JP7115417B2 - Abnormal diagnosis device for reduction catalyst - Google Patents

Description

The present invention relates to an abnormality diagnosis device for a reduction catalyst.

As a conventional abnormality diagnosis device for a reduction catalyst, for example, the technology described in Patent Document 1 is known. In the technique described in Patent Document 1, the _NH3 adsorption amount of the reduction catalyst is estimated based on the amount of NOx contained in the exhaust gas upstream of the reduction catalyst, and when the NH3 adsorption amount is equal to or greater than a specified amount, abnormality diagnosis is performed. Processing is performed.

Japanese Patent No. 6087866

In this technical field, there is a case of diagnosing an abnormality of the reduction catalyst by paying attention to the measured slip amount, which is the measured value of the amount of NOx or _NH3 contained in the exhaust gas downstream of the reduction catalyst. When diagnosing the abnormality of the reduction catalyst, in order to avoid erroneous diagnosis of the abnormality of the reduction catalyst, for example, the virtual slip amount calculated using the physical model of the reduction catalyst is used. It is desirable to appropriately estimate that the actually measured slip amount has increased to the extent that it can be diagnosed as abnormal.

An object of the present invention is to avoid erroneous diagnosis of abnormality of a reduction catalyst.

A reduction catalyst abnormality diagnosis device according to one aspect of the present invention includes a reduction catalyst provided in an exhaust passage of an internal combustion engine, an addition valve provided upstream of the reduction catalyst for adding urea water, and an addition valve upstream of the reduction catalyst. An upstream NOx amount acquisition unit that acquires an upstream NOx amount that is the NOx amount contained in the exhaust gas, an addition amount acquisition unit that acquires the addition amount of the urea water based on the upstream NOx amount, and the exhaust gas downstream of the reduction catalyst. Using a physical model of the reduction catalyst that inputs at _least the upstream NOx amount and the addition amount, the reduction catalyst A virtual slip amount calculator that calculates a virtual slip amount that is a virtual value of the amount of NOx or _NH3 contained in the downstream exhaust gas, and the presence or absence of an abnormality in the reduction catalyst based on the actually measured slip amount and the virtual slip amount. a diagnostic unit that performs a diagnosis, and the virtual slip amount calculation unit uses the first model, which is a physical model that is of a delayed rise type compared to the case of using a physical model that corresponds to the abnormal state of the reduction catalyst in terms of design. , a first virtual slip amount that is a virtual slip amount for determining whether or not the diagnosis can be performed by the diagnosis unit, and the diagnosis unit executes the diagnosis when the first virtual slip amount is equal to or greater than a predetermined permission threshold. do.

In the reduction catalyst abnormality diagnosis device according to the aspect of the present invention, the diagnosis is performed by the diagnosis unit when the first virtual slip amount is equal to or greater than the predetermined permission threshold. The first virtual slip amount is calculated using the first model, which is a physical model that is of a delayed rise type compared to the case of using a physical model corresponding to the abnormal state of the reduction catalyst in terms of design. Therefore, for example, when the actually measured slip amount rises in the abnormal state of the reduction catalyst, if the first virtual slip amount for determining whether the diagnosis can be executed is equal to or greater than the predetermined permission threshold, the reduction catalyst is diagnosed as abnormal. It can be assumed that the measured slip amount has already increased to the extent that it is obtained. As a result, erroneous diagnosis of abnormality in the reduction catalyst can be avoided.

In one embodiment, the first model has a higher peak and a smaller half-value width than when using a physical model that is designed to correspond to an abnormal state of the reduction catalyst in comparison of the impulse response waveform of the virtual slip amount for the same input. A physical model that provides an impulse response waveform may also be used. In this case, the rise of the first virtual slip amount is slower than in the case of using a physical model corresponding to the abnormal state of the reduction catalyst by design, and the sharp peak characteristic is such that the peak after the delayed rise is high. be able to. Therefore, it is possible to use the first model suitable for the delayed rise type.

In one embodiment, the first model may be a physical model with a larger number of catalyst stages than a physical model corresponding in design to an abnormal state of the reduction catalyst. In this case, the rise of the first virtual slip amount can be delayed according to the increase in the number of catalyst stages.

In one embodiment, the first model may be a physical model in which the virtual slip amount has a higher slip speed than the physical model corresponding to the abnormal state of the reduction catalyst by design. In this case, it becomes easier to increase the delayed first virtual slip amount after the rise in accordance with the increase in the slip speed of the virtual slip amount.

In one embodiment, the virtual slip amount calculation unit uses the second model, which is a physical model that is set to start earlier than when using the physical model corresponding to the normal state of the reduction catalyst in terms of design. The diagnostic unit calculates a second virtual slip amount that is a virtual slip amount for temporarily stopping the Diagnosis may be temporarily suspended when . In this case, the diagnosis is temporarily stopped by the diagnosis unit when the second virtual slip amount is equal to or greater than the predetermined stop threshold. The second virtual slip amount is calculated using the second model, which is a physical model that is designed to start faster than the physical model corresponding to the normal state of the reduction catalyst. Therefore, for example, when a measured slip amount occurs even when the reduction catalyst is in a normal state, if the second virtual slip amount for temporarily stopping the diagnosis is equal to or greater than a predetermined stop threshold, the first virtual slip amount is permitted. Even if it is equal to or greater than the threshold value, the diagnosis can be temporarily stopped assuming that the increase in the measured slip amount is not caused by the abnormality of the reduction catalyst. As a result, erroneous diagnosis of abnormality of the reduction catalyst can be avoided with higher accuracy.

According to the present invention, it is possible to avoid erroneous diagnosis of abnormality of the reduction catalyst.

1 is a schematic configuration diagram showing an abnormality diagnosis device for a reduction catalyst according to an embodiment; FIG. FIG. 2 is a block diagram of a configuration relating to an ECU in FIG. 1; FIG. FIG. 10 is a diagram showing an example setting of the NH ₃ slip speed in the physical model; 4 is a timing chart illustrating a first virtual slip amount; 4 is a timing chart illustrating a second virtual slip amount; FIG. 2 is a flowchart illustrating a reduction catalyst diagnosis process by the ECU of FIG. 1; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and overlapping descriptions are omitted.

[Configuration of reduction catalyst abnormality diagnosis device]
FIG. 1 is a schematic configuration diagram showing an abnormality diagnosis device for a reduction catalyst according to an embodiment. In FIG. 1, a reduction catalyst abnormality diagnosis device 10 is a device for diagnosing whether or not there is an abnormality in a reduction catalyst provided in a diesel engine (internal combustion engine) 1, and is mounted on a vehicle, for example. A diesel engine 1 has an intake passage 2, an exhaust passage 3, and an injector (not shown) that injects fuel into a combustion chamber. In the diesel engine 1 , each catalyst provided in the exhaust passage 3 purifies the exhaust gas discharged from the diesel engine 1 .

The reduction catalyst abnormality diagnosis device 10 includes, as catalysts, a diesel particulate filter (DPF: Diesel Particulate Filter) 4 provided in the exhaust passage 3 and a selective reduction catalyst [SCR: Selective Catalytic Reduction] (reduction catalyst ) 5. The DPF 4 is provided upstream of the SCR 5 in the exhaust passage 3 . The DPF 4 removes PM from the exhaust gas by collecting particulate matter [PM: Particulate Matter] contained in the exhaust gas. The SCR 5 reduces and purifies NOx contained in the exhaust gas.

The reduction catalyst abnormality diagnosis device 10 includes an addition valve 6 disposed upstream of the SCR 5 in the exhaust passage 3 , specifically in the exhaust passage 3 between the DPF 4 and the SCR 5 . The addition valve 6 is connected to a urea water tank (not shown) via a supply pipe, and adds urea water to the SCR 5 . When the urea water is added to the SCR 5 by the addition valve 6, the urea water becomes NH ₃ and is adsorbed by the SCR 5, and the NH ₃ reacts with NOx in the exhaust gas to reduce NOx.

There is an upper limit to the amount of _NH3 that can be adsorbed on SCR5. For example, if _NH3 is supplied to SCR5 in excess of its upper limit, _NH3 that has not been adsorbed on SCR5 may flow out (slip) from SCR5.

The SCR 5 has a normal state and an abnormal state regarding the purification performance and adsorption performance of the SCR 5 . The normal state of the SCR 5 means, for example, a state in which the purification performance and adsorption performance of the SCR 5 are maintained to such an extent that the NOx concentration downstream of the SCR 5 satisfies the legal exhaust gas regulations. The abnormal state of the SCR 5 means, for example, a state in which the purification performance and the adsorption performance of the SCR 5 are degraded to such an extent that the NOx concentration downstream of the SCR 5 may not meet the legal exhaust gas regulations. In the abnormal state of SCR5, the amount of _NH3 that can be adsorbed decreases compared to the normal state of SCR5, and the slip amount of _NH3 tends to increase.

FIG. 2 is a block diagram of the configuration relating to the ECU of FIG. As shown in FIGS. 1 and 2, the reduction catalyst abnormality diagnosis device 10 includes an intake air amount sensor 11, an engine state sensor 12, an exhaust temperature sensor 13, a NOx sensor (upstream NOx amount acquisition unit) 14, An NH ₃ sensor (measured slip amount detector) 15 and an ECU [Electronic Control Unit] 20 are provided. The sensors 11 to 15 and the addition valve 6 are connected to the ECU 20 .

The intake air amount sensor 11 is a detector that is provided, for example, in the intake passage 2 of the diesel engine 1 and detects the intake air amount of the diesel engine 1 . The intake air amount sensor 11 transmits a detection signal of the detected intake air amount to the ECU 20 .

The engine state sensor 12 is a sensor for acquiring the engine state. The engine state sensor 12 is, for example, a detector that detects the rotational speed of the diesel engine 1 (hereinafter referred to as engine rotational speed), the load of the diesel engine 1, and the like. The engine state sensor 12 transmits a detection signal regarding the detected engine state to the ECU 20 .

The exhaust temperature sensor 13 is a detector that detects the temperature (inlet temperature) of the exhaust gas between the DPF 4 and the SCR 5 in the exhaust passage 3 as the exhaust temperature. The exhaust temperature sensor 13 transmits a detection signal of the detected exhaust temperature to the ECU 20 .

The NOx sensor 14 is a detector that detects the upstream NOx concentration of exhaust gas between the DPF 4 and the SCR 5 in the exhaust passage 3 . The upstream NOx concentration is the NOx concentration (NOx amount) contained in the exhaust gas upstream of the SCR5. The NOx sensor 14 transmits a detection signal of the detected upstream NOx concentration to the ECU 20 .

The NH ₃ sensor 15 is a detector that detects the NH ₃ concentration of exhaust gas downstream of the SCR 5 in the exhaust passage 3 . The NH ₃ concentration here is the actually measured slip amount, which is the actually measured value of the NH ₃ concentration (NH ₃ amount) contained in the exhaust gas downstream of the SCR 5 . The NH ₃ sensor 15 transmits a detection signal of the actually measured slip amount to the ECU 20 .

The ECU 20 is an electronic control unit having a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], a CAN [Controller Area Network] communication circuit, and the like. The ECU 20 implements various functions by loading programs stored in the ROM into the RAM and executing the programs loaded into the RAM by the CPU. The ECU 20 may be composed of a plurality of electronic control units.

The ECU 20 has an engine state acquisition section 21, an addition amount acquisition section 22, a virtual slip amount calculation section 23, and a diagnosis section 24 as functional configurations.

The engine state acquisition unit 21 acquires various engine states based on detection signals from the intake air amount sensor 11 , the engine state sensor 12 , the exhaust temperature sensor 13 , the NOx sensor 14 and the NH ₃ sensor 15 .

Based on the detection signal of the exhaust temperature sensor 13, the engine state acquisition unit 21 acquires the exhaust temperature between the DPF 4 and the SCR 5 in the exhaust passage 3 as the temperature of the SCR 5. Alternatively, the engine state acquisition unit 21 may calculate the fuel injection amount from the engine speed and the load, and acquire the estimated temperature of the SCR 5 from the fuel injection amount and the intake air amount. In this case, the exhaust temperature sensor 13 may be omitted.

The engine state acquisition unit 21 acquires the upstream NOx concentration based on the detection signal of the NOx sensor 14 . Alternatively, the engine state obtaining unit 21 may calculate the fuel injection amount from the engine speed and the load, and obtain the estimated value of the upstream NOx concentration as the engine state from the fuel injection amount and the intake air amount. In this case, the engine state acquiring section 21 may function as an upstream NOx amount acquiring section, and the NOx sensor 14 may be omitted.

The engine state acquisition unit 21 acquires the actually measured slip amount of NH ₃ based on the detection signal of the NH ₃ sensor 15 . The actually measured slip amount of NH ₃ is used for diagnosis of the presence or absence of an abnormality in SCR5, which will be described later.

The addition amount acquisition unit 22 acquires the amount of urea water added by the addition valve 6 based on the upstream NOx concentration. The addition amount acquisition unit 22 acquires the addition amount of urea water necessary for purifying NOx contained in the exhaust gas upstream of the SCR 5, for example, according to the acquired upstream NOx concentration or the estimated upstream NOx concentration. The addition amount acquisition unit 22 may acquire a preset addition amount of urea water necessary for maintaining the NH ₃ adsorption amount to the SCR 5 . The added amount may be, for example, an amount corresponding to the amount of NH ₃ required to purify all the NOx of the NOx concentration detected by the NOx sensor 14 . The addition amount acquisition unit 22 causes the addition valve 6 to add the urea water at a predetermined addition timing at the acquired addition amount of the urea water.

The virtual slip amount calculation unit 23 uses a physical model of the SCR 5 to which at least the upstream NOx amount and the additive amount are input, and uses a virtual value of the NH ₃ amount (here, NH ₃ concentration) contained in the exhaust gas downstream of the SCR 5. A certain virtual slip amount is calculated. The virtual slip amount calculation unit 23, for example, according to a known calculation method using a physical model of the SCR 5, inputs the upstream NOx amount, the addition amount, and the temperature of the SCR 5, and calculates the amount of NH ₃ associated with the NOx reduction reaction in the SCR 5. A virtual adsorption amount and a virtual slip amount of NH ₃ are calculated from the balance and the upper limit value of the NH ₃ adsorption amount in SCR5. The virtual adsorption amount and virtual slip amount of NH ₃ here differ from the physical model that conforms to general SCR 5 design specifications, for example, to determine whether diagnosis by the diagnosis unit 24 described later can be executed. By using a physical model, the approximate values of the actual NH ₃ adsorption amount and slip amount are calculated intentionally different.

A physical model conforming to the design specifications of the SCR5 means a physical model of the SCR5 in which model design parameters are determined so as to exhibit characteristics similar to those of the actual SCR5. As a characteristic of the SCR 5, for example, the rising response of the NH ₃ slip amount to a constant change in the addition amount when the upstream NOx amount and the temperature of the SCR 5 are constant as inputs (hereinafter simply referred to as "addition amount change input"). and the peak after the rise.

The physical model that conforms to the design specifications of the SCR 5 includes a physical model corresponding to the normal state of the SCR 5 in terms of design and a physical model corresponding to the abnormal state of the SCR 5 in terms of design. A physical model that corresponds to the normal state of the SCR5 in terms of design is, for example, a new state or a state that is legally categorized as normal deterioration (for example, a deteriorated product equivalent to running 4 km or 120 km) that has the same characteristics as the actual SCR5. It means a physical model of SCR5 in which model design parameters are determined so as to show characteristics. The physical model corresponding to the abnormal state of the SCR 5 in terms of design is a model design parameter that exhibits the same characteristics as the characteristics of a real SCR 5 in which an abnormal state is created by, for example, an endurance operation that promotes deterioration of the failure level. Denotes the physical model of the determined SCR5.

The virtual slip amount calculation unit 23 uses the first model as the physical model of the SCR 5, receives the upstream NOx amount, the additive amount, and the temperature of the SCR 5 as inputs, and uses the virtual slip amount calculation unit 23 to determine whether diagnosis by the diagnosis unit 24 can be executed. A first virtual slip amount is calculated.

The first model is a physical model that has a delayed rise compared to the case of using a physical model corresponding to the abnormal state of the SCR 5 by design. The delayed rise type means that the first virtual slip amount is the same addition than the virtual slip amount in the physical model (hereinafter simply referred to as "abnormal virtual slip amount") corresponding to the abnormal state of SCR 5 in terms of design. It means the characteristics of the rise response that rises with a delay with respect to the amount change input. In addition to the delayed rise type, the first model has a sharp peak such that the first virtual slip amount rises later than the abnormal virtual slip amount with respect to the same addition amount change input, and the peak becomes higher. It may be a characterized physical model.

As an example, the first model has a higher peak and a smaller half-value width than the physical model corresponding to the abnormal state of the SCR5 in comparison of the impulse response waveform of the virtual slip amount with respect to the same additive amount change input. A physical model that provides an impulse response waveform may also be used.

Specifically, in order to obtain such characteristics, the first model may be a physical model having a larger number of catalyst stages than the physical model corresponding to the abnormal state of the SCR 5 in terms of design. For example, if the number of stages of the catalyst in the physical model corresponding to the abnormal state of the SCR 5 in design is one, the number of stages of the catalyst in the first model can be, for example, two. Note that the number of catalyst stages in the first model may be two or more.

Also, specifically, the first model may be a physical model in which the NH ₃ slip speed (the slip speed of the virtual slip amount) is larger than the physical model corresponding to the abnormal state of the SCR 5 by design. FIG. 3 is a diagram showing an example setting of the NH ₃ slip speed in the physical model. As shown in FIG. 3, when the temperature of the SCR 5 is constant and compared, the larger the NH ₃ adsorption amount, the larger the NH ₃ slip speed. In FIG. 3, when the NH ₃ slip speed of the physical model corresponding to the abnormal condition of SCR 5 is represented by curve L1, for example, the NH ₃ slip speed of the first model is represented by curve L2. may The NH ₃ slip rate of the first model may be approximately twice the NH ₃ slip rate of the physical model, which by design corresponds to the abnormal condition of SCR5. When the number of catalyst stages in the first model is two or more, the NH ₃ slip speed in the first model is at least twice the NH ₃ slip speed in the physical model corresponding to the abnormal state of the SCR 5 by design. may

FIG. 4 is a timing chart illustrating the first virtual slip amount. In FIG. 4, the first hypothetical slip amount SL ₁ is indicated by a solid line and the abnormal hypothetical slip amount SL _MAL is indicated by a broken line for the same addition amount change input. As shown in FIG. 4 , by using the first model, the waveform of the first virtual slip amount SL ₁ can be changed to the above-described delayed rise type and a sharp peak as compared with the abnormal virtual slip amount SL _MAL . can be a characteristic. Therefore, for example, the permission threshold _TH1 , which is the threshold value of the _first virtual slip amount _SL1 for determining whether diagnosis can be executed, is set to By appropriately setting the value of SL ₁ , for example, when the actually measured slip amount rises in an abnormal state of the actual SCR 5, if the first virtual slip amount SL ₁ is equal to or greater than the permission threshold TH ₁ , the SCR 5 is judged to be abnormal. It can be assumed that the measured slip amount has already increased to the extent that it can be diagnosed.

The virtual slip amount calculation unit 23 uses the second model as the physical model of the SCR 5, inputs the upstream NOx amount, the addition amount, and the temperature of the SCR 5, and calculates a virtual slip amount for temporarily stopping the diagnosis by the diagnosis unit 24. A certain second virtual slip amount is calculated.

The second model is a physics model that has an earlier rise than the physics model that corresponds to the normal state of the SCR 5 by design. The early rise type means that the second virtual slip amount is the same addition than the virtual slip amount in the physical model (hereinafter simply referred to as "normal virtual slip amount") corresponding to the normal state of SCR 5 in terms of design. It refers to the characteristics of a rise response that rises early to a quantity change input. In the second model, in addition to the early rise type, the second virtual slip amount is broader than the normal virtual slip amount, and the peak is lower and smoother after rising earlier with respect to the same addition amount change input. It may be a physical model that has a peak characteristic of

As an example, the second model has a lower peak and a larger half width than the physical model corresponding to the normal state of the SCR 5 in comparison of the impulse response waveform of the virtual slip amount with respect to the same additive amount change input. A physical model that provides an impulse response waveform may also be used.

Specifically, in order to obtain such characteristics, the second model is a physical model having the same number of catalyst stages as the physical model corresponding to the normal state of the SCR 5 in terms of design, and corresponds to the normal state of the SCR 5 in terms of design. It may be a physical model with a smaller NH ₃ slip rate than the physical model. For example, as shown in FIG. 3, if the physical model NH ₃ slip rate corresponding by design to the normal state of SCR 5 is represented by, for example, curve L3, then the second model NH ₃ slip rate is represented by curve L4. may be represented. The second model NH ₃ slip rate may be approximately half the NH ₃ slip rate of the physical model that corresponds by design to the SCR5 normal state. As described above, in the abnormal state of SCR 5, the amount of NH ₃ that can be adsorbed decreases compared to the normal state of SCR 5, and the slip amount of NH ₃ tends to increase. The ₃ -slip speed and the NH ₃ -slip speed of the second model have different characteristics. More specifically, when the temperature of the SCR 5 is constant and compared, the NH ₃ slip speed of the first model represented by the curve L1 is a larger value than the NH ₃ slip speed of the second model represented by the curve L3. It's becoming

FIG. 5 is a timing chart illustrating the second virtual slip amount. In FIG. 5, the second virtual slip amount SL ₂ is indicated by a solid line and the normal virtual slip amount SL _NRM is indicated by a broken line for the same addition amount change input. As shown in FIG. 5 , by using the second model, the waveform of the second virtual slip amount SL ₂ has a broad peak in addition to the early rise type as described above, compared to the normal virtual slip amount SL _NRM . can be a characteristic. Therefore, for example, the stop threshold TH2, which is the threshold value of the _second virtual slip amount SL2 for temporarily stopping diagnosis, is set to the _second virtual slip amount SL2 of the broad peak portion where the _second virtual slip amount _SL2 increases By appropriately setting the value of , for example, when the actually measured slip amount occurs even in the normal state of SCR 5, if the second virtual slip amount SL ₂ is equal to or greater than the stop threshold TH ₂ , the first virtual slip amount SL ₁ is equal to or greater than the permission threshold TH ₁ , the increase in the measured slip amount is not caused by an abnormality in SCR5 (that is, it is not an abnormality because slip occurs even in normal SCR5), and the diagnosis is temporarily stopped. can do.

The diagnosis unit 24 diagnoses whether or not there is an abnormality in the SCR 5 based on the measured slip amount and the virtual slip amount. The diagnosis unit 24 diagnoses whether or not the SCR 5 is abnormal, for example, when the first virtual slip amount SL ₁ is equal to or greater than the permission threshold TH ₁ described above. For example, when the first virtual slip amount SL ₁ is equal to or greater than the permission threshold TH ₁ and the second virtual slip amount SL ₂ is equal to or greater than the above-described stop threshold TH ₂ , the diagnosis unit 24 determines whether the SCR 5 is abnormal. Presence/absence diagnosis may be suspended temporarily.

Diagnosis unit 24, when diagnosing the presence or absence of abnormality in SCR 5 (for example, the first virtual slip amount SL ₁ is equal to or greater than the permission threshold TH ₁ and the second virtual slip amount SL ₂ is equal to or greater than the above-described stop threshold TH ₂ ), the measured slip amount of NH ₃ is compared with a predetermined abnormality determination threshold value, and, for example, when the actually measured slip amount is equal to or greater than the abnormality determination threshold value, it is diagnosed that SCR 5 is abnormal. When diagnosing whether or not the SCR 5 is abnormal, the diagnosis unit 24 may diagnose that the SCR 5 is abnormal when, for example, the measured slip amount continues to be equal to or greater than the abnormality determination threshold for a certain period of time.

[Processing by ECU]
Next, an example of processing by the ECU 20 will be described with reference to FIG. FIG. 6 is a flowchart illustrating the reduction catalyst diagnosis process by the ECU 20. As shown in FIG. The ECU 20 of the reduction catalyst abnormality diagnosis device 10 repeatedly executes the reduction catalyst diagnosis process shown in FIG.

As shown in FIG. 6, in S01, the ECU 20 acquires the upstream NOx concentration using the engine state acquiring section 21. As shown in FIG. In S<b>02 , the ECU 20 acquires the amount of urea water added by the addition valve 6 using the addition amount acquisition unit 22 . In S03, the ECU 20 uses the NH ₃ sensor 15 to detect the actually measured slip amount of NH ₃ .

In S04, the ECU 20 uses the first model to calculate the _first virtual slip amount SL1 by the virtual slip amount calculation unit 23 . In S05, the ECU 20 uses the diagnostic unit 24 to determine whether or not the _first virtual slip amount SL1 is equal to or greater _than the permission threshold TH1.

If the diagnosis unit 24 determines that the first virtual slip amount SL ₁ is equal to or greater than the permission threshold TH ₁ (S05: YES), the ECU 20 causes the virtual slip amount calculation unit 23 to use the second model in S06. A _second virtual slip amount SL2 is calculated. In S07, the ECU 20 uses the diagnostic unit 24 to determine whether or not the _second virtual slip amount SL2 is less _than the stop threshold TH2. When the diagnosis unit 24 determines that the _second virtual slip amount SL2 is less than the stop threshold TH2 (S07: YES), the ECU ₂₀ diagnoses whether or not the SCR5 is abnormal in S08. After that, the ECU 20 terminates the processing of FIG.

On the other hand, when the diagnosis unit 24 determines that the first virtual slip amount SL ₁ is less than the permission threshold TH ₁ (S05: NO), the ECU 20 causes the diagnosis unit 24 to diagnose whether there is an abnormality in the SCR 5. Then, the process of FIG. 6 is terminated.

Also, when the diagnostic unit 24 determines that the first virtual slip amount SL ₁ is equal to or greater than the permission threshold TH ₁ , the diagnostic unit 24 determines that the second virtual slip amount SL ₂ is equal to or greater than the stop threshold TH ₂ . If so (S05: YES and S07: NO), the ECU 20 terminates the process of FIG.

[Action and effect]
As described above, in the reduction catalyst abnormality diagnosis device 10, the diagnosis is performed by the diagnosis unit 24 when the _first virtual slip amount SL1 is equal to or greater _than the predetermined permission threshold TH1. The first virtual slip amount SL1 is calculated using a first model, which is a physical model that is of a delayed rise type rather than a physical model that corresponds to the abnormal state of the _SCR5 in terms of design. Therefore, for example, when the measured slip amount rises in the abnormal state of SCR5, if the _first virtual slip amount SL1 for determining whether diagnosis can be executed is equal to or greater than the permission threshold TH1, _SCR5 is diagnosed as abnormal. It can be assumed that the measured slip amount has already increased to the extent that it is obtained. As a result, erroneous diagnosis of abnormality in the SCR 5 can be avoided.

In the reduction catalyst abnormality diagnosis device 10, the first model has a peak in the comparison of the impulse response waveform of the virtual slip amount with respect to the same addition amount change input as compared with the case of using the physical model corresponding to the abnormal state of the SCR 5 by design. The physical model is such that the impulse response waveform is high and has a small half-value width. As a result, the rise of the _first virtual slip amount SL1 is slower than when a physical model corresponding to the abnormal state of the SCR 5 is used in design, and the sharp peak characteristic is obtained such that the peak after the delayed rise is high. can do. Therefore, it is possible to use the first model suitable for the delayed rise type.

In the reduction catalyst abnormality diagnosis device 10, the first model is a physical model having a larger number of catalyst stages than the physical model corresponding to the abnormal state of the SCR 5 in terms of design. As a result, the rise of the _first virtual slip amount SL1 can be delayed in accordance with the increase in the number of catalyst stages.

In the reduction catalyst abnormality diagnosis device 10 , the first model is a physical model having a higher NH ₃ slip rate than the physical model corresponding to the abnormal state of the SCR 5 in terms of design. This makes it easier to increase the delayed first virtual slip amount SL ₁ after the rise in accordance with the increase in the NH ₃ slip speed.

In the reduction catalyst abnormality diagnosis device 10, the virtual slip amount calculation unit 23 uses the second model, which is a physical model that is set to an earlier start-up type than when using a physical model corresponding to the normal state of the SCR 5 in terms of design, A _second virtual slip amount SL2, which is a virtual slip amount for temporarily stopping diagnosis by the diagnosis unit 24, is calculated, and the diagnosis unit 24 determines that the _first virtual slip amount SL1 is equal to or greater _than the permission threshold TH1, and , the diagnosis is temporarily stopped when the _second virtual slip amount SL2 is equal to or greater _than the stop threshold TH2. As a result, the diagnosis is temporarily stopped by the diagnosis unit 24 when the _second virtual slip amount SL2 is equal to or greater _than the stop threshold TH2. The second virtual slip amount SL2 is calculated using the _second model, which is a physical model that is designed to rise earlier than the physical model corresponding to the normal state of the SCR 5 in terms of design. Therefore, for example, when a measured slip amount occurs even when the SCR 5 is in a normal state, if the second virtual slip amount SL2 for temporarily stopping the diagnosis is equal to or greater _than the stop threshold TH2, the _first virtual slip amount SL Even if ₁ is equal to or greater than the permission threshold TH ₁ , the diagnosis can be temporarily stopped assuming that the increase in the measured slip amount is not caused by the abnormality of SCR5. As a result, erroneous diagnosis of abnormality in the SCR 5 can be avoided with higher accuracy.

[Modification]
Although the embodiments according to the present invention have been described above, the present invention is not limited to the above-described embodiments.

In the above embodiment, the first model is a physical model with a larger number of catalyst stages and a larger NH ₃ slip rate than the physical model corresponding to the abnormal state of the SCR 5 by design, but is not limited to this. . In addition, in the comparison of the impulse response waveform of the virtual slip amount for the same additive amount change input, the first model is an impulse with a higher peak and a smaller half-value width than when using a physical model corresponding to the abnormal state of the SCR 5 in terms of design. Although the physical model has a response waveform, it is not limited to this. The point is that if the first model is a physical model that is more delayed rising than when using a physical model that corresponds to the abnormal state of the SCR 5 by design, a physical model parameter setting different from the above is used. may be used as the first model.

In the above embodiment, the upstream NOx concentration was exemplified as the NOx amount.

In the above embodiment, the NH ₃ concentration was exemplified as the NH ₃ amount, but the NH ₃ amount may be various physical quantities such as the mass flow rate and mass of NH ₃ contained in the exhaust gas downstream of the SCR 5 .

In the above-described embodiment, as the measured slip amount and the virtual slip amount, the measured value and the virtual value of the amount of NH ₃ contained in the exhaust gas downstream of the SCR 5 were exemplified. It may be a measured value and a hypothetical value of the amount of NOx contained in the exhaust gas. That is, the presence or absence of an abnormality in the SCR 5 may be diagnosed by focusing on the slip amount of NOx from the SCR 5 . In this case, instead of the NH ₃ sensor 15, the actually measured slip amount detector may be, for example, a NOx sensor that detects the actually measured amount of NOx contained in the exhaust gas downstream of the SCR 5. Instead of the virtual slip amount of _NH3 , the virtual slip amount calculation unit 23 uses the physical model of SCR5 to which at least the upstream NOx amount and the addition amount are input, to calculate the NOx amount contained in the exhaust gas downstream of SCR5. A value (virtual slip amount of NOx) may be calculated. Further, the diagnosis unit 24 may diagnose whether or not there is an abnormality in the SCR 5 based on, for example, an actually measured slip amount of NOx instead of the actually measured slip amount of _NH3 .

The diagnosis unit 24 temporarily stops diagnosis when the first virtual slip amount is equal to or greater than the permission threshold and the second virtual slip amount is equal to or greater than the stop threshold. Even if is not equal to or greater than the permission threshold, if the second virtual slip amount is equal to or greater than the stop threshold, diagnosis may not be performed. In this case, the processing of S06 and S07 in FIG. 6 may be performed between S04 and S05.

The virtual slip amount calculator 23 does not necessarily have to use the second model to calculate the second virtual slip amount. The diagnosis unit 24 does not necessarily have to temporarily stop diagnosis when the first virtual slip amount is equal to or greater than the permission threshold and the second virtual slip amount is equal to or greater than the stop threshold.

In the above-described embodiment, the diesel engine 1, which is a four-cylinder in-line engine, is exemplified as the internal combustion engine, but the internal combustion engine is not limited to this.

3 Exhaust passage 5 SCR (selective reduction catalyst, reduction catalyst) 6 Addition valve 10 Reduction catalyst abnormality diagnosis device 14 NOx sensor (upstream NOx amount acquisition unit) 15 NH ₃ sensor (actual measurement slip amount detection unit), 22...addition amount acquisition unit, 23...virtual slip amount calculation unit, 24...diagnosis unit.

Claims (5)

a reduction catalyst provided in an exhaust passage of an internal combustion engine;
an addition valve provided upstream of the reduction catalyst for adding urea water;
an upstream NOx amount acquisition unit that acquires an upstream NOx amount that is the amount of NOx contained in the exhaust gas upstream of the reduction catalyst;
an addition amount acquisition unit that acquires the addition amount of the urea water based on the upstream NOx amount;
a measured slip amount detection unit that detects a measured slip amount that is a measured value of the NOx amount or the _NH3 amount contained in the exhaust gas downstream of the reduction catalyst;
A virtual slip amount, which is a virtual value of the amount of NOx or _NH3 contained in the exhaust gas downstream of the reduction catalyst, is calculated using a physical model of the reduction catalyst that inputs at least the upstream NOx amount and the addition amount. a virtual slip amount calculator for
a diagnosis unit that diagnoses whether or not there is an abnormality in the reduction catalyst based on the measured slip amount and the virtual slip amount;
with
The virtual slip amount calculation unit uses the first model, which is the physical model that is of a delayed rise type compared to the case of using the physical model that corresponds to the abnormal state of the reduction catalyst in terms of design, to calculate the calculating a first virtual slip amount that is the virtual slip amount for determining whether diagnosis can be executed;
A reduction catalyst abnormality diagnosis device, wherein the diagnosis unit executes the diagnosis when the first virtual slip amount is equal to or greater than a predetermined permission threshold. The first model has a higher peak and a smaller half width than when the physical model corresponding to the abnormal state of the reduction catalyst is used in comparison of impulse response waveforms of the virtual slip amount with respect to the same input. 2. The apparatus for diagnosing abnormality of a reduction catalyst according to claim 1, wherein said physical model is such that said impulse response waveform is obtained. 3. The reducing catalyst abnormality diagnosis device according to claim 1, wherein the number of catalyst stages of the first model is larger than that of the physical model corresponding in design to the abnormal state of the reducing catalyst. 4. The reduction catalyst abnormality diagnosis device according to claim 3, wherein the slip speed of the virtual slip amount of the first model is larger than that of the physical model corresponding to the abnormal state of the reduction catalyst in terms of design. The virtual slip amount calculation unit uses the second model, which is the physical model that is set to start earlier than when using the physical model that corresponds to the normal state of the reduction catalyst in terms of design, to calculate the calculating a second virtual slip amount that is the virtual slip amount for suspending the diagnosis;
The diagnosis unit temporarily stops the diagnosis when the first virtual slip amount is greater than or equal to the permission threshold and the second virtual slip amount is greater than or equal to a predetermined stop threshold. 5. The apparatus for diagnosing abnormality of a reduction catalyst according to any one of 1 to 4.

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