Internal combustion engine system

Abstract

This invention provides an internal combustion engine system that can effectively utilize the purification capacity of an exhaust gas purification catalyst by taking into account the effects of variations in the air-fuel ratio from cylinder to cylinder and variations in the amount of gas per unit of the air-fuel ratio sensor for each cylinder. [Solution] The internal combustion engine system performs the following processes: feedback control of the air-fuel ratio so that the exhaust gas of the internal combustion engine reaches a target air-fuel ratio; target air-fuel ratio switching process that alternately causes the target air-fuel ratio to swing between lean and rich sides from the air-fuel ratio center value; setting the air-fuel ratio center value; calculating a first parameter that indicates the air-fuel ratio variation for each cylinder; calculating a second parameter that indicates the cylinder-specific variation in the degree to which the exhaust gas emitted from each cylinder hits the second air-fuel ratio sensor downstream of the first exhaust gas purification catalyst; and setting the amplitude of the target air-fuel ratio in the target air-fuel ratio switching process based on the first and second parameters.

Description

Technical Field

[0001] The present disclosure relates to an internal combustion engine system, and more particularly to an internal combustion engine system that purifies exhaust gas exhausted from an internal combustion engine using an exhaust purification catalyst.

Background Art

[0002] Patent Document 1 discloses a technique related to a control device for suppressing the outflow of NOx and unburned gas from an exhaust purification catalyst. The internal combustion engine of this technique includes an exhaust purification catalyst, a downstream air-fuel ratio sensor disposed downstream of the exhaust purification catalyst, and an air flow meter that detects the intake air amount. Then, the control device performs feedback control so that the exhaust air-fuel ratio of the internal combustion engine becomes the target air-fuel ratio, sets the target air-fuel ratio to a lean air-fuel ratio when the output air-fuel ratio of the downstream air-fuel ratio sensor becomes a rich air-fuel ratio, and sets the target air-fuel ratio to a rich air-fuel ratio when the output air-fuel ratio of the downstream air-fuel ratio sensor becomes a lean air-fuel ratio.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technology described in Patent Document 1, if the output air-fuel ratio of the downstream air-fuel ratio sensor is constantly shifted to the rich or lean side, it is conceivable to perform learning control to learn and correct the deviation in the control center value of the target air-fuel ratio. However, in an internal combustion engine with multiple cylinders, the gas intensity at which the exhaust gas from each cylinder hits the downstream air-fuel ratio sensor installed downstream of the exhaust gas purification catalyst and the air-fuel ratio of the exhaust gas from each cylinder may vary depending on the operating conditions of the internal combustion engine. Therefore, if the learning control is performed in the device described in Patent Document 1, when there is variation in the gas intensity at which the downstream air-fuel ratio sensor hits the downstream air-fuel ratio sensor and the air-fuel ratio of the exhaust gas from cylinder to cylinder, it may be mistakenly detected that the average air-fuel ratio of all cylinders is off, and the control center value may be changed based on this mistakenly detected value. As a result, if the amount of reduction or oxidation flowing into the exhaust gas purification catalyst is insufficient, the purification capacity of the exhaust gas purification catalyst may not be fully utilized.

[0005] This disclosure has been made in view of the above-mentioned problems, and aims 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 effects of variations in the air-fuel ratio for each cylinder of the internal combustion engine and variations in the amount of gas per unit of the air-fuel ratio sensor for each cylinder. [Means for solving the problem]

[0006] To solve the above problems, this disclosure provides an internal combustion engine system comprising: a first exhaust gas purification catalyst arranged in the exhaust passage of an internal combustion engine having multiple cylinders; a second exhaust gas purification catalyst arranged downstream of the first exhaust gas purification catalyst in the exhaust flow direction; a first air-fuel ratio sensor arranged upstream of the first exhaust gas purification catalyst in the exhaust flow direction in the exhaust passage; a second air-fuel ratio sensor arranged downstream of the first exhaust gas purification catalyst in the exhaust flow direction and upstream of the second exhaust gas purification catalyst in the exhaust passage; and a control device for controlling the internal combustion engine. The control device is configured to perform the following: a feedback process that feedback-controls the air-fuel ratio of the exhaust gas discharged from the internal combustion engine so that the first air-fuel ratio detected by the first air-fuel ratio sensor becomes the target air-fuel ratio; a target air-fuel ratio switching process that alternately causes the target air-fuel ratio to oscillate between lean and rich sides from the air-fuel ratio center value; a learning control process that sets the air-fuel ratio center value in the target air-fuel ratio switching process based on the second air-fuel ratio detected by the second air-fuel ratio sensor; a first parameter calculation process that calculates a first parameter indicating the air-fuel ratio variation for each cylinder of the internal combustion engine; a second parameter calculation process that calculates a second parameter indicating the cylinder-by-cylinder variation in the degree to which the exhaust gas discharged from each cylinder of the internal combustion engine hits the second air-fuel ratio sensor; and an amplitude setting process that sets the amplitude of the target air-fuel ratio in the target air-fuel ratio switching process based on the first and second parameters.

[0007] Furthermore, in the amplitude setting process of this disclosure, the control device may set the amplitude to a larger value as the first parameter indicates a larger variation in the air-fuel ratio for each cylinder.

[0008] Furthermore, in the amplitude setting process of this disclosure, the control device may set the amplitude to a larger value the greater the second parameter is indicative of the variation in gas distribution between cylinders. [Effects of the Invention]

[0009] According to the internal combustion engine system of this disclosure, the purification capacity of the exhaust gas purification catalyst can be effectively utilized by taking into account the effects of variations in the air-fuel ratio for each cylinder and variations in the amount of gas per unit of the air-fuel ratio sensor for each cylinder. [Brief explanation of the drawing]

[0010] [Figure 1] This is a diagram illustrating the configuration of an internal combustion engine system according to an embodiment. [Figure 2] This diagram shows the functional blocks of the ECU. [Figure 3] This is a time chart showing the changes in various states when the amplitude setting process is performed by the internal combustion engine system of the embodiment. [Figure 4] This figure shows an example of a map that defines rich and lean setting values ​​for the degree of variation in the air-fuel ratio between cylinders and the degree of variation in the exhaust gas per-gas ratio between cylinders. [Figure 5] This flowchart shows the processing routines performed in the internal combustion engine system of the embodiment. [Modes for carrying out the invention]

[0011] Embodiments of this disclosure will be described below. However, when the number of elements, quantities, amounts, ranges, etc., are mentioned in the embodiments described below, this disclosure is not limited to the number mentioned unless it is specifically stated or clearly defined in principle. Furthermore, structures, steps, etc., described in the embodiments described below are not necessarily essential to this disclosure unless they are specifically stated or clearly defined in principle.

[0012] Embodiment. 1. Configuration of the Embodiment Figure 1 is a diagram illustrating the configuration of an internal combustion engine system according to this embodiment. As shown in Figure 1, the internal combustion engine system 100 of this embodiment includes an internal combustion engine 10 having 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 at the stoichiometric air-fuel ratio. The engine 10 has four cylinders, from cylinder #1 to cylinder #4, arranged in series, and each cylinder is provided with an injector 8. An intake manifold and an exhaust manifold are attached to the engine 10 (neither is shown in the diagram). An intake passage 12 for taking in intake air into the engine 10 is connected to the intake manifold. An exhaust passage 14 for releasing exhaust gas from the engine 10 into the atmosphere is connected to the exhaust manifold.

[0013] An airflow meter 16 for detecting the intake air volume Ga is located in the middle of the intake passage 12. A throttle valve 18 is provided downstream of the airflow meter 16 in the intake passage 12 in the direction of intake air flow. A first exhaust gas purification catalyst 22 is located in the exhaust passage 14. A second exhaust gas purification catalyst 24 is located downstream of the first exhaust gas purification catalyst 22 in the direction of exhaust air flow in the exhaust passage 14.

[0014] For example, the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 both have similar configurations. 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 made of a ceramic substrate on which a noble metal such as platinum (Pt) with catalytic activity and ceria (CeO2) with oxygen storage capacity are supported. When the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 reach a predetermined activation temperature, they exhibit catalytic activity that simultaneously purifies unburned gases (HC and CO, etc.) and nitrogen oxides (NOx), as well as oxygen storage capacity.

[0015] According to 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 leaner than the stoichiometric air-fuel ratio, they store oxygen in the exhaust gas. On the other hand, when the air-fuel ratio of the incoming exhaust gas is richer than the stoichiometric air-fuel ratio, the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 release the oxygen they have stored. The first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 are not limited in type or structure, as long as they have catalytic action to purify exhaust gas and oxygen storage capacity.

[0016] The internal combustion engine system 100 according to this embodiment includes an ECU (Electronic Control Unit) 30. The ECU 30 is a control device that comprehensively controls the entire internal combustion engine system 100. The control device according to this disclosure is embodied as one of the functions of the ECU 30.

[0017] The ECU 30 has at least an input / output interface, a ROM, a RAM, and a CPU (Central Processing Unit). The input / output interface captures the signals of the sensors provided in the internal combustion engine system 100 and outputs an operation signal to the actuators provided in the engine 10. The sensors are attached at various locations in the internal combustion engine system 100. A first air-fuel ratio sensor 32 is provided upstream of the first exhaust purification catalyst 22 in the exhaust passage 14. The first air-fuel ratio sensor 32 detects the air-fuel ratio of the exhaust gas exhausted from the engine 10 to the exhaust passage 14 as the first air-fuel ratio. A second air-fuel ratio sensor 34 is provided downstream of the first exhaust purification catalyst 22 in the exhaust flow direction in the exhaust passage 14 and upstream of the second exhaust purification catalyst 24 in the exhaust flow direction. The second air-fuel ratio sensor 34 detects the air-fuel ratio of the exhaust gas flowing out of the first exhaust purification catalyst 22 and flowing into the second exhaust purification catalyst 24 as the second air-fuel ratio. Further, a rotational speed sensor 36 for detecting the engine rotational speed NE of the engine 10 and various sensors for detecting the state of the engine 10 are also attached. The ECU 30 processes the signals of the captured sensors and operates each actuator according to a predetermined control program.

[0018] The actuators operated by the ECU 30 include an injector 8, a throttle valve 18, etc. The ROM stores various control data including various control programs and maps for controlling the engine 10. The CPU reads out the control program from the ROM and executes it, and generates an operation signal based on the captured sensor signals. Although there are many actuators and sensors connected to the ECU 30 other than those shown in the figure, their descriptions are omitted in this specification.

[0019] FIG. 2 is a diagram showing the functional blocks of the ECU. The ECU 30 includes a feedback processing unit 310, a target air-fuel ratio switching processing unit 312, a learning control processing unit 314, and an amplitude setting processing unit 316 as functional blocks for controlling the internal combustion engine system 100. Hereinafter, the processes executed in each functional block will be described in detail.

[0020] 2. Basic Operations of the Internal Combustion Engine System in the Embodiment 2-1. Feedback Processing The control of the engine 10 executed by the ECU 30 of the internal combustion engine system 100 includes feedback processing. The feedback processing is executed in the feedback processing unit 310 of the ECU 30. In the feedback processing of the present embodiment, the fuel injection amount from the injector 8 is feedback-controlled so that the first air-fuel ratio detected by the first air-fuel ratio sensor 32 becomes the target air-fuel ratio. The target air-fuel ratio here is, for example, the theoretical air-fuel ratio (A / F 14.60).

[0021] 2-2. Target Air-Fuel Ratio Switching Processing The control of the engine 10 executed by the ECU 30 of the internal combustion engine system 100 includes target air-fuel ratio switching processing. The target air-fuel ratio switching processing is executed in the target air-fuel ratio switching processing unit 312 of the ECU 30. In the target air-fuel ratio switching processing of the present embodiment, the target air-fuel ratio is alternately switched between the lean set value and the rich set value so that the air-fuel ratio of the exhaust gas oscillates alternately between the lean side and the rich side from the air-fuel ratio center value. Specifically, in the target air-fuel ratio switching processing, when the second air-fuel ratio detected by the second air-fuel ratio sensor 34 becomes equal to or less than the rich determination value that is richer than the theoretical air-fuel ratio, the target air-fuel ratio is set to the lean set value, and when the second air-fuel ratio becomes equal to or greater than the lean determination value that is leaner than the theoretical air-fuel ratio, the target air-fuel ratio is set to the rich set value. The air-fuel ratio center value here is a value set in the learning control processing described later, and for example, the initial value is set to the theoretical air-fuel ratio.

[0022] If the oxygen-storing capacity of an exhaust gas purification catalyst is kept nearly constant, it will lead to a decrease in oxygen storage capacity. Therefore, in order to maintain oxygen storage capacity as much as possible, it is preferable to alternately change the amount of oxygen stored inside the exhaust gas purification catalyst between a storage amount close to zero and a storage amount close to the maximum when using 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 setting and a rich setting, so the oxygen storage capacity of the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 increases and decreases repeatedly. As a result, the oxygen storage capacity of the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 can be kept 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.

[0023] 2-3. Learning and Control Processing The control of the engine 10 performed by the ECU 30 of the internal combustion engine system 100 includes a learning control process. The learning control process is performed in the learning control processing unit 314 of the ECU 30. In the learning control process of this embodiment, the air-fuel ratio center value in the target air-fuel ratio switching process is set. Specifically, in the learning control process, the initial value of the air-fuel ratio center value is set to the stoichiometric air-fuel ratio. When the engine 10 is operated, the amount of oxygen absorbed during the period when the target air-fuel ratio is oscillated to the lean side and the amount of oxygen consumed during the period when the target air-fuel ratio is oscillated to the rich side are calculated based on the second air-fuel ratio detected by the second air-fuel ratio sensor 34 and the intake air amount Ga detected by the airflow meter 16 in the target air-fuel ratio switching process. The air-fuel ratio center value is then set so that the calculated amount of oxygen absorbed and the amount of oxygen consumed are equal.

[0024] 3. Characteristics and operation of the internal combustion engine system of the embodiment 3-1. Amplitude setting process The control of the engine 10, performed by the ECU 30 of the internal combustion engine system 100, includes an amplitude setting process. The amplitude setting process is performed in the amplitude setting processing unit 316 of the ECU 30.

[0025] Figure 3 is a time chart showing the changes in various states when the amplitude setting process is performed by the internal combustion engine system of the embodiment. In Figure 3, the solid line shows an example of the operation of the internal combustion engine system 100 of the embodiment in which the amplitude setting process is performed, and the dashed line shows an example of the operation of the internal combustion engine system of the comparative example in which the amplitude setting process is not performed.

[0026] Consider the case where engine 10 is, for example, a 4-cylinder naturally aspirated engine, and the engine speed NE and engine load KL change, causing engine 10 to change to the following state at time t1 in the time chart shown in Figure 3. The air-fuel ratio of the exhaust gases from cylinders #1 and #2 varies towards the lean side, while the air-fuel ratio of the exhaust gases from cylinders #3 and #4 varies towards the rich side. • The exhaust gas pressure on cylinders #1 and #2 is strong relative to the second air-fuel ratio sensor 34, while the exhaust gas pressure on cylinders #3 and #4 is weaker compared to cylinders #1 and #2.

[0027] In this case, the value detected by the second air-fuel ratio sensor 34 is strongly influenced by the air-fuel ratio of the exhaust gases of cylinders #1 and #2, which have a stronger gas-to-air ratio. As a result, the second air-fuel ratio becomes leaner than the average value of the air-fuel ratios of all cylinders. Therefore, when there is variation in the air-fuel ratio and gas-to-air ratio between cylinders as described above, if the learning control process is executed based on the second air-fuel ratio detected by the second air-fuel ratio sensor 34, the air-fuel ratio center value is shifted to the rich side, as shown in Figure 3. In this case, the exhaust gases of cylinders #3 and #4 are shifted even further to the rich side, and the purification performance of the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 deteriorates.

[0028] Furthermore, as shown in the comparative example in Figure 3, when the target air-fuel ratio is set to a lean setting value by the target air-fuel ratio switching process at time t1, the learning control process causes the air-fuel ratio center value to shift towards the rich side, resulting in a decrease in the leanness of the lean setting value. As a result, at time t2, the second air-fuel ratio may not reach the lean judgment value, or the time to reach the lean judgment value may be prolonged, and the continued lean operation may reduce the purification performance of the first exhaust purification catalyst 22 and the second exhaust purification catalyst 24. This reduction in the purification performance of the first exhaust purification catalyst 22 and the second exhaust purification catalyst 24 can also occur when there is variation in the air-fuel ratio between cylinders and per gas unit, and the second air-fuel ratio becomes richer than the average value of the air-fuel ratio of all cylinders.

[0029] Therefore, in the amplitude setting process of the internal combustion engine system 100 of this embodiment, the lean setting value and rich setting value are set such that the larger the variation in the air-fuel ratio between cylinders and the larger the variation in the degree to which the exhaust gas discharged from each cylinder hits the second air-fuel ratio sensor 34, the larger the amplitude of the target air-fuel ratio in the target air-fuel ratio switching process.

[0030] Figure 4 shows an example of a map that defines rich and lean setting values ​​for the degree of variation in the air-fuel ratio between cylinders and the degree of variation in the gas-to-gas ratio of exhaust gas between cylinders. In the map shown in Figure 4, the rich and lean setting values ​​used in the target air-fuel ratio switching process are defined in correspondence with a first parameter that quantifies the degree of variation in the air-fuel ratio between cylinders and a second parameter that quantifies the degree of variation in the gas-to-gas ratio of exhaust gas between cylinders. The ECU 30 stores the map shown in Figure 4 in its ROM.

[0031] The amplitude setting processing unit 316 reads, for example, the map shown in Figure 4 from the ROM and identifies the rich setting value and lean setting value corresponding to the first parameter and the second parameter. According to the map shown in Figure 4, the greater the variation in the air-fuel ratio between cylinders for the first parameter, and the greater the variation in the degree of gas contact between cylinders for exhaust gases

[0032] As shown in the embodiment in Figure 3, when the amplitude setting process is executed in response to the increased variation in air-fuel ratio between cylinders and the variation in gas density between cylinders at time t1, the amplitude of the target air-fuel ratio from the air-fuel ratio center value is expanded. As a result, the leanness of the target air-fuel ratio for the period after time t1 becomes greater than before the amplitude expansion. Consequently, the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 can be effectively utilized, and the amount of insufficiently purified gases such as NOx flowing downstream in the flow direction of the second exhaust gas purification catalyst 24 can be reduced compared to the comparative example.

[0033] 3-2. Parameter Calculation Process The control of the engine 10 performed by the ECU 30 of the internal combustion engine system 100 includes parameter calculation processing. The parameter calculation processing is performed in the parameter calculation processing unit 318 of the ECU 30. The parameter calculation processing in this embodiment includes a first parameter calculation process that calculates a first parameter used for amplitude setting processing based on the operating conditions of the engine 10, and a second parameter calculation process that calculates a second parameter used for amplitude setting processing based on the operating conditions of the engine 10.

[0034] In the first parameter calculation process, the operating conditions of the engine 10 are the fuel flow rate of each cylinder, 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 amount Ga detected by the airflow meter 16. The fuel flow rate may be the indicated value of the amount of fuel injected from the injector 8 of each cylinder, or the fuel flow rate for each cylinder may be detected by a fuel flow meter. The ECU 30 stores a first parameter calculation map in ROM that defines the relationship between the engine rotational speed NE, engine load KL, the fuel flow rate of each cylinder, and the first parameter. In the first parameter calculation process, the first parameter corresponding to the detected engine rotational speed NE, engine load KL, and the fuel flow rate of each cylinder is identified from the first parameter calculation map.

[0035] Alternatively, if the internal combustion engine system 100 is configured as an HEV system equipped with a motor generator MG, the torque variation for each cylinder may be calculated using the motor generator MG, and the air-fuel ratio variation for each cylinder may be estimated from the torque variation for each cylinder to determine the first parameter z.

[0036] In the second parameter calculation process, the engine speed NE detected by the rotational speed sensor 36 and the engine load KL calculated based on the engine speed NE and the intake air volume Ga detected by the airflow meter 16 are used as operating conditions for the engine 10. The ECU 30 stores a second parameter calculation map in its ROM that defines the relationship between the engine speed NE, the engine load KL, and the second parameter. In the second parameter calculation process, the second parameter corresponding to the detected engine speed NE and engine load KL is identified from the second parameter calculation map.

[0037] In a supercharged engine equipped with a wastegate port and a wastegate valve for opening and closing the wastegate port, the gas flow velocity through the wastegate port is faster than the gas flow velocity through the turbine. Therefore, when engine operating conditions change and the ratio of gas passing through the turbine and the wastegate port changes, the degree to which the gas passing through the wastegate port hits the second air-fuel ratio sensor 34 also changes.

[0038] Therefore, if the engine 10 is a supercharged engine equipped with a wastegate port and a wastegate valve, the parameter calculation processing unit 318 may, in addition to the engine rotational speed NE and engine load KL, further reflect the state of the wastegate valve in the calculation of the second parameter in the second parameter calculation processing. In this case, the ECU 30 only needs to store in ROM a second parameter calculation map that defines the relationship between the engine rotational speed NE, engine load KL, the opening degree of the wastegate valve, and the second parameter.

[0039] 4. Specific processes performed in the internal combustion engine system of the embodiment Next, we will explain the specific processes of the routines that the ECU 30 executes while the engine 10 is running, following the flowchart.

[0040] Figure 5 is a flowchart showing the processing routine performed in the internal combustion engine system of the embodiment. The routine shown in Figure 5 is repeatedly executed in the ECU 30 while the engine 10 is running.

[0041] In step 100 of the routine shown in Figure 5, the fuel flow rate of each cylinder is detected. Here, for example, the indicated value of the amount of fuel injected from the injector 8 of each cylinder is detected as the fuel flow rate of each cylinder. Once the processing of step 100 is complete, the process proceeds to step 102. In the processing of step 102, the intake air amount Ga is detected using the airflow meter 16. Once the processing of step 102 is complete, the process proceeds to step 104. In step 104, the engine rotational speed NE is detected using the rotational speed sensor 36, and the engine load KL is detected from the intake air amount Ga and the engine rotational speed NE. Once the processing of step 104 is complete, the process proceeds to step 106.

[0042] In step 106, the parameter calculation processing unit 318 performs a first parameter calculation process to calculate a first parameter representing the degree of variation in the air-fuel ratio for each cylinder. Here, the first parameter corresponding to the fuel flow rate for each cylinder detected in step 100, and the engine speed NE and engine load KL detected in step 104, is calculated from the first parameter calculation map described above. Once the processing in step 106 is completed, the process proceeds to step 108.

[0043] In step 108, the parameter calculation processing unit 318 performs a second parameter calculation process to calculate a second parameter that represents the degree of variation in gas intensity for each cylinder. Here, the second parameter corresponding to the engine rotational speed NE and engine load KL detected in step 104 is calculated from the aforementioned second parameter calculation map. Once the processing in step 108 is completed, the process proceeds to step 110.

[0044] In step 110, rich and lean setting values ​​are calculated to cause fluctuations in the air-fuel ratio during the target air-fuel ratio switching process. Here, using the map shown in Figure 4, rich and lean setting values ​​corresponding to the first parameter calculated in step 106 and the second parameter calculated in step 108 are calculated. Once the processing in step 110 is complete, the processing of this routine is terminated.

[0045] In the internal combustion engine system 100 of the embodiment configured as described above, if the air-fuel ratio center value is learned to deviate from the stoichiometric air-fuel ratio in the learning control process due to large variations in the air-fuel ratio for each cylinder and the strength of the gas per cylinder, the amplitude of the air-fuel ratio in the target air-fuel ratio switching process is increased. As a result, the first exhaust gas purification catalyst 22 and the second exhaust gas purification catalyst 24 can be effectively utilized, and the amount of insufficiently purified gases such as NOx flowing out to the downstream side in the flow direction of the second exhaust gas purification catalyst 24 can be reduced. [Explanation of Symbols]

[0046] 8 Injectors 10. Internal combustion engine 12 Intake passage 14 Exhaust passage 16. Airflow Meter 18 Throttle valve 22 First exhaust gas purification catalyst 24 Second exhaust gas purification catalyst 30 ECU(Electronic Control Unit) 32 First air-fuel ratio sensor 34 Second air-fuel ratio sensor 36. Rotation speed sensor 100 Internal Combustion Engine Systems 310 Feedback Processing Unit 312 Target air-fuel ratio switching processing unit 314 Learning Control Processing Unit 316 Amplitude setting processing unit 318 Parameter calculation processing unit

Claims

1. A first exhaust gas purification catalyst is positioned in the exhaust passage of an internal combustion engine having multiple cylinders, A second exhaust gas purification catalyst is positioned downstream of the first exhaust gas purification catalyst in the exhaust flow direction, A first air-fuel ratio sensor is positioned upstream of the first exhaust gas purification catalyst in the exhaust flow direction in the exhaust passage, A second air-fuel ratio sensor is positioned in the exhaust passage downstream of the first exhaust gas purification catalyst in the exhaust flow direction and upstream of the second exhaust gas purification catalyst in the exhaust flow direction. The system comprises a control device for controlling the internal combustion engine, The control device is A feedback process that provides feedback control to the air-fuel ratio of exhaust gas discharged from the internal combustion engine so that the first air-fuel ratio detected by the first air-fuel ratio sensor becomes the target air-fuel ratio, A target air-fuel ratio switching process that alternately causes the target air-fuel ratio to fluctuate between lean and rich sides from the air-fuel ratio center value, A learning control process that sets the air-fuel ratio center value in the target air-fuel ratio switching process based on the second air-fuel ratio detected by the second air-fuel ratio sensor, A first parameter calculation process that calculates a first parameter indicating the air-fuel ratio variation for each cylinder of the internal combustion engine, A second parameter calculation process calculates a second parameter that indicates the variation in the degree to which exhaust gas emitted from each cylinder of the internal combustion engine hits the second air-fuel ratio sensor, based on the operating conditions of the internal combustion engine, and An amplitude setting process is performed to set the amplitude of the target air-fuel ratio in the target air-fuel ratio switching process based on the first parameter and the second parameter, An internal combustion engine system configured to perform the following actions.

2. In the amplitude setting process, the control device sets the amplitude to a larger value as the first parameter indicates a greater variation in the air-fuel ratio for each cylinder. The internal combustion engine system according to claim 1.

3. In the amplitude setting process, the control device sets the amplitude to a larger value as the second parameter indicates a greater variation in the degree of gas per cylinder from cylinder to cylinder. The internal combustion engine system according to claim 1 or claim 2.

4. In the target air-fuel ratio switching process, the control device adjusts the target air-fuel ratio toward the lean side when the second air-fuel ratio detected by the second air-fuel ratio sensor falls below a rich determination value that is richer than the air-fuel ratio center value, and adjusts the target air-fuel ratio toward the rich side when the second air-fuel ratio falls above a lean determination value that is leaner than the air-fuel ratio center value. The internal combustion engine system according to claim 1, configured as follows.

5. In the learning control process, the control device In the target air-fuel ratio switching process, the amount of oxygen stored during the period when the target air-fuel ratio is oscillating toward the lean side and the amount of oxygen consumed during the period when the target air-fuel ratio is oscillating toward the rich side are calculated based on the second air-fuel ratio detected by the second air-fuel ratio sensor, and the air-fuel ratio center value is set so that the amount of oxygen stored and the amount of oxygen consumed are equal. The internal combustion engine system according to claim 1, configured as follows.

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