JP2013108452A - Device for detecting failure of filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy in detecting a failure of a filter using an output value of a particulate matter (PM) sensor, in a configuration where a NOx selective reduction-type catalyst is provided between the filter and the PM sensor in an exhaust passage.SOLUTION: A device for detecting a failure of a filter includes the steps of: calculating an oxidation amount of the PM deposited on the PM sensor on the basis of a nitrous oxide concentration or nitrous oxide content of the downstream exhaust gas of the NOx selective reduction-type catalyst; correcting the PM deposition amount in the PM sensor which is calculated by assuming that the filter is in a predetermined state on the basis of the PM oxidation amount; and determining whether the filter is in failure or not on the basis of the output value of the PM sensor on condition that the corrected PM deposition amount in the PM sensor is more than a predetermined amount.

Description

  The present invention relates to a filter failure detection device that detects a failure of a filter that is provided in an exhaust passage of an internal combustion engine and collects particulate matter in exhaust gas.

In some cases, a filter that collects particulate matter (hereinafter referred to as PM) in the exhaust gas is provided in the exhaust passage of the internal combustion engine. In such a case, a technique is known in which a PM sensor is provided in the exhaust passage downstream of the filter and a filter failure is detected based on the output value of the PM sensor. In some cases, a selective reduction type NOx catalyst that reduces NOx in exhaust gas using ammonia (NH ₃ ) as a reducing agent may be provided in the exhaust passage of the internal combustion engine.

  Patent Document 1 discloses a configuration in which a selective reduction type NOx catalyst is provided downstream of a filter in an exhaust passage of an internal combustion engine. Further, in Patent Document 1, the ammonia concentration in the exhaust flowing through the selective reduction type NOx catalyst is suitable for reducing NOx in the exhaust during forced regeneration of the filter that burns the PM collected by the filter. Has been disclosed that keeps the temperature increase of the selective reduction type NOx catalyst at a set gradient so that the concentration becomes higher.

  Patent Document 2 discloses a configuration in which a filter, a urea injection valve, a selective reduction type NOx catalyst, an ammonia detection means, an ammonia slip prevention catalyst, and a nitrous oxide detection means are sequentially provided in the exhaust passage of the internal combustion engine from the upstream side. Has been. Patent Document 2 discloses a technique for controlling the amount of urea supplied from a urea injection valve in accordance with the nitrous oxide concentration detected by the nitrous oxide detection means.

  Patent Document 3 discloses a configuration in which a PM sensor is provided downstream of a filter in an exhaust passage of an internal combustion engine. Further, this Patent Document 3 discloses a technique for starting regeneration of a sensor element that burns and removes PM adhering to the sensor element of the PM sensor in accordance with the regeneration timing of the filter that burns and removes PM collected by the filter. It is disclosed.

JP 2010-261331 A JP2011-122552A JP 2011-089430 A

  A PM sensor that outputs a signal corresponding to the amount of PM deposited on itself may be used as a PM sensor provided in the exhaust passage downstream of the filter for detecting a filter failure. When a failure such as erosion or breakage occurs in the filter, the amount of PM that passes through the filter without being collected by the filter increases. As a result, the PM accumulation amount in the PM sensor provided on the downstream side of the filter is larger than when the filter is normal. Therefore, a filter failure can be detected using the output value of the PM sensor as described above.

Here, a selective reduction type NOx catalyst may be provided between the filter and the PM sensor in the exhaust passage. In addition, nitrous oxide (N ₂ O) may be generated in the process in which NOx is reduced using ammonia as a reducing agent in the selective reduction type NOx catalyst. When nitrous oxide is generated in the selective reduction type NOx catalyst, PM deposited on the PM sensor provided on the downstream side of the selective reduction type NOx catalyst may be oxidized by the nitrous oxide. is there. When the PM deposited on the PM sensor is reduced by being oxidized by nitrous oxide, the output value of the PM sensor is lowered. Therefore, in order to detect a filter failure with high accuracy using the output value of the PM sensor, it is necessary to consider oxidation of PM by nitrous oxide.

  The present invention has been made in view of the above problems, and uses the output value of the PM sensor in a configuration in which the selective reduction type NOx catalyst is provided between the filter and the PM sensor in the exhaust passage. The object is to improve the accuracy of filter failure detection.

The filter failure detection apparatus according to the first invention is
A filter failure detection device for detecting a failure of a filter provided in an exhaust passage of an internal combustion engine and collecting particulate matter in exhaust gas,
A PM sensor that is provided in an exhaust passage downstream of the filter and outputs a signal corresponding to the amount of particulate matter deposited on the filter;
A selective reduction type NOx catalyst provided in an exhaust passage between the filter and the PM sensor, for reducing NOx in the exhaust gas using ammonia as a reducing agent;
Estimating means for estimating a PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state;
Obtaining means for obtaining the concentration of nitrous oxide in the exhaust downstream of the selective catalytic reduction NOx catalyst or the amount of nitrous oxide in the exhaust;
Based on at least the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst acquired by the obtaining means or the amount of nitrous oxide in the exhaust, the amount of PM oxidized on the PM sensor is calculated. Oxidation amount calculating means for
PM accumulation amount correction means for correcting the PM accumulation amount in the PM sensor estimated by the estimation means based on the oxidation amount of PM calculated by the oxidation amount calculation means;
A determination unit that determines failure of the filter based on an output value of the PM sensor on the condition that the PM deposition amount in the PM sensor corrected by the PM deposition amount correction unit is a predetermined amount or more;
Is provided.

  The PM sensor does not output a signal corresponding to the PM deposition amount when the PM deposition amount in the PM sensor is very small. Here, the predetermined amount is a value equal to or higher than the threshold of the PM accumulation amount at which the output value of the PM sensor becomes a value corresponding to the PM accumulation amount in the PM sensor itself.

  In the present invention, the PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state is estimated by the estimating means. Here, the predetermined state may be, for example, a normal state, or may be a state where the filter failure level has reached a predetermined level.

  Furthermore, in the present invention, the oxidation amount calculation means calculation means calculates the oxidation of PM deposited on the PM sensor based on the nitrous oxide concentration in the exhaust downstream of the selective reduction type NOx catalyst or the amount of nitrous oxide in the exhaust. A quantity is calculated. At this time, the higher the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst, or the greater the amount of nitrous oxide in the exhaust, the greater the amount of oxidation of PM is calculated.

Then, the PM accumulation amount is corrected by subtracting the oxidation amount of PM calculated by the oxidation amount calculation means from the PM accumulation amount in the PM sensor estimated by the estimation means by the PM accumulation amount correction means. Thereby, it is possible to calculate the PM accumulation amount in the PM sensor with high accuracy when it is assumed that the filter is in a predetermined state. When the correction value of the PM accumulation amount is equal to or greater than a predetermined amount, the determination unit determines that the filter is malfunctioning based on the output value of the PM sensor.

  According to the present invention, the filter failure determination is performed based on the PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state, which is calculated in consideration of the oxidation amount of nitrous oxide in the exhaust gas. The execution timing is determined. Therefore, the accuracy of filter failure detection using the output value of the PM sensor can be improved.

The failure detection device for a filter according to the second invention is:
A filter failure detection device for detecting a failure of a filter provided in an exhaust passage of an internal combustion engine and collecting particulate matter in exhaust gas,
A PM sensor that is provided in an exhaust passage downstream of the filter and outputs a signal corresponding to the amount of particulate matter deposited on the filter;
A selective reduction type NOx catalyst provided in an exhaust passage between the filter and the PM sensor, for reducing NOx in the exhaust gas using ammonia as a reducing agent;
Estimating means for estimating a PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state;
Obtaining means for obtaining the concentration of nitrous oxide in the exhaust downstream of the selective catalytic reduction NOx catalyst or the amount of nitrous oxide in the exhaust;
Based on at least the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst acquired by the obtaining means or the amount of nitrous oxide in the exhaust, the amount of PM oxidized on the PM sensor is calculated. Oxidation amount calculating means for
PM accumulation amount correction means for correcting the PM accumulation amount in the PM sensor estimated by the estimation means based on the oxidation amount of PM calculated by the oxidation amount calculation means;
A determination unit that determines a failure of the filter by comparing the output value of the PM sensor with a threshold value that is determined based on the PM accumulation amount in the PM sensor corrected by the PM accumulation amount correction unit;
Is provided.

  Also in the present invention, the PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state is estimated by the estimation means, as in the first invention. Furthermore, in the present invention, the PM deposition amount is corrected by subtracting the PM oxidation amount calculated by the oxidation amount calculation unit from the PM deposition amount in the PM sensor estimated by the estimation unit by the PM deposition amount correction unit. It is corrected. Then, the failure of the filter is determined by comparing the threshold value determined based on the correction value of the PM deposition amount with the output value of the PM sensor by the determination means.

  According to the present invention, the failure determination threshold value is determined based on the PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state, which is calculated in consideration of the oxidation amount of nitrous oxide in the exhaust gas. It is done. Therefore, the accuracy of filter failure detection using the output value of the PM sensor can be improved.

The failure detection device for a filter according to the third invention is
A filter failure detection device for detecting a failure of a filter provided in an exhaust passage of an internal combustion engine and collecting particulate matter in exhaust gas,
A PM sensor that is provided in an exhaust passage downstream of the filter and outputs a signal corresponding to the amount of particulate matter deposited on the filter;
A selective reduction type NOx catalyst provided in an exhaust passage between the filter and the PM sensor, for reducing NOx in the exhaust gas using ammonia as a reducing agent;
Obtaining means for obtaining the concentration of nitrous oxide in the exhaust downstream of the selective catalytic reduction NOx catalyst or the amount of nitrous oxide in the exhaust;
Based on at least the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst acquired by the acquisition means or the amount of nitrous oxide in the exhaust, the amount of oxidation of PM deposited on the PM sensor is calculated. Oxidation amount calculating means for
Sensor output correction means for correcting the output value of the PM sensor based on the oxidation amount of PM calculated by the oxidation amount calculation means;
A determination unit that determines a failure of the filter by comparing an output value of the PM sensor corrected by the sensor output correction unit with a threshold value;
Is provided.

  The larger the amount of oxidation of PM deposited on the PM sensor, the smaller the output value of the PM sensor. As a result, the difference between the integrated value of the PM amount passing through the filter and adhering to the PM sensor (that is, the PM accumulation amount in the PM sensor when PM is not oxidized) and the output value of the PM sensor becomes large.

  Therefore, in the present invention, the output value of the PM sensor is corrected by the sensor output correction means based on the oxidation amount of PM calculated by the oxidation amount calculation means. At this time, the output value of the PM sensor is corrected to increase as the amount of oxidation of PM increases. Thereby, the divergence between the integrated value of the PM amount passing through the filter and adhering to the PM sensor and the output value of the PM sensor can be reduced.

  Then, the determination unit determines the filter failure by comparing the corrected output value of the PM sensor with the threshold value. That is, if the output value of the corrected PM sensor is equal to or greater than the threshold, it is determined that the amount of PM that has passed through the filter is excessively large, that is, the filter has failed. On the other hand, if the corrected output value of the PM sensor is smaller than the threshold value, it is determined that the filter is normal.

  According to the present invention, filter failure determination is performed based on the output value of the PM sensor corrected in consideration of the amount of oxidation by nitrous oxide in the exhaust gas. Therefore, the accuracy of filter failure detection using the output value of the PM sensor can be improved.

  In the first, second, or third invention, the oxidation amount calculation means includes the temperature of the PM sensor in addition to the nitrous oxide concentration of the exhaust downstream of the selective reduction type NOx catalyst or the amount of nitrous oxide in the exhaust. Based on the above, the oxidation amount of PM deposited on the PM sensor may be calculated. At this time, as the temperature of the PM sensor is higher, the oxidation amount of PM is calculated as a larger value.

  According to this, the oxidation amount of PM deposited on the PM sensor can be calculated with higher accuracy. As a result, in the first and second inventions, the PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state can be calculated with higher accuracy. In the third invention, the difference between the integrated value of the PM amount that has passed through the filter and adhered to the PM sensor and the output value of the PM sensor can be further reduced. Therefore, the accuracy of filter failure detection using the output value of the PM sensor can be further improved.

  The filter failure detection device according to the first, second, or third invention prohibits the determination of the filter failure by the determining means when the temperature of the PM sensor is higher than a predetermined temperature for a predetermined period or longer. Means may further be provided.

Here, the predetermined temperature is a temperature equal to or higher than the lower limit value of the temperature at which PM deposited on the PM sensor is oxidized. In addition, the predetermined period is a period during which it can be determined that when the temperature of the PM sensor is equal to or higher than the predetermined temperature for a predetermined period or longer, the amount of PM oxidized in the PM sensor increases and the variation becomes excessively large. When the variation in the amount of PM oxidized in the PM sensor becomes large, it becomes difficult to calculate the amount with high accuracy by the oxidation amount calculation means.

  In the present invention, when the state where the temperature of the PM sensor is equal to or higher than the predetermined temperature continues for a predetermined period of time, that is, when the amount of PM oxidized in the PM sensor increases and its variation becomes excessively large, Filter failure determination is prohibited. Thereby, the fall of the precision of the filter failure determination can be suppressed.

  Further, as described above, the higher the concentration of nitrous oxide in the exhaust downstream of the selective reduction type NOx catalyst or the greater the amount of nitrous oxide in the exhaust, the easier the oxidation of PM deposited on the PM sensor is promoted. Become. Therefore, in the above case, the filter failure detection device is configured so that the predetermined temperature is based on the nitrous oxide concentration in the exhaust downstream of the selective reduction type NOx catalyst acquired by the acquiring means or the amount of nitrous oxide in the exhaust. Or you may further provide the setting means which sets at least any one of the said predetermined period. At this time, the predetermined temperature is set to a lower temperature as the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst is higher and as the amount of nitrous oxide in the exhaust is larger. The predetermined period is set to be shorter as the nitrous oxide concentration in the exhaust downstream of the selective reduction NOx catalyst is higher, and as the amount of nitrous oxide in the exhaust is larger.

  According to this, it is possible to suppress the failure determination of the PM sensor with higher probability that it is difficult to calculate the amount of PM oxidized in the PM sensor with high accuracy by the oxidation amount calculating means. it can. Therefore, the accuracy of filter failure detection using the output value of the PM sensor can be improved.

  In the present invention, when the predetermined temperature is the first predetermined temperature, the prohibiting means completes the PM removal process for oxidizing and removing the PM deposited on the PM sensor by increasing the temperature of the PM sensor. From this time, the PM accumulation amount in the PM sensor may not be estimated by the estimating means until the temperature of the PM sensor becomes lower than the second predetermined temperature, and the filter failure determination may be prohibited.

  In the PM removal process, the temperature of the PM sensor is raised to a temperature at which PM can be oxidized. Therefore, for a while after the PM removal process is completed, the temperature of the PM sensor continues to be high enough to oxidize PM. Here, the second predetermined temperature is a temperature equal to or lower than the lower limit value of the temperature at which PM can be oxidized.

  According to this, immediately after completion of the PM removal process, it can be suppressed that the failure determination of the filter is performed based on the output value of the PM sensor in a state where the PM accumulated on the PM sensor is oxidized. . Therefore, the accuracy of filter failure detection using the output value of the PM sensor can be further improved.

A filter failure detection apparatus according to a fourth invention is
A filter failure detection device for detecting a failure of a filter provided in an exhaust passage of an internal combustion engine and collecting particulate matter in exhaust gas,
A PM sensor provided in an exhaust passage downstream of the filter and outputting a signal corresponding to particulate matter deposited on the filter;
A selective reduction type NOx catalyst provided in an exhaust passage between the filter and the PM sensor, for reducing NOx in the exhaust gas using ammonia as a reducing agent;
Estimating means for estimating a PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state;
Determination means for determining a failure of the filter using an output value of the PM sensor and a PM accumulation amount in the PM sensor estimated by the estimation means;
When the state where the temperature of the PM sensor is equal to or higher than a predetermined temperature continues for a predetermined period or longer, a prohibiting unit for prohibiting the filter failure determination
Obtaining means for obtaining the concentration of nitrous oxide in the exhaust downstream of the selective catalytic reduction NOx catalyst or the amount of nitrous oxide in the exhaust;
At least one of the predetermined temperature or the predetermined period is set based on the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst acquired by the acquiring means or the amount of nitrous oxide in the exhaust. Setting means;
Is provided.

  Here, the predetermined temperature is a temperature equal to or higher than the lower limit value of the temperature at which PM deposited on the PM sensor is oxidized. In addition, the predetermined period is that when the temperature of the PM sensor is higher than the predetermined temperature for a predetermined period or longer, the decrease amount of the PM deposition amount that is decreased by being oxidized in the PM sensor becomes large. This is a period during which it can be determined that the difference between the integrated value of the PM amount slipped through and attached to the PM sensor and the output value of the PM sensor becomes excessively large.

  In the present invention, when the temperature of the PM sensor is equal to or higher than the predetermined temperature for a predetermined period of time, that is, the deviation between the integrated value of the PM amount passing through the filter and adhering to the PM sensor and the output value of the PM sensor is excessive. When it becomes larger, the filter failure determination is prohibited by the prohibiting means. Thereby, the fall of the precision of the filter failure determination can be suppressed.

  The filter failure detection apparatus according to the present invention includes setting means. Then, the setting means sets at least one of the predetermined temperature and the predetermined period based on the concentration of nitrous oxide in the exhaust downstream of the selective reduction type NOx catalyst or the amount of nitrous oxide in the exhaust. At this time, the predetermined temperature is set to a lower temperature as the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst is higher or as the amount of nitrous oxide in the exhaust is larger. The predetermined period is set to a shorter period as the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst is higher or the amount of nitrous oxide in the exhaust is larger.

  According to the present invention, in the state where the deviation between the integrated value of the PM amount passing through the filter and adhering to the PM sensor and the output value of the PM sensor is excessively large, the failure determination of the filter is performed based on the output value of the PM sensor. Can be suppressed with a higher probability. Therefore, the accuracy of filter failure detection using the output value of the PM sensor can be improved.

  Also in the present invention, when the predetermined temperature is set to the first predetermined temperature, the prohibiting unit estimates the time from the completion of the PM removal process until the temperature of the PM sensor becomes lower than the second predetermined temperature. The filter failure determination may be prohibited without estimating the PM accumulation amount in the PM sensor by the means.

  According to the present invention, in the configuration in which the selective reduction type NOx catalyst is provided between the filter and the PM sensor in the exhaust passage, it is possible to improve the accuracy of the filter failure detection using the output value of the PM sensor.

1 is a diagram illustrating a schematic configuration of an intake / exhaust system of an internal combustion engine according to Embodiment 1. FIG. 1 is a schematic configuration diagram of a PM sensor according to Embodiment 1. FIG. 3 is a time chart showing a transition of an output value of the PM sensor according to the first embodiment. It is a 1st figure which shows the relationship between the integrated value of PM amount which passed through the filter based on Example 1, and the output value of PM sensor. It is a 2nd figure which shows the relationship between the integrated value of PM amount which passed through the filter based on Example 1, and the output value of PM sensor. FIG. 6 is a third diagram illustrating the relationship between the integrated value of the PM amount that has passed through the filter and the output value of the PM sensor according to the first embodiment. 6 is a flowchart illustrating a flow of filter failure detection according to the first embodiment. It is a figure which shows the relationship between the nitrous oxide density | concentration of the exhaust_gas | exhaustion downstream from a NOx catalyst based on Example 1, the addition amount of urea water from an addition valve, and the temperature of a NOx catalyst. It is a figure which shows the relationship between the oxidation amount of PM deposited on the PM sensor, and the temperature of the PM sensor and the nitrous oxide concentration in the exhaust downstream of the NOx catalyst according to the first embodiment. 10 is a flowchart illustrating a flow of filter failure detection according to the second embodiment. 12 is a flowchart illustrating a part of a flow of filter failure detection according to the third embodiment. 12 is a flowchart illustrating another part of the flow of filter failure detection according to the third embodiment. 12 is a flowchart illustrating a part of a flow of filter failure detection according to the fourth embodiment. 14 is a flowchart illustrating another part of the flow of filter failure detection according to the fourth embodiment.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
[Schematic configuration of intake and exhaust system]
FIG. 1 is a diagram showing a schematic configuration of an intake / exhaust system of an internal combustion engine according to the present embodiment. An internal combustion engine 1 shown in FIG. 1 is a diesel engine for driving a vehicle. However, the internal combustion engine according to the present invention is not limited to a diesel engine, and may be a gasoline engine or the like.

  An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. A turbocharger 9 is provided in the intake / exhaust system of the internal combustion engine 1. The compressor 9 a of the turbocharger 9 is provided in the intake passage 2, and the turbine 9 b of the turbocharger 9 is provided in the exhaust passage 3.

  An air flow meter 11 and a throttle valve 8 are provided in the intake passage 2 upstream of the compressor 9 a of the turbocharger 9. The air flow meter 11 detects the amount of intake air flowing through the intake passage 2. The throttle valve 8 controls the amount of intake air flowing through the intake passage 2. On the other hand, in the exhaust passage 3 downstream of the turbine 9 b of the turbocharger 9, the oxidation catalyst 4, the filter 5, the addition valve 6, and the selective reduction type NOx catalyst 7 (hereinafter referred to as NOx catalyst) are sequentially arranged from the upstream side in the exhaust flow direction. 7).

  The oxidation catalyst 4 may be a catalyst having an oxidation ability, and may be, for example, a three-way catalyst. Further, the oxidation catalyst 4 may be carried on the filter 5.

The filter 5 collects PM in the exhaust. The filter 5 may carry a catalyst. As PM is collected by the filter 5, PM gradually accumulates on the filter 5. Then, by executing a so-called filter regeneration process for forcibly increasing the temperature of the filter 5, the PM deposited on the filter 5 can be oxidized and removed. For example,
By supplying HC to the oxidation catalyst 4, the temperature of the filter 5 can be raised by the oxidation heat of the HC. Moreover, you may provide the other apparatus which raises the temperature of the filter 5 without providing the oxidation catalyst 4. FIG. Furthermore, the temperature of the filter 5 may be raised by discharging hot gas from the internal combustion engine 1.

The addition valve 6 adds urea water into the exhaust. The addition valve 6 repeats injection and stop of urea water in a short cycle when adding urea water. That is, the addition valve 6 periodically adds urea water. Urea added as urea water from the addition valve 6 is hydrolyzed by the heat of the exhaust to become ammonia (NH ₃ ), and part or all of it is adsorbed on the NOx catalyst 7. In addition, the addition valve 6 may add an ammonia-derived compound other than urea water.

  The NOx catalyst 7 reduces NOx in the exhaust gas using ammonia as a reducing agent. For example, if ammonia is adsorbed in advance on the NOx catalyst 7, the NOx can be reduced by the ammonia when the NOx passes through the NOx catalyst 7.

  A first exhaust temperature sensor 12 is provided in the exhaust passage 3 downstream from the oxidation catalyst 4 and upstream from the filter 5. A second exhaust temperature sensor 13, an A / F sensor 14, and a NOx sensor 15 are provided in the exhaust passage 3 downstream from the filter 5 and upstream from the addition valve 6. A PM sensor 16 and a third exhaust temperature sensor 17 are provided in the exhaust passage 3 on the downstream side of the NOx catalyst 7.

  The first, second, and third exhaust temperature sensors 12, 13, and 17 detect the temperature of the exhaust. The A / F sensor 14 detects the air-fuel ratio of the exhaust. The NOx sensor 15 detects the NOx concentration in the exhaust. The PM sensor 16 detects the amount of PM in the exhaust. Details of the PM sensor 16 will be described later. Moreover, not all of these sensors are essential, and can be provided as necessary.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 10. The ECU 10 is a unit that controls the operating state and the like of the internal combustion engine 1. In addition to the first, second, and third exhaust temperature sensors 12, 13, 17, the A / F sensor 14, the NOx sensor 15, and the PM sensor 16, an accelerator opening sensor 18 and a crank position sensor 19 are electrically connected to the ECU 10. Connected. The accelerator opening sensor 18 detects the accelerator opening of a vehicle on which the internal combustion engine 1 is mounted. The crank position sensor 19 detects the crank angle of the internal combustion engine 1. And the output signal of each sensor is input into ECU10.

  The ECU 10 derives the engine load of the internal combustion engine 1 based on the output value of the accelerator opening sensor 18. Further, the ECU 10 derives the engine rotation speed of the internal combustion engine 1 based on the output value of the crank position sensor 19.

  In addition, a throttle valve 8 and an addition valve 6 are electrically connected to the ECU 10. Then, these devices are controlled by the ECU 10.

  Further, the ECU 10 estimates the PM accumulation amount in the filter 5. Then, the ECU 10 executes the regeneration process of the filter when the estimated PM accumulation amount becomes equal to or greater than a predetermined regeneration start threshold. The filter regeneration process may be executed when the travel distance from the completion of the previous filter regeneration process of the vehicle in which the internal combustion engine 1 is mounted becomes equal to or greater than a predetermined distance. Alternatively, the filter regeneration process may be performed every time the specified period elapses.

[PM sensor]
FIG. 2 is a schematic configuration diagram of the PM sensor 16. PM sensor 16 is the PM deposited on itself.
It is a sensor that outputs an electrical signal corresponding to the quantity. The PM sensor 16 includes a pair of electrodes 161 and an insulator 162 provided between the pair of electrodes 161. When PM adheres between the pair of electrodes 161, the electrical resistance between the pair of electrodes 161 changes. Since this change in electrical resistance has a correlation with the amount of PM in the exhaust, the amount of PM in the exhaust can be detected based on the change in the electrical resistance. This amount of PM may be the mass of PM per unit time, or may be the mass of PM in a predetermined time. The PM sensor 16 only needs to output an electrical signal corresponding to the amount of PM deposited on itself, and is not limited to the one shown in FIG.

  FIG. 3 is a time chart showing the transition of the output value of the PM sensor 16. If the amount of PM discharged from the internal combustion engine 1 per unit time is constant, the amount of accumulated PM in the PM sensor 16 increases at a constant rate with the passage of time. A period indicated by A immediately after the start of the internal combustion engine 1 is a period in which water condensed in the exhaust passage 3 may adhere to the PM sensor 16. When water adheres to the PM sensor 16, the output value of the PM sensor 16 changes or the PM sensor 16 breaks down. Therefore, the PM amount is not detected by the PM sensor 16 during this period.

  In a period indicated by B after a period indicated by A, a process for removing PM deposited on the PM sensor 16 during the previous operation of the internal combustion engine 1 (hereinafter referred to as PM removal process) is performed. This PM removal process is performed by raising the temperature of the PM sensor 16 to a temperature at which PM is oxidized. Even during the period indicated by B, the PM amount is not detected by the PM sensor 16.

  Then, PM is detected in a period indicated by C after a period indicated by B. However, even during the period indicated by C, the output value of the PM sensor 16 does not increase until a certain amount of PM is deposited on the PM sensor 16. That is, when a certain amount of PM is deposited, the output value starts increasing after a current flows between the pair of electrodes 161. Thereafter, the output value increases as the amount of PM deposited on the PM sensor 16 increases.

[Filter failure detection]
The PM sensor 16 is provided on the downstream side of the filter 5. Therefore, PM that has passed through the filter 5 adheres to the PM sensor 16 without being collected by the filter 5. Therefore, the PM accumulation amount in the PM sensor 16 is an amount corresponding to the integrated value of the PM amount that has passed through the filter 5.

  When a failure such as melting or breakage occurs in the filter 5, the amount of PM that passes through the filter 5 without being collected by the filter 5 increases. As a result, the amount of PM adhering to the PM sensor 16 provided on the downstream side of the filter 5 increases, so that the amount of accumulated PM in the PM sensor 16 increases as compared with the case where the filter 5 is normal. Therefore, in this embodiment, the failure of the filter 5 is detected using the output value of the PM sensor 16.

  The failure detection of the filter 5 is performed after the PM accumulated on the PM sensor 16 is once removed by executing the PM removal process. Here, as described above, after the PM accumulated on the PM sensor 16 is removed, even if the PM sensor 16 is normal, if the PM accumulation amount does not reach a certain amount, the output value of the PM sensor 16 Is not a value corresponding to the PM deposition amount. Therefore, on the condition that the estimated value of the PM accumulation amount (hereinafter referred to as normal PM accumulation amount) in the PM sensor 16 when the filter 5 is assumed to be normal is equal to or greater than a predetermined amount, the output of the PM sensor 16 A failure determination of the filter 5 based on the value is performed.

Here, the predetermined amount is a value equal to or greater than the threshold of the PM accumulation amount at which the output value of the PM sensor 16 becomes a value corresponding to the PM accumulation amount in the PM sensor 16. This predetermined amount is determined in advance based on experiments or the like.

  Further, the failure determination of the filter 5 is performed by comparing the threshold value determined based on the normal PM accumulation amount with the output value of the PM sensor 16.

  Hereinafter, the calculation method of the normal PM deposition amount according to the present embodiment will be described. The amount of PM adhering to the PM sensor 16 increases as the amount of PM discharged from the internal combustion engine 1 (hereinafter referred to as engine discharged PM amount) increases. The engine exhaust PM amount changes according to the operating state (engine speed and engine load) of the internal combustion engine 1.

  Further, even if the engine exhaust PM amount is the same and the filter 5 is normal, the ratio of the PM amount that passes through the filter 5 to the PM amount flowing into the filter 5 (hereinafter referred to as the filter slip-through rate) 5 depending on the amount of PM deposition. That is, the smaller the amount of accumulated PM in the filter 5, the higher the filter slip-through rate.

  Further, the ratio of the PM amount adhering to the PM sensor 16 to the PM amount passing through the filter 5 (hereinafter referred to as sensor adhering rate) also depends on the PM accumulation amount in the filter 5 and the flow rate (flow velocity) of the exhaust gas passing through the filter 5. Will change accordingly. That is, the smaller the amount of accumulated PM in the filter 5 and the greater the flow rate of exhaust gas that passes through the filter 5 (the greater the flow rate of the exhaust gas), the greater the flow rate of exhaust gas that flows around the PM sensor 16. The sensor adhesion rate is low.

  FIG. 4 is a diagram showing the relationship between the integrated value of the PM amount that has passed through the filter 5 and the output value of the PM sensor 16. In FIG. 4, L1 indicates a case where the intake air amount is relatively small (that is, a case where the flow rate of exhaust gas is relatively small), and L2 indicates a case where the intake air amount is relatively large (that is, the flow rate of exhaust gas is relatively low). If there are many).

  As described above, the sensor adhesion rate decreases as the exhaust gas flow rate increases. In other words, the smaller the exhaust flow rate, the higher the sensor adhesion rate. Therefore, when the intake air amount is relatively small, more PM accumulates on the PM sensor 16 when the integrated value of the PM amount that has passed through the filter 5 is smaller than when the intake air amount is relatively large. As a result, as shown in FIG. 4, the PM sensor 16 outputs an electrical signal corresponding to the PM amount deposited on itself when the integrated value of the PM amount that has passed through the filter 5 is smaller.

  Therefore, in this embodiment, the normal PM accumulation amount is estimated based on the engine exhaust PM amount, the filter slip-through rate, and the sensor adhesion rate.

  However, when the temperature of the exhaust gas rises and the temperature of the PM sensor 16 reaches a temperature at which PM can be oxidized (hereinafter referred to as PM oxidation temperature), the PM deposited on the PM sensor 16 is oxidized. When the PM deposited on the PM sensor 16 is oxidized, the amount of PM deposited on the PM sensor 16 decreases. Therefore, in order to calculate the normal amount of PM deposition with high accuracy, it is necessary to consider the amount of oxidation of PM deposited on the PM sensor 16.

  FIG. 5 is a diagram showing the relationship between the integrated value of the PM amount that has passed through the filter 5 and the output value of the PM sensor 16. 5, L1 indicates a case where the exhaust temperature around the PM sensor 16 (that is, the temperature of the PM sensor 16) is lower than the PM oxidation temperature, and L2 indicates that the exhaust temperature around the PM sensor 16 is PM oxidation. The case above the temperature is shown. Note that the intake air amount of the internal combustion engine 1 is the same (that is, the exhaust gas flow rate is the same) in the case indicated by L1 and the case indicated by L2.

  As described above, when the temperature of the PM sensor 16 becomes equal to or higher than the PM oxidation temperature, the PM that has passed through the filter 5 and once adhered to the PM sensor 16 is oxidized. Therefore, as shown in FIG. 5, when the exhaust temperature around the PM sensor 16 is equal to or higher than the PM oxidation temperature, the filter 5 passes through the filter 5 as compared with the case where the exhaust temperature around the PM sensor 16 is lower than the PM oxidation temperature. If the integrated value of the PM amount does not become larger, the PM sensor 16 does not output an electrical signal corresponding to the PM amount deposited on itself.

Further, in the present embodiment, the NOx catalyst 7 is provided upstream of the PM sensor 16 in the exhaust passage 3. In the process of reducing NOx using ammonia as a reducing agent in the NOx catalyst 7, nitrous oxide (N ₂ O) may be generated. When nitrous oxide is generated in the NOx catalyst 7, PM deposited on the PM sensor 16 provided on the downstream side of the NOx catalyst 7 is oxidized by the nitrous oxide. That is, as the amount of nitrous oxide produced in the NOx catalyst 7 increases, the amount of nitrous oxide in the exhaust downstream of the NOx catalyst 7 increases, and the oxidation of PM deposited on the PM sensor 16 is promoted. .

  FIG. 6 is a diagram showing the relationship between the integrated value of the PM amount that has passed through the filter 5 and the output value of the PM sensor 16. In FIG. 6, L1 is the case where urea water is not added from the addition valve 6 (that is, NOx reduction using ammonia as a reducing agent is not performed in the NOx catalyst 7, and nitrous oxide is generated. L2 represents a case where urea water is added from the addition valve 6 (that is, NOx is reduced in the NOx catalyst 7 by reducing NOx using ammonia as a reducing agent). (When nitric oxide is produced).

  As described above, when nitrous oxide is generated in the NOx catalyst 7, the oxidation of PM deposited on the PM sensor 16 is promoted. Therefore, as shown in FIG. 6, when the urea water was added from the addition valve 6, the filter 5 passed through compared to the case where the urea water was not added from the addition valve 6. If the integrated value of the PM amount does not become larger, the PM sensor 16 does not output an electrical signal corresponding to the PM amount deposited on itself.

  Therefore, in this embodiment, the oxidation amount of PM deposited on the PM sensor 16 is calculated based on the temperature of the PM sensor 16 and the nitrous oxide concentration in the exhaust downstream of the NOx catalyst 7. Then, the estimated value of the normal PM deposition amount estimated as described above is corrected based on the oxidation amount of the PM.

[Filter failure detection flow]
The flow of filter failure detection according to the present embodiment will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10 at predetermined intervals.

  In this flow, first, in step S101, it is determined whether or not PM removal processing is completed. If a negative determination is made in step S101, the execution of this flow is temporarily terminated. On the other hand, when an affirmative determination is made in step S101, the process of step S102 is executed next.

  In step S102, the engine exhaust PM amount egpmeng is calculated. The engine exhaust PM amount egpmeng is calculated based on the engine rotation speed and the engine load. The relationship between the engine exhaust PM amount egpmeng, the engine rotation speed, and the engine load can be obtained based on experiments or the like, and is stored in advance in the ECU 10 as a map or a function. In step S102, the engine exhaust PM amount egpmeng is calculated using this map or function.

Next, in step S103, a filter pass-through rate Kpmctslp is calculated. The filter slip-through rate Kpmctslp is calculated based on the PM accumulation amount in the filter 5 when the filter 5 is assumed to be normal. When it is assumed that the filter 5 is normal, the PM accumulation amount in the filter 5 can be calculated based on the history of the engine speed and engine load of the internal combustion engine 1, the temperature of the filter 5, and the like. The relationship between the filter slipping rate Kpmctslp and the PM accumulation amount in the filter 5 when the filter 5 is assumed to be normal can be obtained based on experiments or the like, and is stored in advance in the ECU 10 as a map or a function. In step S103, the filter pass-through rate Kpmctslp is calculated using this map or function.

  Next, in step S104, the sensor adhesion rate Kpmsdp is calculated. The sensor adhesion rate Kpmsdp is also calculated based on the PM accumulation amount in the filter 5 and the flow rate of the exhaust gas passing through the filter 5 when the filter 5 is assumed to be normal. The relationship between the sensor adhesion rate Kpmdsdp and the PM accumulation amount in the filter 5 and the flow rate of the exhaust gas passing through the filter 5 when the filter 5 is assumed to be normal can be obtained based on experiments or the like, and can be a map or function. As stored in the ECU 10 in advance. In step S104, the sensor adhesion rate Kpmsdp is calculated using this map or function.

  Next, in step S105, the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 is calculated. The amount of nitrous oxide produced in the NOx catalyst 7 varies depending on the amount of urea water added from the addition valve 6 (that is, the amount of ammonia supplied as a reducing agent to the NOx catalyst 7) and the temperature of the NOx catalyst 7. . Therefore, the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 can be obtained based on the amount of urea water added from the addition valve 6 and the temperature of the NOx catalyst 7.

  FIG. 8 is a graph showing the relationship between the nitrous oxide concentration in the exhaust downstream of the NOx catalyst 7, the amount of urea water added from the addition valve 6, and the temperature of the NOx catalyst 7. In the present embodiment, the relationship between the nitrous oxide concentration in the exhaust downstream of the NOx catalyst 7 and the amount of urea water added from the addition valve 6 and the temperature of the NOx catalyst 7 is based on experiments and the like. And is stored in advance in the ECU 10 as a map or a function. In step S105, the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 is calculated using this map or function.

  Next, in step S106, the oxidation amount egpmsox of PM deposited on the PM sensor 16 is calculated. The PM oxidation amount egpmsox deposited on the PM sensor 16 is calculated based on the temperature etpms of the PM sensor 16 and the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 calculated in step S105. The exhaust temperature detected by the third exhaust temperature sensor 17 may be adopted as the temperature ethpms of the PM sensor 16. Further, a temperature sensor that detects the temperature of the PM sensor 16 may be provided separately.

  FIG. 9 is a diagram showing the relationship between the oxidation amount egpmsox of PM deposited on the PM sensor 16, the temperature ethpms of the PM sensor 16, and the nitrous oxide concentration ecn 2 o of the exhaust downstream of the NOx catalyst 7. In the present embodiment, the relationship between the oxidation amount egpmsox of PM deposited on the PM sensor 16, the temperature ethpms of the PM sensor 16, and the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 is an experiment. Etc., and is stored in advance in the ECU 10 as a map or function. In step S106, the oxidation amount egpmsox of the PM deposited on the PM sensor 16 is calculated using this map or function. Therefore, the higher the temperature of the PM sensor 16 and the higher the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7, the higher the PM oxidation amount egpmsox accumulated on the PM sensor 16 is calculated.

Note that, instead of the nitrous oxide concentration ecn2o in the exhaust downstream of the NOx catalyst 7, the amount of nitrous oxide in the exhaust is calculated, and the oxidation amount of PM deposited on the PM sensor 16 using the nitrous oxide amount. You may calculate egpmsox.

  Next, in step S107, the normal PM deposition amount egpmsdp is calculated. The normal PM deposition amount egpmsdp is the normal PM deposition amount egpmsdp calculated when the processing of step S107 was executed last time, the engine exhaust PM amount egpmeng calculated in step S102, and the filter calculated in step S103. A value obtained by multiplying the slipping rate Kpmctslp by the sensor adhesion rate Kpmdsdp calculated in step S104 is added, and further calculated by subtracting the PM oxidation amount egpmsox deposited on the PM sensor 16 calculated in step S106. Is done.

  That is, a value obtained by multiplying the normal PM accumulation amount egpmsdp calculated when the process of step S107 was executed last time by the engine exhaust PM amount egpmmen, the filter slip-through rate Kpmctslp, and the sensor adhesion rate Kpmdsdp is added. Thus, the normal PM deposition amount before considering the PM oxidation amount is calculated. Then, the normal PM deposition amount before considering the PM oxidation amount is corrected by subtracting the PM oxidation amount egpmsox.

  Next, in step S108, it is determined whether or not the normal PM deposition amount eggpmsdp at the current time calculated in step S107 is equal to or greater than a predetermined amount. If a negative determination is made in step S108, the processing from step S102 to S107 is executed again. On the other hand, if an affirmative determination is made in step S108, the process of step S109 is then executed.

  In step S109, the failure judgment threshold value epms0 of the filter 5 is calculated based on the normal PM accumulation amount egpmmsdp at the current time calculated in step S107. The relationship between the threshold value epms0 and the normal PM deposition amount egpmsdp is determined in advance based on experiments or the like, and is stored in advance in the ECU 10 as a map or a function. In step S109, the threshold epms0 is calculated using this map or function. Here, for example, the threshold value epms0 may be a value obtained by adding an allowable margin to the normal PM deposition amount eggpmsdp. Further, the normal PM deposition amount egpmsdp may be set to the threshold value epms0. The threshold epms0 is calculated as a larger value as the value of the normal PM deposition amount egpmsdp is larger.

  Note that the failure determination of the filter 5 may be performed when the normal PM accumulation amount egpmmsdp calculated in step S107 reaches a certain amount that is equal to or greater than a predetermined amount. In this case, the threshold value epms0 is a constant value determined in advance based on the constant amount.

  Next, in step S110, it is determined whether or not the output value epms of the PM sensor 16 is equal to or greater than the threshold value epms0 for failure determination of the filter 5 calculated in step S109. If an affirmative determination is made in step S110, it can be determined that the actual PM accumulation amount in the PM sensor 16 is excessively larger than the normal PM accumulation amount. Therefore, in this case, in step S111, it is determined that the filter 5 has failed. On the other hand, if a negative determination is made in step S110, it is then determined in step S112 that the filter 5 is normal.

As described above, in this embodiment, the oxidation amount of PM deposited on the PM sensor 16 is calculated based on the temperature of the PM sensor 16 and the nitrous oxide concentration in the exhaust downstream of the NOx catalyst 7. The timing for executing the filter failure determination is determined based on the normal PM accumulation amount calculated in consideration of the oxidation amount of the PM. Further, a failure determination threshold value of the filter 5 is determined based on the normal PM accumulation amount calculated in consideration of the oxidation amount of the PM. Therefore, the accuracy of filter failure detection can be improved.

  The amount of oxidation of PM deposited on the PM sensor 16 is not necessarily limited to both the temperature of the PM sensor 16 and the concentration of nitrous oxide in the exhaust downstream of the NOx catalyst 7 (or the amount of nitrous oxide in the exhaust). It is not necessary to calculate based on this. That is, the oxidation amount of PM deposited on the PM sensor 16 may be calculated based only on either the temperature of the PM sensor 16 or the nitrous oxide concentration in the exhaust downstream of the NOx catalyst 7. However, the amount of PM oxidation can be calculated with higher accuracy by calculating based on both of these values. As a result, the accuracy of filter failure detection can be further improved.

  In this embodiment, the failure determination execution timing of the filter 5 and the failure determination threshold value of the filter 5 are determined based on the normal PM accumulation amount. However, these do not necessarily need to be determined based on the normal amount of PM deposition. That is, assuming that the state of the filter 5 is a state in which the failure level of the filter 5 has reached a predetermined level (hereinafter referred to as a predetermined failure state), the amount of accumulated PM in the PM sensor 16 is calculated, The execution timing of the failure determination of the filter 5 and the threshold for failure determination of the filter 5 may be determined based on the PM accumulation amount.

  The filter slip-through rate differs between when the filter 5 is normal and when the filter 5 is in a predetermined failure state. Therefore, in the above case, the state of the filter 5 is determined based on the filter slipping rate, the engine exhaust PM amount, and the sensor adhesion rate when the filter 5 is assumed to be in a predetermined failure state. Estimate the amount of PM deposition.

  Then, the estimated value is corrected based on the oxidation amount of PM deposited on the PM sensor 16. Accordingly, it is possible to calculate the PM accumulation amount in the PM sensor 16 when it is assumed that the state of the filter 5 is a predetermined failure state in consideration of the oxidation amount of PM.

  Note that the filter slipping rate when the state of the filter 5 is assumed to be a predetermined failure state varies depending on the amount of PM accumulated in the filter 5 and the flow rate (flow velocity) of the exhaust gas passing through the filter 5. When the state of the filter 5 is a predetermined failure state, the filter pass-through rate increases as the amount of PM accumulated in the filter 5 increases. Further, the higher the flow rate of the exhaust gas passing through the filter 5 (the higher the flow rate of the exhaust gas), the higher the filter slipping rate. The relationship between the filter slip-through rate, the PM accumulation amount in the filter 5 and the flow rate of the exhaust gas passing through the filter 5 when it is assumed that the state of the filter 5 is a predetermined failure state is based on experiments and the like in advance. Can be sought.

<Example 2>
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 this embodiment, as in the first embodiment, a failure of the filter 5 is detected using the output value of the PM sensor 16. Hereinafter, the filter failure detection method according to the present embodiment will be described only with respect to differences from the first embodiment.

[Filter failure detection]
Also in the present embodiment, as in the first embodiment, the normal PM accumulation amount is estimated based on the engine exhaust PM amount, the filter slip-through rate, and the sensor adhesion rate. However, unlike the first embodiment, the normal PM deposition amount estimated in this way is not corrected based on the oxidation amount of PM deposited on the PM sensor 16. Instead, in this embodiment, the output value of the PM sensor 16 is corrected based on the oxidation amount of PM deposited on the PM sensor 16.

Here, the greater the amount of oxidation of PM deposited on the PM sensor 16, the smaller the output value of the PM sensor 16. As a result, there is a large discrepancy between the integrated value of the PM amount passing through the filter 5 and adhering to the PM sensor 16 (that is, the PM accumulation amount in the PM sensor 16 when PM is not oxidized) and the output value of the PM sensor 16. Become. Therefore, in this embodiment, the output value of the PM sensor 16 is corrected to increase as the amount of oxidation of PM deposited on the PM sensor 16 increases. Thereby, the divergence between the integrated value of the PM amount passing through the filter 5 and adhering to the PM sensor 16 and the output value of the PM sensor 16 can be reduced. Then, the failure of the filter 5 is determined by comparing the output value of the corrected PM sensor 16 with a threshold value.

[Filter failure detection flow]
The flow of filter failure detection according to the present embodiment will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10 at predetermined intervals. Note that steps in which the same processing as the steps in the flow shown in FIG. 7 is executed are denoted by the same reference numerals and description thereof is omitted.

  In this flow, the process of step S207 is executed after the process of step S106. In step S207, the normal PM deposition amount egpmsdp is calculated. Here, the normal PM deposition amount egpmsdp is calculated in step S103 to the normal PM deposition amount egpmsdp calculated in the previous execution of the process in step S207 and the engine exhaust PM amount egpmeng calculated in step S102. It is calculated by adding a value obtained by multiplying the filtered filter slip-through rate Kpmctslp and the sensor adhesion rate Kpmdsdp calculated in step S104. In other words, the normal PM deposition amount egpmsdp is calculated without considering the oxidation amount of PM deposited on the PM sensor 16.

  Next, in step S208, it is determined whether or not the normal PM deposition amount eggpmsdp at the current time calculated in step S207 is equal to or greater than a predetermined amount. If a negative determination is made in step S208, the processing from step S102 to S207 is executed again. On the other hand, if an affirmative determination is made in step S108, the process of step S209 is then executed.

  In step 209, a failure judgment threshold value epms1 of the filter 5 is calculated based on the normal PM accumulation amount egpmmsdp at the current time calculated in step S207. The relationship between the threshold value epms1 and the normal PM deposition amount egpmsdp is determined in advance based on experiments or the like, and is stored in advance in the ECU 10 as a map or a function. In step S209, the threshold epms0 is calculated using this map or function. Here, for example, the threshold value epms1 may be a value obtained by adding an allowable margin to the normal PM deposition amount eggpmsdp. Further, the normal PM deposition amount egpmsdp may be set as the threshold value epms1. The threshold epms1 is calculated as a larger value as the value of the normal PM deposition amount egpmsdp is larger.

  It should be noted that the failure determination of the filter 5 may be performed when the normal PM deposition amount egpmsdp calculated in step S207 reaches a certain amount that is equal to or greater than a predetermined amount. In this case, the threshold value epms1 is a constant value determined in advance based on the constant amount.

  Next, in step S210, the output value epms of the PM sensor 16 is corrected based on the oxidation amount egpmsox of PM deposited on the PM sensor 16 calculated in step S106. At this time, the output value epms of the PM sensor 16 is corrected to increase as the oxidation amount egpmsox of the PM increases. The relationship between the PM oxidation amount egpmsox and the correction value of the output value of the PM sensor 16 is obtained based on experiments or the like, and is stored in advance in the ECU 10 as a map or a function. In step S210, the correction value calculated using this map or function is added to correct the output value epms of the PM sensor 16.

  Next, in step S211, it is determined whether or not the corrected output value epms of the PM sensor 16 calculated in step S210 is equal to or greater than the failure determination threshold value epms1 calculated in step S209. If an affirmative determination is made in step S211, it can be determined that the actual PM accumulation amount in the PM sensor 16 is excessively large. Therefore, in this case, in step S111, it is determined that the filter 5 has failed. On the other hand, if a negative determination is made in step S211, next, in step S112, it is determined that the filter 5 is normal.

  As described above, in this embodiment, the failure determination of the filter 5 is performed based on the output value of the PM sensor 16 corrected in consideration of the oxidation amount of PM accumulated on the PM sensor 16. Therefore, the accuracy of filter failure detection can be improved.

  Also in the present embodiment, as in the first embodiment, the execution timing of the failure determination of the filter 5 and the failure determination threshold value of the filter 5 are not necessarily determined based on the normal PM accumulation amount. That is, assuming that the state of the filter 5 is a predetermined failure state, the PM accumulation amount in the PM sensor 16 is calculated, and the failure determination execution timing of the filter 5 and the failure determination of the filter 5 are calculated based on the PM accumulation amount. A threshold may be determined.

<Example 3>
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 this embodiment, as in the first embodiment, a failure of the filter 5 is detected using the output value of the PM sensor 16. Hereinafter, the filter failure detection method according to the present embodiment will be described only with respect to differences from the first embodiment.

[Filter failure detection]
When the amount of oxidation of PM deposited on the PM sensor 16 increases, the variation increases, and it is difficult to calculate the amount with high accuracy. As a result, it is difficult to calculate the normal PM accumulation amount with high accuracy. Therefore, in the present embodiment, when the amount of PM oxidized in the PM sensor increases and the variation becomes excessively large, failure determination of the filter 5 is prohibited.

  Specifically, when the temperature of the PM sensor 16 is equal to or higher than the first predetermined temperature for a predetermined period or longer, failure determination of the filter 5 is prohibited. Here, the first predetermined temperature is a temperature equal to or higher than the lower limit value of the temperature at which PM deposited on the PM sensor 16 is oxidized. In addition, the predetermined period according to the present embodiment is that when the temperature of the PM sensor 16 is equal to or higher than the predetermined temperature, the amount of PM oxidized in the PM sensor 16 increases, and the variation is excessively large. It is a period during which it can be determined that

  Further, the more the amount of nitrous oxide produced when NOx is reduced in the NOx catalyst 7 using ammonia as a reducing agent, that is, the higher the concentration of nitrous oxide in the exhaust downstream of the NOx catalyst 7 (or As the amount of nitrous oxide in the exhaust gas increases, the oxidation of PM deposited on the PM sensor 16 is facilitated. Therefore, the first predetermined temperature and the predetermined period are set based on the nitrous oxide concentration in the exhaust downstream of the NOx catalyst 7. That is, the higher the nitrous oxide concentration in the exhaust gas downstream of the NOx catalyst 7, the lower the predetermined temperature, and the shorter the predetermined period.

Further, in this embodiment, after the PM removal process is completed, the PM accumulation amount at the normal time is not estimated and the failure determination of the filter 5 is performed until the temperature of the PM sensor 16 becomes lower than the second predetermined temperature. It is forbidden. For a while after the PM removal process is completed, the temperature of the PM sensor 16 is
The state continues to be high enough to oxidize. Here, the second predetermined temperature is a temperature equal to or lower than the lower limit value of the temperature at which PM can be oxidized. That is, in the state where the PM deposited on the PM sensor 16 is oxidized immediately after the completion of the PM removal process, the normal PM deposition amount is not estimated.

[Filter failure detection flow]
The flow of filter failure detection according to this embodiment will be described based on the flowcharts shown in FIGS. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10 at predetermined intervals. Note that steps in which the same processing as the steps in the flow shown in FIG. 7 is executed are denoted by the same reference numerals and description thereof is omitted.

  In this flow, if an affirmative determination is made in step S101, the process of step S301 is executed next. In step S301, it is determined whether the temperature ethpms of the PM sensor 16 is lower than the second predetermined temperature ethpmsl2. The second predetermined temperature ethpmsl2 is determined in advance based on experiments or the like.

  If a negative determination is made in step S301, the execution of this flow is temporarily terminated. That is, after the PM removal process is completed, the PM accumulation amount in the PM sensor 16 is not estimated until the temperature ethpms of the PM sensor 16 becomes lower than the second predetermined temperature ethpmsl2, and the filter failure determination is prohibited. Is done. On the other hand, if an affirmative determination is made in step S301, then the processing from step S102 to S107 is executed.

  Following step S107, the process of step S307 is executed. In step S307, the first predetermined temperature ethpmsl1 is calculated based on the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 calculated in step S105. The relationship between the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 and the first predetermined temperature ethpmsl1 is determined in advance based on experiments or the like, and is stored in advance in the ECU 10 as a map or a function. In step S307, the first predetermined temperature ethpmsl1 is calculated using this map or function. As described above, the higher the nitrous oxide concentration ecn2o of the exhaust downstream from the NOx catalyst 7, the lower the first predetermined temperature ethpmsl1 is calculated.

  Note that, instead of the nitrous oxide concentration ecn2o in the exhaust downstream of the NOx catalyst 7, the amount of nitrous oxide in the exhaust is calculated, and the first predetermined temperature ethpmsl1 is calculated using the amount of nitrous oxide. Good.

  Next, in step S308, it is determined whether the temperature ethpms of the PM sensor 16 is equal to or higher than the first predetermined temperature ethpmsl1 calculated in step S307. If an affirmative determination is made in step S308, the process of step S309 is executed next, and if a negative determination is made, the process of step S108 is executed next.

  In step S309, a time (hereinafter referred to as a sensor high temperature duration) ethpmsc during which the temperature ethpms of the PM sensor 16 is equal to or higher than the first predetermined temperature ethpmsl1 is calculated.

Next, in step S310, a predetermined period ethpmsc11 is calculated based on the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 calculated in step S105. The relationship between the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 and the predetermined period ethpmscl1 is determined in advance based on experiments or the like, and is stored in advance in the ECU 10 as a map or a function. In step S310, a predetermined period ethpmscl1 is calculated using this map or function. As described above, the predetermined period ethpmscl1 is calculated as a shorter period as the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 is higher.

  Instead of the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7, the amount of nitrous oxide in the exhaust may be calculated, and the ethpmsccl1 may be calculated for a predetermined period using the amount of nitrous oxide.

  Next, in step S311, it is determined whether or not the sensor high temperature duration ethpmsc calculated in step S309 is shorter than the predetermined period ethpmsc1 calculated in step S310. If a negative determination is made in step S311, the execution of this flow is temporarily terminated. That is, when the temperature ethpms of the PM sensor 16 is equal to or higher than the first predetermined temperature ethpmsll1, the estimation of the PM accumulation amount in the PM sensor 16 is stopped and the failure determination of the filter 5 is prohibited. On the other hand, if a positive determination is made in step S311, the process of step S108 is then executed.

  As described above, in this embodiment, when the amount of PM oxidized in the PM sensor 16 increases and the variation becomes excessively large, failure determination of the filter 5 is prohibited. Further, even when the PM deposited on the PM sensor 16 is oxidized immediately after the PM removal process is completed, the failure determination of the filter 5 is prohibited. Thereby, the fall of the precision of the filter failure determination can be suppressed.

  In the present embodiment, the first predetermined temperature and the predetermined period are set based on the nitrous oxide concentration ecn2o (or the amount of nitrous oxide in the exhaust) downstream of the NOx catalyst 7. Therefore, it is suppressed with higher probability that the failure determination of the filter 5 is performed based on the output value of the PM sensor 16 in a state where it is difficult to calculate the amount of PM oxidized in the PM sensor 16 with high accuracy. Can do. Therefore, the accuracy of failure detection of the filter 5 can be improved.

  Note that it is not always necessary to set both the first predetermined temperature and the predetermined period based on the nitrous oxide concentration ecn2o (or the amount of nitrous oxide in the exhaust) in the exhaust downstream of the NOx catalyst 7. That is, any one of the first predetermined temperature and the predetermined period may be a predetermined constant value. However, by setting both of these values based on the nitrous oxide concentration ecn2o (or the amount of nitrous oxide in the exhaust gas) downstream of the NOx catalyst 7, the accuracy of the failure detection of the filter 5 is set. Can be further improved.

  Further, instead of the normal PM accumulation amount, the failure determination execution timing of the filter 5 and the filter based on the estimated value of the PM accumulation amount in the PM sensor 16 when the filter 5 is assumed to be in a predetermined failure state. Even when the failure determination threshold value 5 is determined, the failure determination prohibition condition according to the present embodiment can be applied.

<Example 4>
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 this embodiment, as in the first embodiment, a failure of the filter 5 is detected using the output value of the PM sensor 16. Hereinafter, the filter failure detection method according to the present embodiment will be described only with respect to differences from the first embodiment.

[Filter failure detection]
Also in the present embodiment, as in the first embodiment, the normal PM accumulation amount is estimated based on the engine exhaust PM amount, the filter slip-through rate, and the sensor adhesion rate. However, unlike the first embodiment, the normal PM deposition amount estimated in this way is not corrected based on the oxidation amount of PM deposited on the PM sensor 16. Instead, in this embodiment, the reduction amount of the PM deposition amount that is reduced by being oxidized in the PM sensor 16 becomes large, and the integrated value of the PM amount that has passed through the filter 5 and adhered to the PM sensor 16 and the PM sensor 16. When the deviation from the output value becomes excessively large, the estimation of the normal PM accumulation amount is stopped, and the failure determination of the filter 5 is prohibited.

  Specifically, when estimating the normal PM deposition amount, if the temperature of the PM sensor 16 is higher than the first predetermined temperature for a predetermined period or longer, the estimation of the normal PM deposition amount is stopped, Failure determination of the filter 5 is prohibited. Here, the first predetermined temperature is a temperature equal to or higher than the lower limit value of the temperature at which the PM deposited on the PM sensor 16 is oxidized, as in the third embodiment. In addition, the predetermined period according to the present embodiment means that when the temperature of the PM sensor 16 is equal to or higher than the predetermined temperature for a predetermined period or longer, the amount of decrease in the PM deposition amount that is reduced by being oxidized in the PM sensor 16 is large. As a result, it is a period during which it can be determined that the difference between the integrated value of the PM amount passing through the filter 5 and adhering to the PM sensor 16 and the output value of the PM sensor 16 becomes excessively large.

  Also in this embodiment, the first predetermined temperature and the predetermined period are set based on the nitrous oxide concentration in the exhaust downstream of the NOx catalyst 7. That is, as the nitrous oxide concentration in the exhaust gas downstream of the NOx catalyst 7 is higher, the predetermined temperature is set to a lower temperature, and the predetermined period is set to a shorter period.

  Further, in this embodiment, after the PM removal process is completed, the PM accumulation amount at the normal time is not estimated until the temperature of the PM sensor 16 becomes lower than the second predetermined temperature, and the failure determination of the filter 5 is prohibited. Is done.

[Filter failure detection flow]
The flow of filter failure detection according to this embodiment will be described based on the flowcharts shown in FIGS. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10 at predetermined intervals. Note that steps in which the same processing as the steps in the flow shown in FIG. 7 is executed are denoted by the same reference numerals and description thereof is omitted.

  In this flow, if an affirmative determination is made in step S101, the process of step S401 is then executed. The processing in step S401 is the same as that in step S301 in the flow shown in FIG. That is, in step S401, it is determined whether the temperature ethpms of the PM sensor 16 is lower than the second predetermined temperature ethpmsl2. The second predetermined temperature ethpmsl2 is determined in advance based on experiments or the like.

  If a negative determination is made in step S401, the execution of this flow is temporarily terminated. That is, after the PM removal process is completed, the PM accumulation amount in the PM sensor 16 is not estimated until the temperature ethpms of the PM sensor 16 becomes lower than the second predetermined temperature ethpmsl2, and the filter failure determination is prohibited. Is done. On the other hand, when an affirmative determination is made in step S401, the processing of steps S102 to S104 is performed next.

  Following step S104, the process of step S405 is executed. In step S405, the normal PM deposition amount egpmsdp is calculated. Here, the normal PM deposition amount egpmsdp is calculated in step S103, in addition to the normal PM deposition amount egpmsdp calculated when the processing of step S405 was executed last time, and the engine exhaust PM amount egpmeng calculated in step S102. It is calculated by adding a value obtained by multiplying the filtered filter slip-through rate Kpmctslp and the sensor adhesion rate Kpmdsdp calculated in step S104. In other words, the normal PM deposition amount egpmsdp is calculated without considering the oxidation amount of PM deposited on the PM sensor 16.

  Next, in step S406, the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 is calculated. In step S406, the nitrous oxide concentration ecn2o is calculated by the same method as in step S105 of the flow shown in FIG.

  Next, in step S407, the first predetermined temperature ethpmsl1 is calculated based on the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 calculated in step S406. The relationship between the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 and the first predetermined temperature ethpmsl1 is determined in advance based on experiments or the like, and is stored in advance in the ECU 10 as a map or a function. In step S407, the first predetermined temperature ethpmsl1 is calculated using this map or function. As described above, the higher the nitrous oxide concentration ecn2o of the exhaust downstream from the NOx catalyst 7, the lower the first predetermined temperature ethpmsl1 is calculated.

  Note that, instead of the nitrous oxide concentration ecn2o in the exhaust downstream of the NOx catalyst 7, the amount of nitrous oxide in the exhaust is calculated, and the first predetermined temperature ethpmsl1 is calculated using the amount of nitrous oxide. Good.

  Next, in step S408, it is determined whether or not the temperature ethpms of the PM sensor 16 is equal to or higher than the first predetermined temperature ethpmsl1 calculated in step S407. If an affirmative determination is made in step S408, the process of step S409 is executed next. If the determination is negative, the process of step S108 is executed next.

  In step S409, the time (sensor high temperature duration) ethpmsc during which the temperature ethpms of the PM sensor 16 is equal to or higher than the first predetermined temperature ethpmsl1 is calculated.

  Next, in step S410, a predetermined period ethpmscl2 is calculated based on the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 calculated in step S406. The relationship between the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7 and the predetermined period ethpmscl2 is determined in advance based on experiments or the like, and is stored in advance in the ECU 10 as a map or a function. In step S410, a predetermined period ethpmscl2 is calculated using this map or function. As described above, the higher the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7, the shorter the predetermined period ethpmscl2 is calculated.

  Instead of the nitrous oxide concentration ecn2o of the exhaust downstream of the NOx catalyst 7, the amount of nitrous oxide in the exhaust may be calculated, and the ethpmscl2 may be calculated for a predetermined period using the amount of nitrous oxide.

  Next, in step S411, it is determined whether or not the sensor high temperature duration ethpmsc calculated in step S409 is shorter than the predetermined period ethpmsc1 calculated in step S410. If a negative determination is made in step S411, the execution of this flow is temporarily terminated. That is, when the temperature ethpms of the PM sensor 16 is equal to or higher than the first predetermined temperature ethpmsl1 for a predetermined period ethpmscl2, the estimation of the PM accumulation amount in the PM sensor 16 is stopped, and the failure determination of the filter 5 is prohibited. On the other hand, if an affirmative determination is made in step 4311, the process of step S108 is then executed.

In this flow, if an affirmative determination is made in step S108, then the process of step S412 is executed. In step S412, based on the normal PM accumulation amount eggpmsdp at the current time calculated in step S405, the failure determination threshold e of the filter 5 is determined.
pms2 is calculated. The relationship between the threshold value epms2 and the normal PM deposition amount egpmsdp is determined in advance based on experiments or the like, and is stored in advance in the ECU 10 as a map or a function. In step S412, the threshold epms2 is calculated using this map or function. Here, for example, the threshold value epms2 may be a value obtained by adding an allowable margin to the normal-time PM deposition amount eggpmsdp. Alternatively, the normal PM deposition amount egpmsdp may be set as the threshold value epms2. The threshold epms2 is calculated as a larger value as the value of the normal PM deposition amount egpmsdp is larger.

  Note that the failure determination of the filter 5 may be performed when the normal PM accumulation amount egpmmsdp calculated in step S405 reaches a certain amount equal to or greater than a predetermined amount. In this case, the threshold value epms2 is a constant value determined in advance based on the constant amount.

  Next, in step S413, it is determined whether or not the output value epms of the PM sensor 16 is equal to or greater than the threshold value epms2 for filter 5 failure determination calculated in step S412. When an affirmative determination is made in step S413, it can be determined that the actual PM deposition amount in the PM sensor 16 is excessively larger than the normal PM deposition amount. Therefore, in this case, in step S111, it is determined that the filter 5 has failed. On the other hand, if a negative determination is made in step S413, it is then determined in step S112 that the filter 5 is normal.

  As described above, in this embodiment, the PM accumulated on the PM sensor 16 is oxidized, so that the difference between the integrated value of the PM amount passing through the filter 5 and adhering to the PM sensor 16 and the output value of the PM sensor 16 is different. Is excessively large, the estimation of the normal PM accumulation amount is stopped, and the failure determination of the filter 5 is prohibited. Even in the state where the PM deposited on the PM sensor 16 is oxidized immediately after the PM removal processing is completed, the normal PM accumulation amount is not estimated, and the failure determination of the filter 5 is prohibited. Thereby, the fall of the precision of the filter failure determination can be suppressed.

  In the present embodiment, the first predetermined temperature and the predetermined period are set based on the nitrous oxide concentration ecn2o (or the amount of nitrous oxide in the exhaust) downstream of the NOx catalyst 7. Therefore, the failure determination of the filter 5 is performed based on the output value of the PM sensor 16 in a state where the deviation between the integrated value of the PM amount passing through the filter 5 and adhering to the PM sensor 16 and the output value of the PM sensor is excessively large. Can be suppressed with a higher probability. Therefore, the accuracy of failure detection of the filter 5 can be improved.

  Note that it is not always necessary to set both the first predetermined temperature and the predetermined period based on the nitrous oxide concentration ecn2o (or the amount of nitrous oxide in the exhaust) in the exhaust downstream of the NOx catalyst 7. That is, any one of the first predetermined temperature and the predetermined period may be a predetermined constant value. However, by setting both of these values based on the nitrous oxide concentration ecn2o (or the amount of nitrous oxide in the exhaust gas) downstream of the NOx catalyst 7, the accuracy of the failure detection of the filter 5 is set. Can be further improved.

The present embodiment can also be applied to the case of estimating the PM accumulation amount in the PM sensor 16 when the filter 5 is assumed to be in a predetermined failure state instead of the normal PM accumulation amount. In this case, the PM accumulation amount in the PM sensor 16 is calculated on the basis of the engine exhaust PM amount, the filter slipping rate when the filter 5 is assumed to be in a predetermined failure state, and the sensor adhesion rate. The amount of oxidized PM is not considered. Then, the decrease amount of the PM accumulation amount that is decreased by being oxidized in the PM sensor 16 becomes large, and the difference between the integrated value of the PM amount that has passed through the filter 5 and adhered to the PM sensor 16 and the output value of the PM sensor 16 is increased. When it becomes excessively large, estimation of the PM accumulation amount in the PM sensor 16 when the state of the filter 5 is assumed to be a predetermined failure state is stopped, and failure determination of the filter 5 is prohibited.

  Examples 1 to 4 can be combined as much as possible. For example, as in Example 2, by correcting the output value of the PM sensor 16 based on the amount of oxidation of PM deposited on the PM sensor 16, and comparing the corrected output value of the PM sensor 16 with a threshold value, Even when a failure of the filter 5 is determined, the failure determination prohibition condition according to the third embodiment may be applied.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake passage 3 ... Exhaust passage 4 ... Oxidation catalyst 5 ... Filter 6 ... Addition valve 7 ... Selective reduction type NOx catalyst (NOx catalyst)
8 ... Throttle valve 9 ... Turbocharger 10 ... ECU
11. ・ Air flow meter 12 ・ ・ First exhaust temperature sensor 13 ・ ・ Second exhaust temperature sensor 14 ・ ・ A / F sensor 15 ・ ・ NOx sensor 16 ・ ・ PM sensor 17 ・ ・ Third exhaust temperature sensor 18 ・ ・ Accelerator Opening sensor 19 ・ ・ Crank position sensor

Claims (8)

A filter failure detection device for detecting a failure of a filter provided in an exhaust passage of an internal combustion engine and collecting particulate matter in exhaust gas,
A PM sensor that is provided in an exhaust passage downstream of the filter and outputs a signal corresponding to the amount of particulate matter deposited on the filter;
A selective reduction type NOx catalyst provided in an exhaust passage between the filter and the PM sensor, for reducing NOx in the exhaust gas using ammonia as a reducing agent;
Estimating means for estimating a PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state;
Obtaining means for obtaining the concentration of nitrous oxide in the exhaust downstream of the selective catalytic reduction NOx catalyst or the amount of nitrous oxide in the exhaust;
Based on at least the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst acquired by the obtaining means or the amount of nitrous oxide in the exhaust, the amount of PM oxidized on the PM sensor is calculated. Oxidation amount calculating means for
PM accumulation amount correction means for correcting the PM accumulation amount in the PM sensor estimated by the estimation means based on the oxidation amount of PM calculated by the oxidation amount calculation means;
A determination unit that determines failure of the filter based on an output value of the PM sensor on the condition that the PM deposition amount in the PM sensor corrected by the PM deposition amount correction unit is a predetermined amount or more;
A filter failure detection apparatus comprising: A filter failure detection device for detecting a failure of a filter provided in an exhaust passage of an internal combustion engine and collecting particulate matter in exhaust gas,
A PM sensor that is provided in an exhaust passage downstream of the filter and outputs a signal corresponding to the amount of particulate matter deposited on the filter;
A selective reduction type NOx catalyst provided in an exhaust passage between the filter and the PM sensor, for reducing NOx in the exhaust gas using ammonia as a reducing agent;
Estimating means for estimating a PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state;
Obtaining means for obtaining the concentration of nitrous oxide in the exhaust downstream of the selective catalytic reduction NOx catalyst or the amount of nitrous oxide in the exhaust;
Based on at least the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst acquired by the obtaining means or the amount of nitrous oxide in the exhaust, the amount of PM oxidized on the PM sensor is calculated. Oxidation amount calculating means for
PM accumulation amount correction means for correcting the PM accumulation amount in the PM sensor estimated by the estimation means based on the oxidation amount of PM calculated by the oxidation amount calculation means;
A determination unit that determines a failure of the filter by comparing the output value of the PM sensor with a threshold value that is determined based on the PM accumulation amount in the PM sensor corrected by the PM accumulation amount correction unit;
A filter failure detection apparatus comprising: A filter failure detection device for detecting a failure of a filter provided in an exhaust passage of an internal combustion engine and collecting particulate matter in exhaust gas,
A PM sensor that is provided in an exhaust passage downstream of the filter and outputs a signal corresponding to the amount of particulate matter deposited on the filter;
A selective reduction type NOx catalyst provided in an exhaust passage between the filter and the PM sensor, for reducing NOx in the exhaust gas using ammonia as a reducing agent;
Obtaining means for obtaining the concentration of nitrous oxide in the exhaust downstream of the selective catalytic reduction NOx catalyst or the amount of nitrous oxide in the exhaust;
Based on at least the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst acquired by the acquisition means or the amount of nitrous oxide in the exhaust, the amount of oxidation of PM deposited on the PM sensor is calculated. Oxidation amount calculating means for
Sensor output correction means for correcting the output value of the PM sensor based on the oxidation amount of PM calculated by the oxidation amount calculation means;
A determination unit that determines a failure of the filter by comparing an output value of the PM sensor corrected by the sensor output correction unit with a threshold value;
A filter failure detection apparatus comprising:   The oxidation amount calculation means accumulates on the PM sensor based on the temperature of the PM sensor in addition to the nitrous oxide concentration or the amount of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst. The filter failure detection device according to any one of claims 1 to 3, wherein an oxidation amount of PM is calculated.   5. The apparatus according to claim 1, further comprising a prohibiting unit that prohibits the determination of the filter failure by the determination unit when the temperature of the PM sensor is equal to or higher than a predetermined temperature for a predetermined period. Filter failure detection device.   At least one of the predetermined temperature or the predetermined period is set based on the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst acquired by the acquiring means or the amount of nitrous oxide in the exhaust. The filter failure detection apparatus according to claim 5, further comprising setting means. A filter failure detection device for detecting a failure of a filter provided in an exhaust passage of an internal combustion engine and collecting particulate matter in exhaust gas,
A PM sensor provided in an exhaust passage downstream of the filter and outputting a signal corresponding to particulate matter deposited on the filter;
A selective reduction type NOx catalyst provided in an exhaust passage between the filter and the PM sensor, for reducing NOx in the exhaust gas using ammonia as a reducing agent;
Estimating means for estimating a PM accumulation amount in the PM sensor when the filter is assumed to be in a predetermined state;
Determination means for determining a failure of the filter using an output value of the PM sensor and a PM accumulation amount in the PM sensor estimated by the estimation means;
When the PM accumulation amount in the PM sensor is estimated by the estimation means, and the state where the temperature of the PM sensor is higher than a predetermined temperature continues for a predetermined period or longer, the PM accumulation amount in the PM sensor by the estimation means is A prohibiting means for stopping the estimation and prohibiting the failure determination of the filter;
Obtaining means for obtaining the concentration of nitrous oxide in the exhaust downstream of the selective catalytic reduction NOx catalyst or the amount of nitrous oxide in the exhaust;
At least one of the predetermined temperature or the predetermined period is set based on the concentration of nitrous oxide in the exhaust downstream of the selective reduction NOx catalyst acquired by the acquiring means or the amount of nitrous oxide in the exhaust. Setting means;
A filter failure detection apparatus comprising: The predetermined temperature is a first predetermined temperature,
After the prohibiting means completes the PM removal process for oxidizing and removing the PM deposited on the PM sensor by increasing the temperature of the PM sensor, the temperature of the PM sensor becomes lower than the second predetermined temperature. The filter failure detection device according to any one of claims 5 to 7, wherein the estimation unit prohibits the filter failure determination without estimating the PM accumulation amount in the PM sensor by the estimation unit.

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