JP2008045413A - Abnormality detecting device of reducing agent adding valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abnormality detecting device of a reducing agent adding valve, capable of accurately detecting abnormality of the reducing agent adding valve, even when the combustion air-fuel ratio changes when performing a rich spike. <P>SOLUTION: Addition of a reducing agent is indicated to the adding valve (Step 122), and its addition indicating quantity is integrated (Step 124). The air-fuel ratio A/Fcal is estimated based on an operation state of an internal combustion engine (Step 126). A measured addition quantity (Δt) of its moment is determined by using the estimated air-fuel ratio A/Fcal and air-fuel ratio sensor output A/Fs (Step 128), and the measured addition quantity is integrated (Step 130). The abnormality of the adding valve is detected by comparing an error between the measured addition quantity and an indicated addition quantity with a reference value. <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 2002-38928 A

  The estimation of the reducing agent addition amount is performed based on the difference between the reference value and the air-fuel ratio detected during the rich spike operation, using the air-fuel ratio detected before the rich spike operation as a reference value. However, if the combustion air-fuel ratio changes during the rich spike, a deviation occurs between the reference value and the actual air-fuel ratio. If so, there is a possibility that the amount of reducing agent addition cannot be estimated with accuracy and the addition valve abnormality cannot be detected with accuracy. Therefore, according to the conventional method, the abnormality of the addition valve can be detected only in a steady state.

  The present invention has been made in order to solve the above-described problems, and it is possible to accurately detect the abnormality of the reducing agent addition valve even when the combustion air-fuel ratio changes during the rich spike operation. An object of the present invention is to provide an abnormality detecting device for a reducing agent addition valve.

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;
First air-fuel ratio detection means for detecting a first air-fuel ratio that is an exhaust air-fuel ratio downstream of the reducing agent addition valve;
Second air-fuel ratio acquisition means for acquiring a second air-fuel ratio that is an exhaust air-fuel ratio of the internal combustion engine during the addition of the reducing agent by the reducing agent addition valve;
Addition of the reducing agent added from the reducing agent addition valve based on the second air-fuel ratio acquired by the second air-fuel ratio acquisition means and the first air-fuel ratio detected by the first air-fuel ratio detection means An additive amount measuring means for measuring the amount;
An abnormality detecting means for detecting an abnormality of the reducing agent addition valve by comparing the addition amount instructed by the addition amount instructing means with the addition amount measured by the addition amount measuring means; Features.

The second invention is the first invention, wherein
Before adding the reducing agent from the reducing agent addition valve, the difference between the first air / fuel ratio detected by the first air / fuel ratio detecting means and the second air / fuel ratio acquired by the second air / fuel ratio acquiring means is calculated. Difference calculating means for
And a correction means for correcting the first air-fuel ratio or the second air-fuel ratio based on the difference calculated by the difference calculation means.

The third invention is the first or second invention, wherein
The second air-fuel ratio acquisition means detects second air-fuel ratio estimation means for estimating the second air-fuel ratio based on the operating state of the internal combustion engine, and detects the second air-fuel ratio upstream of the reducing agent addition valve. It has at least any one of a 2nd air fuel ratio detection means.

  According to the first aspect of the invention, the reducing agent addition amount is measured based on the second air-fuel ratio that is the exhaust air-fuel ratio of the internal combustion engine and the first air-fuel ratio that is the exhaust air-fuel ratio downstream of the reducing agent addition valve. The This second air-fuel ratio can follow the change in the combustion air-fuel ratio of the internal combustion engine. Therefore, even when the combustion air-fuel ratio changes during addition of the reducing agent, the amount of reducing agent added can be accurately measured. Therefore, even when the combustion air-fuel ratio changes during the addition of the reducing agent, it is possible to accurately detect the abnormality of the reducing agent addition valve.

  According to the second invention, by correcting the first air-fuel ratio or the second air-fuel ratio, it is possible to eliminate the difference existing when the reducing agent is not added. Therefore, the amount of reducing agent added can be detected with higher accuracy.

  According to the third invention, by having at least one of the second air-fuel ratio estimating means and the second air-fuel ratio detecting means, the change in the combustion air-fuel ratio of the internal combustion engine is followed even when the reducing agent is being added. The second air / fuel ratio can be acquired.

  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 24 b and the oxidation catalyst 40, an exhaust fuel addition valve (hereinafter abbreviated as “addition valve”) 44 for adding fuel as a reducing agent to the exhaust gas is provided. The addition valve 44 communicates with the supply pump 8 through a fuel supply pipe (not shown).

  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 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 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]
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 that is the reducing agent is added from the addition valve 44, and the purification ability recovery processing (regeneration processing) of the NOx catalyst 42 is performed by this reducing agent.

By the way, there is a case where it is required to accurately detect abnormality of the addition amount (injection amount) control of the addition valve 44.
FIG. 2 is a diagram for explaining an example of a method for determining an abnormality of the addition valve 44. The horizontal axis in FIG. 2 is the addition amount (indicated addition amount) instructed from the ECU 60 to the addition valve 44, and the vertical axis is the addition amount (measured addition amount) measured (estimated) by a method described later. .
As shown in FIG. 2, the abnormality of the 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 instruction addition amount is 1, that is, when the reducing agent is added from the addition valve 44 in accordance with the instruction amount, it is naturally determined that the addition valve 44 is normal. However, it is also necessary to consider variations and changes with time of the addition valve 44. Therefore, when the ratio R is within the reference range shown in FIG. 2, it is determined that the addition valve 44 is normal, and when the ratio R is outside this reference range, the addition valve 44 is abnormal (failure). Can be determined. In other words, when the indicated addition amount is the predetermined amount A, if the error (absolute value) between the indicated addition amount A and the measured addition amount is equal to or less than the reference value Dth, it is determined that the addition valve 44 is normal. If the value is larger than the reference value Dth, it can be determined that the addition valve 44 is abnormal (failure). These reference ranges or reference values Dth can be set in advance according to the vehicle type.

FIG. 3 is a diagram showing a change in the output (hereinafter referred to as “air-fuel ratio sensor output”) A / Fs of the first air-fuel ratio sensor 46 when the rich spike is performed.
When the rich spike is not performed, that is, when fuel addition is not performed from the addition valve 44, the air-fuel ratio sensor output A / Fs becomes an output A / F_A as shown by a one-dot chain line in FIG. On the other hand, fuel addition is performed from the addition valve 44 during the rich spike time t. For this reason, the air-fuel ratio sensor output A / Fs changes to an output A / F_B as shown by a solid line in FIG.

  Although details will be described later, the air-fuel ratio sensor output A / F_A when the rich spike is not executed is set as a reference value A / Fbase, and the difference between the reference value A / Fbase and the air-fuel ratio sensor output A / F_B when the rich spike is executed Based on this, the amount of fuel added from the addition valve 44 can be measured (estimated). That is, the measured addition amount can be obtained based on the air-fuel ratio sensor output A / Fs (A / F_A, A / F_B).

  FIG. 4 is a diagram for explaining a method of measuring the amount of fuel added from the addition valve 44. In FIG. 4, the symbol “A / Fs” represents the air-fuel ratio sensor output. The symbol “A / Fs (t0)” represents the air-fuel ratio sensor output at time t0 when the rich spike is not performed, specifically, immediately before the rich spike is performed.

The air-fuel ratio sensor output A / Fs (t0) at time t0 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 / Fs (t0) = Ga / Q ... (1)
When the above equation (1) is transformed, the following equation (2) is obtained.
Q = Ga / (A / F (t0)) ... (2)

Further, the air-fuel ratio sensor output A / Fs at the time of rich spike execution can be expressed as the following equation (3). In the following equation (3), “Qex” is the amount of fuel added from the addition valve 44.
A / Fs = Ga / (Q + Qex) ... (3)
When the above equation (3) is transformed, the following equation (4) is obtained.
Q + Qex = Ga / (A / Fs) ... (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 / Fs) -1 / (A / Fs (t0))} ... (5)
= Ga × {(A / Fs (t0))-(A / Fs)} / (A / Fs (t0)) / (A / Fs) ... (6)

  The air / fuel ratio sensor output A / Fs (t0) in the above equation (6) can be obtained at time t0 immediately before the rich spike operation. Accordingly, if the intake air amount Ga and the air-fuel ratio sensor output A / Fs are known, the instantaneous amount of fuel added (at a certain time) during the rich spike can be calculated according to the above equation (6). By accumulating the amount of added fuel only during the rich spike time t shown in FIG. 4, the amount of fuel added from the addition valve 44 at the time of rich spike execution can be measured. That is, the measured addition amount is determined.

  According to the above method, the air-fuel ratio sensor output A / Fs (t0) immediately before the rich spike is performed is the reference value A / Fbase, and based on the difference between the reference value A / Fbase and the air-fuel ratio sensor output A / Fs. Thus, the measured addition amount is obtained (see FIGS. 3 and 4).

  However, as shown in FIG. 5, the combustion air-fuel ratio may fluctuate (for example, a transient state) during the rich spike operation. In such a case, if the air-fuel ratio sensor output A / Fs (t0) immediately before the rich spike is performed as the reference value A / Fbase as in the above method, the reference value A / Fbase and the actual exhaust air-fuel ratio A / Fact (addition valve) 44 upstream air-fuel ratio). FIG. 5 is a diagram showing a difference between the reference value A / Fbase and the actual exhaust air-fuel ratio A / Fact when the combustion air-fuel ratio fluctuates during execution of rich spike. In this case, since the measurement addition amount is obtained using the inaccurate reference value A / Fbase, the calculation accuracy of the measurement addition amount is lowered.

Therefore, in the first embodiment, the exhaust air / fuel ratio A / Fcal is estimated based on the operating state (Ga, Ne, Q) of the internal combustion engine 1 during the rich spike operation. For example, in the case of the in-line four-cylinder diesel engine shown in FIG. 1, the fuel is injected twice per revolution. The air-fuel ratio A / Fcal can be estimated.
A / Fcal = Ga / {(Ne / 60) × 2 × Q × 0.833} ... (7)

FIG. 6 is a diagram showing the reference value A / Fbase for obtaining the measured addition amount in the first embodiment.
In the first embodiment, as shown in FIG. 6, the exhaust air / fuel ratio A / Fcal estimated by the above equation (7) is set as the reference value A / Fbase. That is, the added fuel amount Qex is calculated using the estimated exhaust air / fuel ratio A / Fcal instead of the air / fuel ratio sensor output A / Fs (t0) in the above equation (6). This exhaust air-fuel ratio A / Fcal follows the fluctuation of the combustion air-fuel ratio. Therefore, the reference value A / Fbase for obtaining the measured addition amount can be made to follow the fluctuation of the combustion air-fuel ratio during the rich spike operation. Therefore, even when the combustion air-fuel ratio fluctuates as in a transient state during execution of rich spike, the measured addition amount can be obtained with high accuracy.

  Further, the air flow meter 26, the injector 6 and the first air-fuel ratio sensor 46 have variations. For this reason, even when all of these operate normally, there is a possibility that the estimated exhaust air-fuel ratio A / Fcal and the air-fuel ratio sensor output A / Fs do not match as shown in FIG. is there. Even in such a case, the measured addition amount cannot be obtained with high accuracy.

  Therefore, in the first embodiment, as shown in FIG. 7, the difference ΔA / F between the exhaust air / fuel ratio A / Fcal and the exhaust air / fuel ratio A / Fs is obtained before the rich spike operation. Then, the exhaust air-fuel ratio A / Fcal is offset-corrected by this difference ΔA / F during the rich spike operation. FIG. 7 is a diagram showing offset correction of the air-fuel ratio A / Fcal in the first embodiment. The offset correction shown in FIG. 7 can absorb the influence of variations in the air flow meter 26, the injector 6, and the first air-fuel ratio sensor 46. Therefore, since the deviation between the air-fuel ratio A / Fcal and the air-fuel ratio sensor output A / Fs existing when the reducing agent is not added can be eliminated, the measured addition amount can be obtained with high accuracy.

[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 the addition valve abnormality detection request flag is ON (step 100). This “addition valve abnormality detection request flag” means that the specified addition amount to the addition valve 44 is a predetermined value when the vehicle travels for a predetermined distance or a predetermined time after the previous abnormality detection is performed, or after the previous abnormality detection is performed. This flag is set to “ON” when the value exceeds.

  If it is determined in step 100 that the addition valve abnormality detection request flag is ON, it is determined whether or not an offset calculation completion flag is ON (step 102). This “offset calculation completion flag” is “ON” when the calculation of the deviation (offset) between the air-fuel ratio sensor output A / Fs and the estimated air-fuel ratio A / Fcal is completed prior to the detection of the abnormality of the addition valve. Flag set to

  If it is determined in step 102 that the offset calculation completion flag is OFF, the process proceeds to step 104. In step 104, the air-fuel ratio A / Fcal is calculated according to the above equation (7) using the intake air amount Ga, the in-cylinder fuel injection amount Q, and the engine speed Ne. That is, in this step 104, the exhaust air-fuel ratio A / Fcal of the internal combustion engine 1 is estimated based on the operating state (Ga, Q, Ne) of the internal combustion engine 1.

  Thereafter, the numerical value obtained by subtracting the air-fuel ratio sensor output (the air-fuel ratio detected by the air-fuel ratio sensor 46) A / Fs from the air-fuel ratio A / Fcal estimated in the above step 104 is obtained as the air-fuel ratio difference ( (Offset) ΔA / F is set (step 106). That is, the difference ΔA / F between the estimated air-fuel ratio A / Fcal and the air-fuel ratio sensor output A / Fs is obtained. This difference ΔA / F is used for offset correction of the estimated air-fuel ratio A / Fcal in step 126 of FIG. 9 described later.

  Then, the offset calculation completion flag is set to “ON” (step 108). Subsequently, the indicated addition amount is set to “0 (zero)” (step 110), and the measured addition amount is set to “0 (zero)” (step 112). That is, in these steps 110 and 112, the indicated addition amount and the measured addition amount are reset.

  After executing the processing of step 112, this routine is temporarily terminated. Thereafter, when this routine is started again, the processing of step 100 is executed. If it is determined in step 100 that the addition valve abnormality detection request flag is OFF, that is, if the abnormality of the addition valve 44 is not detected, the offset calculation completion flag is set to “OFF” (step 114).

  On the other hand, if it is determined in step 100 that the addition valve abnormality detection request flag is ON, the process of step 102 is executed. Here, in step 108 of the routine executed last time, the offset calculation completion flag is set to ON. Therefore, “YES” is determined in the process of step 102. Then, the addition valve abnormality detection flow shown in FIG. 9 is started. FIG. 9 is a flowchart showing a routine for addition valve abnormality detection executed by the ECU 60 in the first embodiment.

  According to the routine shown in FIG. 9, first, it is determined whether or not the indicated addition amount is a predetermined value or more (step 120). This predetermined value is an amount of fuel that can detect the abnormality of the addition valve, that is, an indicated addition amount that can accurately compare the indicated addition amount and the measured addition amount, and may be determined in advance for each vehicle type. it can. If it is determined in step 120 that the indicated addition amount is less than the predetermined value, the addition valve 44 is instructed to add fuel as a reducing agent (step 122). Thereafter, a numerical value obtained by adding the current command addition amount specified in step 122 to the previous command addition amount is set as the command addition amount (step 124). In step 124, the command addition amount after the reset in step 110 is integrated.

  Next, the air-fuel ratio A / Fcal that becomes the reference value A / Fbase (see FIGS. 6 and 7) is estimated based on the operating state (Ga, Q, Ne) of the internal combustion engine 1 (step 126). In step 126, the air-fuel ratio A / Fcal is calculated according to the above equation (7) using the intake air amount Ga, the in-cylinder fuel injection amount Q, and the engine speed Ne. Further, this step 126 is obtained by subtracting the offset ΔA / F calculated in step 106 (FIG. 8) from the exhaust air-fuel ratio A / Fcal of the internal combustion engine 1 calculated according to the above equation (7). A numerical value is set as the air-fuel ratio A / Fcal. That is, the estimated air-fuel ratio A / Fcal is offset corrected.

  Thereafter, the measured addition amount (Δt) is calculated (step 128). This measured addition amount (Δt) is the measured addition amount at the instant Δt. In step 128, the intake air amount Ga is offset-corrected in step 126 from the numerical value (Ga / A / Fs) obtained by dividing the intake air amount Ga by the air-fuel ratio sensor output A / Fs. The numerical value obtained by subtracting the numerical value (Ga / A / Fcal) obtained by dividing by A / Fcal is set as the measured addition amount (Δt).

  Next, the numerical value obtained by adding the measured addition amount (Δt) calculated in step 128 to the previously measured addition amount is set as the measured addition amount (step 130). In step 130, the measured addition amount after the reset in step 112 is integrated. Thereafter, this routine is temporarily terminated.

  When this routine is started from the next time onward, the processing of steps 122 to 130 is sequentially executed until the indicated addition amount reaches a predetermined value. Thereby, integration of the indicated addition amount and the measured addition amount is performed.

  On the other hand, when the amount of supplied fuel exceeds a predetermined value, “YES” is determined in the process of step 120. Thereafter, an estimated error is obtained by subtracting the indicated addition amount from the measured addition amount (step 132). Thereafter, it is determined whether or not the estimation error obtained in step 132 is larger than a reference value (step 134). This reference value is an allowable value of an estimation error when it is determined that the addition valve 44 is normal, and is a determination value for performing an abnormality determination of the addition valve 44. As an example of the reference value, a reference value Dth is shown in FIG.

  If it is determined in step 134 that the estimation error is larger than the reference value, it is determined that the addition valve 44 is abnormal (failure). In this case, the addition valve abnormality flag is set to “ON” (step 136). On the other hand, when it is determined in step 134 that the estimation error is equal to or less than the reference value, it is determined that the addition valve 44 is normal. In this case, the addition valve abnormality flag is set to “OFF” (step 138). After the process of step 136 or 138, the addition valve abnormality detection request flag is set to “OFF” (step 140).

As described above, according to the routines shown in FIGS. 8 and 9, the operation of the internal combustion engine 1 is not performed during the rich spike execution but the air-fuel ratio sensor output A / Fs (t 0) immediately before the rich spike execution (time t 0). The measured addition amount is obtained based on the air-fuel ratio A / Fcal estimated based on the state (Ga, Q, Ne) and the air-fuel ratio sensor output A / Fs. This air-fuel ratio A / Fcal can follow the change in the combustion air-fuel ratio of the internal combustion engine 1 during the rich spike operation. For this reason, even if the combustion air-fuel ratio fluctuates during execution of rich spike as in a transient state, the measured addition amount can be obtained with high accuracy. Therefore, even if the combustion air-fuel ratio fluctuates, the abnormality detection of the addition valve 44 can be performed with high accuracy.
In addition, since the abnormality detection can be performed even when the combustion air-fuel ratio fluctuates, the frequency of performing abnormality detection can be increased. Therefore, the injection amount control of the addition valve 44 can be frequently monitored.

  Further, according to this routine, the difference ΔA / F between the estimated air-fuel ratio A / Fcal and the air-fuel ratio sensor output A / Fs is calculated prior to the rich spike. During the rich spike operation, the air-fuel ratio A / Fcal is offset-corrected by the calculated difference ΔA / F. Therefore, since the air-fuel ratio deviation ΔA / F existing when the rich spike is not performed can be eliminated, the calculation accuracy of the measured addition amount can be further improved.

  In the first embodiment, the estimated air-fuel ratio A / Fcal is offset-corrected, but the air-fuel ratio sensor output A / Fs may be offset-corrected by the difference ΔA / F. FIG. 10 is a flowchart illustrating a routine for detecting an addition valve abnormality executed by the ECU 60 in the modification of the first embodiment. The routine shown in FIG. 10 has the process of step 127 instead of step 126 of the routine shown in FIG. In this step 127, the air-fuel ratio sensor output A / Fs is offset-corrected by the air-fuel ratio deviation ΔA / F calculated in step 106 of FIG. Also according to the present modification, the air-fuel ratio deviation ΔA / F that exists when the rich spike is not performed can be eliminated, so that the same effect as in the first embodiment can be obtained.

  In the first embodiment, the measured addition amount is obtained using the output A / Fs of the first air-fuel ratio sensor 46. However, it can also be obtained using 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 air-fuel ratio sensor output A / Fs is used as it is without correction, assuming that there is no change in the air-fuel ratio before and after the oxidation catalyst 40. It is also possible to use a correction to the fuel ratio sensor output A / Fs.

  In the first embodiment, the addition valve 44 is provided between the turbine 24b and the oxidation catalyst 40, but may be provided upstream of the turbine 24b (for example, the exhaust port 30 or the exhaust manifold 36). . Also in this case, the same effect as in the first embodiment can be obtained.

  In the first embodiment, the abnormality of the addition valve 44 is determined by comparing the estimation error with the reference value. However, the abnormality R is determined by comparing the ratio R of the measured addition amount with respect to the indicated addition amount with the reference value. A determination may be made.

  In the first embodiment, the NOx catalyst 42 is the “catalyst” in the first invention, the addition valve 44 is the “reducing agent addition valve” in the first invention, and the first air-fuel ratio sensor 46 is the first. This corresponds to the “first air-fuel ratio detection means” in the present invention. In the first embodiment, the ECU 60 executes the process of step 122 so that the “addition amount instruction means” in the first invention executes the process of step 126. The “second air-fuel ratio obtaining means” and the “second air-fuel ratio estimation means” in the third invention execute the processing of step 128, whereby the “addition amount measuring means” in the first invention becomes steps 132, 134, By executing the processes 136 and 138, the “abnormality detection means” in the first invention is realized. Further, in the first embodiment or a modification thereof, the ECU 60 executes the process of step 106, whereby the “difference calculating means” in the second invention executes the process of step 126 or step 127. The “correction means” in the second invention is realized respectively.

Embodiment 2. FIG.
Next, Embodiment 2 of the present invention will be described with reference to FIG.
FIG. 11 is a diagram for explaining the system configuration of the second embodiment. The system shown in FIG. 11 is different from the system shown in FIG. 1 in that an air-fuel ratio sensor 45 is further provided upstream of the addition valve 44. The air-fuel ratio sensor 45 can detect the exhaust air-fuel ratio of the internal combustion engine 1 even when fuel is being added by the addition valve 44. The other configuration of this system is the same as that of the system shown in FIG.

[Features of Embodiment 2]
As shown in FIG. 4, the output A / Fs of the air-fuel ratio sensor 46 during the rich spike is different from the exhaust air-fuel ratio of the internal combustion engine 1. This is because the air-fuel ratio sensor 46 is provided downstream of the addition valve 44. Therefore, according to the method shown in FIG. 4, during the rich spike operation, the air-fuel ratio sensor output A / Fs (t0) immediately before the rich spike operation is used as the reference value A / Fbase for obtaining the measured addition amount. Yes.

  However, as described in the first embodiment, the reference value A / Fbase cannot follow the fluctuation of the combustion air-fuel ratio during the rich spike operation. Therefore, in the first embodiment, the air-fuel ratio A / Fcal estimated based on the operating state (Ga, Q, Ne) of the internal combustion engine 1 is used as the reference value A / Fbase for obtaining the measured addition amount. That is, the measured addition amount is obtained based on the difference between the air-fuel ratio A / Fcal and the air-fuel ratio sensor output A / Fs.

  Incidentally, the system of the second embodiment shown in FIG. 11 includes an air-fuel ratio sensor 45 upstream of the addition valve 44. Therefore, even when fuel is being added from the addition valve 44, the exhaust air / fuel ratio of the internal combustion engine 1 can be detected using the air / fuel ratio sensor 45. That is, the output A / Fsu of the air-fuel ratio sensor 45 can follow the fluctuation of the fuel air-fuel ratio during the rich spike operation.

  Therefore, in the second embodiment, the air-fuel ratio sensor output A / Fsu is used as a reference value A / Fbase for obtaining the measured addition amount. That is, the measured addition amount is obtained based on the difference between the air-fuel ratio sensor output A / Fsu and the air-fuel ratio sensor output A / Fs. Therefore, even if the combustion air-fuel ratio fluctuates during a rich spike operation as in a transient state, the measured addition amount can be obtained with high accuracy.

  Further, the air-fuel ratio sensor 45 and the air-fuel ratio sensor 46 have variations. For this reason, even when both of these two air-fuel ratio sensors 45 and 46 operate normally, the air-fuel ratio sensor output A / Fsu and the air-fuel ratio sensor output A / Fs may not match when the rich spike is not performed. There is sex.

  Therefore, in the second embodiment, the difference amount ΔA / Fs between the two air-fuel ratio sensor outputs A / Fsu and A / Fs is obtained before the rich spike operation. Any one of the air-fuel ratio sensor outputs is offset-corrected by this difference ΔA / Fs. By this offset correction, the influence of variations in the air-fuel ratio sensors 45 and 46 can be absorbed. Therefore, since the difference ΔA / Fs between the two air-fuel ratio sensor outputs A / Fsu and A / Fs existing when the reducing agent is not added can be eliminated, the measured addition amount can be obtained with high accuracy.

[Specific Processing in Second Embodiment]
FIG. 12 is a flowchart showing a routine executed by ECU 60 in the second embodiment. The routine shown in FIG. 12 is started at predetermined intervals. The routine shown in FIG. 12 has a process of step 142 instead of steps 104 and 106 of the routine shown in FIG. Hereinafter, the process of step 142 that is different will be mainly described.

  According to the routine shown in FIG. 12, if it is determined in step 102 that the offset calculation completion flag is not ON, the process proceeds to step 142. In this step 142, a numerical value obtained by subtracting the output A / Fs of the air-fuel ratio sensor 46 from the output A / Fsu of the air-fuel ratio sensor 45 is set as an air-fuel ratio difference (offset) ΔA / Fs. This difference ΔA / Fs is used for offset correction of the air-fuel ratio sensor output A / Fsu in step 144 of FIG. After the process of step 142, the offset calculation completion flag is set to “ON” as in the routine shown in FIG. 8 (step 108).

  When it is determined in step 102 that the offset calculation completion flag is ON, the addition valve abnormality detection flow shown in FIG. 13 is started. FIG. 13 is a flowchart showing a routine for addition valve abnormality detection executed by the ECU 60 in the second embodiment. The routine shown in FIG. 13 has processes of steps 144, 146, and 148 instead of steps 126, 128, and 130 of the routine shown in FIG. Hereinafter, the processing of these different steps will be mainly described.

  According to the routine shown in FIG. 13, after the instruction addition amount is integrated in step 124, the process proceeds to step 144. In step 144, a numerical value obtained by subtracting the offset ΔA / Fs calculated in step 142 (FIG. 12) from the air-fuel ratio sensor output A / Fsu is set as the air-fuel ratio sensor output A / Fsu. . That is, the air-fuel ratio sensor output A / Fsu is offset corrected.

  Thereafter, the measured addition amount (Δt) is calculated (step 146). This measured addition amount (Δt) is the measured addition amount at the instant Δt. In this step 146, the intake air amount Ga is divided by the air-fuel ratio sensor output A / Fs from the numerical value (Ga / A / Fsu) obtained by dividing the intake air amount Ga by the air-fuel ratio sensor output A / Fsu. The numerical value obtained by subtracting the numerical value (Ga / A / Fs) obtained by this is set as the measured addition amount (Δt).

  Next, a numerical value obtained by adding the measured addition amount (Δt) calculated in step 146 to the previous measured addition amount is set as the measured addition amount (step 148). In this step 148, integration of the measured addition amount after the reset in step 112 of FIG. 12 is performed. Thereafter, this routine is temporarily terminated.

  When this routine is started from the next time onward, the processing of steps 122, 124, 144 to 148 is sequentially executed until the command addition amount reaches a predetermined value. Thereby, integration of the indicated addition amount and the measured addition amount is performed.

  On the other hand, when the indicated addition amount is equal to or greater than the predetermined value, “YES” is determined in the process of step 120 as in the routine shown in FIG. Thereafter, similarly to the routine shown in FIG. 9, the processes of steps 132 to 140 are executed.

  As described above, according to the routines shown in FIGS. 12 and 13, not the air-fuel ratio sensor output A / Fs (t0) immediately before the rich spike operation (time t0) but the air-fuel ratio sensor output A during the rich spike operation. Based on / Fsu and the air-fuel ratio sensor output A / Fs, the measured addition amount is obtained. This air-fuel ratio sensor output A / Fsu can follow the change in the combustion air-fuel ratio of the internal combustion engine 1 during the rich spike operation. For this reason, even if the combustion air-fuel ratio fluctuates during execution of rich spike as in a transient state, the measured addition amount can be obtained with high accuracy. Therefore, even if the combustion air-fuel ratio fluctuates, the abnormality detection of the addition valve 44 can be performed with high accuracy.

  Further, according to this routine, prior to the rich spike, the difference ΔA / Fs between the air-fuel ratio sensor output A / Fsu and the air-fuel ratio sensor output A / Fs is calculated. Then, during rich spike execution, the air-fuel ratio sensor output A / Fsu is offset-corrected by the calculated difference ΔA / Fs. Therefore, since the air-fuel ratio sensor output deviation ΔA / Fs existing when the rich spike is not performed can be eliminated, the calculation accuracy of the measured addition amount can be further improved.

  In the second embodiment, the air-fuel ratio sensor output A / Fsu is offset-corrected by the difference ΔA / Fs, but the air-fuel ratio sensor output A / Fs may be offset-corrected by the difference ΔA / Fs. Also in this case, the air-fuel ratio sensor output deviation ΔA / Fs existing when the rich spike is not performed can be eliminated.

  In the second embodiment, the case where the air-fuel ratio sensor output A / Fsu is larger by ΔA / Fs than the air-fuel ratio sensor output A / Fs has been described. However, the present invention is also applied when ΔA / Fs is smaller. It is clear that it can be applied. In this case, the numerical value obtained by adding the difference ΔA / Fs to the air-fuel ratio sensor output A / Fsu in step 144 may be set as the air-fuel ratio sensor output A / Fsu.

  In the second embodiment, the air-fuel ratio sensor 45 corresponds to the “second air-fuel ratio acquisition means” in the first invention and the “second air-fuel ratio detection means” in the third invention. In the second embodiment, the ECU 60 executes the process of step 142, so that the “difference calculating means” in the second invention executes the process of step 144, and the “correction” in the second invention is executed. Each means is realized.

It is a figure for demonstrating the system configuration | structure by Embodiment 1 of this invention. It is a figure for demonstrating an example of the method of determining abnormality of the exhaust fuel addition valve. It is a figure which shows the change of the output A / Fs 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 amount added from the exhaust fuel addition valve. FIG. 5 is a diagram showing a difference between a reference value A / Fbase and an actual exhaust air / fuel ratio A / Fact when the combustion air / fuel ratio fluctuates during rich spike execution. In Embodiment 1 of this invention, it is a figure which shows the reference value A / Fbase for calculating | requiring the measurement addition amount. In Embodiment 1 of this invention, it is a figure which shows the offset correction of air fuel ratio A / Fcal. 5 is a flowchart showing a routine that is executed by the ECU 60 in the first embodiment of the present invention. In Embodiment 1 of this invention, it is a flowchart which shows the routine for the addition valve abnormality detection which ECU60 performs. 7 is a flowchart illustrating a routine for detecting an addition valve abnormality executed by an ECU 60 in a modification of the first embodiment of the present invention. It is a figure for demonstrating the system configuration | structure of Embodiment 2 of this invention. In Embodiment 2 of this invention, it is a flowchart which shows the routine which ECU60 performs. In Embodiment 2 of this invention, it is a flowchart which shows the routine for the addition valve abnormality detection which ECU60 performs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Crank angle sensor 40 Oxidation catalyst 42 NOx catalyst 44 Exhaust fuel addition valve 45 Air fuel ratio sensor 46 First air fuel ratio sensor 60 ECU

Claims (3)

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;
First air-fuel ratio detection means for detecting a first air-fuel ratio that is an exhaust air-fuel ratio downstream of the reducing agent addition valve;
Second air-fuel ratio acquisition means for acquiring a second air-fuel ratio that is an exhaust air-fuel ratio of the internal combustion engine during the addition of the reducing agent by the reducing agent addition valve;
Addition of the reducing agent added from the reducing agent addition valve based on the second air-fuel ratio acquired by the second air-fuel ratio acquisition means and the first air-fuel ratio detected by the first air-fuel ratio detection means An additive amount measuring means for measuring the amount;
An abnormality detecting means for detecting an abnormality of the reducing agent addition valve by comparing the addition amount instructed by the addition amount instructing means with the addition amount measured by the addition amount measuring means; An apparatus for detecting abnormality of a reducing agent addition valve. In the reducing agent addition valve abnormality detection device according to claim 1,
Before adding the reducing agent from the reducing agent addition valve, the difference between the first air / fuel ratio detected by the first air / fuel ratio detecting means and the second air / fuel ratio acquired by the second air / fuel ratio acquiring means is calculated. Difference calculating means for
A reducing agent addition valve abnormality detection device, further comprising: a correction unit that corrects the first air-fuel ratio or the second air-fuel ratio based on the difference calculated by the difference calculation unit. In the abnormality detection apparatus of the reducing agent addition valve according to claim 2 or 3,
The second air-fuel ratio acquisition means detects second air-fuel ratio estimation means for estimating the second air-fuel ratio based on the operating state of the internal combustion engine, and detects the second air-fuel ratio upstream of the reducing agent addition valve. A reducing agent addition valve abnormality detection device comprising at least one of second air-fuel ratio detection means.

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