JP4650245B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine including a particulate filter and an NOx storage reduction catalyst provided in an exhaust passage of the internal combustion engine.

  In an internal combustion engine, an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) may be installed in an exhaust passage. The NOx catalyst is a catalyst that stores NOx in the exhaust when the ambient atmosphere is an oxidizing atmosphere, and releases and reduces the stored NOx when the ambient atmosphere is a reducing atmosphere.

  When such a NOx catalyst is provided in the exhaust passage, NOx reduction control is performed to reduce NOx when the NOx occlusion amount in the NOx catalyst reaches a certain amount. This NOx reduction control is performed by setting the ambient atmosphere of the NOx catalyst as a reducing atmosphere, that is, by supplying a reducing agent to the NOx catalyst and lowering the air-fuel ratio of the exhaust.

  Patent Document 1 discloses a technique for determining the deterioration of the NOx catalyst based on the amount of NOx reduction from the NOx catalyst when the NOx reduction control is executed.

  In Patent Document 2, after shifting from a period in which the reducing agent is not supplied to the NOx catalyst to a period in which the reducing agent is supplied to the NOx catalyst, the NOx concentration of the exhaust gas in the exhaust passage downstream of the NOx catalyst is changed to a predetermined period. A technology for prohibiting the determination of deterioration of the NOx catalyst based thereon is disclosed.

  In addition to the NOx catalyst, a particulate filter (hereinafter referred to as a filter) that collects particulate matter (hereinafter referred to as PM) in the exhaust gas may be installed in the exhaust passage. In this case, the NOx catalyst is installed in a state where it is disposed in the exhaust passage upstream of the filter or is supported by the filter.

When the filter is provided in the exhaust passage, the filter regeneration control for oxidizing and removing PM collected by the filter is performed by raising the temperature of the filter.
Japanese Patent No. 3412472 JP 2002-221028 A Japanese Patent No. 3430879 JP 2003-148136 A JP 2002-97938 A

  An object of the present invention is to provide a technique capable of more accurately determining deterioration of a NOx catalyst in an exhaust purification system of an internal combustion engine including a filter provided in an exhaust passage of the internal combustion engine and a NOx catalyst. And

An internal combustion engine exhaust gas purification system according to a first aspect of the invention includes:
A particulate filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
A NOx storage reduction catalyst that is carried by the particulate filter or provided in the exhaust passage upstream of the particulate filter;
The temperature of the particulate filter is raised to a predetermined regeneration temperature by raising the temperature of the NOx storage reduction catalyst, thereby executing filter regeneration control for removing particulate matter collected in the particulate filter. Filter regeneration control execution means for
By supplying a reducing agent to the NOx storage reduction catalyst and reducing the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to a predetermined reduction air-fuel ratio, NOx stored in the NOx storage reduction catalyst is reduced. NOx reduction control execution means for executing NOx reduction control for releasing and reducing;
NOx occlusion amount estimation means for estimating an NOx occlusion amount in the NOx storage reduction catalyst based on a history of operating states of the internal combustion engine;
NOx reduction amount estimation means for estimating a NOx reduction amount that is the amount of NOx released and reduced from the NOx storage reduction catalyst when NOx reduction control is executed by the NOx reduction control execution means;
The NOx reduction control is executed by the NOx reduction control execution means, and at that time, the NOx reduction amount estimated by the NOx reduction amount estimation means and the NOx storage control at the start of NOx reduction control execution estimated by the NOx storage amount estimation means Deterioration determining means for determining that the NOx storage reduction catalyst is deteriorated when the difference from the amount is a predetermined amount or more,
When the filter regeneration control is being executed by the filter regeneration control executing means, execution of the deterioration determination of the storage reduction type NOx catalyst by the deterioration determining means is prohibited.

  Here, the predetermined regeneration temperature is a temperature at which PM collected by the filter can be oxidized and removed, and the possibility of excessively promoting the deterioration of the filter is low. The predetermined reduction air-fuel ratio is an air-fuel ratio lower than the air-fuel ratio of the exhaust when the internal combustion engine is normally operated, and the air-fuel ratio at which NOx stored in the NOx catalyst can be released and reduced. The fuel ratio.

  Further, when the predetermined amount is in a state where the NOx catalyst is not deteriorated, it may be determined that the amount of NOx stored in the NOx catalyst and reduced when the NOx reduction control is executed is not reduced by the NOx reduction control. It is a value that is a possible threshold.

    In the present invention, when the filter regeneration control is executed, the temperature of the NOx catalyst becomes higher than when the filter regeneration control is not executed. Therefore, when the filter regeneration control is executed, the amount of NOx stored in the NOx catalyst is reduced compared to when the filter regeneration control is not executed. As a result, when NOx reduction control is executed while filter regeneration control is being executed, the amount of NOx that is reduced is reduced compared to when NOx reduction control is executed when filter regeneration control is not being executed.

  Therefore, when the deterioration determination of the NOx catalyst is performed by the deterioration determination means when the filter regeneration control is being performed, as in the case where the filter regeneration control is not being performed, the deterioration determination of the NOx catalyst is accurately performed. May become difficult.

  According to the present invention, when the filter regeneration control is being executed, the execution of the NOx catalyst deterioration determination is prohibited. That is, the NOx catalyst deterioration determination is executed when the filter regeneration control is not executed. As a result, it is possible to more accurately determine the deterioration of the NOx catalyst.

An internal combustion engine exhaust purification system according to a second aspect of the present invention includes:
A particulate filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
A NOx storage reduction catalyst that is carried by the particulate filter or provided in the exhaust passage upstream of the particulate filter;
The temperature of the particulate filter is raised to a predetermined regeneration temperature by raising the temperature of the NOx storage reduction catalyst, thereby executing filter regeneration control for removing particulate matter collected in the particulate filter. Filter regeneration control execution means for
By supplying a reducing agent to the NOx storage reduction catalyst and reducing the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to a predetermined reduction air-fuel ratio, NOx stored in the NOx storage reduction catalyst is reduced. NOx reduction control execution means for executing NOx reduction control for releasing and reducing;
NOx occlusion amount estimation means for estimating an NOx occlusion amount in the NOx storage reduction catalyst based on a history of operating states of the internal combustion engine;
NOx reduction amount estimation means for estimating a NOx reduction amount that is the amount of NOx released and reduced from the NOx storage reduction catalyst when NOx reduction control is executed by the NOx reduction control execution means;
The NOx reduction control is executed by the NOx reduction control execution means, and at that time, the NOx reduction amount estimated by the NOx reduction amount estimation means and the NOx storage control at the start of NOx reduction control execution estimated by the NOx storage amount estimation means Deterioration determining means for determining that the NOx storage reduction catalyst is deteriorated when the difference from the amount is a predetermined amount or more,
When performing the deterioration determination of the NOx storage reduction catalyst by the deterioration determination means when the filter regeneration control is being executed by the filter regeneration control execution means, the deterioration determination is performed when the filter regeneration control is not being executed. The predetermined amount is set to a smaller amount as compared with the case of execution.

  The predetermined regeneration temperature and the predetermined reduced air-fuel ratio according to the present invention are the same values as in the first invention.

  As described above, when the filter regeneration control is being executed, the amount of NOx stored in the NOx catalyst is reduced compared to when the filter regeneration control is not being executed. As a result, when the NOx reduction control is executed at this time, the amount of NOx reduced is reduced as compared with the case where the NOx reduction control is executed in a state where the filter regeneration control is not executed.

  Therefore, it is possible to more accurately determine the deterioration of the NOx catalyst by changing the predetermined amount as the threshold value for determining the deterioration of the NOx catalyst as in the present invention. Further, according to the present invention, it is possible to more accurately determine the deterioration of the NOx catalyst even during the execution of the filter regeneration control.

  In the first and second aspects of the invention, the NOx reduction amount estimation means calculates the NOx reduction amount based on changes in the air-fuel ratio and exhaust NOx concentration downstream of the NOx catalyst during execution of NOx reduction control. It may be estimated.

  According to the exhaust gas purification system for an internal combustion engine according to the present invention, when the filter and the NOx catalyst are provided in the exhaust passage of the internal combustion engine, it is possible to more accurately determine the deterioration of the NOx catalyst.

  Hereinafter, specific embodiments of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings.

<Schematic configuration of intake and exhaust system of internal combustion engine>
Here, the case where the present invention is applied to a diesel engine for driving a vehicle will be described as an example. FIG. 1 is a diagram showing a schematic configuration of an intake / exhaust system of an internal combustion engine according to the present embodiment.

  The internal combustion engine 1 is a diesel engine for driving a vehicle. An intake passage 3 and an exhaust passage 2 are connected to the internal combustion engine 1. A filter 4 is provided in the exhaust passage 2. The filter 4 carries a NOx catalyst 9. A fuel addition valve 5 for adding fuel to the exhaust gas is provided upstream of the filter 4 in the exhaust passage 2.

  An upstream air-fuel ratio sensor 11 that detects the air-fuel ratio of exhaust gas and an upstream temperature sensor 12 that detects the temperature of exhaust gas are provided downstream of the fuel addition valve 5 and upstream of the filter 4 in the exhaust passage 2. . A downstream air-fuel ratio sensor 13 for detecting the air-fuel ratio of exhaust gas and a downstream temperature sensor 14 for detecting the temperature of exhaust gas are provided downstream of the filter 4 in the exhaust passage 2. Further, a differential pressure sensor 6 that detects a differential pressure between the upstream side and the downstream side of the filter 4 is provided in the exhaust passage 2.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. The ECU 10 detects the upstream air-fuel ratio sensor 11, the upstream temperature sensor 12, the downstream air-fuel ratio sensor 13, the downstream temperature sensor 14, the differential pressure sensor 6, and the rotation angle of the crankshaft of the internal combustion engine 1. A crank position sensor 7 and an accelerator position sensor 8 for detecting the accelerator position of a vehicle equipped with the internal combustion engine 1 are electrically connected. These output signals are input to the ECU 10.

  The ECU 10 estimates the temperature of the filter 4 based on the detection value of the upstream temperature sensor 12 and / or the downstream temperature sensor 14. Further, the ECU 10 calculates the rotation speed of the internal combustion engine 1 based on the detection value of the crank position sensor 7 and calculates the load of the internal combustion engine 1 based on the detection value of the accelerator opening sensor 8.

  Further, the ECU 10 is electrically connected to the fuel addition valve 5 and the fuel injection valve of the internal combustion engine 1. These are controlled by the ECU 10.

  In this embodiment, filter regeneration control is performed to remove PM collected by the filter 4. In the filter regeneration control according to this embodiment, when the NOx catalyst 9 is in an active state, fuel is added from the fuel addition valve 5, thereby supplying the fuel to the NOx catalyst 9 supported on the filter 4. Done. The supplied fuel is oxidized by the NOx catalyst 9, and the temperature of the NOx catalyst 9 rises and the temperature of the filter 4 rises due to the oxidation heat generated at that time.

  In the filter regeneration control, the temperature of the filter 4 is raised to a predetermined regeneration temperature by controlling the amount of fuel added from the fuel addition valve 5. The predetermined regeneration temperature is a temperature at which PM collected by the filter 4 can be oxidized and removed, and the possibility of excessively promoting the deterioration of the filter 4 is low. When the temperature of the filter 4 reaches the predetermined regeneration temperature, PM is oxidized and the PM is removed from the filter 4.

  In the present embodiment, the ECU 10 estimates the PM collection amount in the filter 4 based on the detection value of the differential pressure sensor 6. And filter regeneration control is performed when PM collection amount becomes more than predetermined collection amount. Here, the predetermined collection amount is an amount smaller than the PM collection amount that can be determined that the pressure in the exhaust passage 2 upstream of the filter 4 may increase excessively.

In the present embodiment, the NOx catalyst 9 is supported by the filter 4, but the NOx catalyst 9 may be disposed upstream of the filter 4 in the exhaust passage 2. Also in this case, when the filter regeneration control is executed, the fuel can be supplied to the NOx catalyst 9 and the temperature of the filter 4 can be raised by the oxidation heat generated when the fuel is oxidized.

<NOx reduction control>
In this embodiment, NOx reduction control is performed to release and reduce the NOx stored in the NOx catalyst 9 carried on the filter 4. In the NOx reduction control according to the present embodiment, when the NOx catalyst 9 is in an active state, fuel is added from the fuel addition valve 5, whereby the air-fuel ratio of the exhaust gas flowing into the filter 4, that is, the NOx catalyst 9. This is performed by lowering the air-fuel ratio of the ambient atmosphere and supplying fuel as a reducing agent to the NOx catalyst 9.

  In the NOx reduction control, the amount of fuel added from the fuel addition valve 5 is controlled to reduce the air-fuel ratio of the exhaust flowing into the filter 4 to a predetermined reduction air-fuel ratio. This predetermined reduction air-fuel ratio is an air-fuel ratio lower than the theoretical air-fuel ratio and is a predetermined value. The predetermined reduction air-fuel ratio is not necessarily a rich air-fuel ratio, and may be any air-fuel ratio that allows NOx stored in the NOx catalyst 9 to be released and reduced.

  The air-fuel ratio of the exhaust gas flowing into the filter 4 becomes a predetermined reduction air-fuel ratio, and fuel is supplied to the NOx catalyst 9, so that the ambient atmosphere of the NOx catalyst 9 becomes a reducing atmosphere. Thereby, NOx occluded in the NOx catalyst 9 is released and reduced.

  In this embodiment, when the filter regeneration control or the NOx reduction control is executed, if the temperature of the NOx catalyst 9 is lower than the activation temperature, the temperature of the exhaust discharged from the internal combustion engine 1 is increased to increase the NOx. After raising the temperature of the catalyst 9 to the activation temperature, the fuel addition from the fuel addition valve 5 is executed.

<NOx catalyst deterioration judgment method>
Here, a method for determining the deterioration of the NOx catalyst 9 according to the present embodiment will be described. FIG. 2 is a time chart showing changes in the output values of the upstream air-fuel ratio sensor 11 and the downstream air-fuel ratio sensor 13 when the NOx reduction control is executed. 2A shows an output value of the upstream air-fuel ratio sensor 11 (hereinafter, this output value is referred to as an upstream air-fuel ratio), and FIG. 2B shows an output value of the downstream air-fuel ratio sensor 13 ( Hereinafter, this output value is referred to as a downstream air-fuel ratio). In (A) and (b), Rn represents the air-fuel ratio of the exhaust when the internal combustion engine 1 is in a normal operating state (hereinafter, this air-fuel ratio is referred to as the normal air-fuel ratio), and Rt represents It represents a predetermined reduction air-fuel ratio that is a target air-fuel ratio at the time of execution of NOx reduction control. Rs (dashed line) represents the stoichiometric air-fuel ratio.

  As described above, in the NOx reduction control, the air-fuel ratio of the exhaust gas flowing into the filter 4 is reduced to the predetermined reduction air-fuel ratio Rt. As a result, the upstream air-fuel ratio decreases from the normal air-fuel ratio Rn to the predetermined reduction air-fuel ratio Rt at the time point (a).

  It takes a certain amount of time for the exhaust gas whose air-fuel ratio has decreased to reach the downstream air-fuel ratio sensor 13 after passing through the upstream air-fuel ratio sensor 11. Therefore, the downstream air-fuel ratio decreases at the time (b) when the arrival delay time Δtd elapses from the time (a).

  At this time, the fuel flowing into the filter 4 is used for NOx reduction by the NOx catalyst 9. Therefore, at the time point (b), the downstream air-fuel ratio does not decrease to the predetermined reduction air-fuel ratio Rt, but becomes a value in the vicinity of the theoretical air-fuel ratio Rs. While the NOx reduction in the NOx catalyst 9 continues, the downstream air-fuel ratio does not decrease to the predetermined reduction air-fuel ratio Rt, and at the time point (c) when the reduction of NOx is completed, The air-fuel ratio becomes the predetermined reduction air-fuel ratio Rt. Hereinafter, the time from (b) to (c) is referred to as a reduction duration Δtstr.

  As the amount of NOx reduced from the NOx catalyst 9 by the NOx reduction control increases, the reduction continuation time Δtstr becomes longer. That is, the NOx reduction amount when the NOx reduction control is executed is based on the reduction continuation time Δtstr and the downstream air-fuel ratio when the reduction continuation time Δtstr has elapsed (between (b) and (c)). Can be estimated.

  On the other hand, the NOx occlusion amount in the NOx catalyst 9 at the start of the NOx reduction control execution can be estimated based on the history of the operating state of the internal combustion engine 1 from the end of the previous NOx reduction control execution.

  However, when the NOx catalyst 9 is deteriorated, the amount of NOx that can be occluded is reduced as compared to when the NOx catalyst 9 is not deteriorated. Therefore, when the NOx catalyst 9 is deteriorated, the actual NOx occlusion amount in the NOx catalyst 9 at the start of execution of the NOx reduction control is estimated based on the operating state history of the internal combustion engine 1 as described above. There is a possibility that it is less than the amount. In such a case, the NOx reduction amount when the NOx reduction control is executed inevitably decreases.

  Further, when the NOx catalyst 9 is deteriorated, it becomes difficult for NOx to be released and reduced. Therefore, even if the NOx occlusion amount in the NOx catalyst 9 is the same, the NOx reduction amount when the NOx reduction control is executed is reduced compared to when the NOx catalyst 9 is not deteriorated.

  Therefore, in this embodiment, when the deterioration determination of the NOx catalyst 9 is performed, NOx reduction control is executed. Whether or not the NOx catalyst 9 has deteriorated is determined based on the difference between the NOx reduction amount estimated by the above method and the estimated value of the NOx occlusion amount in the NOx catalyst 9 at the start of execution of the NOx reduction control. judge.

  That is, when the difference between the estimated value of the NOx reduction amount and the estimated value of the NOx occlusion amount is equal to or greater than a predetermined amount, it is determined that the NOx catalyst 9 has deteriorated. Here, the predetermined amount is a lower limit of a value at which it can be determined that the NOx catalyst 9 has deteriorated. This predetermined amount can be determined in advance by experiments or the like.

<Prohibition of NOx catalyst deterioration determination>
As described above, in this embodiment, when the filter regeneration control is executed, the temperature of the NOx catalyst 9 becomes higher than when the filter regeneration control is not executed. That is, when the filter regeneration control is executed, not only the temperature of the filter 4 but also the temperature of the NOx catalyst 9 rises to a predetermined regeneration temperature.

  When the temperature of the NOx catalyst 9 rises to a predetermined regeneration temperature at which the PM collected by the filter 4 can be oxidized and removed, the temperature of the NOx catalyst 9 is a normal temperature (filter regeneration control is executed). The amount of NOx occluded in the NOx catalyst 9 is reduced as compared to the case where the temperature is not set). As a result, when NOx reduction control is also executed during the execution of filter regeneration control, the amount of NOx reduction is reduced compared to when NOx reduction control is executed without filter regeneration control being executed.

  As described above, in the deterioration determination method for the NOx catalyst 9 according to the present embodiment, the NOx catalyst is based on the difference between the NOx reduction amount when the NOx reduction control is executed and the NOx occlusion amount when the NOx reduction control is started. It is determined whether 9 is deteriorated. Therefore, as described above, when the NOx reduction amount changes due to the influence of the filter regeneration control, the deterioration determination of the NOx catalyst 9 is performed in the same manner as when the filter regeneration control is not performed when the filter regeneration control is performed. If this is done, it may be difficult to accurately determine the deterioration of the NOx catalyst 9.

  Therefore, in this embodiment, when the filter regeneration control is being executed, the execution of the deterioration determination of the NOx catalyst 9 is prohibited.

  Hereinafter, the NOx catalyst deterioration determination routine according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 10 and is repeated every predetermined time.

  In this routine, the ECU 10 first determines in S101 whether or not a condition for executing the deterioration determination of the NOx catalyst 9 is satisfied. Examples of this condition include a case where the travel distance of the vehicle on which the internal combustion engine 1 is mounted has become equal to or greater than a predetermined distance from the end of the previous determination of deterioration of the NOx catalyst 9. If an affirmative determination is made in S101, the ECU 10 proceeds to S102, and if a negative determination is made, the ECU 10 ends the execution of this routine.

  In S102, the ECU 10 determines whether or not the filter regeneration control is being executed. If an affirmative determination is made in S102, the ECU 10 proceeds to S103, and if a negative determination is made, the ECU 10 proceeds to S104.

  The ECU 10 that has proceeded to S104 executes the NOx reduction control, and executes the above-described deterioration determination of the NOx catalyst 9. Thereafter, the ECU 10 ends the execution of this routine.

  On the other hand, the ECU 10 that has proceeded to S <b> 103 prohibits execution of the deterioration determination of the NOx catalyst 9. Thereafter, the ECU 10 ends the execution of this routine.

  According to the present embodiment, when the filter regeneration control is being performed, the deterioration determination of the NOx catalyst 9 is prohibited, and the deterioration determination is performed when the filter regeneration control is not being performed. Thereby, deterioration of the NOx catalyst 9 can be determined more accurately.

  The schematic configuration of the intake and exhaust system of the internal combustion engine according to the present embodiment is the same as that of the first embodiment. Also in the present embodiment, the same filter regeneration control and NOx reduction control as in the first embodiment are executed.

<NOx catalyst deterioration judgment method>
Also in this embodiment, when the deterioration determination of the NOx catalyst 9 is performed, the determination is performed by the same method as in the embodiment. That is, when the NOx reduction control is executed and the difference between the estimated value of the NOx reduction amount at that time and the estimated value of the NOx occlusion amount at the start of execution of the NOz reduction control is greater than or equal to a predetermined amount, the NOx catalyst 9 is deteriorated. Is determined.

  In this embodiment, the deterioration determination of the NOx catalyst 9 is executed even when the filter regeneration control is being executed by changing the predetermined amount that is the threshold value for determining the deterioration of the NOx catalyst 9.

  As described above, when the NOx reduction control is executed in the state where the filter regeneration control is being executed, the NOx to be reduced is reduced compared to the case where the NOx reduction control is executed in a state where the filter regeneration control is not being executed. The amount decreases.

  Therefore, when the deterioration determination of the NOx catalyst 9 is performed when the filter regeneration control is being performed, a predetermined amount is compared with the case where the deterioration determination of the NOx catalyst 9 is performed when the filter regeneration control is not being performed. Set to a smaller amount.

  Hereinafter, the NOx catalyst deterioration determination routine according to this embodiment will be described based on the flowchart shown in FIG. Since S101 and S102 in this routine are the same as those in the flowchart shown in FIG. This routine is stored in advance in the ECU 10 and is repeated every predetermined time.

  In this routine, if an affirmative determination is made in S102, the ECU 10 proceeds to S203, and if a negative determination is made, the ECU 10 proceeds to S204.

  The ECU 10 having proceeded to S204 sets the predetermined amount to the first predetermined amount ΔQn1, and executes the deterioration determination of the NOx catalyst 9. Here, the first predetermined amount ΔQn1 is an amount equivalent to a predetermined amount serving as a threshold for determining the deterioration of the NOx catalyst 9 according to the first embodiment. Thereafter, the ECU 10 ends the execution of this routine.

  On the other hand, the ECU 10 that has proceeded to S203 sets the predetermined amount to the second predetermined amount ΔQn2, and executes the deterioration determination of the NOx catalyst 9. Here, the second predetermined amount ΔQn2 is smaller than the first predetermined amount ΔQn1. Similarly to the first predetermined amount ΔQn1, the second predetermined amount ΔQn2 is determined in advance by experiments or the like. Thereafter, the ECU 10 ends the execution of this routine.

  According to the present embodiment, it is possible to more accurately determine the deterioration of the NOx catalyst 9 by changing the predetermined amount serving as the threshold for determining the deterioration of the NOx catalyst 9 as described above. Further, the deterioration determination of the NOx catalyst 9 can be performed more accurately even during the execution of the filter regeneration control.

The figure which shows schematic structure of the intake / exhaust system of the internal combustion engine which concerns on an Example. The time chart which shows the change of the output value of an upstream air-fuel-ratio sensor and downstream air-fuel-ratio sensor when performing NOx reduction | restoration control. 3 is a flowchart showing a NOx catalyst deterioration determination routine according to the first embodiment. 9 is a flowchart showing a NOx catalyst deterioration determination routine according to Embodiment 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 4 ... Particulate filter 5 ... Fuel addition valve 6 ... Differential pressure sensor 7 ... Crank position sensor 8 ... Accelerator opening sensor 9・ ・ Occlusion reduction type NOx catalyst 10 ・ ・ ECU
11. Upstream air-fuel ratio sensor 12. Upstream temperature sensor 13 Downstream air-fuel ratio sensor 14 Downstream temperature sensor

Claims (1)

A particulate filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
A NOx storage reduction catalyst that is carried by the particulate filter or provided in the exhaust passage upstream of the particulate filter;
The temperature of the particulate filter is raised to a predetermined regeneration temperature by raising the temperature of the NOx storage reduction catalyst, thereby executing filter regeneration control for removing particulate matter collected in the particulate filter. Filter regeneration control execution means for
By supplying a reducing agent to the NOx storage reduction catalyst and reducing the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst to a predetermined reduction air-fuel ratio, NOx stored in the NOx storage reduction catalyst is reduced. NOx reduction control execution means for executing NOx reduction control for releasing and reducing;
NOx occlusion amount estimation means for estimating an NOx occlusion amount in the NOx storage reduction catalyst based on a history of operating states of the internal combustion engine;
NOx reduction amount estimation means for estimating a NOx reduction amount that is the amount of NOx released and reduced from the NOx storage reduction catalyst when NOx reduction control is executed by the NOx reduction control execution means;
The NOx reduction control is executed by the NOx reduction control execution means, and at that time, the NOx reduction amount estimated by the NOx reduction amount estimation means and the NOx storage control at the start of NOx reduction control execution estimated by the NOx storage amount estimation means Deterioration determining means for determining that the NOx storage reduction catalyst is deteriorated when the difference from the amount is a predetermined amount or more,
An exhaust gas purification system for an internal combustion engine, wherein when the filter regeneration control is executed by the filter regeneration control execution means, execution of the deterioration determination of the storage reduction type NOx catalyst by the deterioration determination means is prohibited.

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