Internal combustion engine system

Abstract

An internal combustion engine system is configured so as to execute: a feedback process for feedback-controlling an air-fuel ratio so that exhaust gas discharged from an internal combustion engine becomes a target air-fuel ratio; a target air-fuel ratio switching process for alternately switching the target air-fuel ratio to a lean set value and a rich set value; a parameter calculation process for calculating, on the basis of the operating conditions of the internal combustion engine, a gas contact parameter indicating the degree of contact between unpurified gas in the exhaust gas discharged from the first exhaust purification catalyst and a second air-fuel ratio sensor on the downstream side of the first exhaust purification catalyst; and a switching cycle changing process for increasing the switching cycle of the target air-fuel ratio in the target air-fuel ratio switching process as the gas contact parameter is a value indicating that the degree of gas contact is strong.

Description

Technical Field

[0001] This disclosure relates to internal combustion engine systems, and more particularly to internal combustion engine systems that use exhaust purification catalysts to purify exhaust gases discharged from an internal combustion engine. Background Technology

[0002] Japanese Patent Application Publication No. 2016-31038 discloses a technology related to a control device for suppressing the outflow of NOx and unburned gases from an exhaust gas purification catalyst. This technology describes an internal combustion engine comprising an exhaust gas purification catalyst, a downstream air-fuel ratio sensor disposed downstream of the exhaust gas purification catalyst, and an air flow meter for detecting the intake air volume. Furthermore, the control device performs feedback control to achieve a target air-fuel ratio for the exhaust gas of the internal combustion engine. When the output air-fuel ratio of the downstream air-fuel ratio sensor becomes a rich air-fuel ratio, the control device sets the target air-fuel ratio to a lean air-fuel ratio. Conversely, when the output air-fuel ratio of the downstream air-fuel ratio sensor becomes a lean air-fuel ratio, the control device sets the target air-fuel ratio to a rich air-fuel ratio.

[0003] Regarding the exhaust gas discharged downstream of the exhaust gas purification catalyst, the ratio of fully purified gas to insufficiently purified unpurified gas, and their distribution within the pipe, sometimes change depending on the operating state of the internal combustion engine. Therefore, the gas contact between the unpurified gas and the downstream air-fuel ratio sensor located downstream of the exhaust gas purification catalyst also varies depending on the operating state of the internal combustion engine. As with the technology in Japanese Patent Application Laid-Open No. 2016-31038, sometimes the timing for changing the target air-fuel ratio is determined based on the detection value of the downstream air-fuel ratio sensor without considering changes in gas contact. In this case, it is possible to falsely detect the purification limit state of the exhaust gas purification catalyst, and the purification capacity of the exhaust gas purification catalyst is not fully utilized. Summary of the Invention

[0004] This disclosure was made in view of the aforementioned problems, and its purpose is to provide an internal combustion engine system that can effectively utilize the purification capacity of an exhaust gas purification catalyst by taking into account the influence of the contact between unpurified gas and the gas at the air-fuel ratio sensor.

[0005] To address the aforementioned issues, this disclosure provides an internal combustion engine system.

[0006] An internal combustion engine system includes: a first exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine; a second exhaust purification catalyst disposed downstream of the first exhaust purification catalyst in the exhaust flow direction; a first air-fuel ratio sensor disposed upstream of the first exhaust purification catalyst in the exhaust passage in the exhaust flow direction; a second air-fuel ratio sensor disposed downstream of the first exhaust purification catalyst and upstream of the second exhaust purification catalyst in the exhaust passage in the exhaust flow direction; and a control device for controlling the internal combustion engine.

[0007] The control device is configured to perform the following processes: feedback processing, which performs feedback control on the air-fuel ratio of the exhaust gas discharged from the internal combustion engine in such a way that the first air-fuel ratio detected by the first air-fuel ratio sensor becomes the target air-fuel ratio; target air-fuel ratio switching processing, which alternately switches the target air-fuel ratio to a lean setpoint (lean than the stoichiometric air-fuel ratio) and a rich setpoint (rich than the stoichiometric air-fuel ratio); parameter calculation processing, which calculates gas contact parameters based on the operating conditions of the internal combustion engine, wherein the gas contact parameters represent the degree of contact between the unpurified gas in the exhaust gas discharged from the first exhaust purification catalyst and the gas in contact with the second air-fuel ratio sensor; and switching cycle modification processing, wherein the stronger the gas contact parameter value, the longer the switching cycle of the target air-fuel ratio in the target air-fuel ratio switching process.

[0008] In the target air-fuel ratio switching process of this disclosure, the control device may also be configured to set the target air-fuel ratio to a lean setting value when the second air-fuel ratio detected by the second air-fuel ratio sensor becomes a rich setting value below the stoichiometric air-fuel ratio, and to set the target air-fuel ratio to a rich setting value when the second air-fuel ratio becomes a lean setting value above the stoichiometric air-fuel ratio.

[0009] Furthermore, in the switching cycle change processing, the control device can also be configured such that the more the gas contact parameter indicates the degree of gas contact, the further away the lean determination value and rich determination value are from the stoichiometric air-fuel ratio.

[0010] Furthermore, when the internal combustion engine disclosed herein is a turbocharged internal combustion engine having an exhaust valve port and an exhaust valve for opening and closing the exhaust valve port, the control device in the parameter calculation processing of this disclosure may also be configured to calculate gas contact parameters based on the rotational speed of the internal combustion engine, the intake air volume, and the opening degree of the exhaust valve.

[0011] According to the internal combustion engine system disclosed herein, by taking into account the effect of contact between unpurified gas and the air-fuel ratio sensor, the purification capacity of the exhaust gas purification catalyst can be effectively utilized. Attached Figure Description

[0012] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and wherein:

[0013] Figure 1 This is a diagram illustrating the structure of an internal combustion engine system for implementing an embodiment.

[0014] Figure 2 This is a diagram representing the functional blocks of an ECU.

[0015] Figure 3This is a diagram illustrating an example of a mapping between set values ​​for concentration and dilution determination values ​​relative to the degree of gas contact with unpurified gas.

[0016] Figure 4 This is a flowchart illustrating the routine of processing performed in the internal combustion engine system of the embodiment.

[0017] Figure 5 It is a time graph showing the changes in various states when the internal combustion engine system of the implementation method performs the switching cycle change process.

[0018] Figure 6A This is an example of a diagram schematically representing the flow of exhaust gas and the internal state of the exhaust purification catalyst.

[0019] Figure 6B This is another example of a diagram schematically representing the flow of exhaust gas and the internal state of the exhaust purification catalyst. Detailed Implementation

[0020] The embodiments of this disclosure will now be described. However, when numerical values ​​such as the number, quantity, amount, and range of each element are mentioned in the embodiments shown below, this disclosure is not limited to those mentioned values, unless specifically stated or clearly determined in principle. Furthermore, the structures and steps described in the embodiments shown below are not necessarily essential in this disclosure, unless specifically stated or clearly determined in principle.

[0021] Implementation

[0022] 1. Structure of the implementation method

[0023] Figure 1 This is a diagram illustrating the structure of an internal combustion engine system used to explain the implementation method. For example... Figure 1 As shown, the internal combustion engine system 100 of this embodiment includes an internal combustion engine (engine) 10 with multiple cylinders. The engine 10 is mounted in a vehicle as a power source. The engine 10 is a gasoline engine based on stoichiometric combustion based on the stoichiometric air-fuel ratio. The engine 10 has four cylinders arranged in a straight line, and each cylinder is provided with an injector 8. An intake manifold and an exhaust manifold (both omitted from the figure) are installed in the engine 10. An intake passage 12 for taking in intake air to the engine 10 is connected to the intake manifold. An exhaust passage 14 for releasing exhaust gas discharged from the engine 10 to the atmosphere is connected to the exhaust manifold.

[0024] An air flow meter 16 for detecting the intake air volume Ga is disposed midway through the intake passage 12. A throttle valve 18 is disposed downstream of the air flow meter 16 in the intake passage 12 in the direction of air intake flow. A first exhaust purification catalyst 22 is disposed in the exhaust passage 14. A second exhaust purification catalyst 24 is disposed downstream of the first exhaust purification catalyst 22 in the direction of exhaust flow in the exhaust passage 14.

[0025] For example, both the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 have the same structure. The first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 are three-way catalysts with oxygen storage capacity. Specifically, the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 are formed by supporting noble metals such as platinum (Pt) with catalytic activity and cerium oxide (CeO2) with oxygen storage capacity on a ceramic substrate. When the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 reach a predetermined activation temperature, they function as catalysts to simultaneously purify unburned gases (HC and CO, etc.) and nitrogen oxides (NOx), and possess oxygen storage capacity.

[0026] Based on the oxygen storage capacity of the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24, when the air-fuel ratio of the exhaust gas flowing into the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 is a lean air-fuel ratio (lean than the stoichiometric air-fuel ratio), oxygen in the exhaust gas is absorbed. On the other hand, when the air-fuel ratio of the exhaust gas flowing into the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 is a rich air-fuel ratio (rich than the stoichiometric air-fuel ratio), the oxygen absorbed in the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 is released. Furthermore, as long as the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 have the catalytic effect of purifying exhaust gas and the oxygen storage capacity, their type and structure are not limited.

[0027] The internal combustion engine system 100 of this embodiment includes an ECU (Electronic Control Unit) 30. The ECU 30 is a control device that performs comprehensive control of the internal combustion engine system 100 as a whole. The control device disclosed herein is embodied as a function of the ECU 30.

[0028] The ECU 30 has at least an input / output interface, ROM, RAM, and a CPU (Central Processing Unit). The input / output interface receives signals from sensors present in the internal combustion engine system 100 and outputs operating signals to actuators present in the engine 10. Sensors are installed in various parts of the internal combustion engine system 100. A first air-fuel ratio sensor 32 is provided upstream of the first exhaust gas purification catalyst 22 in the exhaust passage 14. The first air-fuel ratio sensor 32 detects the air-fuel ratio of the exhaust gas discharged from the engine 10 into the exhaust passage 14 as the first air-fuel ratio. A second air-fuel ratio sensor 34 is provided downstream of the exhaust flow direction of the first exhaust gas purification catalyst 22 and upstream of the exhaust flow direction of the second exhaust gas purification catalyst 24 in the exhaust passage 14. The second air-fuel ratio sensor 34 detects the air-fuel ratio of the exhaust gas flowing out of the first exhaust gas purification catalyst 22 and into the second exhaust gas purification catalyst 24 as the second air-fuel ratio. Furthermore, a rotational speed sensor 36 for detecting the engine rotational speed NE of the engine 10 and various other sensors for detecting the state of the engine 10 are also installed. The ECU30 processes the signals from the various sensors and operates each actuator according to a predetermined control program.

[0029] The actuators operated by ECU 30 include injector 8, throttle valve 18, etc. The ROM stores various control programs and mapped control data for controlling engine 10. The CPU reads the control program from the ROM and executes it, generating operating signals based on the input sensor signals. In addition to those shown in the figure, there are several other actuators and sensors connected to ECU 30, but their description is omitted in this specification.

[0030] Figure 2 This is a diagram representing the function blocks of the ECU. The ECU 30, as a function block for controlling the internal combustion engine system 100, includes a feedback processing unit 310, a target air-fuel ratio switching processing unit 312, a switching cycle change processing unit 314, and a parameter calculation processing unit 316. The processes performed in each function block will be described in detail below.

[0031] 2. Basic Operation of the Internal Combustion Engine System in the Implementation Method

[0032] 2-1. Feedback Processing

[0033] The control of the engine 10 performed by the ECU 30 of the internal combustion engine system 100 includes feedback processing. This feedback processing is performed in the feedback processing unit 310 of the ECU 30. In the feedback processing of this embodiment, the fuel injection quantity from the injector 8 is controlled in such a way that the first air-fuel ratio detected by the first air-fuel ratio sensor 32 becomes the target air-fuel ratio. Here, the target air-fuel ratio is, for example, the stoichiometric air-fuel ratio (A / F 14.60).

[0034] 2-2. Target air-fuel ratio switching process

[0035] The control of the engine 10 executed by the ECU 30 of the internal combustion engine system 100 includes a target air-fuel ratio switching process. This target air-fuel ratio switching process is executed in the target air-fuel ratio switching processing unit 312 of the ECU 30. In the target air-fuel ratio switching process of this embodiment, the target air-fuel ratio is alternately switched between a lean setting value (lean than the stoichiometric air-fuel ratio) and a rich setting value (rich than the stoichiometric air-fuel ratio). Specifically, in the target air-fuel ratio switching process, when the second air-fuel ratio detected by the second air-fuel ratio sensor 34 becomes a rich setting value (rich than the stoichiometric air-fuel ratio) or lower, the target air-fuel ratio is set to a lean setting value. Alternatively, the target air-fuel ratio is set to a rich setting value when the second air-fuel ratio becomes a lean setting value (lean than the stoichiometric air-fuel ratio) or higher.

[0036] Exhaust gas purification catalysts capable of absorbing oxygen will experience a decrease in oxygen absorption capacity when the internal oxygen absorption amount is maintained at a substantially constant level. Therefore, in order to maintain oxygen absorption capacity as much as possible, it is preferable to alternate the internal oxygen absorption amount between near-zero and near-maximum absorption amounts during the use of the exhaust gas purification catalyst. According to the target air-fuel ratio switching process of this embodiment, the target air-fuel ratio is alternately switched between a lean set value and a rich set value, thus the oxygen absorption amount of the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 repeatedly increases and decreases. As a result, the oxygen absorption amount of the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 can be maintained as high as possible, thereby improving the effective utilization of the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24.

[0037] 3. Characteristic Operations of the Internal Combustion Engine System in the Implementation Method

[0038] 3-1. Handling of Switching Cycle Changes

[0039] The control of the engine 10 performed by the ECU 30 of the internal combustion engine system 100 includes cycle change processing. The cycle change processing is performed in the cycle change processing unit 314 of the ECU 30.

[0040] As an example of a naturally aspirated engine with 4 cylinders, considering the changes in engine rotation speed NE and engine load KL, the gas flow rate in cylinder #1 is fast, and the gas contact with cylinder #1 is strong relative to the second air-fuel ratio sensor 34. In this case, when the target air-fuel ratio is set to a rich setting during the target air-fuel ratio switching process, sometimes insufficiently purified gas flows downstream of the first exhaust gas purification catalyst 22. This is because the gas in cylinder #1 has less time to fully react in the first exhaust gas purification catalyst 22. As a result, when the second air-fuel ratio sensor 34 detects a rich air-fuel ratio, it mistakenly judges that the first exhaust gas purification catalyst 22 has a rich fault, and the target air-fuel ratio is changed to a lean setting during the target air-fuel ratio switching process. Consequently, the effective utilization of the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 is reduced.

[0041] As another example, in the case where engine 10 is a multi-cylinder engine with a turbocharger, the gas flow rate through the exhaust valve port is faster than the gas flow rate through the turbine. Therefore, sometimes the ratio of gas flowing through the turbine and exhaust valve port changes depending on engine operating conditions, resulting in a state where the gas flowing through the exhaust valve port has stronger contact with the second air-fuel ratio sensor 34. In this case, similar to the example above, the effective utilization of the first exhaust purification catalyst 22 and the second exhaust purification catalyst 24 may be reduced.

[0042] Therefore, in the switching cycle change processing of the internal combustion engine system 100 of the embodiment, the stronger the contact between the insufficiently purified unpurified gas in the exhaust gas discharged from the first exhaust purification catalyst 22 and the gas in contact with the second air-fuel ratio sensor 34, the longer the switching cycle of the target air-fuel ratio in the target air-fuel ratio switching process. The switching cycle of the target air-fuel ratio in the target air-fuel ratio switching process can be adjusted based on the setting of the rich and lean determination values ​​used in the target air-fuel ratio switching process. Figure 3 This is a diagram illustrating an example of a mapping between setpoints for concentration and dilution determination values ​​relative to the degree of gas contact with unpurified gas. Figure 3 In the mapping shown, the rich and lean determination values ​​used for target air-fuel ratio switching are specified corresponding to the gas contact parameters, which are quantified by the degree of gas contact between the unpurified gas and the second air-fuel ratio sensor 34. The ECU 30 will... Figure 3 The mapping shown is stored in ROM. The switching cycle change processing unit 314 reads it from ROM, for example. Figure 3 The mapping shown determines the concentration and dilute determination values ​​corresponding to the gas contact parameters. Based on... Figure 3As shown in the mapping, the stronger the gas contact parameter value, the further the rich and lean determination values ​​used in the target air-fuel ratio switching process will be from the stoichiometric air-fuel ratio. Therefore, the stronger the gas contact parameter value, the longer the target air-fuel ratio switching cycle in the target air-fuel ratio switching process.

[0043] 3-2. Parameter Calculation and Processing

[0044] The control of the engine 10, executed by the ECU 30 of the internal combustion engine system 100, includes parameter calculation processing. This parameter calculation processing is performed in the parameter calculation processing unit 316 of the ECU 30. In the parameter calculation processing of this embodiment, gas contact parameters used in the switching cycle change processing are calculated based on the operating conditions of the engine 10. In calculating the gas contact parameters, the engine rotational speed NE detected by the rotational speed sensor 36 and the engine load KL calculated based on the engine rotational speed NE and the intake air volume Ga detected by the air flow meter 16 are used as the operating conditions of the engine 10. The ECU 30 stores a parameter calculation mapping that defines the relationship between the engine rotational speed NE, the engine load KL, and the gas contact parameters in a ROM. In the parameter calculation processing, the gas contact parameters corresponding to the detected engine rotational speed NE and engine load KL are determined based on the parameter calculation mapping.

[0045] 4. Specific processing performed in the internal combustion engine system of the implementation method

[0046] Next, the specific processing of the routines executed by ECU30 during the operation of engine 10 will be explained along the flowchart.

[0047] Figure 4 This is a flowchart illustrating the routine of processing performed in the internal combustion engine system of the embodiment. Figure 4 The routine shown is repeatedly executed in ECU30 during the operation of engine 10.

[0048] exist Figure 4 In step S100 of the illustrated routine, the intake air volume Ga is detected using an air flow meter 16. When step S100 is completed, the process proceeds to step S102. In step S102, the engine rotational speed NE is detected using a rotational speed sensor 36, and the engine load KL is detected based on the intake air volume Ga and the engine rotational speed NE. When step S102 is completed, the process proceeds to step S104.

[0049] In step S104, parameter calculation processing is performed in the parameter calculation processing unit 316 to calculate the gas contact parameters. Here, a mapping is calculated based on the parameters to calculate the gas contact parameters corresponding to the engine rotation speed NE and engine load KL detected in step S102. When the processing in step S104 is completed, the process proceeds to step S106.

[0050] In step S106, the concentration determination value and the dilute determination value are calculated. Here, using Figure 3 The mapping shown calculates the concentration and dilute determination values ​​corresponding to the gas contact parameters calculated in step S104. The process ends when step S106 is completed.

[0051] 5. The function and effect of the processing performed by the internal combustion engine system of the implementation method.

[0052] The internal combustion engine system 100 of the embodiment has the following functions and effects. Figure 5 This is a timeline showing the changes in various states when the internal combustion engine system of the implementation method performs a switching cycle change process. Furthermore, in Figure 5 In the diagram, solid lines represent operational examples of the internal combustion engine system 100 that perform switching cycle change processing, while dashed lines represent operational examples of the internal combustion engine system that do not perform switching cycle change processing.

[0053] Figure 6A and Figure 6B This is a schematic diagram illustrating the flow of exhaust gas and the internal state of the exhaust purification catalyst. Furthermore, Figure 6A express Figure 5 The state of the internal combustion engine system at time t1 in the comparative example. Figure 6B express Figure 5 The state at time t2 in the internal combustion engine system 100 of the embodiment. In the comparative example internal combustion engine system, such as Figure 6A As shown, the second air-fuel ratio reaches the rich setting value, and the target air-fuel ratio is switched to the lean setting value. Due to the strong contact between the insufficiently purified gas and the oxygen remaining in the first exhaust gas purification catalyst 22, the timing t1 of the second air-fuel ratio is detected by the second air-fuel ratio sensor 34. Therefore, in the comparative example's internal combustion engine system, the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 cannot be utilized to the maximum extent, and insufficiently purified gases such as HC flow downstream in the flow direction of the second exhaust gas purification catalyst 24.

[0054] In contrast, in the internal combustion engine system 100 of this embodiment, when the gas contact degree with insufficiently purified exhaust gas is strong, a switching cycle change process is performed to change the richness determination value to a value far from the stoichiometric air-fuel ratio. Thus, as... Figure 6BAs shown, at a time t2 after the oxygen stored in the first exhaust purification catalyst 22 is effectively utilized, the second air-fuel ratio detected by the second air-fuel ratio sensor 34 reaches the rich setting value. Therefore, the target air-fuel ratio is switched to the lean setting value. Thus, in the internal combustion engine system 100 of this embodiment, the first exhaust purification catalyst 22 and the second exhaust purification catalyst 24 can be effectively utilized. Therefore, compared to the comparative example, the amount of insufficiently purified gases such as HC flowing downstream in the flow direction of the second exhaust purification catalyst 24 can be reduced.

[0055] 6. Variations of the internal combustion engine system of the embodiment

[0056] The internal combustion engine system 100 of the embodiment can also be modified as follows.

[0057] 6-1. Handling of Switching Cycle Changes

[0058] In the switching cycle change processing, the method for extending the switching cycle of the target air-fuel ratio in the target air-fuel ratio switching process is not limited to changing the richness and leanness determination values ​​used in the target air-fuel ratio switching process. That is, in the switching cycle change processing, the switching cycle change processing unit 314 sets a delay time from the time point when the second air-fuel ratio reaches the richness or leanness determination value to the actual switching of the target air-fuel ratio. The switching cycle change processing unit 314 may also process the process in such a way that the more the gas contact parameter indicates the strength of gas contact, the longer the delay time is set.

[0059] 6-2. Parameter Calculation and Processing

[0060] In a turbocharged internal combustion engine equipped with an exhaust valve port and an exhaust valve that opens and closes that exhaust valve port, the gas velocity through the exhaust valve port is faster than the gas velocity through the turbine. Therefore, when the engine operating conditions change and the ratio of gas passing through the turbine and the exhaust valve port changes, the degree of contact between the gas passing through the exhaust valve port and the second air-fuel ratio sensor 34 also changes.

[0061] Therefore, when the engine 10 is a turbocharged internal combustion engine equipped with an exhaust valve port and an exhaust valve, the parameter calculation and processing unit 316 can also, in addition to the engine rotation speed NE and engine load KL, reflect the state of the exhaust valve in the calculation of gas contact parameters during parameter calculation and processing. In this case, the ECU 30 can calculate and map the parameters that define the relationship between the engine rotation speed NE, engine load KL, exhaust valve opening, and gas contact parameters, and store them in the ROM.

[0062] 6-3. Target air-fuel ratio switching process

[0063] In the target air-fuel ratio switching process, the target air-fuel ratio switching processing unit 312 can also set the lean and rich setpoints to values ​​closer to the stoichiometric air-fuel ratio than before the change in the intake air volume Ga produces a predetermined increase pattern. An example of this predetermined increase pattern is when the intake air volume Ga exceeds a predetermined value. Thus, when the intake air volume Ga increases, the lean and rich setpoints are set to values ​​closer to the stoichiometric air-fuel ratio than before the increase in the intake air volume Ga. This prevents unpurified gas from flowing downstream of the exhaust gas purification catalyst under conditions of increased exhaust gas velocity.

Claims

1. An internal combustion engine system, wherein, The internal combustion engine system includes: The first exhaust purification catalyst is installed in the exhaust passage of the internal combustion engine; The second exhaust purification catalyst is disposed downstream of the exhaust flow direction of the first exhaust purification catalyst. The first air-fuel ratio sensor is disposed on the upstream side of the exhaust flow direction of the first exhaust purification catalyst in the exhaust passage; A second air-fuel ratio sensor is disposed downstream of the first exhaust gas purification catalyst and upstream of the second exhaust gas purification catalyst in the exhaust passage; and Control device, controls the internal combustion engine. The control device is configured to perform the following processing: Feedback processing is used to control the air-fuel ratio of the exhaust gas discharged from the internal combustion engine in such a way that the first air-fuel ratio detected by the first air-fuel ratio sensor becomes the target air-fuel ratio. The target air-fuel ratio switching process alternately switches the target air-fuel ratio to a lean setpoint (lean than the stoichiometric air-fuel ratio) and a rich setpoint (rich than the stoichiometric air-fuel ratio). Parameter calculation and processing, based on the operating conditions of the internal combustion engine, calculates gas contact parameters, which represent the degree of contact between the unpurified gas in the exhaust gas discharged from the first exhaust purification catalyst and the gas in contact with the second air-fuel ratio sensor; and In the switching cycle change processing, the stronger the gas contact parameter value, the longer the switching cycle of the target air-fuel ratio in the target air-fuel ratio switching processing.

2. The internal combustion engine system according to claim 1, wherein, In the target air-fuel ratio switching process, the control device is configured to set the target air-fuel ratio to the lean setting value when the second air-fuel ratio detected by the second air-fuel ratio sensor is below the richness determination value (richer than the stoichiometric air-fuel ratio), and to set the target air-fuel ratio to the richness setting value when the second air-fuel ratio is above the leanness determination value (leaner than the stoichiometric air-fuel ratio). In the switching cycle change process, the control device is configured such that the more the gas contact parameter indicates the degree of gas contact, the further the lean determination value and the rich determination value are from the stoichiometric air-fuel ratio.

3. The internal combustion engine system according to claim 2, wherein, In the target air-fuel ratio switching process, the control device is configured to set the lean setpoint and the rich setpoint to values ​​closer to the stoichiometric air-fuel ratio than before the change in the intake air volume of the internal combustion engine produces a predetermined increase mode.

4. The internal combustion engine system according to any one of claims 1 to 3, wherein, The internal combustion engine is a turbocharged internal combustion engine equipped with an exhaust valve port and an exhaust valve valve for opening and closing the exhaust valve port. In the parameter calculation and processing, the control device is configured to calculate the gas contact parameters based on the rotational speed of the internal combustion engine, the intake air volume, and the opening degree of the exhaust valve.

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