JP2007032396A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology optimizing the distance from a reducing agent supply position to an exhaust emission control means in accordance with processing with respect to the exhaust emission control means and performing each processing under optimal conditions. <P>SOLUTION: This exhaust emission control device for an internal combustion engine 1 is provided with the exhaust emission control means arranged inside an exhaust passage extending from the internal combustion engine 1 and having a NOx catalyst and a filter; a first fuel addition valve supplying fuel to the upstream side of the exhaust emission control means; and a second fuel addition valve supplying fuel to the downstream side of the first fuel addition valve and the upstream side of the exhaust emission control means. At the time of NOx reduction processing and SOx poisoning cancellation processing, fuel is supplied from the first fuel addition valve, and at the time of PM oxidation and removal processing, fuel is supplied from the second fuel addition valve. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  A technique for purifying nitrogen oxides (hereinafter referred to as “NOx”) by arranging an NOx storage reduction catalyst (hereinafter also referred to as “NOx catalyst”) in an exhaust path of an internal combustion engine, particularly a diesel engine. Are known. Further, a particulate filter (hereinafter sometimes simply referred to as a “filter”) is arranged so as to carry the NOx catalyst or be arranged in series with the NOx catalyst, and particulates such as soot discharged from the internal combustion engine (PM) : Particulate Matter (hereinafter, sometimes referred to as “PM”) is known (see, for example, Patent Document 1). Here, the integral means constituted by the NOx catalyst and the filter is referred to as exhaust purification means.

  Before the NOx retention capacity of the NOx catalyst of the exhaust purification means is saturated, NOx or sulfur oxide (hereinafter sometimes referred to as “SOx”) retained (occluded) in the NOx catalyst is released and reduced to be removed. It is necessary to perform processing (NOx reduction processing, SOx poisoning elimination processing). In this process, the reducing agent is supplied from the reducing agent supply means arranged on the upstream side of the exhaust gas purification means in the exhaust path, so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is reduced below the stoichiometric air-fuel ratio if necessary ( NOx or SOx is reduced and removed.

  In addition, it is necessary to perform a process for removing PM collected by the filter of the exhaust gas purification means (PM oxidation removal process). In this process, the reducing agent is oxidized in the NOx catalyst by supplying the reducing agent from the reducing agent supply means arranged upstream of the exhaust gas purification means in the exhaust path, and the heat generated during the oxidation causes the filter to be oxidized. The temperature is increased to a high temperature range of about 500 ° C to 700 ° C. In addition to raising the temperature of the filter, the exhaust gas flowing into the filter is made into an oxygen-excess atmosphere, and PM is oxidized and removed.

In the NOx reduction process, the SOx poisoning elimination process, and the PM oxidation removal process for the exhaust purification unit, a reducing agent must be supplied. However, if the distance from the reducing agent supply position to the exhaust purification means is long, a delay in arrival occurs due to adhesion to the inner wall surface of the exhaust path before reaching the exhaust purification means, resulting in a shortage with respect to the optimum supply amount. . Therefore, there is a problem that the reducing agent cannot be effectively used. On the other hand, Patent Document 1 discloses a technique in which exhaust purification means is disposed immediately downstream of the reducing agent supply position so as to effectively use the reducing agent.
JP 2000-205005 A Japanese Patent Laid-Open No. 11-13456 JP 2003-97254 A

  However, if the distance from the reducing agent supply position to the exhaust purification unit is too short, the reducing agent may not sufficiently diffuse into the exhaust before reaching the exhaust purification unit. In this case, during the NOx reduction process and the SOx poisoning elimination process, the reducing agent does not reach the entire NOx catalyst, and NOx or SOx of the NOx catalyst is reduced only by a part of the NOx catalyst, resulting in incompleteness. There is a risk that. The diffusion includes both physical spread and chemical cracking (lightening).

In addition, if the distance from the reducing agent supply position to the exhaust gas purification means is long, the following problems can be considered. That is, even if the operating condition that tends to cause excessive temperature rise of the filter, such as when the vehicle equipped with the internal combustion engine is decelerated during the PM oxidation removal processing, is caused, even if the reducing agent supply is immediately stopped. There is a risk that the reducing agent that has already been supplied arrives at the NOx catalyst, and the reducing agent that arrives late causes an excessive temperature rise in the filter.

  As described above, in the NOx reduction process and the SOx poisoning elimination process, if the distance from the reducing agent supply position to the exhaust gas purification unit is short, the above-described problem occurs. In the PM oxidation removal process, the reducing agent supply is performed. If the distance from the position to the exhaust gas purification means is long, the above-described problems occur. That is, the optimum distance from the reducing agent supply position to the exhaust gas purification means differs depending on the process for the exhaust gas purification means, and the optimum conditions for each process are different.

  An object of the present invention is to provide a technique for optimizing the distance from the reducing agent supply position to the exhaust gas purification unit in accordance with the process for the exhaust gas purification unit, and performing each process under optimal conditions.

In order to achieve the above object, the present invention adopts the following configuration. That is,
An exhaust purification means that is disposed in an exhaust path extending from the internal combustion engine and has a NOx storage reduction catalyst that stores and reduces NOx in the exhaust and a filter that collects particulates discharged from the internal combustion engine;
First reducing agent supply means for supplying a reducing agent to the exhaust path upstream of the exhaust purification means;
Second reducing agent supply means for supplying a reducing agent to the exhaust path downstream of the first reducing agent supply means and upstream of the exhaust purification means;
With
When reducing NOx occluded in the NOx catalyst from the NOx catalyst and reducing SOx occluded in the NOx catalyst from the NOx catalyst, the reducing agent is supplied from the first reducing agent supply means. Supply
The exhaust gas purifying apparatus for an internal combustion engine is characterized in that when fine particles collected by the filter are oxidized and removed, a reducing agent is supplied from the second reducing agent supply means.

  Accordingly, when NOx stored in the NOx catalyst is reduced from the NOx catalyst, and when SOx stored in the NOx catalyst is reduced from the NOx catalyst, that is, in the NOx reduction process and the SOx poisoning elimination process. In this case, the reducing agent is supplied from the first reducing agent supply means to the exhaust gas purification means. Therefore, the distance from the reducing agent supply position to the exhaust gas purification unit is longer than when the reducing agent is supplied from the second reducing agent supply unit. Then, the reducing agent supplied over the long distance is sufficiently diffused into the exhaust gas, and the reducing agent is spread over the entire exhaust gas purification means, and the NOx or SOx reduction and removal reaction in the NOx catalyst can be promoted. The diffusion includes both physical spread and chemical cracking (lightening).

  Further, when the fine particles collected by the filter are oxidized and removed, that is, during the PM oxidation removal process, the reducing agent is supplied from the second reducing agent supply unit to the exhaust gas purification unit. Accordingly, the distance from the reducing agent supply position to the exhaust gas purification unit is shorter than when the reducing agent is supplied from the first reducing agent supply unit. Then, at this short distance, there is no delay in reaching the reducing agent to the NOx catalyst of the exhaust purification means, and if the supply of the reducing agent is stopped by the second reducing agent supply means, the reducing agent does not reach the exhaust purification means as soon as it stops. Therefore, it is possible to prevent excessive temperature rise of the filter due to the reducing agent that arrives, and to obtain quick response of avoiding excessive temperature rise by stopping the supply of reducing agent in the reducing agent supply means.

  As described above, according to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the distance from the reducing agent supply position to the exhaust gas purification unit is optimized according to the process for the exhaust gas purification unit, and each process is performed under optimal conditions. can do.

  When the particulates collected by the filter are oxidized and removed, if the exhaust purification unit is at a predetermined temperature or lower, it is preferable to supply a reducing agent from the first reducing agent supply unit.

  When the temperature of the exhaust purification means is relatively low, even if the temperature rises to some extent during the PM oxidation removal process, the temperature does not rise excessively. Therefore, when the exhaust gas purification means is at a predetermined temperature or less during the PM oxidation removal process, there is a delay in reaching the reducing agent to the NOx catalyst of the exhaust gas purification means, and the filter is somewhat affected by the reducing agent that arrives late. Even if the temperature rises, overheating of the filter can be prevented.

  On the other hand, during the PM oxidation removal process, the distance from the reducing agent supply position to the exhaust gas purification means is increased to ensure the reaction promoting property by fuel diffusion, and the low temperature activity is increased or the temperature non-uniformity in the NOx catalyst is increased. It is preferable to improve.

  Therefore, when oxidizing and removing the particulates collected by the filter, if the exhaust purification means is below a predetermined temperature, in other words, there is no possibility that the filter will overheat during PM oxidation removal processing. If present, the reducing agent is supplied from the first reducing agent supply means having a long distance to the exhaust gas purification means, thereby preventing the overheating of the filter while increasing the low temperature activity or the temperature non-uniformity in the NOx catalyst. Can be improved.

  In addition, when NOx or SOx stored in the NOx catalyst is reduced, the NOx catalyst includes site estimation means for estimating whether the NOx catalyst is reduced from an upstream site or a downstream site, and from the NOx catalyst When the NOx stored in the NOx catalyst is reduced and when the SOx stored in the NOx catalyst is reduced from the NOx catalyst, it is estimated that the part estimation means is reduced from the downstream part. In this case, it is preferable to supply the reducing agent from the second reducing agent supply means.

  When NOx or SOx stored in the downstream portion of the NOx catalyst is reduced, the reduction and removal performance of NOx or SOx does not deteriorate even if the distance from the reducing agent supply position to the NOx catalyst is short. This is because the oxygen in the exhaust gas reacts and decreases in the process where the exhaust gas reaches the downstream site, and the exhaust gas that reaches the downstream site contains mainly HC without much oxygen. This is because the reduction reaction of NOx or SOx at the site is promoted.

  Therefore, when it is estimated that the part estimation means is reduced from the downstream part, the reduction reaction is promoted by supplying the reducing agent from the second reducing agent supply means having a short distance to the exhaust purification means. In addition, it is possible to prevent a problem that fuel consumption deteriorates due to an increase in the amount of fuel attached to the exhaust path and a decrease in fuel that contributes to reduction.

  According to the present invention, the distance from the reducing agent supply position to the exhaust gas purification means can be optimized according to the process for the exhaust gas purification means, and each process can be performed under optimal conditions.

  Hereinafter, specific examples of the present invention will be described.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus according to Embodiment 1 of the present invention is applied and its intake / exhaust system.

The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders # 1 to # 4, and includes a fuel injection valve 3 that directly injects fuel into the combustion chamber of each cylinder 2. ing. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4, and the common rail 4 communicates with a fuel pump 6 through a fuel supply pipe 5.

  An exhaust passage 7 extends from the internal combustion engine 1. The exhaust passage 7 is continuous from the exhaust port of the cylinder 2 of the internal combustion engine 1, and an exhaust path is formed by the exhaust passage 7 and the exhaust port of each cylinder 2. The exhaust passage 7 is connected to a muffler at a downstream (not shown). A turbine housing 9 of the supercharger 8 is disposed in the middle of the exhaust passage 7, and an exhaust purification for purifying exhaust discharged from the cylinder 2 is provided in a portion downstream of the turbine housing 9 in the exhaust passage 7. Means 10 are arranged. The exhaust purification means 10 is a storage reduction type NOx catalyst carried on a filter that collects PM such as soot discharged from the internal combustion engine 1. Further, the exhaust purification means 10 may be a NOx catalyst and a filter arranged in series, or those in which they are alternately multiplexed.

  The exhaust port of the first cylinder (# 1) of the internal combustion engine 1 is attached with a first fuel addition valve 11 (first reducing agent supply means) for supplying fuel as a reducing agent into the exhaust gas flowing through the exhaust port. It has been. The first fuel addition valve 11 is connected to the fuel pump 6 via the fuel passage 12.

  A second fuel addition valve 13 (second reducing agent supply means) that supplies fuel as a reducing agent into the exhaust gas flowing through the exhaust passage 7 is attached to the exhaust passage 7 in the vicinity of the upstream side of the exhaust purification means 10. It has been. The second fuel addition valve 13 is connected to the fuel pump 6 via the fuel passage 12.

  That is, the first fuel addition valve 11 adds fuel to the exhaust path upstream of the exhaust purification unit 10, specifically, to the exhaust port of the internal combustion engine 1. The second fuel addition valve 13 adds fuel to the exhaust passage downstream of the first fuel addition valve 11 and upstream of the exhaust purification means 10, specifically, to the exhaust passage 7 immediately upstream of the exhaust purification means 10. To do. A turbine housing 9 is interposed between the first fuel addition valve 11 and the second fuel addition valve 13.

  Thus, since the first fuel addition valve 11 and the second fuel addition valve 13 are arranged apart from the upstream and downstream of the exhaust path, the distance to the exhaust purification means 10 is different, and the first fuel addition valve 11 and the second fuel addition valve 13 are different. The distance from the valve 11 to the exhaust purification unit 10 is longer than the distance from the second fuel addition valve 13 to the exhaust purification unit 10. If this condition is satisfied, the positions of the two fuel addition valves are not limited to the arrangement positions in the present embodiment.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 14 for controlling the internal combustion engine 1. The ECU 14 is an arithmetic logic circuit including a CPU, ROM, RAM, backup RAM, and the like.

  The ECU 14 is connected to the fuel injection valve 3 and the first and second fuel addition valves 11 and 13 by electric wiring, and the ECU 14 supplies fuel at the fuel injection valve 3 and the first and second fuel addition valves 11 and 13.・ It is possible to control stoppage and fuel supply.

  In the basic routine to be executed at regular intervals, the ECU 14 executes, for example, input of output signals of various sensors, calculation of engine speed, calculation of fuel supply amount, calculation of fuel supply timing, and the like. Various signals input by the ECU 14 in the basic routine and various control values obtained by the ECU 14 are temporarily stored in the RAM of the ECU 14.

Further, the ECU 14 reads various control values from the RAM in the interrupt processing triggered by the input of signals from various sensors and switches, the elapse of a predetermined time, or the input of a pulse signal from the crank position sensor. The fuel injection valve 3, the first and second fuel addition valves 11, 13 and the like are controlled according to the control value.

  The ECU 14 operates in accordance with an application program stored in the ROM, and executes processing for the exhaust purification means 10 such as NOx reduction processing, SOx poisoning elimination processing, and PM oxidation removal processing described later.

  First, the NOx reduction process will be described. The NOx reduction process is a process for releasing / reducing NOx stored in the NOx catalyst by setting the air-fuel ratio of the exhaust gas flowing into the NOx catalyst of the exhaust gas purification means 10 to be a rich air-fuel ratio.

  In order to execute the NOx reduction process, the ECU 14 determines whether or not the NOx reduction process execution condition is satisfied every predetermined cycle. As this NOx reduction processing execution condition, for example, the output signal value of an exhaust temperature sensor (not shown) in which the NOx amount occluded in the NOx catalyst is equal to or greater than a predetermined NOx occlusion amount and the NOx catalyst is in an active state. It can be exemplified that the condition (exhaust temperature) is equal to or lower than a predetermined upper limit value, the SOx poisoning elimination process is not executed, or the like is satisfied.

  When it is determined that the NOx reduction processing execution condition is satisfied, the ECU 14 temporarily injects the air-fuel ratio of the exhaust gas injected from the fuel addition valve and flowing into the NOx catalyst of the exhaust gas purification means 10 into a predetermined amount. The target rich air-fuel ratio is set.

  As a result, in the NOx reduction process, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst of the exhaust purification means 10 becomes the target rich air-fuel ratio, and NOx stored in the NOx catalyst is released / reduced.

  Next, the SOx poisoning elimination process will be described. The NOx catalyst of the exhaust purification means 10 stores SOx in the exhaust by the same mechanism as NOx. Therefore, when the storage amount of SOx increases, the NOx storage capacity of the NOx catalyst decreases accordingly, so-called SOx poisoning. appear.

  When SOx poisoning occurs in the NOx catalyst in this way, the NOx storage capacity is saturated, and NOx in the exhaust is released into the atmosphere without being purified by the NOx catalyst. In order to prevent this, SOx poisoning elimination processing for releasing and reducing SOx stored in the NOx catalyst is performed.

  In order to execute the SOx poisoning elimination process, the ECU 14 determines whether or not the SOx poisoning elimination process execution condition is satisfied every predetermined cycle. The SOx poisoning elimination process execution condition is, for example, an output of an exhaust gas temperature sensor (not shown) in which the SOx amount occluded in the NOx catalyst is equal to or greater than a predetermined SOx occlusion amount and the NOx catalyst is in an active state. It can be exemplified that the condition that the signal value (exhaust temperature) is equal to or lower than a predetermined upper limit value, the NOx reduction process is not executed, or the like is satisfied.

  When it is determined that the SOx poisoning elimination process execution condition is satisfied, the ECU 14 first raises the NOx catalyst bed temperature of the exhaust gas purification means 10 to about 600 ° C., and then exhausts into the NOx catalyst. The air / fuel ratio of the engine is set to be equal to or lower than the stoichiometric air / fuel ratio.

Specifically, as means for increasing the temperature of the NOx catalyst at an early stage, in addition to normal main fuel injection near the top dead center of the compression stroke of the internal combustion engine 1, fuel is injected into the cylinder during the exhaust stroke or the expansion stroke. It is effective to perform sub-injection such as post-injection in which fuel is injected as a secondary injection, or rubber injection in which fuel is injected into the cylinder in the vicinity of the top dead center of the intake stroke or exhaust stroke.

  Further, instead of the above-mentioned sub-injection or together with the sub-injection, by adding fuel as a reducing agent from the fuel addition valve into the exhaust, those unburned fuel components are oxidized in the NOx catalyst and generated during the oxidation. The bed temperature of the NOx catalyst may be increased by heat.

  Then, when the bed temperature of the NOx catalyst rises to about 600 ° C., the ECU 14 supplies fuel as a reducing agent from the fuel addition valve so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is equal to or lower than the stoichiometric air-fuel ratio. When fuel is supplied from the fuel addition valve, the fuel mixes with the exhaust discharged from the cylinder 2 to form an air-fuel mixture that is less than the stoichiometric air-fuel ratio, flows into the NOx catalyst, and is stored in the NOx catalyst. Will be released and reduced.

  The PM oxidation removal process will be described. When PM is excessively collected in the filter of the exhaust gas purification means 10, the filter is clogged, the exhaust resistance is increased, and the output of the internal combustion engine 1 is decreased. Therefore, it is necessary to execute a filter regeneration process for removing PM collected by the filter, and the ECU 14 executes the PM oxidation removal process.

  The PM oxidation removal process is executed by the ECU 14 to remove the PM collected by the filter when the PM oxidation removal process execution condition for the filter is satisfied. An example of the PM oxidation removal processing execution condition is a condition that the amount of PM collected by the filter is equal to or greater than a predetermined amount of accumulated PM. The predetermined PM accumulation amount is more than the limit amount that causes clogging of the filter due to PM accumulating on the filter, and this clogging causes an increase in exhaust resistance and a decrease in output of the internal combustion engine. The amount is set slightly lower.

  When it is determined that the PM oxidation removal process execution condition is satisfied, the ECU 14 executes a temperature increase process for increasing the temperature of the filter to a high temperature range of about 500 ° C. to 700 ° C. The inflowing exhaust gas has an oxygen-excess atmosphere.

  In the temperature raising process, fuel as a reducing agent is added into the exhaust gas from the fuel addition valve to oxidize those unburned fuel components in the NOx catalyst of the exhaust gas purification means 10, and the heat generated during the oxidation causes the filter to This is a process for increasing the temperature.

  In the air-fuel ratio process to make the atmosphere excessive in oxygen, the amount of fuel injected from the fuel injection valve 3 or the fuel added to the exhaust from the fuel addition valve so that the air-fuel ratio of the exhaust flowing into the filter becomes a lean air-fuel ratio. This is control for adjusting the supply amount.

  When such a PM oxidation removal process is executed, the PM collected in the filter is oxidized, and the PM is removed from the filter.

  Here, in order to improve the NOx or SOx reduction performance of the NOx catalyst of the exhaust gas purification means 10, it is preferable that the fuel added by the fuel addition valve reaches the NOx catalyst in a state where the fuel is sufficiently diffused in the exhaust gas. . Further, when the fuel is a heavy fuel with low volatility, it is preferable that the fuel is sufficiently vaporized before reaching the NOx catalyst.

  Therefore, in the NOx reduction process and the SOx poisoning elimination process, it is preferable that the distance from the fuel supply position by the fuel addition valve to the NOx catalyst is long. Further, in order to increase the temperature increase rate in the temperature increase process of the PM oxidation removal process, it is preferable that the distance from the fuel supply position by the fuel addition valve to the NOx catalyst is long.

  However, if the distance from the fuel supply position by the fuel addition valve to the exhaust purification means 10 is long, the following problems may be considered. That is, even if the operating condition that tends to cause excessive temperature rise of the filter, such as when the vehicle equipped with the internal combustion engine is decelerated during the PM oxidation removal processing, is caused, even if the reducing agent supply is immediately stopped. There is a risk that the fuel that has already been supplied arrives at the NOx catalyst, and the fuel that arrives late may cause the filter to overheat.

  As described above, in the NOx reduction process, the SOx poisoning elimination process, and the PM oxidation removal process for the exhaust gas purification means 10 described above, fuel supply from the fuel addition valve is required, but importance is attached to each process. The optimum distance from the fuel addition position to the exhaust purification means 10 varies depending on what is to be done.

  In view of the above-described matters, in the present embodiment, two first and second fuel addition valves 11 and 13 having different distances to the exhaust purification unit 10 are arranged, and the first and second fuel addition valves 11 and 13 are arranged according to the processing on the exhaust purification unit 10. The fuel supply is performed by selecting one of the first and second fuel addition valves 11 and 13.

  As an outline, in the NOx reduction process and the SOx poisoning elimination process, the fuel is added from the first fuel addition valve 11 with an emphasis on the reduction efficiency of NOx or SOx. On the other hand, in the PM oxidation removal process, the fuel is added from the second fuel addition valve 13 with an emphasis on preventing overheating of the filter.

  Specifically, in the present embodiment, the ECU 14 selects whether to supply fuel from one of the two first and second fuel addition valves 11 and 13 according to the flow of FIG. This flow is a routine executed by the ECU as an interrupt process triggered by a certain time interval or input of a pulse signal from the crank position sensor. Hereinafter, description will be given along the flowchart of FIG.

  This control routine is a routine stored in advance in the ROM of the ECU 14. The ECU 14 first determines in step (hereinafter also simply referred to as “S”) 101 whether or not NOx reduction processing or SOx poisoning elimination processing is requested. In this embodiment, when the above-mentioned NOx reduction process execution condition is satisfied, it is determined that the NOx reduction process is required, and when the above-mentioned SOx poisoning elimination process execution condition is satisfied. It is determined that SOx poisoning elimination processing is requested. If it is determined that NOx reduction processing or SOx poisoning elimination processing is requested, the process proceeds to S102, and if it is determined that NOx reduction processing is not requested, the process proceeds to S103.

  In S102, the first fuel addition valve 11 is selected, and NOx reduction processing or SOx poisoning elimination processing is executed. Accordingly, fuel is supplied from the first fuel addition valve 11 to the exhaust during the NOx reduction process or the SOx poisoning elimination process. As a result, the distance from the fuel supply position to the exhaust purification unit 10 is from the exhaust port of the internal combustion engine 1 to the exhaust purification unit 10 and becomes longer. As a result, the supplied fuel is sufficiently diffused into the exhaust. In particular, the turbine housing 9 is located downstream of the first fuel addition valve 11 and sufficiently diffuses when passing through the turbine housing 9. As a result, the fuel spreads over the entire exhaust gas purification means 10, and the reduction and removal process of NOx or SOx stored in the NOx catalyst is promoted to improve the reduction efficiency.

  On the other hand, in S103, it is determined whether PM oxidation removal processing is required. In this embodiment, it is determined that the PM oxidation removal process is required when the above-described PM oxidation removal process execution condition is satisfied. If it is determined that the PM oxidation removal process is requested, the process proceeds to S104. If it is determined that the PM oxidation removal process is not requested, the execution of this routine is terminated.

  In S104, the second fuel addition valve 13 is selected and the PM oxidation removal process is executed. Therefore, fuel is supplied from the second fuel addition valve 13 to the exhaust purification unit 10 during the PM oxidation removal process. As a result, the distance from the fuel supply position to the exhaust gas purification unit 10 is from the immediately upstream side of the exhaust gas purification unit 10 to the exhaust gas purification unit 10 and is shortened. As a result, at this short distance, there is no delay in the arrival of fuel to the NOx catalyst of the exhaust purification means 10 so that the fuel does not reach the exhaust purification means 10 as soon as the fuel supply from the second fuel addition valve 13 is stopped. can do. Thereby, the excessive temperature rise of the filter due to the fuel that arrives late can be prevented, and quick response of avoiding the excessive temperature rise due to the stop of fuel supply at the second fuel addition valve 13 can be obtained.

  In this way, either the first or second fuel addition valve 11 or 13 is selected by the processing (NOx reduction processing, SOx poisoning elimination processing, PM oxidation removal processing) for the exhaust gas purification means 10, and the fuel addition position is set. Since the switching is performed, the distance from the fuel addition position to the exhaust purification unit 10 can be optimized according to the process for the exhaust purification unit 10, and each process can be performed under the optimum conditions.

  In the first embodiment, the fuel is uniformly supplied from the second fuel addition valve 13 to the exhaust purification unit 10 during the PM oxidation removal process. However, if there is no possibility that the temperature of the filter is excessively increased during the PM oxidation removal process, the distance from the fuel addition position to the exhaust purification means 10 is increased to ensure the reaction promoting property by fuel diffusion, and the low temperature It is preferable to increase the activity or improve the temperature non-uniformity in the NOx catalyst.

  Therefore, in this embodiment, the fuel supply is performed by selecting one of the first and second fuel addition valves 11 and 13 in accordance with the filter temperature during the PM oxidation removal process. That is, during the PM oxidation removal process, it is determined whether or not the filter temperature in the exhaust purification unit 10 is higher than a predetermined temperature. If it is determined that the filter temperature is higher than the predetermined temperature, the second fuel addition valve 13 is set. When it is determined that the temperature is equal to or lower than the predetermined temperature, the first fuel addition valve 11 is selected, and the PM oxidation removal process is executed.

  Specifically, in the present embodiment, the ECU 14 selects whether to supply fuel from one of the two first and second fuel addition valves 11, 13 according to the flow of FIG. Note that the steps S201 to S204 in this flow are the same as the steps S101 to S104 in the first embodiment, and a description thereof will be omitted.

  When it is determined in S203 that the PM oxidation removal process is required, the process proceeds to S210, and in this step, it is determined whether or not the filter temperature in the exhaust purification unit 10 is higher than a predetermined temperature. If it is determined that the filter temperature is higher than the predetermined temperature, the process proceeds to S204, the second fuel addition valve 13 is selected, and the PM oxidation removal process is executed. On the other hand, if it is determined that the temperature is equal to or lower than the predetermined temperature, the process proceeds to S202, the first fuel addition valve 11 is selected, and the PM oxidation removal process is executed.

  An example of the predetermined temperature is 600 ° C. Further, the temperature detection of the filter can be estimated from the history of the exhaust gas temperature that can be derived from the intake air amount and the engine speed after the internal combustion engine 1 is started. Moreover, what detects by the sensor which detects filter temperature directly may be used.

In S202 when it is determined that the filter temperature after S210 is equal to or lower than the predetermined temperature, fuel is supplied from the first fuel addition valve 11 to the exhaust purification unit 10 during the PM oxidation removal process. In this case, the filter temperature is equal to or lower than the predetermined temperature, and even if a certain degree of temperature rise occurs, the temperature does not rise excessively. Therefore, during the PM oxidation removal process, fuel arrival delay to the exhaust purification means 10 occurs. The excessive temperature rise of the filter resulting from this can be prevented. For this reason, the quick response of avoiding excessive temperature rise by stopping the fuel supply at the fuel addition valve may not be obtained.

  The distance from the first fuel addition valve 11 to the exhaust purification means 10 is between the exhaust port of the internal combustion engine 1 and the exhaust purification means 10, and the distance from the second fuel addition valve 13 to the exhaust purification means 10. Longer than. Then, the fuel supplied over the long distance is sufficiently diffused into the exhaust gas, the fuel is spread over the entire radial direction of the exhaust gas purification means 10, and the oxidation of the fuel in the NOx catalyst can be performed completely, and the oxidation reactivity Can be secured. As a result, the temperature non-uniformity in the NOx catalyst can be improved, and the low temperature activity can be increased.

  As described above, also in the PM oxidation removal processing, either the first or second fuel addition valve 11 or 13 is selected and the fuel addition position is switched depending on whether or not there is a possibility of excessive temperature rise of the filter. Can be carried out under optimal conditions.

  In the above description, if the filter temperature is equal to or lower than the predetermined temperature, the filter temperature is set as a condition that there is no risk of overheating of the filter, such as selecting the first fuel addition valve 11 and executing the PM oxidation removal process. Illustrated.

  Other examples of the condition that there is no risk of overheating of the filter include that the vehicle speed is 120 km / h or less, the PM accumulation amount is 1 g or less, and the estimated fuel arrival delay time is 0.5 sec or less. be able to.

  Further, for example, when the vehicle speed is 120 km / h, the PM accumulation amount is 1 g, and the estimated fuel delay time is 0.5 sec, the filter temperature is set to 600 ° C. without any risk of overheating of the filter. Conditions that do not pose a risk of overheating of the filter may be determined by comprehensively considering the temperature, the vehicle speed, the PM accumulation amount, and the estimated fuel arrival delay time.

  In the first and second embodiments, the fuel is uniformly supplied from the first fuel addition valve 11 to the NOx catalyst during the NOx reduction process and the SOx poisoning elimination process. However, if the target site for the NOx reduction process or the SOx poisoning elimination process is a downstream part of the NOx catalyst, the NOx or SOx reduction and removal performance will not deteriorate even if the distance from the fuel addition position to the NOx catalyst is short. . This is because the oxygen in the exhaust gas reacts and decreases in the process where the exhaust gas reaches the downstream site, and the exhaust gas that reaches the downstream site contains mainly HC without much oxygen. This is because the reduction reaction of NOx or SOx at the site is promoted.

  On the other hand, if the distance from the fuel addition position to the exhaust purification means 10 is long, there is a problem that the amount of fuel adhering to the inner wall of the exhaust path increases and fuel consumption deteriorates.

  Therefore, in the present embodiment, when the ECU 14 executes the NOx reduction process and the SOx poisoning elimination process, first, when the NOx catalyst is divided into two parts, an upstream part and a downstream part in the exhaust flow direction. It is estimated from which site NOx or SOx is reduced.

  Then, the first and second fuel addition valves 11 and 13 are determined according to the estimated portion to be reduced during the NOx reduction process or the SOx poisoning elimination process (hereinafter also referred to as “processing target part”). Select either of them to supply fuel. That is, if it is estimated that the NOx catalyst is reduced from the upstream site, the first fuel addition valve 11 is selected. If it is estimated that the NOx catalyst is the downstream site, the second fuel addition valve 13 is selected, and the NOx reduction treatment and the SOx coverage are selected. Perform poison elimination processing.

  The method for estimating the processing target part is as follows. For example, when either the upstream part or the downstream part is at the activation temperature, it is estimated that the part that has reached the activation temperature is the treatment target part. However, this is not the case when NOx or SOx is not occluded in the part. On the other hand, when the upstream part and the downstream part are both at the activation temperature, it is estimated that the upstream part is the processing target part. However, when NOx or SOx is not occluded in the upstream part, it is estimated that the downstream part is the processing target part.

  The temperature distribution of the NOx catalyst is determined by the history of the energy of the exhaust gas that has flowed into the NOx catalyst so far, the amount of fuel supplied from the fuel addition valve during the NOx reduction process or the SOx poisoning elimination process, and the characteristics of the NOx catalyst. It can be grasped based on the purification rate. Further, it may be detected by a sensor that directly detects the temperature of the NOx catalyst.

  In this embodiment, the ECU 14 selects whether to supply fuel from one of the two first and second fuel addition valves 11 and 13 according to the flow of FIG. Note that the steps S301 to S304 in this flow are the same as the steps S101 to S104 in the first embodiment, and a description thereof will be omitted.

  First, in S301, the ECU 14 determines whether NOx reduction processing or SOx poisoning elimination processing is requested. If it is determined that the NOx reduction process or the SOx poisoning elimination process is requested, the process proceeds to S310. If it is determined that the NOx reduction process or the SOx poisoning elimination process is not requested, the process proceeds to S303.

  In S310, it is estimated whether the site to be treated in the NOx reduction process or the SOx poisoning elimination process is the upstream part or the downstream part in the NOx catalyst, and the estimated part is the upstream part in the NOx catalyst. Determine whether or not. If it is determined that the site to be processed is an upstream site in the NOx catalyst, the process proceeds to S302, the first fuel addition valve 11 is selected, and NOx reduction processing or SOx poisoning elimination processing is executed. On the other hand, when it is determined that the NOx catalyst is not the upstream part (downstream part), the process proceeds to S304, the second fuel addition valve 13 is selected, and the NOx reduction process or the SOx poisoning elimination process is executed.

  In S304 when it is determined that the processing target site in the NOx reduction processing or SOx poisoning elimination processing after S310 is not the upstream side site in the NOx catalyst, during the NOx reduction processing or SOx poisoning elimination processing, Fuel is supplied from the second fuel addition valve 13 to the exhaust. Therefore, the distance from the second fuel addition valve 13 to the exhaust purification unit 10 is shortened from the position immediately upstream of the exhaust purification unit 10 to the exhaust purification unit 10.

  As a result, fuel consumption deterioration caused by a decrease in the amount of fuel that contributes to reduction due to the added fuel adhering to the exhaust passage while maintaining the reduction and removal performance of NOx or SOx can be suppressed.

  Thus, also in the NOx reduction process and the SOx poisoning elimination process, the first and second fuels depend on whether the site to be treated in the NOx reduction process or the SOx poisoning elimination process is the upstream part or the downstream part of the NOx catalyst. Since either the addition valve 11 or 13 is selected and the fuel addition position is switched, the NOx reduction process and the SOx poisoning elimination process can be performed under optimum conditions.

  Although the above-described Examples 2 and 3 are described independently, it is not limited thereto, and it goes without saying that both may be combined.

1 is a diagram illustrating a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus according to Embodiment 1 is applied and an intake / exhaust system thereof. 3 is a flowchart illustrating a control routine for selecting a fuel addition valve in accordance with processing performed on an exhaust purification unit according to the first embodiment. 7 is a flowchart showing a control routine for selecting a fuel addition valve in accordance with processing for an exhaust purification unit according to a second embodiment. 10 is a flowchart illustrating a control routine for selecting a fuel addition valve in accordance with processing performed on an exhaust purification unit according to a third embodiment.

Explanation of symbols

1 Internal combustion engine 2 Cylinder 3 Fuel injection valve 4 Common rail 5 Fuel supply pipe 6 Fuel pump 7 Exhaust passage 8 Supercharger 9 Turbine housing 10 Exhaust purification means 11 First fuel addition valve 12 Fuel passage 13 Second fuel addition valve

Claims (3)

An exhaust purification means that is disposed in an exhaust path extending from the internal combustion engine and has a NOx storage reduction catalyst that stores and reduces NOx in the exhaust and a filter that collects particulates discharged from the internal combustion engine;
First reducing agent supply means for supplying a reducing agent to the exhaust path upstream of the exhaust purification means;
Second reducing agent supply means for supplying a reducing agent to the exhaust path downstream of the first reducing agent supply means and upstream of the exhaust purification means;
With
When reducing NOx occluded in the NOx catalyst from the NOx catalyst and reducing SOx occluded in the NOx catalyst from the NOx catalyst, the reducing agent is supplied from the first reducing agent supply means. Supply
An exhaust gas purifying apparatus for an internal combustion engine, wherein a reducing agent is supplied from the second reducing agent supply means when the particulates collected by the filter are oxidized and removed.   2. The reducing agent is supplied from the first reducing agent supply unit when the exhaust gas purification unit is at a predetermined temperature or less when oxidizing and removing the particulates collected by the filter. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. When reducing NOx or SOx occluded in the NOx catalyst, it is provided with site estimation means for estimating from the upstream site or the downstream site in the NOx catalyst,
When the NOx stored in the NOx catalyst is reduced from the NOx catalyst, and when the SOx stored in the NOx catalyst is reduced from the NOx catalyst, the site estimation means is reduced from the downstream site. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein when it is estimated, a reducing agent is supplied from the second reducing agent supply means.

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