JP2023145069A - Exhaust emission control device - Google Patents

Abstract

To provide an exhaust emission control device that enables enhancement of frequency for detecting an abnormality of an exhaust sensor.SOLUTION: An exhaust emission control device 1 includes: a three-way catalyst 31 for purifying exhaust gas to be discharged from an internal combustion engine 10; a particulate filter 32 for collecting particulate matters in exhaust gas; an exhaust sensor 33 for detecting a state value related to an air-fuel ratio of exhaust gas; and a control section that executes filter regeneration control for burning the collected particulate matters by controlling the air-fuel ratio in the exhaust passage and on the upstream side of the three-way catalyst 31 to a value larger than a theoretical air-fuel ratio when the accumulation amount of the particulate matters is specified amount or larger. The control section prohibits the filter regeneration control when an abnormality diagnosis prerequisite of the exhaust sensor 33 is satisfied, and determines an abnormality of the exhaust sensor 33 on the basis of a response time of the exhaust sensor 33 from start of fuel cut control until the state value reaches a specified value on the lean side from a specified air-fuel ratio that is equal to or smaller than the theoretical air-fuel ratio in a period when the filter regeneration control is prohibited.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device that purifies exhaust gas discharged from an internal combustion engine.

In internal combustion engines, feedback control of the air-fuel ratio is performed based on the output of an exhaust sensor that detects the state of exhaust gas discharged from the internal combustion engine. If an abnormality occurs in this exhaust sensor, there is a risk that the accuracy of the air-fuel ratio feedback control will decrease, so it is necessary to diagnose the exhaust sensor for abnormality.

Patent Document 1 includes a reaction delay determination section that determines that an abnormality of reaction delay has occurred in the air-fuel ratio sensor when a reaction delay condition is satisfied a predetermined number of times, and an air-fuel ratio determination section that determines that a reaction delay abnormality has occurred in the air-fuel ratio sensor, and An air-fuel ratio detection sensor abnormality diagnosing device is disclosed that includes a sensor abnormality diagnosing section that diagnoses an abnormality in the sensor. According to the technique described in Patent Document 1, it is described that it is possible to accurately determine that an abnormality has occurred in an air-fuel ratio detection sensor that detects the air-fuel ratio of exhaust gas.

Japanese Patent Application Publication No. 2011-157938

Incidentally, the exhaust passage of an internal combustion engine is sometimes provided with a three-way catalyst that purifies the exhaust gas discharged from the internal combustion engine, and a particulate filter that collects particulate matter in the exhaust gas. As particulate filters are used, particulate matter accumulates inside them and the passage resistance increases, so filter regeneration control is used to remove particulate matter collected by the particulate filter by varying the air-fuel ratio. It will be done.

In such filter regeneration control, by supplying oxygen to the particulate filter, particulate matter collected in the particulate filter can be burned and removed. Therefore, during filter regeneration control, the air-fuel ratio of the exhaust gas flowing into the particulate filter becomes an oxidizing atmosphere (lean).

On the other hand, when the exhaust gas is controlled to the lean side due to filter regeneration control, if an abnormality diagnosis is performed on the exhaust sensor that detects the status value of the exhaust gas flowing into the particulate filter, an abnormality in the exhaust sensor may be incorrectly diagnosed. There is a possibility that In order to prevent such misdiagnosis of exhaust sensor abnormalities, it is possible to disable exhaust sensor abnormality diagnosis during filter regeneration control, but in this case, the frequency of detecting exhaust sensor abnormalities will decrease. There was a problem with putting it away.

The present invention has been made to solve such problems, and an object of the present invention is to provide an exhaust gas purification device that increases the frequency of detecting abnormalities in exhaust sensors.

An exhaust gas purification device according to one embodiment includes a three-way catalyst that is installed in an exhaust passage of an internal combustion engine to purify exhaust gas discharged from the internal combustion engine, and a three-way catalyst that is installed in an exhaust passage downstream of the three-way catalyst to purify exhaust gas discharged from the internal combustion engine. A particulate filter that collects particulate matter, an exhaust sensor that detects a state value related to the air-fuel ratio of exhaust gas that has passed between the three-way catalyst and the particulate filter, and particles that are collected by the particulate filter. If the amount of accumulated particulate matter is more than a predetermined amount, the particulate matter is collected in a particulate filter by controlling the air-fuel ratio in the exhaust passage and upstream of the three-way catalyst to a value larger than the stoichiometric air-fuel ratio. and a control unit that executes filter regeneration control to regenerate the particulate filter by burning the particulate matter, and the control unit executes filter regeneration control when exhaust sensor abnormality diagnosis preconditions are satisfied. and the state value reaches a predetermined value on the lean side from a specified air-fuel ratio that is less than or equal to the stoichiometric air-fuel ratio after starting fuel cut control that stops fuel injection of the internal combustion engine during a period when filter regeneration control is prohibited. The abnormality of the exhaust sensor is determined based on the response time of the exhaust sensor.

According to the present invention, it is possible to provide an exhaust gas purification device that increases the frequency of detecting an abnormality in an exhaust sensor.

1 is a block diagram showing the configuration of an exhaust gas purification device according to a first embodiment; FIG. It is a flowchart which shows the flow of the process of exhaust sensor OBD which an ECU performs.

Embodiment 1
Embodiments of the present invention will be described below with reference to the drawings. Further, in order to clarify the explanation, the following description and drawings are simplified as appropriate. What is shown in the figure is only a part of the whole, and many other components not shown are actually included. Furthermore, in the following description, the same or equivalent elements are given the same reference numerals, and redundant description will be omitted.

First, with reference to FIG. 1, the configuration of an exhaust gas purification device 1 according to this embodiment will be described.
FIG. 1 is a block diagram illustrating the configuration of an exhaust gas purification device according to a first embodiment. FIG. 1 shows the main parts of a vehicle 100 related to the exhaust gas purification device 1. As shown in FIG. In the present embodiment, an example will be described in which the exhaust purification device 1 is applied to a vehicle 100 equipped with a gasoline engine.

An internal combustion engine 10 mounted on a vehicle 100 has a cylinder 11, a piston 12, an intake valve 13, an exhaust valve 14, a fuel injection valve 15, and a spark plug 16. Furthermore, an intake passage 20 and an exhaust passage 30 communicate with the internal combustion engine 10.

The piston 12 moves up and down within the cylinder 11. The intake valve 13 is provided at an intake port of an intake passage 20 facing the cylinder 11. The exhaust valve 14 is provided at an exhaust port of the exhaust passage 30 facing the cylinder 11. The fuel injection valve 15 and the spark plug 16 are provided so that their tips face into the cylinder 11. The fuel injection valve 15 and the spark plug 16 are driven and controlled by a control unit (ECU 50). Further, the internal combustion engine 10 is provided with a water temperature sensor 17 that detects the temperature of cooling water passing through a cooling water passage formed in the housing of the internal combustion engine 10. Water temperature sensor 17 outputs the detected coolant temperature to ECU 50 as engine coolant temperature.

The intake passage 20 is provided with an air filter 21, an air flow meter 22, and a throttle valve 23. Air filter 21 is arranged at the upstream end of intake passage 20 . An intake air temperature sensor (not shown) is attached to the air filter 21 to detect the air intake air temperature (ie, outside air temperature). An air flow meter 22 is arranged downstream of the air filter 21. The air flow meter 22 is a sensor that detects the amount of intake air flowing through the intake passage 20. The air flow meter 22 outputs the detected intake air amount to the ECU 50. A slot valve is arranged downstream of the air flow meter 22. A throttle sensor 24 is arranged near the throttle valve 23 to detect the throttle opening. The throttle valve 23 is driven by the ECU 50 and adjusts the amount of intake air supplied to the cylinder 11.

In the internal combustion engine 10, when the piston 12 descends, the intake valve 13 is opened and air is taken into the cylinder 11 from the intake passage 20, and fuel is injected from the fuel injection valve 15 to form an air-fuel mixture in the cylinder 11. (Intake stroke). The next time the piston 12 moves up, the intake valve 13 is closed and the formed air-fuel mixture is compressed (compression stroke). The compressed air-fuel mixture is ignited by the spark plug 16 and expands, pushing down the piston 12 (expansion stroke). The next time the piston 12 moves up, the exhaust valve 14 is opened and combustion gas (exhaust gas) is discharged into the exhaust passage 30 (exhaust stroke).

The exhaust passage 30 is provided with a three-way catalyst 31 and a particulate filter (GPF) 32. The three-way catalyst 31 is a catalyst that has oxygen storage and release performance, and oxidizes or reduces hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides ( _NOx ) in the exhaust gas discharged from the internal combustion engine 10. This purifies the exhaust gas. For example, the three-way catalyst 31 adsorbs oxygen in the exhaust when the exhaust is in a rich state, and releases the adsorbed oxygen when the exhaust is in a lean state to eliminate HC, CO, _NOx , etc. in the exhaust. Purify.

A particulate filter 32 is arranged downstream of the three-way catalyst 31. The particulate filter 32 collects particulate matter (PM) contained in exhaust gas. PM captured by the particulate filter 32 is combusted (oxidized) by oxygen being supplied to the particulate filter 32 when the particulate filter 32 is in a high temperature state.

Further, the particulate filter 32 may be, for example, a filter having an oxygen storage and release function and configured by supporting a catalyst component on the surface of a filter carrier. The particulate filter 32 carrying catalyst components also functions as a three-way catalyst 31, and purifies the exhaust gas by oxidizing or reducing HC, CO, and _NOx in the exhaust gas. By providing not only the three-way catalyst 31 but also the particulate filter 32 with the function of a three-way catalyst, the purification efficiency of exhaust gas can be increased.

Furthermore, an exhaust sensor 33 is provided in the exhaust passage 30. The exhaust sensor 33 is disposed between the three-way catalyst 31 and the particulate filter 32, downstream of the three-way catalyst 31 and upstream of the particulate filter 32.

The exhaust sensor 33 is a sensor that detects a state value related to the air-fuel ratio of the exhaust gas that has passed between the three-way catalyst 31 and the particulate filter 32. The exhaust sensor 33 outputs the detected state value to the ECU 50. As the exhaust sensor 33, an air-fuel ratio sensor or an oxygen concentration sensor can be used. The air-fuel ratio sensor is a sensor that outputs a linear signal according to the air-fuel ratio of exhaust gas, and detects the air-fuel ratio (A/F) as a state value. The oxygen concentration sensor is a sensor that outputs a signal according to the oxygen concentration in gas, and detects the oxygen concentration as a state value.

An exhaust gas temperature sensor that measures the temperature of exhaust gas may be provided in the exhaust passage 30 downstream of the three-way catalyst 31 and upstream of the particulate filter 32. Based on the output of the exhaust gas temperature sensor, the temperature of the three-way catalyst 31 or the particulate filter 32 can be estimated. Note that even if an exhaust temperature sensor is not provided, the temperatures of the three-way catalyst 31 and the particulate filter 32 can be estimated based on the operating state of the internal combustion engine 10.

The exhaust gas purification device 1 includes an ECU (Electronic Control Unit) 50 as a control section. The ECU 50 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a storage device, and the like. The CPU expands various control programs stored in the ROM and data referred to when executing the various control programs into the RAM and executes arithmetic processing.

In addition to the above-described sensors, the ECU 50 is connected to various sensors that detect the operating state of the internal combustion engine 10, including an accelerator opening sensor and a crank position sensor. The ECU 50 receives a signal corresponding to the accelerator opening from the accelerator opening sensor, and calculates the accelerator operation amount, the engine load required of the internal combustion engine 10, etc. in accordance with this signal. Further, the ECU 50 receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 10 from the crank position sensor, and calculates the engine speed of the internal combustion engine 10. Further, various actuators such as a throttle valve 23, a fuel injection valve 15, a spark plug 16, etc. are connected to the ECU 50.

The ECU 50 controls internal combustion, including fuel injection amount control of the fuel injection valve 15, ignition timing control of the spark plug 16, and throttle opening (intake air amount) control of the throttle valve 23, based on signals input from various sensors. Various controls of the engine 10 are executed.

During normal operation of the vehicle 100, the ECU 50 adjusts the air-fuel ratio of the exhaust gas to the stoichiometric air-fuel ratio, which is the target air-fuel ratio, based on the state value of the exhaust sensor 33 when a predetermined air-fuel ratio feedback control execution condition is satisfied. Air-fuel ratio feedback control is performed to feedback-control the air-fuel ratio (fuel injection amount and intake air amount) of the air-fuel mixture so that they match.

Furthermore, in the fuel injection amount control, the ECU 50 executes fuel cut control to stop fuel injection of the internal combustion engine 10 when the vehicle 100 is decelerating or coasting. During the fuel cut control, the ECU 50 supplies air into the cylinder 11 while stopping fuel injection by the fuel injection valve 15. For example, while the vehicle 100 is running and the engine rotation speed is equal to or higher than a predetermined rotation speed, when the accelerator operation amount becomes zero, fuel cut control is started. The fuel cut control reduces fuel consumption, increases the oxygen concentration in the exhaust gas, and makes it possible to burn PM collected in the particulate filter 32.

Further, the ECU 50 estimates the amount of accumulated PM captured by the particulate filter 32 (hereinafter referred to as the amount of accumulated PM). When the ECU 50 estimates the PM accumulation amount, it may be estimated based on the past engine speed and engine load, or it may be estimated based on the exhaust pressure upstream of the particulate filter 32 and downstream of the three-way catalyst 31. It may be estimated based on the difference between the pressure of the exhaust gas downstream of the particulate filter 32 (hereinafter referred to as filter differential pressure) and the flow rate of the exhaust gas.

Here, since the engine speed and engine load are related to the amount of PM emitted from the internal combustion engine 10, the amount of PM emitted from the internal combustion engine 10 is calculated based on the engine speed and engine load. You can ask for it. By integrating the amount of PM discharged from the internal combustion engine 10, the amount of PM accumulation can be determined. On the other hand, as the PM deposition amount increases, the filter differential pressure increases. This filter differential pressure also changes depending on the flow rate of exhaust gas. Therefore, if the relationship between the PM deposition amount, the filter differential pressure, and the exhaust flow rate is determined in advance through experiments or simulations, the PM deposition amount can be determined from the filter differential pressure and the exhaust flow rate. Furthermore, since the PM accumulation amount increases depending on the operating time of the internal combustion engine 10 or the travel distance of the vehicle 100, the PM accumulation amount can be easily estimated based on these values.

Then, when the amount of accumulated PM is equal to or greater than a predetermined amount, the ECU 50 executes filter regeneration control to burn PM in order to regenerate the particulate filter 32. Specifically, the ECU 50 appropriately adjusts the fuel injection amount, injection timing, or number of injections by the fuel injection valve 15, the ignition timing or number of ignitions of the spark plug 16, etc. The air-fuel ratio on the upstream side is controlled to a value larger than the stoichiometric air-fuel ratio (lean control). By controlling in this way, it is possible to supply oxygen to the particulate filter 32 and burn the PM captured by the particulate filter 32, thereby regenerating the particulate filter 32. Note that the predetermined amount is the amount of PM accumulated in which it is desirable to perform regeneration of the particulate filter 32. If the predetermined amount is too small, the particulate filter 32 will be regenerated frequently, leading to concerns about deterioration of fuel efficiency and the like. On the other hand, if the predetermined amount is too large, there is a concern that the output of the internal combustion engine 10 may decrease due to an increase in exhaust pressure. Taking these into consideration, the predetermined amount is determined in advance through experiments, simulations, etc.

Further, the ECU 50 prohibits filter regeneration control when a precondition for abnormality diagnosis of the exhaust sensor 33 (exhaust sensor OBD precondition), which will be described later, is satisfied, and performs fuel cut control during the period in which filter regeneration control is prohibited. An abnormality (responsiveness deterioration) of the exhaust sensor 33 is determined based on the response time of the exhaust sensor 33 from the time when the state value reaches a predetermined value on the lean side from the specified air-fuel ratio that is less than the stoichiometric air-fuel ratio (stoichiometric). do.

Therefore, with reference to FIG. 2, a processing flow of abnormality diagnosis of the exhaust sensor 33 (exhaust sensor OBD) executed by the ECU 50 will be described. FIG. 2 is a flowchart showing the process flow of the exhaust sensor OBD executed by the ECU. Hereinafter, a case where the exhaust sensor 33 is an air-fuel ratio sensor will be described as an example. Further, in this embodiment, a case will be described in which the above-mentioned specified air-fuel ratio is stoichiometric, but the specified air-fuel ratio is not limited to stoichiometric and may be a rich side air-fuel ratio.

The processing flow shown in FIG. 2 is realized by repeatedly executing a program stored in the ECU 50 in advance at predetermined intervals while the ECU 50 is powered on (during the ignition switch is turned on). Alternatively, it is also possible to implement the processing by constructing part or all of the steps of the program using dedicated hardware.

When the process shown in FIG. 2 is started while filter regeneration control is being executed, the ECU 50 determines whether exhaust sensor OBD preconditions for executing exhaust sensor OBD are satisfied (step S1). Specifically, when all of the following conditions (1) to (3) are satisfied, the ECU 50 determines that the exhaust sensor OBD preconditions are satisfied (step S1: YES), and advances the process to step S2.

Condition (1): The engine cooling water temperature detected by the water temperature sensor 17 is equal to or higher than a predetermined value (for example, 75° C.).
Condition (2): The state value detected by the exhaust sensor 33 is stoichiometric (for example, 16).
Condition (3): The three-way catalyst 31 is in an active state.

Note that whether or not the three-way catalyst 31 is in an active state can be determined based on the temperature of the three-way catalyst 31.

On the other hand, if at least one of the exhaust sensor OBD preconditions is not satisfied, the ECU 50 determines that the exhaust sensor OBD preconditions are not satisfied (step S1: NO), and returns the process to step S1 (return). .

If the exhaust sensor OBD preconditions are satisfied in step S1, the ECU 50 prohibits filter regeneration control (step S2). The ECU 50 sets the regeneration control prohibition request flag to ON. The regeneration control prohibition request flag is a flag that is set to ON when filter regeneration control is prohibited, and is set to OFF when it is not prohibited. When the regeneration control prohibition request flag is set to ON, air-fuel ratio control associated with filter regeneration control is stopped.

Next, the ECU 50 determines whether fuel cut control is being executed (step S3). This determination is made based on the state of the fuel cut flag. The fuel cut flag is a flag that is set to ON when fuel cut control is being executed, and is set to OFF when fuel cut control is not executed. Here, while the vehicle 100 is running, the EUC 50 executes fuel cut control when the accelerator operation amount becomes zero while the engine speed is equal to or higher than a predetermined speed. On the other hand, when the accelerator operation amount increases while the fuel cut control is being executed, the EUC 50 stops the fuel cut control and restarts fuel injection.

If fuel cut control is being executed (step S3: YES), the process advances to step S4. If fuel cut control is not being executed (step S3: NO), the process returns to step S1 (return).

If the fuel cut control is being executed, the ECU 50 determines whether the state value of the exhaust sensor 33 before the start of the fuel cut control is stoichiometric (specified air-fuel ratio) (step S4). If the state value of the exhaust sensor 33 before the start of the fuel cut control is stoichiometric (step S4: YES), the process advances to step S5. If the state value of the exhaust sensor 33 before the start of the fuel cut control is not stoichiometric (step S4: NO), steps S5 and S6 are skipped and the process flow shown in FIG. 2 is ended.

If the state value of the exhaust sensor 33 before the start of the fuel cut control is stoichiometric, the ECU 50 measures the response time of the exhaust sensor 33 (step S5). Specifically, when the fuel cut control is started, the state value of the exhaust sensor 33 changes toward the lean side due to the stop of fuel injection. Therefore, the ECU 50 measures the time required for the state value of the exhaust sensor 33 to change from stoichiometric to a lean state value (for example, 18), which is a predetermined value on the leaner side than stoichiometric, as the response time of the exhaust sensor 33. Note that the stoichiometric and lean state values are set as appropriate depending on the properties of the internal combustion engine 10 and the fuel.

Then, the ECU 50 performs processing to determine whether the exhaust sensor 33 is normal or abnormal (step S6). Specifically, when the response time measured in step S5 is less than or equal to a preset reference response time, it is determined that the exhaust sensor 33 is normal (normality determination), and the abnormality flag is maintained OFF. On the other hand, if the measured response time exceeds a preset reference response time, it is determined that an abnormality has occurred in the exhaust sensor 33 (abnormality determination), and the abnormality flag is set to ON.

Note that the reference response time is appropriately set depending on the exhaust sensor 33 that is the target of abnormality diagnosis. Furthermore, when an abnormality occurs in the exhaust sensor 33, a failure flag may be held internally or an abnormality lamp may be turned on to notify the driver, as necessary.

The ECU 50 stores the results of the abnormality diagnosis in the memory of the ECU 50 as necessary. In this way, a series of processing flows for the exhaust sensor OBD are performed. If there is a history of normality/abnormality determination, the next processing cycle is not executed.

In this way, in the configuration in which the three-way catalyst 31 and the particulate filter 32 are provided in the exhaust passage 30, and the exhaust sensor 33 is provided between the three-way catalyst 31 and the particulate filter 32, the amount of PM accumulated can be reduced. When the number increases, filter regeneration control is performed.

During filter regeneration control, the temperature of the particulate filter 32 is higher than the temperature at which particulate matter collected by the particulate filter 32 can be combusted, and the air-fuel ratio of the exhaust gas flowing into the particulate filter 32 is on the lean side. controlled. Therefore, if filter regeneration control and exhaust sensor 33 abnormality diagnosis are executed simultaneously, even if the exhaust sensor 33 is operating normally, if the status value indicates a lean state due to filter regeneration control, the exhaust sensor 33 There is a risk of misdiagnosing an abnormality. In order to prevent such a misdiagnosis of an abnormality in the exhaust sensor 33, it is possible to disable abnormality diagnosis of the exhaust sensor 33 during filter regeneration control, but in this case, the frequency of detecting an abnormality in the exhaust sensor 33 may be reduced. It will drop.

In contrast, the exhaust gas purification device 1 according to the present embodiment includes a three-way catalyst 31 that is provided in the exhaust passage 30 of the internal combustion engine 10 and purifies the exhaust gas discharged from the internal combustion engine 10, and a three-way catalyst 31 that is provided downstream of the three-way catalyst 31. A particulate filter 32 that is provided in the exhaust passage 30 and collects particulate matter in the exhaust gas, and a state value related to the air-fuel ratio of the exhaust gas that has passed between the three-way catalyst 31 and the particulate filter 32 is detected. When the amount of accumulated particulate matter collected by the exhaust sensor 33 and the particulate filter 32 is a predetermined amount or more, the air-fuel ratio in the exhaust passage 30 and upstream of the three-way catalyst 31 is set to be higher than the stoichiometric air-fuel ratio. and a control unit that executes filter regeneration control that regenerates the particulate filter 32 by burning the particulate matter collected in the particulate filter 32 by controlling the particulate filter 32 so that the particulate filter 32 has a certain value. Then, the control unit prohibits filter regeneration control when the abnormality diagnosis preconditions for the exhaust sensor 33 are satisfied, and performs fuel cut control to stop fuel injection of the internal combustion engine 10 during a period in which the filter regeneration control is prohibited. An abnormality in the exhaust sensor 33 is determined based on the response time of the exhaust sensor 33 from the start of the process until the state value reaches a predetermined value on the lean side from a specified air-fuel ratio that is less than or equal to the stoichiometric air-fuel ratio.

In the exhaust gas purification device 1 configured as described above, filter regeneration control is stopped when the preconditions for executing the abnormality diagnosis of the exhaust sensor 33 are satisfied. As a result, since the abnormality diagnosis of the exhaust sensor 33 is performed from the state where the filter regeneration control is stopped, it is possible to increase the frequency of detecting abnormalities of the exhaust sensor 33 while suppressing erroneous diagnosis of abnormalities of the exhaust sensor 33. .

As explained above, according to the exhaust gas purification device 1 according to the present embodiment, it is possible to increase the frequency of detecting abnormalities in the exhaust sensor 33. As a result, the accuracy of abnormality diagnosis of the exhaust sensor 33 is improved.

1 Exhaust purification device 10 Internal combustion engine 11 Cylinder 12 Piston 13 Intake valve 14 Exhaust valve 15 Fuel injection valve 16 Spark plug 17 Water temperature sensor 20 Intake passage 21 Air filter 22 Air flow meter 23 Throttle valve 24 Throttle sensor 30 Exhaust passage 31 Three-way catalyst 32 Particulate filter 33 Exhaust sensor 50 ECU
100 vehicles

Claims (1)

a three-way catalyst provided in an exhaust passage of an internal combustion engine to purify exhaust gas discharged from the internal combustion engine;
a particulate filter that is provided in the exhaust passage downstream of the three-way catalyst and that collects particulate matter in the exhaust gas;
an exhaust sensor that detects a state value related to an air-fuel ratio of the exhaust gas that has passed between the three-way catalyst and the particulate filter;
The air-fuel ratio in the exhaust passage and upstream of the three-way catalyst is set to a value greater than the stoichiometric air-fuel ratio when the amount of particulate matter collected on the particulate filter is equal to or greater than a predetermined amount. a control unit that executes filter regeneration control for regenerating the particulate filter by burning the particulate matter collected in the particulate filter;
has
The control unit includes:
Prohibiting the filter regeneration control when a precondition for abnormality diagnosis of the exhaust sensor is satisfied;
During the period in which the filter regeneration control is prohibited, the state value reaches a predetermined value on the lean side from a specified air-fuel ratio that is less than or equal to the stoichiometric air-fuel ratio after starting fuel cut control that stops fuel injection of the internal combustion engine. determining whether the exhaust sensor is abnormal based on the response time of the exhaust sensor up to
Exhaust purification device.

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