JP2021014827A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

To improve diagnostic accuracy of an oxidation catalyst.SOLUTION: An exhaust emission control device for an internal combustion engine 1 includes a first oxidation catalyst 22 and a second oxidation catalyst 23 provided in order from an upstream side in an exhaust passage 4, and a control unit 100 constituted to execute temperature rise control for raising an outlet exhaust gas temperature of the first oxidation catalyst and to diagnose the first oxidation catalyst on the basis of an outlet exhaust gas temperature of the second oxidation catalyst during execution of the temperature rise control.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an exhaust gas purification device for an internal combustion engine.

In an exhaust gas purification device for an internal combustion engine, particularly a diesel engine, one in which an oxidation catalyst and a filter are provided in the exhaust passage in order from the upstream side is known. The filter collects particulate matter contained in the exhaust. An oxidation catalyst is supported on the filter to burn the collected particulate matter. Therefore, the filter can be regarded as a kind of oxidation catalyst.

When the amount collected by the filter reaches near full capacity, regeneration is performed to burn and remove particulate matter and restore the performance of the filter. At this time, a temperature rise control for raising the outlet exhaust temperature of the oxidation catalyst is executed.

JP-A-2018-96313

In such an exhaust gas purification device, it may be diagnosed whether or not the oxidation catalyst is normal. Generally, this diagnosis is performed based on the outlet exhaust temperature of the oxidation catalyst at one timing when the outlet exhaust temperature of the oxidation catalyst rises after the start of temperature rise control.

However, with the method of diagnosing at such timing, accurate diagnosis results cannot always be obtained because there is a relatively large variation in the way the outlet exhaust temperature rises due to changes in the operating state of the internal combustion engine and the external environment. There is a drawback.

Therefore, the present disclosure was devised in view of such circumstances, and an object thereof is to provide an exhaust gas purification device for an internal combustion engine capable of improving the diagnostic accuracy of an oxidation catalyst.

According to one aspect of the present disclosure
The first oxidation catalyst and the second oxidation catalyst provided in order from the upstream side in the exhaust passage of the internal combustion engine,
The temperature rise control for raising the outlet exhaust temperature of the first oxidation catalyst is executed, and the first oxidation catalyst is diagnosed based on the outlet exhaust temperature of the second oxidation catalyst during the execution of the temperature rise control. With the configured control unit
An exhaust gas purification device for an internal combustion engine is provided.

Preferably, the control unit diagnoses the first oxidation catalyst as abnormal when the outlet exhaust temperature of the second oxidation catalyst is equal to or higher than a predetermined threshold value.

Preferably, the control unit diagnoses the first oxidation catalyst as abnormal when the temperature difference between the outlet exhaust temperature and the inlet exhaust temperature of the second oxidation catalyst is equal to or greater than a predetermined threshold value.

Preferably, the control unit has a cumulative time in which the outlet exhaust temperature of the second oxidation catalyst is equal to or higher than a predetermined threshold value or more than a predetermined time threshold, or is equal to or higher than the outlet exhaust temperature of the second oxidation catalyst. When the cumulative time in a state where the temperature difference between the inlet and exhaust temperatures is equal to or greater than a predetermined threshold exceeds a predetermined time threshold, the first oxidation catalyst is diagnosed as abnormal.

Preferably, the control unit sets the threshold value based on the integrated value of the heating fuel supplied during the execution of the temperature rising control.

Preferably, the control unit executes the diagnosis of the first oxidation catalyst after the outlet exhaust temperature of the first oxidation catalyst reaches a predetermined target temperature during the execution of the temperature rise control.

Preferably, the control unit executes a preliminary diagnosis of the first oxidation catalyst at a timing before the outlet exhaust temperature of the first oxidation catalyst reaches the target temperature, and based on the result of the preliminary diagnosis, the first 1 Perform oxidation catalyst diagnosis.

Preferably, the second oxidation catalyst is a filter for collecting particulate matter on which an oxidation catalyst is supported, or an oxidation catalyst for oxidizing a soluble organic component of the particulate matter.

According to the present disclosure, the diagnostic accuracy of the oxidation catalyst can be improved.

It is a schematic diagram which shows the structure of the Embodiment of this disclosure. It is a time chart which shows the transition of each value at the time of temperature rise control. It is a flowchart of the diagnostic process based on the 1st diagnostic method. It is a flowchart of the diagnostic process based on the 2nd diagnostic method. It is a flowchart of the diagnostic process based on the 3rd diagnostic method. It is a flowchart of the diagnostic process based on the 4th diagnostic method. It is a flowchart of the diagnosis process of the preliminary diagnosis which concerns on the 5th diagnosis method. It is a flowchart of the diagnosis process of the comprehensive diagnosis which concerns on the 5th diagnosis method.

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the following embodiments.

FIG. 1 is a schematic view showing the configuration of the present embodiment. The internal combustion engine (also referred to as an engine) 1 is a multi-cylinder engine mounted on a vehicle (not shown). In the present embodiment, the vehicle is a large vehicle such as a truck, and the engine 1 as a vehicle power source mounted on the large vehicle is an in-line 4-cylinder diesel engine. However, the type, type, use, and the like of the vehicle and the internal combustion engine are not particularly limited. For example, the vehicle may be a small vehicle such as a passenger car, and the engine 1 may be a gasoline engine.

The engine may be mounted on a moving body other than a vehicle, for example, a ship, a construction machine, or an industrial machine. Further, the engine does not have to be mounted on a moving body, and may be a stationary engine.

The engine 1 includes an engine main body 2, an intake passage 3 and an exhaust passage 4 connected to the engine main body 2, a turbocharger 14, and a fuel injection device 5. The engine body 2 includes structural parts such as a cylinder head, a cylinder block, and a crankcase, and movable parts such as a piston, a crankshaft, and a valve housed therein.

The fuel injection device 5 includes a common rail type fuel injection device, and includes a fuel injection injector 7 provided in each cylinder and a common rail 8 connected to the injector 7. The injector 7 is an in-cylinder injector for supplying fuel into the cylinder of the corresponding cylinder, and in the case of the present embodiment, the fuel is directly injected into the cylinder. The common rail 8 stores the fuel injected from the injector 7 in a high pressure state.

The intake passage 3 is mainly defined by an intake manifold 10 connected to the engine body 2 (particularly a cylinder head) and an intake pipe 11 connected to the upstream end of the intake manifold 10. The intake manifold 10 distributes and supplies the intake air sent from the intake pipe 11 to the intake ports of each cylinder. The intake pipe 11 is provided with an air cleaner 12, an air flow meter 13, a turbocharger 14 compressor 14C, an intercooler 15, and an electronically controlled intake throttle valve 16 in this order from the upstream side. The air flow meter 13 is a sensor for detecting the intake air amount per unit time of the engine 1, that is, the intake flow rate, and is also called a mass air flow (MAF) sensor or the like.

The exhaust passage 4 is mainly defined by an exhaust manifold 20 connected to the engine body 2 (particularly a cylinder head) and an exhaust pipe 21 connected to the downstream side of the exhaust manifold 20. The exhaust manifold 20 collects the exhaust gas sent from the exhaust port of each cylinder. A turbine 14T of a turbocharger 14 is provided between the exhaust pipe 21 or the exhaust manifold 20 and the exhaust pipe 21.

An oxidation catalyst 22 and a filter 23 are provided in the exhaust passage 4 on the downstream side of the turbine 14T in this order from the upstream side. Further, in the exhaust passage 4 on the downstream side of the filter 23, the selective reduction NOx catalyst 24 and the ammonia oxidation catalyst 26 are provided in this order from the upstream side. An addition valve 25 for adding urea water as a reducing agent is provided in the exhaust passage 4 between the filter 23 and the NOx catalyst 24.

The oxidation catalyst 22 oxidizes and purifies the unburned components (hydrocarbon HC and carbon monoxide CO) in the exhaust gas, heats and raises the exhaust gas with the heat of reaction at this time, and NO ₂ in the exhaust gas. Oxidizes to.

The filter 23 is composed of a so-called continuously regenerating type filter with a catalyst, and collects particulate matter (PM (Particulate Matter)) contained in the exhaust gas and burns the collected PM by catalytic action. An oxidation catalyst is supported on the carrier of the filter 23 in order to burn the collected PM. Therefore, the filter can be regarded as a kind of oxidation catalyst. As the filter 23, a so-called wall flow type filter in which the openings at both ends of the ceramic honeycomb carrier are alternately sealed is used.

The oxidation catalyst 22 and the filter 23 form the first oxidation catalyst and the second oxidation catalyst, respectively, as defined in the claims.

The NOx catalyst 24 reacts ammonia derived from urea water added from the addition valve 25 with NOx to reduce and purify NOx in the exhaust gas. The ammonia oxidation catalyst 26 oxidizes and purifies the excess ammonia discharged from the NOx catalyst 24.

An exhaust pipe injector 38 is provided in the exhaust passage 4 on the upstream side of the oxidation catalyst 22. The exhaust pipe injector 38 can inject fuel into the exhaust passage 4 or the exhaust pipe 21 at the time of temperature rise control described later. Hereinafter, such fuel injection into the exhaust passage 4 will be referred to as exhaust pipe injection. In the present embodiment, the exhaust pipe injector 38 is provided on the downstream side of the turbine 14T, but the installation position thereof can be changed.

The engine 1 also includes an exhaust gas recirculation (EGR) device 30. The EGR device 30 includes an EGR passage 31 for recirculating a part (referred to as EGR gas) of exhaust gas in the exhaust passage 4 (particularly in the exhaust manifold 20) into the intake passage 3 (particularly in the intake manifold 10), and an EGR. An EGR cooler 32 for cooling the EGR gas flowing through the passage 31 and an EGR valve 33 for adjusting the flow rate of the EGR gas are provided.

The vehicle is equipped with a control device for controlling the engine 1. The control device includes a control unit, a circuit element (circuitry), or an electronic control unit (referred to as an ECU (Electronic Control Unit)) 100 that forms a controller. The ECU 100 includes a CPU (Central Processing Unit) having a calculation function, ROM (Read Only Memory) and RAM (Random Access Memory) as storage media, an input / output port, and a storage device other than ROM and RAM. The ECU 100 is configured and programmed to control an in-cylinder injector 7, an intake throttle valve 16, an addition valve 25, an EGR valve 33, and an exhaust pipe injector 38.

The control device includes the following sensors in addition to the above-mentioned air flow meter 13. That is, a rotation speed sensor 40 for detecting the rotation speed of the engine, specifically, the rotation speed (rpm) per minute, and an accelerator opening degree sensor 41 for detecting the accelerator opening degree are provided. Further, an exhaust temperature sensor 42 for detecting the inlet exhaust temperature of the oxidation catalyst 22, an exhaust temperature sensor 43 for detecting the outlet exhaust temperature of the oxidation catalyst 22, and an exhaust for detecting the outlet exhaust temperature of the filter 23. A temperature sensor 44 is provided. Further, a differential pressure sensor 45 for detecting the differential pressure between the inlet exhaust pressure and the outlet exhaust pressure of the filter 23 is provided. The output signals of these sensors are sent to the ECU 100.

The outlet exhaust temperature of the oxidation catalyst 22 is synonymous with the inlet exhaust temperature of the filter 23, and the outlet exhaust temperature of the oxidation catalyst 22 is synonymous with the inlet exhaust temperature of the NOx catalyst 24.

The ECU 100 also has a function as a diagnostic unit for diagnosing the oxidation catalyst 22. Hereinafter, the diagnostic method of this embodiment will be described.

Generally, the ECU 100 is configured to execute a temperature rise control for raising the outlet exhaust temperature of the oxidation catalyst 22, and to diagnose the oxidation catalyst 22 based on the outlet exhaust temperature of the filter 23 during the execution of the temperature rise control. There is.

First, the temperature rise control will be described. When the differential pressure detected by the differential pressure sensor 45 reaches a predetermined upper limit threshold value or more, the ECU 100 considers that the PM collection amount of the filter 23 has reached the vicinity of fullness, and burns and removes the collected PM. Control the temperature rise. At this time, the ECU 100 causes the in-cylinder injector 7 to execute a well-known post injection, and injects the post-injection fuel as the heating fuel from the in-cylinder injector 7. Then, the post-injection fuel is burned by the oxidation catalyst 22, and the outlet exhaust temperature of the oxidation catalyst 22 rises. By supplying the heated exhaust gas to the filter 23, PM is burned and removed in the filter 23. Then, the PM collecting ability of the filter 23 is restored, and the filter 23 is regenerated.

During the temperature rise control, the ECU 100 feedback-controls the post injection amount so that the outlet exhaust temperature of the oxidation catalyst 22 detected by the exhaust temperature sensor 43 approaches a predetermined target temperature.

In addition, instead of the post injection, the exhaust pipe injection by the exhaust pipe injector 38 may be performed.

Next, the principle of diagnosis of this embodiment will be described. In FIG. 2, the horizontal axis is time t, and on the vertical axis, (A) is the integrated value (referred to as fuel integrated value) Q of the post injection amount, and (B) is the inlet exhaust temperature T1 and (C) of the oxidation catalyst 22. Is the outlet exhaust temperature T2 of the oxidation catalyst 22, and (D) is the outlet exhaust temperature T3 of the filter 23.

After the temperature rise control is started at time t0, the fuel integrated value Q gradually increases. Then, the inlet exhaust temperature T1 rises slightly and then stabilizes at a constant value.

The outlet exhaust temperature T2 starts to rise at the same time as the temperature rise control is started, eventually reaches the target temperature T2t (for example, 600 ° C.), and is maintained near the target temperature T2t. The solid line a in the figure is the case of the normal oxidation catalyst 22, and the broken line b is the case of the abnormal oxidation catalyst 22. The temperature rise rate is higher in the normal state than in the abnormal state, and the target temperature T2t is reached at an earlier timing. This is because the oxidation catalyst 22 can burn the post-injection fuel with higher efficiency. In other words, the amount of heat possessed by the post-injection fuel can be converted into exhaust temperature energy with higher efficiency.

By the way, in the comparative example before the idea of the present disclosure, the diagnosis of the oxidation catalyst 22 is executed at the timing t1 during the rise of the outlet exhaust temperature T2. That is, the ECU 100 compares the detected value of the outlet exhaust temperature T2 with the predetermined threshold T2s when the fuel integrated value Q reaches the predetermined threshold Qsp (t1), and when the outlet exhaust temperature T2 is equal to or higher than the threshold T2s, the oxidation catalyst 22 is determined to be normal, and when the outlet exhaust temperature T2 is less than the threshold value T2s, the oxidation catalyst 22 is determined to be abnormal. The threshold value T2s is a value set in advance through a test or the like. For example, a test is performed using an oxidation catalyst at the boundary between normal and abnormal conditions (reference state, criteria state), and the outlet exhaust temperature T2 when the fuel integrated value Q reaches the threshold value Qsp is set as the threshold value T2s. There is. As described above, in the comparative example, the diagnosis is executed at the timing t1 such that the outlet exhaust temperature T2 is rising.

However, this method has a drawback that accurate diagnostic results cannot always be obtained because there is a relatively large variation in how the outlet exhaust temperature T2 rises due to changes in the operating state of the engine and the external environment.

That is, for example, when a driver performs an operation method with many deceleration fuel cuts such as frequently releasing the accelerator pedal, the oxidation catalyst 22 is cooled by the outside air as compared with the time when the oxidation catalyst 22 is heated by the post-injection fuel. Since the time required for the fuel is long, it becomes difficult for the outlet exhaust temperature T2 to rise, and there is a possibility that the temperature falls below the threshold value T2s even though it is normal. Further, when the outside air temperature is low in a cold region or the like, or when rain and snow adhere to the oxidation catalyst 22 in a rainy and snowy environment, the oxidation catalyst 22 is remarkably cooled by them, so that the outlet exhaust temperature T2 also rises. It becomes difficult to do so, and there is a risk that the threshold value T2s will be exceeded even though it is normal.

Dealing with these problems is difficult in comparative examples. This is because the diagnosis is performed at the only timing within a short period of time when the outlet exhaust temperature T2 is rising. If the outlet exhaust temperature T2 shifts to the low temperature side at such a timing due to the above-mentioned reason, there is a risk of erroneous diagnosis as an abnormality, and improvement measures are desired.

Therefore, in the present embodiment, the diagnosis is executed based on the outlet exhaust temperature T3 of the filter 23 instead of the outlet exhaust temperature T2 of the oxidation catalyst 22. The ECU 100 executes the diagnosis of the oxidation catalyst 22 at the timing after the outlet exhaust temperature T2 of the oxidation catalyst 22 reaches the target temperature T2t during the execution of the temperature rise control. The timing at which the outlet exhaust temperature T2 reaches the target temperature T2t can be defined as the timing at which the outlet exhaust temperature T2 of the oxidation catalyst 22 in the criterion state reaches the target temperature T2t. In the illustrated example, such a diagnosis timing corresponds to the timing t2 at which the fuel integrated value Q reaches a predetermined threshold value Qs. That is, the threshold value Qs is predetermined so that the above diagnosis timing is obtained when the fuel integrated value Q reaches the threshold value Qs.

It is preferable that the diagnostic timing is later than the timing at which the outlet exhaust temperature T3 of the filter 23 changes from rising to stable when the oxidation catalyst 22 in the criterion state is used.

Also in FIG. 2D, the solid line c shows the case of the normal oxidation catalyst 22, and the broken line d shows the case of the abnormal oxidation catalyst 22. First, in the case of the normal oxidation catalyst 22, the outlet exhaust temperature T3 of the filter 23 starts to rise later than the outlet exhaust temperature T2 of the oxidation catalyst 22. Then, when the outlet exhaust temperature T2 of the oxidation catalyst 22 becomes stable near the target temperature T2t, the outlet exhaust temperature T3 of the filter 23 also becomes stable correspondingly. However, since the amount of heat supplied increases as the integrated fuel value Q increases, the outlet exhaust temperature T3 of the filter 23 rises slowly and then becomes constant.

The heat of the exhaust gas flowing into the filter 23 is taken away by the filter 23 having a relatively large heat capacity, while the PM burns in the filter 23 to generate heat. Generally, the heat dissipation amount of the former is larger than the heat generation amount of the latter. Therefore, as a result of summarizing the transfer of heat, when the oxidation catalyst 22 is normal, the outlet exhaust temperature T3 of the filter 23 tends to be equal to or less than or slightly higher than the outlet exhaust temperature T2 of the oxidation catalyst 22. As shown in the figure, when the outlet exhaust temperature T2 of the oxidation catalyst 22 is constant near the target temperature T2t, the outlet exhaust temperature T3 (solid line c) of the filter 23 tends to be higher than or slightly higher than the target temperature T2t. is there.

However, when the oxidation catalyst 22 is abnormal, it becomes difficult for the oxidation catalyst 22 to burn out the post-injection fuel. Therefore, the post-injection fuel that could not be completely burned by the oxidation catalyst 22, that is, HC, flows into the filter 23 and burns in the filter 23. Therefore, the amount of heat generated by this combustion is added, and the outlet exhaust temperature T3 of the filter 23 becomes higher. When the oxidation catalyst 22 is abnormal, the outlet exhaust temperature T3 of the filter 23 tends to be significantly higher than the outlet exhaust temperature T2 of the oxidation catalyst 22. As shown in the figure, when the outlet exhaust temperature T2 of the oxidation catalyst 22 is constant near the target temperature T2t, the outlet exhaust temperature T3 (broken line d) of the filter 23 tends to be significantly higher than the target temperature T2t.

Therefore, in the present embodiment, the oxidation catalyst 22 is diagnosed based on the outlet exhaust gas temperature T3 of the filter 23 by utilizing this characteristic. A more specific diagnostic method is as follows.

First, regarding the first diagnostic method, the ECU 100 diagnoses the oxidation catalyst 22 as abnormal when the outlet exhaust temperature T3 of the filter 23 is equal to or higher than a predetermined threshold value T3s. Specifically, the ECU 100 compares the detected value of the outlet exhaust temperature T3 with the threshold value T3s at the diagnosis timing t2, and if the detected value is the threshold value T3s or more, diagnoses the oxidation catalyst 22 as abnormal, and if the detected value is less than the threshold value T3s. If there is, the oxidation catalyst 22 is diagnosed as normal.

According to this first diagnostic method, the oxidation catalyst 22 can be suitably diagnosed by utilizing the characteristic that the outlet exhaust temperature T3 of the filter 23 becomes remarkably high when the oxidation catalyst 22 is abnormal.

Here, the ECU 100 sets the threshold value T3s based on the integrated value of the heating fuel supplied during the execution of the temperature rising control, that is, the fuel integrated value Q. Specifically, a map (may be a function; the same applies hereinafter) that defines the relationship between the fuel integrated value Q and the threshold value T3s (shown by the alternate long and short dash line e in FIG. 2D) is stored in the ECU 100 in advance. Then, the ECU 100 calculates the threshold value T3s corresponding to the actual fuel integrated value Q from the map. As the integrated fuel value Q increases, the amount of heat supplied to the filter 23 increases, so that the filter outlet exhaust temperature T3 tends to increase. Therefore, in line with this tendency, the threshold value T3s is also set to increase as the fuel integrated value Q increases. Further, the map is created based on the relationship between the fuel integrated value Q and the filter outlet exhaust temperature T3 when the oxidation catalyst in the criterion state is used.

By using such a threshold value T3s, it is possible to use an optimum threshold value T3s corresponding to the outlet exhaust temperature T3 that changes according to the fuel integrated value Q, and the diagnostic accuracy can be improved.

Next, regarding the second diagnostic method, the ECU 100 determines the oxidation catalyst when the temperature difference ΔT32 between the outlet exhaust temperature T3 of the filter 23 and the inlet exhaust temperature (that is, the outlet exhaust temperature of the oxidation catalyst 22) T2 is equal to or greater than a predetermined threshold value ΔT32s. 22 is diagnosed as abnormal. Specifically, the ECU 100 calculates the temperature difference ΔT32 by subtracting the detected value of the inlet exhaust temperature T2 from the detected value of the outlet exhaust temperature T3 at the diagnosis timing t2, and compares the temperature difference ΔT32 with the threshold value ΔT32s. If the temperature difference ΔT32 is equal to or greater than the threshold value ΔT32s, the oxidation catalyst 22 is diagnosed as abnormal, and if the temperature difference ΔT32 is less than the threshold value ΔT32s, the oxidation catalyst 22 is diagnosed as normal.

Here, too, the ECU 100 sets the threshold value ΔT32s based on the fuel integrated value Q. Specifically, the ECU 100 calculates the threshold value ΔT32s by subtracting the detected value of the inlet / exhaust temperature T2 from the threshold value T3s calculated by the above method.

When the oxidation catalyst 22 is abnormal, the temperature difference ΔT32 between the outlet exhaust temperature T3 and the inlet exhaust temperature T2 of the filter 23 also increases. Therefore, according to the second diagnostic method, the oxidation catalyst 22 can be suitably diagnosed by utilizing this characteristic. In particular, the inlet exhaust temperature T2 of the filter 23 is made substantially constant by feedback control, but slightly fluctuates according to changes in the engine operating state and the like. According to the second diagnostic method, since the diagnosis is performed using the difference between the fluctuating filter 23 and the inlet / exhaust temperature T2, the diagnostic accuracy can be improved.

A map defining the relationship between the fuel integrated value Q and the threshold value ΔT32s may be stored in advance, and the threshold value ΔT32s corresponding to the fuel integrated value Q may be calculated using this map.

Next, with respect to the third diagnostic method, the ECU 100 calculates the cumulative time when the state is abnormal by the first diagnostic method, that is, the outlet exhaust temperature T3 is the threshold value T3s or more. At this time, the ECU 100 continuously increases the cumulative time if the state occurs continuously, and intermittently increases the cumulative time if the state occurs intermittently. Then, when the cumulative time exceeds a predetermined time threshold value, the oxidation catalyst 22 is diagnosed as abnormal. The calculation of the cumulative time can be executed until the end of temperature rise control (that is, the end of filter regeneration). Therefore, if the cumulative time exceeds the time threshold value by the end of the temperature rise control, the oxidation catalyst 22 is diagnosed as abnormal.

According to this third diagnostic method, an abnormality is diagnosed only when the abnormal state continues for more than the time threshold. Therefore, although it is originally normal, it temporarily becomes apparently abnormal due to a change in the engine operating state or the like. Occasionally, it is possible to suppress erroneous diagnosis as an abnormality and improve the accuracy of diagnosis.

Alternatively, the cumulative time when the state made abnormal by the second diagnostic method, that is, the state where the temperature difference ΔT32 is equal to or greater than the threshold value ΔT32s is calculated, and when the cumulative time becomes equal to or greater than the predetermined time threshold value, oxidation occurs. The catalyst 22 may be diagnosed as abnormal.

By the way, according to the diagnostic method of the present embodiment, not within a short period during which the outlet exhaust temperature T2 of the oxidation catalyst 22 is rising, but within a long period after the outlet exhaust temperature T2 of the oxidation catalyst 22 reaches the target temperature T2t. The diagnosis is performed at. For convenience, FIG. 2 shows only an early part of the latter period, but in reality the latter period is many times longer than the period shown. Moreover, the outlet exhaust temperature T3 of the filter 23 is stable during this period, and the diagnosis can be executed at any timing (for example, t2) within the stable long period. Therefore, even if the way in which the outlet exhaust temperature T2 rises varies greatly due to changes in the operating state of the engine, the external environment, or the like, accurate diagnostic results can be obtained regardless of the difference. Therefore, it is possible to improve the diagnostic accuracy of the oxidation catalyst 22.

As a fourth diagnostic method, diagnosis is performed at a plurality of timings (for example, t2 and t3) after the outlet exhaust temperature T2 of the oxidation catalyst 22 reaches the target temperature T2t, and a comprehensive diagnosis is made in consideration of the diagnosis results. You may go. For example, if the results of the diagnosis performed at a plurality of timings are all abnormal, or if the results are abnormal with a probability of 50% or more, the result of the comprehensive diagnosis may be abnormal.

Alternatively, as a fifth diagnostic method, the diagnosis of the above-mentioned comparative example may also be performed as a preliminary diagnosis, and a comprehensive diagnosis may be performed based on the diagnosis result. For example, when the result of the diagnosis of the comparative example is abnormal and the result of the diagnosis of any of the first to fourth diagnostic methods (referred to as the main diagnosis) is also abnormal, the result of the comprehensive diagnosis may be abnormal.

According to these, since the comprehensive diagnosis is performed based on a plurality of diagnosis results, the diagnosis accuracy can be further improved.

Next, the contents of the diagnostic processing executed by the ECU 100 will be described. First, the contents of the diagnostic process based on the first diagnostic method will be described with reference to FIG. The illustrated routine is repeatedly executed by the ECU 100 every predetermined calculation cycle τ (for example, 10 msec).

First, in step S101, the ECU 100 determines whether or not the fuel integrated value Q integrated from the start of the temperature rise control has reached a predetermined threshold value Qs or more. If it has not been reached, the routine is terminated as it is not yet diagnostic timing. On the other hand, when it is reached, the process proceeds to step S102.

In step S102, the ECU 100 calculates the threshold value T3s corresponding to the fuel integrated value Q from a predetermined map.

Next, in step S103, the ECU 100 compares the detected value of the outlet exhaust temperature T3 with the threshold value T3s. When the detected value is less than the threshold value T3s, the routine is terminated. As a result, the oxidation catalyst 22 is substantially diagnosed as normal.

On the other hand, when the detected value is equal to or higher than the threshold value T3s, the process proceeds to step S104 to diagnose the oxidation catalyst 22 as abnormal. At this time, the ECU 100 activates a warning device (for example, a warning light) (not shown) to urge the driver to perform necessary inspections and maintenance (the same applies hereinafter).

Next, the contents of the diagnostic process based on the second diagnostic method will be described with reference to FIG. First, in step S201, the ECU 100 determines whether or not the fuel integrated value Q has reached the threshold value Qs or more, as in step S101. If it has not been reached, the routine is terminated, and if it has been reached, the process proceeds to step S202.

In step S202, the ECU 100 calculates the threshold value ΔT32s corresponding to the fuel integrated value Q by the above method.

Next, in step S203, the ECU 100 compares the temperature difference ΔT32 calculated by the above method with the threshold value ΔT32s. If the temperature difference ΔT32 is less than the threshold value ΔT32s, the routine is terminated, and if the temperature difference ΔT32 is the threshold value ΔT32s or more, the process proceeds to step S204 to diagnose the oxidation catalyst 22 as abnormal.

Next, the content of the diagnostic process based on the third diagnostic method will be described with reference to FIG. Although the combination with the second diagnostic method will be described here, those skilled in the art will recognize that the combination with the first diagnostic method can be easily transformed.

First, in step S301, the ECU 100 determines whether or not the fuel integrated value Q has reached the threshold value Qs or more, as in step S101. If it has not been reached, the routine is terminated, and if it has been reached, the process proceeds to step S302.

In step S302, the ECU 100 calculates the threshold value ΔT32s corresponding to the fuel integrated value Q by the above method.

Next, in step S303, the ECU 100 compares the temperature difference ΔT32 calculated by the above method with the threshold value ΔT32s. If the temperature difference ΔT32 is less than the threshold value ΔT32s, the routine is terminated, and if the temperature difference ΔT32 is greater than or equal to the threshold value ΔT32s, the process proceeds to step S304.

In step S304, the ECU 100 calculates the cumulative time tA which is the cumulative value or the integrated value of the time when ΔT32 ≧ ΔT32s. Assuming that the current value of the cumulative time is tA _n and the previous value is tA _n-1 , the current value of the cumulative time is calculated from the formula: tA _n = tA _n-1 + τ.

Then, in step S305, the ECU 100 compares the cumulative time tA with the predetermined time threshold tAs. If the cumulative time tA is less than the time threshold tAs, the routine is terminated, and if the cumulative time tA is greater than or equal to the time threshold tAs, the process proceeds to step S306 to diagnose the oxidation catalyst 22 as abnormal.

According to this routine, the cumulative time tA is accumulated in step S304 every time ΔT32 ≧ ΔT32s in step S303. Then, before the cumulative time tA reaches the time threshold tAs or more, step S305 is no, so that the oxidation catalyst 22 is not yet diagnosed as abnormal (substantially diagnosed as normal). When the cumulative time tA reaches the time threshold tAs or more, step S305 becomes yes, and the oxidation catalyst 22 is diagnosed as abnormal.

Next, the content of the diagnostic process based on the fourth diagnostic method will be described with reference to FIG. Although the combination with the first diagnostic method will be described here, those skilled in the art will recognize that the combination with the second or third diagnostic method can be easily transformed.

First, in step S401, the ECU 100 determines whether or not the fuel integrated value Q has reached the first threshold value Qs1 (= Qs, see FIG. 2) or more. If it has not been reached, the routine is terminated, and if it has been reached, the process proceeds to step S402.

In step S402, the ECU 100 determines whether or not the fuel integrated value Q has reached the second threshold value Qs2 (see FIG. 2), which is higher than the first threshold value Qs1. If it has not been reached, the process proceeds to step S403, and if it has been reached, the process proceeds to step S408.

When the process proceeds to step S403, the ECU 100 calculates the first threshold value T3s1 corresponding to the fuel integrated value Q from the map. Then, in step S404, the detected value of the outlet exhaust temperature T3 is compared with the first threshold value T3s1. When the detected value is less than the first threshold value T3s1, the process proceeds to step S406. On the other hand, when the detected value is equal to or higher than the first threshold value T3s1, the process proceeds to step S405, and the abnormality flag 1 tentatively indicating that the oxidation catalyst 22 is abnormal is turned on. Then, the process proceeds to step S406.

On the other hand, when the process proceeds to step S408, the ECU 100 calculates the second threshold value T3s2 corresponding to the fuel integrated value Q from the map. Then, in step S409, the detected value of the outlet exhaust temperature T3 is compared with the second threshold value T3s2. When the detected value is less than the second threshold value T3s2, the process proceeds to step S406. On the other hand, when the detected value is equal to or higher than the second threshold value T3s2, the process proceeds to step S410, and the abnormality flag 2 tentatively indicating that the oxidation catalyst 22 is abnormal is turned on. Then, the process proceeds to step S406.

In step S406, the ECU 100 determines whether or not both the abnormality flag 1 and the abnormality flag 2 are on. Exit the routine if both are not on, that is, if both are off or only one is on. On the other hand, when both are on, the oxidation catalyst 22 is diagnosed as abnormal as a result of the comprehensive diagnosis in step S407.

When either the abnormality flag 1 or the abnormality flag 2 is on, the diagnosis may be made as an abnormality as a result of the comprehensive diagnosis. In addition, the diagnosis timing and the number of abnormality flags may be increased, and a comprehensive diagnosis may be performed based on the results of more individual diagnoses.

Next, the content of the diagnostic process of the fifth diagnostic method will be described. First, with reference to FIG. 7, the contents of the diagnostic process of the comparative example combined with the fifth diagnostic method, that is, the diagnostic process of the preliminary diagnosis will be described.

First, in step S501, the ECU 100 determines whether or not the fuel integrated value Q has reached a predetermined threshold value Qsp (see FIG. 2) or more. This threshold value Qsp is a value lower than the above-mentioned threshold value Qs, and is a value corresponding to the rising period before the outlet exhaust temperature T2 of the oxidation catalyst 22 reaches the target temperature T2t. If it has not been reached, the routine is terminated, and if it has been reached, the process proceeds to step S502.

In step S502, the ECU 100 compares the detected value of the outlet exhaust temperature T2 of the oxidation catalyst 22 with the predetermined threshold value T2s. When the detected value is the threshold value T2s or more, the routine is terminated, and when the detected value is less than the threshold value T3s, the process proceeds to step S503 to diagnose the oxidation catalyst 22 as abnormal. As a result of the preliminary diagnosis, when the detected value is the threshold value T2s or more, the oxidation catalyst 22 is diagnosed as normal, and when the detected value is less than the threshold value T2s, the oxidation catalyst 22 is diagnosed as abnormal.

Here, the outlet exhaust temperature T2 is diagnosed by comparing it with the threshold value T2s, but instead, the temperature difference ΔT21 = T2-T1 between the outlet exhaust temperature T2 and the inlet exhaust temperature T1 is diagnosed by comparing it with the predetermined threshold value ΔT21s. You may. In this case, it is diagnosed as normal when ΔT21 ≧ ΔT21s and abnormal when ΔT21 <ΔT21s.

Next, the content of the diagnostic process of the comprehensive diagnosis based on the result of the preliminary diagnosis and the result of the main diagnosis by any of the first to fourth diagnostic methods will be described with reference to FIG.

In step S601, the ECU 100 determines whether or not this diagnosis has been completed. If it is not finished, the routine is finished, and if it is finished, the process proceeds to step S602.

In step S602, the ECU 100 determines whether or not the result of the preliminary diagnosis is abnormal. If it is not abnormal, the routine is terminated, and if it is abnormal, the process proceeds to step S603.

In step S603, the ECU 100 determines whether or not the result of this diagnosis is abnormal. If it is not abnormal, the routine is terminated, and if it is abnormal, the process proceeds to step S604.

In step S604, the ECU 100 diagnoses the oxidation catalyst 22 as abnormal as a result of the comprehensive diagnosis. In this way, when the results of both the preliminary diagnosis and the main diagnosis are abnormal, a comprehensive diagnosis with the abnormality is performed.

On the other hand, when the results of at least one of the preliminary diagnosis and the main diagnosis are not abnormal, a comprehensive diagnosis of substantially normal is performed.

Although the embodiments of the present disclosure have been described in detail above, various other embodiments and modifications of the present disclosure can be considered.

(1) For example, as the second oxidation catalyst, a SOF oxidation catalyst may be used instead of the filter 23. The SOF oxidation catalyst is an oxidation catalyst for oxidizing a soluble organic component (SOF (Soluble Organic Fraction)) of PM. Since this SOF oxidation catalyst also has a function of oxidizing HC like the filter 23, the diagnostic method of the present disclosure can be suitably applied.

(2) As a matter of course, a normal oxidation catalyst may be used as the second oxidation catalyst.

(3) The temperature rise control can be performed not only for the regeneration of the filter 23 but also for any other purpose.

The embodiments of the present disclosure are not limited to the above-described embodiments, and all modifications, applications, and equivalents included in the ideas of the present disclosure defined by the scope of claims are included in the present disclosure. Therefore, this disclosure should not be construed in a limited way and can be applied to any other technique that belongs within the scope of the ideas of this disclosure.

1 Internal combustion engine (engine)
4 Exhaust passage 7 Injector 22 Oxidation catalyst (first oxidation catalyst)
23 Filter (second oxidation catalyst)
38 Exhaust pipe injectors 42, 43, 44 Exhaust temperature sensor 100 Electronic control unit (ECU)

Claims (8)

The first oxidation catalyst and the second oxidation catalyst provided in order from the upstream side in the exhaust passage of the internal combustion engine,
The temperature rise control for raising the outlet exhaust temperature of the first oxidation catalyst is executed, and the first oxidation catalyst is diagnosed based on the outlet exhaust temperature of the second oxidation catalyst during the execution of the temperature rise control. With the configured control unit
An exhaust gas purification device for an internal combustion engine, which comprises. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the control unit diagnoses the first oxidation catalyst as abnormal when the outlet exhaust temperature of the second oxidation catalyst is equal to or higher than a predetermined threshold value. The exhaust gas of the internal combustion engine according to claim 1, wherein the control unit diagnoses the first oxidation catalyst as abnormal when the temperature difference between the outlet exhaust temperature and the inlet exhaust temperature of the second oxidation catalyst is equal to or more than a predetermined threshold value. Purification device. In the control unit, the cumulative time in which the outlet exhaust temperature of the second oxidation catalyst is equal to or higher than a predetermined threshold is equal to or longer than a predetermined time threshold, or the outlet exhaust temperature and inlet exhaust temperature of the second oxidation catalyst are equal to or higher. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the first oxidation catalyst is diagnosed as abnormal when the cumulative time in a state where the temperature difference is equal to or greater than a predetermined threshold is equal to or greater than a predetermined time threshold. The exhaust gas purification device for an internal combustion engine according to any one of claims 2 to 4, wherein the control unit sets the threshold value based on the integrated value of the temperature raising fuel supplied during the execution of the temperature rising control. Any one of claims 1 to 5, wherein the control unit executes the diagnosis of the first oxidation catalyst after the outlet exhaust temperature of the first oxidation catalyst reaches a predetermined target temperature during execution of the temperature rise control. Exhaust gas purification device for internal combustion engine described in. The control unit executes a preliminary diagnosis of the first oxidation catalyst at a timing before the outlet exhaust temperature of the first oxidation catalyst reaches the target temperature, and based on the result of this preliminary diagnosis, the first oxidation catalyst The exhaust gas purification device for an internal combustion engine according to claim 6, wherein the diagnosis is performed. The second oxidation catalyst is either a filter for collecting particulate matter on which an oxidation catalyst is carried, or an oxidation catalyst for oxidizing a soluble organic component of the particulate matter, according to any one of claims 1 to 7. The exhaust purification device for an internal combustion engine according to item 1.

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