JP2008025381A - Deterioration detector of nox catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a deterioration detector of an NOx catalyst, detecting deterioration of an NOx catalyst with good accuracy without any influence of PM and the like discharged from an engine. <P>SOLUTION: In performing rich spike operation, a surplus HC quantity Ghc passing through an NOx catalyst and NOx catalyst purification rate Rnox are calculated (step 104, 106). In the case where a correlation point P determined by the surplus HC quantity Ghc and the NOx purification rate Rnox is within a predetermined range R, when the NOx purification rate Rnox is smaller than the reference value Rth, deterioration of the NOx catalyst is decided (step 108, 112, 114). When the correlation point P is not within the predetermined range R, HC quantity added from an exhaust fuel addition valve is changed (step 110). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  An apparatus is known in which air-fuel ratio sensors are arranged upstream and downstream of a NOx catalyst provided in an exhaust passage of a diesel engine, respectively, and the deterioration of the NOx catalyst is detected based on the output of those air-fuel ratio sensors when a rich spike is executed. (For example, refer to Patent Document 1).

JP 2004-308455 A JP 2000-274279 A JP 2002-47979 A JP-A-11-93742

However, PM or the like discharged from the engine may accumulate on the air-fuel ratio sensor upstream of the catalyst. In this case, the output of the air-fuel ratio sensor upstream of the catalyst is lowered, and there is a possibility that deterioration of the NOx catalyst cannot be accurately detected.
In addition, if the air-fuel ratio sensor is provided with a cover in order to prevent adhesion of PM or the like to the air-fuel ratio sensor upstream of the catalyst, the output responsiveness of the air-fuel ratio sensor may be lowered. .

  The present invention has been made to solve the above-described problems, and is capable of accurately detecting the deterioration of the NOx catalyst without being affected by PM or the like discharged from the engine. An object is to provide a detection device.

In order to achieve the above object, a first invention is a deterioration detection device for a NOx catalyst,
A NOx catalyst that is provided in an exhaust passage of the internal combustion engine and occludes or reduces NOx according to an exhaust air-fuel ratio;
An air-fuel ratio sensor for detecting an exhaust air-fuel ratio in an exhaust passage downstream of the NOx catalyst;
A NOx sensor for detecting a NOx concentration in an exhaust passage downstream of the NOx catalyst;
Rich spike execution means for executing a rich spike for supplying a reducing agent to the exhaust passage upstream of the NOx catalyst;
Surplus reducing agent amount calculating means for calculating an amount of excess reducing agent that passes through the NOx catalyst based on the exhaust air-fuel ratio when the rich spike is executed;
NOx purification rate calculating means for calculating a NOx purification rate of the NOx catalyst based on the NOx concentration during execution of the rich spike;
Deterioration detecting means for detecting deterioration of the NOx catalyst based on the surplus reducing agent amount and the NOx purification rate is provided.

The second invention is the first invention, wherein
The deterioration detecting means is configured to detect deterioration of the NOx catalyst when a correlation point defined by the surplus reducing agent amount and the NOx purification rate is included in a predetermined range.

The third invention is the second invention, wherein
The method further comprises reducing agent amount changing means for changing the amount of reducing agent supplied by the rich spike execution means when the correlation point is not included in the predetermined range.

Moreover, 4th invention is set in 3rd invention,
The NOx purification rate calculating means has NOx inflow amount estimating means for estimating the NOx inflow amount flowing into the NOx catalyst,
The apparatus further comprises NOx inflow amount changing means for changing the NOx inflow amount when the amount of the reducing agent changed by the reducing agent amount changing means is a predetermined value or more.

  According to the first invention, the deterioration of the NOx catalyst is detected using the NOx sensor and the air-fuel ratio sensor downstream of the NOx catalyst. Thereby, deterioration of the NOx catalyst can be detected without being affected by adhesion of PM or the like. Furthermore, according to the first invention, the deterioration detection of the NOx catalyst is performed based on the surplus reducing agent amount and the NOx purification rate. Here, the NOx catalyst that is determined to be normal based only on the NOx purification rate includes a NOx catalyst that causes a deterioration in emission characteristics. On the other hand, by considering the amount of surplus reducing agent in addition to the NOx purification rate, it is possible to detect the NOx catalyst degradation with higher accuracy than when the NOx catalyst degradation is detected only from the NOx purification rate. it can.

  According to the second invention, when the correlation point defined by the surplus reducing agent amount and the NOx purification rate is included within the predetermined range, the deterioration detection of the NOx catalyst is executed. This predetermined range is a range in which the deterioration detection of the NOx catalyst can be performed without being affected by the failure of parts other than the NOx catalyst. Therefore, it is possible to accurately detect the deterioration of the NOx catalyst without being affected by the failure of parts other than the NOx catalyst.

  According to the third invention, when the correlation point is not included in the predetermined range, the amount of the reducing agent supplied when the rich spike is executed is changed. Thereby, a correlation point can be included in a predetermined range at the time of the next rich spike execution. Therefore, at the next rich spike execution, it is possible to accurately detect the deterioration of the NOx catalyst without being affected by the failure of parts other than the NOx catalyst.

  According to the fourth aspect of the invention, the NOx inflow amount is changed when the changed amount of the reducing agent is not less than a predetermined value. Therefore, even when the correlation point is greatly deviated from the predetermined range, the correlation point can be included in the predetermined range at the next rich spike execution, coupled with the change in the amount of the reducing agent according to the third invention. .

  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.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to Embodiment 1 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. Downstream of the NOx catalyst 40, an air-fuel ratio sensor 44 for detecting the exhaust air-fuel ratio A / Fout and a NOx sensor 46 for detecting the NOx concentration are provided.

  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. A crank angle sensor 5, an accelerator opening sensor 21, an air flow meter 26, an air-fuel ratio sensor 44, a NOx 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 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 Embodiment 1]
As described above, the system according to the first embodiment includes the NOx catalyst 40. As a method for detecting the deterioration of the NOx catalyst 40, a method using outputs of two air-fuel ratio sensors respectively provided upstream and downstream of the NOx catalyst is known, as described in Patent Document 1 described above. However, if PM or the like discharged from the engine accumulates on the air-fuel ratio sensor upstream of the NOx catalyst, the output of the air-fuel ratio sensor will drop, and it may not be possible to accurately detect the deterioration of the NOx catalyst. . Therefore, in order to prevent PM and the like from adhering to the air-fuel ratio sensor upstream of the NOx catalyst, measures are taken to provide a cover (soot countermeasure cover) on the air-fuel ratio sensor.

  However, when the air-fuel ratio sensor is provided with a cover, the response performance of the output of the air-fuel ratio sensor (hereinafter referred to as “sensor output”) is degraded as shown in FIG. FIG. 2 is a diagram for comparing the response performance of the sensor output when the air-fuel ratio sensor is provided with a cover for preventing adhesion of PM or the like and when it is not provided. In FIG. 2, the straight line with the symbol A indicates the actual change of the air-fuel ratio upstream of the catalyst. An alternate long and short dash line with a symbol B indicates a change in sensor output when a cover is provided on the air-fuel ratio sensor. A broken line with a symbol C indicates a change in sensor output when the air-fuel ratio sensor is not provided with a cover.

  As shown in FIG. 2, the straight line A and the broken line C substantially coincide with each other. For this reason, when the cover is not provided, it turns out that the response performance of a sensor output is high. On the other hand, the change in the alternate long and short dash line B is greatly delayed with respect to the change in the straight line A. For this reason, when a cover is provided, it turns out that the response performance of a sensor output will fall. As described above, when a PM adhesion prevention cover is provided on the air-fuel ratio sensor, the response performance of the sensor output is lowered, so that it is difficult to accurately detect the deterioration of the NOx catalyst.

  Therefore, a method of detecting the deterioration of the NOx catalyst by using only the sensor downstream of the NOx catalyst at the time of rich spike execution without using the sensor upstream of the NOx catalyst is conceivable. For example, a method of detecting the deterioration of the NOx catalyst by using only the output of the NOx sensor arranged downstream of the NOx catalyst can be considered. According to this method, the NOx concentration discharged from the NOx catalyst when the rich spike is executed is detected by the NOx sensor, and the NOx purification rate is calculated using the detection result. Then, the deterioration detection of the NOx catalyst is performed based on the calculated NOx purification rate. That is, when the NOx purification rate is lower than the reference value, it is determined that the NOx catalyst has deteriorated.

  However, as a result of the study by the present inventors, it has been found that the NOx purification rate varies greatly according to the amount of surplus reducing agent that passes through the NOx catalyst 40 during the rich spike execution (hereinafter referred to as “surplus HC amount”). Specifically, it has been found that there is a correlation as shown in FIG. 3 between the surplus HC amount Ghc that passes through the NOx catalyst 40 during rich spike execution and the NOx purification rate Rnox of the NOx catalyst 40. FIG. 3 is a diagram showing a correlation between the surplus HC amount Ghc and the NOx purification rate Rnox at the time of rich spike execution. FIG. 3 shows the correlation between four NOx catalysts C1 to C4 having different purification performances. As can be seen from the correlation between the catalysts C1 to C4, the NOx purification rate Rnox increases as the surplus HC amount Ghc increases.

  Therefore, depending on the method of detecting the catalyst deterioration only by the NOx purification rate described above, the deterioration detection of the NOx catalyst cannot be accurately performed when the surplus HC amount Ghc is large. That is, the NOx catalyst C2 whose NOx purification rate Rnox exceeds the reference value Rth only when the surplus HC amount Ghc is large should be judged as a deteriorated catalyst from the viewpoint of exhaust emission characteristics, but only the NOx purification rate Rnox is determined. As a reference, it can be determined that the catalyst is a normal catalyst.

  Therefore, in the first embodiment, when the rich spike is executed, the deterioration of the NOx catalyst 40 is detected in consideration of both the surplus HC amount Ghc and the NOx purification rate Rnox. Here, the “excess HC amount Ghc” is the amount of HC that is not used for the reduction of NOx in the NOx catalyst 40 out of the HC amount added from the exhaust fuel addition valve 42 at the time of rich spike execution, but has passed through the NOx catalyst. That means. This surplus HC amount Ghc is also referred to as “a slip-through HC amount” by those skilled in the art. The “NOx purification rate Rnox” refers to the ratio of the amount of NOx reduced by the reducing agent supplied at the time of rich spike execution to the NOx amount flowing into the NOx catalyst 40 after the end of the previous rich spike. Hereinafter, the method for detecting deterioration of the NOx catalyst 40 according to the first embodiment will be specifically described.

  The predetermined range R with hatching in FIG. 3 is defined by the surplus HC amount Ghc and the NOx purification rate Rnox. The predetermined range R is a range in which the purification capability of the NOx catalyst 40 can be determined without being affected by the failure of components other than the NOx catalyst 40 (for example, the exhaust fuel addition valve 42).

  Therefore, in the first embodiment, when the correlation point P determined by the surplus HC amount Ghc and the NOx purification rate Rnox is included in the predetermined range R, the deterioration detection of the NOx catalyst 40 is executed. Specifically, when the correlation point P is included in the predetermined range R, if the NOx purification rate Rnox is smaller than a reference value Rth (for example, 40%), it is determined that the NOx catalyst 40 has deteriorated, and NOx If the purification rate Rnox is equal to or greater than the reference value Rth, it is determined that the NOx catalyst 40 is normal.

  In light of the deterioration detection method according to the first embodiment, for the catalysts C1 and C2 shown in FIG. 3, the correlation points P1 and P2 are included in the predetermined range R, and the NOx purification rate Rnox at the correlation points P1 and P2 Is smaller than the reference value Rth, it is determined that the catalyst is a deteriorated catalyst. In addition, for the catalysts C3 and C4 shown in the figure, the correlation points P3 and P4 are included in the predetermined range R, and the NOx purification rate Rnox at the correlation points P3 and P4 is equal to or higher than the reference value Rth. It is determined that there is. The predetermined range R differs depending on the type of the vehicle and the NOx catalyst 40, and therefore is created in advance as a map and stored in the ECU 60.

Next, a method for calculating the surplus HC amount Ghc and the NOx purification rate Rnox will be described.
First, a method for calculating the surplus HC amount Ghc will be described with reference to FIG. FIG. 4 is a diagram for explaining a method of calculating the surplus HC amount Ghc. FIG. 4 shows changes in the air-fuel ratio sensor output A / Fout when the rich spike is executed. As shown in FIG. 4, the rich spike is started at time t1. That is, the addition of HC as a reducing agent is started from the exhaust fuel addition valve 42 to the exhaust gas flowing through the exhaust passage 38. In addition, the addition of HC may be added only once, or the predetermined amount may be divided and added in multiple times. The added HC is used for reduction and purification of NOx stored in the NOx catalyst 40.
While NOx is being reduced by this HC (for example, time t2), HC does not slip through the NOx catalyst 40. For this reason, the air-fuel ratio sensor output A / Fout is maintained at the theoretical air-fuel ratio A / Fst. Then, after all the NOx of the NOx catalyst 40 is reduced (for example, at time t3), the added HC is not used for the reduction of NOx, and thus passes through the NOx catalyst 40. For this reason, the air-fuel ratio sensor output A / Fout changes to a richer side than the theoretical air-fuel ratio A / Fst. When all the HC added from the exhaust fuel addition valve 42 passes through the NOx catalyst 40 (for example, time t4), the air-fuel ratio sensor output A / Fout changes again to the lean side from the theoretical air-fuel ratio A / Fst. . The total amount of HC passing through the NOx catalyst 40 corresponds to the “excess HC amount Ghc”. This surplus HC amount Ghc can be calculated by the following equation (1) using the air-fuel ratio sensor output A / Fout. In the following equation (1), “Ga” is the amount of intake air.
Ghc = ∫ {(Ga / (A / Fout))-(Ga / (A / Fst))} dt (1)

Next, a method for calculating the NOx purification rate Rnox will be described. As described above, the “NOx purification rate Rnox” is the ratio of the amount of NOx reduced by the reducing agent supplied at the time of rich spike execution to the amount of NOx flowing into the NOx catalyst 40 after the end of the previous rich spike. Say. Therefore, the NOx purification rate Rnox can be calculated by the following equation (2). In the following equation (2), “Nin” is the amount of NOx flowing into the NOx catalyst 40, and “Nout” is the amount of NOx discharged from the NOx catalyst 40 when the rich spike is executed. This “Nin” can be estimated with reference to a map (not shown) defined by the relationship between the engine speed Ne and the fuel injection amount Q. “Nout” can be calculated using the NOx sensor output and the intake air amount Ga. This “Nin” can also be obtained by model calculation without using the map.
Rnox = {1- (Nout / Nin)} × 100 ... (2)

According to the first embodiment, based on the surplus HC amount Ghc obtained using the output of the air-fuel ratio sensor 44 downstream of the NOx catalyst 40 and the output of the NOx sensor 46 and the NOx purification rate Rnox, the NOx catalyst 40 Detection of deterioration was performed. Therefore, it is possible to detect the deterioration of the NOx catalyst 40 without being affected by PM discharged from the engine 1 or the like. Furthermore, by considering not only the NOx purification rate Rnox but also the surplus HC amount Ghc, it is possible to detect the degradation of the NOx catalyst 40 with higher accuracy than when the NOx catalyst degradation is detected only by the NOx purification rate Rnox. it can.
Further, according to the first embodiment, when the correlation point P determined by the surplus HC amount Ghc and the NOx purification rate Rnox is included in the predetermined range R, the deterioration detection of the NOx catalyst 40 is performed. Therefore, it is possible to accurately detect the deterioration of the NOx catalyst 40 without being affected by the failure of parts other than the NOx catalyst 40.

  By the way, the injection accuracy of the exhaust fuel addition valve 42 may decrease with time. Then, there is a possibility that the correlation points P41, 42 are not included in the predetermined range R like the correlation points indicated by reference numerals P41, 42 in FIG. In such a case, the amount of HC added by the exhaust fuel addition valve 42 is changed. For example, in the case of the correlation point P41, the change amount of the HC amount is calculated by a map or a calculation formula according to the difference d between the surplus HC amount Ghc and the predetermined range R. By changing the HC amount in this way, that is, by changing the rich depth, the correlation point determined by the surplus HC amount Ghc and the NOx purification rate Rnox is included in the predetermined range R at the next rich spike execution. be able to. Therefore, it is possible to detect the deterioration of the NOx catalyst 40 without being affected by the failure of parts other than the NOx catalyst 40 at the next rich spike execution.

[Specific Processing in Embodiment 1]
FIG. 5 is a flowchart showing a routine executed by the ECU 60 in the first embodiment. This routine is started at predetermined intervals.

  According to the routine shown in FIG. 5, first, it is determined whether or not a precondition for executing the deterioration determination of the NOx catalyst 40 is satisfied (step 100). In this step 100, it is determined by monitoring the outputs of the signal lines of the exhaust fuel addition valve 42, the air-fuel ratio sensor 44 and the NOx sensor 46 that there is no disconnection. If it is determined in step 100 that the preconditions are not satisfied, this routine is temporarily terminated.

  If it is determined in step 100 that the precondition is satisfied, it is determined whether or not the rich spike is executed (step 102). The deterioration detection of the NOx catalyst 40 according to the first embodiment is performed when the rich spike is executed. Therefore, if it is determined in step 102 that the rich spike is not being executed, this routine is temporarily terminated.

  On the other hand, if it is determined in step 102 that the rich spike is being executed, the surplus HC amount Ghc is calculated according to the above equation (1) using the air-fuel ratio sensor output (step 104). Thereafter, the NOx purification rate Rnox is calculated according to the above equation (2) using the NOx sensor output (step 106). Then, it is determined whether or not the surplus HC amount Ghc at the calculated NOx purification rate Rnox is included in a predetermined range (step 108). That is, in this step 108, it is determined whether or not the correlation point P determined by the surplus HC amount Ghc calculated in step 104 and the NOx purification rate Rnox calculated in step 106 is included in the predetermined range R. . The predetermined range R is a range determined in advance according to the type of the vehicle or the NOx catalyst, and a range in which the deterioration detection of the NOx catalyst 40 can be performed without being affected by the failure of parts other than the NOx catalyst 40. It is. In this step 108, a map that is stored in advance in the ECU 60 and in which the predetermined range R is determined is read out, and a correlation point determined by the surplus HC amount Ghc and the NOx purification rate Rnox calculated in the above steps 104 and 106, respectively. It is determined whether or not P is included in the predetermined range R of the map.

  When it is determined in step 108 that the correlation point P is not included in the predetermined range R, for example, in the case of correlation points P41 and P42 shown in FIG. 3, the amount of HC added from the exhaust fuel addition valve 42 Is changed (step 110). In this step 110, when the surplus HC amount Ghc is larger than the predetermined range, the HC amount is decreased, and when the surplus HC amount Gha is smaller than the predetermined range, the HC amount is increased. Here, the amount of change in the HC amount can be determined according to the difference between the surplus HC amount Ghc at the correlation point P and the predetermined range R (for example, the difference d shown in FIG. 3). Specifically, the change amount of the HC amount can be obtained according to the difference by referring to a map stored in advance in the ECU 60 or using a mathematical expression. After the process of step 110, the process returns to the determination process of step 102.

  On the other hand, when it is determined in step 108 that the correlation point P is included in the predetermined range R, it is determined whether or not the NOx purification rate Rnox calculated in step 106 is smaller than the reference value Rth (step 112). ). This reference value Rth is a reference value for determining the deterioration of the NOx catalyst 40, and is, for example, 40 (%). If it is determined in step 112 that the NOx purification rate Rnox is smaller than the reference value Rth, it is determined that the NOx catalyst 40 has deteriorated (step 114). In this case, processing such as lighting of a warning lamp is performed in order to make the vehicle driver recognize the catalyst deterioration. When it is determined that the NOx purification rate Rnox is equal to or greater than the reference value Rth, it is determined that the NOx catalyst 40 is normal (step 116).

As described above, according to the routine shown in FIG. 5, when the correlation point P determined by the surplus HC amount Ghc and the NOx purification rate Rnox is included in the predetermined range R when the rich spike is executed, the NOx purification rate Rnox The deterioration detection of the NOx catalyst 40 is executed by comparing with the reference value Rth. Therefore, the surplus HC amount Ghc is taken into consideration when detecting the deterioration of the NOx catalyst 40. For this reason, it is possible to detect the deterioration of the NOx catalyst 40 with higher accuracy than when the deterioration of the NOx catalyst is detected only by the NOx purification rate Rnox.
Further, when the correlation point P is included in the predetermined range R, the purification performance of the NOx catalyst 40 can be accurately determined without being affected by the failure of parts other than the NOx catalyst 40.
When the correlation point P is not included in the predetermined range R, the amount of HC added by the exhaust fuel addition valve 42 is changed. Thereby, the correlation point P can be included in the predetermined range R at the next rich spike execution. Therefore, even when the exhaust fuel addition valve 42 changes with time, the purification performance of the NOx catalyst 40 can be accurately improved without being affected by the failure of parts other than the NOx catalyst 40 at the next rich spike execution. Can be determined.

  By the way, although the diesel engine was demonstrated in this Embodiment 1, this invention is applicable also to a spark ignition type gasoline engine. It is preferable to apply the present invention to an in-cylinder fuel injection type gasoline engine with a relatively large PM emission amount (the same applies to a second embodiment described later).

  In the first embodiment, the NOx catalyst 40 is the “NOx catalyst” in the first invention, the air-fuel ratio sensor 44 is the “air-fuel ratio sensor” in the first invention, and the NOx sensor 46 is the first invention. The exhaust fuel addition valve 42 corresponds to the “rich spike execution means” in the first aspect of the invention. In the first embodiment, the ECU 60 executes the process of step 102, so that the “rich spike execution means” in the first invention executes the process of step 104, and “ The “excess reducing agent amount calculating means” executes the processing of step 106, whereby the “NOx purification rate calculating means” in the first invention and the “NOx inflow amount estimating means” in the fourth invention are the steps 108, 112, By executing the process 114, the “deterioration detecting means” in the first and second inventions is realized, and by executing the process in step 110, the “reducing agent amount changing means” in the third invention is realized. Yes.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG.
The system of the second embodiment can be realized by causing the ECU 60 to execute a routine shown in FIG. 6 to be described later using the hardware configuration shown in FIG.

[Features of Embodiment 2]
In the first embodiment, when the correlation point P determined by the surplus HC amount Ghc and the NOx purification rate Rnox is not included in the predetermined range R, the amount of HC added by the exhaust fuel addition valve 42 is changed. Yes. This is because the amount of HC injected from the exhaust fuel addition valve 42 is likely to change due to changes over time. By changing the amount of HC, the correlation point P can be included in the predetermined range R at the next rich spike execution. Therefore, it is possible to accurately detect the deterioration of the NOx catalyst 40 at the next rich spike execution.

  However, when the HC change amount is larger than the reference value, for example, when the correlation point P is greatly deviated from the predetermined range R, it can be estimated that the exhaust fuel addition valve 42 is not the main factor. In this case, it is estimated that the NOx purification rate Rnox cannot be accurately calculated. Here, in the above equation (2) for calculating the NOx purification rate Rnox, the NOx amount Nin flowing into the NOx catalyst 40 is obtained by a map or model calculation.

  Therefore, in the second embodiment, when the HC change amount is larger than the reference value, the NOx amount Nin obtained by a map or model calculation is changed. Thereby, the NOx purification rate Rnox can be accurately calculated. Therefore, the correlation point P can be included in the predetermined range R at the next rich spike execution. Therefore, according to the second embodiment, it is possible to accurately detect the deterioration of the NOx catalyst 40 without being affected by the failure of parts other than the NOx catalyst 40.

[Specific Processing in Second Embodiment]
FIG. 6 is a flowchart showing a routine executed by the ECU 60 in the second embodiment. This routine can be executed in parallel with the routine shown in FIG. 5, and is started at predetermined intervals.

  According to the routine shown in FIG. 6, first, it is determined whether or not the amount of HC (so-called rich depth) added from the exhaust fuel addition valve 42 at the time of rich spike execution has been changed (step 120). In step 120, it is possible to determine whether or not the HC amount has been changed by referring to the execution history in step 110 of the routine shown in FIG. If it is determined in step 120 that the HC amount has not been changed, this routine is temporarily terminated. Therefore, after the process of step 110 of the routine shown in FIG. 5 is executed, the process of this routine is effectively executed.

  If it is determined in step 120 that the HC amount has been changed, the HC change amount is read (step 122). Thereafter, it is determined whether or not the HC change amount read in step 122 is larger than a predetermined value (step 124). This predetermined value is a reference value for determining whether or not the exhaust fuel addition valve 42 is the main factor that the correlation point P is not included in the predetermined range R. This predetermined value can be determined by the result of an endurance test performed using a vehicle. If it is determined in step 124 that the HC change amount is less than or equal to the predetermined value, for example, if the difference between the correlation point P and the predetermined range R is small, only the change of the HC amount is correlated at the next rich spike execution. It is determined that the point P can be included in the predetermined range R. Therefore, in this case, this routine is once ended.

  On the other hand, when the HC change amount is larger than the predetermined value in step 124, it is determined that only the change with time of the exhaust fuel addition valve 42 is not a factor. In this case, it is determined whether or not the correlation point P (that is, the surplus HC amount Ghc at the correlation point P, the NOx purification rate Rnox, hereinafter the same) is larger than the predetermined range R (step 126). When it is determined in step 126 that the correlation point P is larger than the predetermined range R (for example, in the case of the correlation point P42 shown in FIG. 3), the NOx flowing into the NOx catalyst 40 calculated by the map or the model calculation. It is determined that the estimated value of the amount (hereinafter referred to as “catalyst inflow NOx estimated amount”), that is, “Nin” in the above equation (2) is smaller than the NOx amount actually flowing into the NOx catalyst 40. Therefore, in this case, the estimated catalyst inflow NOx amount Nin is increased (step 128). Specifically, the map value is changed or the coefficient for model calculation is changed so that the estimated catalyst inflow NOx amount Nin is increased.

  If it is determined in step 126 that the correlation point P is not larger than the predetermined range R, it is determined whether or not the correlation point P is smaller than the predetermined range R (step 130). If it is determined in step 130 that the correlation point P is not smaller than the predetermined range R, that is, if the correlation point P is included in the predetermined range R, it is not necessary to change the estimated catalyst inflow NOx amount. Therefore, this routine is terminated.

  On the other hand, if it is determined in step 130 that the correlation point P is smaller than the predetermined range R (for example, in the case of the correlation point P41 shown in FIG. 3), the estimated catalyst inflow NOx value calculated by the map or model calculation is used. It is determined that Nin is larger than the amount of NOx actually flowing into the NOx catalyst 40. Therefore, in this case, the estimated catalyst inflow NOx amount Nin is decreased (step 132). Specifically, the map value is changed or the model calculation coefficient is changed so that the estimated catalyst inflow NOx amount Nin is reduced.

  As described above, according to the routine shown in FIG. 6, when the change amount of the HC amount added by the exhaust fuel addition valve 42 is larger than a predetermined value, the estimated catalyst inflow NOx amount is changed. Thereby, coupled with the change of the HC amount, the correlation point P can be included in the predetermined range R at the next rich spike execution. Therefore, at the next rich spike execution, the deterioration detection of the NOx catalyst 40 can be accurately executed without being affected by the failure of parts other than the NOx catalyst 40.

  In the second embodiment, when the HC change amount is larger than the predetermined value, the estimated NOx amount flowing into the NOx catalyst 40 is increased or decreased. Instead of this increase or decrease in the estimated NOx amount, Alternatively, the output characteristic of the air flow meter 26 (that is, the intake air amount Ga) may be changed along with the increase / decrease of the estimated NOx amount. By changing the output characteristics of the air flow meter 26, the NOx purification rate Rnox can be accurately obtained and the correlation point P can be included in the predetermined range R as in the second embodiment.

  In the second embodiment, the “NOx inflow amount changing means” according to the fourth aspect of the present invention is realized by the ECU 60 executing the process of step 128 or 132.

It is a figure for demonstrating the system configuration | structure by Embodiment 1 of this invention. It is a figure for comparing the response performance of a sensor output with the case where the cover for adhesion prevention, such as PM, is not provided in the air-fuel ratio sensor. It is a figure which shows the correlation of the excess HC amount Ghc at the time of rich spike execution, and NOx purification rate Rnox. It is a figure for demonstrating the calculation method of the surplus HC amount Ghc. 5 is a flowchart showing a routine that is executed by the ECU 60 in the first embodiment of the present invention. In Embodiment 2 of this invention, it is a flowchart which shows the routine which ECU60 performs.

Explanation of symbols

1 Internal combustion engine 26 Air flow meter 40 NOx catalyst 42 Exhaust fuel addition valve 44 NOx sensor 46 Air-fuel ratio sensor 60 ECU

Claims (4)

A NOx catalyst that is provided in an exhaust passage of the internal combustion engine and occludes or reduces NOx according to an exhaust air-fuel ratio;
An air-fuel ratio sensor for detecting an exhaust air-fuel ratio in an exhaust passage downstream of the NOx catalyst;
A NOx sensor for detecting a NOx concentration in an exhaust passage downstream of the NOx catalyst;
Rich spike execution means for executing a rich spike for supplying a reducing agent to the exhaust passage upstream of the NOx catalyst;
Surplus reducing agent amount calculating means for calculating an amount of excess reducing agent that passes through the NOx catalyst based on the exhaust air-fuel ratio when the rich spike is executed;
NOx purification rate calculating means for calculating a NOx purification rate of the NOx catalyst based on the NOx concentration during execution of the rich spike;
A deterioration detection device for NOx catalyst, comprising deterioration detection means for detecting deterioration of the NOx catalyst based on the excess reducing agent amount and the NOx purification rate. In the NOx catalyst deterioration detection device according to claim 1,
The deterioration detecting means performs deterioration detection of the NOx catalyst when a correlation point defined by the surplus reducing agent amount and the NOx purification rate is included within a predetermined range. Deterioration detection device. The deterioration detection device for a NOx catalyst according to claim 2,
NOx catalyst deterioration detection further comprising reducing agent amount changing means for changing the amount of reducing agent supplied by the rich spike execution means when the correlation point is not included in the predetermined range. apparatus. In the NOx catalyst deterioration detection device according to claim 3,
The NOx purification rate calculating means has NOx inflow amount estimating means for estimating the NOx inflow amount flowing into the NOx catalyst,
The NOx catalyst deterioration detecting device further comprising NOx inflow amount changing means for changing the NOx inflow amount when the amount of the reducing agent changed by the reducing agent amount changing means is a predetermined value or more. .

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