JP2009270503A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of accurately estimating an ash deposit quantity after finishing complete regeneration of a DPF (diesel particulate filter). <P>SOLUTION: Regeneration operation is performed up to the time t2 while erecting a regeneration performing flag as it is even after the time t1 when the complete regeneration of the DPF is finished. DPF differential pressure is measured up to t2 from the tine t1, and the ash deposit quantity in the DPF is estimated from a differential pressure value, and a characteristic between longitudinal differential pressure and a PN despot quantity in the DPF is corrected based on an estimate value. Since the regeneration operation is continued up to t2 from the tine t1, an exhaust flow rate is sufficient, and a DPF differential pressure value is improved in accuracy without reducing. Since the regeneration operation is further continued up to t2 from the time t1, PM is not deposited again, and the DPF differential pressure value is not influenced by redeposit of the PM. Thus, the ash deposit quantity can be accurately calculated from the DPF differential pressure value up to t2 from the time t1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  Today, with increasing awareness of environmental protection, excellent exhaust purification performance is required for internal combustion engines. In particular, in diesel engines, 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.

  Most of the PM in the exhaust gas is removed by the DPF collecting the PM. However, while the PM continues to accumulate in the DPF, the DPF is clogged, so the amount of accumulated PM increases. Then, it is necessary to regenerate the DPF by burning and removing the accumulated PM. In order to burn the PM accumulated in the DPF, a method such as post injection after main injection in the cylinder is employed.

  Since fuel is consumed to regenerate the DPF, frequent DPF regeneration leads to deterioration of fuel consumption. On the other hand, if the number of times of DPF regeneration is too small, the amount of deposition becomes excessive, and the temperature rises during the regeneration process, which may damage the DPF. Therefore, DPF regeneration must be performed at an appropriate time. Therefore, it is necessary to develop a system for estimating the amount of PM deposited in the DPF as accurately as possible by some method.

  There is a method of using the characteristics shown in FIG. FIG. 5 is a characteristic between the PM deposition amount and the DPF differential pressure. The point indicating the PM deposition amount and the DPF differential pressure rises from the initial point 100 through the characteristic lines 110 and 130 during PM deposition, and returns to the initial point 100 through dashed lines 150 and 170 during PM combustion. The differential pressure across the DPF is measured, and the PM deposition amount is estimated from the measured value and the characteristics shown in FIG.

  However, the characteristics of FIG. 5 need to be corrected in consideration of ash accumulation on the DPF. Ash is mainly oxidized metal components in engine oil. As the ash is deposited on the DPF, the characteristics shown in FIG. 5 are changed as shown in FIG. . In FIG. 6, only characteristic lines 110 and 130 are shown. As shown in FIG. 6, as the ash accumulates on the DPF, the value of the DPF differential pressure is increased. Further, as the ash deposition amount increases, the effective filtration area decreases and the PM deposition layer in the DPF becomes thicker earlier, so that the slope of the characteristic line in FIG. 6 tends to increase.

  In order to accurately estimate the PM accumulation amount, it is necessary to accurately obtain the ash accumulation amount. In the prior art, as an estimation of the ash accumulation amount, there is a method of measuring the DPF differential pressure after completing the complete regeneration of the DPF, that is, regenerating the DPF until the PM accumulation amount becomes zero. This is because it can be considered that there is no PM accumulation after the completion of the complete regeneration of the DPF, and therefore, it is considered that the differential pressure value of the DPF correlates with the ash accumulation amount. For example, Patent Document 1 below discloses a technique for estimating the amount of accumulated ash each time complete regeneration ends.

JP 2004-21650 A

  However, in the method of Patent Document 1, immediately after the completion of the DPF complete regeneration, the temperature of the exhaust gas is lowered and the volume of the exhaust gas is reduced, so that the volume flow rate of the exhaust gas is reduced. When the volume flow rate of the exhaust gas decreases, the differential pressure value across the DPF decreases. In general, variation is observed in the DPF differential pressure value, so that the front-rear differential pressure value of the DPF becomes smaller means that the variation in the front-rear differential pressure measurement value or the specific gravity occupied by the error increases. Therefore, the reliability of the DPF differential pressure measurement value may be low immediately after the completion of the DPF complete regeneration.

  In addition, immediately after the completion of DPF complete regeneration, the operating conditions such as sudden acceleration and sudden deceleration may change rapidly. Since the exhaust gas flow rate fluctuates greatly even when the operating conditions fluctuate rapidly, the reliability of the DPF differential pressure value is low. Therefore, the reliability of the ash deposition amount estimated using the DPF differential pressure value is low even when the operating conditions fluctuate immediately after the complete regeneration of the DPF.

  Thus, the DPF differential pressure value after completion of DPF complete regeneration, and the ash deposition amount estimated using the DPF may be low in reliability. However, in order to avoid such problems, DPF differential pressure measurement is performed after complete regeneration completes. Another problem arises when waiting for the reliability of the value to recover. That is, PM accumulates again as time elapses from the end of DPF regeneration. Therefore, the DPF differential pressure value is affected by the redeposition of PM. Therefore, the accuracy of the ash accumulation amount estimated from the DPF differential pressure value is reduced.

  The avoidance of such problems that occur when the DPF differential pressure is measured and the ash deposition amount is estimated immediately after the completion of the complete regeneration of the DPF is not taken into consideration in the prior art including the above-mentioned Patent Document 1.

  Therefore, in view of the above problems, the problem to be solved by the present invention is to measure the DPF differential pressure after completion of the DPF complete regeneration, estimate the ash accumulation amount, and correct the characteristics of the DPF differential pressure and the PM accumulation amount. It is an object of the present invention to provide an exhaust gas purification apparatus for an internal combustion engine that can avoid the problem that the ash deposition amount cannot be accurately estimated when the DPF differential pressure cannot be measured quickly after the DPF complete regeneration is completed.

Means for Solving the Problems and Effects of the Invention

  In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a collector arranged in the middle of an exhaust passage for collecting particulate matter, and deposition of particulate matter in the collector An estimation means for estimating the amount, and when the estimated value of the accumulation amount by the estimation means is greater than a first predetermined value, the particulate matter deposited on the collector is burned to regenerate the collector. A regenerating means, a recognizing means for recognizing that the accumulated amount of the particulate matter in the collector is equal to or less than a second predetermined value by regenerating by the regenerating means, and the complete regenerating by the determining means. A regeneration operation extending means for extending the regeneration operation after being determined to be in a state, and information indicating a degree of ash accumulation in the collector while the regeneration operation is being extended by the regeneration operation extending means. Obtaining means Tokusuru, the information acquired by the acquisition unit, characterized by comprising a correction means for correcting the estimation method according to the estimating means.

  Thus, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the regeneration operation is extended after the complete regeneration of the collector, and information indicating the degree of accumulation of ash, which is an incombustible substance, on the collector is acquired during that time. Since the method for estimating the amount of particulate matter accumulated is corrected based on this, it is possible to prevent particulate matter from re-depositing on the collector while the degree of ash accumulation is being investigated. Is kept in a state where only ash is accumulated. Therefore, it is avoided that the accuracy of the information on the degree of ash deposition is deteriorated due to the redeposition of the particulate matter. Accumulated amount of particulate matter can be estimated. Then, the amount of particulate matter deposited on the collector is estimated based on the estimated value, and the collector is regenerated when it exceeds a predetermined value. Therefore, the collector can be regenerated at a more appropriate timing. it can. Therefore, the true value of the accumulation amount is less than the estimated value and regeneration is too frequent, resulting in poor fuel consumption. It is possible to realize an exhaust emission control device capable of avoiding damage to the vessel.

  Also, a measuring means for measuring the differential pressure across the collector, and a storage means for storing characteristics between the differential pressure across the collector and the amount of particulate matter deposited in the collector, The estimating means estimates the amount of particulate matter deposited in the collector from the value of the differential pressure before and after measured by the measuring means and the characteristics stored in the storage means, and the acquiring means The value of the differential pressure measured by the measuring means while the regeneration operation of the collector is extended by the regeneration operation extending means is acquired, and the correcting means is the information acquired by the acquiring means. The characteristic stored in the storage means may be corrected by the above.

  As a result, the amount of particulate matter deposited is estimated using the measured value of the differential pressure across the collector and the characteristics between the differential pressure before and after and the amount of particulate matter deposited. Since the same characteristic is corrected by the differential pressure across the collector measured while the regenerative operation of the vessel is extended, it does not include the effects of particulate matter redeposition, so it accurately indicates the degree of ash deposition. The characteristic between the front-rear differential pressure and the particulate matter deposition amount can be appropriately corrected by the value of the front-rear differential pressure as information. Therefore, since the amount of particulate matter deposited is estimated using appropriately corrected characteristics, the collector can be regenerated at an appropriate timing. Therefore, it can be avoided that the regeneration is too frequent and the fuel consumption is deteriorated, and that the true accumulation amount is excessive and the temperature rises during the regeneration and the collector is damaged.

  Further, the ash accumulation amount for estimating the ash accumulation amount in the collector based on the value of the differential pressure measured by the measuring means while the regeneration operation of the collector is extended by the regeneration operation extending means. An estimation means may be provided, and the acquisition means may acquire the ash accumulation amount estimated by the ash accumulation amount estimation means.

  As a result, the amount of ash deposited in the collector is calculated from the differential pressure across the collector measured while the regeneration operation of the collector is extended in the complete regeneration state. Since the effect of particulate matter redeposition is not included, the degree of ash accumulation can be accurately indicated, and the amount of ash accumulation can be accurately calculated from the differential pressure value before and after. And, since the characteristics between the differential pressure before and after the collector and the particulate matter accumulation amount are corrected appropriately using the accurate ash accumulation amount, the particulate matter is accurately detected using the appropriately corrected property. The amount of deposition can be estimated, and the collector can be regenerated at an appropriate timing. Therefore, it can be avoided that the regeneration is too frequent and the fuel consumption is deteriorated, and that the true accumulation amount is excessive and the temperature rises during the regeneration and the collector is damaged.

  Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 is a schematic view of an embodiment 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.

  Air is supplied from the intake pipe 3 to the engine 2, and the exhaust is discharged to the exhaust pipe 4. The intake pipe 3 is equipped with an air flow meter 31. The intake air amount is measured by the air flow meter 31. The engine 2 is equipped with an injector 21 to supply fuel into the cylinder.

  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.

  A DPF 6 is disposed in the middle of the exhaust pipe 4. An oxidation catalyst is supported on the DPF 6 and may be a so-called DPF with an oxidation catalyst. 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.

  The exhaust emission control device 1 includes an electronic control unit 7 (ECU: Electronic Control Unit). The ECU 7 has a structure having a CPU for performing various calculations, a RAM for its work area, a memory 71 for storing various information, and the like. The ECU 7 controls fuel injection to the engine 2 by the injector 21 and adjustment of the opening of an intake throttle (not shown). The measured values of the air flow meter 31, the exhaust temperature sensors 61 and 62, and the differential pressure sensor 63 are sent to the ECU 7. The ECU 7 includes a timer 72 and can measure time.

  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 13 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.

  In the present embodiment, the characteristics of the PM deposition amount and the DPF front-rear differential pressure (DPF differential pressure, front-rear differential pressure, differential pressure) are stored in the memory 71 under the above configuration, and the same characteristics and the DPF differential pressure are stored. The PM deposition amount is estimated from the measured value. When the estimated value of the PM accumulation amount exceeds a predetermined value, the DPF 6 is regenerated. Each time the regeneration process of the DPF 6 is completed as a complete regeneration, the amount of ash accumulated in the DPF 6 is estimated. Then, the characteristic line between the DPF differential pressure and the PM accumulation amount is corrected according to the estimated value of the ash accumulation amount. Details will be described below.

  As described above, the relationship between the PM deposition amount and the DPF differential pressure is generally the relationship shown in FIG. 5 (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. The slope is the ratio between the increase in the DPF differential pressure and the increase in the PM deposition amount.

  If the PM accumulation amount is determined to be a predetermined value 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 PM deposition amount and the DPF differential pressure during PM deposition and PM combustion change according to the parallelogram (or approximate) characteristics shown in FIG. The characteristics shown in FIG. 5 are obtained in advance and stored in the memory 71.

  Next, regeneration of the DPF 6 and correction processing of the characteristic lines 110 and 130 in the present invention will be described. The procedure is shown in FIG. The procedure shown in FIG. 2 may be automatically executed by the ECU 7.

  First, in step S10, the ECU 7 estimates the amount of PM accumulated in the DPF 6. The PM accumulation amount may be estimated by measuring the differential pressure across the DPF 6 and calling the above-described characteristic of FIG. 5 from the memory 71 to obtain the PM accumulation amount at the differential pressure measurement value on the characteristic line 110 or 130. . The differential pressure across the DPF 6 may be measured by the differential pressure sensor 63.

  Next, in S20, the ECU 7 determines whether or not the PM accumulation amount estimated in S10 is greater than or equal to a predetermined value (first predetermined value). In FIG. 2, this predetermined value (first predetermined value) is indicated by M1. The ECU 7 proceeds to S30 when the PM accumulation amount is equal to or greater than the predetermined value (S20: Yes), and returns to S10 again when the PM accumulation amount is less than the predetermined value (S20: No). repeat.

  When the process proceeds to S30, the PM accumulation amount is considered to be sufficiently large. Therefore, in S30, the ECU 7 performs regeneration of the DPF 6. As a method for regenerating the DPF 6, for example, post injection may be executed as described above.

  In S40, the ECU 7 estimates the PM accumulation amount in the DPF 6. The estimation of the PM deposition amount in S40 is an estimation during regeneration of the DPF 6. (On the other hand, the estimation of the PM deposition amount in S10 is not during regeneration of the DPF 6.) That is, the decrease state of the PM accumulation amount during regeneration of the DPF 6 can be grasped by S40. The estimation of the PM accumulation amount in S40 may be performed by measuring the differential pressure across the DPF 6 and calling the characteristics shown in FIG. 5 from the memory 71 to obtain the PM accumulation amount at the differential pressure measurement value at the broken line 150 or 170. . The differential pressure across the DPF 6 may be measured by the differential pressure sensor 63.

  Alternatively, in S40, a map showing the relationship between the internal temperature of the DPF 6 and the combustion amount per unit time of the accumulated PM at that temperature is stored in the memory 71 in advance, and the DPF is calculated from the map and the internal temperature history of the DPF 6. The amount of accumulated PM during regeneration may be estimated. In this case, the internal temperature of the DPF 6 may be a measured value of either the exhaust temperature sensor 61 or 62, or may be an average value of both measured values. Also, 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 sensors is obtained in advance and stored in the memory 71, and the internal temperature of the DPF is estimated using this model. Also good. Further, the estimation of the PM deposition amount in S40 may be a combination of the above two methods.

  In S50, the ECU 7 determines whether or not the PM accumulation amount estimated in S40 is equal to or less than a predetermined value (second predetermined value). In FIG. 2, this predetermined value (second predetermined value) is indicated by M2. The ECU 7 proceeds to S60 when the PM accumulation amount is equal to or smaller than the predetermined value (S50: Yes), and returns to S40 again when it is larger than the predetermined value (S50: No), until the PM accumulation amount becomes equal to or smaller than the predetermined value. Repeat the procedure. Hereinafter, a case where M2 is set to a minute value in consideration of, for example, 0 or the presence of an error will be described. That is, this is a case where the regeneration of the DPF 6 executed in S30 is completed as complete regeneration.

  When the process proceeds to S60, it can be considered that the PM accumulation amount is zero or the error range is reached by the complete regeneration of the DPF 6. Therefore, as will be described below, the regeneration operation is extended for a predetermined time, during which the ash accumulation amount is estimated and the characteristics of FIG. 5 are corrected. Here, the regeneration operation refers to an operation at the time of regeneration of the DPF 6 by S30, and post injection is performed.

  First, in S60, the ECU 7 decides to extend the regeneration operation and starts the timer 72. Thereby, the elapsed time after the completion of the complete reproduction is measured. Next, in S70, the ECU 7 determines whether or not the elapsed time is within a predetermined time. Here, the elapsed time is the elapsed time since the timer 72 was started in S60. That is, the elapsed time after the complete regeneration of the DPF 6 is completed. In FIG. 2, the predetermined time is indicated by T1.

  For example, the predetermined time should be secured for at least about 5 seconds, wait for the differential pressure detection condition shown below to be satisfied, and be less than about 1 minute at the longest, and the regeneration operation extension may be too long, resulting in deterioration of fuel consumption. It is preferable to avoid this. If the elapsed time is within the predetermined time (S70: Yes), the ECU 7 proceeds to S80, and if the predetermined time has passed (S70: No), the ECU 7 proceeds to S120.

  Next, in S80, the ECU 7 determines whether a condition suitable for detecting the DPF differential pressure is satisfied. If the condition suitable for detecting the DPF differential pressure is satisfied (S80: Yes), the ECU 7 proceeds to S90, and if the condition suitable for detecting the DPF differential pressure is not satisfied (S80: No) returns to S70 again and repeats the above procedure.

  As described above, generally, if the exhaust gas flow rate (exhaust flow rate) is too small, the differential pressure of the DPF 6 cannot be detected with high accuracy. Further, even when the exhaust flow rate changes greatly during sudden acceleration or sudden deceleration, the differential pressure of the DPF 6 cannot be detected with high accuracy. Therefore, the condition suitable for detecting the DPF differential pressure in S80 is, for example, that the exhaust flow rate is equal to or higher than a predetermined flow rate and that the operating condition of the engine 2 can be regarded as close to a steady state. Therefore, in S80, for example, the flow rate of the exhaust gas is calculated, and it is determined that the flow rate value is larger than a predetermined threshold value and that the exhaust gas flow rate value in the past predetermined time is within a predetermined range. . A method for calculating the exhaust gas flow rate will be described later.

  Next, in S90, the ECU 7 detects the differential pressure of the DPF 6. This may be measured by the differential pressure sensor 63. The detection of the differential pressure of the DPF 6 in S90 is performed, for example, a plurality of times, and the average value is calculated, so that the influence of the variation in the measured value can be suppressed. Next, in S100, the ECU 7 calculates the flow rate of the exhaust gas. This calculation method will be described later.

  In S110, the ECU 7 calculates the amount of ash accumulated in the DPF 6. This calculation is performed using the map of FIG. FIG. 3 shows the relationship between the differential pressure of the DPF 6 and the exhaust gas flow rate using the ash deposition amount in the DPF 6 as a parameter. In S110, the point consisting of the value of the DPF differential pressure detected in S80 and the exhaust gas flow rate calculated in S85 is shown on FIG. 3, and the number of ash deposition amounts on that point is obtained. The ash deposition amount is calculated by The map shown in FIG. 3 may be obtained in advance and stored in the memory 71.

  The process proceeds to S120 after the ash accumulation amount is calculated in S110, or after a predetermined time elapses after the complete regeneration of the DPF 6 without calculating the ash accumulation amount. Accordingly, in S120, the ECU 7 ends the regeneration operation.

  In S130, the ECU 7 corrects the characteristic lines 110 and 130. The correction in S130 is to select the characteristic lines 110 and 130 at the ash deposition amount calculated in S110 in FIG. In accordance with the correction of the characteristic lines 110 and 130, the broken lines 150 and 170 in FIG. The corrected broken lines 150 and 170 may be parallel to the corrected characteristic lines 110 and 130, respectively. The map shown in FIG. 6 may be obtained in advance and stored in the memory 71. The above is the processing procedure of FIG. When the processing of FIG. 2 is completed, the ECU 7 may automatically start the processing of FIG. 2 again from S10.

  FIG. 4 shows time transitions of various numerical values when the processing of FIG. 2 is executed. The regeneration execution flag is a variable that takes binary values of zero and non-zero, and is set when the ECU 7 is performing regeneration of the DPF 6 (set to a non-zero value). The ECU 7 may set the regeneration execution flag at the time of processing S30 in FIG. The differential pressure detection request flag is also a variable that takes binary values of zero and non-zero, and is set when the ECU 7 requests detection of the differential pressure of the DPF 6 (set to a non-zero value). The ECU 7 may set the differential pressure detection request flag at the time of processing S90 in FIG.

  The time t1 is the time when the complete reproduction is finished, that is, the time when S50 in FIG. 2 is affirmative (Yes). Time t2 is the time when the regeneration operation ends, and is the time when S120 of FIG. 2 is processed. Therefore, as shown in FIG. 4, the regeneration execution flag is raised from time t2 and the differential pressure detection request flag is raised from time t1 to t2.

  In FIG. 4, as for the time transition of the exhaust gas flow rate, the DPF differential pressure, and the PM deposition amount, the solid line represents the present invention, and the broken line represents the prior art. The conventional exhaust flow rate has been reduced by ending the regeneration operation immediately after completion of the complete regeneration after time t1. On the other hand, the exhaust flow rate in the present invention extends the regeneration operation until time t2 even after time t1, so the exhaust flow rate does not decrease until time t2. That is, the exhaust gas flow rate required for differential pressure detection is maintained from time t1 to time t2.

  In the prior art, the DPF differential pressure has been reduced after time t1 due to the influence of the decrease in the exhaust flow rate after time t1. On the other hand, in the present invention, since the exhaust flow rate does not decrease after time t1, the DPF differential pressure does not decrease rapidly after time t1. Therefore, in the prior art, since the DPF differential pressure value decreases after time t1, the specific gravity of the error in the measured pressure value is high. However, in the present invention, the DPF differential pressure value is maintained even after time t1, so Accuracy degradation is suppressed.

  In the prior art, since the regeneration operation ends at time t1, PM redeposition starts from time t1. On the other hand, in the present invention, the regeneration operation is extended until time t2, so that PM does not re-deposit until time t2. Therefore, in the present invention, there is no redeposition of PM from time t1 to time t2, so there is no influence of redeposited PM on the DPF differential pressure value measured in the same time interval, and the amount of ash accumulated from the DPF differential pressure value. Can be estimated accurately.

Next, a method for calculating the exhaust gas flow rate 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). 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, an injection amount command value 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. Further, a model for estimating the internal temperature of the DPF 6 is obtained in advance from the measured values of either or both of the exhaust temperature sensors 61 and 62 and stored in the memory 71, and the DPF temperature Tdpf (K) is estimated using this model. May be. In addition, this formula treats the downstream of DPF 6 as atmospheric pressure, but if the DPF downstream pressure is not atmospheric pressure due to muffler pressure loss, etc., the downstream pressure is further added to the DPF differential pressure to calculate the volume flow rate. do it. The above is the method for calculating the exhaust gas flow velocity.

  The characteristics shown in FIGS. 5 and 6 are characteristics when the exhaust gas flow rate is constant. The memory 71 may store the characteristics among the three amounts of the DPF differential pressure, the exhaust gas flow rate, and the PM accumulation amount. In S130, it is only necessary that the characteristics between these three quantities are corrected.

  In the said Example, DPF6 comprises a collector. The procedures of S10 and S40 and the ECU 7 constitute the estimation means. The procedure of S30 and the ECU 7 constitute a regeneration means. The procedure of S50 and the ECU 7 constitute the determining means. The procedure of S60 and the ECU 7 constitute a regeneration operation extending means. The procedure of S90 and the ECU 7 constitute acquisition means.

  The procedure of S130 and the ECU 7 constitute correction means. The differential pressure sensor 63 constitutes a measuring unit. The memory 71 constitutes a storage unit. The procedure of S110 and the ECU 7 constitute ash accumulation amount estimation means. The time from time t1 to t2 is a predetermined time. 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. 7 is a flowchart showing DPF regeneration / characteristic curve correction processing. The figure which shows the relationship between the DPF differential pressure and exhaust gas flow volume which made the ash accumulation amount the parameter. The figure which shows the time transition of the regeneration implementation flag, the differential pressure detection request flag, the exhaust gas flow rate, the DPF differential pressure, and the PM accumulation amount. The figure which shows the relationship between DPF differential pressure | voltage and PM deposition amount. The figure which shows the relationship between the DPF differential pressure which made the ash deposition amount the parameter, and PM deposition amount.

Explanation of symbols

1 Exhaust purification device 2 Diesel engine (engine, internal combustion engine)
3 Intake pipe 5 Exhaust pipe 6 Diesel particulate filter (DPF, collector)
21 Injector 31 Air flow meter 61, 62 Exhaust temperature sensor 63 Differential pressure sensor 10 Electronic control unit (ECU)
71 Memory 72 Timer

Claims (3)

A collector arranged in the middle of the exhaust passage to collect particulate matter;
Estimating means for estimating the amount of particulate matter deposited in the collector;
Regenerating means for regenerating the collector by burning the particulate matter deposited on the collector when the estimated value of the accumulation amount by the estimating means is greater than a first predetermined value;
Discriminating means for discriminating that the particulate matter is deposited in the completely regenerated state when the accumulated amount of the particulate matter in the collection and recording becomes a second predetermined value or less by regeneration by the regeneration means;
A regeneration operation extending means for extending the regeneration operation after it is determined by the determination means that the complete regeneration state;
Obtaining means for obtaining information indicating a degree of ash accumulation in the collector while the regeneration operation is extended by the regeneration operation extending means;
An exhaust emission control device for an internal combustion engine, comprising: correction means for correcting an estimation method by the estimation means based on information acquired by the acquisition means. Measuring means for measuring the differential pressure across the collector;
Storage means for storing characteristics between the differential pressure across the collector and the amount of particulate matter deposited in the collector;
The estimation means estimates the amount of particulate matter deposited in the collector from the value of the differential pressure before and after measured by the measurement means and the characteristics stored in the storage means,
The acquisition means acquires the value of the differential pressure before and after measured by the measurement means while the regeneration operation of the collector is extended by the regeneration operation extension means,
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the correction unit corrects the characteristic stored in the storage unit based on information acquired by the acquisition unit. Ash accumulation amount estimation for estimating the ash accumulation amount in the collector based on the differential pressure value measured by the measuring means while the regeneration operation of the collector is extended by the regeneration operation extending means. With means,
The exhaust purification device for an internal combustion engine according to claim 2, wherein the acquisition means acquires the ash accumulation amount estimated by the ash accumulation amount estimation means.

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