JP2008184916A - Exhaust gas purification system for internal combustion engine - Google Patents

Abstract

In an exhaust purification system having an NOx storage reduction catalyst in an exhaust passage of an internal combustion engine and an SOx storage agent upstream thereof, the SOx regeneration processing of the NOx storage reduction catalyst can be performed more efficiently. Provide technology.
In an exhaust purification system in which an exhaust pipe (5) of an internal combustion engine (1) is provided with a DPNR (11) and an S trap catalyst (10) upstream thereof, a bypass pipe (6) for bypassing the S trap catalyst (10) to exhaust gas passing through the exhaust pipe (5). In addition, during the SOx regeneration processing of the DPNR 11, the S trap catalyst 10 is bypassed to the exhaust.
[Selection] Figure 1

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

The exhaust gas of an internal combustion engine contains harmful substances such as NOx. In order to reduce the emission of these harmful substances, it is known to provide a NOx catalyst for purifying NOx in the exhaust gas in the exhaust system of the internal combustion engine. In this technique, when a NOx storage reduction catalyst is provided that stores NOx when the air-fuel ratio of the exhaust gas is lean and releases NOx stored when the oxygen concentration in the exhaust gas decreases, the stored NOx is provided. As the amount of the catalyst increases, the purification ability decreases. For example, by performing rich spike control, a reducing agent is supplied to the NOx storage reduction catalyst, and NOx stored in the catalyst is reduced and released (hereinafter, referred to as “NOx”). This is called “NOx reduction treatment”).

Moreover, SOx is contained in the exhaust gas of the internal combustion engine, and this SOx is similar to the above NOx.
It is stored in the NOx storage reduction catalyst. When the amount of stored SOx increases, SOx poisoning may occur in which the NOx storage capacity of the NOx storage reduction catalyst decreases.

  In order to eliminate this SOx poisoning, there is a case in which the NOx catalyst bed temperature is raised and the oxygen concentration in the exhaust gas is lowered to release SOx accumulated in the NOx storage reduction catalyst (hereinafter referred to as “NOx catalyst”). "SOx regeneration process").

Furthermore, an SOx storage agent that stores SOx when the air-fuel ratio of the exhaust gas is lean is disposed upstream of the NOx storage reduction catalyst in the exhaust passage, and the SOx in the exhaust before flowing into the NOx storage reduction catalyst is disposed. The SOx occlusion agent may be occluded and removed to reduce the need for SOx regeneration treatment of the NOx storage reduction catalyst (see, for example, Patent Documents 1 to 3).

  By the way, even in the exhaust purification system in which the SOx storage agent is disposed upstream of the NOx storage reduction catalyst as described above, a part of the SOx in the exhaust gas is not removed by the SOx storage agent but stored in the NOx storage reduction catalyst. In some cases, SOx poisoning may occur. Therefore, even in such a system, the SOx regeneration processing of the NOx storage reduction catalyst may be performed.

When the reducing agent is supplied to the exhaust gas from the internal combustion engine when performing the SOx regeneration process of the NOx storage reduction catalyst, the SOx stored in the upstream SOx storage agent is also released at the same time. In some cases, SOx released from the storage agent flows into the NOx storage reduction catalyst. As a result, it may be difficult to efficiently perform the SOx regeneration process of the NOx storage reduction catalyst.
Japanese Patent No. 2605580 JP 2004-150382 A Japanese Patent Laid-Open No. 2004-28030

An object of the present invention is to more efficiently perform SOx regeneration of an NOx storage reduction catalyst in an exhaust purification system having an NOx storage reduction catalyst in an exhaust passage of an internal combustion engine and an SOx storage agent upstream thereof. It is to provide a technology that enables processing.

To achieve the above object, the present invention provides an NOx storage reduction catalyst in the exhaust passage of an internal combustion engine,
In the exhaust gas purification system having a SOx storage agent upstream thereof, the exhaust purification system further includes a bypass passage for bypassing the SOx storage agent to the exhaust gas passing through the exhaust passage, and at the time of SOx regeneration processing of the NOx storage reduction catalyst, The biggest feature is that the SOx storage agent is bypassed.

More specifically, it is provided in the exhaust passage of the internal combustion engine, and NOx when the air-fuel ratio of the exhaust is lean.
NOx catalyst that stores the NOx stored when the oxygen concentration in the exhaust gas decreases, and
An SOx occlusion agent that is disposed upstream of the NOx catalyst in the exhaust passage and occludes SOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean;
The SOx storage agent branches from the exhaust passage upstream of the SOx storage agent, and joins the exhaust passage at a portion between the SOx storage agent and the NOx catalyst, and the SOx storage agent is added to the exhaust passing through the exhaust passage. A bypass passage to bypass,
When the amount of SOx stored and accumulated in the NOx catalyst exceeds a predetermined amount, the reducing agent is supplied to the exhaust gas from the internal combustion engine to reduce the oxygen concentration of the exhaust gas, and the temperature of the NOx catalyst. SOx regeneration means for performing SOx regeneration processing for raising SOx and releasing SOx accumulated in the NOx catalyst;
When the SOx regeneration means performs the SOx regeneration process, the amount of exhaust passing through the bypass passage out of the exhaust passing through the exhaust passage is increased, and the amount of exhaust passing through the SOx storage agent is decreased. SOx regeneration exhaust control means,
It is characterized by providing.

That is, in the SOx regeneration processing of the NOx storage reduction catalyst, the reducing agent is supplied to the exhaust gas passing through the exhaust passage to reduce the oxygen concentration of the exhaust gas, and the reducing agent flows into the NOx storage reduction catalyst to store the NOx reduction. The temperature of the NOx catalyst increases. At that time, if the reducing agent flows into the SOx storage agent, SOx stored in the SOx storage agent is released, so the amount of exhaust gas passing through the bypass passage is relatively increased and reduced to the SOx storage agent. Suppresses inflow of agent.

In this way, in the SOx regeneration process of the NOx storage reduction catalyst, the SOx storage agent from the upstream side becomes S
Ox can be prevented from being discharged and flowing into the NOx storage reduction catalyst. Thereby, the SOx regeneration process of the NOx storage reduction catalyst can be performed more efficiently.

  In the above description, occlusion includes absorption and adsorption in addition to or in place of occlusion. The means for solving the problems in the present invention can be used in combination as much as possible.

In the present invention, in an exhaust purification system provided with an NOx storage reduction catalyst in the exhaust passage of an internal combustion engine and a SOx storage agent upstream thereof, the SOx of the NOx storage reduction catalyst is more efficiently obtained.
x reproduction processing can be performed.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

  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.

In FIG. 1, an exhaust pipe 5 is connected to the internal combustion engine 1 as an exhaust passage through which the exhaust discharged from the internal combustion engine 1 flows. This exhaust pipe 5 is connected downstream to a muffler (not shown). In the middle of the exhaust pipe 5, there is provided an S trap catalyst 10 as an SOx occlusion agent that occludes SOx in the exhaust while the air-fuel ratio of the exhaust is lean and removes SOx in the exhaust. Further, on the downstream side of the S trap catalyst 10, a filter that collects particulate matter in the exhaust gas is occluded in a state where the exhaust air-fuel ratio is lean and NOx in the exhaust gas is occluded. A DPNR 11 formed by supporting a NOx storage reduction catalyst that releases the generated NOx is disposed. This DPNR 11 corresponds to the NOx catalyst in this embodiment.

  Further, a bypass pipe 6 as a bypass passage is branched from the exhaust pipe 5 at a branch portion 5 a upstream of the S trap catalyst 10. The branch portion 5a is provided with a switching valve 15 that is a three-way valve that switches whether exhaust gas from the internal combustion engine 1 passes through the bypass pipe 6 or passes through the exhaust pipe 5 as it is. Further, the bypass pipe 6 joins the exhaust pipe 5 at a portion between the S trap catalyst 10 and the DPNR 11.

  Here, both the S trap catalyst 10 and the DPNR 11 can be passed through the exhaust gas by operating the switching valve 15 and allowing the exhaust gas from the internal combustion engine 1 to pass through the exhaust pipe 5 as it is. Similarly, by allowing the exhaust from the internal combustion engine 1 to pass through the bypass pipe 6, only the DPNR 11 can be passed through the exhaust by bypassing the S trap catalyst 10.

The internal combustion engine 1 configured as described above and its exhaust system are provided with an electronic control unit (ECU) 20 for controlling the internal combustion engine 1 and the exhaust system. The ECU 20 controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the driver's request, and also performs control related to the exhaust purification system including the S trap catalyst 10 and the DPNR 11 of the internal combustion engine 1. The unit to perform.

  Sensors related to control of the operating state of the internal combustion engine 1 such as an air flow meter, a crank position sensor, and an accelerator position sensor (not shown) are connected to the ECU 20 via electric wiring so that an output signal is input to the ECU 20. It has become. On the other hand, a fuel injection valve (not shown) in the internal combustion engine 1 is connected to the ECU 20 via an electrical wiring, and a switching valve 15 in this embodiment is connected to the ECU 20 via an electrical wiring and is controlled by the ECU 20. It is like that.

The ECU 20 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. As will be described later, a routine for performing SOx regeneration processing of the S trap catalyst 10 and the DPNR 11 is also one of the programs stored in the ROM of the ECU 20.

In the above configuration, when the exhaust pipe 5 is directly passed through the exhaust by the switching valve 15, both the S trap catalyst 10 and the DPNR 11 can be passed through the exhaust from the internal combustion engine 1. Then, the exhaust gas from the internal combustion engine 1 first passes through the S trap catalyst 10, and SOx in the exhaust gas is removed by being occluded by the S trap catalyst 10. Therefore, SOx poisoning in the downstream DPNR 11 is suppressed, and the necessity of performing the SOx regeneration process of the DPNR 11 can be suppressed.

However, even in the above configuration, SOx that has not been occluded in the S trap catalyst 10 is discharged from the S trap catalyst 10 and flows into the DPNR 11, and SOx poisoning may occur in the DPNR 11. In particular, when the operating state of the internal combustion engine 1 is high load or high speed, the temperature of the exhaust gas from the internal combustion engine 1 rises, so that a large amount of SOx stored in the S trap catalyst 10 is released. In other words, there was a case where it flows into DPNR11. Therefore, even in the above configuration, it is difficult to completely eliminate the need for the SOx regeneration process of DPNR11.

In such a high load or high rotational speed operating state, the switching valve 15 is opened to bypass the S trap catalyst 10 to the exhaust gas from the internal combustion engine 1, and a large amount of SOx stored in the S trap catalyst 10 is obtained. Although control to suppress the release may be performed, in this case as well, since SOx is contained in the exhaust gas that has passed through the bypass pipe 6, it is necessary to perform SOx regeneration processing of the DPNR 11 in the long term.

<DPNR SOx regeneration process>
Here, consider the case where the SOx regeneration process of DPNR11 is performed for the above reason. In this case, in this embodiment, before or after the main injection in the internal combustion engine 1, fuel is sub-injected from a fuel injection valve (not shown) to reduce the oxygen concentration of the exhaust gas and supply fuel as a reducing agent to the DPNR 11. Increase the bed temperature. As a result, fuel as a reducing agent also flows into the S trap catalyst 10, and the SOx stored in the S trap catalyst 10.
May also be released. As a result, the SOx released from the S trap catalyst 10
May flow into the DPNR 11 on the downstream side, making it difficult to perform the SOx regeneration process of the DPNR 11 efficiently.

Therefore, in this embodiment, when performing SOx regeneration processing of DPNR 11, the bypass valve 6 is allowed to pass through the exhaust by the switching valve 15, the S trap catalyst 10 is bypassed to the exhaust, and the SO trap catalyst 10 is connected to the SOx. Was not released.

According to this, it is possible to suppress the SOx from being released from the S trap catalyst 10 and flowing into the DPNR 11 in the SOx regeneration process of the DPNR 11, and the efficiency of the SOx regeneration process of the DPNR 11 can be improved.

In this embodiment, the ECU 20 corresponds to SOx regeneration means. Further, the ECU 20 and the switching valve 15 constitute an exhaust control means during SOx regeneration.

  In the above embodiment, the switching valve 15 selectively switches whether the exhaust pipe 5 and the S trap catalyst 10 pass through the exhaust gas from the internal combustion engine 1 as it is or the bypass pipe 6.

On the other hand, by adjusting the opening of the switching valve 15, the ratio of the amount passing through the S trap catalyst 10 and the amount passing through the bypass pipe 6 in the exhaust from the internal combustion engine 1 is continuously controlled. You may do it. In this case, in the SOx regeneration process of the DPNR 11, if the amount of exhaust passing through the bypass pipe 6 is made larger than the amount of exhaust passing through the S trap catalyst 10, the S trap catalyst 10 is added to more exhaust. Can be bypassed. Then, the amount of SOx released from the S trap catalyst 10 and flowing into the DPNR 11 can be further reduced.

  Further, in this embodiment, instead of providing the switching valve 15 as a three-way valve in the branch part 5a, the switching pipe 15 is provided in the bypass pipe 6, and the exhaust gas flowing into the S trap catalyst 10 is adjusted by adjusting the opening degree. And the amount of exhaust gas flowing into the bypass pipe 6 may be adjusted.

In this embodiment, the NOx storage reduction catalyst (NSR) is used instead of DPNR11.
) And a filter that collects particulates in the exhaust gas may be arranged in series independently.

  Next, a second embodiment according to the present invention will be described. FIG. 2 is a diagram showing a schematic configuration of the internal combustion engine 1 according to the present embodiment and its exhaust system and control system. In the system of FIG. 2, a second bypass pipe 7 that bypasses the DPNR 11 is provided in addition to the system shown in FIG. 1. The second bypass pipe 7 is provided with a filter 12. In addition, a second switching valve 16 having a function equivalent to that of the switching valve 15 is provided at a branch portion from the exhaust pipe 5 to the second bypass pipe 7. Furthermore, a fuel addition valve 14 is provided on the upstream side of the branch portion 5 a in the exhaust pipe 5 to add fuel as a reducing agent to the exhaust gas passing through the exhaust pipe 5.

In addition, during the SOx regeneration process of the DPNR 11, fuel may be supplied to the exhaust by sub-injection of the internal combustion engine 1 as in the first embodiment, but in this embodiment, fuel is added from the fuel addition valve 14. To supply fuel to the exhaust. Even in this case, the control for bypassing the S trap catalyst 10 to the exhaust gas in the SOx regeneration process of the DPNR 11 is performed, and the SOx of the DPNR 11 is controlled.
It is effective to improve the efficiency of the reproduction process.

Here, a case where SOx regeneration processing of the S trap catalyst 10 itself is performed in order to release SOx stored in the S trap catalyst 10 in this embodiment will be considered. In this case, fuel is added from the fuel addition valve 14, and the S trap catalyst 10 is passed through the exhaust gas by the switching valve 15. As a result, the oxygen concentration of the exhaust gas flowing into the S trap catalyst 10 can be lowered, and fuel as a reducing agent can be supplied to the S trap catalyst 10 to raise the bed temperature.

However, in this case, a large amount of SOx released from the S trap catalyst 10 by the SOx regeneration process may flow into the DPNR 11 and poison the DPNR 11 with SOx.

Therefore, in this embodiment, the SOx released from the S trap catalyst 10 becomes DPNR1.
2, the second switching valve 16 allows the exhaust gas discharged from the S trap catalyst 10 to pass through the second bypass pipe 7 during the SOx regeneration process of the S trap catalyst 10. As a result, the DPNR 11 can be bypassed to the exhaust gas discharged from the S trap catalyst 10, and the SONR poisoning of the DPNR 11 in the SOx regeneration process of the S trap catalyst 10 can be suppressed.

In addition, since the second bypass pipe 7 in the present embodiment is provided with the filter 12, it is possible to suppress the particulate matter from being diffused into the atmosphere without being purified in the SOx regeneration process of the S trap catalyst 10.

In this embodiment, when the SOx regeneration process for the S trap catalyst 10 is performed, the PM regeneration process for the filter 12 may be performed simultaneously. Then, the temperature of the filter 12 is increased by using the temperature increase of the exhaust gas from the S trap catalyst 10 when the fuel is added to the exhaust gas from the fuel addition valve 14 and the bed temperature of the S trap catalyst 10 is increased. Can be made. As a result, the SOx regeneration process of the S trap catalyst 10 and the PM regeneration process of the filter 12 can be efficiently performed at a time, and the fuel efficiency can be improved.

1 is a diagram illustrating a schematic configuration of an internal combustion engine according to a first embodiment of the present invention and an exhaust system and a control system thereof. FIG. It is the figure which showed schematic structure of the internal combustion engine which concerns on Example 2 of this invention, its exhaust system, and a control system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Exhaust pipe 5a ... Branch part 6 ... Bypass pipe 7 ... 2nd bypass pipe 10 ... S trap catalyst 11 ... DPNR
DESCRIPTION OF SYMBOLS 12 ... Filter 14 ... Fuel addition valve 15 ... Switching valve 16 ... 2nd switching valve 20 ... ECU

Claims (1)

A NOx catalyst that is provided in an exhaust passage of the internal combustion engine and that stores NOx when the air-fuel ratio of the exhaust is lean and releases the stored NOx when the oxygen concentration in the exhaust gas decreases;
An SOx occlusion agent that is disposed upstream of the NOx catalyst in the exhaust passage and occludes SOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean;
The SOx storage agent branches from the exhaust passage upstream of the SOx storage agent, and joins the exhaust passage at a portion between the SOx storage agent and the NOx catalyst, and the SOx storage agent is added to the exhaust passing through the exhaust passage. A bypass passage to bypass,
When the amount of SOx stored and accumulated in the NOx catalyst exceeds a predetermined amount, the reducing agent is supplied to the exhaust gas from the internal combustion engine to reduce the oxygen concentration of the exhaust gas, and the temperature of the NOx catalyst. SOx regeneration means for performing SOx regeneration processing for raising SOx and releasing SOx accumulated in the NOx catalyst;
When the SOx regeneration means performs the SOx regeneration process, the amount of exhaust passing through the bypass passage out of the exhaust passing through the exhaust passage is increased, and the amount of exhaust passing through the SOx storage agent is decreased. SOx regeneration exhaust control means,
An exhaust gas purification system for an internal combustion engine, comprising:

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