JP2006274978A - 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 preventing the excessive regeneration and defective regeneration of a filter by accurately estimating the accumulated amount of particulates collected by the filter in consideration of the accumulated state of ash different from the accumulated state of particulates. <P>SOLUTION: This exhaust emission control device of the internal combustion engine comprises a correction factor calculation means 60 for providing a correction factor S corresponding to the effective collection surface area of the particulate filter 2 which is reduced when ash contained in the exhaust gases is accumulated on the particulate filter 2, an accumulated amount estimating means 56 estimating the accumulated amount of particulates in the particulate filter 2 based on an exhaust gas pressure difference across the particulate filter 2 and correcting the estimation of the accumulated amount by the correction factor S, and a forced regenerating means forcibly regenerating the particulate filter 2 based on the estimated accumulated amount of particulates. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus for an internal combustion engine provided with a particulate filter that collects particulates in the exhaust gas.

2. Description of the Related Art Conventionally, a particulate filter (hereinafter referred to as a filter) is provided in an exhaust passage of an internal combustion engine such as a diesel engine, and particulates contained in exhaust discharged from the internal combustion engine are collected by the filter. Techniques for preventing release are known.
In such a filter, the collected particulate matter accumulates in the filter, and the exhaust resistance increases. Therefore, the deposited particulate matter is forcibly burned in some way to regenerate the filter, that is, the filter is removed. It is necessary to force regeneration.

As a method of forced regeneration of the filter, HC is supplied into the exhaust from a fuel addition valve provided in the exhaust passage, or fuel is injected into the cylinder during an expansion stroke or an exhaust stroke of the internal combustion engine, so that the HC is discharged into the exhaust passage. It is known to supply and raise the exhaust temperature.
Such forced regeneration is performed when the estimated amount of particulates accumulated on the filter exceeds a predetermined amount, and the estimated particulate accumulation amount is the difference between the exhaust pressure before and after the filter and the exhaust flow rate to the filter. Etc. At this time, if the amount of particulate accumulation is not accurately estimated, the forced regeneration of the filter is performed more than necessary, resulting in consumption of fuel, resulting in deterioration of fuel consumption, or insufficient regeneration. There may be a problem that the state in which the particulate collection ability of the filter continues to be lowered continues.

  On the other hand, in addition to the particulates, the exhaust contains a substance called ash caused by engine oil or wear powder generated in the internal combustion engine. This ash also accumulates on the filter together with the particulate, but unlike the particulate, it is not incinerated by forced regeneration of the filter and remains in the filter. If the amount of ash remaining in the filter increases, it becomes difficult to accurately estimate the amount of particulates that accumulate in the filter, making it impossible to perform forced regeneration of the filter at an appropriate time. Occurs.

  Therefore, since almost no particulates have accumulated on the filter immediately after the forced regeneration of the filter, the amount of ash deposited is estimated based on the exhaust pressure difference before and after the filter and the exhaust flow rate to the filter. Therefore, an exhaust emission control device has been proposed in which the occurrence of such a problem is prevented by determining the timing of forced regeneration based on the estimated accumulation amount of particulates corrected with this estimated accumulation amount of ash. (For example, Patent Document 1 or Patent Document 2).

More specifically, the accumulated amount of particulates is estimated by subtracting the accumulated amount of ash estimated during forced regeneration of the filter from the accumulated amount estimated based on the difference in exhaust pressure before and after the filter and the exhaust flow rate to the filter. The forced regeneration is performed when the particulate deposition amount estimated in this way exceeds a predetermined determination value.
JP 2003-83036 A JP 2004-21650 A

  In the exhaust gas purification apparatus of Patent Document 1 or Patent Document 2, the ash is considered to be equivalent to the particulate, and immediately after the forced regeneration is completed, the amount of ash deposited is estimated by the same method as the amount of particulate deposited. The accumulated amount of particulates is estimated by subtracting the estimated accumulated amount of ash from the accumulated amount estimated based on the exhaust pressure difference and the exhaust gas flow rate to the filter.

That is, the estimation of the ash accumulation amount is made based on the premise that the ash is accumulated in the filter in the same form as the particulates.
However, in practice, the ash deposition pattern in the filter is completely different from the particulate deposition pattern. Here, the difference between the particulate deposition form and the ash deposition form in the filter will be described below with reference to FIGS.

  FIG. 4 is a conceptual diagram showing a particulate deposition state in a state where no ash is deposited on the filter 2. The filter 2 is made of a honeycomb type ceramic carrier, and a large number of passages 2a communicating the upstream side and the downstream side are arranged side by side, and the upstream side opening and the downstream side opening of the passage are alternately closed. Therefore, the exhaust gas flowing into the filter 2 from the passage 2a having an opening on the upstream side passes through the porous wall 2b forming each passage 2a and has an opening on the downstream side, as indicated by arrows. It flows out out of the filter 2 from the passage 2a.

Then, assuming that the flow of exhaust gas into the filter 2 starts from a state in which nothing is deposited on the porous wall 2b of the filter 2, when the exhaust gas passes through the wall 2b, the particulates contained in the exhaust gas are included. The curate 4 is captured by the porous wall 2b and is deposited almost uniformly from the upstream end to the downstream end of the porous wall 2b as shown in FIG.
On the other hand, FIG. 5 is a conceptual diagram showing the deposition state of the particulates 4 in a state where the ash 6 is deposited on the filter 2. 5, the filter 2 is the same as the filter described in FIG. 4, and portions common to FIG. 4 will be described using the same reference numerals as in FIG. 4.

  The ash 6 is discharged from the internal combustion engine while being included in the exhaust together with the particulates 4, and once trapped by the porous wall 2b when the exhaust passes through the porous wall 2b, like the particulate 4. And deposited almost uniformly from the upstream end to the downstream end of the wall 2b. Thereafter, when a predetermined amount of the particulates 4 is deposited and the filter 2 is forcibly regenerated, the particulates 4 are combusted, but the ash 6 is not combusted. As the particulates 4 are combusted, the ash 6 is formed in the passage 2a. Float. Then, with the subsequent inflow of exhaust gas, the ash 6 floating in the passage 2a is accumulated from the most downstream side of the passage 2a opening upstream.

  As a result, the effective collection surface area of the filter 2 is reduced by the amount of ash 6 deposited, and the particulates 4 are collected only in the portion where the ash 6 is not deposited as shown in FIG. Therefore, assuming that the filter 2 needs to be forcibly regenerated when the particulates 4 are deposited to a predetermined thickness, and the ash 6 occupies almost half of the passage 2a in FIG. Therefore, when almost half of the particulates 4 are deposited, it is necessary to perform forced regeneration of the filter 2.

  Thus, since the particulate accumulation state and the ash accumulation state in the filter are completely different, the ash is in the same form as the particulates as in the exhaust purification device of Patent Document 1 or Patent Document 2. If the amount of particulate deposition is estimated based on the premise that it is deposited in the filter, a large error will occur in the estimated amount.

For this reason, in the exhaust gas purification apparatus of Patent Document 1 or Patent Document 2, the filter regeneration capability is deteriorated more frequently than necessary, so that the fuel consumption is deteriorated or the filter collecting ability is not achieved without sufficient filter regeneration. The problem arises that is still reduced.
The present invention has been made in view of such a problem, and the object of the present invention is to take into account the ash accumulation form different from the particulate accumulation form, so that the particulates collected by the filter can be obtained. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can accurately estimate the amount of accumulation and prevent excessive regeneration and poor regeneration of a filter.

  In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a particulate filter disposed in an exhaust passage for collecting and depositing particulates in exhaust gas, and an exhaust pressure before and after the particulate filter. A differential pressure detecting means for detecting a difference; a correction coefficient calculating means for obtaining a correction coefficient corresponding to an effective collection surface area of the particulate filter that is reduced by accumulation of ash of incombustible components on the particulate filter; A deposition amount for estimating the accumulation amount of the particulates in the particulate filter based on the exhaust pressure difference detected by the pressure detecting means and correcting the estimation of the accumulation amount by a correction coefficient obtained by the correction coefficient calculating means. Estimating means, and particulates estimated by the accumulation amount estimating means Based on the amount of deposition bets, characterized in that said by burning particulate matter accumulated in the particulate filter and a forced regeneration means for performing the forced regeneration of the particulate filter (claim 1).

  According to the exhaust gas purification apparatus for an internal combustion engine configured as described above, when the accumulation amount of the particulates is estimated based on the exhaust pressure difference before and after the particulate filter, the ash is reduced due to the accumulation of ash on the particulate filter. Correction using a correction coefficient corresponding to the effective collection surface area of the curate filter is performed, and the particulate filter is forcibly regenerated based on the corrected particulate accumulation amount.

  More specifically, an exhaust flow rate detecting means for detecting the flow rate of the exhaust gas flowing into the particulate filter is further provided, and the accumulation amount estimating means is configured to detect an exhaust pressure difference before and after the particulate filter and to the particulate filter. The particulate pressure accumulation amount and the exhaust flow rate to the particulate filter are corrected using the correction coefficient obtained by the correction coefficient calculating means, and the differential pressure detecting means is based on the corrected relation. The particulate deposition amount is estimated using the exhaust pressure difference detected by the exhaust gas flow rate and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means (claim 2).

Further, the accumulation amount estimating means is configured such that the exhaust pressure difference is ΔP, the accumulation amount of particulates on the particulate filter is PM, the exhaust flow rate to the particulate filter is Qe, the correction coefficients are S, A and B And C and D are constants obtained in advance by experiment, the equation ΔP = A · (PM / S ^D + B) · (Qe / S ^D ) ^C
The particulate deposition amount is estimated based on the relationship expressed by (Claim 3).

  The correction coefficient calculating means obtains the correction coefficient S from the equation with the particulate quantity PM = 0 in the equation when the forced regeneration of the particulate filter by the forced regeneration device is completed. (Claim 4).

  According to the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, the particulate accumulation amount corrected by the correction coefficient corresponding to the effective collection surface area of the particulate filter, which is reduced by the accumulation of ash on the particulate filter, Thus, the correction is made in accordance with the ash accumulation form different from the particulate accumulation form, and the amount of particulates accumulated on the particulate filter can be accurately estimated. In addition, it is possible to accurately determine the time when forced regeneration of the particulate filter is required, and to prevent excessive regeneration and regeneration failure of the particulate filter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a system configuration diagram of a four-cylinder diesel engine (hereinafter referred to as an engine) to which an exhaust emission control device according to an embodiment of the present invention is applied. The exhaust emission control device according to the present invention is based on FIG. The structure of will be described.
The engine 10 includes a high-pressure accumulator chamber (hereinafter referred to as a common rail) 12 common to each cylinder, and supplies high-pressure light oil stored in the common rail 12 to an injector 14 provided in each cylinder. Light oil is injected into the cylinder.

  The intake passage 16 is equipped with a turbocharger 18. The intake air drawn from an air cleaner (not shown) flows into the compressor 18a of the turbocharger 18 from the intake passage 16, and the intake air supercharged by the compressor 18a is intercooler. 20 and the intake control valve 64 are introduced into the intake manifold 22. An intake flow rate sensor 24 for detecting the intake air flow rate to the engine 10 is provided upstream of the compressor 18 a in the intake passage 16.

On the other hand, an exhaust port (not shown) through which exhaust is discharged from each cylinder of the engine 10 is connected to an exhaust pipe (exhaust passage) 28 via an exhaust manifold 26. Note that an EGR passage 32 that communicates the exhaust manifold 26 and the intake manifold 22 via the EGR valve 30 is provided between the exhaust manifold 26 and the intake manifold 22.
The exhaust pipe 28 passes through the turbine 18 b of the turbocharger 18 and is connected to the exhaust aftertreatment device 34 via the exhaust throttle valve 66. The turbine 18b is connected to the compressor 18a, receives the exhaust flowing in the exhaust pipe 28, and drives the compressor 18a.

In addition, the exhaust aftertreatment device 34 accommodates an oxidation catalyst 36 on the upstream side in the casing, and a particulate filter (hereinafter referred to as a filter) that captures particulates in the exhaust on the downstream side of the oxidation catalyst 36. 2 is housed.
The oxidation catalyst 36 is NO in the exhaust is oxidized to generate NO _2, and supplies to the filter 2 of the NO ₂ as oxidizing agent. The filter 2 is the same as that described above, and is made of a honeycomb-type ceramic carrier. A plurality of passages communicating the upstream side and the downstream side are arranged side by side, and the upstream side opening and the downstream side opening of the passage are provided. And are closed alternately.

The particulates accumulated in the filter 2 react with NO ₂ supplied from the oxidation catalyst 36 and burn, and the filter 2 is continuously regenerated.
Between the oxidation catalyst 36 and the filter 2, a catalyst temperature sensor 40 that detects the exhaust temperature on the outlet side of the oxidation catalyst 36 as the temperature of the oxidation catalyst 36, and an upstream pressure sensor 42 that detects the exhaust pressure on the upstream side of the filter 2. And are provided. A downstream pressure sensor 44 that detects the exhaust pressure downstream of the filter 2 and a filter temperature sensor 46 that detects the exhaust temperature on the outlet side of the filter 2 as the temperature of the filter 2 are provided on the downstream side of the filter 2. ing.

The ECU 48 is a control device for performing comprehensive control of the exhaust emission control device according to the present invention, including the engine 10, and includes a CPU, a memory, a timer counter, and the like, and calculates various control amounts. Various devices are controlled based on the control amount.
Various sensors such as an intake flow sensor 24, a catalyst temperature sensor 40, an upstream pressure sensor 42, a downstream pressure sensor 44, and a filter temperature sensor 46 are collected on the input side of the ECU 48 in order to collect information necessary for performing various controls. Various devices such as the injector 14, the EGR valve 30, the intake control valve 64, and the exhaust throttle valve 66 of each cylinder that are controlled based on the calculated control amount are connected to the output side. .

  The ECU 48 also performs calculation of the fuel supply amount to each cylinder of the engine 10 and control of fuel supply from the injector 14 based on the calculated fuel supply amount. The fuel supply amount (main injection amount) necessary for the operation of the engine 10 is stored in advance based on the engine speed detected by the speed sensor 50 and the accelerator opening detected by the accelerator opening sensor 52. Read from the map and decide. The amount of fuel supplied to each cylinder is adjusted by the valve opening time of the injector 14, and each injector 14 is driven to open in a driving time corresponding to the determined fuel amount.

  In the exhaust gas purification apparatus for an internal combustion engine configured as described above, the particulates accumulated on the filter 2 are incinerated and removed by continuous regeneration using the oxidation catalyst 36. In low speed, low load operation, etc., the exhaust temperature does not rise to the activation temperature of the oxidation catalyst 36, and NO in the exhaust may not be oxidized and continuous regeneration may not be performed. If such a state continues, particulates excessively accumulate in the filter 2 and the filter 2 may be clogged. Therefore, forced regeneration is appropriately performed according to the particulate accumulation state in the filter 2. .

The forced regeneration control is performed by each control block in the ECU 48 as shown in FIG.
The differential pressure detection unit (differential pressure detection means) 54 determines the filter 2 from the exhaust pressure upstream of the filter 2 detected by the upstream pressure sensor 42 and the exhaust pressure downstream of the filter 2 detected by the downstream pressure sensor 44. The difference between the front and rear exhaust pressures is obtained and sent to the accumulation amount estimation unit (deposition amount estimation means) 56.

  On the other hand, the exhaust flow rate detection unit (exhaust flow rate detection means) 58 is based on the intake air flow rate detected by the intake flow rate sensor 24 and the fuel supply amount to the engine 10 determined by the ECU 48, and the catalyst temperature sensor 40 at this time. By obtaining the exhaust gas flow rate by calculation using the detection value of the upstream pressure sensor 42, the flow rate of the exhaust gas flowing into the filter 2 is detected and sent to the accumulation amount estimation unit 56.

The accumulation amount estimation unit 56 accumulates on the filter 2 using the exhaust pressure difference before and after the filter 2 detected by the differential pressure detection unit 54 and the exhaust flow rate to the filter 2 detected by the exhaust flow rate detection unit 58. Estimate the amount of particulate deposition.
A method of estimating the particulate deposition amount by the deposition amount estimation unit 56 will be specifically described below.

The accumulation amount estimation unit 56 estimates the particulate accumulation amount based on the following expression (1) representing the relationship between the exhaust pressure difference before and after the filter 2, the particulate accumulation amount on the filter 2, and the exhaust flow rate to the filter 2. .
ΔP = A · (PM / S ^D + B) · (Qe / S ^D ) ^C (1)
In the above formula (1), ΔP represents the exhaust pressure difference before and after the filter 2, PM represents the particulate accumulation amount on the filter 2, Qe represents the exhaust flow rate to the filter 2, and S represents a filter that decreases due to ash accumulation. The correction factors A, B, C, and D that decrease in accordance with the effective collection surface area of 2 are constants obtained by experiments.

The PM / ^SD part of the above formula (1) indicates that the exhaust pressure difference before and after the filter 2 due to particulate deposition is reduced, and the effective collection surface area of the filter 2 is reduced when the particulate deposition amount is the same. That is, it corresponds to the increase with the decrease of S.
The Qe / ^SD part corresponds to the fact that the exhaust pressure difference before and after the filter 2 increases as the effective collection surface area of the filter 2 decreases, that is, the S decreases when the exhaust flow rate is the same. Is.

The accumulation amount estimation unit 56 stores in advance the following equation (2) obtained by modifying such equation (1), and the exhaust pressure difference before and after the filter 2 detected in this equation (2) and By substituting the exhaust flow rate to the filter 2, the amount of particulates accumulated is calculated.
PM = [(ΔP / A) / (Qe / S ^D ) ^C −B] · S ^D (2)
Here, the correction coefficient S is obtained by a correction coefficient calculation unit (correction coefficient calculation means) 60. The correction coefficient calculation unit 60 calculates the correction coefficient S in response to completion of forced regeneration of the filter 2 by a forced regeneration unit (forced regeneration unit) 62 described later. In the state where the forced regeneration of the filter 2 has been completed, it is assumed that almost no particulates have accumulated on the filter 2, and PM = 0 is substituted into the above equation (2), and the exhaust pressure before and after the filter 2 detected at this time is detected. Substituting the difference and the exhaust gas flow rate to the filter 2 into the equation (2), the correction coefficient S is calculated backward and sent to the accumulation amount estimation unit 56.

  The estimated accumulation amount of the particulates obtained by the accumulation amount estimation unit 56 according to the expression (2) is sent to the forced regeneration unit 62, and the forced regeneration unit 62 determines the forced regeneration start determination value in which the estimated particulate accumulation amount is set in advance. If it becomes above, it will judge that the forced regeneration of the filter 2 is required, and the forced regeneration of the filter 2 is implemented by controlling the fuel supply from the fuel injection valve 14 to each cylinder. When the estimated accumulation amount of the particulates is equal to or less than a preset forced regeneration end determination value due to the forced regeneration, it is determined that the forced regeneration of the filter has been completed, the forced regeneration is terminated, and the correction coefficient calculation unit 60 Notification that forced regeneration is complete.

The forced regeneration control of the filter 2 as described above is executed at a predetermined control cycle according to the flowchart shown in FIG.
First, in step S2 in FIG. 3, the particulate deposition amount PM on the filter 2 is estimated by the above-described equation (2). Next, in step S4, it is determined whether or not the value of the forced regeneration flag F1 is 1. The forced regeneration flag F1 indicates whether or not forced regeneration is being performed. If the value is 1, forced regeneration is being performed, and if the value is 0, forced regeneration is not being performed. Show. The initial set value of the forced regeneration flag F1 is 0, and the process proceeds from step S4 to step S6 in the first control cycle.

In step S6, the particulate accumulation amount PM that is estimated in step S2, by comparing pre-set forced regeneration start determination value PM _1, determines whether or not it is necessary to forced regeneration of the filter 2 is made . That is, it is determined that when the estimated accumulation amount PM of the particulate is forced regeneration start determination value PM ₁ or more, are needed forced regeneration. In this case, the process proceeds to step S8, where the value of the forced regeneration flag F1 is set to 1, and the forced regeneration flag F1 is changed to indicate that the forced regeneration is being executed. On the other hand, when the estimated accumulation amount PM of the particulate is forced regeneration start determination value PM less than _1, the forced regeneration at the present time is judged to be unnecessary, and ends this control cycle, again in the next control cycle steps Processing is performed from S2.

In step S6, it is determined that forced regeneration is necessary, and the process proceeds to step S8. The value of the forced regeneration flag F1 is set to 1, and then the process proceeds to step S10. Based on the detected value of the catalyst temperature sensor 40, It is determined whether the temperature Tc is 250 ° C. or higher and the oxidation catalyst 36 is activated.
When the catalyst temperature Tc is less than 250 ° C., the process proceeds to step S12, and the temperature increase control of the oxidation catalyst 36 is performed.

  In this temperature raising control, the temperature of the oxidation catalyst 36 is raised to an activation temperature (for example, 250 ° C.) by supplying high-temperature exhaust gas to the oxidation catalyst 36, and the intake control valve 64 and the exhaust throttle valve 66 are raised. Is controlled in the closing direction, and the first additional fuel injection is performed in the expansion stroke of each cylinder. The injection timing of the first additional fuel is relatively earlier than the end of the expansion stroke. By injecting the additional fuel into the cylinder at such timing, the additional fuel and the high-temperature combustion gas in the cylinder are generated. As a result of mixing, additional fuel is combusted in the exhaust port and the exhaust manifold 26, and high temperature exhaust gas is supplied to the oxidation catalyst 36, whereby the temperature of the oxidation catalyst 36 rises.

Then In step S20, the accumulation amount PM of the current control cycle particulates estimated in step S2 in it is determined whether a forced regeneration termination determination value PM ₂ below. Because the oxidation catalyst 36 as described above is a situation that is not sufficiently activated, incineration of particulates is not performed, the estimated accumulation amount PM This time is determined to be larger than the forced regeneration termination determination value PM ₂ The control cycle is finished, and control is performed again from step S2 in the next control cycle.

  In this case, since the value of the forced regeneration flag F1 has already been 1, after estimating the particulate deposition amount in step S2, the process proceeds from step S4 to step S10, and the temperature Tc of the oxidation catalyst 36 is 250 ° C. If it is less than the value, the catalyst temperature increase control by the injection of the first additional fuel is performed again in step S12. Therefore, while the temperature Tc of the oxidation catalyst 36 is lower than 250 ° C., the first additional fuel is injected in step S12.

  When the injection of the first additional fuel is repeated in this way and the temperature Tc of the oxidation catalyst 36 becomes 250 ° C. or higher, the process proceeds from step S10 to step S14. In step S14, based on the detected value of the catalyst temperature sensor 40, it is determined whether or not the temperature Tc of the oxidation catalyst 36 is equal to or higher than a predetermined temperature. This predetermined temperature is a temperature at which the particulates burn most efficiently in the filter 2, and in this embodiment, the predetermined temperature is 600 ° C.

If it is determined in step S14 that the catalyst temperature Tc is 600 ° C. or higher, the process proceeds to step S16, and if it is determined that the catalyst temperature Tc is less than 600 ° C., the process proceeds to step S18.
In steps S16 and S18, the second additional fuel is injected into each cylinder so that the temperature of the exhaust gas supplied to the filter 2 is maintained at 600 ° C., and the second additional fuel is injected in the exhaust stroke. It has come to be. By injecting the second additional fuel into each cylinder at such injection timing, the second additional fuel reaches the oxidation catalyst 36 without being burned in the cylinder or the exhaust manifold 26, and is at the activation temperature. Combustion occurs in the oxidation catalyst 36 and the filter 2. By this combustion, the exhaust temperature rises to 600 ° C., and the particulates deposited on the filter 2 are incinerated.

  The second additional fuel is stored in a map in which the engine speed detected by the speed sensor 50 and the main injection amount (load) determined by the ECU 48 are parameters. This map is the second additional fuel injection. There are two types of maps, an increase map with a relatively large amount and a decrease map with a relatively small amount. In step S16, since the catalyst temperature Tc is 600 ° C. or higher, a relatively small amount of second additional fuel is injected using the reduction map. In step S18, the catalyst temperature Tc is less than 600 ° C. Used to inject a relatively large amount of the second additional fuel. As a result, the temperature of the exhaust gas discharged from the oxidation catalyst 36 and supplied to the filter 2 is maintained at 600 ° C.

When injecting a second additional fuel in step S16 or S18, the process proceeds to step S20, or deposited amount PM of the current control cycle particulates estimated in step S2 in is the forced regeneration termination determination value PM ₂ below not Judgment is made. When the estimated accumulation amount PM of the particulate is larger than the forced regeneration termination determination value PM ₂ it is still determined that the forced regeneration of the filter 2 is required, finishing this control cycle, again in the next control cycle Control is performed from step S2. Accordingly, the estimated accumulation amount PM of particulate matter compared with forced regeneration termination determination value PM ₂ in step S20 will be updated every control period.

In step S20, it is deposited amount PM of particulates and forced regeneration termination determination value PM ₂ below steps when forced regeneration of the filter 2 is determined to be completed, the process proceeds to step S22, the value of the forced regeneration flag F1 0 Proceed to S24. When the value of the forced regeneration flag F1 becomes 0 in this way, the process proceeds from step S4 to step S6 in the next control cycle. Therefore, the process from step S2 to step S6 is performed until the forced regeneration of the filter 2 is required again. Is repeated, and whether or not forced regeneration is necessary is determined based on the estimated accumulation amount of the particulates updated every control cycle.

  In step S24, PM = 0 is substituted into the above-described equation (2) on the assumption that almost no particulates have accumulated in the filter 2 in response to the completion of the forced regeneration, and before and after the detected filter 2 The correction coefficient S is calculated by substituting the exhaust gas pressure difference and the exhaust gas flow rate to the filter 2 into the equation (2). The correction coefficient S calculated in this way is used for estimating the particulate deposition amount in step S2 in the next and subsequent control cycles.

  As described above, when estimating the particulate accumulation amount on the filter 2 using the exhaust pressure difference before and after the filter 2 and the exhaust gas flow rate to the filter 2, the effective collection surface area of the filter 2 that decreases due to the accumulation of ash. By performing the correction using the correction coefficient S that decreases corresponding to the above, it is possible to estimate the particulate deposition amount with high accuracy corresponding to the ash deposition form different from the particulate system form.

Then, by determining the forced regeneration execution timing of the filter 2 based on the estimated accumulation amount of the particulate with high accuracy, proper forced regeneration is performed, and fuel consumption is deteriorated due to excessive forced regeneration or insufficient forced regeneration. It is possible to prevent a reduction in the collection ability of the filter 2 due to regeneration.
Although the description of the exhaust gas purification apparatus for an internal combustion engine according to one embodiment of the present invention has been completed above, the present invention is not limited to the above embodiment.

  For example, in the above embodiment, the back calculation of the correction coefficient S based on the formula (2) is always performed after the completion of the forced regeneration of the filter 2, but it is performed once every several forced regenerations. Also good. Further, the back calculation of the correction coefficient S is performed only once immediately after the completion of the forced regeneration. However, after the forced regeneration of the filter 2 is completed, the correction coefficient S is back calculated over several control cycles and averaged. The final value of the correction coefficient S may be determined.

Further, the exhaust pressure difference before and after the filter 2 is detected based on the exhaust pressure upstream of the filter 2 detected by the upstream pressure sensor 42 and the exhaust pressure downstream of the filter 2 detected by the downstream pressure sensor 44. However, the present invention is not limited to this, and for example, the differential pressure across the filter 2 may be directly detected.
Further, the exhaust flow rate is detected based on the intake flow rate detected by the intake flow rate sensor 24 and the amount of fuel supplied to each cylinder. However, the present invention is not limited to this. An exhaust flow rate sensor may be provided in the aftertreatment device 34 to directly detect the exhaust flow rate.

  For forced regeneration of the filter 2, the oxidation catalyst 36 is activated by the first additional fuel injection, and then the exhaust temperature is raised by the second additional fuel injection to incinerate the particulates of the filter 2. However, the present invention is not limited to this. For example, a fuel addition device may be provided in the exhaust pipe 28 or the exhaust post-treatment device 34 so that fuel is directly injected into the exhaust, or the exhaust pipe 28 or the exhaust post-treatment may be used. The temperature of the exhaust gas may be raised by an electric heater provided in the device 34.

  Finally, in the above-described embodiment, the present invention is applied to an exhaust emission control device for a diesel engine. However, the engine type is not limited to this, and particulates are removed using a filter. Any engine that regenerates the filter by incineration can be applied.

1 is an overall configuration diagram of an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention. FIG. 2 is a control block diagram of forced regeneration control performed by the exhaust emission control device of FIG. 1. It is a flowchart of the forced regeneration control performed with the exhaust gas purification device of FIG. It is a conceptual diagram which shows the accumulation condition of the particulate matter trapped by the filter. It is a conceptual diagram which shows the deposition condition of the particulates and ash trapped by the filter.

Explanation of symbols

2 Filter 10 Engine 28 Exhaust pipe (exhaust passage)
54 Differential pressure detection part (Differential pressure detection means)
56 Accumulation amount estimation unit (accumulation amount estimation means)
58 Exhaust flow rate detector (exhaust flow rate detection means)
60 Correction coefficient calculation unit (correction coefficient calculation means)
62 Forced regeneration section (forced regeneration means)

Claims (4)

A particulate filter disposed in the exhaust passage for collecting and depositing particulates in the exhaust;
Differential pressure detecting means for detecting an exhaust pressure difference before and after the particulate filter;
Correction coefficient calculation means for obtaining a correction coefficient corresponding to an effective collection surface area of the particulate filter, which is reduced by ash of incombustible components being deposited on the particulate filter;
Based on the exhaust pressure difference detected by the differential pressure detecting means, the particulate accumulation amount in the particulate filter is estimated, and the accumulation amount is corrected by the correction coefficient obtained by the correction coefficient calculating means. Deposit amount estimation means;
Forcibly regenerating means for forcibly regenerating the particulate filter by burning the particulate accumulated on the particulate filter based on the accumulated amount of the particulate estimated by the accumulated amount estimating means. An exhaust purification device for an internal combustion engine. An exhaust flow rate detecting means for detecting the flow rate of the exhaust gas flowing into the particulate filter,
The accumulation amount estimation means obtains a relationship between an exhaust pressure difference before and after the particulate filter, a particulate accumulation amount on the particulate filter, and an exhaust flow rate to the particulate filter by the correction coefficient calculation means. Using the corrected correction coefficient, and based on the corrected relationship, using the exhaust pressure difference detected by the differential pressure detection means and the exhaust flow rate detected by the exhaust flow rate detection means. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the amount of curate accumulation is estimated. The accumulation amount estimating means is configured such that the exhaust pressure difference is ΔP, the accumulation amount of particulates on the particulate filter is PM, the exhaust flow rate to the particulate filter is Qe, the correction coefficients are S, A, B, and C And D are constants obtained in advance by experiment, the equation ΔP = A · (PM / S ^D + B) · (Qe / S ^D ) ^C
The exhaust purification device for an internal combustion engine according to claim 2, wherein the amount of accumulated particulates is estimated on the basis of a relationship expressed by:   The correction coefficient calculating means obtains the correction coefficient S from the expression when the forced regeneration of the particulate filter by the forced regeneration means is completed, with the particulate quantity PM = 0 in the expression. 3. An exhaust emission control device for an internal combustion engine according to 3.

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