JP2009293518A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine accurately detecting failure of DPF in regard to an exhaust emission purifier measuring a PM amount passing through the DPF to detect failure of the DPF. <P>SOLUTION: After executing a process (S30) of increasing a PM amount flowing into the DPF, an amount of soot having passed through the DPF is measured by a soot sensor disposed downstream of the DPF (S40), a threshold for failure detection is calculated (S60) based on an estimate (S50) of a PM deposit amount in the DPF, degrees of the soot sensor measured value and the threshold are determined (S70), and it is determined that the DPF is broken when the soot sensor measured value is the same or more than the threshold (S80). By proceeding (S20) to failure detection even when an elapsed time or a traveling distance from prior failure determination exceeds predetermined values, too much elongation of a blank period of DPF failure detection is avoided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  In a diesel engine, it is important to remove so-called particulate matter (PM) such as black smoke discharged from the engine. For this purpose, a diesel particulate filter (DPF) is often provided in the middle of the exhaust pipe.

  When the DPF collects PM, most of the PM in the exhaust gas is removed. However, while PM continues to accumulate in the DPF, the DPF will become clogged. Therefore, when the PM accumulation amount exceeds a certain level, the accumulated PM is burned and removed by a technique such as post injection. , Regenerate the DPF. The DPF may break down if it is used for a long time. The failure includes damage or melting caused by excessive heating during regeneration.

  When the DPF fails, PM passes through the DPF and the emission deteriorates, so a technique for detecting the DPF failure is required. For example, Patent Document 1 below discloses a technique for detecting a DPF failure by a soot amount measured by a soot sensor provided downstream of the DPF. When the DPF fails, the amount of PM that passes through the DPF increases as compared with the case where there is no failure. Therefore, the failure is detected by the measured value of the soot sensor downstream of the DPF.

JP 2007-315275 A

  In Patent Document 1, when the amount of PM accumulated in the DPF is small, failure detection of the DPF is not executed. The reason for this is that the PM collection rate of the DPF is low in the first place when the amount of accumulated PM is low, so it is difficult to determine whether the PM has slipped through due to failure or whether it has slipped through even if it has not failed. .

  However, there are several problems with the idea of this document. First, as described above, in the same document, DPF failure detection is performed when the amount of accumulated PM is large. However, when the amount of accumulated PM is large, the PM collection rate is high, so the amount of PM passing through the DPF is small. Therefore, the measurement value of the soot sensor becomes minute, but when the measurement value of the soot sensor is minute, the error gravity in the measurement value is high, so there is a possibility that the failure of the DPF cannot be detected accurately.

  In addition, when the amount of accumulated PM is large, even if the DPF is out of order, the accumulated PM may collect the newly flowing PM. Therefore, there is a possibility that the influence of the failure of the DPF hardly appears in the measurement value of the downstream soot sensor. On the other hand, when the PM accumulation amount is small, the possibility of PM collection by the accumulated PM is small, so it is considered that the influence of the DPF failure is reflected sharply in the measurement value of the downstream soot sensor. In other words, contrary to the above-mentioned patent document 1, the idea that the case where the PM accumulation amount is small is more suitable for detecting a DPF failure.

  Further, as described above, in Patent Document 1, since the failure detection of the DPF is performed when the PM accumulation amount is large, the amount of PM that passes through the DPF is small, and the measurement value of the soot sensor may be minute. Therefore, unless the sensitivity of the soot sensor is high, the DPF failure cannot be detected accurately. When the amount of PM passing through the DPF is small and difficult to be detected by the soot sensor, it is conceivable to intentionally increase the amount of PM flowing into the DPF. However, Patent Document 1 does not consider such a countermeasure. .

  Furthermore, when the PM accumulation amount is small as in Patent Document 1, if the DPF failure detection is not performed, a period during which the DPF failure detection is not performed naturally occurs. However, in order to quickly detect a DPF failure, it is desirable to avoid an excessively long blank period for DPF failure detection.

  For the above reasons, unlike Patent Document 1, it is desirable to detect a DPF failure when the PM accumulation amount is small (or for any PM accumulation amount). Furthermore, in order to be able to detect a DPF failure accurately without depending on the sensitivity of the soot sensor, intentionally increase the amount of PM flowing into the DPF, or avoid a blank period during which the DPF failure detection is too long. Is also desirable.

  In view of the above problems, the problem to be solved by the present invention is to measure the amount of PM that passes through the DPF and detect a DPF failure in an exhaust purification device that detects a PM deposition amount is small (or any PM deposition). DPF fault detection (with respect to the amount), intentionally increasing the amount of PM flowing into the DPF, avoiding an excessively long blank period of DPF fault detection, etc. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can detect a failure.

Means for Solving the Problems and Effects of the Invention

  To achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to a first aspect of the present invention includes a collector that is disposed in an exhaust passage and collects particulate matter, and an exhaust passage that is more than the collector. A sensor disposed downstream to measure the amount of soot of particulate matter, control means for increasing particulate matter flowing into the collector, and particulate matter flowing into the collector by the control means; And a discriminating means for discriminating whether or not the collector is out of order from the measured value of the amount of soot by the sensor.

  Thus, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect of the present invention, the particulate matter that flows into the collector when determining the failure of the collector that is disposed in the exhaust passage and collects the particulate matter. And the amount of soot that passes through the collector is measured to determine the failure of the collector, so the amount of soot that slips through the intentionally increased particulate matter also increases, It is avoided that the measured value of the sensor becomes minute, and the reliability of the measured value of the sensor is improved. Therefore, it is possible to accurately determine the failure of the collector using the measurement value of the highly reliable sensor.

  Moreover, the said control means is good also as providing the 1st increase means to increase the exhaust flow volume which flows in into the said collector.

  As a result, the amount of particulate matter flowing into the collector can be increased by increasing the exhaust flow rate flowing into the collector, so that the amount of soot passing through increases and the measured value of the sensor becomes minute. Is avoided, and the reliability of the measured value of the sensor is improved. Therefore, by increasing the exhaust flow rate, a highly reliable sensor measurement value can be obtained, and thereby the collector failure can be accurately determined.

  Further, the control means may include a second increase means for increasing smoke discharged from the internal combustion engine.

  As a result, by increasing the smoke discharged from the internal combustion engine, it is possible to increase the amount of particulate matter flowing into the collector, so that the amount of soot that passes through increases and the measured value of the sensor becomes minute. By avoiding this, the reliability of the measured value of the sensor is improved. Therefore, by increasing the amount of smoke that is discharged, a highly reliable sensor measurement value can be obtained, whereby the collector failure can be accurately determined.

  The first increasing means includes an exhaust gas recirculation passage for recirculating exhaust gas from the exhaust passage to the intake air passage, an exhaust gas recirculation valve provided in the exhaust gas recirculation passage, and an intake valve provided in the intake passage. May comprise opening degree adjusting means for lowering the opening degree of the exhaust gas recirculation valve and raising the opening degree of the intake valve.

  Thus, the exhaust flow rate flowing into the collector can be reliably increased by lowering the opening degree of the exhaust gas recirculation valve and increasing the opening degree of the intake valve. Therefore, since the particulate matter flowing into the collector can be increased by increasing the exhaust flow rate, the amount of soot that passes through is also increased, and the measurement value of the sensor is avoided from becoming minute. Since the reliability of the measurement value is improved, the failure of the collector can be accurately determined using the measurement value of the highly reliable sensor.

  The second increasing means may include an injection adjusting means for adjusting at least one of a fuel injection pressure, a fuel injection amount, and a fuel injection timing in the internal combustion engine.

  As a result, the smoke discharged from the internal combustion engine can be reliably increased by adjusting at least one of the fuel injection pressure, the fuel injection amount, and the fuel injection timing in the internal combustion engine. Therefore, by increasing the smoke discharged from the internal combustion engine, the amount of particulate matter flowing into the collector can be increased, so the amount of soot that passes through increases and the measurement value of the sensor does not become minute. Is done. Therefore, it is possible to accurately determine the failure of the collector based on the measurement value of the highly reliable sensor.

  The exhaust emission control device for an internal combustion engine according to the second aspect of the present invention further comprises an estimation means for estimating the accumulation amount of particulate matter in the collector, and the discrimination means is an estimated value of the accumulation amount by the estimation means. When the value is smaller than a predetermined accumulation amount, it is determined whether or not the collector is out of order.

  Thus, in the exhaust gas purification apparatus for an internal combustion engine according to the second aspect of the present invention, the amount of particulate matter accumulated in the collector is estimated, and the collector fails when the estimated amount of accumulation is smaller than the predetermined amount of deposit. Therefore, when the amount of accumulated particulate matter is large, the accumulated particulate matter traps the particulate matter that newly flows into the collector. The amount of soot that passes through the collector even though the collector is broken can avoid the trouble that it is difficult to determine the failure of the collector. Therefore, a minute failure of the collector can be detected with high accuracy by utilizing a situation in which the amount of particulate matter deposited is small and the influence of the failure of the collector appears remarkably in the amount of soot passing through the collector.

  The determination means determines that the collector has failed when the measurement value of the amount of soot by the sensor is greater than a threshold value, and determines the threshold value based on the amount of particulate matter accumulated in the collector. Correction means for correcting may be provided.

  As a result, if the measurement value of the amount of soot by the sensor is larger than the threshold value, it is determined that the collector has failed, and the threshold value is corrected by the amount of particulate matter accumulated in the collector. This is not limited to the case where the particulate matter in the vessel is large, and can be applied to the case where the failure detection of the collector is performed for a small accumulation amount or an arbitrary accumulation amount. The failure of the collector can be detected with high accuracy by the threshold value appropriately adjusted according to the amount of particulate matter deposited in the collector.

  Further, there may be provided a discrimination execution means for executing the next fault discrimination by the discrimination means before the elapsed time or / and travel distance from the time of the previous fault discrimination by the discrimination means does not exceed a predetermined value. Good.

  As a result, the period from the previous determination of the collector failure to the next determination is not too long than the predetermined range, so the blank period during which the collector does not fail is too long. Therefore, it is possible to avoid the trouble that the collector failure cannot be detected quickly.

  Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 is a schematic diagram of Embodiment 1 of an exhaust gas purification apparatus 1 for an internal combustion engine according to the present invention. The example of the exhaust emission control device 1 shown in FIG. 1 is configured for a four-cylinder diesel engine 2 (hereinafter simply referred to as an engine), and includes an intake pipe 3, an exhaust pipe 4, and an EGR pipe 5. The engine 2 and the exhaust emission control device 1 may be mounted on an automobile.

  Air is supplied from the intake pipe 3 to the engine 2, and the exhaust is discharged to the exhaust pipe 5. The intake pipe 3 is equipped with an air flow meter 31 and an intake throttle 32. The intake air amount is measured by the air flow meter 31. The intake air amount is adjusted by increasing or decreasing the opening of the intake throttle 32.

  The engine 2 is equipped with an injector 21 to supply fuel into the cylinder. The engine 2 is equipped with an engine speed sensor 22 and measures the engine speed.

  Exhaust gas recirculation (EGR) for recirculating exhaust gas from the exhaust pipe 4 to the intake pipe 3 is performed by the EGR pipe 5. By exhaust gas recirculation, the combustion temperature in the engine 2 can be suppressed and the amount of NOx emissions can be reduced. The EGR pipe 5 is equipped with an EGR valve 51 to adjust the amount of exhaust gas recirculated.

  A DPF 6 is disposed in the middle of the exhaust pipe 5. Exhaust temperature sensors 61 and 62 are disposed on the inlet side and the outlet side of the DPF 6, respectively, and the exhaust temperature at each position is measured. Also provided is a differential pressure sensor 63 that measures a front-rear differential pressure (differential pressure, DPF differential pressure), which is a difference in exhaust pressure between the inlet side and the outlet side of the DPF 6.

  For example, the DPF 6 may have a structure in which the inlet side and the outlet side are alternately packed in a so-called honeycomb structure. The DPF 6 may be a DPF with an oxidation catalyst on which an oxidation catalyst is supported. The exhaust gas discharged during the operation of the engine 2 contains particulate matter (PM), and this PM is collected inside or on the surface of the DPF wall when the exhaust gas passes through the DPF wall having the above structure of the DPF 6. Is done.

  Every time the amount of PM deposited on the DPF 6 becomes sufficiently large, the deposited PM is removed by burning, and the DPF 6 is regenerated. As a method for regenerating the DPF 6, for example, post injection is performed from the injector 21 at a timing after the main injection. The unburned fuel sent to the DPF 6 by the post-injection is heated by the action of the oxidation catalyst supported on the DPF 6 to burn the PM deposited on the DPF 6.

  A soot sensor 64 is provided downstream of the DPF 6 in the exhaust pipe 4. The amount of PM that has passed through the DPF 6 without being collected by the DPF 6 is measured by the soot sensor 64. The amount of PM (PM amount) may be the amount of only soot (PM) in PM (soot amount). The PM amount or the soot amount may be the PM concentration or the soot concentration in the exhaust gas.

  The exhaust emission control device 1 includes an electronic control unit 7 (ECU: Electronic Control Unit). The ECU 7 is assumed to have a computer structure, and includes a CPU for performing various calculations, a RAM for its work area, a memory 71 for storing various types of information, and the like. The ECU 7 controls the fuel injection to the engine 2 by the injector 21 and the opening adjustment of the intake throttle 32 and the EGR valve 51. The measured values of the air flow meter 31, the engine speed sensor 22, the exhaust temperature sensors 61 and 62, the differential pressure sensor 63, and the soot sensor 64 are sent to the ECU 7.

  The ECU 7 also has a function of calculating a travel distance by obtaining information from a vehicle speed sensor 80 that measures the vehicle speed, for example. The ECU 7 includes a timer 72 and has a function of measuring elapsed time. It is assumed that the ECU 7 can display information on the display unit 81 and transmit the information to the driver.

  In the first embodiment, the failure detection (failure determination) process of the DPF 6 is executed under the above configuration. The processing procedure of the DPF failure detection process is shown in FIG. This will be described below. The procedure shown in FIG. 2 may be automatically processed by the ECU 7.

  First, in step S10, it is determined whether the exhaust gas flow rate or smoke concentration is equal to or higher than a predetermined value. Here, the smoke concentration is a concentration in the exhaust gas of smoke discharged from the engine 2. PM is included in the smoke. In FIG. 2, the predetermined values are indicated by A1 and A2. If the exhaust flow rate or smoke concentration is greater than or equal to the predetermined value (S10: YES), the ECU 7 proceeds to S40, and if both the exhaust flow rate and smoke concentration are less than the predetermined value (S10: NO), the process proceeds to S20.

  In S10, the process may proceed to S40 when either the exhaust flow rate or the smoke concentration is a predetermined value or more. In this case, the conditions for executing the DPF failure detection become gentler, which is suitable when it is desired to perform failure detection at a higher frequency. In S10, the process may proceed to S40 when both the exhaust flow rate and the smoke concentration are equal to or greater than a predetermined value. In this case, conditions for executing DPF failure detection become more severe, which is suitable when there is a strong demand for avoiding failure detection in a situation that is not suitable for failure detection. A method for calculating the exhaust flow rate will be described later. The smoke concentration discharged from the engine 2 is considered to be determined by the operating conditions (load, engine speed) of the engine 2.

  The functional relationship (map) from the operating condition of the engine 2 to the smoke concentration is stored in the memory 71 in advance, and the ECU 7 may acquire the smoke concentration from this map and the operating condition. Of the operating conditions, the load may be, for example, a command value for the fuel injection amount from the injector 21. The engine speed may be a value measured by the engine speed sensor 22.

  In general, when the exhaust flow rate and smoke concentration are too small, the measured value of the soot sensor described later is too small to detect the failure of the DPF 6 with high accuracy. The determination in S10 is a procedure for avoiding this. When the exhaust gas flow rate and smoke concentration are too small, the process proceeds to S30 described later, and processing for increasing the amount of PM flowing into the DPF 6 is performed.

  Next, in S20, it is determined whether the elapsed time or the travel distance from the previous DPF 6 failure determination process is greater than or equal to a predetermined value. In FIG. 2, the predetermined values are indicated by A3 and A4. When the elapsed time or travel distance from the previous DPF 6 failure determination process is equal to or greater than a predetermined value (S20: YES), the ECU 7 proceeds to S30, and when it is less than the predetermined value (S20: NO), the process of FIG. . The elapsed time from the previous DPF 6 failure determination process may be measured by the timer 72. The travel distance from the previous failure determination process of the DPF 6 may be calculated by the ECU 7 from the measured value of the vehicle speed sensor 80.

  S20 is a process for the purpose of surely proceeding to the failure determination (in S70 described later) if the elapsed time or travel distance from the previous failure detection is equal to or greater than a predetermined value. Therefore, if the process of FIG. 2 is executed every certain period, the elapsed time and travel distance from the previous failure determination to the next failure determination can always be within a predetermined value. The predetermined value here may be a value obtained by adding A3 or A4 to a value determined from the above period. As a result, it is possible to quickly detect a failure when the failure occurs without leaving the failure and leaving the PM outside the vehicle.

  In S20, the process may proceed to S30 when either the elapsed time from the previous DPF 6 failure determination process or the travel distance is greater than or equal to a predetermined value. In this case, the conditions for executing the DPF failure detection become gentler, which is preferable when it is not desired to extend the blank period for failure detection. In S20, the process may proceed to S30 when both the elapsed time from the previous DPF 6 failure determination process and the travel distance are equal to or greater than a predetermined value. In this case, the conditions for executing the DPF failure detection become more severe, which is suitable when it is desired to avoid unnecessary failure detection.

  Next, in S30, the ECU 7 executes a process for increasing the amount of PM flowing into the DPF 6. A method for increasing the amount of PM flowing into the DPF 6 is as follows. As one method, there is a method of increasing the exhaust flow rate flowing into the DPF 6. The exhaust flow rate may be the exhaust flow rate per unit time.

  FIG. 4 shows the relationship between the exhaust flow rate that flows into the DPF 6 and the PM amount that passes through the DPF 6. As the exhaust flow rate flowing into the DPF 6 increases as shown in the figure, more PM tends to pass through the DPF 6 without being collected by the DPF 6. Therefore, by utilizing this tendency, in S30, the amount of PM passing through the DPF 6 is increased by increasing the exhaust flow rate flowing into the DPF 6. As a method of increasing the exhaust flow rate flowing into the DPF 6, for example, the opening degree of the EGR valve 51 may be lowered and the opening degree of the intake throttle 32 may be raised.

  Another method for increasing the amount of PM flowing into the DPF 6 at S30 is to increase the smoke concentration in the exhaust discharged from the engine 2. FIG. 5 shows the relationship between the smoke concentration of the exhaust gas flowing into the DPF 6 and the amount of PM that passes through the DPF 6. As the smoke concentration in the exhaust gas flowing into the DPF 6 increases, the amount of PM flowing into the DPF 6 increases, so that the amount of PM that passes through the DPF 6 also increases.

  Therefore, using this tendency, in S30, the amount of PM passing through the DPF 6 may be increased by increasing the smoke concentration in the exhaust gas flowing into the DPF 6. A method of increasing the smoke concentration in the exhaust gas flowing into the DPF 6 is, for example, adjusting the fuel injection pressure, the injection amount, and the injection timing from the injector 21 by the ECU 7 so that the smoke concentration increases. What kind of value the smoke concentration will have depending on what injection pressure, injection amount, and injection timing is stored in advance in the memory 71 as a map and can be used. After S30 ends, the ECU 7 proceeds to S40.

  Next, in S40, the ECU 7 measures the amount of soot that has passed through the DPF 6. This may be measured by the soot sensor 64. In S50, the ECU 7 estimates the amount of PM accumulated in the DPF 6. A method for estimating the amount of accumulated PM in the DPF 6 will be described later.

  Next, in S60, the ECU 7 calculates a threshold value (failure determination threshold value) used in the failure determination of the DPF 6 in S70 described later. The method for calculating the threshold is shown in FIG. FIG. 6 is a diagram showing the PM accumulation amount in the DPF 6 and the PM amount passing through the DPF 6 on the horizontal axis and the vertical axis, respectively. In FIG. 6, the solid line shows the relationship between the PM accumulation amount when the DPF 6 has not failed and the PM amount passing through the DPF 6.

  The solid line in FIG. 6 may be an actual measurement value obtained in advance by experiments or the like for the DPF 6 actually used in the configuration of FIG. As shown in FIG. 6, the smaller the amount of accumulated PM in the DPF 6, the lower the collection rate of the DPF 6, and the more the amount of PM that passes through the DPF 6 tends to increase. A value obtained by adding a predetermined amount to this solid line is indicated by a broken line. In S60, the threshold value may be calculated from the broken line.

  That is, in S60, the value on the vertical axis when the PM accumulation amount obtained in S50 is taken on the horizontal axis in the broken line in FIG. 6 is calculated as the threshold value. Since the threshold value is calculated by the broken line in FIG. 6, an appropriate threshold value can be set according to the PM accumulation amount. The characteristics shown in FIG. 6 may be stored in the memory 71 in advance.

  Note that FIG. 6 may be a diagram in which the amount of PM flowing into the DPF 6 per unit time or the exhaust flow rate is constant. Then, FIG. 6 may be three-dimensionally changed and used in S60 as follows. That is, the solid line in FIG. 6 is changed to a functional relationship (map) from the amount of PM flowing into the DPF 6 per unit time or the exhaust flow rate value and the amount of PM accumulated in the DPF 6 to the amount of PM passing through the DPF 6. For example, the exhaust flow rate and smoke concentration are obtained in the same manner as in S10, and the PM amount flowing into the DPF 6 per unit time is calculated from these two. Further, as described above, the PM accumulation amount in the DPF 6 is estimated in S50. The PM amount that passes through the DPF 6 is obtained from these numerical values and the three-dimensional map, and a value added by a predetermined value is calculated as a threshold value in S60.

  Note that the amount of PM that passes through the DPF 6 may mean the PM concentration in the exhaust gas that passes through the DPF 6. Further, the amount of PM flowing into the DPF 6 per unit time may be an indexed value when the reference value is 1, for example.

  Next, in S70, the ECU 7 determines whether or not the DPF 6 has failed. In the failure determination, the soot sensor measurement value obtained in S40 and the threshold value calculated in S60 are used. If the soot sensor measurement value is equal to or greater than the threshold value (S70: YES), the process proceeds to S80, and if the soot sensor measurement value is less than the threshold value (S70: NO), the process proceeds to S90.

  When the routine proceeds to S80, that is, when the soot sensor measurement value is equal to or greater than the threshold value, the ECU 7 determines that the DPF 6 has failed because the soot amount that has passed through the DPF 6 is too large. When the routine proceeds to S90, that is, when the soot sensor measurement value is smaller than the threshold value, the ECU 7 determines that the DPF 6 has not failed.

  After S80 ends, the ECU 7 proceeds to S100. In S100, in response to the determination result of the failure in S80, the ECU 7 displays on the driver that the DPF 6 has failed by the display unit 81. As a result, the driver can acquire information on the failure, so that the driver can quickly move to a procedure such as repair of the DPF 6. The above is the processing procedure of FIG.

  FIG. 3 shows a processing procedure of the failure detection (failure determination) processing of the DPF 6 in the second embodiment. This will be described below. In the second embodiment, when the PM accumulation amount in the DPF 6 is equal to or less than a predetermined value, the PM amount flowing into the DPF 6 is increased, and then the failure detection of the DPF 6 using the soot sensor 64 is executed. Thereby, as described above, the failure of the DPF 6 can be detected with high accuracy. The procedure of FIG. 3 may be automatically processed by the ECU 7. The apparatus configuration in the second embodiment may be the same as in FIG.

  First, in step S110, the ECU 7 estimates the PM accumulation amount in the DPF 6. A method for estimating the PM accumulation amount in the DPF 6 will be described later. Next, in S120, the ECU 7 determines whether or not the PM accumulation amount is a predetermined value or less. In FIG. 3, this predetermined value is indicated by A5. When the PM accumulation amount is equal to or less than the predetermined value (S120: YES), the ECU 7 proceeds to S130, and when the PM accumulation amount is larger than the predetermined value (S120: NO), the processing of FIG.

  In S130, the ECU 7 executes a process for increasing the amount of PM flowing into the DPF 6. The process in S130 may be performed in the same manner as S30 described above. In the next S140, the ECU 7 acquires the measured value of the soot sensor 64. Further, in S150, the ECU 7 calculates a threshold value used in determining the failure of the DPF 6. The threshold value calculation in S150 may be performed in the same manner as the threshold value calculation in S60 of FIG.

  Next, in S160, the ECU 7 determines whether or not the DPF 6 has failed. In the failure determination, the soot sensor measurement value obtained in S140 and the threshold value calculated in S150 are used. If the soot sensor measurement value is greater than or equal to the threshold value (S160: YES), the process proceeds to S170, and if the soot sensor measurement value is less than the threshold value (S160: NO), the process proceeds to S180.

  When the routine proceeds to S170, that is, when the soot sensor measurement value is equal to or greater than the threshold value, the ECU 7 determines that the DPF 6 has failed because the soot amount that has passed through the DPF 6 is too large. When the routine proceeds to S180, that is, when the soot sensor measurement value is smaller than the threshold value, the ECU 7 determines that the DPF 6 has not failed.

  After S170 ends, the ECU 7 proceeds to S190. In S190, in response to the determination result of the failure in S170, the ECU 7 displays on the driver that the DPF 6 has failed by the display unit 81. As a result, the driver can acquire information on the failure, so that the driver can quickly move to a procedure such as repair of the DPF 6. The above is the processing procedure of FIG.

  Hereinafter, a method for estimating the PM deposition amount of the DPF 6 executed in S50 of FIG. 2 and S110 of FIG. 3 will be described. The relationship between the PM deposition amount and the DPF differential pressure is generally the relationship shown in FIG. 7 (or approximated). That is, as the PM accumulation on the DPF proceeds as the internal combustion engine continues to operate, the point indicating the PM accumulation amount and the DPF differential pressure moves from the initial point 100 to the upper right in the figure on the first characteristic line 110 (characteristic line). When the transition point 120 is further reached, the second characteristic line 130 (characteristic line) is moved to the upper right in the figure.

  The first characteristic line 110 corresponds to a stage where PM accumulates in the pores of the filter wall of the DPF, and the second characteristic line 130 corresponds to a stage where PM accumulates on the wall surface of the filter wall. When PM is accumulated in the wall of the filter wall, the degree of newly narrowing the exhaust gas flow path is greater than when PM is accumulated on the wall surface, thereby increasing the differential pressure value. The slope is larger than the characteristic line 130 as shown in the figure. Here, the slope is the ratio between the increase in the DPF differential pressure and the increase in the PM deposition amount.

  If it is determined that the PM accumulation amount is excessive when the point 140 is reached and DPF regeneration is started, the subsequent PM accumulation amount and the DPF differential pressure change as indicated by the broken line in FIG. That is, the PM accumulation amount and the DPF differential pressure value first decrease along the broken line 150, and after the transition point 160, decrease along the broken line 170 and return to the initial point 100.

  A broken line 150 is a stage where PM deposited in the pores of the filter wall is burning, and therefore, the broken line 150 has the same inclination as the first characteristic line 110. The broken line 170 is a stage where PM deposited on the wall surface of the filter wall is burning. Therefore, the broken line 170 has the same inclination as the second characteristic line 130. As described above, the values of the PM deposition amount and the DPF differential pressure during PM deposition and PM combustion change according to the characteristics of the parallelogram shown in FIG. 7 (or approximate to the parallelogram). The characteristics shown in FIG. 7 may be obtained in advance and stored in the memory 71, and the PM deposition amount may be obtained from the measured DPF differential pressure value.

Next, a method for calculating the flow rate of the exhaust gas (exhaust gas) used in S10 of FIG. 2 will be described. Here, the flow rate may be a volume flow rate per unit time. The mass flow rate per unit time of intake air measured by the air flow meter 31 is converted into the exhaust gas volume flow rate. The calculation of the volume flow rate of the exhaust gas is performed according to the following equation (E1) (when the downstream of the DPF is atmospheric pressure). V (m ³ / sec) is a volume flow rate per unit time of exhaust gas, G (g / sec) is a mass flow rate per unit time of intake air, Tdpf (K) is a DPF temperature, and P0 (kPa) is an atmospheric pressure. , ΔP (kPa) indicates the DPF differential pressure, and Q (cc / sec) indicates the fuel injection amount per unit time.
V (m ³ / sec)
= [G (g / sec) /28.8 (g / mol)]
× 22.4 × 10 ⁻³ (m ³ / mol)
× [Tdpf (K) / 273 (K)]
× [P0 (kPa) / (P0 (kPa) + ΔP (kPa))]
+ Q (cc / sec) /207.3 (g / mol)
× 0.84 (g / cc) × 6.75
× 22.4 × 10 ⁻³ (m ³ / mol)
× [P0 (kPa) / (P0 (kPa) + ΔP (kPa))] (E1)

The first term on the right side of the equation (E1) is obtained by converting the mass flow rate of the intake air into the volume flow rate, and the second term is an increase from the intake air to the exhaust gas due to the combustion of the injected fuel. In the second term, 0.84 (g / cc) is a typical liquid density of light oil. 22.4 × 10 ⁻³ (m ³ / mol) is a volume per 1 mol of an ideal gas at 0 degree Celsius and 1 atmosphere (atm). 6.75 is an increase rate of the number of moles of exhaust gas with respect to the fuel injection amount 1 (mol).

The increase rate (6.75) is obtained as follows. The composition of light oil is typically represented as C ₁₅ H _27.3 (molecular weight 207.3), and combustion is represented by the following reaction formula (E2). Therefore, the number of moles of exhaust gas is 6.75 (= (15 + 13.5) -21.75) times the fuel injection amount 1 (mol).
C ₁₅ H _27.3 +21.75 O ₂ → ₁₅ CO ₂ + 13.5H ₂ O (E2)

  Further, the fuel is injected only at a predetermined injection timing determined by the ECU 7, and becomes intermittent injection. The fuel injection amount Q in the formula (E1) is an average fuel injection amount including the non-injection period.

  The mass flow rate G (g / sec) per unit time of intake may be measured by the air flow meter 31. The DPF temperature Tdpf (K) may be measured by the exhaust temperature sensors 61 and 62. The differential pressure ΔP (kPa) before and after the DPF may be measured by the differential pressure sensor 63. As the fuel injection amount Q (cc / sec) per unit time, a command value of the injection amount to the injector 21 by the ECU 7 may be used.

  The DPF temperature Tdpf (K) may be a measured value of either the exhaust temperature sensor 61 or 62, or may be an average value of both measured values. In addition, a model for estimating the internal temperature of the DPF 6 from one of the exhaust temperature sensors 61 and 62 or the measured values of both the sensors 61 and 62 is obtained in advance and stored in the memory 71, and the DPF temperature Tdpf (K) is stored using this model. May be estimated. The above is the method for calculating the exhaust gas flow velocity.

  In the above embodiment, the procedure of S30 and the ECU 7 constitute the control means. The procedure of S70 and the ECU 7 constitute the determining means. The procedure of S30, the ECU 7, and the EGR valve 51 constitute first increasing means and opening degree adjusting means. The procedure of S30, the ECU 7, and the injector 21 constitute second increasing means and injection adjusting means. The procedures of S50 and S110 and the ECU 7 constitute an estimation means. The procedures of S60 and S150 and the ECU 7 constitute a threshold setting means. The procedure of S20 and the ECU 7 constitute a discrimination execution means. In the above embodiment, the same effect as described above can be obtained even if the engine 2 is a lean burn gasoline engine instead of a diesel engine.

1 is a schematic configuration diagram of an exhaust emission control device for an internal combustion engine in an embodiment of the present invention. The flowchart which shows the process sequence of DPF failure determination. The flowchart which shows the process sequence of DPF failure determination. The figure which shows the relationship between PM amount which passes through DPF, and the exhaust gas flow volume which flows in into DPF. The figure which shows the relationship between the amount of PM which slips through DPF, and the density | concentration of the smoke which flows in into DPF. The figure which shows the relationship between the amount of PM which passes through DPF, and the amount of PM deposits in DPF, and the setting of a threshold value. The figure which shows the relationship between DPF differential pressure | voltage and PM deposition amount.

Explanation of symbols

1 Exhaust purification device 2 Diesel engine (engine, internal combustion engine)
3 Intake pipe 4 Exhaust pipe (exhaust passage)
5 Exhaust gas recirculation pipe (exhaust gas recirculation passage)
6 Diesel particulate filter (DPF, collector)
10 Electronic control unit (ECU)
21 Injector 31 Air flow meter 32 Intake throttle (intake valve)
51 EGR valve (exhaust gas recirculation valve)
61, 62 Exhaust temperature sensor 63 Differential pressure sensor 64 Soot sensor (sensor)
71 memory

Claims (8)

A collector disposed in the exhaust passage for collecting particulate matter;
A sensor that is disposed downstream of the exhaust passage from the collector and measures the amount of particulate matter soot;
Control means for increasing particulate matter flowing into the collector;
Discriminating means for increasing particulate matter flowing into the collector by the control means, and discriminating whether or not the collector is faulty from the measurement value of the amount of soot by the sensor;
An exhaust emission control device for an internal combustion engine, comprising:   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control means includes first increasing means for increasing an exhaust flow rate flowing into the collector. 3.   3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control means includes second increase means for increasing smoke discharged from the internal combustion engine. An exhaust gas recirculation passage through which exhaust gas is recirculated from the exhaust passage to the intake passage;
An exhaust gas recirculation valve provided in the exhaust gas recirculation passage;
An intake valve provided in the intake passage,
3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the first increasing means includes opening degree adjusting means for lowering an opening degree of the exhaust gas recirculation valve and increasing an opening degree of the intake valve.   The exhaust purification device for an internal combustion engine according to claim 3, wherein the second increasing means includes an injection adjusting means for adjusting at least one of a fuel injection pressure, a fuel injection amount, and a fuel injection timing in the internal combustion engine. Comprising estimation means for estimating the amount of particulate matter deposited in the collector;
The exhaust gas purifying apparatus for an internal combustion engine, wherein the discriminating unit discriminates whether or not the collector is malfunctioning when an estimated value of the accumulation amount by the estimating unit is smaller than a predetermined accumulation amount. The discriminating unit discriminates that the collector is out of order when the measured value of the amount of soot by the sensor is larger than a threshold value,
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 6, further comprising a threshold value setting unit configured to set the threshold value according to an accumulation amount of particulate matter in the collector.   2. A determination execution means for executing determination of the next failure by the determination means before the elapsed time or / and travel distance from the time of determination of the previous failure by the determination means does not exceed a predetermined value. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 7.

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