JP2006242072A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine preventing poor regeneration and excess regeneration of a filter by accurately judging completion of regeneration of the filter. <P>SOLUTION: This device is provided with a target regeneration rate establishing means 42 establishing a target regeneration rate of a filter 28 based on accumulation quantity of a particulate, a target integration value establishing means 44 establishing a target oxygen flow rate integration value corresponding to the target regeneration rate based on relation between a pre-established filter regeneration rate and an integration value of oxygen flow rate supplied to the filter 28, and a regeneration completion judgment means 48 judging completion of regeneration when an integration value of detected oxygen flow rate reaches the target oxygen flow rate integration value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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 suitable for removing particulates from exhaust gas from a diesel engine or the like.

Conventionally, a diesel particulate filter (hereinafter referred to as a filter) has been provided in the exhaust passage of a diesel engine so that particulates contained in the exhaust discharged from the engine are captured by the filter so that the particulates are not released into the atmosphere. Technology is known.
In such a filter, since the trapped particulates accumulate in the filter and the exhaust resistance gradually increases, it is necessary to regenerate the filter by incinerating the appropriately deposited particulates.

For this reason, for example, an oxidation catalyst is provided in the exhaust passage on the upstream side of the filter. In this oxidation catalyst, NO in the exhaust is oxidized to generate NO _2, and particulates deposited on the filter using NO ₂ as an oxidant are used. It is known to perform continuous regeneration of the filter by burning.
However, depending on the operating state of the engine, the exhaust temperature may not rise to the activation temperature of the oxidation catalyst, and continuous regeneration may not be performed. In such a case, regardless of continuous regeneration using the oxidation catalyst, It is necessary to forcefully regenerate the filter.

Methods for forced regeneration of the filter include burning the particulates with a heat source such as an electric heater provided in the filter, or supplying HC to the oxidation catalyst and raising the temperature of the filter with the heat generated by the HC oxidation reaction. What incinerates curate is known.
In such forced regeneration, it is necessary to accurately determine that the incineration of the particulate has been completed, and to prevent the electric heater from being energized or the temperature of the filter not being increased more than necessary. For this reason, the completion of filter regeneration is estimated based on the forced regeneration execution time, etc., but the time required for filter regeneration actually varies depending on the vehicle running conditions and engine operating conditions. Could not be judged.

Therefore, focusing on the fact that there is a correlation between the integrated value of the oxygen supply amount supplied to the filter and the combustion amount of the particulates under specific conditions, the integrated value of the mass flow rate of oxygen supplied to the filter Has been proposed, and when this integrated value reaches a predetermined value, it is determined that the reproduction has been completed (Patent Document 1).
JP 2004-293340 A

  However, in the exhaust purification device of Patent Document 1, there is a correlation between the integrated value of the oxygen supply amount to the filter and the particulate combustion amount under the condition that the particulate deposition amount at the start of regeneration is assumed to be constant. The end of regeneration of the filter is determined based on the relationship, and when regeneration is started with an arbitrary particulate accumulation amount, completion of regeneration cannot be accurately determined. For this reason, there is a possibility that the filter may not be sufficiently regenerated or that forced regeneration continues excessively even though the regeneration is completed.

  The present invention has been made in view of such problems, and an object of the present invention is to determine the completion of filter regeneration with high accuracy, and to prevent defective regeneration and excessive regeneration of the filter. An object of the present invention is to provide an exhaust emission control device for an engine.

  In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention is disposed in an exhaust passage and captures particulates in exhaust discharged from the internal combustion engine, while incinerating the accumulated particulates. A filter for performing regeneration, a deposition amount detecting means for detecting the amount of particulate deposition in the filter, and a target regeneration for setting a target regeneration rate of the filter based on the deposition amount detected by the deposition amount detecting means A target integrated value for setting a target oxygen flow rate integrated value corresponding to the target regeneration rate, based on a rate setting means, and a relationship between a preset regeneration rate of the filter and an integrated value of the oxygen flow rate supplied to the filter A setting means, an oxygen flow rate detection means for detecting an oxygen flow rate supplied to the filter, and the oxygen flow rate detection means during regeneration of the filter. A regeneration end determining means for determining that the regeneration of the filter is completed when the detected integrated value of the oxygen flow reaches a target oxygen flow integrated value set by the target integrated value setting means; It is characterized (claim 1).

According to the exhaust gas purification apparatus for an internal combustion engine configured as described above, when the integrated value of the oxygen flow supplied to the filter reaches the target oxygen flow integrated value corresponding to the target regeneration rate of the filter, it is determined that the regeneration of the filter is completed. To do.
The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising filter temperature detection means for detecting a temperature of the filter, wherein the target integrated value setting means is configured to set a preset regeneration rate of the filter and the filter. Based on the relationship with the integrated value of the supplied oxygen flow rate, the integrated value of the oxygen flow rate determined corresponding to the target regeneration rate is corrected based on the filter temperature detected by the filter temperature detecting means, and the target oxygen flow rate is corrected. An integrated value is set (claim 2).

More specifically, the target integrated value setting means corrects so that the target oxygen integrated value becomes smaller as the filter temperature is higher (Claim 3).
The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising exhaust gas flow rate detecting means for detecting an exhaust gas flow rate flowing into the filter, wherein the target integrated value setting means has a preset regeneration rate of the filter. Based on the relationship with the integrated value of the oxygen flow rate supplied to the filter, the integrated value of the oxygen flow rate corresponding to the target regeneration rate is corrected based on the exhaust flow rate detected by the exhaust flow rate detecting means. Then, a target oxygen flow rate integrated value is set (claim 4).

More specifically, the target integrated value setting means corrects the target oxygen integrated value so that it decreases as the exhaust flow rate decreases.
The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising filter temperature detection means for detecting the temperature of the filter, and exhaust flow rate detection means for detecting an exhaust flow rate flowing into the filter, wherein the target integrated value The setting means is configured to obtain an integrated value of the oxygen flow rate corresponding to the target regeneration rate based on a relationship between a preset regeneration rate of the filter and an integrated value of the oxygen flow rate supplied to the filter. The target oxygen flow rate integrated value is set by correcting based on the filter temperature detected by the temperature detection means and the exhaust flow rate detected by the exhaust flow rate detection means.

More specifically, the target integrated value setting means corrects the target oxygen integrated value so that it decreases as the filter temperature increases, and also decreases the target oxygen integrated value as the exhaust flow rate decreases. The correction is made (claim 7).
According to the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 2 to 7, the target oxygen flow rate integrated value corrected based on at least one of the filter temperature and the exhaust flow rate is used when determining completion of regeneration of the filter.

  According to the exhaust gas purification apparatus for an internal combustion engine of claim 1, it is determined that the regeneration of the filter is completed when the integrated value of the oxygen flow supplied to the filter reaches the target oxygen flow integrated value corresponding to the target regeneration rate of the filter. As a result, there is no restriction assuming that the particulate deposition amount at the start of regeneration is constant, and even if regeneration is started from an arbitrary particulate deposition amount, the completion of regeneration of the filter can always be accurately determined. It becomes possible.

  Further, the amount of particulate combustion during regeneration varies depending on the exhaust gas temperature and the exhaust flow rate during regeneration. According to the exhaust gas purification apparatus for an internal combustion engine according to claim 2 to 7, at least the filter temperature and the exhaust gas flow rate Since the regeneration completion determination is performed using the target oxygen flow rate integrated value corrected based on one of them, an accurate regeneration end determination can always be performed even if the above fluctuation occurs.

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 1 includes a high-pressure accumulator chamber (hereinafter referred to as a common rail) 2 common to each cylinder, and supplies high-pressure light oil stored in the common rail 2 to an injector 4 provided in each cylinder. Light oil is injected inside.

  The intake passage 6 is equipped with a turbocharger 8. The intake air drawn from an air cleaner (not shown) flows into the compressor 8a of the turbocharger 8 from the intake passage 6, and the intake air supercharged by the compressor 8a is intercooler. 10 and the intake control valve 52 are introduced into the intake manifold 12. An intake flow rate sensor 14 for detecting the mass flow rate of intake air to the engine 1 is provided upstream of the compressor 8a in the intake passage 6.

On the other hand, an exhaust port (not shown) through which exhaust is discharged from each cylinder of the engine 1 is connected to an exhaust pipe (exhaust passage) 18 via an exhaust manifold 16. An EGR passage 22 is provided between the exhaust manifold 16 and the intake manifold 12 to communicate the exhaust manifold 16 and the intake manifold 12 via the EGR valve 20.
After passing through the turbine 8 b of the turbocharger 8, the exhaust pipe 18 is connected to the exhaust aftertreatment device 24 via the exhaust throttle valve 54. The turbine 8b is connected to the compressor 8a, and receives the exhaust gas flowing in the exhaust pipe 18 to drive the compressor 8a.

Further, the exhaust aftertreatment device 24 accommodates an oxidation catalyst 26 on the upstream side in the casing, and a diesel particulate filter (hereinafter referred to as a filter) that captures particulates in the exhaust on the downstream side of the oxidation catalyst 26. ) 28 is housed.
The oxidation catalyst 26, the NO in the exhaust by oxidation to generate NO _2, and supplies the NO ₂ to the filter 28 as an oxidizing agent. In the filter 28, the accumulated particulates react with NO ₂ supplied from the oxidation catalyst 26 and burnt, and the filter 28 is continuously regenerated.

  Between the oxidation catalyst 26 and the filter 28, a catalyst temperature sensor 30 that detects the exhaust temperature on the outlet side of the oxidation catalyst 26 as the temperature of the oxidation catalyst 26, and an upstream pressure sensor 32 that detects the exhaust pressure on the upstream side of the filter 28. And are provided. Further, on the downstream side of the filter 28, a filter temperature sensor 34 for detecting the exhaust temperature on the outlet side of the filter 28 as the temperature of the filter 28, and a downstream pressure sensor 36 for detecting the exhaust pressure on the downstream side of the filter 28 are provided. ing.

The ECU 38 is a control device for performing comprehensive control of the exhaust gas purification apparatus according to the present invention including the engine 1, 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 14, a catalyst temperature sensor 30, an upstream pressure sensor 32, a filter temperature sensor 34, and a downstream pressure sensor 36 are collected on the input side of the ECU 38 in order to collect information necessary for performing various controls. Various devices such as the injector 4, the EGR valve 20, the intake control valve 52, and the exhaust throttle valve 54 of each cylinder that are controlled based on the calculated control amount are connected to the output side. Yes.

  The ECU 38 also performs calculation of the fuel supply amount to each cylinder of the engine 1 and fuel supply control from the injector 4 based on the calculated fuel supply amount. The calculation of the fuel supply amount (main injection amount) necessary for the operation of the engine 1 is stored in advance based on the engine speed and the accelerator opening detected by an engine speed sensor and an accelerator opening sensor (not shown). It is determined by reading from the 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 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 28 are incinerated and removed by continuous regeneration using the oxidation catalyst 26. However, the operating state where the exhaust temperature of the engine 1 is low, for example, In low speed, low load operation, etc., the exhaust temperature does not rise to the activation temperature of the oxidation catalyst 26, and NO in the exhaust is not oxidized and continuous regeneration may not be performed. If such a state continues, particulates excessively accumulate in the filter 28 and the filter 28 may be clogged. For this reason, the forced regeneration is appropriately performed according to the accumulation state of the particulates in the filter 28.

The forced regeneration control is executed by the ECU 38 at a predetermined control cycle in accordance with the flowchart shown in FIG.
First, in step S102 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 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 S102 to step S104 in the first control cycle.

  In step S104, it is determined whether or not the forced regeneration of the filter 28 is necessary. Specifically, the difference between the detected value of the upstream pressure sensor 32 and the detected value of the downstream pressure sensor 6, that is, the differential pressure between the inlet and outlet of the filter 28 is obtained, and the accumulated amount of particulates estimated based on this differential pressure Is determined to be necessary for forced regeneration. In this case, the process proceeds to step S106, 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 it is determined that the differential pressure of the filter 28 is less than the predetermined value and the forced regeneration at the present time is not necessary, this control cycle is ended, and the processing is performed again from step S102 in the next control cycle.

In step S104, it is determined that forced regeneration is necessary, and the process proceeds to step S106. The value of the forced regeneration flag F1 is set to 1, and then the process proceeds to step S108. Based on the detected value of the catalyst temperature sensor 30, the oxidation catalyst 26 It is determined whether or not the temperature Tc is higher than the activation temperature (for example, 250 ° C.) and the oxidation catalyst 26 is activated.
When the catalyst temperature Tc is less than 250 ° C., the process proceeds to step S110, and the temperature increase control of the oxidation catalyst 26 is performed. In this temperature raising control, the temperature of the oxidation catalyst 26 is raised to the activation temperature of 250 ° C. by supplying high-temperature exhaust gas to the oxidation catalyst 26, and the intake control valve 52 and the exhaust throttle valve 54 are closed. 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. After mixing, additional fuel burns in the exhaust port and the exhaust manifold 16, and high-temperature exhaust gas is supplied to the oxidation catalyst 26, and the temperature of the oxidation catalyst 26 rises.

  In this manner, the temperature increase control of the oxidation catalyst 26 is performed in step S110, and this control cycle is completed, and control is performed again from step S102 in the next control cycle. In this case, since the value of the forced regeneration flag F1 is already 1, the process proceeds from step S102 to step S108, and while the catalyst temperature Tc is lower than 250 ° C., the process proceeds from step S108 to step S110 and the first addition. The temperature increase control of the oxidation catalyst 26 is performed by fuel injection.

  When the injection of the first additional fuel is repeated in this manner and the temperature Tc of the oxidation catalyst 26 becomes 250 ° C. or higher, the process proceeds from step S108 to step S112. In step S112, based on the detection value of the catalyst temperature sensor 30, it is determined whether or not the temperature Tc of the oxidation catalyst 26 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 28, and in this embodiment, the predetermined temperature is 600 ° C.

If it is determined in step S112 that the catalyst temperature Tc is 600 ° C. or higher, the process proceeds to step S114, and if it is determined that the catalyst temperature Tc is less than 600 ° C., the process proceeds to step S116.
In steps S114 and S116, the second additional fuel is injected into each cylinder so that the temperature of the exhaust gas supplied to the filter 28 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 26 without being burned in the cylinder or the exhaust manifold 16 and is at the activation temperature. Combustion occurs in the oxidation catalyst 26 and the filter 28. By this combustion, the exhaust temperature rises to 600 ° C., and the particulates deposited on the filter 28 are incinerated.

  The second additional fuel is stored in a map having the engine speed and the main injection amount (load) as parameters, and this map includes an increase map in which the second additional fuel injection amount is set to be relatively large, There are two types of weight loss maps set relatively small. In step S114, since the catalyst temperature Tc is 600 ° C. or higher, the second additional fuel is injected using the reduction map. In step S116, the catalyst temperature Tc is lower than 600 ° C., so the second increase fuel is used. Inject additional fuel. As a result, the temperature of the exhaust gas discharged from the oxidation catalyst 26 and supplied to the filter 28 is maintained at 600 ° C.

When the second additional fuel is injected in step S114 or S116, the process proceeds to step S118, and it is determined whether or not the value of the forced regeneration end flag F2 is zero.
The forced regeneration end flag F2 becomes 0 when forced regeneration end is determined in forced regeneration end determination control (described later) that is separately executed when the value of the forced regeneration flag F1 becomes 1. The value is 1 when the end of forced regeneration is not determined. Accordingly, the value of the forced regeneration end flag F2 is 1 until the forced regeneration end determination is determined in the forced regeneration end determination control. Therefore, the control cycle ends, and control is again performed from step S102 in the next control cycle. Do. On the other hand, if the forced regeneration end determination control determines that the forced regeneration is terminated, the forced regeneration end flag F2 is 0, and the process proceeds to step S120.

  In step S120, since the end of forced regeneration is determined, the value of the forced regeneration flag F1 is set to 0, and the control in this control cycle is terminated. When the value of the forced regeneration flag F1 becomes 0 in this way, the process proceeds from step S102 to step S104 in the next control cycle. Therefore, until the forced regeneration of the filter 28 becomes necessary again, the processing in steps S102 and S104 is performed. Is repeated.

Next, forced regeneration end determination control will be described below.
The forced regeneration end determination control is executed at a predetermined control cycle according to the flowchart of FIG. 4 by a control block provided in the ECU 38 as shown in FIG.
That is, the forced regeneration end determination control is performed based on the accumulation amount detection unit (deposition amount detection means) 40 that detects the accumulation amount of particulates in the filter 28 and the accumulation amount detected by the accumulation amount detection unit 40. Based on the relationship between the target regeneration rate setting unit (target regeneration rate setting means) 42 for setting the target regeneration rate ηt, and the preset regeneration rate of the filter 28 and the integrated value of the oxygen flow rate supplied to the filter 28, A target integrated value setting unit (target integrated value setting unit) 44 that sets a target oxygen flow rate integrated value Dt corresponding to the regeneration rate ηt, and an oxygen flow rate detecting unit (oxygen flow rate detecting unit) that detects the oxygen flow rate supplied to the filter 28. 46) When the integrated value of the oxygen flow detected by the oxygen flow rate detection unit reaches the target oxygen flow integrated value ηt during the regeneration of the filter 28, the regeneration of the filter 28 is completed. A reproduction end determination section (reproduction end determination means) 48 determines that the exhaust flow rate detector for detecting the flow rate of the exhaust gas flowing into the filter 28 (exhaust gas flow rate detection means) is performed by 50.

  More specifically, when control is started in accordance with the flowchart of FIG. 4, it is first determined in step S202 whether or not the value of the forced regeneration flag F1 is 1. The value of the forced regeneration flag F1 is 0 when forced regeneration is not performed, and is 1 when it is determined that forced regeneration is necessary in the forced regeneration control performed according to the flowchart shown in FIG. It is set (step S106 in FIG. 2). Therefore, when the forced regeneration control is being executed, the process proceeds from step S202 to step S204, and when the forced regeneration control is not being executed, the process in the current control cycle is finished.

  In step S204, it is determined whether or not the value of the forced regeneration end flag F2 is zero. The forced regeneration end flag F2 has a value of 0 when it is determined that the forced regeneration is complete, and a value of 1 when the completion of the forced regeneration is not determined during the forced regeneration, and its initial value is 0. It is. Accordingly, when the process proceeds from step S202 to step S204 for the first time after the value of the forced regeneration flag F1 becomes 1, the process proceeds to step S206. In step S206, the value of the forced regeneration end flag F2 is set to 1. Further, if the value of the forced regeneration flag F1 continues to be 1 after the next control cycle, the value of the forced regeneration end flag F2 is already 1, so that the process proceeds directly from step S204 to step S212. The processing from S206 to S210 is omitted.

In the first control cycle, the process proceeds from step S204 to step S206 to set the value of the forced regeneration end flag F2 to 1, and then proceeds to step S208. When the process proceeds to step S208, the amount of particulates accumulated on the filter 28 by the accumulation amount detection unit 40. PMw is detected.
The accumulation amount detection unit 40 receives detection signals from the upstream pressure sensor 32 and the downstream pressure sensor 36, and the exhaust pressure upstream of the filter 28 detected by the upstream pressure sensor 32 and the filter 28 detected by the downstream pressure sensor 36. Based on the differential pressure from the exhaust pressure on the downstream side, the amount PMw of particulates accumulated in the filter 28 is calculated and detected. The particulate accumulation amount PMw is sent to the target regeneration rate setting unit 42.

  Particulates accumulated in the filter 28 are not incinerated at the time of forced regeneration, and a part thereof remains in the filter 28. Therefore, the target regeneration rate setting unit 42 stores the residual allowable particulate amount PMr in advance, and the difference between the accumulated particulate amount PMw detected by the deposition amount detecting unit 40 and the residual allowable particulate amount PMr is forced. Since the particulate amount PMb is to be incinerated by regeneration, the target regeneration rate ηt is set by the following equation (1) (step S210).

ηt = PMb / PMw = 1− (PMr / PMw) (1)
If the target regeneration rate ηt is set in the first control cycle of the forced regeneration end determination control, it is not necessary to set the target regeneration rate again until the completion of forced regeneration is determined after the next control cycle. As described above, the processes in steps S206 to S210 are omitted.

When the process proceeds from step S210 to step S212, the target integrated value setting unit 44 reproduces the target oxygen flow rate integrated value Dt corresponding to the target regeneration rate ηt set by the target regeneration rate setting unit 42 by regenerating the preset filter 28. It is set based on the relationship between the rate and the integrated value of the oxygen flow rate supplied to the filter 28.
Here, the relationship between the regeneration rate of the filter 28 and the integrated value of the oxygen flow rate supplied to the filter 28 will be described in more detail.

It is known that the particulate burning rate ΔPM is expressed by the following equation (2).
ΔPM = A · Dα · PM · exp {−E / (R · T)} (2)
A is a constant (frequency factor) obtained by experiment, D is an oxygen concentration, α is a constant according to the contribution of oxygen, PM is a particulate deposition amount at that time, E is a hardware such as the presence or absence of the oxidation catalyst 26, etc. The activation energy constant determined by the wear configuration, R is the gas constant, and T is the temperature of the filter 28.

Here, assuming that the filter temperature T is constant, the particulate combustion rate ΔPM _{k at} an arbitrary timing k after the start of regeneration is expressed by the following equation (3).
ΔPM _k = B · D _k α · PM _k (3)
However, B is represented by the following formula (4).
B = A · exp {−E / (R · T)} (4)
Accordingly, the combustion speed ΔPM _{k at} the timing k = 0, 1, 2 is expressed by the following equations (5) to (7), respectively.

ΔPM ₀ = B · D ₀ α · PM ₀ (5)
ΔPM ₁ = B · D ₁ α · PM ₁ (6)
ΔPM ₂ = B · D ₂ α · PM ₂ (7)
In the above equation (6), PM ₁ is PM ₀ −ΔPM ₀ , and therefore, when the relationship of the above equation (5) is substituted and arranged, the following is obtained.

ΔPM ₁ = B · D ₁ α · PM ₀ · (1−B · D ₀ α) (8)
Further, in the above equation (7), PM ₂ = PM ₀ −ΔPM ₀ −ΔPM ₁ , and therefore, when the relations of the above equations (5) and (8) are substituted and arranged, the following is obtained.
ΔPM ₂ = B · D ₂ α · PM ₀ · (1−B · D ₀ α) · (1−B · D ₁ α) (9)
Therefore, the particulate combustion time ΔPM _{k at} an arbitrary timing k is expressed by the following equation (10).

ΔPM _k = B · D _k α · PM ₀ · f (B, D ₀ to _k-1 α) (10)
The total combustion amount of the particulates from the start of regeneration of the filter 28 (k = 0) to the timing k = n can be calculated by obtaining the integrated value of the combustion speed ΔPM expressed by the above equation (10). .
ΣΔPM = B · PM ₀ · Σ {D _i α · f (B, D ₀ to _n-1 α)} (11)
Since the regeneration rate η of the filter 28 is obtained by dividing the total particulate combustion amount ΣΔPM by the particulate accumulation amount PM ₀ at the start of regeneration, the regeneration rate η is expressed as follows based on the above equation (11). become.

η = B · Σ {D _i α · f (B, D ₀ to _n-1 α)} (12)
From the above equation (12), it can be seen that the regeneration rate η of the filter 28 is closely related to the oxygen concentration integrated value, and that the history of the oxygen concentration affects the regeneration rate η.
Based on such analysis results, the relationship between the regeneration rate η of the filter 28 and the integrated oxygen concentration value can be obtained. In an actual engine, it is necessary to pay attention to the number of oxygen molecules passing through the filter 28 in consideration of fluctuations in the exhaust gas flow rate and oxygen concentration. Therefore, an integrated value of the oxygen mass flow rate is used instead of the integrated oxygen concentration value. Moreover, even if f (B, D ₀ to _n-1 α) indicating the history of oxygen concentration is omitted, it is experimentally shown that the correlation between the regeneration rate η and the oxygen mass flow rate integrated value can be maintained well. confirmed.

FIG. 5 shows the relationship between the regeneration rate η thus obtained and the oxygen mass flow rate integrated value.
The target integrated value setting unit 44 stores in advance the relationship between the regeneration rate η and the oxygen mass flow integrated value shown in FIG. 5 in the regeneration rate-oxygen mass flow integrated value map, and is set by the target regeneration rate setting unit 42. The provisional target oxygen flow rate integrated value Sto corresponding to the target regeneration rate ηt is read and set from the regeneration rate-oxygen mass flow rate integrated value map.

  The provisional target oxygen flow rate integrated value Sto set by the target integrated value setting unit 44 is in a preset standard state, and the actual particulate combustion amount in the filter 28 is the exhaust temperature or exhaust flow rate during regeneration. It changes by fluctuation. For this reason, the target integrated value setting unit 44 corrects the provisional target oxygen flow integrated value Sto read from the regeneration rate-oxygen mass flow integrated value map based on the filter temperature and the exhaust gas flow to obtain the final target oxygen flow integrated. Set the value St. Then, the exhaust gas temperature downstream of the filter 28 is used as it is for the temperature of the filter 28 used for correction, and the exhaust volume flow rate Qe detected by the exhaust flow rate detector 50 is used for the exhaust flow rate. That is, the exhaust flow rate detector 50 adds the amount of fuel supplied to each cylinder to the intake mass flow rate Qiw detected by the intake flow rate sensor 14, and the filter temperature and downstream pressure sensor 36 detected by the filter temperature sensor 34 The exhaust flow rate Qe is detected by performing calculation using the detected exhaust pressure on the downstream side of the filter.

  As shown in FIG. 6, the target integrated value setting unit 44 stores in advance a correction coefficient map in which a correction coefficient R is set corresponding to the filter temperature and the exhaust gas flow rate. From this correction coefficient map, the filter temperature sensor The correction coefficient R corresponding to the filter temperature detected by 34 and the exhaust flow rate Qe detected by the exhaust flow rate detection unit 50 by the above equation (13) is read out. Then, the final target oxygen flow rate integrated value St is determined by multiplying the provisional target oxygen flow rate integrated value Sto set corresponding to the target regeneration rate ηt by the correction coefficient R.

  In this correction coefficient map, the correction coefficient R is set so as to increase as the exhaust flow rate Qe increases as the filter temperature is integrated, and to decrease as the filter temperature increases as the exhaust flow rate Qe is constant. ing. Therefore, the target oxygen flow rate integrated value St is corrected to a larger value as the exhaust flow rate Qe increases or the filter temperature decreases.

  Further, the target oxygen flow rate integrated value St set by the target integrated value setting unit 44 indicates the integrated value of the oxygen mass flow rate necessary for achieving the target regeneration rate ηt as described above. The fact that the integrated value of the actual oxygen mass flow rate becomes the target oxygen flow rate integrated value St set by the target regeneration rate setting unit 42 means that the regeneration rate of the filter 28 has reached the target regeneration rate ηt, that is, before the forced regeneration. This indicates that the particulates accumulated in the filter 28 have been reduced to the residual allowable particulate amount.

The target oxygen flow rate integrated value St set by the target integrated value setting unit 44 in this way is sent to the regeneration end determination unit 48.
On the other hand, the oxygen flow rate detection unit 46 detects the mass flow rate Qow of oxygen supplied to the filter 28 by performing a calculation based on the intake air mass flow rate Qiw detected by the intake flow rate sensor 14. From (13), the oxygen mass flow rate Qow is calculated.

Qow = (Qiw−q · a) · b (13)
Here, q is the fuel injection amount, a is the equivalent ratio (for example, 14.7), and b is the oxygen mass ratio.
The oxygen mass flow rate Qow detected by the oxygen flow rate detection means 46 in this way is sent to the regeneration end determination unit 48.
In the regeneration end determination unit 48, the oxygen mass flow rate Qow detected by the oxygen flow rate detection means 46 is integrated for each control period (step S214), and the actual oxygen flow rate integrated value Sa after the start of forced regeneration is obtained. Then, the actual oxygen flow rate integrated value Sa is compared with the target oxygen flow rate integrated value St set by the target integrated value setting unit (step S216). If the actual oxygen flow rate integrated value Sa has not reached the target oxygen flow rate integrated value St, it is determined that the forced regeneration has not been sufficiently performed yet, the process in the current control cycle is terminated, and the step is again performed in the next control cycle. The process from S202 is executed. When the actual oxygen flow rate integrated value Sa becomes equal to or greater than the target oxygen flow rate integrated value St, it is determined that the incineration of the particulates deposited on the filter 28 by the forced regeneration is completed, and the process proceeds to step S218 to set the forced regeneration end flag F2. The value is 0.

  By changing the value of the forced regeneration end flag F2 from 1 to 0, as described above, the forced regeneration control proceeds from step S118 to step S120 in the flowchart of FIG. 2, and in step S120, the value of the forced regeneration flag F1 is set. 0. As a result, the forced regeneration control ends, and the forced regeneration end determination control also determines that the value of the forced regeneration flag F1 is not 1 in step S202, and the processing of steps S204 to S218 is not performed.

As described above, the forced regeneration end determination of the filter 28 is performed using the target oxygen flow rate integrated value set based on the target regeneration rate of the filter 28. Therefore, the forced termination of the filter 28 at an arbitrary particulate accumulation amount. Even if the operation is started, it is possible to accurately determine the end of forced regeneration.
Further, the particulate combustion reaction in the filter 28 being regenerated becomes slower as the exhaust gas flow rate is higher, that is, as the exhaust gas flow rate is higher or the exhaust gas temperature is lower. However, as described above, the target integrated value setting unit 44 corrects the target oxygen flow rate integrated value St to a larger value as the exhaust flow rate Qe increases or the filter temperature decreases. The forced regeneration end determination is delayed under conditions where the combustion reaction is slow, while the forced regeneration end determination is advanced under an environment where the combustion reaction is performed rapidly. Therefore, even if the speed of the particulate combustion reaction varies depending on the exhaust flow speed or the exhaust temperature, the end of forced regeneration can always be determined with high accuracy.

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, the correction of the target oxygen flow rate integrated value in the target integrated value setting unit 44 is performed based on both the filter temperature and the exhaust flow rate, but may be performed based on only one of them.

  That is, a correction coefficient map in which the correction coefficient R is set corresponding to the filter temperature is stored in advance, and the correction coefficient R corresponding to the filter temperature detected by the filter temperature sensor 34 is read from the correction coefficient map, and temporarily The final target oxygen flow rate integrated value St may be determined by multiplying the target oxygen flow rate integrated value Sto by the correction coefficient R. In this case, the correction coefficient R is set so that the correction coefficient map has a smaller value as the filter temperature increases.

  Alternatively, a correction coefficient map in which the correction coefficient R is set corresponding to the exhaust flow rate is stored in advance, and the exhaust flow rate Qe detected by the exhaust flow rate detection unit 50 according to the equation (13) is stored from this correction coefficient map. The final target oxygen flow rate integrated value St may be determined by reading the correction coefficient R to be read and multiplying the provisional target oxygen flow rate integrated value Sto by the correction coefficient R. In this case, the correction coefficient R is set so that the correction coefficient map has a larger value as the exhaust flow rate Qe increases.

In this case, the completion of forced regeneration can be accurately determined even if there is a fluctuation in the speed of the particulate combustion reaction caused by either the exhaust flow speed or the exhaust temperature.
Further, in the accumulation amount detection unit 40, the particulate amount accumulated on the filter 28 is detected by the exhaust pressure upstream of the filter 28 detected by the upstream pressure sensor 32 and the filter 28 detected by the downstream pressure sensor 36. However, the present invention is not limited to this, and the amount of particulates may be detected by various known methods.

  Further, regarding the exhaust flow rate, the amount of fuel supplied to each cylinder is added to the intake mass flow rate Qiw detected by the intake flow rate sensor 14, and the exhaust flow rate Qe is detected based on the filter temperature and the exhaust pressure downstream of the filter. However, the present invention is not limited to this. For example, the exhaust flow rate Qe may be calculated using the intake mass flow rate Qiw detected by the intake flow rate sensor 14 ignoring the fuel amount, or the exhaust pipe 18 or An exhaust flow rate sensor may be provided in the exhaust aftertreatment device 24 to directly detect the exhaust flow rate.

  Further, the flow rate of oxygen supplied to the filter 28 is also detected by calculation based on the intake mass flow rate Qiw detected by the intake flow rate sensor 14. However, the present invention is not limited to this. For example, the exhaust pipe 18 or An oxygen sensor may be provided in the exhaust aftertreatment device 24, and the flow rate of oxygen supplied to the filter 28 may be detected based on the detection result of the oxygen sensor.

  Regarding the forced regeneration of the filter 28, after the oxidation catalyst 26 is activated by the first additional fuel injection, the exhaust temperature is raised by the second additional fuel injection to incinerate the particulates of the filter 28. However, the present invention is not limited to this. For example, a fuel addition device may be provided in the exhaust pipe 18 or the exhaust aftertreatment device 24 so that the fuel is directly injected into the exhaust gas. The temperature of the exhaust gas may be raised by an electric heater, a light oil burner, or the like.

  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. It is a flowchart of the forced regeneration control in the exhaust gas purification apparatus of FIG. FIG. 2 is a control block diagram of forced regeneration end determination control in the exhaust gas purification apparatus of FIG. 1. 3 is a flowchart of forced regeneration end determination control in the exhaust purification device of FIG. 1. FIG. 2 is a characteristic diagram of a regeneration rate-oxygen mass flow rate integrated value map used in forced regeneration end determination control in the exhaust gas purification apparatus of FIG. 1. FIG. 2 is a characteristic diagram of a correction coefficient map used in forced regeneration end determination control in the exhaust gas purification apparatus of FIG. 1.

Explanation of symbols

1 Engine 18 Exhaust pipe (exhaust passage)
28 Filter 34 Filter temperature sensor (filter temperature detection means)
40 Deposition amount detection unit (deposition amount detection means)
42 Target playback rate setting unit (target playback rate setting means)
44 Target integrated value setting section (Target integrated value setting means)
46 Oxygen flow rate detector (oxygen flow rate detection means)
48 Playback end determination unit (playback end determination means)
50 Exhaust flow rate detector (exhaust flow rate detection means)

Claims (7)

A filter that is disposed in the exhaust passage and captures particulates in the exhaust discharged from the internal combustion engine, while incinerating the accumulated particulates to regenerate,
A deposition amount detecting means for detecting a deposition amount of the particulates in the filter;
Target regeneration rate setting means for setting a target regeneration rate of the filter based on the accumulation amount detected by the accumulation amount detection means;
A target integrated value setting means for setting a target oxygen flow rate integrated value corresponding to the target regeneration rate based on a relationship between a preset regeneration rate of the filter and an integrated value of the oxygen flow rate supplied to the filter;
Oxygen flow rate detection means for detecting the oxygen flow rate supplied to the filter;
When the integrated value of the oxygen flow detected by the oxygen flow rate detection means reaches the target oxygen flow integrated value set by the target integrated value setting means during regeneration of the filter, it is determined that the regeneration of the filter is completed. An exhaust purification device for an internal combustion engine, comprising: a regeneration end determination unit. A filter temperature detecting means for detecting the temperature of the filter;
The target integrated value setting means calculates an integrated value of the oxygen flow rate corresponding to the target regeneration rate based on a relationship between a preset regeneration rate of the filter and an integrated value of the oxygen flow rate supplied to the filter. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the target oxygen flow rate integrated value is set by correcting based on the filter temperature detected by the filter temperature detecting means.   The exhaust purification device for an internal combustion engine according to claim 2, wherein the target integrated value setting means corrects the target oxygen integrated value to be smaller as the filter temperature is higher. An exhaust flow rate detecting means for detecting an exhaust flow rate flowing into the filter;
The target integrated value setting means is an integrated value of the oxygen flow rate determined corresponding to the target regeneration rate based on a relationship between a preset regeneration rate of the filter and an integrated value of the oxygen flow rate supplied to the filter. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the target oxygen flow rate integrated value is set by correcting the flow rate based on the exhaust flow rate detected by the exhaust flow rate detection means.   The exhaust purification apparatus for an internal combustion engine according to claim 4, wherein the target integrated value setting means corrects the target oxygen integrated value to be smaller as the exhaust flow rate is smaller. Filter temperature detecting means for detecting the temperature of the filter;
An exhaust flow rate detecting means for detecting an exhaust flow rate flowing into the filter;
The target integrated value setting means is an integrated value of the oxygen flow rate determined corresponding to the target regeneration rate based on a relationship between a preset regeneration rate of the filter and an integrated value of the oxygen flow rate supplied to the filter. The target oxygen flow rate integrated value is set by correcting the correction based on the filter temperature detected by the filter temperature detection unit and the exhaust flow rate detected by the exhaust flow rate detection unit. Exhaust gas purification device for internal combustion engine.   The target integrated value setting means corrects the target oxygen integrated value so that it decreases as the filter temperature increases, and corrects the target oxygen integrated value to decrease as the exhaust flow rate decreases. The exhaust emission control device for an internal combustion engine according to claim 6.

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