JP2009174349A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology capable of detecting abnormality when the abnormality occurs in a bypass passage bypassing a NOx catalyst. <P>SOLUTION: A bypass passage is provided so as to bypass a reducer adding valve, the NOx catalyst and an air-fuel ratio sensor provided in an exhaust gas passage in an order form an upstream. An integration value of drop quantity of detection value of the air-fuel ratio sensor is calculated when reducer is added from the reducer adding valve (S103). When the integration value of the drop quantity of the detection value of the air-fuel ratio sensor under a condition where it is assumed that separation ratio which is a ratio of flow rate of exhaust gas passing through the NOx catalyst and flow rate of exhaust gas flowing in the bypass passage is a target value, and actually calculated integration value are different (S104), it is determined that abnormality occurs in the bypass passage (S107, S108). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine provided with a NOx storage reduction catalyst provided in an exhaust passage.

NOx storage reduction catalyst in exhaust passage of internal combustion engine (hereinafter simply referred to as NOx catalyst)
When a reducing agent addition valve is provided on the upstream side of the NOx catalyst, when reducing NOx or SOx stored in the NOx catalyst, the reducing agent is added into the exhaust from the reducing agent addition valve. Reduce the air / fuel ratio of the atmosphere. At this time, the air-fuel ratio in the ambient atmosphere of the NOx catalyst is controlled to the target air-fuel ratio by adding a reducing agent in an amount corresponding to the flow rate of the exhaust gas passing through the NOx catalyst from the reducing agent addition valve.

In some cases, a bypass passage that bypasses the NOx catalyst is provided in the exhaust passage. Patent Document 1 discloses an exhaust emission control device that includes a bypass passage that bypasses the NOx catalyst and a switching valve that distributes exhaust gas to the NOx catalyst and the bypass passage. In Patent Document 1, a reducing agent is added to the exhaust gas flowing in the exhaust passage upstream of the NOx catalyst, and when it is determined that the reducing agent has reached the NOx catalyst, the exhaust gas is caused to flow to the bypass passage. The flow rate of the exhaust gas passing through the NOx catalyst is reduced. Further, in Patent Document 1, a NOx sensor is provided on the downstream side of the connection portion of the exhaust passage with the downstream end of the bypass passage, and the amount of NOx detected by the NOx sensor when exhaust flows through the bypass passage is determined. A technique for determining that an abnormality has occurred in the switching valve when there is no quantitative change is also disclosed.
JP 2006-233894 A Japanese Patent Laid-Open No. 5-98947 JP 2005-106065 A

  If any abnormality occurs in the bypass passage that bypasses the NOx catalyst and the flow rate of the exhaust gas flowing through the bypass passage changes, the flow rate of the exhaust gas that passes through the NOx catalyst also changes accordingly.

  Further, in some cases, a bypass passage is provided so as to bypass not only the NOx catalyst but also the reducing agent addition valve provided in the exhaust passage on the upstream side of the NOx catalyst. In this case, if the flow rate of exhaust gas passing through the NOx catalyst changes due to an abnormality in the bypass passage, the NOx catalyst is added when the reducing agent is added from the reducing agent addition valve to reduce NOx or SOx stored in the NOx catalyst. There is a possibility that the air-fuel ratio of the surrounding atmosphere may deviate from the target air-fuel ratio.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of detecting an abnormality when an abnormality occurs in a bypass passage that bypasses the NOx catalyst.

  In the present invention, when the reducing agent is added from the reducing agent addition valve, the integral value of the decrease amount of the air-fuel ratio of the exhaust downstream of the NOx catalyst is calculated. Then, when it is assumed that the shunt ratio, which is the ratio of the flow rate of exhaust gas passing through the NOx catalyst and the flow rate of exhaust gas flowing through the bypass passage, is the target value, integration of the amount of decrease in the air-fuel ratio of the exhaust gas downstream from the NOx catalyst If the value is different from the actually calculated integral value, it is determined that an abnormality has occurred in the bypass passage.

More specifically, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
A bypass passage having one end connected to the exhaust passage upstream of the NOx storage reduction catalyst and the other end connected to the exhaust passage downstream of the NOx storage reduction catalyst;
A reducing agent addition valve that is provided downstream of a connection portion of one end of the bypass passage in the exhaust passage and upstream of the NOx storage reduction catalyst, and adds a reducing agent into the exhaust;
An air-fuel ratio sensor that is provided downstream of the NOx storage reduction catalyst in the exhaust passage and upstream of the connecting portion of the other end of the bypass passage;
The flow rate of the exhaust gas passing through the NOx storage reduction catalyst and the bypass passage when the air-fuel ratio of the exhaust gas exhausted from the NOx storage reduction catalyst is reduced by adding the reducing agent from the reducing agent addition valve. A target integral value calculating means for calculating a target integral value that is an integral value of the amount of decrease in the detected value of the air-fuel ratio sensor when it is assumed that the shunt ratio that is a ratio with the flow rate of the flowing exhaust gas is the target shunt ratio;
This is an integrated value of the amount of decrease in the actual detected value of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas discharged from the NOx storage reduction catalyst is reduced by adding a reducing agent from the reducing agent addition valve. An actual integral value calculating means for calculating an integral value;
The flow rate of the exhaust gas passing through the NOx storage reduction catalyst and the bypass passage when the air-fuel ratio of the exhaust gas exhausted from the NOx storage reduction catalyst is reduced by adding the reducing agent from the reducing agent addition valve. A target integral value calculating means for calculating a target integral value that is an integral value of the amount of decrease in the detected value of the air-fuel ratio sensor when it is assumed that the shunt ratio that is a ratio with the flow rate of the flowing exhaust gas is the target shunt ratio;
An abnormality detection unit that determines that an abnormality has occurred in the bypass passage when the actual integration value calculated by the actual integration value calculation unit is different from the target integration value calculated by the target integration value calculation unit; It is characterized by.

  Here, the target diversion ratio is a diversion ratio at a normal time, that is, when no abnormality occurs in the bypass passage, and is a predetermined value.

In the present invention, when the reducing agent is added from the reducing agent addition valve, a part of the added reducing agent passes through the NOx catalyst, so that the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst is lowered. For this reason, the detection value of the air-fuel ratio sensor decreases. At this time, the amount of the reducing agent that passes through the NOx catalyst changes according to the flow rate of the exhaust gas that passes through the NOx catalyst. As a result, the manner of transition of the detection value of the air-fuel ratio sensor changes.

  Therefore, when the shunt ratio is assumed to be the target shunt ratio, the target integral value that is the integral value of the amount of decrease from when the detected value of the air-fuel ratio sensor starts to drop until the drop ends is calculated by the target integral value calculation means. calculate. Further, an actual integral value that is an integral value of the actual amount of decrease from when the detected value of the air-fuel ratio sensor starts to decrease until the decrease ends is calculated by the actual integral value calculation means.

  When the target integral value calculated in this way is different from the actual integral value, it can be determined that the actual diversion ratio is different from the target diversion ratio. That is, in this case, it can be determined that an abnormality has occurred in the bypass passage.

  The diversion ratio in the present invention may be any value as long as it represents a ratio between the flow rate of exhaust gas passing through the NOx catalyst and the flow rate of exhaust gas flowing through the bypass passage.

Abnormalities that occur in the bypass passage include exhaust leakage caused by breakage of the bypass passage and clogging caused by particulate matter or soot in the exhaust attached to the bypass passage. When exhaust leakage occurs in the bypass passage, the flow rate of exhaust flowing through the bypass passage increases and the flow rate of exhaust passing through the NOx catalyst decreases. As a result, the amount of reducing agent added from the reducing agent addition valve becomes excessive with respect to the flow rate of the exhaust gas passing through the NOx catalyst, so that the total amount of reducing agent passing through the NOx catalyst increases.

  On the other hand, when clogging occurs in the bypass passage, the flow rate of the exhaust gas flowing through the bypass passage decreases and the flow rate of the exhaust gas passing through the NOx catalyst increases. As a result, the amount of reducing agent added from the reducing agent addition valve becomes too small with respect to the flow rate of the exhaust gas passing through the NOx catalyst, so that the total amount of reducing agent passing through the NOx catalyst is reduced.

  Therefore, in the present invention, when the actual integral value calculated by the actual integral value calculation means is larger than the target integral value calculated by the target integral value calculation means, the abnormality detection means causes exhaust leakage in the bypass passage. You may judge. Further, when the actual integral value calculated by the actual integral value calculating means is smaller than the target integral value calculated by the target integral value calculating means, the abnormality detecting means may determine that clogging has occurred in the bypass passage. Good.

  The present invention may further include bypass flow rate control means for controlling the flow rate of the exhaust gas flowing through the bypass passage. In this case, the target diversion ratio is variable, and the diversion ratio is controlled by the bypass flow rate control means. Therefore, even when an abnormality occurs in the bypass flow rate control valve, the actual diversion ratio is different from the target diversion ratio.

  Therefore, in this configuration, when the actual integrated value calculated by the actual integrated value calculating means is different from the target integrated value calculated by the target integrated value calculating means, the abnormality detecting means detects an abnormality in the bypass passage or the bypass flow control means. It may be determined that has occurred.

  According to the present invention, when an abnormality occurs in the bypass passage that bypasses the NOx catalyst, the abnormality can be detected.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

<Example 1>
<Schematic configuration of internal combustion engine and intake / exhaust system thereof>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle having four cylinders 2. Each cylinder 2 is provided with a fuel injection valve 3 that directly injects fuel into the cylinder 2.

  An intake manifold 5 and an exhaust manifold 7 are connected to the internal combustion engine 1. One end of an intake passage 4 is connected to the intake manifold 5. One end of an exhaust passage 6 is connected to the exhaust manifold 7.

  A compressor housing 8 a of a turbocharger 8 is installed in the intake passage 4. A turbine housing 8 b of a turbocharger 8 is installed in the exhaust passage 6.

  An air flow meter 11 is provided in the intake passage 4 upstream of the compressor housing 8a. A throttle valve 12 is provided in the intake passage 4 on the downstream side of the compressor housing 8a.

  A NOx catalyst 9 is provided downstream of the turbine housing 8 b in the exhaust passage 6. An oxidation catalyst 10 is provided downstream of the NOx catalyst 9 in the exhaust passage 6.

  The exhaust passage 6 is provided with a bypass passage 15 that bypasses the NOx catalyst 9. One end of the bypass passage 15 is connected to the downstream side of the turbine housing 8 b and the upstream side of the NOx catalyst 9 in the exhaust passage 6. The other end of the bypass passage 15 is connected to the downstream side of the NOx catalyst 9 and the upstream side of the oxidation catalyst 10 in the exhaust passage 6. Further, in this embodiment, the bypass passage 15 is formed so that the diversion ratio, which is the ratio of the flow rate of the exhaust gas passing through the NOx catalyst 9 and the flow rate of the exhaust gas flowing through the bypass passage 15, becomes a predetermined target diversion ratio. . In this embodiment, the shunt ratio is expressed as a ratio of the flow rate of the exhaust gas flowing through the bypass passage 15 to the sum of the flow rate of the exhaust gas passing through the NOx catalyst 9 and the flow rate of the exhaust gas flowing through the bypass passage 15. However, this is one aspect of the method of expressing the flow dividing ratio. If the flow rate of exhaust gas passing through the NOx catalyst 9 and the flow rate of exhaust gas flowing through the bypass passage 15 can be expressed, what is the flow dividing ratio? It may be expressed as

  Further, a fuel addition valve 13 for adding fuel as a reducing agent into the exhaust gas is provided on the downstream side of the connection portion of one end of the bypass passage 15 in the exhaust passage 6 and on the upstream side of the NOx catalyst 9. In this embodiment, the fuel addition valve 13 corresponds to the reducing agent addition valve according to the present invention.

  An air-fuel ratio sensor 14 for detecting the air-fuel ratio of the exhaust gas is provided downstream of the NOx catalyst 9 in the exhaust passage 6 and upstream of the connection portion of the other end of the bypass passage 15.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 20. The ECU 20 is a unit that controls the operating state of the internal combustion engine 1 and the like. The ECU 20 is electrically connected to an air flow meter 11, an air-fuel ratio sensor 14, a crank position sensor 21, and an accelerator opening sensor 22. The crank position sensor 21 detects the crank angle of the internal combustion engine 1. The accelerator opening sensor 22 detects the accelerator opening of a vehicle on which the internal combustion engine 1 is mounted. Output signals from the sensors are input to the ECU 20.

  The ECU 20 derives the engine speed of the internal combustion engine 1 based on the detected value of the crank position sensor 21. Further, the ECU 20 derives the engine load of the internal combustion engine 1 based on the detection value of the accelerator opening sensor 22.

  In addition, each fuel injection valve 3, throttle valve 12, and fuel addition valve 13 are electrically connected to the ECU 20. These are controlled by the ECU 20.

<NOx reduction control and SOx poisoning recovery control>
In the present embodiment, NOx reduction control for reducing NOx stored in the NOx catalyst 9 and SOx poisoning recovery control for reducing SOx stored in the NOx catalyst 9 are performed. During the execution of the NOx reduction control and the SOx poisoning recovery control, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 9 is reduced by adding fuel from the fuel addition valve 13, thereby the air-fuel ratio of the ambient atmosphere of the NOx catalyst 9 Is reduced to a predetermined target air-fuel ratio in accordance with each control.

In the present embodiment, a part of the exhaust discharged from the internal combustion engine 1 flows through the bypass passage 15 without flowing into the NOx catalyst 9. Therefore, when the NOx reduction control and the SOx poisoning recovery control are executed, first, the NOx catalyst 9 is passed based on the intake air amount of the internal combustion engine 1, that is, the flow rate of exhaust gas discharged from the internal combustion engine 1 and the target diversion ratio. Calculate the flow rate of exhaust gas. Then, by adjusting the amount of fuel added from the fuel addition valve 13 in accordance with the calculated flow rate of exhaust gas passing through the NOx catalyst 9, the air-fuel ratio in the ambient atmosphere of the NOx catalyst 9 is controlled to the target air-fuel ratio.

<Detection of bypass passage abnormality>
However, when the abnormality occurs in the bypass passage 15, the diversion ratio may deviate from the target diversion ratio. For example, if the exhaust passage leaks due to breakage of the bypass passage 15, the flow rate of the exhaust gas flowing through the bypass passage 15 increases. That is, the actual diversion ratio (hereinafter referred to as the actual diversion ratio) is larger than the target diversion ratio. Further, when clogging occurs due to particulate matter or soot in the exhaust gas adhering to the bypass passage 15, the flow rate of the exhaust gas flowing through the bypass passage 15 decreases. That is, the actual diversion ratio is smaller than the target diversion ratio.

  In such a case, when the same amount of fuel is added from the fuel addition valve 13 as when the actual diversion ratio is equal to the target diversion ratio, the air-fuel ratio of the ambient atmosphere of the NOx catalyst 9 becomes a value deviated from the target air-fuel ratio. Therefore, when the above abnormality occurs in the bypass passage 15, it is necessary to detect the abnormality.

  Here, the abnormality detection method of the bypass passage which concerns on a present Example is demonstrated based on FIG. FIG. 2 is a diagram showing the transition of the detected value of the air-fuel ratio sensor 14 when a predetermined amount of fuel is added from the fuel addition valve 13 for a predetermined period in order to realize NOx reduction control. In FIG. 2, the vertical axis represents the detection value A / F of the air-fuel ratio sensor 14, and the horizontal axis represents time t. A solid line L1 indicates a case where the actual diversion ratio is equal to the target diversion ratio. An alternate long and short dash line L2 indicates a case where the actual diversion ratio is larger than the target diversion ratio. Broken lines L3 and L4 indicate a case where the actual diversion ratio is smaller than the target diversion ratio.

  When fuel is added from the fuel addition valve 13, a part of the added fuel passes through the NOx catalyst 9 without being consumed for NOx reduction in the NOx catalyst 9. For this reason, the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst 15 is lowered. As a result, the detection value of the air-fuel ratio sensor 14 decreases.

  When the flow rate of the exhaust gas passing through the NOx catalyst 9 changes due to the change of the actual flow ratio, the amount of fuel that passes through the NOx catalyst 9 changes. For this reason, as shown in FIG. 2, the manner of transition of the detection value of the air-fuel ratio sensor 14 also changes. At this time, since the detected value of the air-fuel ratio sensor 14 starts to decrease due to the addition of fuel from the fuel addition valve 13, the integrated value of the decrease amount of the detected value from when the decrease ends (hereinafter referred to as the air-fuel ratio decrease amount). 3, that is, the area of the hatched portion in FIG. 3 is a value correlated with the total amount of fuel that passes through the NOx catalyst 9.

  For example, when the flow rate of exhaust gas passing through the NOx catalyst 9 decreases due to the increase of the actual flow ratio, the amount of fuel added from the fuel addition valve 13 becomes excessive with respect to the flow rate of exhaust gas that passes through the NOx catalyst 9. . Therefore, the total amount of fuel that passes through the NOx catalyst 9 increases. In this case, the detected value of the air-fuel ratio sensor 14 changes as indicated by a one-dot chain line L2 in FIG. That is, the integrated value of the air-fuel ratio reduction amount is larger than when the actual diversion ratio is equal to the target diversion ratio (indicated by the solid line L1 in FIG. 2).

  On the contrary, if the flow rate of the exhaust gas passing through the NOx catalyst 9 increases due to the reduction of the actual diversion ratio, the amount of fuel that passes through the NOx catalyst 9 increases. Therefore, when the actual diversion ratio is smaller than the target diversion ratio, the amount of fuel added from the fuel addition valve 13 is too small with respect to the flow rate of the exhaust gas passing through the NOx catalyst 9. Therefore, the total amount of fuel that passes through the NOx catalyst 9 decreases. In this case, the detected value of the air-fuel ratio sensor 14 changes as indicated by broken lines L3 and L4 in FIG. In other words, the air-fuel ratio decrease integrated value is smaller than when the actual diversion ratio is equal to the target diversion ratio (in the case indicated by the solid line L1 in FIG. 2).

  Therefore, in this embodiment, an air-fuel ratio reduction amount integral value (hereinafter referred to as a target integral value) is calculated when it is assumed that the actual shunt ratio is equal to the target shunt ratio when the NOx reduction control is executed. This target integral value can be calculated based on the operating state of the internal combustion engine 1 that is executing the NOx reduction control, the amount of fuel added from the fuel addition valve 13, and the target diversion ratio. Further, an actual air-fuel ratio decrease amount integral value (hereinafter referred to as an actual integral value) during execution of the NOx reduction control is calculated. When the actual integral value is different from the target integral value, it is determined that the actual diversion ratio is different from the target diversion ratio, that is, an abnormality has occurred in the bypass passage 15.

  Hereinafter, a routine for detecting an abnormality of the bypass passage according to the present embodiment will be described based on a flowchart shown in FIG. This routine is stored in advance in the ECU 20 and is repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1. In this embodiment, the ECU 20 that executes this routine corresponds to the abnormality detection means according to the present invention.

  In this routine, the ECU 20 first determines in step S101 whether or not NOx reduction control is being executed. If an affirmative determination is made in S101, the ECU 20 proceeds to S102, and if a negative determination is made, the ECU 20 once ends the execution of this routine.

  In S102, the ECU 20 calculates the target integral value Qit at the time of execution of the current NOx reduction control based on the operating state of the internal combustion engine 1, the fuel addition amount from the fuel addition valve 13, and the target diversion ratio. In the present embodiment, the ECU 20 that executes S102 corresponds to the target integral value calculation means according to the present invention.

  Next, the ECU 20 proceeds to S103, and calculates the actual integral value Qi when the current NOx reduction control is executed. In the present embodiment, the ECU 20 that executes S103 corresponds to the actual integral value calculating means according to the present invention.

  Next, the ECU 20 proceeds to S104, and determines whether or not the actual integral value Qi calculated in S103 is equal to the target integral value Qit calculated in S102. If an affirmative determination is made in S104, the ECU 20 proceeds to S105, and if a negative determination is made, the ECU 20 proceeds to S106. In S104, even if the actual integration value Qi and the target integration value Qit are not completely equal, it may be determined that they are equal if the difference is within an allowable range.

  In S105, the ECU 20 determines that no abnormality has occurred in the bypass passage 15, and temporarily ends the execution of this routine.

  In S106, the ECU 20 determines whether or not the actual integral value Qi calculated in S103 is larger than the target integral value Qit calculated in S102. If an affirmative determination is made in S106, the ECU 20 proceeds to S107, and if a negative determination is made, the ECU 20 proceeds to S108.

  In S107, the ECU 20 determines that exhaust leakage has occurred in the bypass passage 15, and temporarily ends the execution of this routine.

  On the other hand, in S108, the ECU 20 determines that the bypass passage 15 is clogged, and once ends the execution of this routine.

  As described above, according to the present embodiment, when an abnormality occurs in the bypass passage 15, the abnormality can be detected. Further, it can be determined whether the abnormality is exhaust leakage or clogging.

  Furthermore, in this embodiment, when it is detected that an abnormality has occurred in the bypass passage 15, a notification device that notifies the driver of the vehicle may be provided.

  In the present embodiment, the abnormality detection of the bypass passage 15 is performed when the NOx reduction control is executed. However, the abnormality of the bypass passage 15 is detected by adding fuel from the fuel addition valve 13 at a timing different from the timing at which the predetermined NOx reduction control is executed, and comparing the target integrated value and the actual integrated value at that time. May be performed. In this case as well, a predetermined amount of fuel is added from the fuel addition valve 13 for a certain period to reduce the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst 15, and the target integrated value and actual integrated value at that time Is calculated.

<Example 2>
<Schematic configuration of internal combustion engine and intake / exhaust system thereof>
FIG. 2 is a diagram showing a schematic configuration of the internal combustion engine and its intake and exhaust system according to the present embodiment. In the present embodiment, the bypass passage 15 is provided with a bypass flow rate control valve 16 for controlling the flow rate of the exhaust gas flowing through the bypass passage 15. The bypass flow rate control valve 16 is electrically connected to the ECU 20, and the opening degree is controlled by the ECU 20. Since the configuration other than this is the same as the configuration shown in FIG. 1, the same reference numerals are given to the same components, and the description thereof is omitted. In this embodiment, the bypass flow rate control valve 16 corresponds to the bypass flow rate control means according to the present invention.

<Detection of abnormality in bypass passage or bypass flow control valve>
According to the structure which concerns on a present Example, the shunt ratio can be controlled by controlling the opening degree of the bypass flow control valve 16. Therefore, the target diversion ratio can be made variable. Therefore, in this embodiment, the target diversion ratio is set in advance when the NOx reduction control is executed and when the SOx reduction control is executed. When the NOx reduction control and the SOx reduction control are executed, the opening degree of the bypass flow control valve 16 is controlled so that the diversion ratio becomes the set target diversion ratio. Note that the target diversion ratio may be changed according to the operating state of the internal combustion engine 1.

  However, there is a possibility that the bypass flow rate control valve 16 may be stuck or the operation range of the bypass flow rate control valve 16 may be limited due to particulate matter or soot adhering to the exhaust gas. As described above, when an abnormality occurs in the bypass flow rate control, the actual diversion ratio becomes a value different from the target diversion ratio as in the case where an abnormality occurs in the bypass passage 15 itself.

  Therefore, in the present embodiment, as in the bypass passage abnormality detection method according to the first embodiment, the target integral value is calculated based on the target shunt ratio and the actual detection of the air-fuel ratio sensor 14 is performed when the NOx reduction control is executed. The actual integral value is calculated based on the value. When the actual integral value is different from the target integral value, it is determined that an abnormality has occurred in the bypass passage 15 or the bypass flow rate control valve 16.

  Hereinafter, a routine for detecting an abnormality of the bypass passage or the bypass flow control valve according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 20 and is repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1. In the flowchart shown in FIG. 6, S107 and S108 in the flowchart shown in FIG. 4 are replaced with S207 and S208. Therefore, only S207 and S208 will be described, and descriptions of other steps will be omitted. In this embodiment, the ECU 20 that executes this routine corresponds to the abnormality detection means according to the present invention.

In this routine, if an affirmative determination is made in S106, the ECU 20 proceeds to S207, and if a negative determination is made, the ECU 20 proceeds to S208.

  In S207, the ECU 20 determines that an exhaust leak has occurred in the bypass passage 15 or that an abnormality has occurred in the bypass flow control valve 16. As an abnormality of the bypass flow rate control valve 16 in this case, the bypass flow rate control valve 16 is stuck in a fully opened state or the operation range of the bypass flow rate control valve 16 is limited by an opening larger than the command value from the ECU 20. It is possible that After S207, the ECU 20 once ends the execution of this routine.

  On the other hand, in S208, the ECU 20 determines that the bypass passage 15 is clogged or that the bypass flow control valve 16 is abnormal. As an abnormality of the bypass flow rate control valve 16 in this case, the bypass flow rate control valve 16 is fixed in a fully closed state or the operation range of the bypass flow rate control valve 16 is limited by an opening smaller than the command value from the ECU 20. It is possible that After S208, the ECU 20 once terminates execution of this routine.

  As described above, according to the present embodiment, when an abnormality occurs in the bypass passage 15 or the bypass flow control valve 16, the abnormality can be detected.

  Furthermore, in the present embodiment, when it is detected that an abnormality has occurred in the bypass passage 15 or the bypass flow control valve 16, when the operation of the bypass flow control valve 16 is possible in the normal range, It can be determined that an abnormality has occurred in the passage 15. In this case, when the next NOx reduction control or SOx poisoning recovery control is executed, the opening degree of the bypass flow rate control valve 16 may be adjusted so that the actual diversion ratio becomes the target diversion ratio. This also makes it possible to control the air-fuel ratio of the atmosphere around the NOx catalyst 9 to the target air-fuel ratio.

  Further, in this embodiment, when it is detected that an abnormality has occurred in the bypass passage 15 or the bypass flow rate control valve 16, a notification device may be provided for notifying the driver of the vehicle.

  In the present embodiment, as with the detection of the abnormality of the bypass passage 15 according to the first embodiment, the fuel addition valve 13 is detected at a timing different from the time when the NOx reduction control is performed to detect the abnormality of the bypass passage 15 or the bypass flow control valve 16. It may be performed by adding a fuel.

1 is a diagram showing a schematic configuration of an internal combustion engine and an intake / exhaust system thereof according to Embodiment 1. FIG. The figure which shows transition of the detected value of an air fuel ratio sensor when a predetermined amount of fuel is added from a fuel addition valve for a predetermined period in order to realize NOx reduction control. The figure for demonstrating the air-fuel-ratio fall amount integrated value. 5 is a flowchart illustrating a routine for detecting an abnormality of a bypass passage according to the first embodiment. FIG. 3 is a diagram illustrating a schematic configuration of an internal combustion engine and an intake / exhaust system thereof according to a second embodiment. 9 is a flowchart showing a routine for detecting an abnormality of a bypass passage or a bypass flow control valve according to the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 4 ... Intake passage 6 ... Exhaust passage 9 ... Occlusion reduction type NOx catalyst 10 ... Oxidation catalyst 11 ... Air flow meter 12 ... Throttle valve 13 ... Fuel addition valve 14 ... -Air-fuel ratio sensor 15-Bypass passage 16-Bypass flow control valve 20-ECU
21 ・ ・ Crank position sensor 22 ・ ・ Accelerator position sensor

Claims (4)

An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
A bypass passage having one end connected to the exhaust passage upstream of the NOx storage reduction catalyst and the other end connected to the exhaust passage downstream of the NOx storage reduction catalyst;
A reducing agent addition valve that is provided downstream of a connection portion of one end of the bypass passage in the exhaust passage and upstream of the NOx storage reduction catalyst, and adds a reducing agent into the exhaust;
An air-fuel ratio sensor that is provided downstream of the NOx storage reduction catalyst in the exhaust passage and upstream of the connecting portion of the other end of the bypass passage;
The flow rate of the exhaust gas passing through the NOx storage reduction catalyst and the bypass passage when the air-fuel ratio of the exhaust gas exhausted from the NOx storage reduction catalyst is reduced by adding the reducing agent from the reducing agent addition valve. A target integral value calculating means for calculating a target integral value that is an integral value of the amount of decrease in the detected value of the air-fuel ratio sensor when it is assumed that the shunt ratio that is a ratio with the flow rate of the flowing exhaust gas is the target shunt ratio;
This is an integrated value of the amount of decrease in the actual detected value of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas discharged from the NOx storage reduction catalyst is reduced by adding a reducing agent from the reducing agent addition valve. An actual integral value calculating means for calculating an integral value;
An abnormality detection unit that determines that an abnormality has occurred in the bypass passage when the actual integration value calculated by the actual integration value calculation unit is different from the target integration value calculated by the target integration value calculation unit; An exhaust gas purification apparatus for an internal combustion engine characterized by the above.   When the actual integral value calculated by the actual integral value calculation means is larger than the target integral value calculated by the target integral value calculation means, the abnormality detection means determines that exhaust leakage has occurred in the bypass passage. The exhaust emission control device for an internal combustion engine according to claim 1, wherein   When the actual integrated value calculated by the actual integrated value calculating means is smaller than the target integrated value calculated by the target integrated value calculating means, the abnormality detecting means determines that clogging has occurred in the bypass passage. The exhaust emission control device for an internal combustion engine according to claim 1 or 2. Further comprising bypass flow rate control means for controlling the flow rate of the exhaust gas flowing through the bypass passage,
When the actual integrated value calculated by the actual integrated value calculating means is different from the target integrated value calculated by the target integrated value calculating means, the abnormality detecting means causes an abnormality in the bypass passage or the bypass flow rate controlling means. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is determined.

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