JP4650370B2 - Catalyst deterioration detector - Google Patents

Description

  The present invention relates to a catalyst deterioration detection device that detects deterioration of a catalyst having oxidation ability.

  An apparatus is known that calculates a temperature difference between an inlet portion and an outlet portion of a catalyst in consideration of a time delay of a change over time, and diagnoses catalyst deterioration based on the calculated temperature difference (for example, Patent Document 1). reference.).

JP 2000-303823 A JP 2003-293745 A JP 2005-146900 A

  However, the sensitivity of the catalyst temperature to the degree of catalyst deterioration is small. For this reason, the method based on the temperature difference as described in Patent Document 1 may not be able to accurately determine the deterioration of the catalyst.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a catalyst deterioration detection apparatus capable of accurately detecting deterioration of a catalyst.

In order to achieve the above object, a first invention is a catalyst deterioration detection device for detecting deterioration of a catalyst,
A catalyst disposed in the exhaust passage of the internal combustion engine and having an oxidizing ability;
Air-fuel ratio detection means for detecting an exhaust air-fuel ratio downstream of the catalyst;
Reducing agent addition means for adding a reducing agent to the exhaust passage upstream of the catalyst;
An addition amount measuring means for measuring the amount of addition of the reducing agent based on the exhaust air / fuel ratio detected when the rich spike is detected and when the rich spike is not performed, detected by the air / fuel ratio detection means;
A deterioration detecting means for detecting deterioration of the catalyst based on a deviation between the indicated addition amount to the reducing agent adding means and the measured addition amount measured by the addition amount measuring means ;
The deterioration detection means includes ratio calculation means for calculating a ratio of the measured addition amount to the indicated addition amount, and detects deterioration of the catalyst when the ratio is smaller than a reference value .

The second invention is the first invention, wherein
The deterioration detection means includes ratio calculation means for calculating a ratio of the measured addition amount to the indicated addition amount, and detects deterioration of the catalyst when the ratio is smaller than a reference value.

  According to the first invention, deterioration of the catalyst is detected based on the difference between the command injection amount and the measured addition amount. The deviation between the command injection amount and the measured addition amount has a correlation with the HC amount or HC concentration that passes through the catalyst, that is, the oxidation ability of the catalyst. Therefore, it is possible to accurately detect the deterioration of the catalyst based on the difference between the command injection amount and the measured addition amount.

  According to the second invention, the deterioration of the catalyst is detected based on the ratio of the measured addition amount to the command injection amount. This ratio has a correlation with the amount or concentration of HC passing through the catalyst, that is, the oxidation ability of the catalyst. Therefore, it is possible to accurately detect the deterioration of the catalyst based on the ratio of the measured addition amount to the command injection amount. Furthermore, even when the commanded injection amount varies depending on the operating conditions, it is possible to accurately detect the deterioration of the catalyst without being affected by variations in the measured addition amount.

  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. An oxidation catalyst 40 is provided downstream of the turbine 24b. The oxidation catalyst 40 is a catalyst having an oxidation function. A NOx catalyst 42 is provided downstream of the oxidation catalyst 40. The NOx catalyst 42 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 42 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 42 may have a function other than collecting soot.

  Between the turbine 24b and the oxidation catalyst 40, there is provided an exhaust fuel addition valve 44 for adding fuel as a reducing agent to the exhaust gas. A first air-fuel ratio sensor 46 is provided between the oxidation catalyst 40 and the NOx catalyst 42. A second air-fuel ratio sensor 48 is provided downstream of the NOx catalyst 42. These air-fuel ratio sensors 46 and 48 are configured to detect the exhaust air-fuel ratio at the installation position, respectively.

  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 44, 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, a first air-fuel ratio sensor 46, a second air-fuel ratio sensor 48, 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 a fuel injection amount (in-cylinder 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]
When the amount of NOx occluded in the NOx catalyst 42 of the system exceeds a predetermined value, so-called rich spike is performed in order to reduce and release NOx. That is, fuel as a reducing agent is added from the exhaust fuel addition valve 44, and the regeneration process of the NOx catalyst 42 is performed by this reducing agent. The first embodiment proposes a method for detecting deterioration of the oxidation catalyst 40 disposed upstream of the NOx catalyst 42 during the rich spike operation.

FIG. 2 is a diagram showing a change in the output of the first air-fuel ratio sensor 46 (hereinafter referred to as “air-fuel ratio sensor output”) when the rich spike is performed.
When the rich spike is not performed, that is, when fuel is not added from the exhaust fuel addition valve 44, the air-fuel ratio sensor output becomes an output A / F_A as shown by a one-dot chain line in FIG.
On the other hand, when rich spike is being performed, that is, when fuel is being added from the exhaust fuel addition valve 44, the air-fuel ratio sensor output changes to output A / F_B as shown by the solid line in FIG.
As will be described later, the amount of fuel added from the exhaust fuel addition valve 44 is determined using the air-fuel ratio sensor output A / F_A when the rich spike is not executed and the air-fuel ratio sensor output A / F_B when the rich spike is executed. It can be measured. That is, the measured addition amount can be obtained based on the air-fuel ratio sensor outputs A / F_A and A / F_B.

  By the way, when the amount of in-cylinder injection is large, the amount of HC discharged into the exhaust passage 38 increases, and the HC concentration in the exhaust gas increases. As a result, as indicated by a broken line in FIG. 2, the air-fuel ratio sensor output becomes an output A / F_C that is leaner than the output A / F_B. That is, the air-fuel ratio sensor output causes a lean shift. The reason for the occurrence of the lean deviation is that the fuel (HC) is a polymer, so that it cannot pass through a diffusion resistance layer (for example, a zirconia layer) (not shown) of the air-fuel ratio sensor 46 and reaches the sensor portion. This is because it cannot be done. Thus, the higher the HC concentration in the exhaust gas, the more the air-fuel ratio sensor output shifts to the lean side.

  FIG. 3 is a diagram for explaining a method of measuring the amount of fuel added from the exhaust fuel addition valve 44 based on the air-fuel ratio sensor outputs A / F_A and A / F_B. In FIG. 3, as in FIG. 2, the symbol “A / F_A” represents the air-fuel ratio sensor output when the rich spike is not performed, and the symbol “A / F_B” represents the air-fuel ratio sensor output when the rich spike is performed. ing.

The air-fuel ratio sensor output A / F_A when the rich spike is not performed can be expressed as the following equation (1). In the following equation (1), “Ga” is the intake air amount, and “Q” is the in-cylinder fuel injection amount.
A / F_A = Ga / Q ... (1)
When the above equation (1) is transformed, the following equation (2) is obtained.
Q = Ga / (A / F_A) ... (2)

Further, the air-fuel ratio sensor output A / F_B when the rich spike is performed can be expressed as the following equation (3). In the following equation (3), “Qex” is the amount of fuel added from the exhaust fuel addition valve 44.
A / F_B = Ga / (Q + Qex) ... (3)
When the above equation (3) is transformed, the following equation (4) is obtained.
Q + Qex = Ga / (A / F_B) ... (4)

The following equation (5) is obtained by subtracting the above equation (2) from the above equation (4), and the following equation (6) is obtained by further modifying the following equation (5).
Qex = Ga × {1 / (A / F_B) -1 / (A / F_A)} (5)
= Ga × {(A / F_A)-(A / F_B)} / (A / F_A) / (A / F_B) (6)

The air-fuel ratio sensor output A / F_A in the above equation (6) can be acquired when rich spike is not performed. Therefore, using the intake air amount Ga and the air-fuel ratio sensor output A / F_B, the amount of fuel added instantaneously (at a certain time) during the rich spike operation is calculated according to the above equation (6). By accumulating the added fuel amount only during the rich spike time t shown in FIG. 3, the amount of fuel added from the exhaust fuel addition valve 44 at the time of rich spike execution can be measured. That is, the measured addition amount is determined.
A method of detecting the deterioration of the oxidation catalyst 40 based on the measured addition amount obtained by such a method is conceivable.

FIG. 4 is a diagram showing the measured addition amount for each operating condition.
As shown in FIG. 4, the measured addition amount (g) is obtained under four operating conditions in which the engine speed Ne (rpm) and the in-cylinder injection amount (mm ³ / st) are different. Further, under each operating condition, measured addition amounts are required for both the normal catalyst (also referred to as “new touch”) and the deteriorated catalyst. As shown in FIG. 4, for the normal catalyst, it was found that the measured addition amount was the same even if the operating conditions were different. However, for the deteriorated catalyst, it was found that when the operating conditions are different, the measured addition amount varies in spite of the same degree of deterioration. From this, it was found that it is difficult to accurately detect the deterioration of the oxidation catalyst 40 only by comparing the measured addition amount with the reference value.

  Further, as a result of investigations by the present inventors, the difference between the measured addition amount and the indicated addition amount given from the ECU 60 to the exhaust fuel addition valve 44 is relative to the HC concentration or HC amount that passes through the oxidation catalyst 40. It was found that there was a correlation. That is, it has been found that the difference between the measured addition amount and the indicated addition amount has a correlation with the oxidation ability of the oxidation catalyst 40.

FIG. 5 is a graph plotting the relationship between the ratio R of the measured addition amount relative to the indicated addition amount and the HC concentration downstream of the oxidation catalyst 40 for each operating condition. FIG. 6 is a diagram showing the relationship between the ratio R and the HC concentration shown in FIG.
As shown in FIG. 5, the relationship between the ratio R and the HC concentration is plotted under four operating conditions in which the engine speed Ne (rpm) and the in-cylinder injection amount (mm ³ / st) are different. The operating conditions shown in FIG. 5 are the same as the operating conditions shown in FIG.

  The HC concentration on the horizontal axis in FIGS. 5 and 6 is an index of the oxidation ability of the oxidation catalyst 40 (that is, the degree of deterioration of the oxidation catalyst 40). This is because when the oxidation ability of the oxidation catalyst 40 decreases (that is, when the oxidation catalyst 40 deteriorates), the amount of HC that passes through the oxidation catalyst 40 increases, and the HC concentration downstream of the oxidation catalyst 40 increases. Therefore, when the HC concentration is low, the oxidation catalyst 40 is normal because the oxidation ability of the oxidation catalyst 40 is high. On the other hand, when the HC concentration is high, the oxidation catalyst 40 is deteriorated because the oxidation ability of the oxidation catalyst 40 is low. Therefore, as shown in FIG. 6, when the HC concentration exceeds the reference value HCth, that is, when the ratio R becomes smaller than the reference value Rth, it can be determined that the oxidation catalyst 40 has deteriorated.

As described above, according to the first embodiment, the deterioration determination of the oxidation catalyst 40 is performed based on the ratio R having a correlation with the HC concentration downstream of the oxidation catalyst 40. Therefore, the deterioration determination of the oxidation catalyst 40 can be accurately performed in consideration of the oxidation ability of the oxidation catalyst 40 having a correlation with the ratio R.
Further, since the deterioration determination of the oxidation catalyst 40 is performed based on the ratio R, the command injection amount may not be constant, and the command injection amount can be changed according to the operating conditions of the internal combustion engine 1. Therefore, the deterioration determination of the oxidation catalyst 40 can be accurately performed under a wide range of operating conditions.

[Specific Processing in Embodiment 1]
FIG. 7 is a flowchart showing a routine executed by the ECU 60 in the first embodiment. The routine shown in FIG. 7 is started at predetermined intervals.

  According to the routine shown in FIG. 7, it is first 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, the exhaust fuel addition valve 44 is instructed to add a predetermined amount of reducing agent (step 102). The fuel addition amount given to the exhaust fuel addition valve 44 from the ECU 60 in this step 102 is the above-described command addition amount. Thereby, a rich spike is performed.

  Next, the reducing agent addition amount is measured according to the above equation (6) using the output A / F_B of the first air-fuel ratio sensor 46 and the intake air amount Ga when the rich spike is performed (step 104). In this step 104, the measured addition amount is obtained.

  Next, the ratio R of the measured addition amount obtained in step 104 to the indicated addition amount instructed to the exhaust fuel addition valve 44 in step 102 is calculated (step 106).

  Next, it is determined whether or not the ratio R calculated in step 106 is smaller than a reference value Rth (step 108). This reference value Rth is a reference value for determining the deterioration of the oxidation catalyst 40 in relation to the HC concentration passing through the oxidation catalyst 40 (see FIG. 6). That is, the reference value Rth has a correlation with the reference value HCth indicating the allowable HC concentration downstream of the oxidation catalyst 40. Therefore, in this step 108, it is determined whether the oxidation capability of the oxidation catalyst 40 is sufficient or has decreased.

  If it is determined in step 108 that the ratio R is smaller than the reference value Rth, it is determined that the oxidation capability of the oxidation catalyst 40 is reduced. In this case, it is determined that the oxidation catalyst 40 has deteriorated (step 110). On the other hand, if it is determined in step 108 that the ratio R is greater than or equal to the reference value Rth, it is determined that the oxidation capability of the oxidation catalyst 40 has not decreased. In this case, it is determined that the oxidation catalyst 40 is normal (step 112). Thereafter, this routine is terminated.

  As described above, according to the routine shown in FIG. 7, the measured addition amount is obtained based on the output A / F_B of the first air-fuel ratio sensor 46, and the ratio R of the measured addition amount to the indicated addition amount is calculated. This ratio R has a correlation with the amount or concentration of HC that passes through the oxidation catalyst 40 (that is, the oxidation ability of the oxidation catalyst 40). Therefore, the deterioration of the oxidation catalyst 40 is detected by comparing the ratio R with the reference value Rth. Therefore, it is possible to accurately detect the deterioration of the oxidation catalyst 40 in consideration of the oxidation ability of the oxidation catalyst 40.

  In the first embodiment, the measured addition amount is obtained based on the output A / F_B of the first air-fuel ratio sensor 46, but can be obtained based on the output of the second air-fuel ratio sensor 48. However, the measured addition amount can be obtained with higher accuracy when the output of the first air-fuel ratio sensor 46 is used than when the output of the second air-fuel ratio sensor 48 is used.

  In the first embodiment, the exhaust fuel addition valve 44 is provided between the turbine 24b and the oxidation catalyst 40, but may be provided upstream of the turbine 24b. Also in this case, the same effect as in the first embodiment can be obtained.

  In the first embodiment, the oxidation catalyst 40 is the “catalyst” in the first invention, the first air-fuel ratio sensor 46 is the “air-fuel ratio detecting means” in the first invention, and the exhaust fuel addition valve 44 is This corresponds to the “reducing agent adding means” in the first invention. In the first embodiment, the ECU 60 executes the process of step 104, so that the “addition amount measuring means” in the first invention executes the process of step 106. By executing the processing of steps 106, 108, 110 and 112 by the “ratio calculating means”, the “deterioration detecting means” in the first and second inventions are realized.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. The system of the eighth embodiment can be realized by causing the ECU 60 to execute a routine shown in FIG. 8 described later using the hardware configuration shown in FIG.

[Features of Embodiment 2]
In the first embodiment, the catalyst deterioration is detected based on the ratio R of the measured addition amount to the indicated addition amount. By the way, the difference between the indicated addition amount and the measured addition amount is not limited to the ratio R.

In the second embodiment, a method for detecting catalyst deterioration based on the difference D between the indicated addition amount and the measured addition amount will be described.
By the way, in the first embodiment, the deterioration of the oxidation catalyst 40 is detected based on the ratio R of the measured addition amount to the indicated addition amount. For this reason, it is considered that even if the command addition amount is changed according to the operating conditions of the internal combustion engine 1, there is almost no influence on the deterioration detection. On the other hand, in the second embodiment, the deterioration of the oxidation catalyst 40 is detected based on the absolute amount, which is the difference D between the indicated addition amount and the measured addition amount. For this reason, if the instruction addition amount is changed in accordance with the operating condition of the internal combustion engine 1, there is a possibility that the detection of deterioration may be affected.

  Therefore, in the second embodiment, the instruction addition amount is constant regardless of the operating conditions of the internal combustion engine. Thereby, a correlation similar to the correlation shown in FIG. 6 can be obtained between the difference D between the indicated addition amount and the measured addition amount and the HC concentration (or HC amount) that passes through the oxidation catalyst 40.

  Further, when based on the difference D, it is necessary that a sufficient amount of air or oxygen is present as compared to the indicated addition amount. This is because, when the amount of air or oxygen is insufficient, there may occur a situation where the HC concentration downstream of the oxidation catalyst 40 becomes high although the oxidation ability of the oxidation catalyst 40 is sufficient.

Therefore, in the second embodiment, the deterioration of the oxidation catalyst 40 is detected when the condition of the following expression (7) is satisfied. In the following equation (7), “Ga” represents the intake air amount, “Q” represents the in-cylinder injection amount, “Co” represents the oxygen concentration in the exhaust gas, and “Gad” represents the commanded injection amount. Yes.
(Ga + Q) × Co >> Qad ... (7)
“Ga + Q” in the above equation (7) is the amount of exhaust gas. Therefore, the above equation (7) means a condition that “the amount of oxygen contained in the exhaust gas is sufficiently larger than the command injection amount”. A typical operation state that satisfies the above equation (7) is high-speed steady operation. Therefore, in the second embodiment, the deterioration detection of the oxidation catalyst 40 based on the difference D is executed during the high-speed steady operation.

  As described above, according to the second embodiment, the deterioration determination of the oxidation catalyst 40 is performed based on the difference D having a correlation with the HC concentration. Therefore, the deterioration determination of the oxidation catalyst 40 can be accurately performed in consideration of the oxidation ability of the oxidation catalyst 40 having a correlation with the difference D.

[Specific Processing in Second Embodiment]
FIG. 8 is a flowchart showing a routine executed by the ECU 60 in the second embodiment. The routine shown in FIG. 8 is started at predetermined intervals.

  According to the routine shown in FIG. 8, similarly to the routine shown in FIG. 7, it is determined whether or not there is a catalyst deterioration determination request (step 100). If it is determined in step 100 that there is a catalyst deterioration determination request, it is determined whether or not the internal combustion engine 1 is in high-speed steady operation (step 114). If it is determined in step 114 that the high-speed steady operation is not being performed, this routine is temporarily terminated.

On the other hand, if it is determined in step 114 that high-speed steady operation is being performed, the addition of the additive is instructed (step 102) and the reducing agent is added according to the above equation (6), as in the routine shown in FIG. The amount is measured (step 104).
Thereafter, a difference D between the indicated addition amount instructed to the exhaust fuel addition valve 44 in step 102 and the measured addition amount obtained in step 104 is calculated (step 116).

  Next, it is determined whether or not the difference D calculated in step 116 is smaller than a reference value Dth (step 118). The reference value Dth is a reference value for determining the deterioration of the oxidation catalyst 40 in relation to the HC concentration that passes through the oxidation catalyst 40, similarly to the reference value Rth of the first embodiment.

  If the difference D is greater than the reference value Dth in step 118, it is determined that the oxidation capability of the oxidation catalyst 40 has decreased. In this case, it is determined that the oxidation catalyst 40 has deteriorated (step 110). On the other hand, if it is determined in step 118 that the difference D is less than or equal to the reference value Dth, it is determined that the oxidation capability of the oxidation catalyst 40 has not decreased. In this case, it is determined that the oxidation catalyst 40 is normal (step 112). Thereafter, this routine is terminated.

  As described above, according to the routine shown in FIG. 8, the measured addition amount is obtained based on the output A / F_B of the first air-fuel ratio sensor 46, and the difference D between the indicated addition amount and the measured addition amount is calculated. . This difference D has a correlation with the amount or concentration of HC passing through the oxidation catalyst 40 (that is, the oxidation ability of the oxidation catalyst 40). Therefore, the deterioration of the oxidation catalyst 40 is detected by comparing the difference D with the reference value Dth. Therefore, it is possible to accurately detect the deterioration of the oxidation catalyst 40 in consideration of the oxygen capability of the oxidation catalyst 40.

  In the second embodiment, the “deterioration detecting means” in the first invention is realized by the ECU 60 executing the processing of steps 116, 118, 110, and 112.

It is a figure for demonstrating the system configuration | structure by Embodiment 1 of this invention. It is a figure which shows the change of the output (henceforth "the air fuel ratio sensor output") of the 1st air fuel ratio sensor 46 at the time of rich spike implementation. It is a figure for demonstrating the method to measure the fuel quantity added from the exhaust fuel addition valve 44 based on air-fuel-ratio sensor output A / F_A, A / F_B. It is a figure which shows the measured addition amount for every driving | running condition. It is the figure which plotted the relationship between the ratio R of the measurement addition amount with respect to the instruction | indication addition amount, and the HC density | concentration downstream of the oxidation catalyst 40 for every operating condition. It is a figure which shows the relationship between the ratio R shown in FIG. 5, and HC density | concentration. 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

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Crank angle sensor 26 Air flow meter 38 Exhaust passage 40 Oxidation catalyst 42 NOx catalyst 44 Exhaust fuel addition valve 46 1st air fuel ratio sensor 48 2nd air fuel ratio sensor 60 ECU

Claims (1)

A catalyst deterioration detection device for detecting catalyst deterioration,
A catalyst disposed in the exhaust passage of the internal combustion engine and having an oxidizing ability;
Air-fuel ratio detection means for detecting an exhaust air-fuel ratio downstream of the catalyst;
Reducing agent addition means for adding a reducing agent to the exhaust passage upstream of the catalyst;
An addition amount measuring means for measuring the amount of addition of the reducing agent based on the exhaust air / fuel ratio detected when the rich spike is detected and when the rich spike is not performed, detected by the air / fuel ratio detection means;
A deterioration detecting means for detecting deterioration of the catalyst based on a deviation between the indicated addition amount to the reducing agent adding means and the measured addition amount measured by the addition amount measuring means ;
The deterioration detecting means has a ratio calculating means for calculating a ratio of the measured addition amount to the indicated addition amount, and detects deterioration of the catalyst when the ratio is smaller than a reference value. Deterioration detection device.

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