JP2007170193A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device in which the regeneration of a filter is efficiently and accurately performed by accurately estimating the deposited amount of particulates on the filter. <P>SOLUTION: Based on the temperature of the filter 48, the basic combustion amount of the particulates in the thin holes of the filter 48 is provided. Based on the amounts of specific components in the exhaust gases such as NOx and oxygen contributing to the combustion of the particulates collected by the filter 48, the basic combustion amount is corrected and the combustion amount of the particulates in the thin hole. Based on the amount of combustion of the particulates, all deposited amount of particulates on the filter 48 is estimated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an engine exhaust purification device, and more particularly to an exhaust purification device including a particulate filter for collecting particulates contained in engine exhaust.

Conventionally, a particulate filter (hereinafter referred to as a filter) has been provided in the exhaust passage of an engine such as a diesel engine, and particulates (hereinafter referred to as PM) contained in the exhaust discharged from the engine are collected by the filter. 2. Description of the Related Art An exhaust gas purification device that is prevented from being discharged into the inside is known.
FIG. 12 is a schematic diagram showing a part of an example of a filter for collecting PM used in such an exhaust purification device, and FIG. 13 is an enlarged view of a part of the filter of FIG. . As shown in FIG. 12, the filter 102 includes a ceramic carrier 102b in which a large number of passages 102a 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 102a are alternately closed. As shown in FIG. 13, the ceramic carrier 102b has a large number of pores 102c formed therein.

The engine exhaust 104 is supplied into the passage 102 a from the upstream side of the filter 102, flows through the pores 102 c in the ceramic carrier 102 b, and is discharged downstream, whereby PM in the exhaust is filtered out. (Reference numeral 106 in FIG. 12).
By continuously collecting PM in the exhaust gas by the filter, when the collected PM gradually accumulates in the filter, the exhaust resistance gradually increases accordingly. When the amount of PM accumulated on the filter reaches a considerable amount, the filter becomes clogged, and the engine output drop due to the pressure loss of the filter cannot be ignored. Therefore, it is necessary to incinerate and remove the accumulated PM as needed to regenerate the filter, and filter regeneration methods include continuous regeneration and forced regeneration.

The continuous regeneration of the filter generates NO ₂ (nitrogen dioxide) by oxidizing NO (nitrogen monoxide) in the exhaust gas by an oxidation catalyst disposed on the upstream side of the filter, and is contained in the NO ₂ and the exhaust gas. By using O ₂ (oxygen) as an oxidizing agent, PM deposited on the filter is oxidized and continuously removed.
Further, since the continuous regeneration as described above is affected by the operating state of the engine, the PM accumulated on the filter cannot be sufficiently removed only by the continuous regeneration. Therefore, forced regeneration is performed to forcibly incinerate and remove the PM accumulated on the filter. As a method of forced regeneration, HC is supplied into the exhaust from a fuel addition valve provided in the exhaust passage, or HC is supplied to the exhaust passage by injecting additional fuel into the cylinder during the expansion stroke or exhaust stroke of the engine. For example, it is known that the exhaust temperature is raised to a temperature at which PM can be combusted.

  Such forced regeneration is performed when it is estimated that the amount of accumulated PM on the filter exceeds a predetermined amount. However, if the amount of accumulated PM is not accurately estimated, the filter is more than necessary. When the forced regeneration is performed, there is a possibility that the fuel is excessively consumed and the fuel consumption is deteriorated, or that the filter is clogged due to insufficient forced regeneration.

The estimation of the PM accumulation amount on the filter is generally performed based on the differential pressure of the exhaust gas before and after the filter, but in order to estimate the PM accumulation amount more accurately, the PM generation amount by the engine and the PM in the filter Patent Document 1 proposes an exhaust purification device that estimates the amount of PM accumulated in a filter based on the combustion speed.
According to the exhaust purification device of Patent Document 1, since PM combustion rate in the filter is changed by NOx concentration and the O ₂ concentration in the exhaust gas flowing into the filter temperature and the filter, the filters temperatures, corrected by the NOx concentration and the O ₂ concentration The PM deposition amount is estimated using the burned rate.
JP 2002-97930 A

  The PM deposition in the filter includes the deposition in the pores formed in the filter and the deposition on the filter surface. The deposition in the pores is performed first, and the PM deposition in the pores is saturated. After that, the filter surface is deposited. Also, the PM is burned first after the PM in the pores, and after the PM in the pores is completely burned, the PM on the filter surface is burned and the PM on the filter surface is not burned completely. PM deposition in the pores is not performed again.

Thus, the form of PM deposition and combustion in the filter is different between the inside of the pores and the surface of the filter, and the filter temperature, NOx concentration, and O ₂ concentration are simply as in the exhaust gas purification device of Patent Document 1 described above. It is difficult to estimate the PM deposition amount accurately because the PM combustion amount in the pores cannot be estimated only by using the PM combustion rate corrected by the above.
In addition, in the estimation of the amount of PM deposition based on the differential pressure before and after the filter, which is a conventional general technique, there is a difference in the form of PM deposition and combustion in such a filter. It is not possible to obtain an accurate PM deposition amount by simply estimating the PM deposition amount.

  This will be specifically described with reference to FIG. FIG. 5 shows the relationship between the differential pressure before and after the filter and the total PM estimation amount of the filter. The solid line indicates that PM is saturated in the pores, and the alternate long and short dash line indicates that PM is not deposited in the pores. For example, when the differential pressure is Pd, the PM deposition amount becomes PM3 corresponding to the point i when PM is saturated in the pores, but in the state where PM in the pores is completely burned, the PM deposition amount is PM2 corresponds to the point h, and even with the same differential pressure, an extremely large error occurs in the estimated amount of PM deposited according to the amount of PM deposited in the pores.

Thus, in a state where PM is deposited in both the pores and the filter surface, the total PM deposition amount of the filter cannot be obtained accurately unless the PM deposition amount in the pores is accurately grasped. There's a problem.
Further, the amount of PM combustion in the pores necessary for obtaining the amount of PM deposited in the pores varies depending on the PM combustion rate in the pores, but the PM combustion rate is in the exhaust gas contributing to PM combustion. Since it varies depending on the components, that is, the amount of NOx and O ₂ supplied to the filter, if the PM deposition amount in the pores is estimated using a predetermined specific PM combustion rate, the total PM deposition on the filter is still There is a problem that the amount cannot be determined accurately.

  Since PM does not accumulate again in the pores when PM is deposited on the filter surface, PM deposition on the filter surface and the amount of PM deposited by combustion after PM in the pores are completely burned With this change, the differential pressure changes on the alternate long and short dash line connecting points a and f in FIG. Therefore, in this state, the PM accumulation amount can be accurately estimated based on the differential pressure before and after the filter.

As described above, even in the estimation of the PM deposition amount based on the general differential pressure, the PM deposition amount cannot always be accurately estimated due to the difference in the PM deposition and combustion modes on the filter surface and the pores. .
For this reason, there is still a possibility that problems such as excessive fuel consumption caused by excessive filter regeneration causing deterioration of fuel consumption or clogging of the filter due to insufficient forced regeneration may occur. There is sex.

  The present invention has been made in view of such problems, and an object of the present invention is to perform exhaust gas purification capable of accurately estimating the amount of PM deposited on the filter and efficiently regenerating the filter. To provide an apparatus.

  In order to achieve the above object, an exhaust emission control device according to the present invention is disposed in an exhaust passage of an engine and collects particulates in the exhaust in and on the surface of the exhaust by circulating the exhaust into the pore. A filter to be deposited, a filter temperature detecting means for detecting the temperature of the filter, and an amount of a specific component contributing to combustion of particulates collected by the filter among components in exhaust gas supplied to the filter. The basic combustion amount of the particulates in the pores based on the temperature of the filter detected by the exhaust gas component amount calculating means and the filter temperature detecting means is calculated as the specific component detected by the exhaust gas component amount calculating means. A combustion amount calculating means for correcting the amount of particulate combustion in the pores based on the amount, and the putty calculated by the combustion amount calculating means. Based on curated combustion amount, characterized in that a deposition amount estimating means for estimating a particulate matter deposit amount to the filter (claim 1).

  According to the exhaust emission control device of the present invention configured as described above, the basic combustion amount of the particulates in the pores of the filter based on the temperature of the filter is increased in the exhaust gas that contributes to the combustion of the particulates collected by the filter. Based on the amount of the specific component, the particulate combustion amount in the pores is obtained. Based on the particulate combustion amount in the pores thus obtained, the particulate deposition amount on the filter is estimated.

  The exhaust gas purification apparatus further includes a differential pressure detection unit that detects a differential pressure before and after the filter, and the accumulation amount estimation unit includes a preset differential pressure and a particulate accumulation amount on the filter. And the amount of particulate accumulation on the filter is estimated based on the differential pressure detected by the differential pressure detection means, and within the pores determined by the combustion amount calculation means The relationship between the differential pressure and the particulate accumulation amount on the filter is corrected in accordance with the particulate combustion amount.

According to the exhaust gas purification apparatus configured as described above, the relationship between the preset differential pressure before and after the filter and the amount of particulate accumulation on the filter is corrected according to the amount of particulate combustion in the pores, Based on the above relationship after correction and the differential pressure before and after the filter, the amount of particulate accumulation on the filter is estimated.
In the exhaust purification apparatus, the accumulation amount estimation means is based on the particulate combustion amount in the pores only when the particulates are accumulated on both the surface of the filter and the pores. The relationship between the differential pressure and the amount of particulate accumulation on the filter is corrected (Claim 3).

According to the exhaust gas purification apparatus configured as described above, the correction of the relationship between the differential pressure based on the particulate combustion amount in the pores of the filter and the particulate deposition amount on the filter is performed by adjusting the surface of the filter and the pores. Only when particulates are deposited on both.
In the exhaust purification apparatus, the exhaust component amount calculating means is disposed in the exhaust passage and detects a NOx concentration in the exhaust, and based on a NOx concentration in the exhaust detected by the NOx sensor. And a NOx supply amount calculating means for calculating the amount of NOx supplied to the filter (claim 4).

Alternatively, the exhaust component amount calculating means reads the NOx emission amount corresponding to the actual engine operating state from a NOx emission amount map set in advance based on the operating state of the engine, thereby determining the NOx supplied to the filter. The quantity is obtained (claim 5).
More specifically, it further comprises forced regeneration means for forcibly regenerating the filter by supplying HC to the filter, and the exhaust component amount calculating means is when forced regeneration by the forced regeneration means is performed. And a different NOx emission amount map when the forced regeneration is not performed (Claim 6).

In these exhaust purification apparatuses, the amount of particulate accumulation on the filter is estimated on the basis of the amount of particulate combustion in the pores corrected based on the amount of NOx supplied to the filter.
Further, as another specific exhaust purification device, the exhaust component amount calculating means is disposed in the exhaust passage and detects an oxygen concentration in the exhaust, and in the exhaust detected by the oxygen sensor. And oxygen supply amount calculation means for calculating the amount of oxygen supplied to the filter based on the oxygen concentration of the filter (claim 7).

Alternatively, the exhaust component amount calculating means obtains the amount of oxygen supplied to the filter based on the amount of fresh air supplied to the engine and the amount of fuel supplied to the engine. Item 8).
In these exhaust purification apparatuses, the amount of particulate deposition on the filter is estimated based on the amount of particulate combustion in the pores corrected based on the amount of oxygen supplied to the filter.

  According to the exhaust emission control device of the present invention, the basic combustion amount of the particulates in the pores of the filter based on the temperature of the filter is changed to the amount of the specific component in the exhaust gas that contributes to the combustion of the particulates collected by the filter. The amount of particulate combustion in the pores can be calculated by correcting based on this, so that the amount of particulate combustion in the pores can be accurately estimated, and as a result, the particulates accumulated in the pores. It is possible to accurately estimate the amount of.

In addition, when estimating the particulate deposition amount on the filter based on the differential pressure before and after the filter, the particulate deposition amount in the pores that has a large effect on the estimated particulate amount has been accurately obtained. It is possible to accurately estimate the total amount of particulate deposits.
In addition, by accurately estimating the total amount of accumulated particulates on the filter in this way, it becomes possible to perform forced regeneration of the filter at an appropriate time, and fuel consumption deteriorates by performing forced regeneration more than necessary, It is also possible to prevent problems such as clogging in the filter due to insufficient forced regeneration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of a four-cylinder diesel engine (hereinafter referred to as an engine) to which an exhaust emission control device according to a first embodiment of the present invention is applied. Based on FIG. The configuration of the apparatus will be described.
The engine 1 includes a high-pressure accumulator chamber (hereinafter referred to as a common rail) 2 common to each cylinder, and light oil that is high-pressure fuel supplied from a fuel injection pump (not shown) and stored in the common rail 2 is provided in each cylinder. The fuel is supplied to the injectors 4 and fuel is injected from the injectors 4 into the combustion chambers 6 of the respective cylinders.

  The intake air sucked from the air cleaner 8 flows into the compressor 12a of the turbocharger 12 provided in the intake passage 10, and the intake air supercharged by the compressor 12a passes through the intercooler 14 and the intake control valve 16 to the intake manifold 18. To be introduced. The intercooler 14 cools intake air in order to improve the intake efficiency of the engine 1. The intake control valve 16 is for controlling the amount of intake air to the engine 1, and is controlled in the valve closing direction when the exhaust temperature of the engine 1 needs to be raised, and is normally controlled to the fully open position. Is done.

The intake air introduced into the intake manifold 18 is introduced into the combustion chamber 6 when the intake valve 20 that is opened and closed by a cam (not shown) is opened. An air flow sensor 22 for detecting the amount of intake air to the engine 1 is provided in the intake passage 10 between the air cleaner 8 and the compressor 12a.
The fuel injected from the injector 4 mixes with the intake air introduced into the combustion chamber 6 and is compressed and ignited by being compressed by the rising piston 24. The piston 24 is pushed down by the explosion force at that time, and the crankshaft 26 is rotated. Let

  Exhaust gas generated by the combustion of fuel in the combustion chamber 6 is discharged from the combustion chamber 6 to the exhaust manifold 30 when the exhaust valve 28 that is opened and closed by a cam (not shown) is opened, and passes through the turbine 12b of the turbocharger 12. It flows into the exhaust pipe 32. The rotating shaft of the turbine 12b is connected to the rotating shaft of the compressor 12a, and the turbine 12b receives the exhaust gas flowing from the exhaust manifold 30 and drives the compressor 12a. An EGR passage 36 is provided between the exhaust manifold 30 and the intake manifold 18 to communicate the exhaust manifold 30 and the intake manifold 18 via an EGR valve 34.

The exhaust pipe 32 is connected to an exhaust aftertreatment device 38, and the exhaust discharged from the engine 1 flows into the exhaust aftertreatment device 38, and the exhaust purified by the exhaust aftertreatment device 38 passes through a silencer (not shown). It is designed to be discharged into the atmosphere.
The exhaust aftertreatment device 38 includes an upstream casing 40 and a downstream casing 44 that is communicated with the downstream side of the upstream casing 40 through a communication passage 42. An oxidation catalyst 46 is accommodated in the upstream casing 40, and a particulate filter (hereinafter referred to as a filter) 48 that collects particulates (hereinafter referred to as PM) in the exhaust is accommodated in the downstream casing 44. .

The oxidation catalyst 46 is NO in the exhaust is oxidized to generate NO _2, and supplies to the filter 48 of the NO ₂ as oxidizing agent. The filter 48 is made of a ceramic carrier having a large number of pores formed therein, and has a large number of passages communicating with the upstream side and the downstream side, and has an upstream opening and a downstream opening. It is closed alternately.
By arranging the oxidation catalyst 46 and the filter 48 in this manner, the PM collected and deposited on the filter 48 is oxidized by reacting with NO ₂ supplied from the oxidation catalyst 46 or O ₂ in the exhaust gas. The filter 48 is continuously reproduced.

The exhaust pipe 32 is provided with a NOx sensor 50 for detecting the NOx concentration in the exhaust gas flowing into the exhaust gas aftertreatment device 38, and the exhaust gas flowing into the exhaust gas aftertreatment device 38 in the vicinity of the inlet of the exhaust gas aftertreatment device 38. That is, an inlet side exhaust temperature sensor 52 for detecting the temperature of the exhaust gas flowing into the oxidation catalyst 46 is provided.
Further, an outlet side exhaust temperature sensor (filter temperature detecting means) 54 for detecting the temperature of the exhaust gas flowing out from the exhaust gas after-treatment device 38, that is, the exhaust gas flowing out from the filter 48, is provided on the outlet side of the exhaust after-treatment device 38. Yes.

Further, an upstream branch passage 56 branched by the communication passage 42 upstream of the filter 48 and a downstream branch passage 58 branched downstream of the filter 48 are connected to a differential pressure sensor (differential pressure detecting means) 60. The differential pressure across the filter 48 is detected by the differential pressure sensor 60.
The ECU 62 is a control device for performing comprehensive control including operation control of the engine 1, and is composed of a CPU, a memory, a timer counter, and the like, and calculates various control amounts and based on the control amounts. Controls various devices.

  In addition to the above-described air flow sensor 22, NOx sensor 50, inlet side exhaust temperature sensor 52, outlet side exhaust temperature sensor 54, and differential pressure sensor 60, the input side of the ECU 62 collects information necessary for various controls. Various sensors such as a rotation speed sensor 64 for detecting the engine speed and an accelerator opening degree sensor 66 for detecting the depression amount of the accelerator pedal are connected, and control is performed on the output side based on the calculated control amount. Various devices such as the injector 4 of each cylinder, the intake control valve 16 and the EGR valve 34 are connected.

  The ECU 62 also performs calculation of the fuel supply amount to each cylinder of the engine 1 and control of fuel supply from the injector 4 based on the calculated fuel supply amount. The fuel supply amount (main injection amount) necessary for the operation of the engine 1, that is, the fuel supply amount necessary for generating torque by the engine 1 is detected by the engine speed detected by the speed sensor 64 and the accelerator opening sensor 66. Based on the accelerator pedal depression amount thus determined, it is determined by reading from a previously stored map. The amount of fuel supplied to each cylinder is adjusted by the valve opening time of the injector 4, and each injector 4 is driven to open by a driving time corresponding to the determined fuel amount, and the main chamber is placed in the combustion chamber 6 of each cylinder. By performing the injection, the fuel amount necessary for the operation of the engine 1 is supplied.

In the exhaust purification device of the engine 1 configured as described above, PM accumulated on the filter 48 is removed by continuous regeneration using NO ₂ supplied from the oxidation catalyst 46 or O ₂ in the exhaust as an oxidant. However, in an operation state in which the exhaust temperature of the engine 1 is low, for example, at a low speed or low load operation, the exhaust temperature does not rise to the activation temperature of the oxidation catalyst 46, and NO in the exhaust is not oxidized and continuous regeneration is not performed. There is a case. If such a state continues, PM may be excessively accumulated in the filter 48 and the filter 48 may be clogged. Therefore, forced regeneration is appropriately performed according to the PM accumulation state in the filter 48.

Forced regeneration control for forcibly regenerating the filter 48 is performed at a predetermined control cycle by the ECU 62 in accordance with the flowchart of FIG.
First, in step S2 of FIG. 2, 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 necessary. A value of 1 indicates that forced regeneration is necessary, and a value of 0 indicates that forced regeneration is not necessary. The initial set value of the forced regeneration flag F1 is 0, and the process proceeds from step S2 to step S4 in the first control cycle.

In step S4, it is determined whether or not forced regeneration of the filter 48 is necessary. Specifically, when the total PM accumulation amount of the filter 48 estimated by the accumulation amount estimation control described later is equal to or greater than a preset forced regeneration start determination value, it is determined that forced regeneration is necessary.
If the estimated accumulation amount of PM is less than the forced regeneration start determination value, it is determined that the forced regeneration at the present time is not necessary, this control cycle is terminated, and the processing is performed again from step S2 in the next control cycle.

On the other hand, if it is determined that forced regeneration is necessary, the process proceeds to step S6, the forced regeneration flag F1 is set to 1 to indicate that forced regeneration is necessary, and the process proceeds to next step S8.
In step S8, it is determined whether or not the oxidation catalyst 46 is activated by determining whether or not the temperature Tin of the exhaust gas flowing into the oxidation catalyst 46 detected by the inlet side exhaust temperature sensor 52 is 250 ° C. or higher. judge.

  If the temperature Tin of the exhaust gas flowing into the oxidation catalyst 46 is less than 250 ° C., it is determined that the oxidation catalyst 46 has not been activated, and the process proceeds to step S10, where temperature control of the oxidation catalyst 46 is performed. In this temperature rise control, the temperature of the oxidation catalyst 46 is raised to the activation temperature (for example, 250 ° C.) by supplying high-temperature exhaust gas to the oxidation catalyst 46, and the intake control valve 16 is controlled in the closing direction. Then, the exhaust gas temperature is raised, and the first additional fuel injection is performed from the injector 4 into the combustion chamber 6 in the expansion stroke of each cylinder as necessary. 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 combustion chamber 6 at such timing, the additional fuel is heated at a high temperature in the combustion chamber 6. When mixed with the combustion gas and combusted in the exhaust port or the exhaust manifold 30, high temperature exhaust gas is supplied to the oxidation catalyst 46, so that the temperature of the oxidation catalyst 46 rises.

Next, in step S18, as in step S4, it is determined whether or not the total PM accumulation amount of the filter 48 estimated by the accumulation amount estimation control described later is equal to or less than a preset forced regeneration end determination value. Make a decision.
As described above, since the oxidation catalyst 46 is not yet fully activated, PM is not incinerated, and it is determined that the estimated accumulation amount of PM is larger than the forced regeneration end determination value, and this control is performed. Since the cycle ends, the forced regeneration control is performed again from step S2 in the next control cycle.

In this case, since the value of the forced regeneration flag F1 is already 1, the process by the ECU 62 proceeds from step S2 to step S8.
If it is determined in step S8 that the temperature Tin of the exhaust gas flowing into the oxidation catalyst 46 is less than 250 ° C. and the oxidation catalyst 46 is not yet activated, the control of the intake control valve 16 in the closing direction is performed again in step S10. Catalyst temperature rise control is performed by injecting the first additional fuel. Therefore, as long as the temperature Tin of the exhaust gas flowing into the oxidation catalyst 46 is less than 250 ° C. and the oxidation catalyst 46 is not activated, the catalyst temperature increase control in step S10 is repeatedly performed every control cycle.

When the catalyst temperature increase control is repeated in this way and the temperature Tin of the exhaust gas flowing into the oxidation catalyst 46 is determined to be 250 ° C. or higher and the oxidation catalyst 46 is activated, the processing by the ECU 62 proceeds from step S8 to step S12. Come on.
In step S12, based on the exhaust temperature Tout on the outlet side of the filter 48 detected by the outlet side exhaust temperature sensor 54, it is determined whether or not the temperature of the filter 48 is equal to or higher than a predetermined temperature. This predetermined temperature is a temperature at which PM burns most efficiently in the filter 48. In this embodiment, the predetermined temperature is 600 ° C., and the exhaust temperature Tout on the outlet side of the filter 48 detected by the outlet side exhaust temperature sensor 54 is filtered. A temperature of 48 is considered.

If it is determined in step S12 that the exhaust temperature Tout on the outlet side of the filter 48 is 600 ° C. or higher, the process proceeds to step S14, and if it is determined that the exhaust temperature Tout is lower than 600 ° C., the process proceeds to step S16.
In steps S14 and S16, the second additional fuel is injected from the injector 4 into the combustion chamber 6 of each cylinder so as to maintain the temperature of the filter 48 at 600 ° C., and the second additional fuel is exhausted. Injected in the stroke. When the second additional fuel is injected into the combustion chamber 6 at such injection timing, the second additional fuel reaches the oxidation catalyst 46 without being burned in the combustion chamber 6 or the exhaust manifold 30 and is activated. The HC of the fuel is oxidized by the oxidation catalyst 46 at the conversion temperature. The temperature of the filter 48 rises to 600 ° C. due to the rise of the exhaust temperature due to the oxidation of HC, and the PM deposited on the filter 48 is incinerated. Therefore, in this embodiment, the injector 4 corresponds to a forced regeneration means.

  The injection amount of the second additional fuel is stored in a map having the engine speed detected by the rotation speed sensor 64 and the main injection amount determined by the ECU 62 as parameters, and this map is the second additional fuel. There are two types of maps, an increase map with a relatively large injection amount and a decrease map with a relatively small injection amount. In step S14, since the exhaust temperature Tout on the filter 48 outlet side is 600 ° C. or higher, a relatively small amount of second additional fuel is injected using the weight reduction map. In step S16, the exhaust temperature Tout on the filter 48 outlet side is injected. Since the temperature is lower than 600 ° C., a relatively large amount of the second additional fuel is injected using the increase map. As a result, the temperature of the filter 48 is maintained at around 600 ° C., and the PM deposited on the filter 48 is well removed by incineration.

  When the second additional fuel is injected in step S14 or S16, the process proceeds to step S18, and as described above, it is determined whether the estimated accumulation amount of PM is equal to or less than the forced regeneration end determination value. When the estimated accumulation amount of PM is larger than the forced regeneration end determination value, it is determined that forced regeneration of the filter 48 is still necessary, this control cycle ends, and control is performed again from step S2 in the next control cycle. I do. Therefore, as long as the estimated accumulation amount of PM is larger than the forced regeneration end determination value, the PM 48 accumulated in the filter 48 is incinerated and removed by the temperature increase of the filter 48 in step S14 or S16.

On the other hand, if the PM accumulated on the filter 48 is incinerated and removed, the total estimated accumulation amount of PM becomes equal to or less than the forced regeneration end determination value, and it is determined in step S18 that the forced regeneration of the filter 48 is completed, the process proceeds to step S20. The value of the advance forced regeneration flag F1 is set to 0, and the current control cycle ends.
When the value of the forced regeneration flag F1 becomes 0 in step S20, the process proceeds from step S2 to step S4 in the next control cycle. Therefore, until the forced regeneration of the filter 48 is required again, the process from step S2 to step S4 is performed. The process is repeated, and whether or not forced regeneration is necessary is determined for each control cycle.

Next, the accumulation amount estimation control for estimating the total PM accumulation amount of the filter 48 used in the above-described forced regeneration control necessity determination in step S4 and the forced regeneration completion determination in step S18 will be described below. To do.
The accumulation amount estimation control is performed at a predetermined control cycle by the ECU 62 in accordance with the flowchart of FIG. Here, it is assumed that the control is started from a state in which no PM is accumulated on the filter 48.

  First, in step S102, it is determined whether or not the value of the surface deposition flag F2 is 1. As described above with reference to FIG. 13, PM is deposited on the filter 48 on the surface of the filter 48 (corresponding to the portion 106 a in FIG. 13) and in the pores of the filter 48 (in FIG. 13). The surface deposition flag F2 indicates that PM is deposited on the surface of the filter 48 when the value of the surface deposition flag F2 is “1”. The initial value of the surface deposition flag F2 is 0, and the process proceeds from step S102 to step S104.

In step S <b> 104, it is determined based on the differential pressure before and after the filter 48 detected by the differential pressure sensor 60 whether there is PM accumulation on the surface of the filter 48.
As described above, deposition of PM on the filter 48 is first performed in the pores, and deposition on the surface of the filter 48 starts when the PM deposition in the pores is saturated. The relationship between the total amount of PM deposited on the filter 48 and the pressure difference across the filter 48 at this time is as shown in FIG. 5, and PM is gradually deposited from the state where PM is not deposited on the filter 48. As the PM accumulates in the pores, the differential pressure increases from the point a in FIG. 5 along the solid line. When the PM deposition in the pores is saturated at the point b, the differential pressure increases along the solid line toward the point c more gently than before, with the PM deposition on the filter 48 surface thereafter. Go. Therefore, if the differential pressure corresponding to the point b is grasped and stored in advance through experiments or the like, whether or not the differential pressure before and after the filter 48 detected by the differential pressure sensor 60 has reached the differential pressure corresponding to the point b. Thus, it can be determined whether PM deposition on the surface of the filter 48 has started.

Since it is assumed that the control is started from the state where PM is not accumulated on the filter 48, the differential pressure before and after the filter 48 does not increase to the value corresponding to the point b in FIG. Then, it is determined that there is no PM accumulation on the surface of the filter 48, and the process proceeds to step S106.
In step S106, based on the previously stored differential pressure before and after the filter 48 detected by the differential pressure sensor 60 from the relationship between the total PM accumulation amount in the filter 48 and the differential pressure before and after the filter 48 indicated by the solid line in FIG. The total amount of PM deposited on the filter 48 is estimated. In the filter 48, the exhaust gas discharged from the engine passes through the filter 48, so that PM accumulates in the pores. In parallel with this, NO ₂ supplied from the oxidation catalyst 46 and O ₂ in the exhaust gas are exhausted. PM is also removed by continuous regeneration. At this time, since PM is deposited and removed only in the pores, the pressure difference between the points a and b in FIG. Will change on the solid line between. Accordingly, here, the relationship between the PM accumulation amount and the differential pressure indicated by the solid line in FIG. 5 is used as it is without being corrected, so that the differential pressure detected by the differential pressure sensor 60 at that time can be completely applied to the filter 48. The amount of PM deposition can be accurately estimated.

  Thus, when the PM deposition amount is estimated in step S106 and the control cycle is completed, the processing is started again from step S102 in the next control, but the value of the surface deposition flag F2 remains 0, so step S104 again. Then, it is determined whether there is PM accumulation on the surface of the filter 48. Therefore, until the PM accumulation in the pores is saturated and the differential pressure before and after the filter 48 detected by the differential pressure sensor 60 reaches a value corresponding to the point b in FIG. 5, the solid line in FIG. Based on the relationship between the PM accumulation amount and the differential pressure shown, the total PM accumulation amount on the filter 48 is estimated.

  When PM deposition progresses and PM deposition in the pores is saturated, the differential pressure before and after the filter 48 detected by the differential pressure sensor 60 exceeds the value corresponding to the point b in FIG. 48. It is determined that there is PM deposition on the surface. In this case, the process proceeds from step S104 to step S108, where the value of the surface deposition flag F2 is set to 1 to indicate that there is PM deposition on the surface of the filter 48.

  Next, in step S110, it is determined whether PM has accumulated in the pores of the filter 48. The absence of PM deposition in the pores is determined by the fact that the PM deposition amount in the pores estimated in the process of step S112 described later substantially disappears. If the process of step S112 is not performed once and the process proceeds to step S110, PM deposition in the pores is saturated and PM deposition is in the pores because it is the first control cycle. Then, the process proceeds to step S112.

In step S112, the total PM deposition amount of the filter 48 is estimated based on the differential pressure before and after the filter 48 detected by the differential pressure sensor 60. However, here, unlike the estimation of the PM deposition amount in step S106, the PM deposition amount is estimated after correcting the relationship between the PM deposition amount and the differential pressure shown by the solid line in FIG.
That is, when PM deposition in the pores is saturated and PM is deposited on the surface of the filter 48, if the PM deposition in the pores remains saturated, the filter accompanies the PM deposition on the surface of the filter 48. The differential pressure around 48 changes on the solid line between points b and c in FIG. However, since the PM in the pores is actually burned by continuous regeneration or forced regeneration of the filter 48, the relationship between the PM deposition amount and the differential pressure is shown in FIG. The solid line portion between the b point and the c point changes so that the portion of the b point moves toward the a point side along the solid line between the a point and the b point with the same inclination. The relationship is from point to point d to point e. When PM in the pores is completely burned, the relationship shown by the alternate long and short dash line connecting points a and f in FIG. 5 is obtained.

  For this reason, in the state where PM is deposited on the surface of the filter 48, how much the solid line portion between the point b and the point c in FIG. 5 is translated toward the one-dot chain line connecting the points a and f. That is, unless the position d between the points a and b is accurately grasped, the relationship between the total PM deposition amount and the differential pressure cannot be accurately corrected and obtained. The amount of deviation from point d to point b corresponds to the amount of PM combustion in the pores, and the amount of deviation from point a corresponds to the amount of PM deposited in the pores at that time.

Therefore, in step S112, the total PM deposition amount of the filter 48 is estimated while correcting the relationship between the PM deposition amount and the differential pressure shown by the solid line in FIG. To do. The estimation of the total PM accumulation amount in step S112 is specifically performed according to the flowchart shown in FIG.
In the first step S202, the exhaust temperature on the outlet side of the filter 48 detected by the outlet side exhaust temperature sensor 54 is read as the temperature of the filter 48, and the process proceeds to step S204. Note that the detection value of the outlet side exhaust temperature sensor 54 is not used as it is as the temperature of the filter 48 as in the present embodiment, but a first-order lag filter or the like is applied to the detection value of the outlet side exhaust temperature sensor 54. The temperature may be estimated.

In step S204, the PM deposition amount in the pore estimated in the previous control cycle is read. Note that when the process proceeds to step S204 for the first time, since the PM accumulation in the pores is saturated, it is the first control cycle, and therefore, the saturated PM in the pores that has been grasped by experiments and stored in the ECU 62 in advance. The amount deposited is used as the previous estimated amount deposited in the pores.
Next, in step S206, based on the intake air amount detected by the air flow sensor 22, the amount of fresh air taken into the engine 1 during one control cycle is calculated, and the process advances to step S208.

In step S208, from the engine 1 during one control cycle, based on the total injection amount of fuel supplied to each cylinder of the engine 1 during one control cycle and the fresh air amount obtained in step S206. Calculate the exhaust flow rate.
Next, when proceeding to Step S210, the NOx concentration in the exhaust gas detected by the NOx sensor 50 is read, and the process proceeds to Step S212.

  In step 212, based on the exhaust gas flow rate calculated in step S208 and the NOx concentration in the exhaust gas read in step S210, the amount Qx of NOx flowing into the filter 48 during one control cycle is calculated (NOx supply). In the next step S214, a deviation ΔQx between the NOx supply amount Qx and a preset reference NOx supply amount Qxr is calculated. Therefore, in this first embodiment, the ECU 62 corresponds to the exhaust component amount calculating means of the present invention.

  Next, in step S216, the basic combustion amount of PM in the pores is calculated based on the temperature of the filter 48 read in step S202. Specifically, the temperature of the filter 48 read in step S202 is determined from the relationship between the temperature of the filter 48 that is preset and stored in accordance with the specifications of the filter 48 and the basic combustion speed of PM in the pores. Read the basic combustion speed of the corresponding PM. Next, by multiplying this basic combustion speed by a time corresponding to one control cycle, the basic combustion amount of PM in the pores during one control cycle is obtained.

The relationship between the filter temperature used in step S216 and the basic combustion rate of PM is as shown in FIG. 6, and the combustion rate of PM in the pores increases as the filter temperature increases. The combustion of PM deposited on the filter 48 is partly because NO ₂ in the exhaust gas supplied to the filter 48 acts as an oxidant as described above, and the filter temperature depends on the amount of NOx flowing into the filter 48. And the combustion rate change. The relationship shown in FIG. 6 corresponds to a specific NOx supply amount, and the NOx supply amount at this time corresponds to the reference NOx supply amount Qxr used in step S214.

  Therefore, in the next step S218, a value obtained by multiplying the deviation ΔQx from the reference NOx supply amount Qxr obtained in step S214 by a predetermined correction gain is added to the PM basic combustion amount in the pores obtained in step S216. The PM basic combustion amount is corrected, and the actual PM combustion amount in the pores during one control cycle is obtained (combustion amount calculating means). This predetermined correction gain indicates how much the actual PM combustion rate differs from the deviation of the NOx supply amount from the reference NOx supply amount Qxr, which is the premise of the relationship between the filter temperature and the PM basic combustion rate in FIG. Is obtained in advance by experiments or the like.

Next, when proceeding to step S220, the PM estimation amount in the current pore is subtracted from the previous PM estimated deposition amount in the pore read in step S204 by subtracting the PM combustion amount in the current pore obtained in step S218. After the accumulation amount is obtained and stored for use in step S204 in the next control cycle, the process proceeds to next step S222.
By the processing in step S220, the estimated PM deposition amount in the pores, which is the amount of deviation from the point a in FIG. 5, is determined. In step S222, the estimated PM deposition amount in the pores obtained in step S220 is set. The relationship between the PM accumulation amount in the filter 48 corrected by translating the solid line portion between the points b and c in FIG. 5 to the corresponding point d and the differential pressure before and after the filter 48 (for example, in FIG. 5) Using the a point to the d point to the e point), the PM accumulation amount in the filter 48 corresponding to the differential pressure before and after the filter 48 detected by the differential pressure sensor 60 is read out, and this is used as the total PM accumulation amount in the filter 48 ( Accumulation amount estimation means), the estimation of the PM accumulation amount in the current control cycle ends.

Thus, when the total PM accumulation amount of the filter 48 is estimated in step S112 of FIG. 3 and the control period is ended by the accumulation amount estimation control shown in FIG. 3, the process is started again from step S102 in the next control period.
At this time, since the value of the surface deposition flag F2 is already 1, the process proceeds from step S102 to step S110.

  In step S110, it is determined whether there is PM deposition in the pores based on the PM deposition amount in the pores obtained in step S112 in the previous control cycle. If it is determined that there is still PM deposition in the pores, the process proceeds to step S112 again, and PM deposition in the filter 48 shown in FIG. 5 is performed according to the amount of NOx supplied to the filter 48 as described above. The total PM accumulation amount of the filter 48 is estimated while correcting the relationship between the amount and the differential pressure before and after the filter 48, and the control cycle ends. Therefore, based on the PM deposition amount in the pores estimated in step S112, the entire filter 48 in step S112 is repeatedly performed every control period until it is determined in step S110 that the PM deposition in the pores has substantially disappeared. The PM accumulation amount is estimated.

  In the state where PM is accumulated on the surface of the filter 48, PM is not further accumulated in the pores, and the PM in the pores is burned and removed by continuous regeneration or forced regeneration of the filter 48, and the fineness estimated in step S112 is obtained. If it is determined in step S110 that PM is not substantially deposited in the pores based on the amount of PM deposited in the pores, the process proceeds to step S114 to determine whether there is PM deposition on the surface of the filter 48. judge.

This determination in step S114 is different from the determination of the presence or absence of surface deposition performed in step S104, and is performed based on the following idea.
Since the PM in the pores is all burned when the process proceeds to step S114, the relationship between the total amount of accumulated PM in the filter 48 and the differential pressure before and after the filter 48 is represented by points a and f in FIG. It will be indicated by a one-dot chain line connecting the two. In addition, in the state where PM is deposited on the surface of the filter 48, PM deposition does not occur in the pores. Therefore, unless all the PM deposited on the surface of the filter 48 burns, the amount of PM deposited in the filter 48 The relationship with the differential pressure before and after the filter 48 is represented by a one-dot chain line.

  That is, the PM deposited on the surface of the filter 48 starts to burn after all the PM in the pores burns, and the pressure difference between the front and rear of the filter 48 is a on the one-dot chain line in FIG. While moving toward the point, as PM contained in the exhaust discharged from the engine 1 accumulates on the surface of the filter 48, the differential pressure across the filter 48 is directed toward the point f on the one-dot chain line in FIG. Moving.

When PM on the surface of the filter 48 burns due to continuous regeneration or forced regeneration of the filter 48 and PM accumulation on the surface of the filter 48 is substantially eliminated, the differential pressure across the filter 48 becomes a value corresponding to the point a in FIG.
Therefore, in step S114, it is determined that PM accumulation has been eliminated on the surface of the filter 48 when the differential pressure before and after the filter 48 detected by the differential pressure sensor 60 has reached a value corresponding to the point a in FIG. Since the differential pressure before and after the filter 48 corresponding to the point a is unique to the filter 48 and is determined by the specifications of the filter 48, the ECU 62 stores the differential pressure corresponding to the point a previously obtained by experiments or the like. is doing.

If it is determined in step S114 that PM is still deposited on the surface of the filter 48, the process proceeds to step S116.
As described above, the relationship between the amount of accumulated PM in the filter 48 and the differential pressure before and after the filter 48 is represented by a one-dot chain line in FIG. 5, and the inclination of the one-dot chain line is the same as the inclination of the solid line connecting the point b and the point c. Therefore, based on the relationship represented by the solid line in FIG. 5, the relationship represented by the alternate long and short dash line can also be obtained in advance. The ECU 62 also stores in advance the relationship between the PM accumulation amount represented by the one-dot chain line and the differential pressure. In step S116, the ECU 62 responds to the differential pressure before and after the filter 48 detected by the differential pressure sensor 60 based on this relationship. The PM accumulation amount to be read is read out, and this is set as the total PM accumulation amount of the filter 48, and the control cycle is completed.

If it is determined in step S114 that PM is not deposited on the surface of the filter 48, the process proceeds to step S118. In step S118, the value of the surface deposition flag F2 is set to 0 to indicate that there is no PM deposition on the surface of the filter 48, and the control cycle ends.
Thus, when the PM 48 is completely deposited on the surface of the filter 48 and in the pores by forced regeneration or continuous regeneration of the filter 48, the value of the surface deposition flag F2 is also 0, so that the processing from step S102 is performed again in the next control cycle. Is started, the total PM accumulation amount on the filter 48 is estimated in the same manner as described above.

  As described above, in the exhaust emission control device according to the first embodiment of the present invention, the PM basic combustion amount in the pores of the filter 48 obtained based on the temperature of the filter 48 is used in the exhaust gas that contributes to the PM combustion rate. By correcting based on the amount of NOx, the amount of PM combustion in the pores can be obtained, so the amount of PM deposited in the pores can be accurately estimated from the amount of PM combustion in the pores. It becomes. The total PM deposition amount of the filter 48 is estimated based on the relationship between the PM deposition amount in the filter 48 corrected using the PM deposition amount in the pores thus obtained and the differential pressure before and after the filter 48. As a result, it is possible to accurately estimate the total amount of PM deposited on the filter 48.

Therefore, when the forced regeneration control of the filter 48 according to the flowchart of FIG. 2 is performed, it is possible to accurately determine whether or not forced regeneration is necessary and finish based on the total PM accumulation amount of the filter 48, and perform forced regeneration more than necessary. As a result, the fuel consumption is not deteriorated, and the filter 48 is not clogged without being sufficiently regenerated.
Further, since the amount of NOx supplied to the filter 48 is obtained based on the NOx concentration in the exhaust gas detected by the NOx sensor 50, the amount of NOx flowing into the filter 48 can be accurately grasped and the amount of accumulated PM can be determined. In addition to being able to estimate, it becomes possible to estimate the PM deposition amount by following the fluctuation of the NOx concentration quickly and accurately.

  In the first embodiment, the NOx sensor 50 is used to obtain the amount of NOx supplied to the filter 48 as described above, but the method for obtaining the NOx supply amount is not limited to this. Therefore, an exhaust purification apparatus that obtains the NOx supply amount to the filter 48 without using the NOx sensor 50 and estimates the total PM accumulation amount of the filter 48 will be described below as a modified example of the first embodiment.

  In this modification, only the method for obtaining the amount of NOx supplied to the filter 48 is different, and the other parts are exactly the same as those in the first embodiment. That is, the overall configuration is as shown in FIG. 1 as in the first embodiment except that the NOx sensor 50 is not used, and the forced regeneration control of the filter 48 is as shown in the flowchart of FIG. Accordingly, the same portions as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted, and different portions are mainly described.

  The accumulation amount estimation control for estimating the total PM accumulation amount of the filter 48 in the present modification is also performed in the same manner as in the first embodiment according to the flowchart of FIG. 3, but only the PM accumulation amount estimation method in step S112 is the first method. Since this embodiment is different from the first embodiment, description of processing contents other than step S112 is omitted. The estimation of the PM accumulation amount in step S112 in this modification is specifically performed according to the flowchart shown in FIG.

  In the first step S302, the exhaust temperature on the outlet side of the filter 48 detected by the outlet side exhaust temperature sensor 54 is read as the temperature of the filter 48, and the process proceeds to step S304. Note that, as described in the description of the first embodiment, the detection value of the outlet side exhaust temperature sensor 54 is not used as the temperature of the filter 48 as it is, but the detection value of the outlet side exhaust temperature sensor 54 is used as a primary delay filter or the like. May be applied to estimate the temperature of the filter 48.

In step S304, the PM deposition amount in the pore estimated in the previous control cycle is read. Note that when the process proceeds to step S304 for the first time, it is the first control cycle after the PM deposition in the pores is saturated, and therefore, the saturated PM in the pores that is grasped in advance by experiments and stored in the ECU 62. The amount deposited is the estimated amount deposited in the previous pore.
Next, in step S306, in order to forcibly regenerate the filter 48, it is determined whether or not HC is added to the exhaust by performing the first additional fuel injection or the second additional fuel injection from the injector 4. If it is determined in step S306 that HC is being added to the exhaust, the process proceeds to step S308. If it is determined that HC is not being added, the process proceeds to step S310.

In steps S308 and S310, a NOx map is selected for estimating the NOx emission amount from the engine 1 based on the engine speed and the accelerator pedal depression amount (engine load).
Since the operating conditions of the engine 1 are different between when HC conversion is performed during exhaust and when it is not performed, the NOx emission amount from the engine 1 is also different accordingly. Therefore, the ECU 62 corresponds to each case, and the engine speed And two types of NOx maps in which the NOx emission amount is determined using the accelerator pedal depression amount as a parameter are stored in advance. When the process proceeds to step S308, the NOx map for HC addition corresponding to the case where HC addition to the exhaust gas is performed is selected. When the process proceeds to step S310, the HC gas into the exhaust gas is selected. The NOx map for normal operation corresponding to the case where the addition is not performed is selected.

In the next step S312, the NOx map selected in step S308 or S310 is used to correspond to the engine speed detected by the engine speed sensor 64 and the accelerator pedal depression amount detected by the accelerator opening sensor 66. The NOx emission amount is read out and used as the NOx supply amount to the filter 48 (exhaust component amount calculating means).
The processing from the next steps S314 to S322 is exactly the same as the processing from steps S214 to S222 in the flowchart of FIG. 4 in the PM accumulation amount estimation control of the first embodiment.

That is, in step S314, a deviation ΔQx between the NOx supply amount Qx read in step S312 and a preset reference NOx supply amount Qxr is calculated, and in step S316, based on the temperature of the filter 48 read in step S302. The basic combustion amount of PM is calculated.
In the next step S318, the PM basic combustion amount obtained by multiplying the deviation ΔQx from the reference NOx supply amount Qxr obtained in step S314 by a predetermined correction gain is added to the PM basic combustion amount in the pores obtained in step S316. The amount of combustion is corrected, and the actual amount of PM combustion in the pores during one control cycle is obtained (combustion amount calculation means).

Further, in the next step S320, the PM estimated deposition amount in the pores this time is subtracted from the previous PM estimated deposition amount in the pores read in step S304, thereby subtracting the PM combustion amount in the current pores obtained in step S318. After determining the quantity and storing it for use in step S304 in the next control cycle, proceed to the next step S322.
In step S322, based on the relationship between the total PM deposition amount in the filter 48 and the differential pressure before and after the filter 48 shown in FIG. 5, the position of the point d corresponding to the estimated PM deposition amount in the pores obtained in step S320 is reached. Relationship between the PM accumulation amount in the filter 48 corrected by translating the solid line portion between the points b and c in FIG. 5 and the differential pressure before and after the filter (points a to d in FIG. 5) The PM accumulation amount in the filter 48 corresponding to the differential pressure before and after the filter 48 detected by the differential pressure sensor 60 is read out, and this is used as the total PM accumulation amount in the filter 48 (deposition amount estimation means). The estimation of the PM accumulation amount in the cycle is finished.

As described above, even when the NOx supply amount to the filter 48 is estimated from the NOx map stored in advance based on the engine speed and the accelerator pedal depression amount without using the NOx sensor 50, the first As in the embodiment, it is possible to accurately grasp the PM accumulation amount in the pores of the filter 48, and as a result, it is possible to accurately estimate the total PM constant volume amount of the filter 48.
Therefore, also in this modification, when the forced regeneration control of the filter 48 according to the flowchart of FIG. 2 is performed, it is possible to accurately determine whether or not forced regeneration is necessary and finish based on the total PM accumulation amount of the filter 48. As described above, the forced regeneration is not performed to reduce the fuel consumption, and the forced regeneration is not performed and the filter 48 is not clogged.

Further, in this modified example, the NOx supply amount to the filter 48 is estimated using the engine speed sensor 64 and the accelerator opening sensor 66 that are originally provided for different purposes without using the NOx sensor 50. As a result, costs can be reduced.
Next, an exhaust emission control device according to a second embodiment of the present invention will be described.
In the first embodiment, attention is paid to the amount of NOx supplied to the filter 48 as a factor that affects the PM combustion rate in the pores of the filter 48. However, the amount of O _{2 in} the exhaust gas supplied to the filter 48 is also considered. It is considered as one of such factors. Therefore, in the second embodiment, the PM combustion amount in the pores of the filter 48 is corrected according to the O ₂ supply amount to the filter 48.

FIG. 8 shows an overall configuration diagram of a four-cylinder diesel engine (hereinafter referred to as an engine) to which the exhaust emission control device according to the second embodiment of the present invention is applied, and is common to the first embodiment described above. The same reference numerals are used for the parts to be performed. 8 differs from the first embodiment only in that a λ sensor (oxygen sensor) 68 for continuously detecting the O ₂ concentration in the exhaust gas is provided instead of the NOx sensor 50. is there. The λ sensor 68 is provided in the communication passage 42 of the exhaust aftertreatment device 38. This is because a part of O ₂ contained in the exhaust discharged from the engine 1 is consumed as an oxidant on the oxidation catalyst 46, so that the amount of O ₂ supplied to the filter 48 is detected downstream of the oxidation catalyst 46. It is necessary to do.

Since the configurations of the first embodiment and the second embodiment are the same except for the NOx sensor 50 and the λ sensor 68 as described above, the description of the overlapping configuration is omitted.
The accumulation amount estimation control for estimating the PM accumulation amount on the filter 48 in the second embodiment is also performed in the same manner as in the first embodiment according to the flowchart of FIG. 3, but only the PM accumulation amount estimation method in step S112 is described above. Since it is different from the first embodiment, the description of the processing contents other than step S112 is also omitted.

The estimation of the PM accumulation amount in step S112 in the second embodiment is specifically performed according to the flowchart shown in FIG.
In the first step S402, the exhaust temperature on the outlet side of the filter 48 detected by the outlet side exhaust temperature sensor 54 is read as the temperature of the filter 48, and the process proceeds to step S404. As described in the description of the first embodiment, the detection value of the outlet side exhaust temperature sensor 54 is not used as it is as the temperature of the filter 48, but a first order lag filter or the like is added to the detection value of the outlet side exhaust temperature sensor 54. The temperature of the filter 48 may be estimated by application.

In step S404, the PM deposition amount in the pore estimated in the previous control cycle is read. Note that when the process proceeds to step S404 for the first time, it is the first control cycle after the PM deposition in the pores is saturated, and therefore, the saturated PM in the pores that is grasped in advance by experiments or the like and stored in the ECU 62. The amount deposited is the estimated amount deposited in the previous pore.
Next, when proceeding to step S406, based on the intake air amount detected by the air flow sensor 22, the amount of fresh air taken into the engine 1 during one control cycle is calculated, and the routine proceeds to step S408.

In step S408, based on the total injection amount of fuel supplied to each cylinder of the engine 1 during one control cycle and the fresh air amount obtained in step S206, the engine 1 performs one control cycle. Calculate the exhaust flow rate.
Next, when proceeding to step S410, the O ₂ concentration in the exhaust gas detected by the λ sensor 68 is read, and the routine proceeds to step S412.

In step 412, based on the exhaust gas flow rate calculated in step S408 and the O ₂ concentration in the exhaust gas read in step S410, the amount Qo of O ₂ supplied to the filter 48 during one control cycle is calculated. (Oxygen supply amount calculation means) In the next step S414, a deviation ΔQo between the O ₂ supply amount Qo and a preset reference O ₂ supply amount Qor is calculated. Therefore, also in the second embodiment, the ECU 62 corresponds to the exhaust component amount calculating means of the present invention.

  Next, in step S416, the basic combustion amount of PM in the pores is calculated based on the temperature of the filter 48 read in step S402. Specifically, based on the relationship between the temperature of the filter 48 that is preset and stored and the basic combustion speed of PM in the pores, the basic combustion speed of PM corresponding to the temperature of the filter 48 read in step S402 is calculated. read out. Next, by multiplying this basic combustion speed by a time corresponding to one control cycle, the basic combustion amount of PM in the pores during one control cycle is obtained.

The relationship between the filter temperature used in step S416 and the basic combustion rate of PM is as shown in FIG. 10, and the combustion rate of PM in the pores increases as the filter temperature increases. Combustion of PM deposited on the filter 48 is a partly that O ₂ in the exhaust gas supplied to the filter 48 as described above acts as an oxidizing agent, filtered by the amount of O ₂ flowing into the filter 48 The relationship between temperature and burning rate changes. Relationship shown in FIG. 10, which corresponds to a particular O ₂ supply amount, O ₂ supply amount at this time corresponds to the reference O ₂ supply amount Qor used in step S414.

Therefore, in the next step S418, a value obtained by multiplying the deviation ΔQo from the reference O ₂ supply amount Qor obtained in step S414 by a predetermined correction gain is added to the PM basic combustion amount in the pores obtained in step S416. The PM basic combustion amount is corrected by the above, and the actual PM combustion amount in the pores during one control cycle is obtained (combustion amount calculating means). The predetermined correction gain indicates how much the actual PM combustion rate is relative to the deviation of the O ₂ supply amount from the reference O ₂ supply amount Qor, which is the premise of the relationship between the filter temperature and the PM basic combustion rate in FIG. It is obtained by confirming beforehand whether or not they are different by experiments or the like.

Next, when proceeding to step S420, the current PM estimation in the pore is subtracted from the previous PM estimated deposition amount read in step S404 by subtracting the PM combustion amount in the current pore obtained in step S418. After the accumulation amount is obtained and stored for use in step S404 in the next control cycle, the process proceeds to the next step S422.
In step S422, similar to the processing in step S222 in the accumulation amount estimation control of the first embodiment shown in FIG. 4, based on the relationship between the total PM accumulation amount in the filter 48 shown in FIG. The PM deposition amount in the filter 48 corrected by translating the solid line portion between the points b and c to the position of the point d corresponding to the PM estimated deposition amount in the pores obtained in step S420 and the filter 48 Using the relationship with the differential pressure before and after (points a to d in FIG. 5), the PM accumulation amount in the filter 48 corresponding to the differential pressure before and after the filter 48 detected by the differential pressure sensor 60 is read. This is regarded as the total PM accumulation amount in the filter 48 (deposition amount estimation means), and the estimation of the PM accumulation amount in the current control cycle ends.

As described above, in the exhaust emission control device according to the second embodiment of the present invention, the PM basic combustion amount in the pores of the filter 48 obtained based on the temperature of the filter 48 is used to determine the PM basic combustion amount in the exhaust gas that contributes to PM combustion. By correcting based on the amount of O _2, the amount of PM combustion in the pores can be obtained, so the amount of PM deposited in the pores can be accurately estimated from the amount of PM combustion in the pores. It becomes. The total PM deposition amount of the filter 48 is estimated based on the relationship between the PM deposition amount in the filter 48 corrected using the PM deposition amount in the pores thus obtained and the differential pressure before and after the filter 48. As a result, it is possible to accurately estimate the total amount of PM deposited on the filter 48.

Therefore, when the forced regeneration control of the filter 48 according to the flowchart of FIG. 2 is performed, it is possible to accurately determine whether or not forced regeneration is necessary and finish based on the total PM accumulation amount of the filter 48, and perform forced regeneration more than necessary. As a result, the fuel consumption is not deteriorated, and the filter 48 is not clogged without being sufficiently regenerated.
Further, since the amount of O ₂ supplied to the filter 48 is obtained based on the O ₂ concentration in the exhaust gas detected by the λ sensor 68, the amount of O ₂ flowing into the filter 48 can be accurately grasped and PM can be obtained. The amount of deposition can be estimated, and the amount of PM deposition can be estimated by accurately following the variation in O ₂ concentration.

In the second embodiment, the λ sensor 68 is used to obtain the amount of O ₂ supplied to the filter 48 as described above, but the method for obtaining the O ₂ supply amount is not limited to this. Therefore, an exhaust purification apparatus that obtains the O ₂ supply amount to the filter 48 without using the λ sensor 68 and estimates the PM accumulation amount of the filter 48 will be described below as a modified example of the second embodiment.

In this modification, only the method for obtaining the O ₂ supply amount to the filter 48 is different, and the other parts are exactly the same as those in the second embodiment. That is, the overall configuration is as shown in FIG. 8 as in the second embodiment except that the λ sensor 68 is not used, and the forced regeneration control of the filter 48 is as shown in the flowchart of FIG. Accordingly, the same parts as those in the second embodiment are denoted by the same reference numerals and the description thereof is omitted, and different parts are described.

The accumulation amount estimation control in this modification is also performed according to the flowchart of FIG. 3 as in the first and second embodiments, but only the method for estimating the PM accumulation amount in step S112 is the first embodiment or the second embodiment. Therefore, description of processing contents other than step S112 is also omitted.
Furthermore, the PM accumulation amount estimation process of step S112 in this modification is for obtaining the O ₂ supply amount Qo to the filter 48 with respect to the specific flowchart of the PM accumulation amount estimation process of the second embodiment shown in FIG. Steps S410 and S412 are replaced with steps S410 ′ and S412 ′ as shown in FIG. 11, and other processing contents of steps S402 to S408 and steps S414 to S422 are completely the same as in the second embodiment. Are the same. Therefore, here, only the O ₂ supply amount calculation processing in steps S410 ′ and S412 ′ will be described with reference to FIG.

In step S410 ′, the fuel injection amount of the main injection is calculated from the fuel injected from the injector 4 into the combustion chamber 6 of each cylinder during one control cycle. When pilot injection is performed from the injector 4 prior to main injection, the fuel injection amount including the fuel injection amount by pilot injection is also used.
Next, when proceeding to step S412 ′, first, based on the fuel injection amount obtained in step S410 ′, the amount of O ₂ consumed when the fuel of the injection amount burns is calculated. Since the atmospheric O ₂ concentration is known, the O ₂ amount corresponding to the exhaust flow rate calculated by calculating in step S408 is calculated using the atmospheric O ₂ concentration, and the fuel burns from there. by reducing the amount of O ₂ consumed when the amount of O ₂ which is actually contained in the exhaust, that is, calculating the O ₂ supply amount Qo of the filter 48 (exhaust gas component amount calculating means).

In this way, using the O ₂ supply amount Qo obtained in step S412 ′, the total PM deposition amount of the filter 48 is estimated in steps S414 to S422 as in the second embodiment.
As described above, even when the O ₂ supply amount to the filter 48 is estimated by calculation without using the λ sensor 68, the PM deposition amount in the pores of the filter 48 is the same as in the second embodiment. As a result, the total PM accumulation amount of the filter 48 can be accurately estimated.

Therefore, also in this modification, when the forced regeneration control of the filter 48 according to the flowchart of FIG. 2 is performed, it is possible to accurately determine whether or not forced regeneration is necessary based on the PM accumulation amount of the filter 48, and to finish it more than necessary. In other words, the forced fuel regeneration is not performed to deteriorate the fuel efficiency, and the filter 48 is not clogged because the forced regeneration is not sufficiently performed.
Further, in this modification, the O ₂ supply amount to the filter 48 is estimated without using the λ sensor 68, so that the cost can be reduced.

Although the description of the exhaust gas purification apparatus according to the first and second embodiments of the present invention is finished above, the present invention is not limited to these embodiments.
For example, the first and second embodiments are implemented separately, but both may be implemented simultaneously. In this case, for example, in step S218 in FIG. 4, step S318 in FIG. 7, or step S418 in FIG. 9, NOx supply amount deviation ΔQx is multiplied by a predetermined correction gain, and O ₂ supply amount deviation ΔQo is predetermined correction. What is multiplied by the gain is added to the PM basic combustion amount in the pores to calculate the PM accumulation amount in the pores.

In the first and second embodiments, the injector 4 is used as a forced regeneration means for supplying the HC to forcibly regenerate the filter 48, and the first additional fuel injection and the second additional fuel injection are performed. However, instead of this, a fuel addition valve that injects fuel into the exhaust gas upstream of the filter 48 and supplies HC to the filter 48 may be provided as a forced regeneration means.
Furthermore, in the first and second embodiments, a four-cylinder diesel engine is used as the engine. However, the number and type of cylinders of the engine are not limited to this, and a filter for collecting PM in the exhaust is used. Whatever you need.

1 is an overall configuration diagram of an engine to which an exhaust emission control device according to a first embodiment of the present invention is applied. 2 is a flowchart of forced regeneration control of a filter performed by the exhaust gas purification apparatus of FIG. It is a flowchart of the accumulation amount estimation control performed by the exhaust gas purification apparatus of FIG. FIG. 4 is a flowchart showing details of estimation of the total PM deposition amount when there is correction based on the PM deposition amount in the pores in the deposition amount estimation control of FIG. 3. It is a figure which shows the relationship between the differential pressure before and behind the filter used in FIG. 4, and the total amount of PM deposits in a filter. It is a figure which shows the relationship between the basic combustion speed of PM in a pore used in FIG. 4, and filter temperature. It is a flowchart which shows the modification of total PM accumulation amount estimation of FIG. It is a whole block diagram of the engine to which the exhaust gas purification apparatus which concerns on 2nd Embodiment of this invention was applied. FIG. 9 is a flowchart showing details of estimation of the total PM deposition amount when there is a correction based on the PM deposition amount in the pores in the exhaust purification device of FIG. It is a figure which shows the relationship between the basic combustion speed of PM in a pore used in FIG. 9, and filter temperature. FIG. 10 is a flowchart showing a partial excerpt of a modified example of the total PM accumulation amount estimation of FIG. 9. It is a schematic diagram which shows the accumulation state of PM in a filter. It is a figure which expands and shows a part of FIG.

Explanation of symbols

1 Engine 4 Injector (Forced regeneration supply means)
48 Filter 50 NOx sensor 54 Outlet side exhaust temperature sensor (filter temperature detection means)
60 Differential pressure sensor (Differential pressure detection means)
62 ECU
68 λ sensor (oxygen sensor)

Claims (8)

A filter that is disposed in the exhaust passage of the engine and collects and deposits particulates in the exhaust in and on the surface of the exhaust by circulating the exhaust in the pore;
Filter temperature detection means for detecting the temperature of the filter;
Among the components in the exhaust gas supplied to the filter, an exhaust component amount calculating means for determining the amount of a specific component contributing to the combustion of the particulates collected by the filter;
The basic combustion amount of the particulates in the pores based on the temperature of the filter detected by the filter temperature detecting means is corrected based on the amount of the specific component detected by the exhaust component amount calculating means. A combustion amount calculating means for obtaining a particulate combustion amount in the hole;
An exhaust emission control device comprising: a deposit amount estimating means for estimating a particulate deposit amount on the filter based on the particulate combustion amount obtained by the combustion amount calculating means. A differential pressure detecting means for detecting a differential pressure before and after the filter;
The accumulation amount estimating means is based on the preset relationship between the differential pressure and the particulate accumulation amount on the filter and the differential pressure detected by the differential pressure detection means. The amount of accumulation is estimated, and the relationship between the differential pressure and the amount of particulate accumulation on the filter is corrected according to the amount of particulate combustion in the pores determined by the combustion amount calculation means. The exhaust emission control device according to claim 1.   The deposition amount estimation means is configured to apply the differential pressure based on the particulate combustion amount in the pores to the filter and to the filter only when particulates are deposited on both the surface of the filter and the pores. The exhaust emission control device according to claim 2, wherein the relationship with the particulate accumulation amount is corrected. The exhaust component amount calculating means includes:
A NOx sensor disposed in the exhaust passage for detecting the concentration of NOx in the exhaust;
The NOx supply amount calculating means for calculating the amount of NOx supplied to the filter based on the NOx concentration in the exhaust gas detected by the NOx sensor. Exhaust purification equipment.   The exhaust component amount calculating means reads the amount of NOx supplied to the filter by reading the NOx emission amount corresponding to the actual engine operating state from a NOx emission amount map set in advance based on the operating state of the engine. The exhaust emission control device according to any one of claims 1 to 3, wherein the exhaust purification device is obtained. A forced regeneration means for forcibly regenerating the filter by supplying HC to the filter;
6. The exhaust gas component amount calculation means uses different NOx emission amount maps when forced regeneration by the forced regeneration means is performed and when forced regeneration is not performed. The exhaust emission control device described. The exhaust component amount calculating means includes:
An oxygen sensor disposed in the exhaust passage for detecting an oxygen concentration in the exhaust;
The oxygen supply amount calculating means for calculating the amount of oxygen supplied to the filter based on the oxygen concentration in the exhaust gas detected by the oxygen sensor. Exhaust purification equipment.   The exhaust gas component amount calculation means obtains the amount of oxygen supplied to the filter based on a fresh air amount supplied to the engine and a fuel supply amount to the engine. The exhaust emission control device described.

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