter 81. The control device 90 obtains a signal indicating the coolant temperature THW from the coolant temperature sensor 82. The control device 90 obtains a signal indicating the intake air temperature THA from the intake air temperature sensor 83. The control device 90 obtains a signal indicating the crank angle SC from the crank angle sensor 84. The control device 90 obtains a signal indicating the accelerator pedal operation amount ACC from the accelerator pedal operation amount sensor 85. The control device 90 obtains a signal indicating the vehicle speed SP from the vehicle speed sensor 86. The control device 90 obtains a signal indicating the upstream air-fuel ratio AF1 from the upstream air-fuel ratio sensor 87. The control device 90 obtains a signal indicating the downstream air-fuel ratio AF2 from the downstream air-fuel ratio sensor 88.

[0023] The control device 90 comprises 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. The storage device 92 pre-stores a control program 92A as one of various programs. The execution device 91 implements various processes described later by executing the control program 92A.

[0024] The control device 90 calculates the required vehicle driving force, which is the driving force required for the vehicle 100 to run, based on the accelerator pedal input amount ACC and the vehicle speed SP. Based on the required vehicle driving force, the control device 90 controls the internal combustion engine 10. Specifically, the control device 90 controls the opening degree of the throttle valve 22, the amount of fuel injected from the fuel injector 23, the ignition timing of the ignition device 24, etc., by outputting a control signal to the internal combustion engine 10.

[0025] The control device 90 calculates the engine speed NE, which is the number of rotations of the crankshaft 12 per unit time, based on the crank angle SC. The control device 90 also calculates the catalyst temperature TSC, which is the temperature of the first three-way catalyst 27, based on the operating conditions of the internal combustion engine 10, such as the intake air charging efficiency and the engine speed NE. The intake air charging efficiency is the value obtained by dividing the mass of intake air actually introduced into the cylinder 11 from the intake passage 21 by the mass of intake air that can be introduced into the cylinder 11 under standard atmospheric conditions.

[0026] <Main Control> Next, the main control performed by the control device 90 will be described. In the main control, the control device 90 adjusts the amount of fuel injected from the fuel injector 23 so that the air-fuel ratio of the mixture burned in cylinder 11 becomes the target air-fuel ratio AFT, based on the upstream air-fuel ratio AF1. The target air-fuel ratio AFT is the target value of the air-fuel ratio. In this embodiment, the main control corresponds to the air-fuel ratio main feedback control.

[0027] <Sub-control> Next, the sub-control performed by the control device 90 will be described. The sub-control corresponds to air-fuel ratio sub-feedback control. In the sub-control, when the downstream air-fuel ratio sensor 88 detects lean failure of the first three-way catalytic converter 27, the control device 90 switches the target air-fuel ratio AFT from the lean air-fuel ratio AFL to the rich air-fuel ratio AFR. In this embodiment, the control device 90 determines that lean failure of 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 equal to or greater than a predetermined lean specified value DL. Here, the lean specified value DL is an air-fuel ratio that is 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 specified value DL is "14.8". The lean air-fuel ratio AFL is an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio AFS. Furthermore, the rich air-fuel ratio (AFR) is the richer air-fuel ratio compared to the stoichiometric air-fuel ratio (AFS).

[0028] Furthermore, in sub-control, when the downstream air-fuel ratio sensor 88 detects a rich breakdown in the first three-way catalytic converter 27, 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. In this embodiment, the control device 90 determines that a rich breakdown 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 less than or equal to a predetermined rich specified value DR. Here, the rich specified value DR is an air-fuel ratio that is a certain value lower than the stoichiometric air-fuel ratio AFS. An example of a rich specified value DR is "14.6".

[0029] <Normal update process for learning control> Next, the normal update process of the learning control performed by the control device 90 will be described. This learning control is a control for updating the learning value LV, which is a correction value for the target air-fuel ratio AFT. Here, the learning value LV corresponds to the subfeedback learning value. Furthermore, the learning control corresponds to subfeedback learning control.

[0030] The learning control includes a normal update process. In the normal update process, the control device 90 calculates the estimated oxygen storage amount DA, which is an estimated value of the oxygen storage amount of the first three-way catalyst 27 during the period from the switching of the target air-fuel ratio AFT to the lean air-fuel ratio AFL by sub-control until lean failure is detected. Specifically, the control device 90 calculates the amount of oxygen absorbed per unit time by the first three-way catalyst 27 based on the upstream air-fuel ratio AF1. Then, the control device 90 calculates the estimated oxygen storage amount DA by integrating the amount of oxygen absorbed per unit time.

[0031] Furthermore, during the normal update process, the control device 90 calculates the estimated desorption amount DB, which is an estimated value of the amount of oxygen desorbed by the first three-way catalyst 27 during the period from the switching of the target air-fuel ratio AFT to the rich air-fuel ratio AFR by sub-control until rich failure is detected. Specifically, the control device 90 calculates the amount of oxygen desorbed per unit time by the first three-way catalyst 27 based on the upstream air-fuel ratio AF1. Then, the control device 90 calculates the estimated desorption amount DB by integrating the amount of oxygen desorbed per unit time.

[0032] Furthermore, in the normal update process, the control device 90 updates the learned value LV according to the difference between the estimated storage amount DA and the estimated desorption 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 desorption amount DB will be the same. On the other hand, for example, if the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is richer than the true value, then the estimated storage amount DA will be smaller than the estimated desorption amount DB. Conversely, for example, if the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is leaner than the true value, then the estimated storage amount DA will be larger than the estimated desorption amount DB. Therefore, for example, if the estimated storage amount DA is smaller than the estimated desorption amount DB, the control device 90 updates the learned value LV according to the difference between the estimated storage amount DA and the estimated desorption amount DB so that after the update, the target air-fuel ratio AFT becomes a richer air-fuel ratio than before the update. In this embodiment, if the estimated storage amount DA is smaller than the estimated desorption amount DB, the learned value LV becomes smaller. On the other hand, for example, if the estimated storage amount DA is larger than the estimated desorption amount DB, the control device 90 updates the learned value LV according to the difference between the estimated storage amount DA and the estimated desorption amount DB, so that after the update, the target air-fuel ratio AFT becomes a leaner air-fuel ratio than before the update. In this embodiment, if the estimated storage amount DA is larger than the estimated desorption amount DB, the learned value LV becomes larger.

[0033] <Regarding the operation of normal update processes for sub-control and learning control> In the example shown in Figure 2, it is assumed that, prior to time t11, the control device 90 has set the target air-fuel ratio AFT to the rich air-fuel ratio AFR. The upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is assumed to be the true value, in other words, the actual air-fuel ratio. In this case, as shown by the solid line in Figure 2(a), prior to time t11, the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is lower by a certain amount compared to the stoichiometric air-fuel ratio AFS. Also, as shown in Figure 2(c), prior to time t11, the actual oxygen storage amount OSA decreases. The actual oxygen storage amount OSA is the amount of oxygen actually absorbed by the first three-way catalyst 27. As the actual oxygen storage amount OSA decreases in this way and approaches the lower limit, it becomes more difficult for oxygen to be released from the first three-way catalyst 27.

[0034] Subsequently, as shown in Figure 2(b), at time t11, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes below the rich specified value DR. In this case, the control device 90 determines that a rich failure of the first three-way catalyst 27 has been detected by the downstream air-fuel ratio sensor 88. The control device 90 then switches the target air-fuel ratio AFT from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL. Then, as shown by the solid line in Figure 2(a), at time t11, the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 becomes a certain value higher than the stoichiometric air-fuel ratio AFS. Then, as shown in Figure 2(c), the actual oxygen storage amount OSA increases from time t11 onward. As the actual oxygen storage amount OSA increases in this way and approaches the upper limit, it becomes more difficult for the first three-way catalyst 27 to absorb oxygen.

[0035] Subsequently, as shown in Figure 2(b), at time t12, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes greater than or equal to the lean specified value DL. In this case, the control device 90 determines that lean failure of the first three-way catalyst 27 has been detected by the downstream air-fuel ratio sensor 88. The control device 90 then switches the target air-fuel ratio AFT from the lean air-fuel ratio AFL to the rich air-fuel ratio AFR. Then, as shown by the solid line in Figure 2(a), at time t12, the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 becomes a certain value lower than the stoichiometric air-fuel ratio AFS. Then, as shown in Figure 2(c), the actual storage amount OSA decreases from time t12 onward.

[0036] Subsequently, as shown in Figure 2(b), at time t13, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes less than or equal to the rich specified value DR. In this case, the control device 90 determines that a rich failure of the first three-way catalytic converter 27 has been detected by the downstream air-fuel ratio sensor 88. The control device 90 then switches the target air-fuel ratio AFT from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL. After that, the control device 90 repeatedly executes the process from time t11 to time t13.

[0037] In contrast, suppose, for example, that the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is richer than the true value. In this case, as shown by the dashed line in Figure 2(a), the actual air-fuel ratio at the location of the upstream air-fuel ratio sensor 87 will be leaner than the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87. Therefore, as shown in Figure 2(d), the estimated storage amount DA at time t11 to t12 will be smaller than the estimated desorption amount DB at time t12 to t13. As a result, as shown in Figure 2(e), at time t13, the control device 90 updates the learned value LV so that the target air-fuel ratio AFT becomes richer after the update than before the update, according to the difference between the estimated storage amount DA and the estimated desorption amount DB. Note that the oxygen surplus / deficit amount OED in Figure 2(d) is an index for showing the estimated storage amount DA and the estimated desorption amount DB. In this embodiment, the control device 90 resets the oxygen deficiency (OED) to zero when it detects one or more rich failures and lean failures.

[0038] <Rich Paste Update Processing under Learning Control> Next, the rich-pair update process executed by the control device 90 will be described. The learning control includes the rich-pair update process. The rich-pair update process is a process for updating the learned value LV when the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is leaner than the true value and the deviation is large. In other words, the rich-pair update process is a process for updating the learned value LV when the actual air-fuel ratio is significantly richer than the upstream air-fuel ratio AF1. Specifically, the control device 90 determines whether the predetermined rich-pair conditions are met after the target air-fuel ratio AFT is switched from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL by sub-control. Then, if the control device 90 determines that the rich-pair conditions are met, it updates the learned value LV so that after the update, the target air-fuel ratio AFT is leaner than before the update. In this embodiment, the learned value LV in the above case becomes large.

[0039] Here, the rich condition is a condition that indicates that a lean breakdown has not been detected after switching the target air-fuel ratio AFT. In this embodiment, the control device 90 determines that the rich condition is met when the intake air cumulative amount GAA, which is the cumulative amount of intake air GA, is equal to or greater than a predetermined specified cumulative amount GZ. Furthermore, the control device 90 resets the intake air cumulative amount GAA to zero when one or more of the following requirements (A-1) to requirements (A-4) are met.

[0040] Requirement (A-1): The target air-fuel ratio AFT was switched from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL by sub-control. Requirement (A-2): The target air-fuel ratio AFT was switched from the lean air-fuel ratio AFL to the rich air-fuel ratio AFR by sub-control.

[0041] Requirement (A-3): The rich paste update process has been executed. Requirement (A-4): The lean paste update process described later has been performed. Therefore, in this embodiment, the intake air integrated amount GAA corresponds to the integrated amount of intake air after the target air-fuel ratio AFT is switched from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL by sub-control.

[0042] <Lean pasting update process for learning control> Next, the lean setting update process executed by the control device 90 will be described. The learning control includes the lean setting update process. The lean setting update process is a process to update the learned value LV when the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is richer than the true value and the deviation is large. In other words, the lean setting update process is a process to update the learned 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 the predetermined lean setting conditions are met after the target air-fuel ratio AFT is switched from the lean air-fuel ratio AFL to the rich air-fuel ratio AFR by sub-control. Then, if the control device 90 determines that the lean setting conditions are met, it updates the learned value LV so that after the update, the target air-fuel ratio AFT is richer than before the update. In this embodiment, the learned value LV in the above case becomes small.

[0043] Here, the lean setting condition is a condition that indicates that a state in which no rich breakdown is detected after switching the target air-fuel ratio AFT continues. In this embodiment, the control device 90 determines that the lean setting condition is met when the intake integrated amount GAA, which is the cumulative amount of intake air GA, is equal to or greater than a predetermined specified cumulative amount GZ. As described above, the control device 90 resets the intake integrated amount GAA to zero when one or more of requirements (A-1) to (A-4) are met. Therefore, in this embodiment, the intake integrated amount GAA corresponds to the cumulative amount of intake air after switching the target air-fuel ratio AFT from a lean air-fuel ratio AFL to a rich air-fuel ratio AFR by sub-control.

[0044] <Regarding the operation of the lean-setting update process for sub-control and learning control> In the example shown in Figure 3, assume that before time t21, the control device 90 has set the target air-fuel ratio AFT to the lean air-fuel ratio AFL. Also, assume, for example, that the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87 is richer than the true value, and that the deviation is large. That is, as shown by the dashed line in Figure 3(a), the actual air-fuel ratio at the location of the upstream air-fuel ratio sensor 87 is significantly leaner than the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87.

[0045] Subsequently, as shown in Figure 3(b), at time t21, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes greater than or equal to the lean specified value DL. In this case, the control device 90 determines that the downstream air-fuel ratio sensor 88 has detected a lean failure in the first three-way catalytic converter 27. The control device 90 then switches the target air-fuel ratio AFT from the lean air-fuel ratio AFL to the rich air-fuel ratio AFR.

[0046] However, as mentioned above, the actual air-fuel ratio at the location of the upstream air-fuel ratio sensor 87 is significantly leaner than the upstream air-fuel ratio AF1 detected by the upstream air-fuel ratio sensor 87. Therefore, as shown in Figure 3(c), the actual storage amount OSA does not decrease easily after time t21.

[0047] Subsequently, as shown in Figure 3(d), at time t22, the intake air total amount GAA becomes equal to or greater than the predetermined total amount GZ. In this case, the control device 90 determines that the predetermined lean setting conditions are met after the target air-fuel ratio AFT is switched from the lean air-fuel ratio AFL to the rich air-fuel ratio AFR by sub-control. Then, as shown in Figure 3(e), at time t22, the control device 90 updates the learned value LV so that after the update, the target air-fuel ratio AFT is richer than before the update. In this case, the control device 90 resets the intake air total amount GAA to zero.

[0048] Subsequently, as shown in Figure 3(d), at time t23, similar to time t22, the intake air total amount GAA becomes equal to or greater than the predetermined total amount GZ. Therefore, as shown in Figure 3(e), at time t23, the control device 90 updates the learned value LV so that after the update, the target air-fuel ratio AFT becomes a richer air-fuel ratio than before the update. In this case, the control device 90 resets the intake air total amount GAA to zero.

[0049] Subsequently, as shown in Figure 3(b), at time t24, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes less than or equal to the rich specified value DR. In this case, the control device 90 determines that a rich failure of the first three-way catalytic converter 27 has been detected by the downstream air-fuel ratio sensor 88. The control device 90 then switches the target air-fuel ratio AFT from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL.

[0050] <Switching control regarding the execution content of learning control> Next, the switching control will be explained with reference to Figure 4. This switching control is a control for switching the execution content of the learning control. In this embodiment, the control device 90 starts the switching control at predetermined control cycles, with the condition that the internal combustion engine 10 is operating.

[0051] As shown in Figure 4, when the control device 90 starts switching control, it executes the process in step S11. In step S11, the control device 90 determines whether or not active control, which will be described later, is in progress. If the control device 90 determines in step S11 that active control is in progress (S11: YES), the control device 90 proceeds to step S21.

[0052] In step S21, the control device 90 prohibits the execution of the rich patch update process and the lean patch update process. However, the control device 90 does not prohibit the execution of the normal update process. After step S21, the control device 90 terminates the current switching control.

[0053] On the other hand, if the control device 90 determines in step S11 above that active control is not being performed (S11:NO), the control device 90 proceeds to step S22. In step S22, the control device 90 permits the execution of the rich patch update process and the lean patch update process. That is, in this case, the control device 90 can execute the normal update process, the rich patch update process, and the lean patch update process. After step S22, the control device 90 terminates the current switching control.

[0054] <Active control> Next, the active control performed by the control device 90 will be described. This active control is a control that forcibly switches the target air-fuel ratio AFT between the lean air-fuel ratio AFL and the rich air-fuel ratio AFR when predetermined specific conditions are met. In other words, the active control corresponds to air-fuel ratio active control. In this embodiment, the control device 90 determines that the specific conditions are met when all of the following requirements (B-1) and (B-2) are met.

[0055] Requirement (B-1): The catalyst temperature TSC must be at or above the predetermined specified temperature TZ. Requirement (B-2): Active control is not performed during the operation of the internal combustion engine 10.

[0056] Here, the specified temperature TZ is predetermined as a temperature at which it can be determined that the first tertiary catalyst 27 is activated. Therefore, under conditions that meet specific requirements, the first tertiary catalyst 27 is in a state where it can fully exhibit its oxygen storage capacity. Note that these specific requirements are different from the conditions for detecting rich failure and lean failure.

[0057] Active control includes a first process, a second process, and a determination process. Specifically, the control device 90 executes a first process to set the target air-fuel ratio AFT to a rich air-fuel ratio AFR after determining that specific conditions have been met. Subsequently, if the control device 90 detects a rich breakdown during the execution of the first process, it executes a second process to set the target air-fuel ratio AFT to a lean air-fuel ratio AFL. Then, the control device 90 executes a determination process. In the determination process, the control device 90 calculates the calculated oxygen storage amount DAZ, which is the calculated value of the oxygen storage amount of the first three-way catalyst 27 during the period from the rich breakdown during the execution of the first process to the detection of a lean breakdown in the second process. Then, the control device 90 determines whether or not there has been a decrease in oxygen storage capacity based on the calculated oxygen storage amount DAZ. As a specific example, the control device 90 determines that the oxygen storage capacity has decreased if the calculated oxygen storage amount DAZ is below a predetermined reference value. The control device 90 calculates the calculated oxygen storage amount DAZ as follows, for example. The control device 90 calculates the amount of oxygen absorbed per unit time by the first three-way catalyst 27 based on the upstream air-fuel ratio AF1. Furthermore, the control device 90 calculates the calculated oxygen absorption amount DAZ by integrating the amount of oxygen absorbed per unit time.

[0058] <About the operation of active control> In the example shown in Figure 5, as shown in Figure 5(d), the catalyst temperature TSC is assumed to be lower than the predetermined specified temperature TZ before time t33. Therefore, as shown in Figure 5(e), the control device 90 is not performing active control before time t33. Then, as shown in Figure 5(c), at time t31, the control device 90 switches the target air-fuel ratio AFT from the lean air-fuel ratio AFL to the rich air-fuel ratio AFR by sub-control. In this case, as shown in Figure 5(f), the actual storage amount OSA decreases after time t31.

[0059] Subsequently, as shown in Figure 5(b), at time t32, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes less than or equal to the rich specified value DR. In this case, the control device 90 determines that a rich failure of the first three-way catalyst 27 has been detected by the downstream air-fuel ratio sensor 88. The control device 90 then switches the target air-fuel ratio AFT from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL through sub-control. As a result, as shown in Figure 5(f), the actual stored amount OSA increases from time t32 onward. Also, as shown in Figure 5(g), the intake integrated amount GAA increases from time t32 onward. Note that, as shown in Figure 5(g), at time t32, the intake integrated amount GAA is reset to zero.

[0060] Subsequently, as shown in Figure 5(d), at time t33, the catalyst temperature TSC becomes equal to or above a predetermined specified temperature TZ. In this case, the control device 90 determines that the specific conditions are met. Then, as shown in Figure 5(e), from time t33 onward, the control device 90 performs active control. Specifically, at time t33, after determining that the specific conditions are met, the control device 90 performs a first process to set the target air-fuel ratio AFT to a rich air-fuel ratio AFR. As a result, as shown in Figure 5(f), from time t33 onward, the actual storage amount OSA decreases. Note that at time t33, none of the above requirements (A-1) to (A-4) are met, so the control device 90 does not reset the intake total amount GAA to zero. Therefore, as shown in Figure 5(g), from time t33 onward, the intake total amount GAA continues to increase.

[0061] Subsequently, as shown in Figure 5(b), at time t34, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes less than or equal to the rich specified value DR. In this case, the control device 90 determines that a rich breakdown has been detected in the first three-way catalyst 27 by the downstream air-fuel ratio sensor 88. The control device 90 then executes a second process. That is, if the control device 90 detects a rich breakdown during the execution of the first process, it executes a second process that sets the target air-fuel ratio AFT to the lean air-fuel ratio AFL. Then, as shown in Figure 5(f), the actual storage amount OSA increases from time t34 onward.

[0062] Subsequently, as shown in Figure 5(b), at time t36, the downstream air-fuel ratio AF2 detected by the downstream air-fuel ratio sensor 88 becomes greater than or equal to the lean specified value DL. In this case, the control device 90 determines that lean failure of the first three-way catalyst 27 has been detected by the downstream air-fuel ratio sensor 88. The control device 90 then executes a determination process. Specifically, the control device 90 calculates the calculated oxygen storage amount DAZ, which is the calculated value of the oxygen storage amount of the first three-way catalyst 27 during the period from rich failure during the execution of the first process to the detection of lean failure in the second process. Subsequently, the control device 90 determines whether or not there has been a decrease in oxygen storage capacity based on the calculated oxygen storage amount DAZ. At time t36, the control device 90 switches the target air-fuel ratio AFT from the lean air-fuel ratio AFL to the rich air-fuel ratio AFR by sub-control.

[0063] <Operation of this embodiment> For example, suppose that the control device 90 does not prohibit the rich-setting update process and the lean-setting update process during the execution of active control from time t33 to time t36. In this case, as shown in Figure 5(g), at time t35, which is after time t34 but before time t36, the intake air integrated amount GAA becomes equal to or greater than the predetermined specified integrated amount GZ. Then, the control device 90 determines that the predetermined rich-setting condition is met after the switching of the target air-fuel ratio AFT from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL by sub-control. Then, as shown by the dashed line in Figure 5(h), at time t35, the control device 90 updates the learned value LV so that after the update, the target air-fuel ratio AFT is a leaner air-fuel ratio than before the update. In other words, as shown in Figure 5(a), even though the actual air-fuel ratio is not significantly richer than the upstream air-fuel ratio AF1, the control device 90 updates the learned value LV so that the target air-fuel ratio AFT becomes leaner after the update than it was before the update.

[0064] <Effects of this embodiment> (1) In this embodiment, the control device 90 prohibits the execution of rich-setting update processing and lean-setting update processing while active control is being performed. This suppresses unnecessary updates of the learned value LV caused by rich-setting update processing and lean-setting update processing resulting from the execution of active control. Furthermore, by suppressing unnecessary updates of the learned value LV in this way, the deterioration of exhaust emissions of the internal combustion engine 10 caused by unnecessary updates can be suppressed.

[0065] (2) As described above, for example, if the period from the switching of the target air-fuel ratio AFT to the lean air-fuel ratio AFL by sub-control to the detection of lean failure becomes longer due to the execution of active control, the intake integrated amount GAA tends to increase. On the other hand, the values ​​of the estimated storage amount DA and the estimated desorption amount DB in the normal update process do not tend to change due to the execution of active control.

[0066] In this regard, the control device 90 prohibits the execution of rich-stick update processing and lean-stick update processing while active control is in progress, but does not prohibit the execution of normal update processing. As a result, even while active control is in progress, the learned value LV can be appropriately updated by normal update processing based on the estimated storage amount DA and estimated desorption amount DB.

[0067] (3) In active control, the control device 90 executes a first process to set the target air-fuel ratio AFT to a rich air-fuel ratio AFR after determining that specific conditions have been met. Subsequently, if the control device 90 detects a rich breakdown during the execution of the first process, it executes a second process to set the target air-fuel ratio AFT to a lean air-fuel ratio AFL. Then, the control device 90 executes a determination process. That is, the control device 90 calculates the calculated oxygen storage amount DAZ, which is the calculated value of the oxygen storage amount of the first three-way catalyst 27 during the period from the rich breakdown during the execution of the first process to the detection of a lean breakdown in the second process. Then, the control device 90 determines whether or not there has been a decrease in oxygen storage capacity based on the calculated oxygen storage amount DAZ. This makes it possible to determine whether or not there has been a decrease in oxygen storage capacity based on the calculated oxygen storage amount DAZ from the rich breakdown to the lean breakdown. In other words, it is possible to determine whether or not there has been a decrease in performance in the first three-way catalyst 27 based on the calculated oxygen storage amount DAZ.

[0068] (4) For example, even if the period after switching the target air-fuel ratio AFT from a rich air-fuel ratio AFR to a lean air-fuel ratio AFL by sub-control is the same, the amount of oxygen in the first three-way catalyst 27 changes depending on the amount of exhaust gas flowing through the exhaust passage 26 per unit time. Therefore, in learning control, if a rich setting condition is set that focuses only on the period after switching the target air-fuel ratio AFT from a rich air-fuel ratio AFR to a lean air-fuel ratio AFL by sub-control, the ease with which the rich setting condition is met is likely to change.

[0069] In this regard, the control device 90 determines that the rich-condition condition is met when the intake air cumulative volume GAA after switching the target air-fuel ratio AFT from a rich air-fuel ratio AFR to a lean air-fuel ratio AFL by sub-control is equal to or greater than a predetermined specified cumulative volume GZ. Furthermore, the control device 90 determines that the lean-condition is met when the intake air cumulative volume GAA after switching the target air-fuel ratio AFT from a lean air-fuel ratio AFL to a rich air-fuel ratio AFR by sub-control is equal to or greater than a predetermined specified cumulative volume GZ. This suppresses the change in the ease of meeting the rich-condition condition, etc., depending on the amount of exhaust gas flowing through the exhaust passage 26 per unit time.

[0070] <Example of changes> This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0071] In the above embodiment, the switching control may be modified. For example, in step S21, the control device 90 may, in addition to prohibiting the execution of the rich paste update process and the lean paste update process, also prohibit the execution of the normal update process.

[0072] In the above embodiment, the learning control may be modified. For example, if the learning control includes rich pasting update processing and lean pasting update processing, the learning control does not need to include normal update processing. In other words, the control device 90 may only be capable of executing rich pasting update processing and lean pasting update processing from the learning control.

[0073] For example, the rich-condition setting can be changed. Specifically, the control device 90 may determine that the rich-condition setting is met if the period after the switch of the target air-fuel ratio AFT from the rich air-fuel ratio AFR to the lean air-fuel ratio AFL by sub-control is longer than or equal to a predetermined specified period. For example, if the change in the amount of exhaust flowing through the exhaust passage 26 per unit time is relatively small, the above-mentioned change is acceptable.

[0074] For example, the lean setting conditions may be changed. Specifically, the control device 90 may determine that the lean setting conditions are met if the period after the switching of the target air-fuel ratio AFT from the lean air-fuel ratio AFL to the rich air-fuel ratio AFR by sub-control is longer than or equal to a predetermined specified period. For example, if the change in the amount of exhaust flowing through the exhaust passage 26 per unit time is relatively small, the above-mentioned changes may be made.

[0075] • In the above embodiment, the active control may be modified. For example, the contents of the first process, second process, and determination process in active control may be changed. As a specific example, the first process, etc. may have the following configuration. First, the control device 90 determines that specific conditions have been met and then executes the first process to set the target air-fuel ratio AFT to the lean air-fuel ratio AFL. Next, if the control device 90 detects a lean breakdown during the execution of the first process, it executes the second process to set the target air-fuel ratio AFT to the rich air-fuel ratio AFR. Then, the control device 90 executes the determination process. In the determination process, the control device 90 calculates the calculated desorption amount DBZ, which is the calculated value of the amount of oxygen desorbed by the first three-way catalyst 27 during the period from the lean breakdown during the execution of the first process to the detection of a rich breakdown in the second process. Then, the control device 90 determines whether or not there has been a decrease in oxygen storage capacity based on the calculated desorption amount DBZ. As an example, the control device 90 determines that there has been a decrease in oxygen storage capacity if the calculated desorption amount DBZ is below a predetermined standard value. With this configuration, it is possible to determine whether or not there is a decrease in oxygen storage capacity based on the calculated desorption amount DBZ from lean failure to rich failure. In other words, it is possible to determine whether or not there is a decrease in performance in the first ternary catalyst 27 based on the calculated desorption amount DBZ.

[0076] • In the above embodiment, the configuration of the vehicle 100 may be changed. For example, the configuration of the control device 90 may be changed. Specifically, the control device 90 may be configured as a circuit including one or more processors that execute various processes according to a computer program (software). The control device 90 may also be configured as a circuit including one or more dedicated hardware circuits, such as application-specific integrated circuits (ASICs), or a combination thereof, that execute at least some of the various processes. The processor includes a CPU and memory such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to execute processes. Memory, or computer-readable media, includes any media that can be accessed by a general-purpose or dedicated computer. [Explanation of Symbols]

[0077] 10...Internal combustion engine 11...Cylinder 12...Crankshaft 21...Intake passage 22...Throttle valve 23...Fuel injector 24...Ignition system 26...Exhaust passage 27...First three-way catalytic converter 28...Second three-way catalytic converter 81...Airflow meter 82...Water temperature sensor 83...Intake air temperature sensor 84...Crankshaft angle sensor 85...Accelerator pedal input sensor 86...Vehicle speed sensor 87...Upstream air-fuel ratio sensor 88...Downstream air-fuel ratio sensor 90...Control device 91...Execution device 92...Memory device 92A...Control program 100...Vehicle

Claims

1. A control device for an internal combustion engine comprising: an exhaust gas purification catalyst having oxygen storage capacity located in the exhaust passage; 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, Air-fuel ratio main feedback control adjusts the fuel injection amount so that the air-fuel ratio of the air-fuel mixture burned in the cylinder becomes the target air-fuel ratio, based on the value detected by the upstream air-fuel ratio sensor. When lean breakdown of the exhaust gas purification catalyst is detected by the downstream air-fuel ratio sensor, the target air-fuel ratio is switched from a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio to a rich air-fuel ratio richer than the stoichiometric air-fuel ratio, and when rich breakdown of the exhaust gas purification catalyst is detected by the downstream air-fuel ratio sensor, the target air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio, and air-fuel ratio sub-feedback control is also provided, which switches the target air-fuel ratio from the rich air-fuel ratio to the lean air-fuel ratio. Subfeedback learning control updates the subfeedback learning value, which is the correction value for the target air-fuel ratio, Active air-fuel ratio control that forcibly switches the target air-fuel ratio between the lean air-fuel ratio and the rich air-fuel ratio when specific conditions predetermined as conditions different from the conditions for detecting rich failure and lean failure are met, It is possible to do this, The aforementioned subfeedback learning control is, When a predetermined rich-setting condition is met, which indicates that the state in which no lean breakdown is detected continues after the target air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio by the air-fuel ratio subfeedback control, the subfeedback learning value is updated after the update so that the target air-fuel ratio is leaner than before the update. The process includes a lean setting update process, in which, if a predetermined lean setting condition is met as a condition indicating that no rich breakdown is detected after the target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio by the air-fuel ratio subfeedback control, the subfeedback learning value is updated so that the target air-fuel ratio becomes a richer air-fuel ratio after the update, compared to before the update. During the execution of the air-fuel ratio active control, the execution of the rich setting update process and the lean setting update process is prohibited. Control device for internal combustion engines.

2. The aforementioned subfeedback learning control is, The process includes calculating the amount of oxygen absorbed by the exhaust gas purification catalyst during the period from the switching of the target air-fuel ratio to the lean air-fuel ratio by the air-fuel ratio subfeedback control until the detection of lean breakdown, and the amount of oxygen desorbed by the exhaust gas purification catalyst during the period from the switching of the target air-fuel ratio to the rich air-fuel ratio by the air-fuel ratio subfeedback control until the detection of rich breakdown, based on the detected values ​​of the upstream air-fuel ratio sensor, and updating the subfeedback learning value according to the difference between the amount of oxygen absorbed and the amount of oxygen desorbed, in a normal update process. During the execution of the air-fuel ratio active control, the execution of the rich-setting update process and the lean-setting update process is prohibited, while the execution of the normal update process is not prohibited. A control device for an internal combustion engine according to claim 1.

3. The air-fuel ratio active control described above is After the above specific conditions are met, a first process is performed to set the target air-fuel ratio to the rich air-fuel ratio, If a rich breakdown is detected during the execution of the first process, a second process is performed to set the target air-fuel ratio to the lean air-fuel ratio, The process includes a determination process that determines whether or not there has been a decrease in the oxygen storage capacity based on the amount of oxygen stored in the exhaust gas purification catalyst during the period from the rich breakdown during the execution of the first process to the detection of the lean breakdown in the second process. A control device for an internal combustion engine according to claim 1.

4. The air-fuel ratio active control described above is After the aforementioned specific conditions are met, a first process is performed to set the target air-fuel ratio to the lean air-fuel ratio, If a lean breakdown is detected during the execution of the first process, a second process is performed to set the target air-fuel ratio to the rich air-fuel ratio, The process includes a determination process that determines whether or not there has been a decrease in the oxygen storage capacity, based on the amount of oxygen desorption from the exhaust gas purification catalyst during the period from the lean breakdown during the execution of the first process to the detection of the rich breakdown in the second process. A control device for an internal combustion engine according to claim 1.

5. In the aforementioned subfeedback learning control, Based on the cumulative amount of intake air after switching the target air-fuel ratio from the rich air-fuel ratio to the lean air-fuel ratio by the air-fuel ratio subfeedback control, it is determined whether or not the rich condition is met. Based on the cumulative amount of intake air after switching the target air-fuel ratio from the lean air-fuel ratio to the rich air-fuel ratio by the air-fuel ratio subfeedback control, it is determined whether or not the lean condition is met. A control device for an internal combustion engine according to claim 1 or claim 2.

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