JP2020060121A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

To provide an exhaust emission control device of an internal combustion engine which can accurately determine deterioration even if a degree of the deterioration of a selective reduction type NOx catalyst is high.SOLUTION: An exhaust emission control device of an internal combustion engine comprises: an SCR catalyst; a reductant supply device for supplying a precursor of ammonia or ammonia to an upstream side of the SCR catalyst as a reductant; a sensor for detecting an ammonia slip concentration; and a determination device for performing deterioration determination processing for determining the presence or absence of the deterioration of the SCR catalyst on the basis of the detected ammonia slip concentration while supplying the reductant of an amount at which an ammonia slip appears to the SCR catalyst when it is assumed that the SCR catalyst is deteriorated. The determination device calculates an integrated value of the ammonia slip amount from the SCR catalyst during a prescribed integration period after a start of the supply of the reductant, and determines that the SCR catalyst is deteriorated when the calculated integrated value is larger than a determination threshold.SELECTED DRAWING: Figure 7

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 provided with a selective reduction type NOx catalyst in an exhaust passage of the internal combustion engine.

  For example, Patent Document 1 discloses an exhaust gas purification device for an internal combustion engine. This exhaust gas purification device includes a selective reduction type NOx catalyst arranged in an exhaust passage and a reducing agent supply device that supplies urea water, which is a precursor of ammonia as a reducing agent of NOx, upstream of the selective reduction type NOx catalyst. I have it. Then, the exhaust emission control device executes a deterioration determination process of the selective reduction type NOx catalyst.

  Specifically, in the above-described deterioration determination process, the amount of consumed ammonia required for purifying NOx in the selective reduction NOx catalyst and the amount of ammonia slip, which is the amount of ammonia in the exhaust flowing downstream of the selective reduction NOx catalyst, are determined. It is calculated. Then, the presence or absence of deterioration of the NOx selective reduction catalyst is determined based on the result of comparison between the amount of consumed ammonia and the amount of ammonia slip.

JP, 2013-227930, A JP, 2005-014213, A

  In an exhaust gas purification apparatus for an internal combustion engine, which includes a selective reduction type NOx catalyst and a reducing agent supply device, as in the exhaust gas purification apparatus for an internal combustion engine described in Patent Document 1, the following deterioration determination is made for a selective reduction type NOx catalyst. It is possible to perform processing. That is, the ammonia slip concentration detected by the sensor at a predetermined determination time is supplied to the selective reduction type NOx catalyst while supplying the reducing agent in an amount that causes ammonia slip when the selective reduction type NOx catalyst is deteriorated. It is conceivable to execute the deterioration determination process for determining that the selective reduction type NOx catalyst is deteriorated when is greater than the determination threshold.

  Here, if the degree of deterioration of the NOx selective reduction catalyst becomes high, ammonia slip may occur early after addition of the reducing agent for deterioration judgment. Therefore, if the ammonia slip develops earlier than the determination time that is supposed to be appropriate for performing the deterioration determination based on the ammonia slip concentration, the ammonia slip may be missed. As a result, the accuracy of deterioration determination may be reduced.

  The present invention has been made in view of the above-mentioned problems, and provides an exhaust gas purification device for an internal combustion engine capable of accurately performing deterioration determination even when the degree of deterioration of the NOx selective reduction catalyst is high. The purpose is to provide.

An exhaust gas purification apparatus for an internal combustion engine according to the present invention,
A selective reduction type NOx catalyst arranged in the exhaust passage of the internal combustion engine to reduce NOx in the exhaust gas with ammonia;
A reducing agent supply device that is arranged in the exhaust passage upstream of the selective reduction type NOx catalyst and that supplies a precursor of ammonia or ammonia as a reducing agent into the exhaust passage,
A sensor for detecting an ammonia slip concentration, which is an ammonia concentration in the exhaust gas flowing downstream of the selective reduction type NOx catalyst,
Based on the ammonia slip concentration detected by the sensor, while supplying the reducing agent in an amount that causes ammonia slip to the selective reduction NOx catalyst when it is assumed that the selective reduction NOx catalyst is deteriorated. And a determination device that executes a degradation determination process for determining whether or not the selective reduction type NOx catalyst is degraded.
Is provided.
The determination device,
Calculating an integrated value of the amount of ammonia slip from the selective reduction type NOx catalyst during a predetermined integrating period from the start of the supply of the reducing agent,
When the integrated value is larger than the determination threshold value, it is determined that the selective reduction type NOx catalyst is deteriorated.

  According to the present invention, the integrated value of the ammonia slip amount from the selective reduction type NOx catalyst during the predetermined integration period from the start of the supply of the reducing agent is calculated. Then, when the calculated integrated value is larger than the determination threshold value, it is determined that the NOx selective reduction catalyst is deteriorated. As a result, even if the ammonia reduction occurs immediately after the supply of the reducing agent is started due to the high degree of deterioration of the NOx selective reduction catalyst, the deterioration determination based on the ammonia slip can be performed. Therefore, even if the degree of deterioration of the NOx selective reduction catalyst is high, the deterioration can be accurately determined.

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 an estimation method of NH ₃ adsorption amount. It is a time chart for explaining the subject of the deterioration judgment processing of the SCR catalyst using OBD active addition. 5 is a time chart for explaining an outline of characteristic deterioration determination processing according to the embodiment of the present invention. 5 is a flowchart showing a routine relating to deterioration determination processing of the SCR 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 the number of each element, the number, the amount, the range, etc. is referred to, the number referred to unless otherwise specified or the principle is clearly specified. However, the present invention is not limited to this. Further, the structures, steps, and the like described in the embodiments below are not necessarily essential to the present invention, unless otherwise specified or clearly specified in principle.

1. System Configuration Example 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. 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 in, 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 collects particulate matter (PM) in exhaust gas, and is made of, for example, a porous ceramic. The DPF 16 carries a catalyst for promoting the oxidation of PM. A fuel addition valve 20 for supplying unburned fuel to the DOC 14 and the DPF 16 is installed upstream of the DOC 14 (exhaust manifold).

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

  A first NOx sensor 24 is installed in the exhaust passage 12 on the upstream side of the DOC 14. A second NOx sensor 26 and an exhaust temperature sensor 28 are installed 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 temperature sensor 28 outputs a signal according to the temperature of the exhaust gas, and is used as an example of a sensor for estimating the temperature of the SCR catalyst 18 (hereinafter, also referred to as “SCR floor temperature”) in the present embodiment.

A third NOx sensor 30 is installed in the exhaust passage 12 on the downstream side of the SCR catalyst 18. The third NOx sensor 30 outputs a signal according to the NOx concentration in the exhaust flowing downstream of the SCR catalyst 18, and in the present embodiment, a sensor for detecting the NH ₃ concentration in the exhaust flowing downstream of the SCR catalyst 18 ( (Corresponding to 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 installed near the inlet of the intake passage 32 of the internal combustion engine 10. The air flow sensor 34 outputs a signal according 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 along with the NOx sensors 24, 26, 30, the exhaust temperature sensor 28, and the air flow sensor 34. In addition to the fuel addition valve 20 and the urea addition valve 22, various actuators (not shown) for controlling the operation of the internal combustion engine 10 are electrically connected to the ECU 40.

The ECU 40 has a processor 40a and a memory 40b. The memory 40b stores programs and maps for controlling the above-mentioned various actuators. Further, various information is input to the ECU 40 from the various sensors described above. The processor 40a determines the operation amount of each actuator by reading the program from the memory and executing the program while utilizing these pieces of information. As a result, the ECU 40 functions as a control device for the internal combustion engine 10.

2. SCR catalyst deterioration determination processing 2-1. Basic Configuration of Deterioration Determination Process The ECU 40 described above also functions as an example of a “determination device” that performs “degradation determination process” for the SCR catalyst 18. That is, the ECU 40 has an OBD (On-Board Diagnostics) function of self-diagnosing whether 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. The term “normal catalyst” as used herein means a new SCR catalyst (that is, purification performance is not deteriorated), and the term “deteriorated catalyst” means that the purification performance is deteriorated at a predetermined detection target deterioration degree. By the resulting SCR catalyst.

The curve indicated by the solid line in FIG. 2 represents the maximum adsorption amount, which is the upper limit value 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 shows the maximum adsorption amount that is the upper limit of the NH ₃ adsorption amount that can be adsorbed by the deteriorated catalyst. NH ₃ slip, which is a phenomenon in which NH ₃ is desorbed from the SCR catalyst 18, is considered to occur when the amount of adsorbed NH ₃ exceeds the above curve in each of the normal catalyst and the deteriorated catalyst.

In the deterioration determination process, ECU 40 is determined amount as NH ₃ slip is expressed only when the SCR catalyst 18 is deteriorated (hereinafter referred to as "active supply NH ₃ amount A") and NH ₃ in SCR The "OBD active addition" to be supplied to the catalyst 18 is executed. Then, the ECU 40 determines whether or not the SCR catalyst 18 is 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 OBD active addition, is a larger amount (surplus) than the NH ₃ amount supplied for the purpose of purifying NOx. Further, as shown in FIGS. 2 and 3, the amount of adsorbed NH ₃ changes according to the SCR bed temperature, so the active supply NH ₃ amount A is calculated as a value according to the SCR bed temperature. In the present embodiment, as an example, the OBD active addition is executed by supplying urea water in an amount that satisfies the active supply NH ₃ amount A.

When the SCR catalyst 18 is a normal catalyst, the maximum adsorption amount is large, as shown in FIG. 2, so the difference between the current estimated NH ₃ adsorption amount and the maximum adsorption amount becomes large. For this reason, even when the active supply NH ₃ amount A ₃ of NH ₃ is supplied, it is unlikely that the maximum adsorption amount is exceeded as illustrated in FIG. 2, and NH ₃ slip does not occur. On the other hand, when the SCR catalyst 18 is a deteriorated catalyst, the maximum adsorption amount is small, as shown in FIG. 3, so the difference between the current estimated NH ₃ adsorption amount and the maximum adsorption amount is small. Therefore, if NH ₃ is supplied in a larger amount than the amount of NH ₃ consumed for purification of NOx, NH ₃ slip easily occurs. 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 To do. As described above, the presence or absence of deterioration of the SCR catalyst 18 can be determined based on whether or not NH ₃ slip appears downstream of the SCR catalyst 18 as a result of the OBD active addition.

In addition, as shown in FIGS. 2 and ₃ , the NH ₃ adsorption amount decreases as the SCR bed temperature increases. Therefore, when the same amount of NH ₃ is supplied, the NH ₃ slip downstream of the SCR catalyst 18 is more likely to occur in an environment where the SCR bed temperature is higher. Further, as can be seen by comparing FIGS. 2 and 3, 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 value of the amount of adsorbed NH ₃ at which NH ₃ slip does not appear when the SCR catalyst 18 is normal. More specifically, this lower limit value corresponds to the lower limit value of the maximum adsorption amount (solid line) obtained when an error that may occur in a normal catalyst is taken into consideration. Therefore, if the SCR catalyst 18 is normal, it is considered that NH ₃ slip does not occur unless the lower limit value is exceeded.

The curve indicated by the broken line in FIG. 3 corresponds to the upper limit value of the amount of adsorbed NH ₃ that reliably causes NH ₃ slip when the SCR catalyst 18 is deteriorated. More specifically, the 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 taken into consideration. The above-mentioned active supply NH ₃ amount A is set to a value that surely becomes larger than the difference between the current estimated NH ₃ adsorption amount and the above upper limit value (broken line). As a result, when the SCR catalyst 18 is deteriorated, NH ₃ slip can be reliably generated by the OBD active addition.

The “limit active supply NH ₃ amount B” in FIG. 2 corresponds to the difference between the NH ₃ adsorption amount at the current SCR bed temperature T1 and the above lower limit (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 in which the NH ₃ slip does not appear and the normal determination is made if the SCR catalyst 18 is normal. In other words, when a larger amount of NH ₃ than the limit active supply NH ₃ amount B is supplied, 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) indicates that OBD active addition is performed. It is a condition for execution. As a result, when the SCR catalyst 18 is normal, it is possible to avoid erroneously determining that deterioration has occurred.

2-3. Adsorbed NH ₃ amount estimating method above-mentioned condition for executing the OBD active additives for (active supply NH ₃ amount A <limit active supply NH ₃ amount B) of the presence or absence of formation of the judgment, adsorbed NH ₃ amount of the SCR catalyst 18 Need to figure out. The calculation (estimation) of the NH ₃ adsorption amount is performed by the ECU 40 onboard.

FIG. 4 is a block diagram for explaining an example of an NH ₃ adsorption amount estimation method. 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).
Amount of adsorbed NH ₃ = amount of supplied NH ₃ −amount of consumed NH ₃ −amount of desorbed 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 so as to have a value corresponding to the amount of NH ₃ supplied for the purpose of purifying NOx when purifying NOx using the SCR catalyst 18, and when performing OBD active addition. Is determined to be a value corresponding to the above-mentioned active supply NH ₃ amount A.

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

More specifically, the NOx purification rate differs depending on whether the SCR catalyst 18 is normal or has deteriorated. Therefore, in the present estimation method, both the case where the SCR catalyst 18 is the normal catalyst and the case where the SCR catalyst is the deteriorated catalyst are assumed, and the maps of the NOx purification rate are individually prepared according to the respective characteristics of the normal catalyst and the deteriorated catalyst. It 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 so as to have 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 adsorbed NH ₃ amount is the same, SCR bed temperature is increased even higher desorption NH ₃ concentration, SCR if the bed temperature is the same, NH ₃ greater the amount of adsorption desorption NH ₃ The amount also increases. The specific correlation can be obtained in advance by experiments 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 a density map. Then, the desorption NH ₃ concentration thus calculated by multiplying the amount of air can be calculated desorption NH ₃ amount.

Similar to 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 the case where the SCR catalyst 18 is a normal catalyst and the case where the SCR catalyst is an abnormally deteriorated catalyst are assumed, and the desorption NH ₃ concentration maps are individually set according to the respective characteristics of the normal catalyst and the abnormally deteriorated catalyst. 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, which are calculated as described above, into the above formula (1). In the deterioration determination process of the present embodiment, the calculated NH ₃ adsorption amount is used as the estimated value of the NH ₃ adsorption amount.

2-4. Issues Regarding Deterioration Determination of SCR Catalyst FIG. 5 is a time chart for explaining the issues of the degradation determination process of the SCR catalyst 18 using OBD active addition. Hereinafter, for convenience of description, the deterioration determination process described with reference to FIG. 5 for comparison with the deterioration determination process of the present embodiment described later is referred to as “deterioration determination process A”.

2-4-1. Overview of Deterioration Judgment Processing A FIG. 5 shows an overview of the deterioration judgment processing A (selection of the judgment time T and calculation method of the judgment threshold value TH1) for a normal time (state where the vehicle speed and the SCR floor temperature are stable) as an example. ) Is used to explain. The deterioration determination process A is performed for the purpose of finding the above-described deterioration catalyst (that is, the SCR catalyst 18 in which the purification performance has deteriorated at the deterioration degree of a predetermined detection target).

The determination time T used in the deterioration determination process A is selected as follows. FIG. 5 shows four estimated NH ₃ slip concentration waveforms 1 to 4 under the condition that the OBD active addition is performed (the OBD active addition execution flag is ON).

Waveform 1 is a waveform at the time of catalyst deterioration (estimated center), that is, the median of the estimated NH ₃ slip concentration when “possible error” is taken into consideration for a deteriorated catalyst having a predetermined degree of detection target deterioration. Corresponds to a waveform. 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. The “possible error” here specifically means an error in the amount of urea water added by the urea addition valve 22, an error in the amount of SCR inflow NOx, and the like.

Waveform 2 corresponds to a waveform at the time of catalyst deterioration (estimation lower limit), that is, a waveform of the lower limit value of the estimated NH ₃ slip concentration that can surely occur when the “possible error” is taken into consideration for the above deteriorated catalyst. To do. Such a waveform 2 is obtained by correcting the estimated NH ₃ slip concentration calculated by the estimation method shown in FIG. 4 with a predetermined correction amount based on the “possible error” while using the map for the deteriorated catalyst. .

Waveform 3 corresponds to a waveform when the catalyst is normal (estimated center), that is, a waveform of the median value of the estimated NH ₃ slip concentration when the “possible error” is taken into consideration for the 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 utilizing the map for the normal catalyst. Therefore, the estimated NH ₃ slip concentration is substantially zero.

The waveform 4 corresponds to the waveform (straight line) when the catalyst is normal (estimated upper limit), that is, the waveform of the upper limit value of the estimated NH ₃ slip concentration that can occur when a possible error is taken into consideration 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” while using the map for the normal catalyst. .

  The determination time T corresponds to a period in which a “determination condition” is established in which the estimated lower limit value (waveform 2) when the catalyst is deteriorated exceeds the estimated upper limit value (waveform 4) when the catalyst is normal. The first deterioration determination process is executed when the determination time T in FIG. 5 corresponding to the period in which this determination condition is satisfied has arrived.

Further, the waveform 5 in FIG. 5 corresponds to the waveform of the average value of the estimated lower limit value (waveform 2) when the catalyst deteriorates and the estimated upper limit value (waveform 4) when the catalyst is normal. According to the deterioration determination process A, the value of the NH ₃ slip concentration of the waveform 5 at the determination time T (the average value) is used as the determination threshold TH1 of the first deterioration determination process. Then, when the actual NH ₃ slip concentration detected by the third NOx sensor 30 exceeds this determination threshold value TH1, it is determined that the SCR catalyst 18 has deteriorated. FIG. 5 shows a waveform 6 of the actual NH ₃ slip concentration of the SCR catalyst 18 that has deteriorated at the detection target deterioration degree, as an example of the NH ₃ slip for which the deterioration determination is made in this way.

The deterioration determination process A described above is performed at the determination time T described above (that is, assuming that the SCR catalyst 18 is deteriorated, NH higher than the upper limit value of the NH ₃ slip concentration that can occur when the normal catalyst is assumed). Will be performed) (in situations where ₃ slip densities are obtained). Further, in order to calculate the estimated NH ₃ slip concentration, which is the basis for calculating the estimated lower limit value when the catalyst is deteriorated and the estimated upper limit value when the catalyst is normal, the SCR bed temperature is calculated by using the estimation method described with reference to FIG. The effects of are being considered sequentially.

Then, in the deterioration determination process A, at the determination time T, the (actual) NH ₃ slip concentration is the average value of the estimated lower limit value when the catalyst is deteriorated and the estimated upper limit value when the catalyst is normal “determination threshold TH1”. When it exceeds, it is determined that the SCR catalyst 18 has deteriorated. According to such a process, the judgment threshold value TH1 larger than the estimated upper limit value when the catalyst is normal is used, so it is possible to prevent the deterioration judgment from being made when the SCR catalyst 18 is normal. Further, since the judgment threshold value TH1 smaller than the estimated lower limit value at the time of catalyst deterioration is used, it is possible to prevent the normal judgment from being made when the SCR catalyst 18 is deteriorated.

  Therefore, according to the deterioration determination process A, it is possible to determine the presence or absence of deterioration of the SCR catalyst 18 by using the appropriate determination threshold TH1 at the appropriate determination time T while considering the change in the SCR bed temperature. Therefore, even if the SCR bed temperature changes, the deterioration determination can be accurately performed.

2-4-2. Problems of Deterioration Judgment Process A As described above, according to the deterioration judgment process A, if the SCR catalyst 18 is deteriorated at a deterioration degree equal to or lower than the detection target deterioration degree, as in the example of the waveform 6, At the determination time T, the actual NH ₃ slip concentration becomes higher than the determination threshold TH1. Therefore, the deterioration determination is appropriately performed. On the other hand, when the degree of deterioration of the SCR catalyst 18 is high (more specifically, when the deterioration of the SCR catalyst 18 has significantly progressed with respect to the detection target level), the waveform 7 in FIG. Thus, NH ₃ slip may develop early after the execution of OBD active addition. Therefore, according to the deterioration determination process A in which the NH ₃ slip concentration is evaluated using the determination time T that is premised on the detection at the predetermined deterioration degree, the NH ₃ slip may be missed if the deterioration degree is high. is there. Specifically, in the example of the waveform 7, the actual NH ₃ slip concentration becomes less than the determination threshold TH1 at the determination time T, even though the deterioration of the SCR catalyst 18 has progressed considerably, so that the SCR catalyst 18 is normal. Will be erroneously determined to be.

2-5. Characteristic part In view of the above-mentioned problem, in the present embodiment, the deterioration determination is appropriately performed even when the deterioration degree of the SCR catalyst 18 is high (more specifically, when the deterioration is progressing as compared with the deterioration degree of the detection target). In order to enable the above, the following deterioration determination processing is executed.

  FIG. 6 is a time chart for explaining the outline of the characteristic deterioration determination processing according to the embodiment of the present invention. The waveforms 2, 4, and 7 and the determination time T in FIG. 6 are the same as those already described with reference to FIG.

A time point t1 in FIG. 6 corresponds to the start time point of the OBD active addition (the OBD active addition execution flag is ON). According to the deterioration determination process of the present embodiment, the accumulation of the (actual) NH ₃ slip amount is started after the start of the OBD active addition.

Figure 6 is a straight line (broken line) showing the time variation of the integrated value A of the estimated NH ₃ slip amount corresponding to the estimated NH ₃ slip concentration of waveform 4, the estimated NH ₃ in accordance with the estimated NH ₃ slip concentration of waveform 2 A polygonal line (broken line) showing the time change of the integrated value B of the slip amount and a polygonal line (solid line) showing the time change of the integrated value C of the actual NH ₃ slip amount according to the actual NH ₃ slip concentration of the waveform 7 are shown. ing.

First, the integrated value A corresponding to the estimated upper limit value (waveform 4) when the catalyst is normal increases continuously from 0 after the start of the OBD active addition at the time point t1. The integrated value B corresponding to the estimated lower limit value (waveform 2) at the time of catalyst deterioration increases from 0 after the occurrence of NH ₃ slip at time t4 and becomes constant after the NH ₃ slip ends at time t6. There is. Then, the integrated value C corresponding to the waveform 7 having the deterioration degree higher than the detection target deterioration degree increases from 0 after the NH ₃ slip appears at the time point t2 immediately after the start of the OBD active addition, and at the time point t3. It remains constant after the end of ₃ slips.

In the deterioration determination process of the present embodiment, the integrated value of the (actual) NH ₃ slip amount during the predetermined integrated period from the start of the OBD active addition is calculated, and when the calculated integrated value is larger than the determination threshold TH2, It is determined that the SCR catalyst 18 has deteriorated. In the example shown in FIG. 6, the above-mentioned integration period corresponds to the period from the time point t1 to the time point t5 during the above-mentioned determination time T. Time point t5 corresponds to a time point when the estimated upper limit value when the catalyst is normal and the estimated lower limit value when the catalyst is deteriorated intersect. In the example shown in FIG. 6, the integrated value B of the estimated lower limit value at the time of catalyst deterioration at time t5 (= the integrated value A of the estimated upper limit value when the catalyst is normal) is used as an example of the determination threshold value TH2. Therefore, in the example of the integrated value C in FIG. 6, since the integrated value C becomes larger than the determination threshold TH2, it is determined that the SCR catalyst 18 has deteriorated. Instead of the above example, the determination threshold TH2 is set such that the integrated value B corresponding to the estimated lower limit value when the catalyst deteriorates during the arrival of the determination time T is greater than the integrated value A corresponding to the estimated upper limit value when the catalyst is normal. Other values that are larger than the integrated value B may also be used, provided that the value is also larger. The determination threshold TH2 corresponds to an example of "determination threshold" according to the present invention.

2-6. Process of Determination Device (ECU) FIG. 7 is a flowchart showing a routine relating to a degradation 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. 7, the ECU 40 first calculates the current (estimated) NH ₃ adsorption amount of the SCR catalyst 18 (step S100). Specifically, the estimation method (estimation model) shown in FIG. 4 is used to calculate the estimated amount of adsorbed NH ₃ for both the normal catalyst assumption and the catalyst deterioration assumption.

Next, the ECU 40 determines whether or not a preliminary condition regarding implementation of the OBD active addition is satisfied (step S102). The preliminary conditions are that no abnormality in parts related to deterioration determination is detected, the vehicle battery voltage is equal to or higher than a predetermined required voltage value of the ECU 40, and the catalyst control mode is a 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 deterioration determination, the NOx sensors 26, 30 used for deterioration determination are in an active state, and one trip. In the above, neither OBD active addition nor deterioration determination is performed (to ensure that the intended NH ₃ slip develops during 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 in step S102 that the preliminary condition is satisfied, 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 OBD active addition execution condition (active supply NH ₃ amount A <limit active supply NH ₃ amount B) is satisfied. As a result, if the determination result of step S104 is negative, the ECU 40 ends this routine.

  When 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-mentioned OBD active addition.

Next, the ECU 40 measures and integrates the (actual) NH ₃ slip amount (step S108). The actual NH ₃ slip amount can be measured (calculated) by multiplying the actual NH ₃ slip concentration measured using the third NOx sensor 30 by the air amount based on the air flow sensor 34.

  Next, the ECU 40 determines whether or not the above determination condition (estimated upper limit value when the catalyst is normal <estimated lower limit value when the catalyst is deteriorated) is satisfied (in other words, whether or not the above determination time T has arrived). The determination is made (step S110). As a result, if the determination result of step S110 is negative (that is, the determination time T shown in FIG. 6 has not arrived), the process proceeds to step S112.

In step S112, the ECU 40 determines whether the elapsed time after the start of the OBD active addition is less than the predetermined time X (for example, 300 seconds). As a result, if the determination result is affirmative (elapsed time <X), the process returns to step S108, and the measurement and integration of the actual NH ₃ slip amount are continued. On the other hand, if the determination result is negative (that is, the determination condition is not satisfied even after the lapse of the predetermined time X after the start of the OBD active addition), the ECU 40 ends this routine (that is, in this case). In order to prevent erroneous determination, the deterioration determination is not performed).

On the other hand, when the ECU 40 determines in step S110 that the determination condition is satisfied (that is, when the determination time T has arrived), the process proceeds to step S114. In step S114, the ECU 40 ends the measurement and integration of the actual NH ₃ slip amount. According to the processes of steps S108, S110, and S114, the actual NH ₃ slip amount is integrated for the period from the start of the OBD active addition until the determination condition is satisfied (an example of the above integration period). Will be done.

Next, the ECU 40 determines whether or not the integrated value of the actual NH ₃ slip amount is equal to or less than the above-mentioned determination threshold TH2 (step S116). As a result, if this determination result is affirmative (integrated value ≦ determination threshold TH2), the ECU 40 determines that the SCR catalyst 18 is normal (step S118). On the other hand, when the determination result is negative (integrated value> determination threshold TH2), the ECU 40 determines that the SCR catalyst 18 is deteriorated (step S120).

3. Effect According to the deterioration determination process of the present embodiment described above, the integrated value of the (actual) NH ₃ slip amount during the predetermined integration period from the start of the OBD active addition is calculated, and the calculated integrated value is the determination threshold value. When it is larger than TH2, it is determined that the SCR catalyst 18 is deteriorated. As a result, even if the NH ₃ slip appears immediately after the start of the OBD active addition due to the high degree of deterioration of the SCR catalyst 18, the deterioration determination based on the NH ₃ slip can be performed. Therefore, even if the degree of deterioration of the SCR catalyst 18 is high, the deterioration can be accurately determined.

In addition, in the present embodiment, an example of the integration period of the integrated value of the (actual) NH ₃ slip amount is a period from the start of the OBD active addition until the determination time T arrives (until time t5 in the example shown in FIG. 6). Is. Determination timing T, as previously described, if detected when the SCR catalyst 18 in the degree of deterioration of the target is assumed to be degraded, higher than the upper limit value of the NH ₃ slip concentrations that may occur during normal catalyst assumed NH ₃ It corresponds to the period in which the slip concentration is obtained. Then, the determination threshold value TH2 is a value equal to the integrated value B corresponding to the estimated lower limit value when the catalyst is deteriorated (= the integrated value A corresponding to the estimated upper limit value when the catalyst is normal) during the arrival of the determination time T. Is set to. Furthermore, the NH ₃ slip amount after the start of the OBD active addition increases as the degree of deterioration of the SCR catalyst 18 increases. Therefore, by performing the deterioration determination when the integrated value of the (actual) NH ₃ slip amount during the integration period is larger than the determination threshold TH2, the SCR catalyst 18 is deteriorated at a degradation level higher than the detection target degradation level. It becomes possible to reliably determine that

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 Airflow sensor 40 Electronic control unit (ECU)

Claims (1)

A selective reduction type NOx catalyst arranged in the exhaust passage of the internal combustion engine to reduce NOx in the exhaust gas with ammonia;
A reducing agent supply device that is arranged in the exhaust passage upstream of the selective reduction type NOx catalyst and that supplies a precursor of ammonia or ammonia as a reducing agent into the exhaust passage,
A sensor for detecting an ammonia slip concentration, which is an ammonia concentration in the exhaust gas flowing downstream of the selective reduction type NOx catalyst,
Based on the ammonia slip concentration detected by the sensor, while supplying the reducing agent in an amount that causes ammonia slip to the selective reduction NOx catalyst when it is assumed that the selective reduction NOx catalyst is deteriorated. And a determination device that executes a degradation determination process for determining whether or not the selective reduction type NOx catalyst is degraded.
An exhaust gas purification device for an internal combustion engine, comprising:
The determination device,
Calculating an integrated value of the amount of ammonia slip from the selective reduction type NOx catalyst during a predetermined integrating period from the start of the supply of the reducing agent,
An exhaust emission control device for an internal combustion engine, wherein it is determined that the selective reduction type NOx catalyst is deteriorated when the integrated value is larger than a determination threshold value.

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