JP2008038738A - DETERIORATION DETECTING DEVICE FOR NOx CATALYST - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a deterioration detecting device for a NOx catalyst which can accurately detect the deterioration of a NOx catalyst without deteriorating an emission characteristic. <P>SOLUTION: When a NOx supply amount to a NOx catalyst is a first reference amount NOx1, a reducing agent amount Grd1(Grd1A, Grd1B) used for NOx reduction is calculated through the utilization of air-fuel ratio sensor output before/after the NOx catalyst. Even when the NOx supply amount is a second reference amount NOx2, a reducing agent amount Grd2(Grd2A, Grd2B) is calculated. The difference ΔGrd(ΔGrdA, ΔGrdB) between these reducing agent amounts is then calculated. When the difference ΔGrd is smaller than the reference value, the NOx catalyst detects the deterioration. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a NOx catalyst deterioration detection device.

  By arranging air-fuel ratio sensors respectively upstream and downstream of the NOx catalyst, obtaining a rich spike time based on an output change of the air-fuel ratio sensor at the time of rich spike execution, and comparing the obtained rich spike time with a reference value, An apparatus that performs NOx catalyst deterioration determination is known (see, for example, Patent Document 1).

JP-A-11-93742 JP 2003-293745 A

By the way, according to the knowledge by the present inventors, in order to accurately detect the deterioration of the NOx catalyst based on the amount of the reducing agent used for NOx reduction, the rich spike is obtained in a state where the amount of NOx supplied to the NOx catalyst is large. It is desirable to implement.
However, in the case of a diesel engine, if the rich spike is performed with a large amount of NOx supplied, the NOx purification rate will be low. If so, the emission characteristics may be deteriorated when the deterioration of the NOx catalyst is detected.

  The present invention has been made to solve the above-described problems, and provides a NOx catalyst deterioration detection device capable of accurately detecting NOx catalyst deterioration without deteriorating emission characteristics. For the purpose.

In order to achieve the above object, a first invention is a deterioration detection device for detecting deterioration of a NOx catalyst,
A NOx catalyst that is provided in an exhaust passage of a compression ignition internal combustion engine and occludes or reduces NOx according to an exhaust air-fuel ratio;
First exhaust air-fuel ratio acquisition means for acquiring a first exhaust air-fuel ratio that is an air-fuel ratio of exhaust gas flowing into the NOx catalyst;
Second exhaust air-fuel ratio acquisition means for acquiring a second exhaust air-fuel ratio that is an air-fuel ratio of exhaust gas flowing out from the NOx catalyst;
Catalyst regeneration means for regenerating the NOx catalyst by supplying a reducing agent to an exhaust passage upstream of the NOx catalyst;
Used to reduce NOx occluded in the NOx catalyst based on the first and second exhaust air-fuel ratios acquired by the first and second exhaust air-fuel ratio acquisition means when the reducing agent is supplied. Reducing agent amount calculating means for calculating the reducing agent amount;
Deterioration detecting means for detecting deterioration of the NOx catalyst based on differences or ratios of the plurality of reducing agent amounts respectively calculated by the reducing agent amount calculating means in a plurality of cases where the NOx supply amounts to the NOx catalyst are different; It is provided with.

The second invention is the first invention, wherein
Of the cases where the plurality of reducing agent amounts are calculated, the larger NOx supply amount is the NOx supply amount when normal regeneration of the NOx catalyst is executed.

  According to the first invention, the deterioration detection of the NOx catalyst is performed based on the difference or ratio of the reducing agent amounts calculated in a plurality of cases where the NOx supply amount is different. Therefore, even when the NOx supply amount is small, that is, even when the NOx occlusion rate is low, it is possible to accurately detect the deterioration of the NOx catalyst. Accordingly, it is possible to detect the deterioration of the NOx catalyst in a state where a high NOx purification rate can be obtained. For this reason, it is possible to accurately detect the deterioration of the NOx catalyst without deteriorating the emission characteristics.

  According to the second invention, normal regeneration of the NOx catalyst and calculation of the amount of reducing agent in detecting deterioration of the NOx catalyst can be performed. Therefore, the amount of reducing agent can be reduced and the emission characteristics can be improved as compared with the case where normal regeneration of the NOx catalyst and detection of deterioration of the NOx catalyst are performed separately and independently.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to an embodiment of the present invention. The system shown in FIG. 1 includes a four-cycle diesel engine (compression ignition internal combustion engine) as the internal combustion engine 1. It is assumed that the diesel engine 1 is mounted on a vehicle and used as a power source. Although the diesel engine 1 shown in FIG. 1 is an in-line four-cylinder type, in the present invention, the number of cylinders and the cylinder arrangement are not limited thereto.

  The piston of each cylinder 2 of the diesel engine 1 is connected to the crankshaft 4 via a crank mechanism. A crank angle sensor 5 that detects a rotation angle (crank angle) of the crankshaft 4 is provided in the vicinity of the crankshaft 4.

  Each cylinder 2 of the diesel engine 1 is provided with an injector 6 that injects fuel directly into the cylinder. The injector 6 for each cylinder is connected to a common common rail 7. Fuel in a fuel tank (not shown) is pressurized to a predetermined fuel pressure by the supply pump 8. This pressurized fuel is stored in the common rail 7 and supplied to each injector 6 from the common rail 7. The injector 6 can inject the fuel into the cylinder at an arbitrary timing a plurality of times during one cycle.

  An intake valve 12 is provided at the intake port 10 of the diesel engine 1. The valve opening characteristics (valve opening timing, lift amount, working angle) of the intake valve 12 can be changed by a known variable valve mechanism (not shown).

  The intake port 10 is connected to an intake passage 18 via an intake manifold 16. An intake throttle valve 20 is provided in the intake passage 18. The intake throttle valve 20 is an electronic control valve whose opening is determined based on the accelerator opening AA detected by the accelerator opening sensor 21. An intercooler 22 is provided upstream of the intake throttle valve 20. A compressor 24 a of the turbocharger 24 is provided upstream of the intercooler 22. The compressor 24a is connected to the turbine 24b of the exhaust passage 38 by a connecting shaft.

  An air flow meter 26 for detecting the intake air amount Ga is provided upstream of the compressor 24a. An air cleaner 28 is provided upstream of the air flow meter 26.

  According to such a configuration, the intake air compressed by the compressor 24 a of the turbocharger 24 is cooled by the intercooler 22. The intake air that has passed through the intercooler 22 is distributed to the intake port 10 of each cylinder by the intake manifold 16.

  An exhaust valve 32 is provided at the exhaust port 30 of the diesel engine 1. The valve opening characteristics (valve opening timing, lift amount, working angle) of the exhaust valve 32 can be changed by a known variable valve mechanism (not shown).

  The exhaust port 30 is connected to an exhaust passage 38 via an exhaust manifold 36. In the exhaust passage 38, a turbine 24b of the turbocharger 24 is provided. A NOx catalyst 40 is provided downstream of the turbine 24b. The NOx catalyst 40 occludes NOx in the exhaust gas in an atmosphere where the air-fuel ratio is larger than the stoichiometric air-fuel ratio, that is, in an atmosphere leaner than the stoichiometric air-fuel ratio, and in the atmosphere where the air-fuel ratio is equal to or lower than the stoichiometric air-fuel ratio, that is, the stoichiometric air-fuel ratio. In the following rich atmosphere, it has a function of reducing and purifying the stored NOx and reducing it. The NOx catalyst 40 may have only a function of storing and reducing NOx, or may be a DPNR (Diesel Particulate-NOx-Reduction system) having a function of collecting soot in exhaust gas. The NOx catalyst 40 may have a function other than collecting soot.

  An exhaust fuel addition valve 42 for adding fuel to the exhaust gas is provided between the turbine 24b and the NOx catalyst 40. Further, an air-fuel ratio sensor (hereinafter also referred to as “pre-catalyst air-fuel ratio sensor”) 44 for detecting an exhaust air-fuel ratio A / Fin upstream of the NOx catalyst is provided between the exhaust fuel addition valve 42 and the NOx catalyst 40. ing. The pre-catalyst air / fuel ratio sensor 44 can detect the air / fuel ratio (first exhaust air / fuel ratio) of the exhaust gas flowing into the NOx catalyst 40. An air-fuel ratio sensor (hereinafter also referred to as “post-catalyst air-fuel ratio sensor”) 46 for detecting an exhaust air-fuel ratio A / Fout downstream of the NOx catalyst is provided downstream of the NOx catalyst 40. The post-catalyst air / fuel ratio sensor 46 can detect the air / fuel ratio (second exhaust air / fuel ratio) of the exhaust gas flowing out from the NOx catalyst 40.

  One end of the external EGR passage 52 is connected to the intake passage 18 in the vicinity of the intake manifold 16. The other end of the external EGR passage 52 is connected to the vicinity of the exhaust manifold 36 of the exhaust passage 38. In the present system, a part of the exhaust gas (burned gas) can be recirculated to the intake passage 18 through the external EGR passage 52, that is, external EGR (Exhaust Gas Recirculation) can be performed.

  In the middle of the external EGR passage 52, an EGR cooler 54 for cooling the external EGR gas is provided. An EGR valve 56 is provided downstream of the EGR cooler 54 in the external EGR passage 52. As the opening degree of the EGR valve 56 is increased, the amount of exhaust gas passing through the external EGR passage 52 (that is, the external EGR amount or the external EGR rate) can be increased.

The system of the first embodiment includes an ECU (Electronic Control Unit) 60 as a control device. An injector 6, a supply pump 8, an intake throttle valve 20, an exhaust fuel addition valve 42, an EGR valve 56, and the like are connected to the output side of the ECU 60. The crank angle sensor 5, the accelerator opening sensor 21, the air flow meter 26, the pre-catalyst air-fuel ratio sensor 44, the post-catalyst air-fuel ratio sensor 46, and the like are connected to the input side of the ECU 60.
Further, the ECU 60 calculates the engine speed NE based on the output of the crank angle sensor 5. Further, the ECU 60 calculates the engine load KL based on the accelerator opening AA and the like. Further, the ECU 60 calculates the fuel injection amount Q from the injector 6 based on the engine load KL. The ECU 60 can calculate the amount of NOx supplied to the NOx catalyst 40 based on the engine speed NE and the fuel injection amount Q (described later). The ECU 60 controls the operating state of the diesel engine 1 by operating each actuator in accordance with a predetermined program based on the signal from each sensor.

[Features of this embodiment]
As described above, the system according to the present embodiment includes the NOx catalyst 40. Conventionally, a method for detecting deterioration of a NOx catalyst has been proposed. For example, in the aforementioned Patent Document 1, air-fuel ratio sensors are provided upstream and downstream of the NOx catalyst, rich spike times are obtained from the outputs of these air-fuel ratio sensors, and the NOx catalyst is determined based on this rich spike time. A method for detecting degradation is disclosed. In this method, the characteristic that the rich spike time is shortened due to deterioration of the NOx catalyst is used. The NOx catalyst deterioration is detected by comparing the obtained rich spike time with a reference value.

  Further, as shown in FIG. 3 to be described later, when the amount of NOx supplied to the NOx catalyst 40 (that is, the NOx occlusion amount) is a predetermined reference amount, the NOx occluded in the NOx catalyst 40 is used for reduction. If the amount of the reducing agent thus obtained can be obtained, the deterioration determination of the NOx catalyst 40 can be performed based on the amount of the reducing agent.

  FIG. 2 is a diagram showing a method for calculating the amount of reducing agent using the exhaust air-fuel ratio upstream and downstream of the NOx catalyst. In FIG. 2, the solid line with the symbol “A / Fin” represents the output of the pre-catalyst air-fuel ratio sensor 44 (that is, the first exhaust air-fuel ratio before the catalyst). The broken line with the symbol “A / Fout” represents the output of the post-catalyst air / fuel ratio sensor 46 (that is, the second exhaust air / fuel ratio after the catalyst).

  When a predetermined amount of NOx is supplied (occluded) to the NOx catalyst 40, a rich spike is performed. Here, a case where rich spike is performed by adding fuel from the exhaust fuel addition valve 42 will be described. When the fuel (HC) as the reducing agent is added to the exhaust gas from the exhaust fuel addition valve 42 at time t1 shown in FIG. 2, the output A / Fin of the pre-catalyst air-fuel ratio sensor 44 changes. At time t2, the output A / Fin of the pre-catalyst air-fuel ratio sensor 44 changes to a richer side than the theoretical air-fuel ratio A / Fst. The fuel added from the exhaust fuel addition valve 42 is used for the reduction and purification of NOx stored in the NOx catalyst 40, that is, for the regeneration of the NOx catalyst 40.

  While NOx is being reduced by the fuel (for example, at time t3), the fuel does not slip through the NOx catalyst 40. For this reason, the output A / Fout of the post-catalyst air-fuel ratio sensor 46 is maintained at the theoretical air-fuel ratio A / Fst. Thereafter, when all of the NOx occluded in the NOx catalyst 40 is reduced and purified, surplus fuel that has not been used for NOx reduction passes through the NOx catalyst 40. Therefore, at time t4, the output A / Fout of the post-catalyst air / fuel ratio sensor 46 changes to the richer side than the theoretical air / fuel ratio A / Fst. The change in the post-catalyst air-fuel ratio sensor output A / Fout at time t4 means the end point of NOx reduction, that is, the end point of the regeneration process of the NOx catalyst 40.

  The fuel supplied to the NOx catalyst 40 between time t2 and time t4 shown in FIG. 2 is used for the reduction of NOx stored in the NOx catalyst 40. That is, the amount of fuel corresponding to the hatched portion in FIG. 2 is the amount of reducing agent used for NOx reduction. Therefore, the amount of the reducing agent can be calculated based on the output A / Fin of the pre-catalyst air-fuel ratio sensor 44 and the output A / Fout of the post-catalyst air-fuel ratio sensor 46.

FIG. 3 is a diagram showing the relationship between the NOx supply amount and the reducing agent amount.
In FIG. 3, the broken line with the symbol “L1” represents the characteristics of a normal NOx catalyst (hereinafter referred to as “normal catalyst”). Also, the alternate long and short dash line with the symbol “L2” represents the characteristics of the deteriorated NOx catalyst (hereinafter referred to as “deteriorated catalyst”). 3 represents the amount of NOx supplied from the internal combustion engine 1 to the NOx catalyst 40. The NOx supply amount has a correlation with the engine speed NE and the fuel injection amount Q of the internal combustion engine 1. Therefore, the NOx supply amount can be calculated by integrating the values (NOx supply amount per unit time) obtained by referring to the map in which this correlation is defined.

  As shown in FIG. 3, when the NOx supply amount is the same, the reducing agent amount of the normal catalyst is larger than the reducing agent amount of the deteriorated catalyst. This is because the amount of NOx stored in the deteriorated catalyst is small. However, the characteristics of the normal catalyst and the deteriorated catalyst may vary depending on the vehicle type. In FIG. 3, the lower limit of the characteristic of the normal catalyst due to variation is indicated by a broken line L1a, and the upper limit of the characteristic of the deteriorated catalyst due to variation is indicated by a one-dot chain line L2a. The characteristics L1a and L2a including these variations intersect at a position where the NOx supply amount is a predetermined value A. Therefore, when the rich spike is performed in a state where the NOx supply amount is equal to or less than the predetermined value A, a situation may occur in which a normal NOx catalyst is erroneously detected as being deteriorated. In order to prevent such erroneous detection due to variations, that is, to accurately perform degradation determination even when variations are taken into account, it is necessary to determine degradation of the NOx catalyst in a state where the NOx supply amount is greater than the predetermined value A. It is believed that there is.

  However, in the diesel engine 1 as shown in FIG. 1, there is a relationship as shown in FIG. 4 between the NOx supply amount and the NOx purification rate when the rich spike is performed. FIG. 4 is a diagram showing the relationship between the NOx supply amount and the NOx purification rate when the rich spike is executed in the diesel engine. Here, the NOx supply amount is proportional to the NOx occlusion rate (or NOx occlusion amount). Specifically, the greater the amount of NOx supplied, the higher the NOx occlusion rate. Therefore, FIG. 4 can also be said to be a diagram showing the relationship between the NOx occlusion rate and the NOx purification rate when the rich spike is performed in the diesel engine.

  As shown in FIG. 4, the NOx purification rate decreases as the NOx supply amount increases (that is, the NOx occlusion rate increases). In recent years, NOx emission regulations have become stricter, and a high NOx purification rate is required. Therefore, instead of detecting the deterioration of the NOx catalyst 40, the normal NOx catalyst regeneration process is performed in a state where the NOx supply amount is equal to or less than the predetermined value B in order to obtain a high NOx purification rate. In other words, this normal NOx catalyst regeneration process is performed in a state where the NOx occlusion rate is a predetermined value (for example, 15%) or less.

  On the other hand, as described above, in order to prevent erroneous detection in the deterioration determination of the NOx catalyst 40, that is, in order to accurately perform deterioration determination including variation, as shown in FIGS. It is necessary to execute the rich spike in a state where the amount is larger than the predetermined value A. In other words, it is necessary to perform the rich spike while the NOx occlusion rate of the NOx catalyst is higher than a predetermined value (for example, 40%). However, if rich spike is performed in a state where the amount of NOx supplied is large, the NOx purification rate becomes low as described above. For this reason, when the deterioration of the NOx catalyst 40 is detected, the emission characteristics are deteriorated.

Therefore, in the present embodiment, as described below, a method for detecting the deterioration of the NOx catalyst 40 without deteriorating the emission characteristics is proposed.
FIG. 5 is a diagram for explaining a method for detecting deterioration of the NOx catalyst in the present embodiment. As shown in FIG. 5, in the present embodiment, first, when the NOx supply amount is the first reference value NOx1, a rich spike is performed, and the amount of reducing agent used for NOx reduction by the method shown in FIG. Grd1 (Grd1A, Grd1B) is calculated. Further, when the NOx supply amount is the second reference value NOx2, rich spike is performed, and the reducing agent amount Grd2 (Grd2A, Grd2B) used for NOx reduction is calculated by the method shown in FIG. In this way, rich spikes are performed with two different NOx supply amounts NOx1 and NOx2, respectively, and reducing agent amounts Grd1 and Grd2 used for NOx reduction are calculated.

  Here, the larger NOx supply amount (first reference value) NOx1 at the time of detecting the deterioration of the NOx catalyst is assumed to be the same as the NOx supply amount at which the normal NOx catalyst regeneration process is executed. That is, the first reference value NOx1 and the second reference value NOx2 are included in the NOx supply amount region where the normal NOx regeneration process is executed in relation to the NOx purification rate. In other words, these reference values NOx1 and NOx2 are both equal to or less than the predetermined value B.

  Then, a reducing agent amount difference ΔGrd (ΔGrdA, ΔGrdB) which is a difference between the plurality of reducing agent amounts Grd1 and Grd2 is calculated. This reducing agent amount difference ΔGrd becomes smaller as the NOx catalyst 40 deteriorates. As shown in FIG. 5, the reducing agent amount difference ΔGrdB of the deteriorated catalyst is smaller than the reducing agent amount difference ΔGrdA of the normal catalyst.

  Therefore, in the present embodiment, the deterioration detection of the NOx catalyst 40 is performed based on the reducing agent amount difference ΔGrd. Specifically, for example, when the reducing agent amount difference ΔGrd is smaller than the reference value ΔGth as ΔGrdB shown in FIG. 5, it is determined that the catalyst is a deteriorated catalyst. Further, for example, when the reducing agent amount difference ΔGrd is equal to or larger than the reference value ΔGth as ΔgrdA shown in FIG. 5, it is determined that the catalyst is a normal catalyst.

  According to this method, rich spike is performed with a small amount of NOx supplied. Therefore, it is possible to detect the deterioration of the NOx catalyst 40 in a state where the NOx purification rate is high. Therefore, it is possible to prevent the emission characteristics from being deteriorated when the deterioration of the NOx catalyst 40 is detected.

  Further, among the plurality of NOx supply amounts NOx1 and NOx2 that are rich spiked when the deterioration of the NOx catalyst 40 is detected, the larger NOx supply amount NOx1 is the same as the NOx supply amount for which the normal NOx catalyst regeneration process is executed. To be. As a result, the normal NOx catalyst regeneration process can be combined with the calculation of the reducing agent amount Grd1 in the NOx catalyst deterioration detection. That is, it is not necessary to perform a rich spike for calculating the reducing agent amount Grd1 separately from the normal NO catalyst regeneration process. Therefore, the total amount of reducing agent added from the exhaust fuel addition valve 42 can be reduced. Thereby, the emission characteristic can be improved.

  The first reference value NOx1 is preferably closer to a predetermined value B, which is the maximum NOx supply amount allowed in relation to the NOx purification rate, and the second reference value NOx2 is preferably closer to zero. It is. Thereby, since the reducing agent amount difference ΔGrd can be increased without deteriorating the emission characteristics, the accuracy of detecting the deterioration of the NOx catalyst 40 can be further improved. Furthermore, by making the second reference value NOx2 close to zero, the next rich spike can be performed in a short time after the reducing agent amount Grd1 is calculated, and the reducing agent amount Grd2 can be calculated. Therefore, since the time required for calculating the reducing agent amount Grd2 can be shortened, the deterioration detection of the NOx catalyst 40 can be executed in a short time.

[Specific processing in the embodiment]
FIG. 6 is a flowchart showing a routine executed by the ECU 60 in the first embodiment. FIG. 7 is a flowchart showing the calculation process of the reducing agent amount difference ΔGrd executed in step 106 of FIG. The routine shown in FIG. 6 is started at predetermined intervals.

  According to the routine shown in FIG. 6, first, it is determined whether or not there is a catalyst deterioration determination request (step 100). Here, for example, the ECU 60 can determine that there is a catalyst deterioration determination request immediately after the catalyst warm-up is completed and after traveling a predetermined distance or a predetermined time after the previous catalyst deterioration determination is executed. If it is determined in step 100 that there is no catalyst deterioration determination request, this routine is temporarily terminated.

  If it is determined in step 100 that there is a catalyst deterioration determination request, it is determined whether the catalyst is warming up and in steady operation (step 102). In this step 102, it is determined whether or not the condition is such that a rich spike can be performed and the amount of reducing agent can be calculated with high accuracy. If it is determined in step 102 that the catalyst has not been warmed up, or if it is determined that steady operation is not being performed, this routine is temporarily terminated.

  On the other hand, if it is determined in step 102 that the catalyst is warmed up and is in steady operation, the reducing agent amount calculation first flag (hereinafter abbreviated as “first flag”) is set to “ON”. (Step 104). The first flag is a flag that is turned on when the first reducing agent amount is calculated and turned off when the second reducing agent amount is calculated.

  Next, the reducing agent amount difference ΔGrd is calculated by executing the routine shown in FIG. 7 (step 106). According to the routine shown in FIG. 7, first, it is determined whether or not the first flag is ON (step 120). If it is determined in step 120 that the first flag is ON, the target NOx supply amount is set to the first reference value NOx1 (step 122). Here, the target NOx supply amount is the NOx supply amount for which the execution of rich spike is permitted. Further, as described above, the first reference value NOx1 is the same as the NOx supply amount when the normal NOx catalyst regeneration process is executed.

  Thereafter, it is determined whether or not the NOx supply amount is larger than the target NOx supply amount set in step 122 (step 126). Here, the ECU 60 calculates the NOx supply amount to the NOx catalyst 40 by a routine different from this routine. This NOx supply amount has a correlation with the engine speed NE and the fuel injection amount Q. The ECU 60 sequentially accumulates the NOx supply amount per unit time to the NOx catalyst 40 with reference to a map defined by the relationship between the engine speed NE and the fuel injection amount Q. In this step 126, it is determined whether or not the NOx supply amount accumulated after resetting after the previous rich spike execution (step 130 described later) is larger than the target NOx supply amount for which the rich spike execution is permitted. . If it is determined in step 126 that the NOx supply amount is equal to or less than the target NOx occlusion amount, this routine is temporarily terminated.

  If it is determined in step 126 that the NOx supply amount is larger than the target NOx supply amount, a rich spike for reducing agent amount calculation is performed (step 128). After the rich spike is performed, the integrated NOx supply amount is reset (step 130). Thereafter, the reducing agent amount Grd is calculated based on the exhaust air / fuel ratios A / Fin and A / Fout before and after the catalyst when the rich spike is performed (step 132). In step 132, the reducing agent amount Grd used for the reduction of NOx stored in the NOx catalyst 40 is calculated by the method shown in FIG.

  Next, it is determined again whether or not the first flag is ON (step 134). In step 134, it is determined whether the reducing agent amount Grd calculated in step 132 is based on the first calculation or the second calculation. If it is determined in step 134 that the first flag is ON, the reducing agent amount Grd calculated in step 132 is set as the first reducing agent amount Grd1 (step 136). Thereafter, the first flag is set to OFF (step 138), and the process returns to step 120.

  Since the first flag is set to OFF in the above step 138, “NO” is determined in this step 120. In step 124, the target NOx supply amount is set to the second reference value NOx2. Thereafter, it is determined whether or not the NOx supply amount is larger than the target NOx supply amount set in step 124 (step 126). In this step 126, the NOx supply amount accumulated after resetting (see step 130) after the execution of the rich spike for calculating the first reducing agent amount Grd1 is the target NOx supply in which the execution of the rich spike is permitted. It is determined whether the amount is greater than the amount.

  If it is determined in step 126 that the NOx supply amount is larger than the target NOx supply amount, a rich spike is performed in the same manner as described above (step 128). Thereafter, the accumulated NOx supply amount is reset (step 130), and the reducing agent amount Grd is calculated (step 132). Since the first flag is turned off after the first reducing agent amount Grd1 is calculated, it is determined as “NO” in step 134 executed after step 132. That is, it is determined that the reducing agent amount Grd calculated in step 132 is based on the second calculation.

  Next, the reducing agent amount Grd calculated in step 132 is set as the second reducing agent amount Grd2 (step 140). Then, a reducing agent amount difference ΔGrd is calculated (step 142). This reducing agent amount difference ΔGrd is a difference between the first reducing agent amount Grd1 set in step 136 and the second reducing agent amount Grd2 set in step 140.

  As described above, after the reducing agent amount difference ΔGrd is calculated by the routine shown in FIG. 7, the process proceeds to step 108 in FIG. In step 108 of the routine shown in FIG. 6, it is determined whether or not the calculated reducing agent amount difference ΔGrd is smaller than a reference value ΔGth. This reference value Gth is a threshold value for determining the deterioration of the NOx catalyst. In this step 108, the deterioration determination of the NOx catalyst 40 is performed based on the reducing agent amount difference ΔGrd.

  If it is determined in step 108 that the reducing agent amount difference ΔGrd is smaller than the reference value ΔGth, it is determined that the NOx catalyst 40 has deteriorated (step 110). That is, the deterioration of the NOx catalyst 40 is detected. In this case, the vehicle driver is informed of catalyst deterioration by a method such as turning on an indicator (not shown).

  On the other hand, if it is determined in step 108 that the reducing agent amount difference ΔGrd is greater than or equal to the reference value ΔGth, it is determined that the NOx catalyst 40 is normal (step 112). Thereafter, this routine is terminated.

  As described above, according to the routines shown in FIGS. 6 and 7, the reducing agent amounts Grd1 and Grd2 are calculated by performing rich spikes in the case of a plurality of different NOx supply amounts NOx1 and NOx2, respectively. . Here, the larger NOx supply amount NOx1 is the same as the NOx supply amount for which the normal NOx catalyst regeneration process is executed. A difference ΔGrd between the plurality of reducing agent amounts Grd1 and Grd2 is calculated, and when the calculated difference ΔGrd is smaller than the reference value ΔGth, it is determined that the NOx catalyst 40 is deteriorated. Rich spike is performed with a small amount of NOx supplied. Therefore, it is possible to detect the deterioration of the NOx catalyst 40 in a state where the NOx purification rate is high. Therefore, it is possible to detect the deterioration of the NOx catalyst 40 without deteriorating the emission characteristics.

In the present embodiment, the air-fuel ratio sensors 44 and 46 are provided before and after the NOx catalyst 40, and the reducing agent amount Grd is calculated based on the outputs A / Fin and A / Fout. The amount of reducing agent may be calculated using an oxygen sensor instead of the fuel ratio sensors 44 and 46. Since the end point of NOx reduction can be set as the end point of the NOx reduction of the oxygen sensor downstream of the catalyst, the amount of reducing agent can be calculated similarly.
Further, instead of the outputs from these sensors, the first and second exhaust air-fuel ratios are estimated based on the engine control state (for example, engine speed NE, engine load KL, etc.), and the estimated first The reducing agent amount Grd may be obtained using the second exhaust air-fuel ratio.

  In the present embodiment, the deterioration detection of the NOx catalyst 40 is executed based on the reducing agent amount difference ΔGrd (= Grd1-Grd2), but the ratio of the plurality of reducing agent amounts Grd1, Grd2 (= Grd1 / Grd2 ), The deterioration detection of the NOx catalyst 40 may be executed. The ratio (Grd1 / Grd2) of the reducing agent amount approaches 1 as the NOx catalyst 40 deteriorates. Further, the ratio of the deteriorated catalyst is smaller than that of the normal catalyst. Therefore, when this ratio is smaller than the reference value, it can be determined that the catalyst is a deteriorated catalyst, and when it is equal to or higher than the reference value, it can be determined that the catalyst is a normal catalyst. Also in this case, the same effect as the above embodiment can be obtained.

  In the present embodiment, the NOx catalyst 40 is used as the “NOx catalyst” in the first invention, the air-fuel ratio sensor 44 is used as the “first exhaust air-fuel ratio acquisition means” in the first invention, and the air-fuel ratio sensor 46 is used. Corresponds to the “second exhaust air-fuel ratio acquisition means” in the first invention, and the exhaust fuel addition valve 42 corresponds to the “catalyst regeneration means” in the first invention. Further, in the present embodiment, the “catalyst regeneration means” in the first invention is executed by the ECU 60 executing the process of step 128, and the “reducing agent” in the first invention is executed by executing the process of step 132. The “quantity calculating means” executes the processing of steps 106, 108, and 112, thereby realizing the “deterioration detecting means” in the first invention.

It is a figure for demonstrating the system configuration | structure by embodiment of this invention. It is a figure which shows the calculation method of the reducing agent amount using the exhaust air-fuel ratio of the upstream and downstream of a NOx catalyst. It is a figure which shows the relationship between the amount of NOx supply at the time of rich spike implementation, and the amount of reducing agents. It is a figure which shows the relationship between the NOx supply amount of a diesel engine, and a NOx purification rate. In embodiment of this invention, it is a figure for demonstrating the deterioration detection method of a NOx catalyst. 4 is a flowchart showing a routine executed by ECU 60 in the embodiment of the present invention. It is a flowchart which shows the calculation process of the reducing agent amount difference (DELTA) Grd performed by step 106 of FIG.

Explanation of symbols

1 diesel engine 5 crank angle sensor 26 air flow meter 38 exhaust passage 40 NOx catalyst 42 exhaust fuel addition valve 44 catalyst upstream air-fuel ratio sensor 46 catalyst downstream air-fuel ratio sensor 60 ECU

Claims (2)

A deterioration detection device for detecting deterioration of a NOx catalyst,
A NOx catalyst that is provided in an exhaust passage of a compression ignition internal combustion engine and occludes or reduces NOx according to an exhaust air-fuel ratio;
First exhaust air-fuel ratio acquisition means for acquiring a first exhaust air-fuel ratio that is an air-fuel ratio of exhaust gas flowing into the NOx catalyst;
Second exhaust air-fuel ratio acquisition means for acquiring a second exhaust air-fuel ratio that is an air-fuel ratio of exhaust gas flowing out from the NOx catalyst;
Catalyst regeneration means for regenerating the NOx catalyst by supplying a reducing agent to an exhaust passage upstream of the NOx catalyst;
Used to reduce NOx occluded in the NOx catalyst based on the first and second exhaust air-fuel ratios acquired by the first and second exhaust air-fuel ratio acquisition means when the reducing agent is supplied. Reducing agent amount calculating means for calculating the reducing agent amount;
Deterioration detecting means for detecting deterioration of the NOx catalyst based on differences or ratios of the plurality of reducing agent amounts respectively calculated by the reducing agent amount calculating means in a plurality of cases where the NOx supply amounts to the NOx catalyst are different; A NOx catalyst deterioration detection device comprising: In the NOx catalyst deterioration detection device according to claim 1,
The NOx catalyst deterioration detection device, wherein the larger NOx supply amount among the plurality of reducing agent amounts calculated is the NOx supply amount when normal NOx catalyst regeneration is performed.

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