JP2008025479A - Abnormality detecting device of reducer addition valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abnormality detecting device of a reducer addition valve, restraining output lean shift of an air-fuel ratio detecting means to detect abnormality of an addition valve with good accuracy. <P>SOLUTION: When abnormality of an exhaust fuel addition valve is detected, an instruction is given to reduce an addition quantity per injection as compared with catalyst regeneration, and increase the frequency of injection, and add a reducer (step 102). After that, an addition quantity of the reducer added from the exhaust fuel addition valve is measured based on the air-fuel ratio sensor output (step 104). the proportion R of the measured addition quantity to the instructed addition quantity is calculated (step 1-6), and when the proportion R is outside the reference range, the exhaust fuel addition valve is determined to be abnormal (step 112). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an abnormality detection device for a reducing agent addition valve that adds a reducing agent to an exhaust passage.

  A reducing agent addition amount added from a reducing agent addition valve (hereinafter sometimes abbreviated as “addition valve”) is estimated based on the air-fuel ratio sensor output, and this estimated reducing agent addition amount is used as an addition instruction amount. An apparatus for performing abnormality determination of an addition valve by comparison is known (see, for example, Patent Document 1).

JP 2005-54723 A JP 2005-146900 A

  By the way, when an abnormality of the addition valve is detected, if a rich spike similar to that at the time of recovery of the catalyst purification performance (also referred to as “at the time of catalyst regeneration”) is performed, the HC concentration in the exhaust gas may increase. As a result, the output of the air-fuel ratio sensor is deviated and there is a possibility that the amount of addition cannot be accurately estimated. For this reason, the abnormality detection of the addition valve may not be performed with high accuracy.

  The present invention has been made in order to solve the above-described problems, and it is possible to suppress an output lean deviation of the air-fuel ratio detection unit and to detect an abnormality of the addition valve with high accuracy. An object is to provide a detection device.

In order to achieve the above object, a first invention is an abnormality detection device for detecting an abnormality of a reducing agent addition valve for adding a reducing agent upstream of the catalyst in order to restore the purification ability of the catalyst,
An addition amount indicating means for instructing an addition amount of a reducing agent to the reducing agent addition valve;
Air-fuel ratio detection means for detecting an exhaust air-fuel ratio downstream of the reducing agent addition valve;
An addition amount measuring means for measuring an addition amount of the reducing agent added from the reducing agent addition valve based on the exhaust air-fuel ratio;
An abnormality detection unit that detects an abnormality of the reducing agent addition valve by comparing the addition amount instructed by the addition amount instruction unit and the addition amount measured by the addition amount measurement unit;
The addition amount instruction means reduces the addition amount per injection when an abnormality of the reducing agent addition valve is detected as compared with when the purification capacity of the catalyst is recovered.

The second invention is the first invention, wherein
The addition amount instructing means increases the number of injections when an abnormality of the reducing agent addition valve is detected as compared with when the purification capacity of the catalyst is recovered.

The third invention is the first or second invention, wherein
Exhaust system temperature acquisition means for acquiring the temperature of the exhaust system;
The exhaust system temperature acquired by the exhaust system temperature acquisition means further comprises prohibiting means for prohibiting the abnormality detection of the reducing agent addition valve in a temperature range where the reducing agent purification ability of the catalyst is low. .

The fourth invention is an abnormality detection device for detecting an abnormality of a reducing agent addition valve for adding a reducing agent upstream of the catalyst in order to recover the purification ability of the catalyst,
An addition amount indicating means for instructing an addition amount of a reducing agent to the reducing agent addition valve;
Air-fuel ratio detection means for detecting an exhaust air-fuel ratio downstream of the reducing agent addition valve;
An addition amount measuring means for measuring an addition amount of the reducing agent added from the reducing agent addition valve based on the exhaust air-fuel ratio;
An abnormality detection unit that detects an abnormality of the reducing agent addition valve by comparing the addition amount instructed by the addition amount instruction unit and the addition amount measured by the addition amount measurement unit;
Exhaust system temperature acquisition means for acquiring the temperature of the exhaust system;
The exhaust system temperature acquired by the exhaust system temperature acquisition means includes prohibiting means for prohibiting detection of abnormality of the reducing agent addition valve in a temperature range where the reducing agent purification ability of the catalyst is low.

  According to the first invention, when the abnormality of the reducing agent addition valve is detected, the addition amount per injection is reduced compared to when the purification capacity of the catalyst is recovered. Thereby, since the reducing agent concentration in the exhaust gas can be lowered, it is possible to avoid the output lean deviation of the air-fuel ratio detecting means. Therefore, the amount of reducing agent added can be accurately measured, so that the abnormality detection of the reducing agent addition valve can be accurately performed.

  According to the second aspect of the invention, the number of reducing agent injections when the abnormality of the reducing agent addition valve is detected is increased compared to the number of reducing agent injections when the purification capacity is recovered. As a result, a situation in which the total amount of the reducing agent is remarkably reduced when an abnormality is detected is avoided, so that it is possible to suppress the influence of the injection variation of the reducing agent addition valve. Therefore, the amount of reducing agent added can be accurately measured.

  According to the third invention, abnormality detection of the reducing agent addition valve is prohibited in a temperature range where the reducing agent purification ability of the catalyst is low. Therefore, an increase in the concentration of the reducing agent in the exhaust gas due to a reduction in the reducing agent purification ability is suppressed, so that an output lean shift of the air-fuel ratio detection means can be avoided.

  According to the fourth aspect of the invention, the abnormality detection of the reducing agent addition valve is prohibited in the temperature range where the reducing agent purification ability of the catalyst is low. Therefore, since the increase in the concentration of the reducing agent in the exhaust gas due to the reduction in the reducing agent purification ability is suppressed, the lean deviation of the output of the air-fuel ratio detecting means can be avoided. Therefore, the amount of reducing agent added can be accurately measured, so that the abnormality detection of the reducing agent addition valve can be accurately performed.

  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 that is a pretreatment catalyst is provided downstream of the turbine 24b. The oxidation catalyst 40 is a catalyst having a function of oxidizing HC and CO.

  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. The oxidation catalyst 40 and the NOx catalyst 42 may be housed in one container.

  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. The exhaust fuel addition valve 44 communicates with the supply pump 8 through a fuel supply pipe (not shown). Further, an exhaust temperature sensor 45 that detects an exhaust gas temperature Texg flowing into the oxidation catalyst 40 is provided upstream of the oxidation catalyst 40.

  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. The oxidation catalyst 40 is provided with a catalyst bed temperature sensor 47 that detects the catalyst bed temperature of the oxidation 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 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, an exhaust temperature sensor 45, a first air-fuel ratio sensor 46, a catalyst bed temperature sensor 47, a second air-fuel ratio sensor 48, and the like are connected to the input side of the ECU 60. ing.

  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, the fuel as the reducing agent is added from the exhaust fuel addition valve 44, and the purification capacity recovery process (regeneration process) of the NOx catalyst 42 is performed by this reducing agent. In the first embodiment, as described below, a method for detecting an abnormality (failure) of the exhaust fuel addition valve 44 is proposed.

FIG. 2 is a diagram for explaining a method of determining an abnormality of the exhaust fuel addition valve 44. The horizontal axis in FIG. 2 is the addition amount (indicated addition amount) instructed from the ECU 60 to the exhaust fuel addition valve 44, and the vertical axis is the addition amount (measured addition amount) measured (estimated) by a method described later. It is.
As shown in FIG. 2, the abnormality of the exhaust fuel addition valve 44 can be detected by comparing the indicated addition amount with the measured addition amount. When the ratio R of the measured addition amount to the indicated addition amount is 1, that is, when the reducing agent is added by the indicated amount from the exhaust fuel addition valve 44, it is naturally determined that the exhaust fuel addition valve 44 is normal. The However, considering the variation and aging of the exhaust fuel addition valve 44, if the ratio R is within the reference range shown in FIG. 2, it is determined that the exhaust fuel addition valve 44 is normal. On the other hand, if the ratio R is outside this reference range, it is determined that the exhaust fuel addition valve 44 is abnormal (failure). The reference range can be set in advance according to the vehicle type.

FIG. 3 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 output of the air-fuel ratio sensor 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 (estimated). That is, the measured addition amount can be obtained based on the air-fuel ratio sensor outputs A / F_A and A / F_B.

  FIG. 4 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. 4, as in FIG. 3, 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 in advance when the rich spike is not performed immediately before the rich spike is 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. 4, 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.

  Incidentally, when the HC concentration in the exhaust gas is high, the air-fuel ratio sensor output becomes the output A / F_C on the leaner side than the output A / F_B, as shown by the broken line in FIG. 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. Therefore, the higher the HC concentration in the exhaust gas, the larger the air-fuel ratio sensor output shifts to the lean side.

  As a result of studies by the present inventors, it has been found that there is a correlation between the ratio R of the measured addition amount relative to the indicated addition amount and the HC concentration (HC amount) in the exhaust gas. FIG. 5 is a graph showing the relationship between the ratio R of the measured addition amount relative to the indicated addition amount and the HC concentration in the exhaust gas.

  As shown in FIG. 5, it was found that when the HC concentration in the exhaust gas is low, the ratio R is close to 100%, and the ratio R decreases as the HC concentration increases. This is because as the HC concentration in the exhaust gas is higher, the degree of lean deviation of the air-fuel ratio sensor output described above increases, and as a result, the measured addition amount is calculated smaller than the original amount. Therefore, when the HC concentration in the exhaust gas is high, the measured addition amount cannot be obtained with high accuracy, so that there is a possibility that the abnormality of the exhaust fuel addition valve 44 cannot be detected with high accuracy. In order to suppress the influence of the lean deviation of the air-fuel ratio sensor output and accurately obtain the measured addition amount, it is desirable to make the HC concentration in the exhaust gas as low as possible. Specifically, it is desirable to suppress the HC concentration in the exhaust gas to 1000 (ppm) or less.

Furthermore, as a result of studies by the present inventors, it has been found that when the addition pattern of the exhaust fuel addition valve 44 is changed, the HC concentration in the exhaust gas changes. FIG. 6 is a diagram showing the HC concentration in the exhaust gas when the addition pattern of the reducing agent (fuel) is changed. The addition pattern is defined by the addition amount per injection (mm ³ / st) and the number of injections. In addition, the five different addition patterns shown in FIG. 6 are adjusted to a total addition amount of about 1000 mm ³ .

  In FIG. 6, the addition patterns “333 × 3” and “250 × 4” are the addition patterns when the normal catalyst purification capacity is recovered (hereinafter referred to as “catalyst regeneration”). At the time of catalyst regeneration, the number of injections is reduced and the amount added per injection is increased in order to complete catalyst regeneration at an early stage. Then, since oxygen necessary for oxidizing a large amount of HC added at once from the exhaust fuel addition valve 44 is insufficient, HC does not sufficiently react in the oxidation catalyst 40, and a large amount of HC passes through the oxidation catalyst 40 as it is. End up. As a result, the HC concentration in the exhaust gas becomes high.

As shown in FIG. 6, the HC concentration in the exhaust gas can be lowered by reducing the addition amount per injection. This is because there is sufficient oxygen to oxidize the added small amount of HC, so that the HC can be reacted with the oxidation catalyst 40.
As described above, from the viewpoint of suppressing the HC concentration in the exhaust gas to 1000 (ppm) or less, for example, the addition patterns “63 × 16” and “32 × 32” shown in FIG. 6 are desirable. Further, considering that the time required for obtaining the measured addition amount increases as the number of injections increases, for example, the addition pattern “63 × 16” shown in FIG. 6 is more desirable.

FIG. 7 is a diagram showing the addition amount per injection of the exhaust fuel addition valve 44. Specifically, FIG. 7A is a diagram showing the addition amount at the time of normal catalyst regeneration, and FIG. 7B is a diagram showing the addition amount when abnormality of the exhaust fuel addition valve 44 is detected. .
When the abnormality of the exhaust fuel addition valve 44 shown in FIG. 7 (B) is detected, the addition amount per injection is reduced as compared with the normal catalyst regeneration shown in FIG. 7 (A). As a result, as shown in FIG. 6, the HC concentration in the exhaust gas during the rich spike operation can be lowered.

  As described above, according to the first embodiment, when the abnormality of the exhaust fuel addition valve 44 is detected, the addition amount per injection of the exhaust fuel addition valve 44 is reduced as compared with the normal catalyst regeneration. . Thereby, since the amount of HC passing through the oxidation catalyst 40 can be reduced, the HC concentration in the exhaust gas can be lowered. Then, the lean deviation of the air-fuel ratio sensor output can be reduced, and the measured addition amount can be obtained with high accuracy. Therefore, the abnormality detection of the exhaust fuel addition valve 44 can be accurately performed by comparing the instruction addition amount with the measured addition amount.

[Specific Processing in Embodiment 1]
FIG. 8 is a flowchart showing a routine executed by the ECU 60 in the first embodiment. The routine shown in FIG. 8 is started at predetermined intervals.

  According to the routine shown in FIG. 8, first, it is determined whether or not there is an abnormality detection request for the exhaust fuel addition valve 44 (step 100). Here, for example, the ECU 60 travels for a predetermined distance or a predetermined time after executing the previous abnormality detection, or the instruction addition amount to the exhaust fuel addition valve 44 exceeds the predetermined value after executing the previous abnormality detection. If it is detected, it can be determined that there is an abnormality detection request. If it is determined in step 100 that there is no abnormality detection request, this routine is temporarily terminated.

  If it is determined in step 100 that there is an abnormality detection request, the amount of addition per injection is reduced and the number of injections is increased with respect to the exhaust fuel addition valve 44 than during normal catalyst regeneration. Instruct to add a 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. As a result, fuel is added from the exhaust fuel addition valve 44 and rich spike is performed.

  Next, using the output A / F_B of the first air-fuel ratio sensor 46 and the intake air amount Ga, the reducing agent addition amount is measured according to the above equation (6) (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 within the reference range (step 108). As shown in FIG. 2, this reference range is a range in which a ratio R that can be taken when the exhaust fuel addition valve 44 is normal is determined. If it is determined in step 108 that the ratio R is within the reference range, it is determined that the difference between the indicated addition amount and the measured addition amount is small. In this case, it is determined that the exhaust fuel addition valve 44 is normal (step 110).

On the other hand, if it is determined in step 108 that the ratio R is out of the reference range, it is determined that the difference between the indicated addition amount and the measured addition amount is large. In this case, it is determined that the exhaust fuel addition valve 44 is abnormal (failure) (step 112). Then, an abnormality of the exhaust fuel addition valve 44 is notified to the vehicle driver by turning on an indicator (not shown).
After step 110 or step 112, 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 ratio R of the measured addition amount to the indicated addition amount is calculated. When the ratio R is within the reference range, it is determined that the exhaust fuel addition valve 44 is normal because the deviation of the measured addition amount from the command addition amount is small. On the other hand, when the ratio R is outside the reference range, the deviation of the measured addition amount with respect to the indicated addition amount is large, so that the exhaust fuel addition valve 44 is determined to be abnormal (failure).
Here, when the abnormality of the exhaust fuel addition valve 44 is detected, the addition amount per injection is reduced as compared with the normal catalyst regeneration. Thereby, since the amount of HC passing through the oxidation catalyst 40 can be reduced, the HC concentration in the exhaust gas can be lowered. Therefore, the lean deviation of the air-fuel ratio sensor output can be reduced. Then, the measured addition amount can be obtained with high accuracy. Therefore, abnormality detection of the exhaust fuel addition valve 44 can be performed with high accuracy.

  By the way, when the abnormality of the exhaust fuel addition valve 44 is detected, the total addition amount and the measured addition amount are remarkably reduced if only the addition amount per injection is reduced without changing the number of injections as compared with the normal catalyst regeneration. There is. In this case, there is a possibility that the accuracy of the obtained measured addition amount is lowered due to the influence of the injection variation of the exhaust fuel addition valve 44. On the other hand, in the first embodiment, as described above, the number of injections is increased as compared with normal catalyst regeneration. Thereby, since the influence of the injection variation of the exhaust fuel addition valve 44 can be suppressed, the measured addition amount can be obtained with high accuracy.

  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 NOx catalyst 42 is the “catalyst” in the first invention, the exhaust fuel addition valve 44 is the “reducing agent addition valve” in the first invention, and the first air-fuel ratio sensor 46 is This corresponds to the “air-fuel ratio detecting means” in the first invention. In the first embodiment, the ECU 60 executes the process of step 102, so that the “addition amount instruction means” in the first and second inventions executes the process of step 104 to execute the first process. The “addition amount measuring means” in the invention executes the processing of steps 106, 108, 110, and 112, thereby realizing the “abnormality detecting means” in the first invention.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. The system of the eighth embodiment can be realized by causing the ECU 60 to execute a routine shown in FIG. 10 to be described later using the hardware configuration shown in FIG.

[Features of Embodiment 2]
In the first embodiment, when the abnormality of the exhaust fuel addition valve 44 is detected, the HC concentration in the exhaust gas is suppressed to be low by reducing the addition amount per injection as compared with the normal catalyst regeneration.

  By the way, even if the oxidation catalyst 40 is normal, the HC purification rate (HC purification ability) may be lowered depending on the temperature of the exhaust system. FIG. 9 is a diagram showing the relationship between the temperature of exhaust gas flowing into the oxidation catalyst 40 (exhaust gas temperature) and the HC purification rate of the oxidation catalyst 40. In FIG. 9, the relationship between the exhaust gas temperature and the NOx purification rate of the NOx catalyst 42 is shown together using a one-dot chain line.

  Normal NOx catalyst regeneration is performed when the exhaust gas temperature Ta (for example, 200 ° C.) with a low NOx purification rate is reached. The exhaust gas temperature Ta is lower than the exhaust gas temperature Tb (for example, 350 ° C.) at which the highest NOx purification rate is obtained. This is because there is a demand for regeneration of the NOx catalyst even at a low exhaust gas temperature Ta. It is also conceivable to detect the abnormality of the exhaust fuel addition valve 44 by reducing the addition amount per injection at the exhaust gas temperature Ta.

  However, as shown in FIG. 9, the HC purification rate of the oxidation catalyst 40 is low at the exhaust gas temperature Ta. For this reason, if the abnormality of the exhaust fuel addition valve 44 is detected at the exhaust gas temperature Ta, the amount of HC that passes through the oxidation catalyst 40 increases. Then, as explained in the first embodiment, the HC concentration in the exhaust gas becomes high, and the lean deviation of the air-fuel ratio sensor output becomes large. As a result, there is a possibility that the measured addition amount cannot be obtained with high accuracy. As a result, the accuracy of abnormality detection of the exhaust fuel addition valve 44 may be reduced.

  Therefore, in the second embodiment, when the oxidation catalyst 40 has reached the exhaust gas temperature Tth (for example, 250 ° C.) at which a sufficiently high HC purification rate is obtained, abnormality detection of the exhaust fuel addition valve 44 is performed. . Specifically, abnormality detection of the exhaust fuel addition valve 44 is executed when the exhaust gas temperature Texg is equal to or higher than the reference value Tth. Thereby, since the raise of HC concentration in exhaust gas can be suppressed, the measurement addition amount can be calculated | required accurately. Therefore, abnormality detection of the exhaust fuel addition valve 44 can be performed with high accuracy.

[Specific Processing in Second Embodiment]
FIG. 10 is a flowchart showing a routine executed by the ECU 60 in the second embodiment. The routine shown in FIG. 10 is started at predetermined intervals.

  According to the routine shown in FIG. 10, as in the routine shown in FIG. 8, first, it is determined whether or not there is an abnormality detection request for the exhaust fuel addition valve 44 (step 100). If it is determined in step 100 that there is no abnormality detection request, this routine is temporarily terminated.

  If it is determined in step 100 that there is an abnormality detection request, it is determined whether or not the exhaust gas temperature Texg is equal to or higher than a reference value Tth (step 114). This reference value Tth is an exhaust gas temperature at which a high HC purification rate is obtained in the oxidation catalyst 40. If it is determined in step 114 that the exhaust gas temperature Texg is lower than the reference value Tth, execution of abnormality detection of the exhaust fuel addition valve 44 is prohibited (step 116). Thereby, when the HC purification rate of the oxidation catalyst 40 is low, that is, when it is estimated that the lean deviation of the air-fuel ratio sensor output becomes large, the abnormality detection of the exhaust fuel addition valve 44 is prohibited. Thereafter, this routine is temporarily terminated.

  On the other hand, when it is determined in step 114 that the exhaust gas temperature Texg is equal to or higher than the reference value Tth, that is, when the exhaust gas temperature Tth at which the high HC purification rate is obtained in the oxidation catalyst 40 has been reached, FIG. In the same manner as the routine shown in FIG. 5, the exhaust fuel addition valve 44 is instructed to add the reducing agent by reducing the addition amount per injection and increasing the number of injections as compared with the normal catalyst regeneration ( Step 102). Thereby, even if the rich spike is performed, an increase in the HC concentration in the exhaust gas due to the HC purification rate can be suppressed.

  Next, similarly to the routine shown in FIG. 8, the reducing agent addition amount (that is, the measured addition amount) is calculated 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. Obtain (step 104). Then, a ratio R of the measured addition amount with respect to the indicated addition amount is calculated (step 106), and it is determined whether or not this ratio R is within the reference range (step 108). If it is determined in step 108 that the ratio R is within the reference range, it is determined that the exhaust fuel addition valve 44 is normal (step 110). On the other hand, when it is determined that the ratio R is out of the reference range, it is determined that the exhaust fuel addition valve 44 is abnormal (failure) (step 112). Thereafter, this routine is terminated.

As described above, according to the routine shown in FIG. 10, 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. When the ratio R is within the reference range, the exhaust fuel addition valve 44 is determined to be normal because the deviation of the measured addition amount from the command addition amount is small. On the other hand, when the ratio R is out of the reference range, the deviation of the measured addition amount with respect to the indicated addition amount is large, so that the exhaust fuel addition valve 44 is determined to be abnormal (failure).
Here, when the abnormality of the exhaust fuel addition valve 44 is detected, the addition amount per injection is reduced as compared with the normal catalyst regeneration. Thereby, the HC concentration in the exhaust gas can be lowered, and the lean deviation of the air-fuel ratio sensor output can be reduced. Further, the abnormality detection of the exhaust fuel addition valve 44 is prohibited until the exhaust gas temperature Tth at which the oxidation catalyst 40 obtains a high HC purification rate is reached. Thereby, when the abnormality of the exhaust fuel addition valve 44 is detected, an increase in the HC concentration due to a decrease in the HC purification rate of the oxidation catalyst 40 can be suppressed. Then, the lean deviation of the output of the first air-fuel ratio sensor 46 can be suppressed, and the measured addition amount can be obtained with high accuracy. Therefore, abnormality detection of the exhaust fuel addition valve 44 can be performed with high accuracy.

  In the second embodiment, the exhaust gas temperature Texg is detected by the exhaust gas temperature sensor 45. However, the exhaust gas temperature Texg may be estimated by a map or a model based on the operation state (NE, Q, etc.). Also in this case, the same effect as in the second embodiment can be obtained.

  Further, the catalyst bed temperature detected by the catalyst bed temperature sensor 47 may be used instead of the exhaust gas temperature Texg. The catalyst bed temperature is the exhaust system temperature as is the exhaust gas temperature. For this reason, the relationship between the catalyst bed temperature and the HC purification rate (HC purification capacity) is similar to the relationship shown in FIG. Therefore, it is possible to determine whether or not the abnormality detection of the exhaust fuel addition valve 44 is prohibited based on the catalyst bed temperature. Also in this case, the same effect as in the second embodiment can be obtained.

Further, in the routine shown in FIG. 10, as in the routine shown in FIG. 8, an instruction is given to add the reducing agent by reducing the addition amount per injection and increasing the number of injections, compared to the normal catalyst regeneration. However, the injection pattern is not limited to this (step 102). For example, the “addition amount per injection” and the “number of injections” similar to those during normal catalyst regeneration shown in FIG.
FIG. 11 is a flowchart showing a routine executed by the ECU 60 in the modification of the second embodiment. The routine shown in FIG. 11 is different from the routine shown in FIG. 10 only in the process of step 118. In step 118, the exhaust fuel addition valve 44 is instructed to add the reducing agent as in the normal catalyst regeneration as described above. According to this modification, as in the second embodiment, when the HC purification ability of the oxidation catalyst 40 is reduced, the abnormality detection of the exhaust fuel addition valve 44 is prohibited. Therefore, since the measured addition amount is obtained while suppressing the increase in the HC concentration due to the decrease in the HC purification rate, the measured addition amount can be obtained with high accuracy.

  In the second embodiment and its modification, the exhaust temperature sensor 45 corresponds to the “exhaust system temperature acquisition means” in the third and fourth inventions. Further, in the present second embodiment and its modification, the “prohibiting means” in the third and fourth inventions is realized by the ECU 60 executing the processing of step 116.

It is a figure for demonstrating the system configuration | structure by Embodiment 1 of this invention. It is a figure for demonstrating the method to discriminate | determine abnormality of the exhaust fuel addition valve. It is a figure which shows the change of the 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 relationship between ratio R of the measurement addition amount with respect to instruction | indication addition amount, and the HC density | concentration in exhaust gas. It is a figure which respectively shows the HC density | concentration in exhaust gas when changing the addition pattern of a reducing agent. FIG. 4 is a diagram showing an addition amount per injection of an exhaust fuel addition valve 44. 5 is a flowchart showing a routine that is executed by the ECU 60 in the first embodiment of the present invention. FIG. 3 is a diagram showing the relationship between the temperature of exhaust gas flowing into the oxidation catalyst 40 and the HC purification rate of the oxidation catalyst 40. In Embodiment 2 of this invention, it is a flowchart which shows the routine which ECU60 performs. 10 is a flowchart showing a routine executed by ECU 60 in a modification of the second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 38 Exhaust passage 40 Oxidation catalyst 42 NOx catalyst 44 Exhaust fuel addition valve 45 Exhaust temperature sensor 46 1st air fuel ratio sensor 47 Catalyst bed temperature sensor 48 2nd air fuel ratio sensor 60 ECU

Claims (4)

An abnormality detection device for detecting an abnormality of a reducing agent addition valve for adding a reducing agent upstream of the catalyst in order to recover the purification ability of the catalyst,
An addition amount indicating means for instructing an addition amount of a reducing agent to the reducing agent addition valve;
Air-fuel ratio detection means for detecting an exhaust air-fuel ratio downstream of the reducing agent addition valve;
An addition amount measuring means for measuring an addition amount of the reducing agent added from the reducing agent addition valve based on the exhaust air-fuel ratio;
An abnormality detection unit that detects an abnormality of the reducing agent addition valve by comparing the addition amount instructed by the addition amount instruction unit and the addition amount measured by the addition amount measurement unit;
The addition amount instruction means detects the abnormality of the reducing agent addition valve when detecting the abnormality of the reducing agent addition valve, and reduces the amount of addition per injection compared to when the purification capacity of the catalyst is recovered. apparatus. In the reducing agent addition valve abnormality detection device according to claim 1,
The apparatus for detecting an abnormality of a reducing agent addition valve, wherein the addition amount instruction means increases the number of injections when detecting an abnormality of the reducing agent addition valve as compared to when the purification capacity of the catalyst is recovered. In the abnormality detection apparatus of the reducing agent addition valve according to claim 1 or 2,
Exhaust system temperature acquisition means for acquiring the temperature of the exhaust system;
The exhaust system temperature acquired by the exhaust system temperature acquisition means further comprises prohibiting means for prohibiting the abnormality detection of the reducing agent addition valve in a temperature range where the reducing agent purification ability of the catalyst is low. Abnormality detection device for reducing agent addition valve. An abnormality detection device for detecting an abnormality of a reducing agent addition valve for adding a reducing agent upstream of the catalyst in order to recover the purification ability of the catalyst,
An addition amount indicating means for instructing an addition amount of a reducing agent to the reducing agent addition valve;
Air-fuel ratio detection means for detecting an exhaust air-fuel ratio downstream of the reducing agent addition valve;
An addition amount measuring means for measuring an addition amount of the reducing agent added from the reducing agent addition valve based on the exhaust air-fuel ratio;
An abnormality detection unit that detects an abnormality of the reducing agent addition valve by comparing the addition amount instructed by the addition amount instruction unit and the addition amount measured by the addition amount measurement unit;
Exhaust system temperature acquisition means for acquiring the temperature of the exhaust system;
The exhaust system temperature acquired by the exhaust system temperature acquiring means includes a prohibiting means for prohibiting the abnormality detection of the reducing agent addition valve in a temperature range where the reducing agent purification ability of the catalyst is low. Agent addition valve abnormality detection device.

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