JP2017115810A - Abnormality diagnosis device for exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve diagnostic accuracy when diagnosing an exhaust emission control system having an SCR filter to determine whether the system has an abnormality on the basis of a detection value obtained by an NOx sensor provided downstream of the SCR filter.SOLUTION: An NOx elimination rate of an SCR filter calculated based on a detection value obtained by an NOx sensor is compared with a prescribed determination elimination rate to diagnose an abnormality of an exhaust emission control system including the SCR filter and an ammonia supply device. Wall inner PM accumulation amount is estimated, and the determination elimination rate is set based on the wall inner PM accumulation amount. In the case where set parameters other than the wall inner PM accumulation amount are the same, if the wall inner PM accumulation amount does not reach saturation accumulation amount, when the wall inner PM accumulation amount is large, the determination elimination rate is set to be a larger value compared to when the amount is small. If the wall inner PM accumulation amount reaches the saturation accumulation amount, the determination elimination rate is set to be a constant value corresponding to the saturation accumulation amount.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an abnormality diagnosis device for an exhaust gas purification system that purifies exhaust gas from an internal combustion engine.

  A technique is known in which an SCR filter having a configuration in which an SCR catalyst (selective reduction type NOx catalyst) is supported on a filter is provided in an exhaust passage of an internal combustion engine. Here, the SCR catalyst has a function of reducing NOx in the exhaust gas using ammonia as a reducing agent. Further, the filter has a function of collecting particulate matter (Particulate Matter: hereinafter also referred to as “PM”) in the exhaust gas. In an exhaust gas purification system for an internal combustion engine having such an SCR filter, ammonia as a reducing agent is supplied to the SCR filter by an ammonia supply device provided in the exhaust passage.

  Patent Document 1 discloses a technique related to a failure diagnosis device for an exhaust purification system including an SCR catalyst provided in an exhaust passage. In the technique described in Patent Document 1, a predetermined threshold for failure diagnosis is based on an intermediate characteristic between a purification characteristic when the exhaust purification system is normal and a purification characteristic when the exhaust purification system is out of order. And a correction coefficient is set. The NOx purification rate calculated using the NOx outflow amount from the SCR catalyst as a parameter is corrected by the set correction coefficient. By comparing the corrected NOx purification rate with a predetermined threshold value, it is diagnosed whether or not the exhaust purification system has failed.

  Further, in Non-Patent Document 1, when the PM accumulation amount in the SCR filter increases, the ammonia adsorption amount that is the amount of ammonia adsorbed on the SCR catalyst supported on the SCR filter tends to increase. It is disclosed.

Japanese Patent Laying-Open No. 2015-010589

"Physico-Chemical Modeling of an Integrated SCR on DPF (SCR / DPF) System," SAE International Journal of Engines, August 2012 vol. 5 no. 3, 958-974

  A technique for diagnosing whether or not an exhaust purification system including an SCR filter has failed based on a NOx purification rate in the SCR filter (a ratio of a NOx amount reduced in the SCR filter to a NOx amount flowing into the SCR filter) It has been known. Here, as disclosed in the above-described prior art documents, in the SCR filter, the ammonia adsorption amount on the SCR catalyst supported on the SCR filter may fluctuate due to the influence of the PM deposition state. When the ammonia adsorption amount at the SCR catalyst varies, the NOx purification rate in the SCR filter varies accordingly. Therefore, in order to perform a failure diagnosis of the exhaust purification system with high accuracy using the NOx purification rate in the SCR filter, it is necessary to consider the influence of the PM accumulation state in the SCR filter.

The present invention has been made in view of the above problems, and based on the detected value of the NOx sensor provided downstream of the SCR filter, whether or not an abnormality has occurred in the exhaust purification system including the SCR filter is determined. The object is to improve the diagnostic accuracy when diagnosing.

  PM in the exhaust gas is collected on the SCR filter, and the collected PM is deposited. At this time, in the SCR filter, first, PM is deposited in the partition walls (that is, in the pores formed in the partition walls). Then, after the deposition amount of PM in the partition wall reaches the saturation deposition amount, PM is deposited on the surface of the partition wall. Hereinafter, the deposition of PM in the partition wall of the SCR filter is sometimes referred to as “in-wall PM deposition”, and the period during which PM deposition in the wall is progressing may be referred to as “in-wall PM deposition period”. Further, the estimated accumulation amount of PM in the partition wall of the SCR filter may be referred to as “in-wall PM accumulation amount”. Further, the deposition of PM on the surface of the partition wall of the SCR filter is sometimes referred to as “surface layer PM deposition”, and the period during which surface layer PM deposition is in progress may be referred to as “surface layer PM deposition period”. In addition, the estimated accumulation amount of PM on the surface of the partition wall of the SCR filter may be referred to as “surface PM accumulation amount”.

  As described above, conventionally, it has been considered that when the amount of PM deposited on the SCR filter increases, the ammonia adsorption amount on the SCR catalyst supported on the SCR filter tends to increase. However, the detailed correlation between the PM accumulation state on the SCR filter and the increasing tendency of the ammonia adsorption amount on the SCR catalyst has been unknown so far. However, the inventor of the present invention tends to increase the ammonia adsorption amount on the SCR catalyst when the PM deposition amount in the wall in the SCR filter is large compared to when the PM deposition amount in the wall is small. It has been newly found that the increase or decrease in the amount of PM deposited on the SCR filter has a tendency to hardly affect the amount of ammonia adsorbed on the SCR catalyst. Here, when the amount of PM deposition in the wall is large, the amount of ammonia adsorbed on the SCR catalyst tends to increase more easily than when the amount of PM deposition in the wall is small. This is thought to be due to an increase in the saturated adsorption amount of ammonia. On the other hand, the increase / decrease in the surface layer PM deposition amount in the SCR filter has little effect on the ammonia adsorption amount on the SCR catalyst. The increase / decrease in the surface layer PM deposition amount hardly affects the saturated adsorption amount of ammonia on the SCR catalyst. This is thought to be because it has no effect. The present invention reflects the above new knowledge in an abnormality diagnosis device for an exhaust purification system. That is, when the amount of PM deposition in the wall in the SCR filter is large, the amount of ammonia adsorption on the SCR catalyst tends to increase more easily than when the amount of PM deposition in the wall is small. This is reflected in the abnormality diagnosis device of the exhaust purification system for diagnosing whether or not an abnormality has occurred in the exhaust purification system.

More specifically, an abnormality diagnosis device for an exhaust purification system according to the present invention is an SCR filter that is provided in an exhaust passage of an internal combustion engine and has a structure in which an SCR catalyst is supported on a filter having a partition wall having pores. The SCR catalyst has a function of reducing NOx in exhaust using ammonia as a reducing agent, and the filter has a function of collecting particulate matter in exhaust, and the SCR filter, Diagnosing whether an abnormality has occurred in an exhaust gas purification system having an ammonia supply device provided in the exhaust passage upstream of the filter and supplying ammonia to the SCR filter In the abnormality diagnosis device of the exhaust purification system, a NOx sensor provided in the exhaust passage downstream of the SCR filter, and the NO The NOx purification rate calculation unit that calculates the NOx purification rate in the SCR filter using the detection value of the sensor and the flow rate of the exhaust gas flowing into the SCR filter is the difference in exhaust pressure between the upstream and downstream of the SCR filter. A differential pressure conversion value acquisition unit that acquires a differential pressure conversion value that is a conversion value converted into a value when it is assumed to be constant, and particulate matter in the SCR filter that is estimated based on parameters other than the differential pressure conversion value The total PM deposition amount is estimated to be the total PM deposition amount, and the estimated deposition amount of the particulate matter in the pores formed in the partition walls of the SCR filter is defined as a wall. When the inner PM deposition amount is set, the intra-wall PM deposition amount estimation unit for estimating the inner PM deposition amount, and the total PM deposition when the particulate matter is sequentially deposited on the SCR filter without being oxidized. Is a storage unit that stores a first gradient, a second gradient, and a reference differential pressure conversion value, which are parameters relating to a correlation between the differential pressure conversion value and the differential pressure conversion value. The increase amount of the differential pressure conversion value per unit increase amount of the total PM deposition amount at the stage where particulate matter is deposited in the hole is defined as the first slope, and the PM deposition amount in the wall is set to the saturation deposition amount. The amount of increase in the differential pressure conversion value per unit increase amount of the total PM deposition amount when the particulate matter is deposited on the surface of the partition wall of the SCR filter after reaching the second slope is defined as the second slope. The storage unit for storing values of the first inclination, the second inclination, and the reference differential pressure conversion value when the differential pressure conversion value when the PM accumulation amount is 0 is used as the reference differential pressure conversion value; The PM deposition amount in the wall estimated by the PM deposition amount estimation unit in the wall A setting unit for setting a predetermined determination purification rate based on predetermined setting parameters including the NOx purification rate in the SCR filter calculated by the NOx purification rate calculation unit, and the determination set by the setting unit A diagnosis unit that diagnoses an abnormality of the exhaust purification system by comparing a purification rate, and the total PM deposition amount estimation unit estimated by the total PM deposition amount estimation unit Based on the accumulation amount, the differential pressure conversion value acquired by the differential pressure conversion value acquisition unit, and the first inclination, the second inclination, and the reference differential pressure conversion value stored in the storage unit The following formula: PM deposition amount in the wall = (differential pressure conversion value−second slope / total PM deposition amount−reference differential pressure conversion value) / (first slope−second slope) Estimate and NOx purification The detection time of the detected value of the NOx sensor used to calculate the NOx purification rate by the rate calculation unit is set as the sensor detection time, and the in-wall PM accumulation amount estimated by the in-wall PM accumulation amount estimation unit is saturated. When the accumulation amount has not reached, the setting unit has the same setting parameter other than the in-wall PM accumulation amount, and when the in-wall PM accumulation amount at the sensor detection time is large, than when it is small. When the determination purification rate corresponding to the sensor detection time is set to a larger value and the in-wall PM accumulation amount estimated by the in-wall PM accumulation amount estimation unit has reached a saturated accumulation amount, the setting unit However, when the setting parameters other than the PM accumulation amount in the wall are the same, the pre-corresponding to the sensor detection time is irrespective of the total PM accumulation amount at the sensor detection time. The decision purification rate, the intramural PM accumulation amount is set to a constant value corresponding to the PM accumulation amount in the wall when reaches the saturation deposition amount.

  ADVANTAGE OF THE INVENTION According to this invention, the diagnostic precision at the time of diagnosing whether abnormality has arisen in the exhaust gas purification system provided with the SCR filter based on the detected value of the NOx sensor provided downstream from the SCR filter is improved. be able to.

It is a figure which shows schematic structure of the internal combustion engine which concerns on the Example of this invention, and its intake / exhaust system. It is a figure which shows transition of the saturated adsorption amount and differential pressure conversion value of ammonia of the SCR catalyst carry | supported by the SCR filter according to the increase in total PM deposition amount. It is a figure for demonstrating the influence which accumulation | storage of PM in an SCR filter has on the saturated adsorption amount of ammonia of this SCR catalyst about the correlation with the filter adsorption temperature and the saturated adsorption amount of ammonia of the SCR catalyst carry | supported by the SCR filter. It is a model figure which shows transition of the differential pressure | voltage conversion value according to the increase in total PM deposit amount. It is a figure which shows the correlation with PM accumulation amount in a wall and the correction coefficient (alpha) based on the Example of this invention, and the correlation with total PM accumulation amount and the correction coefficient (alpha). It is a flowchart which shows the abnormality diagnosis flow of the exhaust gas purification system based on the Example of this invention. It is a figure which shows an example of the comparison with the NOx purification rate in a SCR filter, the predetermined | prescribed determination purification rate, and the predetermined | prescribed corrected purification rate after correction | amendment based on the Example of this invention with a bar graph.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

(Outline configuration)
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) using light oil as fuel. However, the present invention can also be applied to a spark ignition type internal combustion engine using gasoline or the like as fuel.

  The internal combustion engine 1 includes a fuel injection valve 3 that injects fuel into the cylinder 2. When the internal combustion engine 1 is a spark ignition type internal combustion engine, the fuel injection valve 3 may be configured to inject fuel into the intake port.

  The internal combustion engine 1 is connected to the intake passage 4. An air flow meter 40 and a throttle valve 41 are provided in the intake passage 4. The air flow meter 40 outputs an electrical signal corresponding to the amount (mass) of intake air (air) flowing through the intake passage 4. The throttle valve 41 is disposed downstream of the air flow meter 40 in the intake passage 4. The throttle valve 41 adjusts the intake air amount of the internal combustion engine 1 by changing the passage cross-sectional area in the intake passage 4.

  The internal combustion engine 1 is connected to the exhaust passage 5. The exhaust passage 5 is provided with an oxidation catalyst 50, an SCR filter 51, a fuel addition valve 52, and a urea water addition valve 53. The SCR filter 51 is configured by supporting a SCR catalyst 51a on a wall flow type filter formed of a porous base material. The filter has a function of collecting PM in the exhaust. The SCR catalyst 51a has a function of reducing NOx in the exhaust gas using ammonia as a reducing agent. Therefore, the SCR filter 51 has a PM collection function and a NOx purification function. The oxidation catalyst 50 is provided in the exhaust passage 5 upstream of the SCR filter 51. The fuel addition valve 52 is provided in the exhaust passage 5 further upstream than the oxidation catalyst 50. The fuel addition valve 52 adds fuel to the exhaust flowing in the exhaust passage 5. The urea water addition valve 53 is provided in the exhaust passage 5 downstream of the oxidation catalyst 50 and upstream of the SCR filter 51. The urea water addition valve 53 adds urea water into the exhaust flowing through the exhaust passage 5. When urea water is added into the exhaust gas from the urea water addition valve 53, the urea water is supplied to the SCR filter 51. That is, urea, which is a precursor of ammonia, is supplied to the SCR filter 51. In the SCR filter 51, ammonia produced by hydrolysis of the supplied urea is adsorbed to the SCR catalyst 51a. Then, NOx in the exhaust is reduced using ammonia adsorbed on the SCR catalyst 51a as a reducing agent. Instead of the urea water addition valve 53, an ammonia addition valve for adding ammonia gas into the exhaust gas may be provided.

In the exhaust passage 5 downstream of the oxidation catalyst 50 and upstream of the urea water addition valve 53, an O ₂ sensor 54, an upstream temperature sensor 55, and an upstream NOx sensor 57 are provided. A downstream temperature sensor 56 and a downstream NOx sensor 58 are provided in the exhaust passage 5 downstream of the SCR filter 51. The O ₂ sensor 54 outputs an electrical signal corresponding to the O ₂ concentration of the exhaust. The upstream temperature sensor 55 and the downstream temperature sensor 56 output an electrical signal corresponding to the exhaust temperature. The upstream NOx sensor 57 and the downstream NOx sensor 58 output an electrical signal corresponding to the NOx concentration of the exhaust. A differential pressure sensor 59 is provided in the exhaust passage 5. The differential pressure sensor 59 outputs an electrical signal corresponding to a difference in exhaust pressure between the upstream and downstream of the SCR filter 51 (hereinafter also referred to as “filter differential pressure”).

The internal combustion engine 1 is also provided with an electronic control unit (ECU) 10. The ECU 10 is a unit that controls the operating state and the like of the internal combustion engine 1. The ECU 10 includes the air flow meter 40, the O ₂ sensor 54, the upstream temperature sensor 55, the upstream NOx sensor 57,
In addition to the downstream temperature sensor 56, the downstream NOx sensor 58, and the differential pressure sensor 59, various sensors such as an accelerator position sensor 7 and a crank position sensor 8 are electrically connected. The accelerator position sensor 7 is a sensor that outputs an electrical signal correlated with an operation amount (accelerator opening) of an accelerator pedal (not shown). The crank position sensor 8 is a sensor that outputs an electrical signal correlated with the rotational position of the engine output shaft (crankshaft) of the internal combustion engine 1. Then, the output signals of these sensors are input to the ECU 10. The ECU 10 estimates the temperature of the SCR filter 51 (hereinafter also referred to as “filter temperature”) based on the output value of the downstream temperature sensor 56. Further, the ECU 10 estimates the flow rate of exhaust gas flowing into the SCR filter 51 (hereinafter sometimes simply referred to as “exhaust gas flow rate”) based on the output value of the air flow meter 40.

  The ECU 10 is electrically connected to various devices such as the fuel injection valve 3, the throttle valve 41, the fuel addition valve 52, and the urea water addition valve 53. The ECU 10 controls the various devices described above based on the output signals of the sensors as described above. For example, the ECU 10 controls the urea water addition amount from the urea water addition valve 53 in order to maintain or adjust the ammonia adsorption amount at the SCR catalyst 51a at a predetermined target adsorption amount. The predetermined target adsorption amount is a value that can secure a desired NOx purification rate in the SCR filter 51 and that can suppress the outflow amount of ammonia from the SCR filter 51 within an allowable range in advance based on experiments and the like. It is a defined value.

(Abnormal diagnosis)
In the present embodiment, the SCR filter 51 and the urea water addition valve 53 are regarded as one exhaust purification system 60, and an abnormality diagnosis is performed to diagnose whether or not an abnormality has occurred in the exhaust purification system 60. In the SCR filter 51, the PM collection function may be broken. In the case where the abnormality of the NOx purification function of the exhaust purification system 60 and the failure of the PM collection function of the exhaust purification system 60 (that is, the failure of the PM collection function of the SCR filter 51) are detected separately, The abnormality diagnosis according to the present embodiment is executed as an abnormality diagnosis for detecting an abnormality in the NOx purification function of the exhaust purification system 60.

  In the abnormality diagnosis device for the exhaust purification system 60 according to this embodiment, a diagnosis is made as to whether an abnormality has occurred in the exhaust purification system 60 based on the NOx purification rate in the SCR filter 51. More specifically, the NOx purification rate in the SCR filter 51 is calculated using the detection value of the downstream NOx sensor 58 provided in the exhaust passage 5 downstream from the SCR filter 51. Note that the NOx concentration of the exhaust gas flowing into the SCR filter 51 (hereinafter sometimes referred to as “inflow exhaust gas”) is detected by an upstream NOx sensor 57 provided in the exhaust passage 5 upstream of the SCR filter 51. . Alternatively, the NOx concentration can be estimated based on the operating state of the internal combustion engine 1 without using the detection value of the upstream NOx sensor 57. Then, the NOx concentration of the exhaust gas flowing out from the SCR filter 51 (hereinafter also referred to as “outflow exhaust gas”) is detected by the downstream NOx sensor 58, and the detected value or estimated value of the NOx concentration of the inflowing exhaust gas, The NOx purification rate in the SCR filter 51 is calculated based on the detected value of the NOx concentration in the exhaust gas. When the NOx purification rate in the SCR filter 51 is equal to or less than a predetermined determination purification rate, it is diagnosed that an abnormality has occurred in the exhaust purification system 60. Here, the predetermined determination purification rate is a value set as a threshold value to be diagnosed as an abnormality in the exhaust purification system 60 when the NOx purification rate in the SCR filter 51 is lowered to the determination purification rate or less. is there.

The predetermined determination purification rate is set based on predetermined setting parameters including the amount of PM accumulation in the wall in the SCR filter 51. The determination purification rate may be calculated based on a map or function set in advance based on experiments or simulations, may be calculated based on the exhaust flow rate and filter temperature, or may be calculated in the SCR catalyst 51a. It may be calculated based on the estimated value of the ammonia adsorption amount. Note that the method for calculating the determination purification rate is not limited to this, and the calculation method using a known technique can be calculated in consideration of the effect of the amount of PM accumulated in the wall. Thus, in the present embodiment, the determination purification rate is calculated based on the PM deposition amount in the wall in the SCR filter 51 together with the predetermined setting parameter described above. This is a reflection of the new knowledge obtained in the present invention in the abnormality diagnosis apparatus according to the present embodiment. That is, based on the tendency that when the amount of PM deposition in the wall in the SCR filter 51 described above is large, the amount of ammonia adsorbed on the SCR catalyst 51a is likely to increase compared to when the amount of PM deposition in the wall is small. The predetermined determination purification rate is corrected according to the PM accumulation amount. Therefore, in the present embodiment, when the PM is not accumulated on the SCR filter 51 (that is, when the PM accumulation amount in the wall is 0), the PM is accumulated on the SCR filter 51. In order to distinguish from the predetermined determination purification rate in the state of being present, the determination purification rate when it is assumed that PM is not deposited on the SCR filter 51 is simply referred to as “predetermined determination purification rate”. In the state where PM is accumulated on the filter 51, the determination purification rate corrected in accordance with the amount of PM deposition in the wall is referred to as a “predetermined predetermined purification rate after correction”.

  On the other hand, as described above, the PM accumulation state in the SCR filter 51 and the increasing tendency of the ammonia adsorption amount in the SCR catalyst 51a have a correlation. And this inventor discovered new knowledge about this correlation. According to this knowledge, the increase in the PM deposition amount in the wall in the SCR filter 51 tends to increase the ammonia adsorption amount in the SCR catalyst 51a, but on the other hand, the surface PM deposition amount in the SCR filter 51 tends to increase. The increase / decrease tends to have little effect on the ammonia adsorption amount on the SCR catalyst 51a.

  The fluctuation tendency of the ammonia adsorption amount in the SCR catalyst 51a with respect to the PM accumulation state in the SCR filter 51 is such that the PM accumulation state in the SCR filter 51 and the saturated adsorption amount of ammonia in the SCR catalyst 51a (adsorption to the SCR catalyst 51a) This is considered to be due to the correlation with the upper limit of the amount of ammonia that can be used. FIG. 2 shows the transition of the saturated adsorption amount and the differential pressure conversion value of the SCR catalyst 51a in accordance with the increase in the total amount of PM deposition in the SCR filter 51 (hereinafter sometimes referred to as “total PM deposition amount”). FIG. 2A and 2B, the horizontal axis represents the total PM deposition amount. 2A, the vertical axis represents the saturated adsorption amount of the SCR catalyst 51a, and in FIG. 2B, the vertical axis represents the differential pressure conversion value. FIG. 2 shows the transition of the saturated adsorption amount and differential pressure conversion value of the SCR catalyst 51a when the filter temperature is constant and PM is deposited on the SCR filter 51 without being oxidized in the middle. Here, the differential pressure conversion value is acquired based on the filter differential pressure and the exhaust gas flow rate, and more specifically is a value obtained by dividing the filter differential pressure detected by the differential pressure sensor 59 by the exhaust gas flow rate.

  In FIG. 2, G1 indicates the saturated PM deposition amount in the in-wall PM deposition. As shown in FIG. 2A, when the total PM deposition amount is G1 or less, the saturated adsorption amount of the SCR catalyst 51a is increased in accordance with the increase in the total PM deposition amount (that is, the increase in the in-wall PM deposition amount). To increase. On the other hand, when the total PM deposition amount is larger than G1, the saturated adsorption amount of the SCR catalyst 51a is not affected by the increase or decrease in the total PM deposition amount (that is, the increase or decrease in the surface PM deposition amount), and the saturated adsorption amount. Becomes a constant amount corresponding to the saturated PM deposition amount in the in-wall PM deposition.

  As shown in FIG. 2B, when the total PM deposition amount is G1 or less, the ratio of the change amount of the differential pressure conversion value to the change amount of the total PM deposition amount is relatively large. On the other hand, when the total PM deposition amount is larger than G1, the ratio of the change amount of the differential pressure conversion value to the change amount of the total PM deposition amount is smaller than that when the total PM deposition amount is G1 or less. This is because, as PM accumulates in the partition wall of the SCR filter 51, the resistance when the exhaust gas passes through the pores increases. However, even if PM accumulates on the surface of the partition wall of the SCR filter 51, the exhaust gas does not flow. This is because the resistance at the time of passing is less affected.

  FIG. 3 is a diagram for explaining the influence of PM deposition on the SCR catalyst 51 on the saturated adsorption amount of the SCR catalyst 51a, regarding the correlation between the saturated adsorption amount of the SCR catalyst 51a and the filter temperature. In FIG. 3, the horizontal axis represents the filter temperature, and the vertical axis represents the saturated adsorption amount of the SCR catalyst 51a. In FIG. 3, a line L <b> 1 indicates the correlation between the saturated adsorption amount and the filter temperature when PM is not deposited on the SCR filter 51. On the other hand, in FIG. 3, the line L <b> 2 indicates the correlation between the saturated adsorption amount and the filter temperature when PM is deposited on the SCR filter 51. At this time, as shown in FIG. 3, the higher the filter temperature, the smaller the saturated adsorption amount of the SCR catalyst 51a. When the filter temperature is high, the PM deposition on the SCR filter 51 becomes the saturated adsorption amount of the SCR catalyst 51a. The effect is small compared to the low filter temperature state.

  Here, when the saturated adsorption amount of the SCR catalyst 51a increases, the ammonia adsorption amount of the SCR catalyst 51a increases as represented by the Langmuir adsorption isotherm. As a result, when other parameters correlated with the NOx purification rate are the same, the NOx purification rate in the SCR filter 51 increases. That is, since the saturated adsorption amount of the SCR catalyst 51a increases as the amount of PM deposition in the wall increases, when the other parameters correlated with the NOx purification rate are the same, the amount of PM deposition in the wall increases. The NOx purification rate in the SCR filter 51 is increased. Here, as described above, when the predetermined determination purification rate is determined to be the determination purification rate when it is assumed that PM is not deposited on the SCR filter 51, it is caused by an increase in the amount of PM deposition in the wall. Even if the NOx purification rate in the SCR filter 51 becomes larger than the determination purification rate, it is not diagnosed that an abnormality has occurred in the exhaust purification system 60. That is, when the other parameters correlated with the NOx purification rate are the same, the NOx calculated based on the detected value or estimated value of the NOx concentration of the inflowing exhaust gas and the detected value of the NOx concentration of the outflowing exhaust gas described above. While the purification rate fluctuates in accordance with the increase or decrease in the amount of PM deposition in the wall, as described above, the predetermined determination purification rate is assumed that PM is not deposited on the SCR filter 51. When the NOx purification rate within the allowable range is not ensured as the exhaust purification system 60 when the NOx purification rate is calculated to a value close to the judgment purification rate. There is a possibility that it is not diagnosed that an abnormality has occurred in the exhaust purification system 60.

  In view of the above, when the predetermined determination purification rate is corrected according to the amount of PM accumulation in the wall, when diagnosing whether or not there is an abnormality in the exhaust purification system 60 than when the determination purification rate is not corrected. Thus, the diagnostic accuracy can be improved. In other words, in the present invention, the abnormality diagnosis device of the exhaust purification system 60 performs the above-described erroneous diagnosis by making the predetermined determination purification rate after correction equal to or greater than the predetermined determination purification rate before correction according to the amount of PM accumulation in the wall. It becomes possible to suppress performing.

  As described above, FIG. 2 shows a case where PM deposited on the SCR filter 51 is not reduced by oxidation. In this case, since the total PM accumulation amount corresponding to the differential pressure conversion value can be uniquely determined, the total PM accumulation amount and the differential pressure conversion value shown in FIG. 2B are obtained from the acquired differential pressure conversion value. It is also considered that the PM accumulation amount in the wall is calculated according to the correlation, and the abnormality diagnosis of the exhaust purification system 60 can be performed using a predetermined determination purification rate corrected according to the PM accumulation amount in the wall. . However, depending on the operating state of the internal combustion engine 1, PM accumulated on the SCR filter 51 may be reduced by being oxidized. In this case, it is conceivable that each of the in-wall PM deposition amount and the surface layer PM deposition amount decreases, and the total PM deposition amount and the differential pressure conversion value do not always have the correlation shown in FIG. That is, the total PM deposition amount corresponding to the differential pressure conversion value cannot be uniquely determined. Therefore, it becomes difficult to calculate the PM deposition amount in the wall from the differential pressure conversion value using the correlation shown in FIG. Therefore, in this embodiment, the PM deposition amount in the wall is estimated based on the estimated value of the total PM deposition amount at the present time (hereinafter also referred to as “estimated PM deposition amount”) and the differential pressure conversion value.

  The estimated PM accumulation amount is obtained without using the detection value of the differential pressure sensor 59. In this embodiment, the estimated PM accumulation amount is obtained by subtracting the PM amount integrated value that decreases due to oxidation per unit time by the SCR filter 51 from the integrated value of the PM amount flowing into the SCR filter 51 per unit time. Can be obtained. The amount of PM flowing into the SCR filter 51 per unit time is related to the operating state (engine rotational speed and engine load) of the internal combustion engine 1. Therefore, if this relationship is obtained in advance by experiment or simulation, the amount of PM flowing into the SCR filter 51 per unit time can be obtained from the operating state of the internal combustion engine 1. The amount of PM that flows into the SCR filter 51 per unit time can also be detected by a sensor. The amount of PM that decreases due to oxidation per unit time by the SCR filter 51 can be calculated based on the filter temperature, the exhaust flow rate, the operating state of the internal combustion engine 1, and the like. Note that the method for calculating the estimated PM deposition amount is not limited to this, and a known technique can also be used.

  FIG. 4 is a model diagram showing the relationship between the total PM accumulation amount and the differential pressure conversion value. FIG. 4 approximates the relationship between the total PM deposition amount and the differential pressure conversion value using a straight line. The solid line shows the locus when PM is deposited on the SCR filter 51 without being oxidized in the PM deposition in the wall, and the alternate long and short dash line is the case where PM is deposited on the SCR filter 51 without being oxidized in the surface layer PM deposition. The trajectory is shown. When PM is not oxidized but is deposited on the SCR filter 51, as described above, first, PM is deposited in the partition wall, and after the PM deposition amount in the partition wall reaches the saturation deposition amount, PM accumulates on the surface. In FIG. 4, when the horizontal axis is X and the vertical axis is Y, the solid line is represented by Y = A1 · X + C1, and the alternate long and short dash line is represented by Y = B1 · X + D1. It should be noted that the locus (solid line) when PM is deposited on the SCR filter 51 without being oxidized in the PM deposition in the wall, and the locus (solid line) when PM is deposited on the SCR filter 51 without being oxidized in the surface layer PM deposition. ) Can be obtained in advance by experiments or simulations. In FIG. 4, the estimated PM accumulation amount at the present time is E1, and the differential pressure conversion value at the present time is F1. That is, the points (E1, F1) are points indicating the estimated PM accumulation amount at the present time and the differential pressure conversion value at the present time.

  Here, when only the PM accumulated in the partition wall of the SCR filter 51 decreases, the relationship between the estimated PM accumulation amount and the differential pressure conversion value changes in parallel with the straight line represented by Y = A1 · X + C1. I think that. On the other hand, when only the PM deposited on the surface of the partition wall of the SCR filter 51 decreases, the relationship between the estimated PM deposition amount and the differential pressure conversion value is parallel to the straight line represented by Y = B1 · X + D1. It is thought to change. For this reason, when the point (E1, F1) deviates from the straight line indicated by Y = B1 · X + D1, the PM deposition amount in the wall is reduced by the oxidation from the saturated PM deposition amount in the PM deposition in the wall. it is conceivable that. At this time, when it is assumed that only PM on the surface of the partition wall is removed from the point (E1, F1), the total PM passes along the line parallel to Y = B1 · X + D1 through the point (E1, F1). It is considered that the deposition amount and the differential pressure conversion value change. A straight line at this time is shown by a two-dot chain line in FIG. 4, and this two-dot chain line can be expressed by an equation of Y = B1 · X + (F1−B1 · E1). The intersection of Y = B1 · X + (F1−B1 · E1) and Y = A1 · X + C1 is the total PM deposition amount and the differential pressure conversion value when it is assumed that all the PM on the surface of the partition wall has disappeared. Is shown. That is, the total PM deposition amount at this time shows only the PM deposition amount in the wall.

In summary, when the estimated PM deposition amount at the present time is E1 and the differential pressure conversion value at the current time is F1, the PM deposition amount in the wall at the current time can be obtained by Expression 1 shown below.
PM deposition amount in the wall = (F1-B1 · E1-C1) / (A1-B1) Equation 1
In FIG. 4, “A1”, “B1”, and “C1” are values that can be obtained in advance, and the values of A1, B1, and C1 are stored in the ROM of the ECU 10. The correlation between the internal PM accumulation amount, the estimated PM accumulation amount and the differential pressure conversion value is stored as a map or a function. A1 corresponds to the first slope in the present invention, B1 corresponds to the second slope in the present invention, C1 corresponds to the reference differential pressure conversion value in the present invention, and E1 represents the total PM deposition amount in the present invention. F1 corresponds to the differential pressure conversion value in the present invention.

  Then, by correcting the predetermined determination purification rate according to the estimated PM accumulation amount, the differential pressure conversion value, and the in-wall PM accumulation amount calculated based on the above formula 1, the determination purification rate is not corrected. In addition, it is possible to improve diagnosis accuracy when diagnosing whether or not an abnormality has occurred in the exhaust purification system 60.

  In the present embodiment, based on the above points, the predetermined determination purification rate is corrected as shown in Equation 4 described later by a predetermined correction coefficient α calculated based on the amount of PM deposition in the wall. As a result, in the predetermined setting parameter for setting the predetermined determination purification rate, when the setting parameter other than the PM deposition amount in the wall is the same, the predetermined determination purification rate is the predetermined value during the PM deposition period in the wall. The correction coefficient α is corrected to a large value according to the increase in the amount of PM deposition in the wall. Further, in the predetermined setting parameter for setting a predetermined determination purification rate, when the setting parameter other than the PM deposition amount in the wall is the same, the PM deposition amount in the wall reaches the saturated PM deposition amount in the PM deposition in the wall. When it is, the predetermined determination purification rate is corrected to a constant value corresponding to the saturated PM accumulation amount by a predetermined correction coefficient α. Details of the method for calculating the correction coefficient α according to the present embodiment will be described below.

As described above, when the predetermined determination purification rate is determined to be the determination purification rate when it is assumed that PM is not deposited on the SCR filter 51, the correction coefficient α is used to indicate an abnormality in the exhaust purification system 60. Based on the PM deposition amount Gw in the wall at the time of diagnosis, it is determined as the following formula 2 and the following formula 3.
If 0 ≦ Gw <G1,
α = f (Gw) (≧ 1) Equation 2
When Gw = G1,
α = const. (> 1) ... Formula 3
Gw: PM deposition amount in the wall G1: Saturated PM deposition amount in the PM deposition in the wall α: Predetermined correction coefficient The correction coefficient α is a predetermined coefficient of 1 or more. More specifically, when the in-wall PM deposition amount Gw is 0, the correction coefficient α is determined to be 1. When the in-wall PM deposition amount Gw is greater than 0 and less than the saturated PM deposition amount G1 in the in-wall PM deposition, the correction coefficient α is determined to be a value greater than 1 as a function of the in-wall PM deposition amount Gw. . Further, when the in-wall PM deposition amount Gw reaches the saturated PM deposition amount G1 in the in-wall PM deposition, the in-wall PM deposition amount Gw is constant regardless of the PM deposition amount in the SCR filter 51 (that is, the surface layer PM deposition). Therefore, the correction coefficient α is determined to be a constant value larger than 1.

FIG. 5A shows that when the predetermined determination purification rate is determined to be the determination purification rate when it is assumed that PM is not deposited on the SCR filter 51, the in-wall PM accumulation amount Gw is the in-wall PM. It is the figure which showed the relationship between in-wall PM deposition amount Gw, filter temperature, and predetermined | prescribed correction coefficient (alpha) in the case where it is smaller than the saturation PM deposition amount G1 in deposition. As described above, during the in-wall PM accumulation period, the saturated adsorption amount of the SCR catalyst 51a increases in accordance with the increase in the in-wall PM accumulation amount, and other parameters correlated with the NOx purification rate are the same. The NOx purification rate in the SCR filter 51 is increased. At this time, since the predetermined determination purification rate is corrected so that the predetermined determination purification rate after correction becomes equal to or higher than the predetermined determination purification rate before correction as shown in Equation 4 described later, the correction coefficient α When the inner PM deposition amount Gw is smaller than the saturated PM deposition amount G1 in the in-wall PM deposition, the inner PM deposition amount Gw is set to a larger value as the in-wall PM deposition amount Gw increases. Note that, as shown in FIG. 3 described above, since the saturated adsorption amount of the SCR catalyst 51a is affected by the filter temperature, the correction coefficient α is set to a smaller value as the filter temperature increases. Also good. The relationship between the in-wall PM accumulation amount Gw, the filter temperature, and the correction coefficient α is obtained in advance by experiments or simulations.

  Further, FIG. 5B shows that the PM accumulation amount Gw in the wall when the predetermined determination purification rate is determined to be the determination purification rate when it is assumed that PM is not deposited on the SCR filter 51. It is the figure which showed the relationship between the total PM deposition amount, filter temperature, and predetermined | prescribed correction coefficient (alpha) in case saturated saturation PM deposition amount G1 in inner PM deposition is reached. When the in-wall PM deposition amount Gw reaches the saturated PM deposition amount G1 in the in-wall PM deposition, the correction coefficient α is increased or decreased in the SCR filter 51 (that is, increase or decrease in the surface layer PM deposition amount). Accordingly, the value is set to a predetermined value corresponding to the saturation PM deposition amount G1 in the PM deposition in the wall as a constant value. Note that this predetermined value may be set to be a small value as the filter temperature increases, and the predetermined value is obtained in advance by experiments or simulations.

(Abnormal diagnosis flow)
FIG. 6 shows an abnormality diagnosis flow of the exhaust purification system according to the present embodiment when the predetermined determination purification rate is determined to be the determination purification rate when it is assumed that PM is not deposited on the SCR filter 51. It is a flowchart to show. In the present embodiment, according to this flow, the ECU 10 performs an abnormality diagnosis of the exhaust purification system 60 during the operation of the internal combustion engine 1.

  In this flow, first, in S101, it is determined whether or not an execution condition for abnormality diagnosis of the exhaust purification system is satisfied. An execution condition for abnormality diagnosis of the exhaust purification system is determined in advance. As the execution conditions, the operating state of the internal combustion engine 1 is a steady state, the downstream NOx sensor 58 is normal, the exhaust flow rate is within a predetermined range, and the filter temperature is within a predetermined range. This can be exemplified. The diagnosis of whether the downstream NOx sensor 58 is normal is performed by the ECU 10 according to a flow different from this flow, and the diagnosis result is stored in the ECU 10. Further, the NOx purification rate in the SCR filter 51 changes according to the ammonia adsorption amount in the SCR filter 51. The ammonia adsorption amount in the SCR filter 51 is affected by the exhaust gas flow rate and the filter temperature. Therefore, when making an abnormality diagnosis of the exhaust purification system based on the NOx purification rate in the SCR filter 51, it is preferable that both the exhaust flow rate and the filter temperature are within a predetermined range.

  If a negative determination is made in S101, the execution of this flow is temporarily terminated. On the other hand, when a positive determination is made in S101, the process of S102 is executed next. In S102, the NOx purification rate Rf in the SCR filter 51 is calculated. Here, as described above, the NOx purification rate Rf in the SCR filter 51 is calculated based on the detected value or estimated value of the NOx concentration of the inflowing exhaust gas and the detected value of the NOx concentration of the outflowing exhaust gas.

Next, in S103, the PM deposition amount Gw in the wall is calculated based on the estimated PM deposition amount and the differential pressure conversion value. Note that the correlation between the PM deposition amount in the wall, the estimated PM deposition amount, and the differential pressure conversion value represented by Equation 1 above is stored in advance in the ROM of the ECU 10 as a map or a function. In S103, the in-wall PM deposition amount Gw is calculated using this function or map. Next, in S104, it is determined whether the in-wall PM deposition amount Gw calculated in S103 is smaller than the saturated PM deposition amount G1 in the in-wall PM deposition. Note that the value of the saturated PM deposition amount G1 in the PM deposition in the wall is stored in advance in the ROM of the ECU 10. If an affirmative determination is made in S104, then in S105, a predetermined correction coefficient α used for correcting a predetermined determination purification rate Rfth in S107, which will be described later, is a function f of the in-wall PM accumulation amount Gw represented by the above equation 2. Calculated by (Gw). Here, in the calculation of the correction coefficient α in S105, a map based on the above equation 2 may be used. As described above, since the saturated adsorption amount of the SCR catalyst 51a is affected by the filter temperature, the filter temperature is read in S105, and the correction coefficient α becomes a small value as the filter temperature increases. It may be calculated. In the ECU 10, the correlation between the PM accumulation amount Gw in the wall as shown in FIG. 5A, the filter temperature, and the correction coefficient α is stored in advance as a map or a function. In S105, the correction coefficient α is calculated using this map or function. On the other hand, if a negative determination is made in S104, then in S106, a predetermined correction coefficient α used for correcting a predetermined determination purification rate Rfth in S107, which will be described later, is calculated to a constant value expressed by the above equation 3. Note that the filter temperature may be read in S106 as well as S105, and the correction coefficient α may be calculated so as to become a smaller value as the filter temperature becomes higher. In the ECU 10, the correction coefficient α corresponding to the saturated PM accumulation amount G1 in the intra-wall PM accumulation as shown in FIG. 5B is stored in advance as a map or a function. In S106, the correction coefficient α is calculated using this map or function.

Next, a predetermined determination purification rate Rfthm after correction is set in S107. The predetermined determination purification rate Rfthm after this correction is calculated by the following equation 4.
Rfthm = Rfth × α (4)
Rfthm: a predetermined determination purification rate after correction Rfth: a predetermined determination purification rate α: a predetermined correction coefficient As described above, it is assumed that the predetermined determination purification rate Rfth has no PM accumulated in the SCR filter 51. When the predetermined purification rate Rfth is determined, the predetermined determination purification rate Rfth is set based on the setting parameter other than the amount of PM deposition in the wall. The value of the determination purification rate Rfth is stored in the ROM of the ECU 10. Equation 4 above calculates a corrected predetermined determination purification rate Rfthm based on the determination purification rate Rfth and a predetermined correction coefficient α determined in accordance with the in-wall PM accumulation amount Gw. As described above, when the filter temperature is the same during the PM deposition period in the wall, the predetermined correction coefficient α becomes a large value as the amount of PM deposition in the wall increases. Further, when the PM deposition amount in the wall reaches the saturation PM deposition amount in the wall PM deposition, the correction coefficient α is a constant value corresponding to the saturation PM deposition amount when the filter temperature is the same.

  Next, in S108, it is determined whether or not the NOx purification rate Rf in the SCR filter 51 calculated in S102 is larger than the corrected predetermined determination purification rate Rfthm calculated in S107. If an affirmative determination is made in S108, then in S109, the exhaust purification system 60 is diagnosed as normal. On the other hand, if a negative determination is made in S108, that is, if the NOx purification rate Rf in the SCR filter 51 is equal to or smaller than the corrected predetermined purification rate Rfthm, then in S110, there is an abnormality in the exhaust purification system 60. Diagnosed. After it is diagnosed that the exhaust purification system 60 is normal in S109, or after it is diagnosed that an abnormality has occurred in the exhaust purification system 60 in S110, the execution of this flow is terminated.

In this embodiment, in the abnormality diagnosis device that diagnoses an abnormality in the exhaust purification system 60 by comparing the NOx purification rate in the SCR filter 51 with a predetermined determination purification rate, a predetermined setting parameter for setting a predetermined determination purification rate In the case where the set parameters other than the PM deposition amount in the wall are the same, during the PM deposition period in the wall, the predetermined determination purification rate is a large value according to the increase in the PM deposition amount in the wall by the predetermined correction coefficient α. It is corrected to. In addition, in the predetermined setting parameter for setting the predetermined determination purification rate, when the setting parameter other than the PM deposition amount in the wall is the same, the PM deposition amount in the wall reaches the saturated PM deposition amount in the PM deposition in the wall. Sometimes, the predetermined determination purification rate is corrected to a constant value corresponding to the saturated PM accumulation amount by a predetermined correction coefficient α. FIG. 7 is a bar graph showing an example of a comparison between the NOx purification rate Rf in the SCR filter 51, the predetermined determination purification rate Rfth, and the corrected predetermined determination purification rate Rfthm in this flow. FIG. 7A shows a comparison between the NOx purification rate Rf in the SCR filter 51 and a predetermined determination purification rate Rfth when it is assumed that PM is not deposited on the SCR filter 51 as described above. . According to FIG. 7A, the NOx purification rate Rf in the SCR filter 51 is a purification rate that should be compared with the predetermined determination purification rate Rfth, and the PM deposition in the wall is greater than the purification rate Rf0 in FIG. 7A. The volume is increased due to the increase in the amount, and is larger than a predetermined determination purification rate Rfth. At this time, if an abnormality diagnosis is performed by comparing the NOx purification rate Rf with a predetermined determination purification rate Rfth, there is an abnormality when the purification rate Rf0 and the predetermined determination purification rate Rfth in FIG. Despite being diagnosed as occurring, the exhaust purification system 60 is erroneously diagnosed as being normal due to the influence of the amount of PM deposition in the wall. On the other hand, FIG. 7B shows a comparison between the NOx purification rate Rf in the SCR filter 51 and the predetermined determination purification rate Rfthm after correction. According to FIG. 7 (b), the NOx purification rate Rf in the SCR filter 51 is smaller than the corrected predetermined judgment purification rate Rfthm corrected according to the amount of PM deposition in the wall, and in S110 of this flow The exhaust gas purification system 60 is diagnosed as having an abnormality. That is, in the present flow, it is possible to prevent the exhaust purification system 60 from being diagnosed as having an abnormality even though the NOx purification rate within the allowable range is not secured. .

  According to the present embodiment, it is possible to improve diagnosis accuracy in the abnormality diagnosis device of the exhaust purification system 60 by correcting the predetermined determination purification rate according to the amount of PM accumulation in the wall.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 4 ... Intake passage 5 ... Exhaust passage 51 ... SCR filter 51a ... SCR catalyst 53 ... Urea water addition valve 58 ... Downstream NOx sensor 59 ... Differential pressure sensor 10・ ECU

Claims (1)

An SCR filter provided in an exhaust passage of an internal combustion engine and having a SCR catalyst supported on a filter having a partition having pores, wherein the SCR catalyst uses NOx in exhaust gas using ammonia as a reducing agent. The SCR filter having a function of reducing, the filter having a function of collecting particulate matter in the exhaust, and
Whether or not an abnormality has occurred in an exhaust gas purification system having an ammonia supply device provided in the exhaust passage upstream of the SCR filter, the ammonia supply device supplying ammonia to the SCR filter. In the abnormality diagnosis device of the exhaust purification system to diagnose,
A NOx sensor provided in the exhaust passage downstream of the SCR filter;
A NOx purification rate calculating unit for calculating a NOx purification rate in the SCR filter using a detection value of the NOx sensor;
Differential pressure conversion for obtaining a differential pressure conversion value, which is a conversion value obtained by converting the difference in exhaust pressure between the upstream and downstream of the SCR filter into a value when the flow rate of exhaust gas flowing into the SCR filter is assumed to be constant. A value acquisition unit;
A total PM deposition amount estimator for estimating the total PM deposition amount when the particulate matter deposition amount in the SCR filter estimated based on parameters other than the differential pressure conversion value is a total PM deposition amount;
When the estimated deposition amount of particulate matter in the pores formed in the partition walls of the SCR filter is the PM deposition amount in the wall, the PM deposition amount estimation unit in the wall that estimates the PM deposition amount in the wall;
A first gradient, a second gradient, and a reference difference, which are parameters related to the correlation between the total PM deposition amount and the differential pressure conversion value when the particulate matter is sequentially deposited on the SCR filter without being oxidized. A pressure conversion value, and the difference per unit increase amount of the total PM deposition amount when particulate matter is deposited in the pores formed in the partition wall of the SCR filter. The total PM deposition at the stage where particulate matter is deposited on the surface of the partition wall of the SCR filter after the increase amount of the pressure conversion value is the first slope and the PM deposition amount in the wall reaches the saturation deposition amount. The amount of increase in the differential pressure conversion value per unit increase amount is the second slope, and the differential pressure conversion value when the total PM deposition amount is 0 is the reference differential pressure conversion value. The first inclination, the second inclination, and the reference differential pressure conversion value Said storage unit for 憶,
A setting unit that sets a predetermined determination purification rate based on a predetermined setting parameter that includes the PM accumulation amount in the wall estimated by the PM accumulation amount estimation unit in the wall;
A diagnostic unit for diagnosing an abnormality of the exhaust purification system by comparing the NOx purification rate in the SCR filter calculated by the NOx purification rate calculation unit and the determination purification rate set by the setting unit; With
The in-wall PM accumulation amount estimation unit is configured to store the total PM accumulation amount estimated by the total PM accumulation amount estimation unit, the differential pressure conversion value acquired by the differential pressure conversion value acquisition unit, and the storage unit. Based on the stored first slope, the second slope, and the reference differential pressure conversion value, the following formula:
PM deposition amount in the wall = (Differential pressure conversion value−Second slope / Total PM deposition amount−Reference differential pressure conversion value) / (First slope−Second slope)
To estimate the amount of PM deposition in the wall,
The time when the detected value of the NOx sensor used for the calculation of the NOx purification rate by the NOx purification rate calculation unit is detected as the sensor detection time,
When the in-wall PM accumulation amount estimated by the in-wall PM accumulation amount estimation unit has not reached the saturation accumulation amount, the setting unit has the same setting parameter other than the in-wall PM accumulation amount, When the amount of PM accumulation in the wall at the sensor detection time is large, the determination purification rate corresponding to the sensor detection time is set to a larger value than when it is small,
When the in-wall PM accumulation amount estimated by the in-wall PM accumulation amount estimation unit has reached a saturated accumulation amount, the setting unit has the same setting parameter other than the in-wall PM accumulation amount, Regardless of the total PM deposition amount at the sensor detection timing, the determination purification rate corresponding to the sensor detection timing is determined according to the PM deposition amount in the wall when the PM deposition amount in the wall reaches the saturation deposition amount. An exhaust gas diagnosis system abnormality diagnosis device that sets a constant value.

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