JP2009013863A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently supply a reducing agent to each exhaust emission control device in an exhaust emission control system of an internal combustion engine equipped with the exhaust emission control devices in series in an exhaust passage of the internal combustion engine. <P>SOLUTION: Exhaust gas flowing from a first branch pipe side (second branch pipe side) containing additional fuel by a first fuel addition valve (second fuel addition valve) to a first merging part (second merging part), and exhaust gas not containing additional fuel and flowing from an exhaust pipe side to the first merging part (second merging part), are merged to thereby stir the additional fuel in the exhaust gas and disperse the additional fuel. Further, by expanding an additional fuel distribution area AHC to a wider range, an additional fuel supply period is increased. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an exhaust purification system that purifies exhaust discharged from an internal combustion engine.

  An exhaust purification device is provided in the exhaust passage of the internal combustion engine for the purpose of removing NOx, particulate matter (PM), etc. contained in the exhaust discharged from the internal combustion engine and purifying the exhaust. As this exhaust purification device, a selective reduction type NOx catalyst that purifies exhaust by selectively reducing NOx in exhaust in a reducing atmosphere, or a storage reduction type that purifies exhaust by storing and reducing NOx in exhaust. NOx catalyst etc. are mentioned. By performing reducing agent supply control for supplying a reducing agent to the NOx catalyst, NOx is reduced in the NOx catalyst (hereinafter referred to as “NOx reduction treatment”).

  Further, as the exhaust purification device, a particulate filter (hereinafter also simply referred to as “filter”) that collects particulate matter in the exhaust and suppresses the release of the particulate matter to the atmosphere can be exemplified. In such a filter, when the amount of collected particulate matter increases, the engine performance deteriorates due to clogging of the filter. Therefore, the collected particulate matter is oxidized and removed by raising the temperature of the filter. (Hereinafter referred to as “PM regeneration process”). In this PM regeneration process, when the filter carries an oxidation catalyst, or when an oxidation catalyst is provided upstream from the filter, the reducing agent is supplied to the oxidation catalyst and the reducing agent is oxidized. The temperature of the filter may be raised by the reaction heat.

In relation to the control for supplying the reducing agent to the exhaust purification device as described above, Patent Document 1 discloses that an NOx catalyst and a filter are arranged in series in the exhaust passage of the internal combustion engine, and are provided immediately upstream of the NOx catalyst. A technique for adding a reducing agent (liquid fuel) to exhaust gas from a reducing agent addition valve is disclosed.
JP 2002-349236 A Japanese Patent Laid-Open No. 2000-282843 JP 2000-220437 A

  However, in the above prior art, the reducing agent added from the reducing agent addition valve disposed immediately upstream of the NOx catalyst may flow into the NOx catalyst as the exhaust purification device before being sufficiently dispersed in the exhaust gas. . As a result, the reducing agent is not uniformly supplied to the entire NOx catalyst, and it may be difficult to purify NOx in the entire NOx catalyst.

  Further, from the viewpoint of reducing the consumption of the reducing agent, it is desired to reduce more NOx with a small reducing agent. For this purpose, it is necessary to efficiently supply the reducing agent to the exhaust purification device.

  The present invention has been made in view of the above-described prior art, and an object of the present invention is to provide each exhaust purification device in an exhaust purification system of an internal combustion engine provided with an exhaust purification device in series in an exhaust passage of the internal combustion engine. It is to provide a technique capable of supplying a reducing agent more efficiently.

In order to achieve the above object, an exhaust gas purification system for an internal combustion engine according to the present invention employs the following means.
That is,
A first exhaust purification device provided in an exhaust passage of the internal combustion engine;
A second exhaust purification device provided downstream of the first exhaust purification device in the exhaust passage;
A first merging portion that branches from the first branching portion on the upstream side of the first exhaust purification device in the exhaust passage and that is downstream of the first branching portion and upstream of the first exhaust purification device. A first branch passage that merges with the exhaust passage;
Branching from the second branch portion upstream of the first exhaust purification device in the exhaust passage, downstream of the first exhaust purification device and upstream of the second exhaust purification device of the exhaust passage. A second branch passage that joins the exhaust passage at the second joining portion of
The exhaust passage is provided downstream of the first branch portion and upstream of the first junction portion or in the first branch passage, and is reduced to the exhaust gas before flowing into the first junction portion. First reducing agent addition means for adding an agent;
The exhaust passage is provided on the downstream side of the first exhaust purification device and upstream of the second merging portion or in the second branch passage, and the exhaust before flowing into the second merging portion. A second reducing agent adding means for adding a reducing agent;
It is characterized by providing.

  In the present invention, when the reducing agent is supplied to the first exhaust gas purification device, the reducing agent is added into the exhaust gas from the first reducing agent addition means. Here, the first reducing agent addition means is a portion downstream of the first branching portion of the exhaust passage and upstream of the first merging portion (hereinafter, this portion is also referred to as “first branching section”). ) Or the first branch passage. In the present invention, before the exhaust gas after the reducing agent is added to the exhaust gas by the first reducing agent addition means is allowed to flow into the first exhaust gas purification device, the exhaust gas that does not contain the reducing agent is joined at the first junction. did.

  That is, when the first reducing agent addition means is provided in the first branch passage, the exhaust gas after the addition of the reducing agent flows into the first junction from the first branch passage and does not contain the reducing agent. Flows into the first junction from the first branch section in the exhaust passage. Conversely, when the first reducing agent addition means is provided in the first branching section of the exhaust passage, the exhaust gas after the reducing agent is added flows from the first branching section of the exhaust passage into the first junction. The exhaust gas not containing the reducing agent flows into the first junction from the first branch passage.

  In any of the above cases, the exhaust gas turbulence increases when the exhaust gas containing the reducing agent and the exhaust gas not containing it collide at the first junction. As a result, the reducing agent added by the first reducing agent adding means in the first junction is stirred in the exhaust gas, so that the reducing agent can be further dispersed. Furthermore, the flow rate of the exhaust gas after the reducing agent is added increases at the first junction. Thereby, the distribution area of the reducing agent in the exhaust (hereinafter referred to as “reducing agent distribution area”) can be expanded as compared with immediately after the first reducing agent addition means adds the reducing agent.

  More specifically, the reducing agent distribution region can be expanded both in the exhaust flow direction and in the exhaust passage radial direction. According to this, the period during which the reducing agent can be supplied to the first exhaust purification catalyst (hereinafter, this period is referred to as “reducing agent supply period”) can be lengthened. The reaction period of the reducing agent in the first exhaust purification device can be extended longer without increasing the reducing agent addition period). Further, since the reducing agent in the exhaust gas is sufficiently dispersed in the radial direction of the exhaust passage, the reducing agent can be uniformly supplied to the entire first exhaust purification device.

On the other hand, when the reducing agent is supplied to the second exhaust purification device, the reducing agent is added into the exhaust from the second reducing agent addition means. The second reducing agent addition means is provided in a portion of the exhaust passage between the first exhaust purification device and the second merging portion (hereinafter, this portion is also referred to as “second branching section”) or in the second branch passage. Therefore, the exhaust gas containing the reducing agent added by the second reducing agent addition means and the exhaust gas not containing the reducing agent merge at the second junction.

  As a result, when the exhaust gas after the reducing agent is added by the second reducing agent addition means flows into the second junction, the reducing agent in the exhaust gas can be stirred and dispersed. Thereby, a reducing agent distribution area can be expanded. Therefore, the reducing agent can be efficiently supplied also to the second exhaust purification device.

  As described above, according to the present invention, in the exhaust gas purification system for an internal combustion engine provided with the first exhaust gas purification device and the second exhaust gas purification device in series, the reducing agent is efficiently supplied to each exhaust gas purification device. can do. As a result, it is possible to reduce the consumption of the reducing agent when supplying the reducing agent to each exhaust purification device.

  Here, comparing the exhaust gas passing through the first branch passage with the exhaust gas passing through the second branch passage, the former flows into the first exhaust gas purification device without bypassing the first exhaust gas purification device, and the latter is the first one. The difference is that the exhaust gas detours and flows into the second exhaust gas purification device. That is, the flow rate of the exhaust gas flowing into the first exhaust gas purification device and the second exhaust gas purification device is different, and all the exhaust gas discharged from the internal combustion engine flows into the second exhaust gas purification device, whereas the first exhaust gas purification device is different from the first exhaust gas purification device. The flow rate of the exhaust gas flowing into the exhaust gas purification device is small by the amount passing through the second branch passage.

  The first exhaust purification device in the present invention may include a NOx catalyst that purifies NOx in the exhaust. That is, the reducing agent is added to the exhaust gas from the first reducing agent adding means, and the NOx catalyst is brought into a rich atmosphere, so that NOx is reduced. In the present invention, as described above, the NOx catalyst can be maintained in a rich atmosphere for a longer period by extending the reducing agent supply period to the first exhaust purification device, so that the NOx purification rate can be improved.

  Furthermore, according to the exhaust purification system of the present invention, a part of the exhaust discharged from the internal combustion engine passes through the second branch passage and bypasses the NOx catalyst, so that the space velocity of the exhaust passing through the NOx catalyst is reduced. In addition, the amount of oxygen passing through the NOx catalyst can be reduced.

  That is, the reduction reaction between NOx and the reducing agent can be promoted by reducing the space velocity of the exhaust gas and retaining the reducing agent in the NOx catalyst longer. In addition, by reducing the amount of oxygen passing through the NOx catalyst, the atmosphere in the NOx catalyst can be easily made rich with less reducing agent. Thereby, the NOx reduction efficiency in the NOx reduction process can be further improved. Examples of the NOx catalyst in the present invention include an occlusion reduction type NOx catalyst, a selective reduction type NOx catalyst, and a three-way catalyst.

  Further, the second exhaust gas purification apparatus according to the present invention may include a filter carrying an oxidation catalyst, or an oxidation catalyst and a filter provided on the downstream side of the oxidation catalyst. That is, there is a PM regeneration process in which a reducing agent is added from the second reducing agent addition means, the temperature of the filter is raised by supplying the reducing agent to the filter, and particulate matter (PM) collected by the filter is oxidized and removed. To be implemented. More specifically, the particulate matter is oxidized and removed by raising the temperature of the filter to a temperature at which the particulate matter is oxidized by the reaction heat generated when the reducing agent supplied to the filter is oxidized.

  Here, in the PM regeneration process, if the amount of oxygen flowing into the filter is excessively reduced, the oxidation reaction of the particulate matter may be suppressed. On the other hand, in the present invention, all the exhaust gas discharged from the internal combustion engine flows into the filter, so that sufficient oxygen can be flowed into the filter for efficient oxidation removal of the particulate matter.

In the present invention, when the exhaust from the second branch passage and the exhaust from the second branch section in the exhaust passage are merged at the second junction, the reducing agent and oxygen are sufficiently mixed in the exhaust. be able to. As a result, the temperature of the filter can be increased more easily, and the oxidation reaction of the particulate matter can be promoted.

  The exhaust gas purification system for an internal combustion engine according to the present invention further includes a flow rate control means for controlling the flow rate of the exhaust gas passing through the second branch passage, and the flow rate control means includes the first reducing agent adding means as the reducing agent. When adding to the exhaust gas, the flow rate of the exhaust gas passing through the second branch passage may be increased compared to when the first reducing agent adding means does not add the reducing agent. According to this, when supplying the reducing agent to the first exhaust purification device (for example, the NOx catalyst), the space velocity of the exhaust gas passing through the first exhaust purification device and the first exhaust purification device are passed. The amount of oxygen can be reduced more effectively.

  In the present invention, the second branch portion may be a portion upstream of the first branch portion in the exhaust passage. That is, the second branch passage may be branched from the upstream side of the first branch portion in the exhaust passage. According to this, since all the exhaust gas from the internal combustion engine once flows into the second branch portion, the flow rate of the exhaust gas flowing into the second branch passage can be increased as much as possible. That is, the flow rate of the exhaust gas that bypasses the first exhaust gas purification device can be increased. Therefore, when supplying the reducing agent to the first exhaust purification device (for example, the NOx catalyst), the space velocity of the exhaust gas passing through the first exhaust purification device and the amount of oxygen passing through the first exhaust purification device Can be further reduced.

  Further, in the present invention, the portion of the exhaust passage downstream of the first branch portion and upstream of the first junction portion (first branching section) and the first branch passage have an exhaust passage area. In other words, the first reducing agent adding means may be provided in one of the smaller flow path areas. In this case, the flow rate of the exhaust gas containing the reducing agent can be relatively reduced with respect to the exhaust gas that does not contain the reducing agent among the exhaust gas flowing into the first junction. According to this, since the exhaust gas containing the reducing agent does not easily pass through the first joining portion, the reducing agent distribution region can be effectively expanded in the exhaust flow direction. Therefore, the reducing agent supply period for the first exhaust gas purification device can be secured for a longer period.

  In the present invention, the portion of the exhaust passage that is downstream of the first exhaust purification device and upstream of the second merging portion (second shunt section) and the second branch passage are the exhaust passage area. And the second reducing agent addition means may be provided in any one of the smaller flow path areas. In that case, the flow rate of the exhaust gas containing the reducing agent can be relatively reduced with respect to the exhaust gas that does not contain the reducing agent among the exhaust gas flowing into the second junction. Thereby, since it becomes difficult for the exhaust gas containing the reducing agent to pass through the second merging portion, the reducing agent distribution region can be effectively expanded in the exhaust flow direction. Therefore, the reducing agent supply period for the second exhaust gas purification device can be secured for a longer period.

  In the present invention, in the exhaust gas purification system for an internal combustion engine in which an exhaust gas purification device is provided in series in the exhaust passage of the internal combustion engine, the reducing agent can be efficiently supplied to each exhaust gas purification device.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention only to those unless otherwise specified. is not.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to the present embodiment and its exhaust system and control system. An internal combustion engine 1 shown in FIG. 1 is a diesel engine. In FIG. 1, the inside of the internal combustion engine 1 and its intake system are omitted.

  An exhaust pipe 5 through which the exhaust discharged from the internal combustion engine 1 flows is connected to the internal combustion engine 1, and this exhaust pipe 5 is connected downstream to a muffler (not shown). Further, an NOx storage reduction catalyst (hereinafter referred to as “NSR”) 10 for purifying NOx in the exhaust is disposed in the middle of the exhaust pipe 5. A filter (hereinafter referred to as “DPR”) 11 carrying an oxidation catalyst is disposed downstream of the NSR 10 in the exhaust pipe 5. The DPR 11 collects particulate matter (PM) in the exhaust. In this embodiment, the exhaust pipe 5 corresponds to the exhaust passage in the present invention. The NSR 10 corresponds to the first exhaust purification device in the present invention, and the DPR 11 corresponds to the second exhaust purification device in the present invention.

  Further, in the first branch part 5a upstream of the NSR 10, the first branch pipe 6 branches from the exhaust pipe 5, and the first branch pipe 6 is downstream of the first branch part 5a. The first merging portion 5b upstream of the NSR 10 merges with the exhaust pipe 5.

  The second branch pipe 7 branches from the exhaust pipe 5 in the second branch section 5c further upstream than the first branch section 5a, and joins the exhaust pipe 5 at a portion between the NSR 10 and the DPR 11. ing. Here, the first branch pipe 6 and the second branch pipe 7 are configured to have a smaller diameter than the exhaust pipe 5. In the present embodiment, the first branch pipe 6 and the second branch pipe 7 correspond to the first branch path and the second branch path in the present invention, respectively.

  The first branch pipe 6 is provided with a first fuel addition valve 12 for adding fuel as a reducing agent when performing NOx reduction processing on the NSR 10. Further, the second branch pipe 7 is provided with a second fuel addition valve 13 for adding fuel as a reducing agent when performing PM regeneration processing on the DPR 11. In the present embodiment, the first fuel addition valve 12 and the second fuel addition valve 13 correspond to the first reducing agent adding means and the second reducing agent adding means in the present invention, respectively.

The internal combustion engine 1 configured as described above and its exhaust system are provided with an electronic control unit (ECU) 15 for controlling the internal combustion engine 1 and the exhaust system. The ECU 15 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operating conditions of the internal combustion engine 1 and the driver's request, and performs control related to the exhaust purification system including the NSR 10 and the DPR 11 of the internal combustion engine 1. is there.

  Sensors related to control of the operating state of the internal combustion engine 1 are connected to the ECU 15 via electric wiring, and these output signals are input to the ECU 15. In addition, the first fuel addition valve 12, the second fuel addition valve 13, and the like are connected via electric wiring and controlled by the ECU 15. The ECU 15 includes a CPU, a ROM, a RAM, and the like. The ROM stores a program for performing various controls of the internal combustion engine 1 and a map storing data. A NOx reduction control routine in the present embodiment, which will be described later, is also one of programs stored in the ROM in the ECU 15.

  Next, fuel supply control for supplying fuel as a reducing agent to the NSR 10 and the DPR 11 in this embodiment will be described. For example, when the amount of NOx stored in the NSR 10 increases, the NOx purification capacity decreases, so that fuel is supplied to the NSR 10 by fuel supply control from the first fuel addition valve 12, and NOx stored in the catalyst is reduced. NOx reduction processing is executed. That is, the air-fuel ratio of the exhaust gas flowing into the NSR 10 (hereinafter referred to as “inflow exhaust air-fuel ratio”) is reduced to a rich air-fuel ratio, and NOx stored in the NSR 10 is reduced.

  Further, if the amount of accumulated PM collected in the DPR 11 increases, the back pressure rises due to clogging of the DPR 11 and the engine performance deteriorates. Therefore, the temperature of the DPR 11 is raised by the fuel supply control from the second fuel addition valve 13. PM regeneration processing for oxidizing and removing PM is executed. That is, PM is oxidized and removed by heat generated when the added fuel is oxidized in the oxidation catalyst supported on the DPR 11.

  By the way, from the viewpoint of improving fuel efficiency related to fuel supply control, it is desired to reduce more NOx or oxidize and remove more PM with a smaller amount of fuel added. For this purpose, it is necessary to efficiently supply the added fuel to the NSR 10 or DPR 11 in order to make maximum use of the catalytic capability of the NSR 10 or DPR 11. Therefore, in the exhaust purification system according to the present embodiment, when the fuel supply control is executed, the reaction time of the added fuel in the catalyst (that is, the NSR 10 or the DPR 11) can be made longer and the reactivity of the added fuel can be further increased. The system configuration that can be used was adopted.

  As shown in FIG. 1, when the added fuel is added from the first fuel addition valve 12, the exhaust gas containing the added fuel flows into the first merging portion 5b from the exhaust pipe 5 side in the first merging portion 5b. Merge with the coming exhaust. On the other hand, when the added fuel is added from the second fuel addition valve 13, the exhaust containing the added fuel joins the exhaust flowing into the second joining portion 5d from the exhaust pipe 5 side in the second joining portion 5d. . As described above, in this embodiment, the added fuel is stirred in the exhaust gas at the first merging portion 5b and the second merging portion 5d. As a result, the added fuel in the exhaust gas is sufficiently dispersed before flowing into the NSR 10 and the DPR 11.

  Here, FIG. 2 is an explanatory diagram for explaining the transition of the added fuel distribution region (hereinafter referred to as “added fuel distribution region”) AHC in the exhaust gas. Here, a case where added fuel is added from the first fuel addition valve 12 will be described as an example. FIG. 2A is a diagram showing the added fuel distribution region AHC immediately after the fuel addition from the first fuel addition valve 12 is completed. FIG. 2B is a diagram showing the added fuel distribution region AHC after the exhaust gas after the added fuel is added flows into the first merging portion 5b. In the figure, the added fuel distribution region AHC is indicated by hatching. Moreover, the arrow in a figure represents the flow of exhaust_gas | exhaustion.

  As shown in FIG. 2 (a), the range of the added fuel distribution region AHC immediately after the fuel addition by the fuel addition valve 12 is completed is the period during which fuel is added from the first fuel addition valve 12 and the first branch pipe. 6 depends on the flow rate of the exhaust gas passing through 6. The added fuel distribution area AHC moves in the direction of the first joining portion 5b along with the flow of the exhaust, and when the exhaust containing the added fuel reaches the first joining portion 5b, it passes through the exhaust pipe 5. It will merge with exhaust that does not contain added fuel.

  Here, as shown by a spiral in the drawing, the exhaust from the first branch pipe 6 and the exhaust passing through the exhaust pipe 5 are joined together, so that the exhaust is greatly disturbed. As a result, the added fuel in the exhaust gas is agitated when the exhaust gas including the added fuel and the exhaust gas not including the added fuel merge, and the added fuel is dispersed in the exhaust gas. Further, since the flow rate of the exhaust gas to which the added fuel is added increases when passing through the first joining portion, as shown in FIG. 2B, the added fuel distribution region AHC is expanded.

Thereby, the period during which the added fuel can be supplied to the NSR 10 (hereinafter, this period is referred to as “added fuel supply period”) can be further extended. Further, since the added fuel is sufficiently dispersed also in the radial direction of the exhaust passage 5 in the first merging portion 5b, the added fuel can be supplied evenly in the entire direction perpendicular to the exhaust flow direction in the NSR 10. Here, the case where fuel addition by the first fuel addition valve 12 is performed has been described as an example, but the same applies to the case where fuel addition by the second fuel addition valve 13 is performed. That is, the added fuel is agitated and dispersed in the exhaust gas when the exhaust gas containing the added fuel passes through the second merging portion 5d. Therefore, the added fuel supply period for the DPR 11 is extended, and the added fuel is supplied evenly in the entire direction perpendicular to the exhaust flow direction in the DPR 11.

  As described above, in the case where the added fuel is supplied to either the NSR 10 or the DPR 11, the reaction time of the added fuel in the catalyst can be increased and the reactivity of the added fuel in the entire catalyst can be increased. . That is, in the NOx reduction process for the NSR 10, the NOx purification rate can be improved by maintaining the entire NSR 10 in a rich atmosphere over a long period of time. Further, in the PM regeneration process for the DPR 11, the accumulated PM can be uniformly oxidized and removed by efficiently raising the temperature of the entire DPR 11.

  Since the first branch pipe 6 has a smaller diameter than the exhaust pipe 5, the flow rate of the exhaust gas flowing from the first branch pipe 6 side to which the added fuel is added into the first junction 5b is set to the exhaust pipe 5 side. The flow rate of the exhaust gas passing through can be relatively reduced. As a result, the exhaust gas containing the added fuel from the first branch pipe 6 is less likely to flow into the first junction 5b, so that the added fuel distribution region AHC can be effectively expanded in the exhaust flow direction. Similarly, since the second branch pipe 7 has a smaller diameter than the exhaust pipe 5, the flow rate of the exhaust gas flowing into the second junction 5 d from the second branch pipe 7 side to which the added fuel is added is set to the exhaust pipe 5. The flow rate of the exhaust gas passing through the side can be relatively reduced. According to these, the addition fuel supply period with respect to NSR10 and DPR11 can be extended longer.

  By the way, since the second branch pipe 7 in this embodiment connects the upstream side and the downstream side of the NSR 10 in the exhaust pipe 5, the exhaust gas passing through the second branch pipe 7 bypasses the NSR 10 and flows into the DPR 11. To do. Accordingly, all the exhaust gas discharged from the internal combustion engine 1 flows into the DPR 11, whereas the flow rate of the exhaust gas flowing into the NSR 10 is smaller than the flow rate flowing into the DPR 11 by the amount passing through the second branch pipe 7. . Hereinafter, the fuel supply control for the NSR 10 and the DPR 11 will be described in detail focusing on the above differences.

  First, fuel addition from the first fuel addition valve 12 when performing NOx reduction processing on the NSR 10 will be described. In the present embodiment, the amount of oxygen passing through the NSR 10 can be reduced by diverting the NSR 10 to the exhaust gas passing through the second branch pipe 7. Therefore, the inflow exhaust air-fuel ratio can be easily reduced with less added fuel.

  In addition, since the space velocity when the exhaust gas passes through the NSR 10 is reduced, the added fuel can be retained in the NSR 10 for a longer period. As a result, NOx reducibility can be improved and the reduction reaction can be promoted over a long period of time, so that NOx purification can be performed more efficiently.

  Next, fuel addition from the second fuel addition valve 13 when performing PM regeneration processing on the DPR 11 will be described. In the PM regeneration process, if the amount of oxygen flowing into the DPR 11 becomes too small, the PM oxidation reaction may be suppressed. On the other hand, in this embodiment, since all the exhaust gas discharged from the internal combustion engine 1 flows into the DPR 11, it is possible to suppress an excessive shortage of the oxygen amount flowing into the DPR 11. Further, when the added fuel is agitated in the exhaust at the second junction 5d, the added fuel and oxygen in the exhaust can be mixed efficiently. As a result, the temperature of the DPR 11 is more easily raised, so that PM can be efficiently oxidized and removed.

As described above, according to the exhaust purification system of the present embodiment, the NSR 10 and the DPR
Since the added fuel can be efficiently supplied to 11, the purification rate of NOx and PM can be improved. In addition, since more NOx and PM can be purified with less additive fuel, consumption of the additive fuel used as the reducing agent can be reduced.

  In this embodiment, the added fuel is vaporized in a portion of the first branch pipe 6 downstream of the first fuel addition valve 12 and a portion of the second branch pipe 7 downstream of the second fuel addition valve 13. -An oxidation catalyst having a small heat capacity for promoting atomization may be further provided. According to this, since the added fuel is lightened, the reactivity of the added fuel in the NSR 10 and the DPR 11 can be preferably improved.

  In this embodiment, no special valve is provided for adjusting the flow rate of the exhaust gas passing through the first branch pipe 6 and the second branch pipe 7. In this case, the flow rate of the exhaust gas passing through the first branch pipe 6 is the flow rate of the exhaust gas exhausted from the internal combustion engine 1 and the flow split ratio of the exhaust gas between the first branch pipe 6 and the exhaust pipe 5 in the first branch portion 5a. It is determined according to the first diversion ratio and the second diversion ratio which is the diversion ratio of the exhaust gas between the second branch pipe 7 and the exhaust pipe 5 in the second branch portion 5c. On the other hand, the flow rate of the exhaust gas passing through the second branch pipe 7 is determined according to the flow rate of the exhaust gas discharged from the internal combustion engine 1 and the second diversion ratio. The first diversion ratio is determined according to the pipe diameters of the exhaust pipe 5 and the first branch pipe 6, and the second diversion ratio is determined according to the pipe diameters of the exhaust pipe 5 and the second branch pipe 7.

  In the present embodiment, when the added fuel is supplied to the NSR 10 and the DPR 11, the first branch pipe 6 and the second branch pipe are based on the flow rate of the exhaust gas from the internal combustion engine 1, the first diversion ratio, and the second diversion ratio. 7 may be estimated, and the fuel addition amount may be determined according to each flow rate. Thereby, in the case where the oxidation catalyst is provided in any of the first branch pipe 6 and the second branch pipe 7, it is appropriate for the flow rate of the exhaust gas passing through each of the first branch pipe 6 and the second branch pipe 7. An amount of added fuel can be added. Thereby, for example, it is possible to reliably prevent the oxidation catalyst from being excessively heated and deteriorated.

  Next, a second embodiment according to the present invention will be described. FIG. 3 is a diagram showing a schematic configuration of the internal combustion engine according to the present embodiment and its exhaust system and control system. Here, the same or equivalent components as those in the exhaust purification system of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the exhaust purification system of the present embodiment, the second branch pipe branches off from a portion between the first branch portion 5a and the first junction portion 5b. A flow rate adjusting valve 8 for adjusting the flow rate of the exhaust gas passing through the second branch pipe 7 is provided upstream of the second fuel addition valve 13 in the second branch pipe 7. In this embodiment, the flow control valve 8 corresponds to the flow control means in the present invention. The flow rate adjusting valve 8 is connected to the ECU 15 via electric wiring and is controlled by the ECU 15.

  In the present embodiment, in the NOx reduction process for the NSR 10, when the added fuel is added from the first fuel addition valve 12, the flow rate control valve 8 is controlled in the valve opening direction compared to when the added fuel is not added. According to this, the flow rate of the exhaust gas that bypasses the NSR 10 by passing through the second branch pipe 7 increases. That is, when the NOx reduction process for the NSR 10 is performed, the space velocity of the exhaust gas passing through the NSR 10 and the amount of oxygen passing through the NSR 10 can be further reduced.

  Hereinafter, fuel supply control related to the NOx reduction process performed by the ECU 15 will be described with reference to the flowchart of FIG. 4. FIG. 4 is a flowchart showing a NOx reduction control routine in the present embodiment. This routine is a program stored in the ROM in the ECU 15 and is executed at predetermined time intervals while the internal combustion engine 1 is in operation.

  When this routine is executed, first, in step S101, it is determined whether a NOx reduction request has been issued to the NSR 10. The NOx reduction request may be issued based on, for example, an integrated value of the intake air amount after the previous NOx reduction process is completed. Further, a reduction request may be issued based on an output value of a NOx sensor (not shown) provided in the exhaust pipe 5. If an affirmative determination is made in this step, the process proceeds to step S102, and if a negative determination is made, this routine is temporarily terminated.

  In step S102, the flow rate adjusting valve 8 is controlled in the valve opening direction. Here, the opening degree of the flow control valve 8 may be changed to fully open. In the subsequent step S103, a command is issued to the first fuel addition valve 12, and the added fuel is added to the exhaust, whereby the NOx stored in the NSR 10 is reduced. When the processing of this step is finished, this routine is once ended.

  According to the present embodiment, the exhaust gas that passes through the first branch pipe 6 and the exhaust gas that has flowed down the exhaust pipe 5 without flowing into the first branch pipe 6 and the second branch pipe 7 merge at the first junction 5b. In this case, the added fuel is agitated in the exhaust gas, so that the added fuel distribution region AHC can be expanded more than immediately after the fuel addition. Thereby, since an additional fuel supply period is extended, the purification rate of NOx can be improved.

  As described above, the embodiments of the present invention have been exemplarily described in the first embodiment and the second embodiment, but the present invention is not limited thereto. For example, instead of arranging the first fuel addition valve 12 in the first branch pipe 6, the first fuel addition valve 12 may be arranged between the first branch part 5 a and the first junction part 5 b in the exhaust pipe 5. Also in this case, the added fuel can be agitated in the exhaust gas by the exhaust gas to which the added fuel is added merged with the exhaust gas from the first branch passage in the first junction 5b. Similarly, the second fuel addition valve 13 may be disposed in a portion of the exhaust pipe 5 between the NSR 10 and the second junction 5d instead of being disposed in the second branch pipe 7. Of course, the present invention may be applied to an exhaust purification system in which the diameters of the first branch pipe 6 and the second branch pipe 7 are equal to or larger than those of the exhaust pipe 5. .

  Further, instead of the NSR 10 as the first exhaust device of the present invention, a selective reduction type NOx catalyst or a three-way catalyst may be adopted. Further, a filter carrying a NOx catalyst may be employed instead of the DPR 11 as the second exhaust purification device, or a filter may be arranged in series downstream of the oxidation catalyst or NOx catalyst.

  For the second branch pipe 7, it is only necessary that the exhaust gas passing through the second branch pipe 7 can bypass the NSR 10. For example, even if the second branch pipe 7 is branched from the exhaust pipe 5 at a portion between the first junction 5 b and the NSR 10. good. In that case, the 2nd branch part 5c will be located in the downstream rather than the 1st junction part 5b. At that time, the degree of opening of the flow rate control valve 8 is controlled to be substantially fully closed until the exhaust gas added from the first fuel addition valve 12 passes through the second branch portion 5c, and the exhaust gas is secondly exhausted. You may make it perform valve-opening control of the flow control valve 8 after passing the branch part 5c. Thereby, it is possible to accurately suppress the added fuel added from the first fuel addition valve 12 from flowing into the second branch pipe 7 together with the exhaust gas.

1 is a diagram illustrating a schematic configuration of an internal combustion engine according to a first embodiment and an exhaust system and a control system thereof. 6 is an explanatory diagram for explaining a transition of an added fuel distribution area AHC in Embodiment 1. FIG. FIG. 2A is a view showing the added fuel distribution region AHC immediately after the fuel addition from the first fuel addition valve is completed. FIG. 2B is a diagram showing the added fuel distribution region AHC after the exhaust gas after the added fuel is added flows into the first junction. It is a figure which shows schematic structure of the internal combustion engine which concerns on Example 2, its exhaust system, and a control system. 7 is a flowchart showing a NOx reduction control routine in Embodiment 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Exhaust pipe 5a ... First branch part 5b ... First junction part 5c ... Second branch part 5d ... Second junction part 6 ... First branch pipe 7・ ・ Second branch pipe 8 ・ Flow control valve 10 ・ ・ NSR
11. DPR
12.-first fuel addition valve 13.-second fuel addition valve 15.-ECU

Claims (6)

A first exhaust purification device provided in an exhaust passage of the internal combustion engine;
A second exhaust purification device provided downstream of the first exhaust purification device in the exhaust passage;
A first merging portion that branches from the first branching portion on the upstream side of the first exhaust purification device in the exhaust passage and that is downstream of the first branching portion and upstream of the first exhaust purification device. A first branch passage that merges with the exhaust passage;
Branching from the second branch portion upstream of the first exhaust purification device in the exhaust passage, downstream of the first exhaust purification device and upstream of the second exhaust purification device of the exhaust passage. A second branch passage that joins the exhaust passage at the second joining portion of
The exhaust passage is provided downstream of the first branch portion and upstream of the first junction portion or in the first branch passage, and is reduced to the exhaust gas before flowing into the first junction portion. First reducing agent addition means for adding an agent;
The exhaust passage is provided on the downstream side of the first exhaust purification device and upstream of the second merging portion or in the second branch passage, and the exhaust before flowing into the second merging portion. A second reducing agent adding means for adding a reducing agent;
An exhaust gas purification system for an internal combustion engine, comprising:   The first exhaust purification device includes a NOx catalyst that purifies NOx in the exhaust, and the second exhaust purification device is a particulate filter carrying an oxidation catalyst or an oxidation catalyst and a downstream side of the oxidation catalyst. The exhaust gas purification system for an internal combustion engine according to claim 1, comprising a particulate filter provided. A flow rate control means for controlling the flow rate of the exhaust gas passing through the second branch passage;
The flow rate control means is configured such that when the first reducing agent addition means adds the reducing agent to the exhaust gas, the exhaust gas that passes through the second branch passage compared to when the first reducing agent addition means does not add the reducing agent. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2, wherein the flow rate of the engine is increased.   4. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the second branch portion is a portion upstream of the first branch portion in the exhaust passage. 5.   A portion of the exhaust passage downstream of the first branch portion and upstream of the first junction portion is different from the first branch passage in the exhaust passage area, and the first reducing agent The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 4, wherein the adding means is provided in any one of the smaller flow passage areas.   A portion of the exhaust passage downstream of the first exhaust purification device and upstream of the second junction is different from the second branch passage, and the second reduction passage is different. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 5, wherein the agent addition means is provided in one of the smaller flow path areas.

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