JP2006274980A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of preventing a particulate filter and an oxidation catalyst from being thermally deteriorated to increase durability by properly controlling the temperature of the particulate filter during the forced regeneration thereof. <P>SOLUTION: This exhaust emission control device comprises a regeneration control means 38 performing the forced regeneration of the particulate filter 28 by supplying HC during exhaustion when predetermined conditions are established, increasing the temperature of the particulate filter 28 to a prescribed temperature by the oxidation reaction of HC by the oxidation catalyst 26, and incinerating particulates accumulated on the particulate filter 28. When starting the forced regeneration, the regeneration control means 38 increases the temperature of the particulate filter 28 to the prescribed temperature after keeping, for a prescribed period, the temperature higher than the active temperature of the oxidation catalyst 26 and lower than the prescribed temperature, and at an intermediate temperature at which particulates accumulated on the particulate filter 28 can be burned. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device provided with a particulate filter that collects particulates in exhaust gas discharged from an engine.

Conventionally, a particulate filter is provided in the exhaust passage of an engine such as a diesel engine, and particulates contained in the exhaust discharged from the engine are collected by the particulate filter so that the particulates are not released into the atmosphere. Technology is known.
In such a particulate filter, the collected particulate matter is deposited in the particulate filter, so that the exhaust resistance gradually increases. Therefore, in order to remove the deposited particulates, placing an oxidation catalyst upstream of the particulate filter, the NO in the exhaust is oxidized to generate NO _2, and supplies the NO ₂ to the particulate filter as the oxidizing agent Thus, it is known that the particulates deposited on the particulate filter react with NO ₂ to be oxidized to continuously regenerate the particulate filter.

  However, in an operating state where the exhaust temperature of the engine is low, for example, at low speed or low load, the exhaust temperature does not rise to the activation temperature of the oxidation catalyst, and NO in the exhaust is not oxidized and continuous regeneration may not be performed. is there. If this condition continues, excessive particulates accumulate in the particulate filter and the particulate filter may become clogged. For this reason, forced regeneration is appropriately performed according to the particulate accumulation state in the particulate filter. Is done.

To forcibly regenerate the particulate filter, HC is supplied from a fuel addition valve provided in the exhaust passage, or HC is supplied to the exhaust passage by injecting fuel into the cylinder during the expansion stroke or exhaust stroke of the engine. Thus, it is known that the exhaust temperature is raised by the oxidation reaction of HC by the oxidation catalyst.
At this time, if the temperature of the particulate filter does not rise to an appropriate temperature, the regeneration of the particulate filter becomes insufficient. On the other hand, if the temperature of the particulate filter rises excessively, the particulate filter will melt. The problem of being lost arises. In order to solve such a problem, there has been proposed one in which the amount of fuel supplied for raising the temperature of the particulate filter is controlled based on the outlet temperature of the oxidation catalyst (Patent Document 1).
JP 2004-293339 A

  However, as in the exhaust gas purification apparatus of Patent Document 1, when the fuel supply amount is controlled based on the outlet temperature of the oxidation catalyst to adjust the particulate filter temperature to a predetermined temperature, for example, the predetermined temperature is 620 ° C. Then, until the outlet temperature of the oxidation catalyst reaches 620 ° C., the fuel is actively supplied to raise the temperature of the filter, and the fuel supply amount starts to decrease after the outlet temperature of the oxidation catalyst reaches 620 ° C. The actual temperature of the oxidation catalyst or the particulate filter greatly exceeds 620 ° C. In particular, if HC is supplied to the oxidation catalyst in order to activate the oxidation catalyst, and the particulate filter is further heated, with a large amount of HC adsorbed on the oxidation catalyst or the particulate filter, Particulates accumulated in the gas burn at a stretch, and the particulate filter tends to overheat.

In general, the larger the amount of particulates deposited on the particulate filter, the greater the temperature difference between the inlet portion and the inside of the particulate filter. In order to prevent this, it is necessary to start the forced regeneration before the amount of particulates deposited on the particulate filter is too large.
As described above, in the exhaust gas purification device of Patent Document 1, excessive temperature rise of the particulate filter and the oxidation catalyst tends to be caused during forced regeneration, and durability of the particulate filter and oxidation catalyst may be lowered. In order to prevent this, the amount of particulates collected by the particulate filter must be limited and frequent forced regeneration must be carried out, resulting in a problem that fuel consumption deteriorates.

  The present invention has been made in view of such problems, and its purpose is to appropriately control the temperature of the particulate filter during forced regeneration and prevent thermal deterioration of the particulate filter and the oxidation catalyst. An object of the present invention is to provide an exhaust purification device capable of improving durability.

  In order to achieve the above object, an exhaust emission control device according to the present invention includes an oxidation catalyst disposed in an exhaust passage of an engine and a particulate matter disposed in an exhaust passage downstream of the oxidation catalyst and collecting particulates in the exhaust. When a predetermined condition is established with the filter, HC is supplied into the exhaust gas, the particulate filter is heated to a predetermined temperature by the oxidation reaction of the HC by the oxidation catalyst, and the particulate deposited on the particulate filter is And a regeneration control means for forcibly regenerating the particulate filter by incineration, and when the regeneration regeneration means starts the forced regeneration, the temperature of the particulate filter is set higher than the activation temperature of the oxidation catalyst. And a particulate matter that is lower than the predetermined temperature and is deposited on the particulate filter. After the rate has held for a predetermined period combustible intermediate temperature, characterized in that raising to the predetermined temperature (claim 1).

  According to the exhaust gas purification apparatus configured as described above, when a predetermined condition is satisfied, the regeneration control means starts forced regeneration of the particulate filter, and the temperature of the particulate filter is set higher than the activation temperature of the oxidation catalyst and predetermined. The temperature is lower than the temperature and the particulate matter accumulated on the particulate filter is maintained at an intermediate temperature at which the particulate matter can be combusted for a predetermined period, and then raised to the predetermined temperature.

More specifically, the predetermined period is a period until a predetermined amount of the particulate deposited on the particulate filter is incinerated (Claim 2).
More specifically, it further comprises differential pressure detection means for detecting an exhaust pressure difference in the exhaust passage before and after the particulate filter, and the predetermined period is detected by the differential pressure detection means after starting the forced regeneration. The exhaust gas pressure difference is a period until it decreases by a predetermined reference decrease value or more (Claim 3).

  Alternatively, the predetermined period is a period until the exhaust pressure difference detected by the differential pressure detecting means becomes equal to or less than a preset reference pressure difference (claim 4).

  According to the exhaust gas purification apparatus of the first to fourth aspects, when forced regeneration is started, the temperature of the particulate filter is higher than the activation temperature of the oxidation catalyst and lower than a predetermined temperature, and the particulates deposited on the particulate filter. Since the temperature of the particulate filter is maintained at a combustible intermediate temperature for a predetermined period and then raised to the predetermined temperature, the temperature of the particulate filter does not increase rapidly, and the particulate filter can be prevented from overheating. Can do.

In addition, since the excessive temperature rise of the particulate filter is less likely to occur, there is no need to limit the amount of particulates deposited on the particulate filter to be relatively small, and the fuel consumption is improved by extending the execution interval of forced regeneration. .
Furthermore, since it is difficult for excessive heating of the particulate filter to occur, increasing the amount of additional fuel when the temperature of the particulate filter is increased reduces the heating time of the particulate filter and improves drivability by performing forced regeneration. It is possible to increase the merchantability by reducing the decrease.

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 the injectors 4 provided in the cylinders. Light oil is injected into the cylinder.

  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 44 are introduced into the intake manifold 12. An intake flow rate sensor 14 for detecting the intake air flow rate to the engine 1 is provided upstream of the compressor 8 a 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.
The exhaust pipe 18 passes through the turbine 8 b of the turbocharger 8 and is connected to the exhaust aftertreatment device 24 via the exhaust throttle valve 46. 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.

In the exhaust aftertreatment device 24, an oxidation catalyst 26 is accommodated on the upstream side in the casing, and on the downstream side of the oxidation catalyst 26, a particulate filter (hereinafter referred to as a filter) 28 that captures particulates in the exhaust gas. Contained.
The oxidation catalyst 26, the NO in the exhaust is oxidized to generate NO _2, and supplies the NO ₂ to the filter 28 as an oxidizing agent. The filter 28 is made of a honeycomb-type ceramic carrier, and has a large number of passages communicating with the upstream side and the downstream side, and the upstream side opening and the downstream side opening of the passage are alternately closed.

Particulates collected and deposited in the filter 28 react with NO ₂ supplied from the oxidation catalyst 26 to be oxidized, and the filter 28 is continuously regenerated.
Between the oxidation catalyst 26 and the filter 28, an inlet temperature sensor 30 for detecting the exhaust temperature on the inlet side of the filter 28 and an inlet pressure sensor 32 for detecting the exhaust pressure on the inlet side of the filter 28 are provided. Further, on the downstream side of the filter 28, an outlet pressure sensor 34 for detecting the exhaust pressure on the outlet side of the filter 28 and an outlet temperature sensor 36 for detecting the exhaust temperature on the outlet side of the filter 28 are provided.

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.
In addition to the above-described intake flow rate sensor 14, inlet temperature sensor 30, inlet pressure sensor 32, outlet pressure sensor 34, and outlet temperature sensor 36, the input side of the ECU 38 collects information necessary for performing various controls. Various sensors such as an engine speed sensor 40 for detecting the engine speed and an accelerator opening sensor 42 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, the EGR valve 20, the intake control valve 44, and the exhaust throttle valve 46 of each cylinder are connected.

  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 fuel supply amount (main injection amount) necessary for the operation of the engine 1 is stored in advance based on the engine speed detected by the speed sensor 40 and the accelerator opening detected by the accelerator opening sensor 42. Read from the map and decide. 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 oxidized and removed by continuous regeneration using the oxidation catalyst 26. 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. Therefore, forced regeneration is appropriately performed according to the particulate accumulation state in the filter 28. .

This forced regeneration control is performed at a predetermined control cycle by the ECU 38 in accordance with the flowchart shown in FIG. That is, the ECU 38 functions as a regeneration control unit.
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 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 S2 to step S4 in the first control cycle.

  In step S4, it is determined whether or not forced regeneration of the filter 28 is necessary. Specifically, based on the differential pressure before and after the filter 28 obtained from the detection values of the inlet pressure sensor 32 and the outlet pressure sensor 34, and the exhaust flow rate to the filter 28 calculated from the detection value of the intake flow sensor 14, the filter 28. The amount of particulate deposition on the surface is estimated, and when this estimated amount of deposition is equal to or greater than the forced regeneration start determination value, it is determined that forced regeneration is necessary. In this case, the process proceeds to step S6, 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, if the estimated accumulation amount of particulates 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 from step S2 is performed again in the next control cycle. I do.

  In step S4, it is determined that forced regeneration is necessary, and the process proceeds to step S6. After the value of the forced regeneration flag F1 is set to 1, the process proceeds to step S8. Since the detected value of the inlet temperature sensor 30 is not only the inlet side temperature of the filter 28 but also the outlet side temperature of the oxidation catalyst 26, the temperature of the oxidation catalyst 26 is determined based on the detected value Ti of the inlet temperature sensor 30 in step S8. It is determined whether or not the oxidation catalyst 26 has become activated at 250 ° C. or higher.

When the inlet side temperature Ti of the filter 28 is less than 250 ° C., the process proceeds to step S10 and the temperature increase control of the oxidation catalyst 26 is performed.
In this temperature increase control, the temperature of the oxidation catalyst 26 is raised to the activation temperature (for example, 250 ° C.) by supplying high-temperature exhaust gas to the oxidation catalyst 26. The intake control valve 44 and the exhaust throttle valve 46 are heated. Is controlled in the closing direction, and the first additional fuel injection is performed in the expansion stroke of each cylinder. The injection timing of the first additional fuel is relatively earlier than the end of the expansion stroke. By injecting the additional fuel into the cylinder at such timing, the additional fuel and the high-temperature combustion gas in the cylinder are generated. As a result of mixing, additional fuel is combusted in the exhaust port and the exhaust manifold 16, and high temperature exhaust gas is supplied to the oxidation catalyst 26.

In this manner, the temperature increase control of the oxidation catalyst 26 is performed in step S10, and this control cycle is completed, and control is performed again from step S2 in the next control cycle. In this case, since the value of the forced regeneration flag F1 is already 1, the process proceeds from step S2 to step S8, where the control of the intake control valve 44 and the exhaust throttle valve 46 and the catalyst temperature increase control by the injection of the first additional fuel are performed. Is done.
Thus, the catalyst temperature increase control is repeated, and when the inlet side temperature Ti of the filter 28 corresponding to the temperature of the oxidation catalyst 26 becomes 250 ° C. or higher, the process proceeds from step S8 to step S12. In step S12, the amount of decrease ΔPd from the maximum value detected after the forced regeneration is started for the differential pressure before and after the filter 28 obtained from the detected values of the inlet pressure sensor 32 and the outlet pressure sensor 34 is set as a preset reference. It is determined whether or not the amount of decrease is greater than or equal to Po.

Therefore, the inlet pressure sensor 32 and the outlet pressure sensor 34 correspond to the differential pressure detecting means.
After the temperature increase control of the oxidation catalyst 26 is performed, the reduction amount ΔPd from the maximum value of the differential pressure before and after the filter 28 is equal to or greater than the reference reduction amount Po until the accumulated particulates due to the forced regeneration of the filter 28 are reduced to some extent. In the meantime, the process proceeds from step S12 to step S14.

In step S14, based on the detected value of the inlet temperature sensor 30, it is determined whether or not the inlet side temperature Ti of the filter 28 is 550 ° C. or higher. This temperature is lower than the temperature at which the particulates burn most efficiently in the filter 28, but is set as a temperature at which the particulates deposited on the filter 28 can burn.
If it is determined in step S14 that the inlet side temperature Ti is lower than 550 ° C., the process proceeds to step S16, and if it is determined that the inlet side temperature Ti is 550 ° C. or higher, the process proceeds to step S18.

  In steps S16 and S18, the second additional fuel is injected into each cylinder so that the temperature of the exhaust gas supplied to the filter 28 is maintained at 550 ° 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. Due to this combustion, the exhaust temperature rises to 550 ° C., and the particulates deposited on the filter 28 are partially incinerated.

  The second additional fuel is an additional fuel necessary for maintaining the inlet side temperature Ti at 550 ° C. with the engine speed detected by the speed sensor 40 and the main injection amount (load) determined by the ECU 38 as parameters. The amount is stored in the first map, and this map includes two types of increase map # 1 in which the second additional fuel injection amount is set to be relatively large and decrease map # 1 in which the amount is set to be relatively small. Is prepared. In step S16, since the inlet side temperature Ti is lower than 550 ° C., a relatively large amount of the second additional fuel is injected using the increase map # 1, and in step S18, the inlet side temperature Ti is 550 ° C. or higher. A relatively small amount of the second additional fuel is injected using the weight reduction map # 1. As a result, the temperature of the exhaust gas discharged from the oxidation catalyst 26 and supplied to the filter 28 is maintained at around 550 ° C.

  When the second additional fuel is injected in step S16 or S18, the process in the current control cycle is finished, and the process is performed again from step S2 in the next control cycle. As described above, until the particulate matter accumulated in the filter 28 is reduced to some extent, the reduction amount ΔPd from the maximum value of the differential pressure before and after the filter 28 does not exceed the reference reduction amount Po. The process proceeds from S12 to step S14, and the second additional fuel is injected in step S16 or S18, whereby the inlet side temperature of the filter 28 is maintained at 550 ° C.

In this way, while the inlet side temperature of the filter 28 is maintained at 550 ° C., a part of the particulates deposited on the filter 28 is incinerated, and the reduction amount ΔPd from the maximum value of the differential pressure before and after the filter 28 is reduced. When the reference decrease amount Po is exceeded, the process proceeds from step S12 to step S20.
In step S20, based on the detected value of the inlet temperature sensor 30, it is determined whether or not the inlet side temperature Ti of the filter 28 is 620 ° C. or higher. This temperature is set as the temperature at which the particulates burn most efficiently in the filter 28.

If it is determined in step S20 that the inlet side temperature Ti is lower than 620 ° C., the process proceeds to step S22, and if it is determined that the inlet side temperature Ti is 620 ° C. or higher, the process proceeds to step S24.
Steps S22 and S24 are to inject the second additional fuel into each cylinder so as to maintain the temperature of the exhaust gas supplied to the filter 28 at 620 ° C., and are the same as those in steps S16 and S18 described above. As described above, the second additional fuel is injected in the exhaust stroke. 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. Due to this combustion, the exhaust temperature rises to 620 ° C., and the particulates deposited on the filter 28 are incinerated.

  The second additional fuel at this time is necessary for maintaining the inlet side temperature Ti at 620 ° C. using the engine speed detected by the speed sensor 40 and the main injection amount (load) determined by the ECU 38 as parameters. The additional fuel amount is stored in the second map, and this map is an increase map # 2 in which the second additional fuel injection amount is set to be relatively large and a decrease map # 2 in which the second additional fuel injection amount is set to be relatively small. There are two types. Since the inlet side temperature Ti is lower than 620 ° C. in step S22, a relatively large amount of the second additional fuel is injected using the increase map # 2, and the inlet side temperature Ti is 620 ° C. or higher in step S24. The relatively small amount of the second additional fuel is injected using the weight reduction map # 2. As a result, the temperature of the exhaust gas discharged from the oxidation catalyst 26 and supplied to the filter 28 is maintained at around 620 ° C.

  When the second additional fuel is injected in step S22 or S24, the process proceeds to step S26, and the particulate accumulation amount estimated based on the differential pressure before and after the filter 28 and the exhaust flow rate to the filter 28 is the same as in step S4. Then, it is determined whether or not it is equal to or less than the forced regeneration end determination value. When the estimated accumulation amount of the particulate is larger than the forced regeneration end determination value, it is determined that the forced regeneration of the filter 28 is still necessary, this control cycle is finished, and from the step S2 again in the next control cycle. Take control.

  On the other hand, if it is determined in step S26 that the estimated accumulation amount of particulates is equal to or less than the forced regeneration end determination value and the forced regeneration of the filter 28 is completed, the process proceeds to step S28, and the value of the forced regeneration flag F1 is set to 0. End the current control cycle. When the value of the forced regeneration flag F1 becomes 0 in this way, the process proceeds from step S2 to step S4 in the next control cycle. Therefore, the process from step S2 to step S4 is performed until the forced regeneration of the filter 2 is required again. Is repeated, and whether or not forced regeneration is necessary is determined at each control cycle.

  As described above, when forced regeneration of the filter 28 is necessary, after the oxidation catalyst 26 is heated to the activation temperature of 250 ° C., the reduction amount ΔPd from the maximum value of the differential pressure before and after the filter 28 is the reference reduction amount Po. The temperature on the inlet side of the filter 28 is maintained at 550 ° C., which is an intermediate temperature lower than 620 ° C., which is the temperature at which the particulates burn most efficiently, over a predetermined period until the temperature reaches 620 ° C. As a result, the oxidation catalyst 26 and the filter 28 are not excessively heated. As a result, thermal deterioration of the oxidation catalyst 26 and the filter 28 is prevented, and durability is improved.

Further, since the filter 28 does not overheat, it is not necessary to limit the amount of particulates deposited on the filter 28 to be relatively small in order to prevent overheating, and fuel consumption is improved by extending the execution interval of forced regeneration. improves.
Further, since the filter 28 does not overheat, the second additional fuel amount supplied when the filter 28 is heated is increased to shorten the temperature rising time of the filter 28 and decrease drivability due to forced regeneration. It is possible to improve the merchantability by reducing the number of products.

In the above embodiment, the period when the inlet side temperature of the filter 28 is set to the intermediate temperature of 550 ° C. is a predetermined period until the decrease amount ΔPd from the maximum value of the differential pressure before and after the filter 28 becomes equal to or more than the reference decrease amount Po. However, it may be a period until a predetermined amount of the particulates deposited on the filter 28 is incinerated.
That is, it may be a period until the differential pressure itself becomes equal to or less than the reference pressure difference, instead of the amount of fluctuation of the differential pressure before and after the filter 28, and the time for holding the inlet side temperature of the filter 28 at an intermediate temperature is a predetermined time. It may be until it is time.

  For example, when the period until the differential pressure before and after the filter 28 is equal to or less than the reference pressure difference is adopted, whether or not the differential pressure before and after the filter 28 is equal to or less than the reference pressure difference in step S12 in the flowchart of FIG. If the differential pressure across the filter 28 is greater than the reference pressure difference, the process proceeds to step S14. If the differential pressure across the filter 28 is equal to or less than the reference pressure difference, the process proceeds to step S20.

  When the time for maintaining the inlet side temperature of the filter 28 at the intermediate temperature is adopted, the elapsed time after the processing of steps S14 to S18 is performed in step S12 in the flowchart of FIG. If it is less than predetermined time, it will progress to step S14, and if it is more than predetermined time, it may progress to step S20.

Although the description of the exhaust emission control device according to one embodiment of the present invention is finished above, the present invention is not limited to the above embodiment.
For example, in the above-described embodiment, the detection value of the inlet temperature sensor 30 that detects the exhaust temperature on the inlet side of the filter 28 is used as the temperature of the filter 28, but the present invention is not limited to this, and is provided inside the filter 28. The detection value of the temperature sensor may be used, or it may be estimated by calculation from the exhaust temperature before and after the filter 28, and various known methods can be employed.

Further, in the above embodiment, the supply of HC for raising the temperature of the oxidation catalyst 26 and the filter 28 is performed by additional fuel injection from the injector 4 provided in each cylinder, but the exhaust pipe 18 or the exhaust aftertreatment device 24 is used. A fuel addition valve may be provided therein, and HC may be supplied from the fuel addition valve.
Further, the determination of the forced regeneration start and end of the filter 28 is based on the accumulated amount of particulates estimated from the differential pressure before and after the filter 28 and the exhaust flow rate to the filter 28, the forced regeneration start determination value and the forced regeneration end determination value. However, the determination method is not limited to this, and the particulate accumulation amount is estimated based on the amount of fuel supplied to the engine 1, the operating time of the engine 1, and the like. Alternatively, the start and end of forced regeneration can be determined using various known methods.

  Finally, in the above embodiment, the present invention is applied to an exhaust emission control device for a diesel engine, but the engine type is not limited to this.

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 performed with the exhaust gas purification device of FIG.

Explanation of symbols

1 Engine 18 Exhaust pipe (exhaust passage)
26 Oxidation catalyst 28 Filter (Particulate filter)
32 Upstream pressure sensor (Differential pressure detection means)
34 Downstream pressure sensor (Differential pressure detection means)
38 ECU (regeneration control means)

Claims (4)

An oxidation catalyst disposed in the exhaust passage of the engine, a particulate filter disposed in the exhaust passage downstream of the oxidation catalyst and collecting particulates in the exhaust, and HC in the exhaust when a predetermined condition is satisfied Control means for forcibly regenerating the particulate filter by heating the particulate filter to a predetermined temperature by the oxidation reaction of the HC by the oxidation catalyst and incinerating the particulate deposited on the particulate filter In an exhaust emission control device comprising:
When the regeneration control means starts the forced regeneration, the temperature of the particulate filter is higher than the activation temperature of the oxidation catalyst and lower than the predetermined temperature, and the particulates deposited on the particulate filter burn An exhaust emission control device, wherein the exhaust gas purifier is maintained at a possible intermediate temperature for a predetermined period and then raised to the predetermined temperature.   The exhaust emission control device according to claim 1, wherein the predetermined period is a period until a predetermined amount of particulates accumulated on the particulate filter is incinerated. A differential pressure detecting means for detecting an exhaust pressure difference in the exhaust passage before and after the particulate filter;
The said predetermined period is a period until the said exhaust pressure difference detected by the said differential pressure | voltage detection means after starting the said forced regeneration reduces more than the preset reference | standard reduction value, The said 2nd period is a period until it decreases. The exhaust emission control device described. A differential pressure detecting means for detecting an exhaust pressure difference in the exhaust passage before and after the particulate filter;
The exhaust purification apparatus according to claim 2, wherein the predetermined period is a period until the exhaust pressure difference detected by the differential pressure detecting means becomes equal to or less than a preset reference pressure difference.

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