JP2020045796A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

To provide an exhaust emission control device for an internal combustion engine, for enabling accurate deterioration determination processing even when the temperature of a selective reduction type NOx catalyst changes.SOLUTION: The exhaust emission control device for the internal combustion engine includes: an SCR catalyst; a reductant supply device for supplying a precursor of ammonia or the ammonia as reductant to the upstream of the SCR catalyst; a sensor for detecting ammonia slip concentration; and a determination device for determining that the SCR catalyst has deteriorated when the detected ammonia slip concentration exceeds a determination threshold value, while supplying the SCR catalyst with the reductant whose amount is enough for ammonia slip to develop at the time of catalyst deterioration. The determination device executes the deterioration determination processing when determination conditions that a normal concentration upper limit value falls below a deterioration concentration lower limit value are established. The determination threshold value is equal to or greater the normal concentration upper limit value and smaller than the deterioration concentration lower limit value.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly, to an exhaust gas purification device having a selective reduction type NOx catalyst in an exhaust passage of an internal combustion engine.

  For example, Patent Document 1 discloses an exhaust gas purification device for an internal combustion engine. This exhaust gas purification apparatus includes a selective reduction type NOx catalyst disposed in an exhaust passage, and a reducing agent supply device for supplying urea water, which is a precursor of ammonia as a NOx reducing agent, upstream of the selective reduction type NOx catalyst. Have. Then, the exhaust gas purification device performs a deterioration determination process of the selective reduction type NOx catalyst.

  Specifically, in the above-described deterioration determination process, the amount of ammonia consumed for purifying NOx in the selective reduction NOx catalyst and the amount of ammonia slip, which is the amount of ammonia in exhaust flowing downstream of the selective reduction NOx catalyst, are determined. Is calculated. Then, based on the comparison result between the consumed ammonia amount and the ammonia slip amount, it is determined whether or not the selective reduction type NOx catalyst has deteriorated.

JP 2013-227930 A JP 2011-220142 A

  When the temperature of the selective reduction type NOx catalyst is high, ammonia slip easily occurs even if the catalyst is normal. Conversely, when the temperature of the catalyst is low, ammonia slip is unlikely to occur even if the catalyst has deteriorated. Thus, the manner in which the ammonia slip appears varies depending on the temperature of the NOx selective reduction catalyst. However, the influence of the temperature of the selective reduction type NOx catalyst on the determination is not considered in the deterioration determination process described in Patent Document 1. For this reason, depending on the temperature of the catalyst, there is a possibility that the presence or absence of deterioration of the catalyst is erroneously determined.

  The present invention has been made in view of the above-described problems, and an exhaust gas purification apparatus for an internal combustion engine that is capable of accurately performing a deterioration determination process even when the temperature of a selective reduction type NOx catalyst changes. The purpose is to provide.

An exhaust gas purifying apparatus for an internal combustion engine according to the present invention is disposed in an exhaust passage of the internal combustion engine, and selectively reduces NOx in the exhaust gas with ammonia. A reducing agent supply device that is disposed in the passage and supplies an ammonia precursor or ammonia as a reducing agent into the exhaust passage; and an ammonia slip concentration that is an ammonia concentration in the exhaust flowing downstream of the selective reduction type NOx catalyst. A sensor to be detected and the ammonia slip concentration detected by the sensor while supplying the reducing agent to the selective reduction NOx catalyst in an amount that causes ammonia slip when the selective reduction NOx catalyst is deteriorated. When the value exceeds the determination threshold, the degradation determination process for determining that the selective reduction type NOx catalyst is deteriorated is performed. And a determination device rows for.
The determination device refers to the upper limit of the ammonia slip concentration estimated in consideration of the temperature of the selective reduction NOx catalyst assuming that the selective reduction NOx catalyst is normal, as a normal concentration upper limit. The lower limit of the ammonia slip concentration estimated in consideration of the temperature of the selective reduction type NOx catalyst when it is assumed that the selective reduction type NOx catalyst has deteriorated at a predetermined degree of degradation is the lower limit of the concentration at the time of deterioration. When the condition is satisfied, the deterioration determination process is executed when a determination condition that the upper limit value of the normal concentration is lower than the lower limit value of the deterioration concentration is satisfied.
The determination threshold value is equal to or higher than the normal concentration upper limit value and smaller than the deterioration concentration lower limit value.

  According to the present invention, the process for determining the deterioration of the selective reduction type NOx catalyst is executed when the determination condition that the upper limit value of the normal concentration is lower than the lower limit value of the concentration when deteriorated is satisfied. That is, in the deterioration determination process, if the selective reduction type NOx catalyst is deteriorated, an ammonia slip concentration higher than the upper limit of the ammonia slip concentration (normal concentration upper limit) that can occur when a normal catalyst is assumed is obtained. It will be performed under the circumstances considered to be performed. Further, the normal concentration upper limit value and the deteriorated concentration lower limit value are respectively estimated in consideration of the temperature of the selective reduction type NOx catalyst.

  In addition, in the deterioration determination process according to the present invention, when the above-described determination condition is satisfied, when the detected ammonia slip concentration exceeds a determination threshold value that is equal to or higher than the normal concentration upper limit value and smaller than the deterioration concentration lower limit value, It is determined that the selective reduction type NOx catalyst has deteriorated. According to such processing, unless the ammonia slip concentration higher than the normal concentration upper limit is detected, it is possible to prevent the deterioration determination from being performed when the selective reduction type NOx catalyst is normal. In addition, unless the ammonia slip concentration equal to or higher than the lower limit value at the time of deterioration is detected, it is possible to prevent the normal determination from being performed when the selective reduction type NOx catalyst is deteriorated.

  Therefore, according to the deterioration determination processing of the present invention, it is possible to determine the presence or absence of deterioration of the selective reduction NOx catalyst using an appropriate determination threshold at an appropriate determination time while considering the temperature change of the selective reduction NOx catalyst. Become like For this reason, even if the temperature of the selective reduction type NOx catalyst changes, the deterioration determination process can be performed accurately.

FIG. 1 is a diagram for explaining a system configuration example of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention. It is a diagram showing the relationship between the SCR bed temperature and NH ₃ adsorption of normal catalyst. It is a diagram showing the relationship between the SCR bed temperature and NH ₃ adsorption amount of deteriorated catalyst. It is a block diagram for explaining an example of a technique of estimating the amount of NH ₃ adsorption. 5 is a time chart showing an example of the behavior of the NH ₃ slip concentration accompanying the execution of the OBD active addition in a normal state. OBD active SCR bed temperature after performing the addition is a time chart showing an example of the behavior of NH ₃ slip concentration in situations that change. 5 is a time chart for explaining a characteristic portion (a method of selecting a determination time and calculating a determination threshold) of the deterioration determination process according to the embodiment of the present invention. 4 is a flowchart illustrating a routine related to a process for determining deterioration of the selective reduction type NOx catalyst according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the embodiments described below, when referring to the number, quantity, amount, range, etc. of each element, the stated number is used, unless otherwise specified or specified in principle. However, the present invention is not limited to this. In addition, structures, steps, and the like described in the embodiments described below are not necessarily essential to the present invention, unless otherwise specified or clearly specified in principle.

1. 1. System Configuration Example FIG. 1 is a diagram for describing a system configuration example of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention. The system shown in FIG. 1 includes a compression ignition type internal combustion engine (diesel engine) 10 as an example. The internal combustion engine 10 is mounted on, for example, a vehicle. An exhaust passage 12 communicates with each cylinder of the internal combustion engine 10. In the exhaust passage 12, a diesel oxidation catalyst (DOC) 14, a diesel particulate filter (DPF) 16, and a selective reduction NOx catalyst (SCR (Selective Catalytic Reduction) catalyst) 18 are arranged in this order from the upstream side.

  The DOC 14 is configured to oxidize unburned gas such as HC in the exhaust gas. The DPF 16 is a member that traps particulate matter (PM) in exhaust gas, and is made of, for example, porous ceramic. The DPF 16 carries a catalyst for promoting PM oxidation. A fuel addition valve 20 for supplying unburned fuel to the DOC 14 and the DPF 16 is provided upstream of the DOC 14 (exhaust manifold).

In the exhaust passage 12 downstream of the DPF 16 and upstream of the SCR catalyst 18, a urea addition valve 22 which is an example of a "reducing agent supply device" is provided. The urea addition valve 22 is an addition valve that supplies urea water, which is a precursor of ammonia (NH ₃ ), into the exhaust passage 12, and is connected to a urea water tank (not shown). Urea water injected from the urea addition valve 22 into the exhaust passage 12 is hydrolyzed into NH ₃ and supplied to the SCR catalyst 18. The SCR catalyst 18 reduces nitrogen oxides (NOx) in the exhaust gas by using the supplied urea water-derived NH ₃ as a reducing agent. In order to reduce NOx, ammonia itself may be added instead of urea water.

  A first NOx sensor 24 is provided in the exhaust passage 12 upstream of the DOC 14. Further, a second NOx sensor 26 and an exhaust gas temperature sensor 28 are provided in the exhaust passage 12 downstream of the DPF 16 and upstream of the SCR catalyst 18. The NOx sensors 24 and 26 are used as examples of sensors for detecting the NOx concentration in the exhaust gas discharged from each cylinder and the NOx concentration in the exhaust gas flowing into the SCR catalyst 18, respectively. The exhaust gas temperature sensor 28 outputs a signal corresponding to the exhaust gas temperature, and is used as an example of a sensor for estimating the temperature of the SCR catalyst 18 (hereinafter also referred to as “SCR bed temperature”) in the present embodiment.

Further, a third NOx sensor 30 is provided in the exhaust passage 12 downstream of the SCR catalyst 18. The third NOx sensor 30 outputs a signal corresponding to the NOx concentration in the exhaust gas flowing downstream of the SCR catalyst 18, and in the present embodiment, a sensor for detecting the NH ₃ concentration in the exhaust gas flowing downstream of the SCR catalyst 18 ( This is used as an example of the “sensor” according to the present invention). This NH ₃ concentration may be detected using an NH ₃ sensor instead of the _third NOx sensor 30. Further, an air flow sensor 34 is provided near the inlet of the intake passage 32 of the internal combustion engine 10. The air flow sensor 34 outputs a signal corresponding to the flow rate of air flowing through the intake passage 32, and is used as an example of a sensor for detecting the flow rate of exhaust gas passing through the SCR catalyst 18 in the present embodiment.

  The system shown in FIG. 1 further includes an electronic control unit (ECU) 40. Various sensors (not shown) mounted on the internal combustion engine 10 are electrically connected to the ECU 40 together with the NOx sensors 24, 26, 30, the exhaust gas temperature sensor 28, and the air flow sensor 34. The ECU 40 is electrically connected to various actuators (not shown) for controlling the operation of the internal combustion engine 10 together with the fuel addition valve 20 and the urea addition valve 22.

The ECU 40 has a processor 40a and a memory 40b. The memory 40b stores programs and maps for controlling the various actuators described above. Further, various information is input to the ECU 40 from the various sensors described above. The processor 40a reads the program from the memory and executes the program while using the information to determine the operation amount of each actuator. As a result, the ECU 40 functions as a control device for the internal combustion engine 10.

2. SCR catalyst deterioration determination process 2-1. Basic Configuration of Deterioration Determination Process The above-described ECU 40 also functions as an example of a “determination device” that performs “deterioration determination process” for the SCR catalyst 18. That is, the ECU 40 has an OBD (On-Board Diagnostics) function of self-diagnosing whether or not the SCR catalyst 18 has deteriorated. FIG. 2 is a diagram showing the relationship between the SCR bed temperature of the normal catalyst and the NH ₃ adsorption amount, and FIG. 3 is a diagram showing the relationship between the SCR bed temperature of the deteriorated catalyst and the NH ₃ adsorption amount. Here, the “normal catalyst” means a new SCR catalyst (that is, the purification performance has not deteriorated), and the “deteriorated catalyst” means that the purification performance deteriorates at a predetermined detection target deterioration degree. The resulting SCR catalyst is meant.

The curve shown by the solid line in FIG. 2 represents the maximum amount of adsorption, which is the upper limit of NH _{3 that} can be adsorbed by the normal catalyst. On the other hand, the curve shown by the solid line in FIG. 3 indicates the maximum adsorption amount, which is the upper limit of the NH ₃ adsorption amount that can be adsorbed by the deteriorated catalyst. NH ₃ slip NH ₃ is a phenomenon desorbed from the SCR catalyst 18, NH ₃ adsorption is considered to be expressed when exceeding the curve in each of the normal catalyst or deteriorated catalyst.

In the deterioration determination process, the ECU 40 converts the NH ₃ into the SCR at an amount determined to cause NH ₃ slip only when the SCR catalyst 18 is deteriorated (hereinafter, referred to as “active supply NH ₃ amount A”). “OBD active addition” supplied to the catalyst 18 is executed. Then, the ECU 40 determines whether or not the SCR catalyst 18 has deteriorated based on whether or not NH ₃ slip appears as a result of performing the OBD active addition.

More specifically, the active supply NH ₃ amount A, which is the supply amount of NH ₃ by the OBD active addition, is a larger (excess) amount than the NH ₃ amount supplied for the purpose of purifying NOx. Also, as shown in FIGS. 2 and ₃ , the NH ₃ adsorption amount changes according to the SCR bed temperature, so the active supply NH ₃ amount A is calculated as a value corresponding to the SCR bed temperature. In the present embodiment, the OBD active addition is performed, for example, by supplying an amount of urea water that satisfies the active supply NH ₃ amount A.

When the SCR catalyst 18 is a normal catalyst, as shown in FIG. 2, since the maximum adsorption amount is large, the difference between the current estimated NH ₃ adsorption amount and the maximum adsorption amount becomes large. Therefore, even if the NH ₃ active supply NH ₃ amount A is supplied, a situation exceeding the maximum adsorption amount as illustrated in FIG. 2 is unlikely to occur, NH ₃ slip is considered not expressed. On the other hand, when the SCR catalyst 18 is a deteriorated catalyst, as shown in FIG. 3, since the maximum adsorption amount is small, the difference between the current estimated NH ₃ adsorption amount and the maximum adsorption amount is small. For this reason, if NH ₃ is supplied in an amount larger than the amount of NH ₃ consumed in NOx purification, NH ₃ slip is likely to occur. Therefore, as illustrated in FIG. 3, OBD by the active addition when the NH ₃ active supply NH ₃ amount A is supplied, NH ₃ adsorption amount of deteriorated catalyst reaches the maximum amount of adsorption, NH ₃ slip expression I do. As described above, whether or not the SCR catalyst 18 has deteriorated can be determined based on whether or not NH ₃ slip occurs downstream of the SCR catalyst 18 as a result of performing the OBD active addition.

When the NH ₃ slip occurs, the slipped NH ₃ flows out downstream of the SCR catalyst 18. Therefore, presence or absence of expression of the NH ₃ slip, NH ₃ concentration in exhaust gas discharged to the downstream side of the SCR catalyst 18 (NH ₃ slip concentration) can be determined based on whether greater than the determination threshold value.

In addition, as shown in FIGS. 2 and 3, as the SCR bed temperature increases, the NH ₃ adsorption amount decreases. Therefore, when the same amount of NH ₃ is supplied, the NH ₃ slip toward the downstream of the SCR catalyst 18 is more likely to occur in an environment where the SCR bed temperature is higher. As can be seen by comparing FIGS. 2 and 3, the magnitude of the change in the NH ₃ adsorption amount according to the change in the SCR bed temperature is larger in the normal catalyst than in the deteriorated catalyst.

2-2. Execution Condition of OBD Active Addition The curve shown by the broken line in FIG. 2 corresponds to the lower limit of the NH ₃ adsorption amount at which the NH ₃ slip does not appear when the SCR catalyst 18 is normal. More specifically, this lower limit corresponds to the lower limit of the maximum adsorption amount (solid line) obtained when an error that can occur in a normal catalyst is taken into account. Therefore, if the SCR catalyst 18 is normal, it is considered that the NH ₃ slip does not occur unless the value exceeds the lower limit.

The curve shown by the broken line in FIG. 3 corresponds to the upper limit value of the NH ₃ adsorption amount at which the NH ₃ slip surely appears when the SCR catalyst 18 is deteriorated. More specifically, this upper limit value corresponds to the upper limit value of the maximum adsorption amount (solid line) obtained when an error that may occur in the deteriorated catalyst is added. The above-mentioned active supply NH ₃ amount A is set to a value that is surely larger than the difference between the current estimated NH ₃ adsorption amount and the upper limit value (broken line). Thereby, when the SCR catalyst 18 has deteriorated, NH ₃ slip can be reliably generated by the OBD active addition.

Figure "limit active supply NH ₃ amount B" in 2 corresponds to the difference between the adsorbed NH ₃ amount and the lower limit at the current SCR bed temperature T1 (broken line). The limit active supply NH ₃ amount B means an upper limit value within the range of the active supply NH ₃ amount A where normal determination is made without occurrence of NH ₃ slip if the SCR catalyst 18 is normal. In other words, when more NH ₃ is supplied than the limit active supply NH ₃ amount B, NH ₃ slip may occur even with a normal catalyst. Therefore, in the deterioration determination process of the present embodiment, the fact that the active supply NH ₃ amount A is larger than the limit active supply NH ₃ amount B (active supply NH ₃ amount A <limit active supply NH ₃ amount B) is the reason for the OBD active addition. Execution condition. Thereby, when the SCR catalyst 18 is normal, it is possible to avoid erroneous determination that deterioration has occurred.

2-3. Method for Estimating NH ₃ Adsorption Amount In order to determine whether or not the above-described execution conditions of OBD active addition (active supply NH ₃ amount A <limit active supply NH ₃ amount B) are satisfied, the NH ₃ adsorption amount of the SCR catalyst 18 is determined. Need to figure out. The calculation (estimation) of the NH ₃ adsorption amount is performed on-board by the ECU 40.

FIG. 4 is a block diagram for explaining an example of a technique for estimating the NH ₃ adsorption amount. According to the present estimation method, the NH ₃ adsorption amount is calculated by subtracting the consumed NH ₃ amount and the desorbed NH ₃ amount from the supplied NH ₃ amount as shown in the following equation (1).
Adsorbed NH ₃ amount = supply NH ₃ amount - consumed amount of NH ₃ - desorption amount of NH ₃ (1)

First, the supply NH ₃ amount in the equation (1) is calculated as a value corresponding to the amount of urea water added by the urea addition valve 22. The amount of urea water added is determined to be a value corresponding to the amount of NH ₃ supplied for the purpose of purifying NOx when purifying NOx using the SCR catalyst 18. Is determined to be a value corresponding to the above-described active supply NH ₃ amount A.

Next, the consumed NH ₃ amount is calculated to be a value corresponding to the SCR inflow NOx amount and the NOx purification rate by the SCR catalyst 18. The SCR inflow NOx amount is the amount of NOx flowing into the SCR catalyst 18. NOx purification ratio is, for example, amount of air and (SCR flow rate of the exhaust gas flowing into the catalyst 18), and the SCR bed temperature, NH ₃ adsorption (previous value stored in the memory 40b) and NOx purification rate map as arguments to Can be calculated using

More specifically, the NOx purification rate differs depending on whether the SCR catalyst 18 is normal or deteriorated. Therefore, in the present estimation method, both the case where the SCR catalyst 18 is a normal catalyst and the case where the SCR catalyst 18 is a deteriorated catalyst are assumed, and maps of the NOx purification rates are individually prepared according to the characteristics of the normal catalyst and the deteriorated catalyst. You. ECU40 uses the respective maps, the consumption NH ₃ amount when the SCR catalyst 18 is assumed to be normal, calculates it and consume NH ₃ amount when assuming that the deteriorated respectively.

Next, the desorbed NH ₃ amount (NH ₃ slip amount) is calculated to be a value corresponding to the air amount and the desorbed NH ₃ concentration (NH ₃ slip concentration). Here, the desorbed NH ₃ concentration, the SCR bed temperature, and the NH ₃ adsorption amount have a correlation. More specifically, if the NH ₃ adsorption amount is the same, the desorbed NH ₃ concentration increases as the SCR bed temperature increases, and if the SCR bed temperature is the same, the desorbed NH ₃ increases as the NH ₃ adsorption amount increases. The amount also increases. The specific correlation can be obtained in advance by an experiment or the like. Here, such a correlation by using as an example, the desorption amount of NH ₃ is SCR and bed temperature, NH ₃ adsorption desorption NH ₃ that the (previous value stored in the memory 40b) as an argument It is calculated using the density map. Then, by multiplying the amount of air against desorbed NH ₃ amount calculated in this manner, it is possible to calculate the desorbed NH ₃ amount.

Like the NOx purification rate described above, the desorbed NH ₃ concentration also differs depending on whether the SCR catalyst 18 is normal or deteriorated. Therefore, in the present estimation method, both when the SCR catalyst 18 is when the abnormal deteriorated catalyst is normal catalyst is assumed, leaving NH ₃ concentration map according to the specifics of each of the normal catalyst and abnormal deteriorated catalyst is individually Be prepared for. ECU40 uses the respective maps, SCR catalyst 18 is calculated respectively desorption NH ₃ concentration of assuming to be normal, and a desorption NH ₃ concentration when it is assumed to be degraded .

The NH ₃ adsorption amount is calculated by substituting the supplied NH ₃ amount, the consumed NH ₃ amount, and the desorbed NH ₃ amount calculated as described above into the above equation (1). In the deterioration determination process of the present embodiment, the calculated NH ₃ adsorption amount is used as an estimated value of the NH ₃ adsorption amount.

2-4. Problems Regarding Deterioration Determination of SCR Catalyst As described above, the “deterioration determination process” of the present embodiment uses the OBD active addition that is performed so that NH ₃ slip appears only when the SCR catalyst 18 has deteriorated. Then, it is executed based on whether or not the NH ₃ slip concentration has exceeded the determination threshold value. Here, as exemplified below with reference to FIGS. 5 and 6, the manner in which NH ₃ slip occurs depends on the SCR bed temperature (more specifically, the SCR bed after execution of the OBD active addition for deterioration determination). Temperature change).

FIG. 5 is a time chart showing an example of the behavior of the NH ₃ slip concentration accompanying the execution of the OBD active addition in a normal state (a condition where the change in the SCR bed temperature is relatively gentle). In the example shown in FIG. 5, the OBD active addition is executed when the OBD active addition execution flag is ON. The amount of urea water added by OBD active addition (active supply NH ₃ amount A) is calculated based on the SCR bed temperature when the OBD active addition execution flag is turned ON and the estimated NH ₃ adsorption amount.

As described above with reference to FIGS. 2 and _{3, the} amount of NH ₃ adsorbed on the SCR catalyst 18 changes depending on the SCR bed temperature. For this reason, the amount of NH ₃ adsorption expressed by the NH ₃ slip changes depending on the SCR bed temperature. In the example shown in FIG. 5, the change in vehicle speed before and after the calculation of the amount of urea water added by OBD active addition is relatively gradual, and as a result, the change in the SCR bed temperature is also relatively gradual. Under circumstances in this way is SCR bed temperature is stable, is considered when the normal SCR catalyst 18 without NH ₃ slip expression, whereas, NH ₃ slip express the SCR catalyst 18 is deteriorated . Therefore, the presence or absence of deterioration of the SCR catalyst 18 can be accurately determined by the deterioration determination processing of the present embodiment.

FIG. 6 is a time chart showing an example of the behavior of the NH ₃ slip concentration under the situation where the SCR bed temperature changes after the OBD active addition is performed. More specifically, in the example shown in FIG. 6, the SCR bed temperature sharply rises with the rapid acceleration after the OBD active addition is performed. In such an example, if the addition amount of urea water (active supply NH ₃ amount A) according to the SCR bed temperature at the time when the OBD active addition execution flag is turned ON is used, after the SCR bed temperature sharply rises, NH _{3 is used.} Slip easily occurs. For this reason, in the example shown in FIG. 6, not only when the SCR catalyst 18 has deteriorated, but also when it is normal, NH ₃ slip has developed. In such an example, even if the SCR catalyst 18 is normal, an erroneous determination that the SCR catalyst 18 has deteriorated is made.

Further, contrary to the example shown in FIG. 6, under the situation where the SCR bed temperature suddenly drops after the execution of the OBD active addition, the NH ₃ slip does not appear even if the SCR catalyst 18 is deteriorated. There is. In such an example, even if the SCR catalyst 18 has deteriorated, an erroneous determination that the SCR catalyst 18 is normal is made.

2-5. FIG. 7 is a time chart for explaining a characteristic portion (a method of selecting a determination time and calculating a determination threshold) of the deterioration determination process according to the embodiment of the present invention. FIG. 7 shows five estimated NH ₃ slip concentration waveforms 1 to 5 in a situation where the OBD active addition is performed (OBD active addition execution flag ON).

Waveform 1 corresponds to a waveform of the estimated NH ₃ slip concentration when a “probable error” is not taken into consideration for a deteriorated catalyst having a predetermined detection target deterioration degree. Such a waveform 1 is obtained by calculating the estimated NH ₃ slip concentration using the estimation method shown in FIG. 4 while using the map for the deteriorated catalyst. Here, the “possible error” specifically means an error in the amount of urea water added by the urea addition valve 22, an error in the NOx amount flowing into the SCR, and the like.

Waveform 2 corresponds to the waveform of the lower limit value of the estimated NH ₃ slip concentration that can surely occur when the “probable error” is considered for the deteriorated catalyst. Such a waveform 2 is obtained by correcting the estimated NH ₃ slip concentration calculated by the estimation method shown in FIG. 4 by a predetermined correction amount based on the “possible error” while using the map for the deteriorated catalyst. . The NH ₃ slip concentration of this waveform 2 corresponds to an example of the “concentration lower limit at the time of deterioration” according to the present invention.

Waveform 3 corresponds to a waveform of the estimated NH ₃ slip concentration when a “probable error” is not taken into consideration for a normal catalyst. Such a waveform 3 is obtained by calculating the estimated NH ₃ slip concentration using the estimation method shown in FIG. 4 while using the map for the normal catalyst. Therefore, the estimated NH ₃ slip concentration becomes substantially zero.

Waveform 4 corresponds to the waveform of the upper limit of the estimated NH ₃ slip concentration that can occur when a “probable error” is considered for a normal catalyst. Such a waveform 4 is obtained by correcting the estimated NH ₃ slip concentration calculated by the estimation method shown in FIG. 4 by a predetermined correction amount based on the “possible error” using a map for a normal catalyst. . The NH ₃ slip concentration of this waveform 4 corresponds to an example of the “normal concentration upper limit value” according to the present invention.

  In view of the above-described problem, the deterioration determination process according to the present embodiment is executed when the “determination condition” that the above “normal upper limit of concentration” is lower than the “lower limit of concentration during deterioration” is satisfied. In the “judgment time” shown in FIG. 7, the value of the waveform 2 (deterioration catalyst; considering possible errors) (that is, the lower concentration limit at the time of degradation) is changed to the waveform 4 (normal catalyst; This corresponds to a period in which the value is larger than the value of “consideration of a possible error” (that is, the upper limit value of the concentration at normal time). Therefore, the deterioration determination process is executed when the determination time in FIG. 7 has come.

Further, a waveform 5 in FIG. 7 corresponds to a waveform of an average value of the density lower limit value at the time of deterioration of the waveform 2 and the density upper limit value at the time of normality of the waveform 4. In the present embodiment, the value of the NH ₃ slip concentration (the above average value) of the waveform 5 at the above determination time is used as a determination threshold value for the deterioration determination process. Then, if the (actual) NH ₃ slip concentration detected by the third NOx sensor 30 exceeds this determination threshold, it is determined that the SCR catalyst 18 has deteriorated.

  If the above determination time is not satisfied due to a large change in the SCR bed temperature after the execution of the OBD active addition, the deterioration determination processing is not performed.

2-6. FIG. 8 is a flowchart showing a routine related to a deterioration determination process of the SCR catalyst 18 according to the embodiment of the present invention. This routine is repeatedly executed while the internal combustion engine 10 is operating.

In the routine shown in FIG. 8, first, ECU 40 calculates the current (estimated) NH ₃ adsorption amount of the SCR catalyst 18 (step S100). Specifically, using the estimation method shown in FIG. 4, the estimated amount of adsorbed NH ₃ is calculated both when the catalyst is normal and when the catalyst is deteriorated.

Next, the ECU 40 determines whether or not the preliminary condition regarding the execution of the OBD active addition is satisfied (step S102). This preliminary condition is that no abnormality of the components related to the deterioration determination is detected, the battery voltage of the vehicle is equal to or higher than a predetermined voltage value of the ECU 40, and the catalyst control mode is the normal mode (PM regeneration execution The atmospheric pressure is equal to or higher than a predetermined value necessary for ensuring the reliability of the sensor used for the deterioration determination, the NOx sensors 26 and 30 used for the deterioration determination are in an active state, and one trip is performed. And that the OBD active addition and the deterioration determination are not performed (to ensure that the intended NH ₃ slip appears during the deterioration).

  If the determination result of step S102 is negative, the ECU 40 ends this routine. On the other hand, if the ECU 40 determines that the preliminary condition is satisfied in step S102, the process proceeds to step S104.

In step S104, the ECU 40 determines whether or not the OBD active addition can be performed. Specifically, it is determined whether or not the above-described execution conditions of the OBD active addition (active supply NH ₃ amount A <limit active supply NH ₃ amount B) are satisfied. If the result of the determination in step S104 is negative, the ECU 40 ends this routine.

  If the ECU 40 determines in step S104 that the execution condition of the OBD active addition is satisfied, the process proceeds to step S106. In step S106, the ECU 40 executes the above-described OBD active addition.

  Next, the ECU 40 determines whether or not the above-described determination condition (normal concentration upper limit value <deterioration concentration lower limit value) is satisfied (step S108). As a result, when the result of the determination in step S108 is negative (that is, when the determination time shown in FIG. 7 has not come), the ECU 40 ends this routine.

On the other hand, when ECU 40 determines that the determination condition is satisfied in step S108 (that is, when the determination time has come), the process proceeds to step S110. In step S110, the ECU 40 determines whether the (actual) NH ₃ slip concentration is equal to or less than the above-described determination threshold.

If the determination result of step S110 is affirmative (NH ₃ slip concentration ≦ determination threshold), the ECU 40 determines that the SCR catalyst 18 is normal (step S112). On the other hand, if the determination result of step S110 is negative (NH ₃ slip concentration> determination threshold), the ECU 40 determines that the SCR catalyst 18 has deteriorated (step S114).

3. Effect As described above, the deterioration determination process of the present embodiment is executed when the “determination condition” that the above “normal upper limit of density” is lower than the “lower limit of density during deterioration” is satisfied. In other words, the deterioration determination process, if Once the SCR catalyst 18 is deteriorated, in a situation where a high NH ₃ slip concentration than the upper limit value is considered to be obtained of the NH ₃ slip concentrations that may occur during normal catalyst contemplated Will be executed. In calculating the estimated NH ₃ slip concentration, which is the basis for calculating the normal concentration upper limit value and the degradation concentration lower limit value, the influence of the SCR bed temperature is sequentially determined by using the estimation method described with reference to FIG. Be considered.

In addition, in the deterioration determination process of the present embodiment, when the above “determination condition” is satisfied, the (actual) NH ₃ slip concentration is an average value of the lower concentration limit during deterioration and the upper limit concentration during normal operation. If it exceeds the “determination threshold value”, it is determined that the SCR catalyst 18 has deteriorated. According to such processing, a determination threshold larger than the normal concentration upper limit value is used, so that it is possible to prevent the deterioration determination from being performed when the SCR catalyst 18 is normal. In addition, since a determination threshold smaller than the lower limit of the concentration at the time of deterioration is used, it is possible to prevent the normal determination from being performed when the SCR catalyst 18 is deteriorated.

  Therefore, according to the deterioration determination process of the present embodiment, it is possible to determine the presence or absence of the deterioration of the SCR catalyst 18 using an appropriate determination threshold at an appropriate determination time while considering a change in the SCR bed temperature. Therefore, even if the SCR bed temperature changes, the deterioration determination process can be performed with high accuracy.

  By the way, in the above-described first embodiment, an average value of the lower limit value of the concentration at the time of deterioration and the upper limit value of the concentration at the normal time is used as an example of the “determination threshold value” used in the deterioration determination process. However, the “determination threshold value” according to the present invention may be any value other than the above average value as long as the value is within the range of being equal to or higher than the normal concentration upper limit value and less than the deterioration concentration lower limit value. Good. Further, the determination threshold may be set as follows, for example. That is, when the integrated traveling distance of the vehicle is short (that is, when the SCR catalyst 18 is in a state close to a new product), the normal concentration upper limit value is used as the determination threshold value. The determination threshold value may be changed so as to approach the lower density limit.

Reference Signs List 10 internal combustion engine 12 exhaust passage 18 selective reduction type NOx catalyst (SCR catalyst)
22 Urea addition valves 24, 26, 30 NOx sensor 28 Exhaust temperature sensor 34 Air flow sensor 40 Electronic control unit (ECU)

Claims (1)

A selective reduction type NOx catalyst disposed in an exhaust passage of an internal combustion engine and reducing NOx in exhaust gas with ammonia;
A reducing agent supply device disposed in the exhaust passage upstream of the selective reduction type NOx catalyst, for supplying a precursor of ammonia or ammonia as a reducing agent into the exhaust passage;
A sensor for detecting an ammonia slip concentration that is an ammonia concentration in exhaust gas flowing downstream of the selective reduction type NOx catalyst;
The ammonia slip concentration detected by the sensor exceeds a determination threshold value while supplying the reducing agent to the selective reduction NOx catalyst in an amount that causes an ammonia slip when the selective reduction NOx catalyst is deteriorated. A determination device for performing a deterioration determination process for determining that the selective reduction type NOx catalyst has deteriorated in the case;
An exhaust purification device for an internal combustion engine comprising:
The determination device,
The upper limit value of the ammonia slip concentration estimated in consideration of the temperature of the selective reduction type NOx catalyst when it is assumed that the selective reduction type NOx catalyst is normal is referred to as a normal concentration upper limit value, When the lower limit value of the ammonia slip concentration estimated in consideration of the temperature of the selective reduction type NOx catalyst when assuming that the NOx catalyst has deteriorated at a predetermined deterioration degree is referred to as a lower concentration limit at the time of deterioration,
Performing the deterioration determination process when the determination condition that the normal concentration upper limit is lower than the deterioration concentration lower limit is satisfied;
The exhaust gas purifying apparatus for an internal combustion engine, wherein the determination threshold value is equal to or more than the normal concentration upper limit value and less than the deterioration concentration lower limit value.

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