JP2015004352A - Filter abnormality determination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately determine an abnormality of a filter in a filter abnormality determination device for collecting PM in exhaust gas discharged from an internal combustion engine.SOLUTION: A filter abnormality determination device includes: a filter for collecting PM in exhaust gas; a differential pressure sensor for detecting differential pressure before and after the filter; and an abnormality determination section for calculating a ratio of variation of the differential pressure to variation of a flow rate of the exhaust gas from first differential pressure and second differential pressure that is acquired when the flow rate of the exhaust gas is within a higher flow rate region, and determining an abnormality of the filter on the basis of the ratio. When an accumulation amount of the PM on the filter that has increased from the acquisition of the first differential pressure to the acquisition of the second differential pressure is a predetermined threshold increase amount or larger, the abnormality determination section prohibits the abnormality determination of the filter.

Description

  The present invention relates to an abnormality determination device for a filter that collects particulate matter in exhaust gas discharged from an internal combustion engine.

  Conventionally, an exhaust passage of an internal combustion engine has been provided with a filter that collects particulate matter (PM) in the exhaust. This filter may be damaged (melted) if, for example, abnormal heat is generated during the filter regeneration process. When the filter is damaged, the PM collection performance of the filter is lowered, and therefore it is necessary to detect the filter damage with high accuracy.

  Incidentally, there is a correlation between the flow rate of the exhaust gas flowing through the filter and the differential pressure across the filter (the difference between the upstream exhaust pressure and the downstream exhaust pressure). However, a damaged filter has poor PM collection performance, and therefore the differential pressure across the filter is unlikely to increase even if the exhaust flow rate increases. Therefore, the ratio of the change amount of the differential pressure across the filter to the change amount of the exhaust flow rate (or the change amount of the intake air amount correlated with the exhaust flow rate) (hereinafter also referred to as “differential pressure change rate”) is used. A technique for determining an abnormality is known (see, for example, Patent Documents 1 and 2). In this technique, when the calculated differential pressure change rate is smaller than a differential pressure change rate as a determination criterion prepared in advance, it is determined that the filter is abnormal.

JP 2007-327392 A JP 2009-216077 A

  By the way, if the PM accumulation amount of the filter increases as the operation of the internal combustion engine continues, the pressure loss of the exhaust gas in the filter also increases. Therefore, even if the exhaust gas flow rate is equal, the detected differential pressure across the filter. To rise. Therefore, when the front-rear differential pressure is acquired when the PM accumulation amount of the filter is increasing, the calculated differential pressure change rate may be different even when the exhaust flow rate change amount is equal. In particular, when the PM accumulation amount is excessively increased before and after the change of the exhaust flow rate, the calculated differential pressure change rate is obtained because the differential pressure before and after the filter obtained when the exhaust flow rate is high becomes excessively high. May become excessively high. In this case, even a damaged abnormal filter may be erroneously determined to be normal because the calculated differential pressure change rate is high.

  On the other hand, when the PM accumulation amount increases excessively before the change in the exhaust flow rate, the differential pressure change rate calculated is increased because the differential pressure across the filter obtained when the exhaust flow rate is low becomes excessively high. May be too low. In this case, even a normal filter may be erroneously determined as abnormal because the calculated differential pressure change rate is low.

  The present invention has been made in view of such circumstances, and an object of the present invention is to accurately determine a filter abnormality in a filter abnormality determination device that collects PM in exhaust gas discharged from an internal combustion engine. To do.

In order to solve the above-described problem, a filter abnormality determination device according to the present invention includes:
A filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
A differential pressure sensor for detecting a differential pressure between the exhaust pressure upstream of the filter and the exhaust pressure downstream;
After the acquisition of the first differential pressure acquired when the flow rate of the exhaust gas flowing through the exhaust passage is in the first flow rate region and the first differential pressure, the flow rate of the exhaust gas is the first flow rate. A ratio of the change amount of the differential pressure to the change amount of the flow rate of the exhaust gas is calculated from the second differential pressure acquired when the second flow rate region is higher than the first flow rate region; An abnormality determination unit for determining an abnormality of the filter based on
A filter abnormality determination device comprising:
The abnormality determining unit, when the accumulated amount of particulate matter of the filter that has increased from the acquisition of the first differential pressure to the acquisition of the second differential pressure is equal to or greater than a predetermined threshold increase amount The abnormality determination of the filter is prohibited.

  There is a correlation between the flow rate of the exhaust gas flowing through the exhaust passage and the differential pressure between the exhaust pressure upstream of the filter and the exhaust pressure downstream (hereinafter also referred to as “front-rear differential pressure”). Here, since the damaged abnormal filter has a small pressure loss of the exhaust gas flowing through the inside, even if the exhaust gas flow rate increases, the differential pressure across the filter hardly increases. That is, in the abnormal filter, the ratio of the change amount of the differential pressure across the filter to the change amount of the exhaust flow rate (hereinafter also referred to as “differential pressure change rate”) is smaller than that of the normal filter. Therefore, the abnormality determination unit according to the present invention determines that the filter is abnormal, for example, when the calculated differential pressure change rate is smaller than a predetermined determination reference value.

  Here, when the accumulation amount of particulate matter (hereinafter also referred to as “PM”) of the filter increases as the operation of the internal combustion engine continues, the pressure loss of the exhaust gas in the filter increases. Even so, the differential pressure across the detected filter increases. That is, when the PM accumulation amount increases excessively from the acquisition of the first differential pressure to the acquisition of the second differential pressure, the amount of change in the exhaust gas flow rate is excessively increased. There is a possibility that the differential pressure change rate becomes higher than the determination reference value. As a result, even an abnormal filter may be erroneously determined to be normal (an erroneous normal determination is made).

  Therefore, the abnormality determination unit according to the present invention, when the accumulated amount of PM of the filter that has increased from the acquisition of the first differential pressure to the acquisition of the second differential pressure is equal to or greater than a predetermined threshold increase amount. The filter abnormality judgment is prohibited. This threshold increase amount may be determined in advance by an experiment or the like from the relationship between the increase amount of PM and the change amount of the differential pressure (difference between the second differential pressure and the first differential pressure). The amount of increase in PM when the amount of change in the differential pressure increases to the extent that is reduced. Therefore, according to the present invention, when the PM accumulation amount increases excessively from the acquisition of the first differential pressure to the acquisition of the second differential pressure, the filter abnormality determination is prohibited. Therefore, erroneous determination of an abnormal filter as normal by the abnormality determination unit is suppressed.

  According to the present invention, the abnormality determination unit determines that the filter is abnormal when the calculated ratio is lower than a predetermined reference ratio, and the predetermined threshold increase amount is equal to the ratio. In the calculation, if it is assumed that the amount of particulate matter deposited on the filter is constant, the assumed ratio corresponding to the calculated ratio is less than the predetermined reference ratio, and the calculated ratio is the predetermined ratio. The increase amount of the particulate matter deposited on the filter may be set so as to exceed the reference ratio.

Here, the assumed ratio corresponding to the calculated ratio is the differential pressure change rate when the influence of PM accumulation on the filter is excluded, in other words, the differential pressure change that reflects the actual filter state. Rate. Therefore, the predetermined threshold increase amount is, in other words, an excessive increase in the PM accumulation amount even though the filter is in an abnormal state where the actual differential pressure change rate is below the predetermined reference ratio. The calculated differential pressure change rate becomes apparently high, and as a result, the calculated differential pressure change rate exceeds a predetermined reference ratio, so that the filter may be erroneously determined to be in a normal state. Such a threshold.

  By the way, if the amount of PM accumulated in the filter increases excessively before the first differential pressure is acquired, even if the exhaust flow rate is within the first flow rate region, it is too high or low. There is a risk that differential pressure is detected. In this case, since the change amount of the differential pressure may be excessively small, the calculated differential pressure change rate may be lower than the determination reference value. As a result, even with a normal filter, there is a risk that an abnormality and an erroneous determination are made (an erroneous abnormality determination is made).

  Therefore, the abnormality determination unit according to the present invention has an accumulation amount of particulate matter deposited on the filter that is less than a predetermined threshold accumulation amount at which the differential pressure becomes excessive when the exhaust gas flow rate is in the first flow rate region. Sometimes the first differential pressure may be acquired. This threshold deposition amount may be determined in advance by experiments or the like from the relationship between the PM deposition amount and the differential pressure when the exhaust gas flow rate is within the first flow rate region. What is necessary is just to set it as the amount of accumulation of PM when the high 1st differential pressure | pressure is acquired. Therefore, according to the present invention, since the first differential pressure is acquired before the PM accumulation amount of the filter increases excessively, it is suppressed that a normal filter is erroneously determined to be abnormal by the abnormality determination unit. The

  According to the present invention, in a filter abnormality determination device that collects PM in exhaust discharged from an internal combustion engine, it is possible to suppress erroneous determination due to the influence of the amount of accumulated PM. It is possible to accurately determine the abnormality.

It is a figure which shows schematic structure of the internal combustion engine and filter abnormality determination apparatus which concern on an Example. It is a graph which shows the relationship between the flow volume of the exhaust_gas | exhaustion which distribute | circulates the inside of a filter, and the differential pressure before and behind a filter. It is a figure which shows the detection result of the differential pressure before and behind the filter by a differential pressure sensor. It is a flowchart which shows the routine of the abnormality determination of the filter which concerns on an Example.

  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]
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and a filter abnormality determination apparatus to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) for an automobile having a plurality of cylinders.

  The internal combustion engine 1 includes a fuel injection valve 1a that injects fuel into a combustion chamber in a cylinder. An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. The intake passage 2 is a passage that guides air taken in from the atmosphere to a cylinder of the internal combustion engine 1, and is provided with an air flow meter 4 that detects the amount of air taken into the cylinder of the internal combustion engine 1. Further, the exhaust passage 3 is a passage for circulating the exhaust discharged from the cylinder of the internal combustion engine 1.

In the exhaust passage 3, an oxidation catalyst 5 having an oxidation capability and a filter 6 for collecting PM in the exhaust are disposed in order from the upstream side. The oxidation catalyst 5 oxidizes unburned fuel, carbon monoxide and the like discharged from the internal combustion engine 1, and suppresses these from being discharged to the atmosphere. Further, in the vicinity of the filter 6, there is provided a differential pressure sensor 7 that detects a front-rear differential pressure that is a differential pressure between the exhaust pressure upstream of the filter 6 and the exhaust pressure downstream. Furthermore, a PM sensor 11 that detects the amount of PM contained in the exhaust gas is provided on the downstream side of the filter 6. Note that an SCR catalyst or the like for reducing NOx in the exhaust may be appropriately provided on the downstream side of the filter 6 in the exhaust passage 3.

  The internal combustion engine 1 is also provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The above-described fuel injection valve 1a is electrically connected to the ECU 10 and controlled by the ECU 10. In addition to the air flow meter 4, the differential pressure sensor 7, and the PM sensor 11, the ECU 10 includes a crank position sensor 8 that detects the engine speed and an accelerator position sensor 9 that detects the amount of depression of the accelerator pedal by the driver. They are electrically connected, and these output signals are input to the ECU 10. Note that. The ECU 10 estimates the operating state of the internal combustion engine 1 based on detection values of the crank position sensor 8, the accelerator position sensor 9, and the like.

  By the way, when the operation of the internal combustion engine 1 continues, the amount of PM accumulated in the filter 6 increases. If PM accumulates excessively, problems such as clogging of the filter 6 may occur. Therefore, in order to prevent such problems from occurring before the PM accumulation amount reaches a predetermined amount, Playback processing is performed. Here, the predetermined amount is an amount set in order to determine the necessity of the regeneration process of the filter 6, and is obtained in advance through experiments or the like. In the present embodiment, when the regeneration process is executed, the sub-injection is performed separately from the main injection for generating torque by the fuel injection valve 1a. The fuel injected by the sub-injection is supplied to the oxidation catalyst 5 through the exhaust gas and burned in the oxidation catalyst 5. As a result, the temperature of the exhaust gas flowing out of the oxidation catalyst 5 and flowing into the filter 6 rises, so that the oxidation removal of the PM deposited on the filter 6 is promoted and the amount of PM deposition decreases. This regeneration process may be executed by supplying fuel to the oxidation catalyst 5 from a fuel addition valve (not shown).

  Here, depending on the accumulation state of PM in the filter 6, abnormal oxidation of heat may occur due to a rapid progress of the oxidation reaction of PM during the regeneration process, and the filter 6 may be partially damaged (melted). When such a breakage occurs, there is a possibility that the PM collection performance by the filter 6 may be lowered. Therefore, it is necessary to determine that the filter 6 is in an abnormal state when the breakage occurs. In addition, when it breaks and becomes an abnormal state, since the pressure loss in the filter 6 becomes small, even if the exhaust gas flow rate increases, the differential pressure across the filter 6 becomes difficult to increase. Therefore, it is possible to determine the abnormality of the filter 6 by using this tendency. Hereinafter, a method for determining abnormality of the filter 6 using this tendency will be described.

FIG. 2 is a graph showing the relationship between the flow rate of the exhaust gas flowing through the filter 6 and the differential pressure across the filter 6. The horizontal axis in FIG. 2 indicates the exhaust gas flow rate, and the vertical axis indicates the front-rear differential pressure. Instead of the exhaust flow rate, an intake air amount correlated with the exhaust flow rate may be used. Graphs L1 and L2 indicate the above-described relationship when the filter 6 is in a normal state and an abnormal state, respectively. Here, the slope of the graph L1 is the ratio of the change amount of the differential pressure before and after the change amount of the exhaust gas flow rate (hereinafter also referred to as “differential pressure change rate”). This differential pressure change rate is obtained by calculating the differential pressure across the filter 6 obtained when the exhaust flow rate is in the first flow rate region and the filter 6 obtained when the exhaust flow rate is in the second flow rate region. It is calculated from the differential pressure across the front and back. For example, the first differential pressure dp1 acquired when the exhaust flow rate is at the flow rate V1 in the first flow rate region, and the second differential pressure dp2 acquired when the exhaust flow rate is at V2 in the second flow rate region. Is used, the differential pressure change rate can be obtained from the arithmetic expression (dp2-dp1) / (V2-V1). Here, as the differential pressure dp1, a value detected by the differential pressure sensor 7 when the exhaust flow rate is V1 may be used. Alternatively, when the exhaust flow rate is within the first flow rate region, the differential pressure sensor 7 is used to detect the differential pressure before and after multiple times, the average value of the exhaust flow rate at the time of detection is V1, and the average of the detected differential pressure before and after The value may be dp1. Note that V2 and dp2 can be similarly obtained. Further, the slope of the graph L2 can be obtained by the same method.

  Here, the first flow rate region is a region of the flow rate of exhaust gas discharged when the internal combustion engine 1 is operated in a low load region, for example. The second flow rate region is a higher flow rate region than the first flow rate region, and is, for example, a flow rate region of exhaust gas that is discharged when the internal combustion engine 1 is operated in a medium to high load region. Both flow regions may be experimentally determined in advance so that the filter abnormality can be suitably determined.

  As described above, in the abnormal filter 6 that has been damaged, the pressure loss of the exhaust gas becomes small, so that the differential pressure across the filter 6 does not easily increase even if the exhaust gas flow rate increases. Therefore, as shown in the graph L2, when the filter 6 is in an abnormal state, the slope of the graph, that is, the rate of change in differential pressure is smaller than when the filter 6 is normal. Therefore, it is possible to determine the abnormality of the filter 6 by determining an appropriate differential pressure change rate (corresponding to a predetermined reference ratio in the present invention) as a reference value for abnormality determination. That is, when determining the abnormality of the filter 6, the differential pressure dp1 when the exhaust flow rate is V1 and the differential pressure dp2 when the exhaust flow rate is V2 are acquired, and the calculated differential pressure change rate is equal to or greater than the reference value. If so, it is determined that the filter 6 is normal. On the other hand, if the differential pressure change rate is less than the reference value, the filter 6 is determined to be abnormal.

  Incidentally, the pressure loss of the exhaust gas flowing through the filter 6 is affected by the amount of PM accumulated in the filter 6. Therefore, when the PM accumulation amount increases during execution of the abnormality determination of the filter 6, the differential pressure acquired by the change in pressure loss increases, so that the required differential pressure change rate changes. Under actual operating conditions, the operating state of the internal combustion engine 1 is changed from a low load region where the exhaust gas flow rate is in the first flow rate region to a medium-high state where the exhaust gas flow rate is in the second flow rate region. Since it may take a relatively long time to move to the load region, the amount of PM deposited may be relatively large. In such a case, since the differential pressure change rate changes due to an increase in the amount of accumulated PM, there is a possibility that the abnormality determination of the filter 6 cannot be performed accurately. Hereinafter, the influence of the increase in the amount of accumulated PM on the differential pressure change rate will be described.

  FIG. 3 is a diagram in which the detected values of the differential pressure across the filter 6 by the differential pressure sensor 7 are plotted. FIG. 3A shows a case where the PM accumulation amount in the filter 6 is substantially constant during the change in the exhaust flow rate, and FIG. 3B shows the PM accumulation amount during the change in the exhaust flow rate. The case where it increased is shown.

  As shown in FIG. 3A, when the PM accumulation amount is substantially constant during the change of the exhaust flow rate, the detection value detected by the differential pressure sensor 7 is approximately on the straight line shown in the figure. To position. In this case, when the differential pressure change rate is obtained, any detected value belonging to the first flow rate region is used as the differential pressure dp1, and it belongs to the second flow rate region as the differential pressure dp2. Regardless of which detection value is used, the calculated differential pressure change rate is approximately equal to the slope of the straight line shown in the figure. That is, in this case, since the calculated differential pressure change rate is substantially constant, it is considered that the possibility that an erroneous determination is made when the abnormality of the filter 6 is determined is extremely low.

  On the other hand, as shown in FIG. 3B, when the PM accumulation amount increases while the exhaust gas flow rate is increased, the differential pressure detected before and after the PM accumulation amount increases (in the figure). (See the thick arrow in the). In this case, even when the exhaust gas flow rate is within the same flow rate region, a higher front-back differential pressure is detected when the PM accumulation amount is increasing.

Here, for example, when the exhaust amount of PM increases due to the operation of the internal combustion engine 1 being continued for a relatively long time in the middle and high load region, the PM of the filter 6 when the exhaust gas flow rate is in the second flow rate region. The amount of deposition may increase excessively. In this case, the detected value of the differential pressure before and after the exhaust flow rate is in the second flow rate region is determined when the PM accumulation amount does not increase excessively (for example, in FIG. 3A). As compared to the case shown). Therefore, when the differential pressure change rate is obtained, if a relatively high detection value P2 belonging to the second flow rate region is used as the differential pressure dp2, it belongs to the first flow rate region as the differential pressure dp1. Even when the average detection value P1 is used from the detection values, the amount of change in the differential pressure may become excessively large. In other words, as indicated by the broken line graph L3, the calculated differential pressure change rate becomes excessively large as compared with the case where there is no influence due to the accumulation of PM (the slope of the straight line shown in FIG. 3A). Sometimes. As a result, even when the filter 6 is actually abnormal and the differential pressure change rate is below the reference value, the calculated differential pressure change rate is excessively high, and thus exceeds the reference value. If it is normal, there is a risk of erroneous determination.

  On the other hand, for example, when the operation of the internal combustion engine 1 continues for a relatively long time in the low load region, the PM accumulation amount in the filter 6 is excessive even when the exhaust gas flow rate is in the first flow rate region. May increase. In this case, the detected value of the front-rear differential pressure detected when the exhaust flow rate is in the first flow rate region becomes larger than when the PM accumulation amount has not increased excessively. Therefore, when the differential pressure change rate is obtained, if a relatively high detection value P3 belonging to the first flow region is used as the differential pressure dp1, it belongs to the second flow region as the differential pressure dp2. Even when the average detection value P4 is used from the detection values, the amount of change in the differential pressure may become excessively small. In this case, as shown by the graph L4, the calculated differential pressure change rate is excessively low as compared with the case where there is no influence due to the accumulation of PM (the slope of the straight line shown in FIG. 3A). May be. As a result, even when the filter 6 is actually normal and the differential pressure change rate exceeds the reference value, the calculated differential pressure change rate becomes excessively low and falls below the reference value. There is a risk that an erroneous determination will be made if it is abnormal.

  Therefore, in the abnormality determination of the filter 6 according to the present embodiment, when the accumulation amount of PM increases excessively from the acquisition of the first differential pressure dp1 to the acquisition of the second differential pressure dp2. In order to avoid erroneous normal determination, abnormality determination is prohibited. Further, in the abnormality determination of the filter 6 according to the present embodiment, when the exhaust gas flow rate is in the first flow rate region, in order to avoid the erroneous abnormality determination, the first time before the PM accumulation amount increases excessively. Acquisition of the differential pressure dp1 of 1 is completed. Hereinafter, a method for determining abnormality of the filter 6 according to the present embodiment will be described with reference to the drawings.

  FIG. 4 is a flowchart showing a routine for determining abnormality of the filter 6 performed by the ECU 10. This routine is executed by the ECU 10 every predetermined time or as necessary. The ECU 10 corresponds to the abnormality determination unit in the present invention.

  In step S101, the ECU 10 determines whether the PM accumulation amount of the filter 6 during execution of this step is less than the threshold accumulation amount and whether the exhaust flow rate is within the first flow rate region. That is, in this step, the start condition of the abnormality determination routine is confirmed. Here, the PM accumulation amount is obtained by calculation based on the detection value of the PM sensor 11. Alternatively, the filter 6 may be obtained by calculation from the operating state of the internal combustion engine 1 and the fuel injection amount by the fuel injection valve 1a in the period from the last execution of the regeneration process of the filter 6 to the execution of this step. In addition, the above-described threshold accumulation amount is the first difference that is high to the extent that a false abnormality determination is made by calculating the differential pressure change rate too low, as in the graph L4 shown in FIG. The amount of PM deposited when the pressure (P3 in FIG. 3B) is acquired may be used. Further, the exhaust flow rate at the time of execution of this step is obtained from the intake air amount detected by the air flow meter 4. In this step, a standby state is entered until the start condition is confirmed. If an affirmative determination is made in this step, the ECU 10 proceeds to step S102.

  In step S <b> 102, the ECU 10 detects the differential pressure across the filter 6 using the differential pressure sensor 7. The detected value in this step corresponds to the first differential pressure dp1 acquired when the exhaust gas flow rate is in the first flow rate region.

  In step S103, the ECU 10 determines from the intake air amount detected by the air flow meter 4 whether or not the exhaust flow rate at the time of executing this step is within the second flow rate region. If a positive determination is made in this step, the ECU 10 proceeds to step S104.

  In step S <b> 104, the ECU 10 detects the differential pressure across the filter 6 using the differential pressure sensor 7. The detected value in this step corresponds to the second differential pressure dp2 acquired when the exhaust gas flow rate is in the second flow rate region.

  In step S105, the ECU 10 acquires an increase amount of PM that has increased from the acquisition of the first differential pressure dp1 to the acquisition of the second differential pressure dp2. The increase amount of PM can be obtained by estimating the PM accumulation amount increased within the time from the execution of step S102 to the execution of step S104.

  In step S106, the ECU 10 determines whether or not the accumulated amount of PM that has increased from the acquisition of the first differential pressure dp1 to the acquisition of the second differential pressure dp2 is equal to or greater than a threshold increase amount. That is, the ECU 10 determines whether or not the difference between the PM accumulation amount acquired in the previous step and the PM accumulation amount acquired in Step S101 is equal to or greater than the threshold increase amount. Note that the threshold increase amount is the second differential pressure that is high to the extent that an erroneous determination is made when the differential pressure change rate is calculated to be excessively high, as in the graph L3 shown in FIG. What is necessary is just to make it the increase amount of PM when (P2 in FIG.3 (b)) is acquired. If an affirmative determination is made in this step, the amount of change in the differential pressure (that is, the difference between the second differential pressure dp2 and the first differential pressure dp1) becomes excessively large due to an increase in the amount of accumulated PM. It means that there is a fear. Therefore, in this case, since the calculated differential pressure change rate may be excessively high, there is a possibility that the filter 6 may be judged to be normal even if it is abnormal. Therefore, the ECU 10 proceeds to step S107 and prohibits the abnormality determination of the filter 6 in this routine. When step S107 is executed, this routine ends.

  On the other hand, if a negative determination is made in step S106, it means that the amount of accumulated PM has not increased to the extent that an erroneous normal determination is made. Therefore, the ECU 10 proceeds to step S108 and executes abnormality determination of the filter 6. In this step, the ECU 10 changes the differential pressure from the first differential pressure dp1 and the second differential pressure dp2 acquired in the previous step, and the exhaust flow rate (or intake air amount) when both differential pressures are acquired. Calculate the rate. The first differential pressure dp1 is the differential pressure obtained before and after the PM accumulation amount in the filter 6 exceeds the threshold accumulation amount in step S102, and therefore the differential pressure change rate calculated in this step. Is prevented from becoming too small. The ECU 10 makes a normal determination when the calculated differential pressure change rate is equal to or higher than a reference value for determining the abnormality of the filter 6, and makes an abnormal determination when the differential pressure change rate is less than the reference value. When this step is executed, this routine is terminated.

As described above, according to the present embodiment, when the PM accumulation amount increases excessively from the acquisition of the first differential pressure dp1 to the acquisition of the second differential pressure dp2, the filter 6 is abnormal. Since the determination is prohibited, it is possible to prevent an erroneous normal determination from being made with respect to the abnormal filter 6. Further, according to the present embodiment, since the first differential pressure dp1 is acquired before the PM accumulation amount of the filter 6 increases excessively, it is normal when the abnormality determination of the filter 6 is executed by the ECU 10. It is suppressed that the erroneous abnormality determination is made with respect to the simple filter 6. As described above, according to the present embodiment, it is possible to suppress the erroneous determination, and therefore it is possible to accurately determine the abnormality of the filter 6.

1 Internal combustion engine 3 Exhaust passage 4 Air flow meter 5 Oxidation catalyst 6 Filter 7 Differential pressure sensor 10 ECU

Claims (3)

A filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
A differential pressure sensor for detecting a differential pressure between the exhaust pressure upstream of the filter and the exhaust pressure downstream;
After the acquisition of the first differential pressure acquired when the flow rate of the exhaust gas flowing through the exhaust passage is in the first flow rate region and the first differential pressure, the flow rate of the exhaust gas is the first flow rate. A ratio of the change amount of the differential pressure to the change amount of the flow rate of the exhaust gas is calculated from the second differential pressure acquired when the second flow rate region is higher than the first flow rate region; An abnormality determination unit for determining an abnormality of the filter based on
A filter abnormality determination device comprising:
The abnormality determining unit, when the accumulated amount of particulate matter of the filter that has increased from the acquisition of the first differential pressure to the acquisition of the second differential pressure is equal to or greater than a predetermined threshold increase amount A filter abnormality determination device that prohibits abnormality determination of the filter. In claim 1,
The abnormality determination unit determines that the filter is abnormal when the calculated ratio is lower than a predetermined reference ratio,
The predetermined threshold increase amount is an assumption ratio corresponding to the calculated ratio when the accumulation amount of the particulate matter of the filter is assumed to be constant in the calculation of the ratio below the predetermined reference ratio, An abnormality determination device for a filter, which is an increased amount of particulate matter deposited on the filter, set so that the calculated ratio exceeds the predetermined reference ratio. In claim 1 or 2,
The abnormality determination unit is configured such that the amount of particulate matter deposited on the filter is less than a predetermined threshold deposition amount at which the differential pressure when the flow rate of the exhaust gas is within the first flow rate region is excessive. A filter abnormality determination device that acquires the first differential pressure.

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