Control device for internal combustion engine

Abstract

To provide a control device of an internal combustion engine suppressed in deterioration of emission.SOLUTION: A control device of an internal combustion engine includes: an engine body; first and second catalysts provided on an exhaust passage connected to the engine body in order from an upstream side to a downstream side; and a filter provided between the first catalyst and the second catalyst of the exhaust passage to collect exhaust fine particles. The control device of the internal combustion engine includes: an air-fuel ratio control part for performing control so as to alternately switch an air-fuel ratio of the internal combustion engine to a rich air-fuel ratio smaller than a stoichiometric air-fuel ratio and a lean air-fuel ratio larger than the stoichiometric air-fuel ratio so as to vary the air-fuel ratio of exhaust flowing into the second catalyst; and a determination part for determining whether or not the temperature of the second catalyst is an activation temperature or higher. The air-fuel control part executes reduction processing for reducing the fluctuation range of the air-fuel ratio of the exhaust flowing into the second catalyst more in the case that the determination part makes a negative determination than in the case that the determination part makes a positive determination.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] BACKGROUND ART There is known an internal combustion engine in which first and second catalysts having oxygen storage capacity are provided in an exhaust passage in this order from upstream to downstream (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-031040 Summary of the Invention [Problem to be solved by the invention]

[0004] If a filter is installed between the first and second catalysts in the exhaust passage, the heat of the exhaust gas may be used to heat the filter, causing the temperature of the second catalyst to fall below its activation temperature, which may reduce the exhaust purification capacity of the second catalyst and worsen emissions.

[0005] Therefore, an object of the present invention is to provide a control device for an internal combustion engine that suppresses the deterioration of emissions. [Means for solving the problem]

[0006] The above object can be achieved by a control device for an internal combustion engine having an engine body, first and second catalysts which are arranged in that order from upstream to downstream in an exhaust passage connected to the engine body and which have oxygen storage capacity, and a filter which is arranged in the exhaust passage between the first catalyst and the second catalyst and which collects exhaust particulates, the control device comprising: an air-fuel ratio control unit which controls the air-fuel ratio of the internal combustion engine to alternately switch between a rich air-fuel ratio which is lower than the stoichiometric air-fuel ratio and a lean air-fuel ratio which is higher than the stoichiometric air-fuel ratio so that the air-fuel ratio of the exhaust flowing into the second catalyst fluctuates; and a judgment unit which judges whether the temperature of the second catalyst is equal to or higher than an activation temperature, wherein when a negative judgment is made by the judgment unit, the air-fuel ratio control unit executes a reduction process which reduces the range of fluctuation in the air-fuel ratio of the exhaust flowing into the second catalyst more than when a positive judgment is made by the judgment unit.

[0007] The internal combustion engine may have a sensor that is provided in the exhaust passage between the first catalyst and the second catalyst and that detects an air-fuel ratio of the exhaust gas, and when the air-fuel ratio detected by the sensor becomes a lean judged air-fuel ratio that is higher than the stoichiometric air-fuel ratio, the air-fuel ratio control unit sets the target air-fuel ratio of the internal combustion engine to a rich target air-fuel ratio that is lower than the stoichiometric air-fuel ratio, and when the air-fuel ratio detected by the sensor becomes a rich judged air-fuel ratio that is lower than the stoichiometric air-fuel ratio, the air-fuel ratio control unit sets the target air-fuel ratio of the internal combustion engine to a lean target air-fuel ratio that is higher than the stoichiometric air-fuel ratio, and when a negative determination is made by the determination unit, the air-fuel ratio control unit may execute the reduction process by setting at least one of the lean judged air-fuel ratio, the rich judged air-fuel ratio, the lean target air-fuel ratio, and the rich target air-fuel ratio to a value closer to the stoichiometric air-fuel ratio than when a positive determination is made by the determination unit.

[0008] When a negative determination is made by the determination unit, the lower the temperature of the second catalyst, the more the air-fuel ratio control unit may execute the reduction process by setting at least one of the lean determined air-fuel ratio, the rich determined air-fuel ratio, the lean target air-fuel ratio, and the rich target air-fuel ratio to a value closer to the stoichiometric air-fuel ratio.

[0009] When a negative determination is made by the determination unit, the air-fuel ratio control unit may execute the reduction process by setting at least one of the lean determined air-fuel ratio and the rich determined air-fuel ratio to a value closer to the stoichiometric air-fuel ratio than when a positive determination is made by the determination unit.

[0010] When a negative determination is made by the determination unit, the air-fuel ratio control unit may execute the reduction process by setting at least one of the lean target air-fuel ratio and the rich target air-fuel ratio to a value closer to the stoichiometric air-fuel ratio than when a positive determination is made by the determination unit. [Effects of the Invention]

[0011] It is possible to provide a control device for an internal combustion engine that suppresses deterioration of emissions. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of an internal combustion engine. [Figure 2] FIG. 2 is a flowchart illustrating an example of air-fuel ratio control. [Figure 3] FIG. 3 is a timing chart illustrating the switching control. [Figure 4] FIG. 4 is a timing chart illustrating an example of switching control when reduction processing is executed. [Figure 5] FIG. 5 is a view showing an example of a map that defines the lean judged air-fuel ratio and the rich judged air-fuel ratio. [Figure 6] FIG. 6 is a timing chart illustrating an example of switching control when the reduction process of the modified example is executed. DETAILED DESCRIPTION OF THE INVENTION

[0013] [General configuration of an internal combustion engine] FIG. 1 is a schematic diagram of an internal combustion engine 1. The internal combustion engine 1 is mounted, for example, on a vehicle, but is not limited thereto and may also be mounted on a vessel or other vehicle. The internal combustion engine 1 has an engine body 10, an intake passage 20, and an exhaust passage 30. The engine body 10 is a multi-cylinder engine having multiple cylinders, each of which is provided with a combustion chamber 11, a piston 12, a spark plug 16, and the like. A connecting rod 13 and a crankshaft 14 are disposed inside the engine body 10. The piston 12 is connected to the crankshaft 14 by the connecting rod 13. The engine body 10 is provided with a rotation speed sensor 15, and each cylinder is provided with an in-cylinder injection valve 17. The rotation speed sensor 15 detects the rotation speed of the crankshaft 14, thereby detecting the rotation speed of the engine body 10. The in-cylinder injection valve 17 directly injects fuel into the combustion chamber 11. Note that a port injection valve that injects fuel toward an intake port of the engine body 10 may be provided instead of the in-cylinder injection valve 17, or a port injection valve may be provided in addition to the in-cylinder injection valve 17. The spark plug 16 ignites the air-fuel mixture in the combustion chamber 11. An intake passage 20 and an exhaust passage 30 are connected to the intake port and exhaust port of the engine body 10, respectively. An intake valve 18a and an exhaust valve 18b open and close the intake port and exhaust port of the engine body 10, respectively.

[0014] In the intake passage 20, an air cleaner 21, an air flow meter 22, and a throttle valve 23 are provided in this order from upstream to downstream. The air cleaner 21 removes dust and other particles from the air flowing in from the outside. The air flow meter 22 acquires the amount of intake air. The throttle valve 23 is driven, for example, by an actuator (not shown) to adjust the amount of intake air. As the opening of the throttle valve 23 increases, the amount of intake air increases, and as the opening decreases, the amount of intake air decreases.

[0015] When intake valve 18a opens, air is introduced from intake passage 20 into combustion chamber 11. A mixture of fuel and air injected from in-cylinder injection valve 17 is compressed by piston 12 and ignited by spark plug 16. Ignition of the mixture causes piston 12 to reciprocate up and down within combustion chamber 11, rotating crankshaft 14. Exhaust gas after combustion is discharged from exhaust passage 30.

[0016] The exhaust passage 30 is provided with a first sensor 31a, a first catalyst 32a, a second sensor 31b, a filter 33, and a second catalyst 32b, arranged in this order from upstream to downstream. The first sensor 31a and the second sensor 31b are air-fuel ratio sensors that detect the air-fuel ratio of the exhaust gas flowing through the exhaust passage 30. However, the present invention is not limited to this. At least one of the sensors may be an oxygen concentration sensor that detects the air-fuel ratio of the exhaust gas by detecting the oxygen concentration of the exhaust gas. The first sensor 31a detects the air-fuel ratio of the exhaust gas discharged from the engine body 10 and flowing into the first catalyst 32a. The second sensor 31b detects the air-fuel ratio of the exhaust gas discharged from the first catalyst 32a and flowing into the filter 33 and the second catalyst 32b. The second sensor 31b may be provided between the filter 33 and the second catalyst 32b. The filter 33 is a porous ceramic structure that captures exhaust particulates in the exhaust gas.

[0017] The first catalyst 32a and the second catalyst 32b are three-way catalysts containing catalytic metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) and possessing oxygen storage capacity. The three-way catalyst, with its catalytic activity and oxygen storage capacity, purifies NOx and HC according to the amount of oxygen stored. Specifically, when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is lean, the three-way catalyst stores oxygen in the exhaust gas when the oxygen storage capacity of the three-way catalyst is low, thereby reducing and purifying NOx in the exhaust gas. When the oxygen storage capacity of the three-way catalyst increases, the concentrations of oxygen and NOx in the exhaust gas flowing out of the three-way catalyst increase. When the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is rich, the three-way catalyst releases the oxygen stored in the three-way catalyst when the oxygen storage capacity of the three-way catalyst is high, and HC in the exhaust gas is oxidized and purified. When the oxygen storage capacity of the three-way catalyst decreases, the concentration of HC in the exhaust gas flowing out of the three-way catalyst increases. According to the three-way catalyst of this embodiment, the purification characteristics of NOx and HC in the exhaust gas change depending on the air-fuel ratio of the exhaust gas flowing into the three-way catalyst and the amount of oxygen stored. Note that at least one of the first catalyst 32a and the second catalyst 32b may be a catalyst other than the three-way catalyst as long as it has catalytic action and oxygen storage capacity.

[0018] [ECU schematic configuration] The ECU (Electric Control Unit) 100 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and a storage device such as a flash memory, and performs various controls by executing programs stored in the ROM and the storage device. The ECU 100 controls the spark plugs 16, the in-cylinder injection valves 17, and the throttle valve 23 based on the amount of operation of the accelerator pedal or the brake pedal operated by the driver, the engine speed and load of the engine body 10, etc. The ECU 100 receives inputs of the engine speed detected by the engine speed sensor 15, the intake air amount detected by the air flow meter 22, and the air-fuel ratios detected by the first sensor 31a and the second sensor 31b.

[0019] As will be described in detail later, the ECU 100 controls the air-fuel ratio of the exhaust gas discharged from the engine body 10 so that it alternates between a rich air-fuel ratio lower than the stoichiometric air-fuel ratio ST and a lean air-fuel ratio higher than the stoichiometric air-fuel ratio ST. Specifically, the ECU 100 controls the air-fuel ratio of the exhaust gas discharged from the engine body 10 as follows.

[0020] The ECU 100 controls the air-fuel ratio of the exhaust gas discharged from the engine body 10 so that the detected air-fuel ratio AFa of the first sensor 31a becomes the target air-fuel ratio TAF. Specifically, the ECU 100 controls the air-fuel ratio of the exhaust gas discharged from the engine body 10 to the target air-fuel ratio TAF by feedback controlling the fuel injection amount from the direct injection valve 17 and the opening degree of the throttle valve 23 based on the detected air-fuel ratio AFa of the first sensor 31a so that the detected air-fuel ratio AFa of the first sensor 31a becomes the target air-fuel ratio TAF. When the detected air-fuel ratio AFb of the second sensor 31b becomes a lean judged air-fuel ratio LD that is greater than the stoichiometric air-fuel ratio ST, the ECU 100 sets the target air-fuel ratio TAF to a rich target air-fuel ratio TR that is smaller than the stoichiometric air-fuel ratio ST. When the detected air-fuel ratio AFb of the second sensor 31b becomes a rich judged air-fuel ratio RD which is smaller than the stoichiometric air-fuel ratio, the ECU 100 sets the target air-fuel ratio TAF to a lean target air-fuel ratio TL which is larger than the stoichiometric air-fuel ratio. As a result, the detected air-fuel ratio AFb of the second sensor 31b periodically fluctuates between the lean judged air-fuel ratio LD and the rich judged air-fuel ratio RD. The ECU 100 is an example of a control device for the internal combustion engine 1. In addition, the ECU 100 functionally realizes an air-fuel ratio control unit and a judgment unit, which will be described later, by the above-mentioned CPU, RAM, ROM, storage device, etc.

[0021] [Air-fuel ratio control] FIG. 2 is a flowchart illustrating air-fuel ratio control. This air-fuel ratio control is repeatedly executed while the internal combustion engine 1 is operating. The ECU 100 determines whether the second sensor 31b is activated (step S1). Specifically, it is determined that the second sensor 31b is activated when the temperature of the element of the second sensor 31b is equal to or higher than the activation temperature. The temperature of the element of the second sensor 31b is calculated based on the impedance of the element of the second sensor 31b. The impedance of the element of the second sensor 31b is calculated based on the current and voltage applied to the element of the second sensor 31b. The higher the impedance of the element, the lower the calculated value of the temperature of the element of the second sensor 31b.

[0022] If the answer is Yes in step S1, it is determined whether the temperature of the second catalyst 32b is equal to or higher than the activation temperature (step S2). The temperature of the second catalyst 32b may be detected by a sensor, calculated based on the temperature of the coolant that cools the internal combustion engine 1 or an integrated value of the intake air amount, or estimated by other known methods. Step S2 is an example of processing executed by the determination unit.

[0023] If the answer is Yes in step S2, the ECU 100 executes switching control (step S3). FIG. 3 is a timing chart illustrating the switching control. FIG. 3 shows the transitions of the target air-fuel ratio TAF and the detected air-fuel ratio AFb. When the detected air-fuel ratio AFb rises to the lean determined air-fuel ratio LD (time t1), the target air-fuel ratio TAF is switched from the lean target air-fuel ratio TL to the rich target air-fuel ratio TR. As a result, HC in the exhaust gas flowing into the first catalyst 32a is oxidized and purified by the oxygen stored in the first catalyst 32a. HC in the exhaust gas that cannot be completely purified by the first catalyst 32a is similarly purified by the second catalyst 32b. As a result, the detected air-fuel ratio AFb decreases from the lean side toward the stoichiometric air-fuel ratio ST. When the oxygen storage amount of the first catalyst 32a approaches zero, the oxygen concentration in the exhaust gas discharged from the first catalyst 32a decreases, and the detected air-fuel ratio AFb decreases toward the rich side.

[0024] When the detected air-fuel ratio AFb drops to the rich-determined air-fuel ratio RD (time t2), the target air-fuel ratio TAF is switched from a predetermined rich target air-fuel ratio TR to a predetermined lean target air-fuel ratio TL. As a result, oxygen in the exhaust gas flowing into the first catalyst 32a is stored in the first catalyst 32a, thereby reducing and purifying NOx in the exhaust gas. Any NOx in the exhaust gas that cannot be completely purified by the first catalyst 32a is similarly purified by the second catalyst 32b. As a result, the detected air-fuel ratio AFb increases from the rich side toward the stoichiometric air-fuel ratio ST. As the amount of oxygen stored in the first catalyst 32a increases, the oxygen concentration in the exhaust gas discharged from the first catalyst 32a increases, and the detected air-fuel ratio AFb increases toward the lean side. In this way, the target air-fuel ratio TAF is alternately switched between the lean target air-fuel ratio TL and the rich target air-fuel ratio TR, and the detected air-fuel ratio AFb, which indicates the air-fuel ratio of the exhaust gas flowing into the second catalyst 32b, fluctuates within a predetermined range.

[0025] 2, if the answer is No in step S1, the above switching control is stopped (step S4). This is because if the second sensor 31b is not activated, the air-fuel ratio flowing into the second sensor 31b cannot be calculated with high accuracy.

[0026] If the answer is Yes in step S1 and No in step S2, the ECU 100 executes switching control and a reduction process (step S5). The reduction process is a process for reducing the fluctuation range of the air-fuel ratio of the exhaust gas flowing into the second catalyst 32b. The modification process in this embodiment is realized by using a lean-determined air-fuel ratio LDA and a rich-determined air-fuel ratio RDa, which are values ​​closer to the stoichiometric air-fuel ratio ST than the lean-determined air-fuel ratio LD and the rich-determined air-fuel ratio RD, respectively. The lean-determined air-fuel ratio LDA is greater than the stoichiometric air-fuel ratio ST and smaller than the lean-determined air-fuel ratio LD. The rich-determined air-fuel ratio RDa is smaller than the stoichiometric air-fuel ratio ST and larger than the rich-determined air-fuel ratio RD. Step S5 is an example of a process executed by the air-fuel ratio control unit.

[0027] FIG. 4 is a timing chart illustrating switching control when the reduction process is executed. Therefore, the detected air-fuel ratio AFb becomes equal to or greater than the lean-determined air-fuel ratio LDA, and the target air-fuel ratio TAF is switched from the lean target air-fuel ratio TL to the rich target air-fuel ratio TR (time t1a) earlier than in the case shown in FIG. 3. Similarly, the detected air-fuel ratio AFb becomes equal to or less than the rich-determined air-fuel ratio RDDA, and the target air-fuel ratio TAF is switched from the rich target air-fuel ratio TR to the lean target air-fuel ratio TL (time t2a) earlier than in the case shown in FIG. 3. In this way, the reduction process is executed when the temperature of the second catalyst 32b is below the activation temperature, so that excessively rich or lean exhaust gas is prevented from flowing into the second catalyst 32b, and deterioration of emissions is suppressed. Furthermore, by switching the lean-determined air-fuel ratio LD and the rich-determined air-fuel ratio RD to the lean-determined air-fuel ratio LDA and the rich-determined air-fuel ratio RDDA, respectively, it is easy to control the air-fuel ratio of the exhaust gas flowing into the second catalyst 32b.

[0028] The lean-determined air-fuel ratio LDA and the rich-determined air-fuel ratio RDa may be fixed values, or may be variable values ​​as described below. FIG. 5 is an example of a map that defines the lean-determined air-fuel ratio LDA and the rich-determined air-fuel ratio RDa. The ECU 100 sets the lean-determined air-fuel ratio LDA and the rich-determined air-fuel ratio RDa by referring to this map. As shown in FIG. 5, the lean-determined air-fuel ratio LDA and the rich-determined air-fuel ratio RDa are set to values ​​that are continuously closer to the stoichiometric air-fuel ratio ST as the temperature of the second catalyst 32b, which is below the activation temperature, decreases. This makes it possible to narrow the fluctuation range of the air-fuel ratio of the exhaust gas flowing into the second catalyst 32b as the temperature of the second catalyst 32b decreases, thereby suppressing deterioration of emissions. Note that the lean-determined air-fuel ratio LDA and the rich-determined air-fuel ratio RDa may be set to values ​​that are gradually closer to the stoichiometric air-fuel ratio ST as the temperature of the second catalyst 32b, which is below the activation temperature, decreases.

[0029] The above-described reduction process may be realized, for example, by switching only the lean judged air-fuel ratio LD to the lean judged air-fuel ratio LDA, or by switching only the rich judged air-fuel ratio RD to the rich judged air-fuel ratio RDa.

[0030] [Variations] Next, a modified example of the reduction process will be described. FIG. 6 is a timing chart illustrating switching control when the reduction process of the modified example is executed. The reduction process of the modified example is realized by using a lean target air-fuel ratio TLa and a rich target air-fuel ratio TRa that are set to values ​​closer to the stoichiometric air-fuel ratio ST than the lean target air-fuel ratio TL and the rich target air-fuel ratio TR described above. The lean target air-fuel ratio TLa is greater than the stoichiometric air-fuel ratio ST and smaller than the lean target air-fuel ratio TL. The rich target air-fuel ratio TRa is smaller than the stoichiometric air-fuel ratio ST and larger than the rich target air-fuel ratio TR. Therefore, the detected air-fuel ratio AFb fluctuates at a slower speed than the case shown in FIG. 3. Therefore, the detected air-fuel ratio AFb gradually increases and becomes equal to or greater than the lean-determined air-fuel ratio LD, and the target air-fuel ratio TAF is switched from the lean target air-fuel ratio TLa to the rich target air-fuel ratio TRa (time t1b). Because the detected air-fuel ratio AFb increases gradually in this manner, the detected air-fuel ratio AFb does not increase significantly from the lean-determined air-fuel ratio LD. Similarly, the detected air-fuel ratio AFb becomes equal to or less than the rich determined air-fuel ratio RD at a speed slower than that shown in Fig. 3, and the target air-fuel ratio TAF is switched from the rich target air-fuel ratio TRa to the lean target air-fuel ratio TLa (time t2b). Because the detected air-fuel ratio AFb decreases gradually in this manner, the detected air-fuel ratio AFb does not decrease significantly from the rich determined air-fuel ratio RD. In this way, excessively rich or lean exhaust gas is prevented from flowing into the second catalyst 32b, and deterioration of emissions is suppressed.

[0031] Furthermore, in the reduction process of the modified example, the fluctuation range of the target air-fuel ratio TAF itself is reduced, so that it is possible to suppress the transient inflow of exhaust gas with an excessively rich or lean air-fuel ratio into the second catalyst 32b, thereby suppressing the transient deterioration of emissions.

[0032] In the reduction process of the modified example, the lean target air-fuel ratio TLa may be set to a value closer to the stoichiometric air-fuel ratio ST as the temperature of the second catalyst 32b that is below the activation temperature becomes lower. Similarly, the rich target air-fuel ratio TRa may be set to a value closer to the stoichiometric air-fuel ratio ST as the temperature of the second catalyst 32b that is below the activation temperature becomes lower. Furthermore, the reduction process of the modified example may be realized by switching only the lean target air-fuel ratio TL to the lean target air-fuel ratio TLa, or may be realized by switching only the rich target air-fuel ratio TR to the rich target air-fuel ratio TRa.

[0033] The reduction process of this embodiment and the reduction process of the modified example may be executed simultaneously, thereby further reducing the fluctuation range of the air-fuel ratio of the exhaust gas flowing into the second catalyst 32b.

[0034] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0035] 1. Internal combustion engine 10. Main body of the organization 30 Exhaust passage 31a First sensor 31b Second sensor 32a 1st catalyst 32b 2nd catalyst 33 Filters 100 ECU (air-fuel ratio control unit, judgment unit)

Claims

1. A control device for an internal combustion engine having an engine body, first and second catalysts having oxygen storage capacity that are provided in this order from upstream to downstream in an exhaust passage connected to the engine body, and a filter that is provided in the exhaust passage between the first catalyst and the second catalyst and that collects exhaust particulates, an air-fuel ratio control unit that controls the air-fuel ratio of the internal combustion engine to alternately switch between a rich air-fuel ratio that is lower than the stoichiometric air-fuel ratio and a lean air-fuel ratio that is higher than the stoichiometric air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing into the second catalyst varies; a determination unit that determines whether the temperature of the second catalyst is equal to or higher than an activation temperature, When a negative determination is made by the determination unit, the air-fuel ratio control unit executes a reduction process to reduce a fluctuation range of the air-fuel ratio of the exhaust gas flowing into the second catalyst compared to when a positive determination is made by the determination unit, the internal combustion engine has a sensor that is provided in the exhaust passage between the first catalyst and the filter and that detects an air-fuel ratio of the exhaust gas, When the detected air-fuel ratio of the sensor becomes a lean judged air-fuel ratio which is higher than the stoichiometric air-fuel ratio, the air-fuel ratio control unit sets the target air-fuel ratio of the internal combustion engine to a rich target air-fuel ratio which is lower than the stoichiometric air-fuel ratio, when the detected air-fuel ratio of the sensor becomes a rich judged air-fuel ratio which is smaller than the stoichiometric air-fuel ratio, the air-fuel ratio control unit sets the target air-fuel ratio of the internal combustion engine to a lean target air-fuel ratio which is larger than the stoichiometric air-fuel ratio, When a negative determination is made by the determination unit, the air-fuel ratio control unit executes the reduction process by setting at least one of the lean determined air-fuel ratio, the rich determined air-fuel ratio, the lean target air-fuel ratio, and the rich target air-fuel ratio to a value closer to the stoichiometric air-fuel ratio than when a positive determination is made by the determination unit, The control device calculates the temperature of the second catalyst based on the temperature of cooling water that cools the internal combustion engine and an integrated value of the intake air amount.

2. 2. The control device for an internal combustion engine according to claim 1, wherein, when a negative determination is made by the determination unit, the lower the temperature of the second catalyst, the more the air-fuel ratio control unit executes the reduction process by setting at least one of the lean determined air-fuel ratio, the rich determined air-fuel ratio, the lean target air-fuel ratio, and the rich target air-fuel ratio to a value closer to the stoichiometric air-fuel ratio.

3. 2. The control device for an internal combustion engine according to claim 1, wherein when a negative determination is made by the determination unit, the air-fuel ratio control unit executes the reduction process by setting at least one of the lean determined air-fuel ratio and the rich determined air-fuel ratio to a value closer to the stoichiometric air-fuel ratio than when a positive determination is made by the determination unit.

4. 2. The control device for an internal combustion engine according to claim 1, wherein when a negative determination is made by the determination unit, the air-fuel ratio control unit executes the reduction process by setting at least one of the lean target air-fuel ratio and the rich target air-fuel ratio to a value closer to the stoichiometric air-fuel ratio than when a positive determination is made by the determination unit.

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