JP2008202409A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for easily performing an S poisoning recovery control for a former NOx catalyst by easily raising the temperature of the former NOx catalyst when two NOx catalysts are arranged in series in an exhaust emission control device of an internal combustion engine. <P>SOLUTION: This exhaust emission control device comprises two storage/reduction NOx catalysts 3, 4 arranged in series in the exhaust passage 2 of the internal combustion engine, an exhaust throttle valve 6 installed in an exhaust passage 2 between the two NOx catalysts 3, 4 and controlling the flow of an exhaust gas, and an S poisoning recovery control means for releasing the sulfur contents stored in the NOx catalysts 3, 4 by supplying a fuel into the exhaust gas to raise the temperature of the NOx catalysts 3, 4 and lower the air/fuel ratio of the exhaust gas for releasing the sulfur contents stored in the NOx catalysts 3, 4. When the stored sulfur contents are released by using the S poisoning recovery control means for the former NOx catalyst 3 on the upstream side out of the two NOx catalysts 3, 4, the exhaust throttle valve 6 is controlled to the closed side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  In a diesel engine, a filter is disposed in the exhaust passage to capture PM from the exhaust. So-called PM regeneration control is performed on this filter.

  PM regeneration control increases the amount of PM trapped in the filter, increases the flow resistance of the exhaust gas that passes through the filter, increases the exhaust resistance of the internal combustion engine, and reduces engine output and fuel consumption. This is done to prevent it from happening. Specifically, the temperature of the filter is raised to a temperature at which PM is ignited and burned by supplying fuel to the exhaust, and the PM collected by the filter is burned to regenerate the filter.

In order to easily raise the temperature of the filter, a technique is disclosed in which the exhaust throttle valve provided in the exhaust passage downstream of the filter is controlled to the closed side to increase the back pressure (for example, Patent Document 1). reference).
JP 2003-83034 A JP 2001-20733 A JP 2005-315189 A

  Incidentally, there are cases where two NOx storage reduction catalysts (hereinafter referred to as NOx catalysts) are arranged in series in the exhaust passage. In such a case, although the downstream NOx catalyst on the downstream side is likely to increase in temperature, the upstream NOx catalyst on the upstream side is difficult to increase in temperature because the exhaust gas flows downstream. For this reason, it is difficult to release the sulfur component occluded by the S poison recovery control with respect to the preceding NOx catalyst. Here, in the S poison recovery control, fuel is added to the exhaust, the temperature of the NOx catalyst is raised to, for example, 600 to 700 ° C., the air-fuel ratio of the exhaust is made the stoichiometric air-fuel ratio or rich, and SOx is released from the NOx catalyst. Control.

  An object of the present invention is to easily raise the temperature of a preceding NOx catalyst and easily perform S poison recovery control on the preceding NOx catalyst when two NOx catalysts are arranged in series in an exhaust gas purification apparatus for an internal combustion engine. It is to provide technology to be implemented.

In the present invention, the following configuration is adopted. That is,
Two NOx storage reduction catalysts arranged in series in the exhaust passage of the internal combustion engine;
An exhaust throttle valve that is provided in an exhaust passage between the two NOx storage reduction catalysts and adjusts an exhaust flow rate;
S poison recovery control means for supplying a reducing agent into the exhaust to raise the temperature of the NOx storage reduction catalyst and lowering the air-fuel ratio of the exhaust to release the sulfur component stored in the NOx storage reduction catalyst;
With
When releasing the sulfur component stored using the S poison recovery control means to the upstream NOx catalyst upstream of the two NOx storage reduction catalysts, the exhaust throttle valve is An exhaust emission control device for an internal combustion engine, which is controlled to a closed side.

  In some cases, two NOx storage reduction catalysts are arranged in series in the exhaust passage. In such a case, although the latter storage-and-reduction NOx catalyst is likely to increase in temperature, the upstream storage-and-reduction NOx catalyst is difficult to increase in temperature because the exhaust gas flows downstream.

  Therefore, in the present invention, the exhaust throttle valve is controlled to the closed side when the stored sulfur component is released to the upstream NOx catalyst by using the S poison recovery control means.

  According to this, by controlling the exhaust throttle valve to the closed side, the exhaust is stopped upstream of the exhaust throttle valve, and the temperature of the NOx storage reduction catalyst in the previous stage is easily increased. For this reason, it is possible to easily release the sulfur component stored by using the S poison recovery control means with respect to the NOx storage reduction catalyst in the previous stage.

  The exhaust passage between the two NOx storage reduction catalysts has a bypass passage that bypasses the exhaust throttle valve for exhaust, and the bypass passage is normally closed and the bypass passage exceeds a predetermined pressure. And a bypass valve that opens.

  According to this, when the exhaust throttle valve is controlled to the closed side and the exhaust pressure exceeds the predetermined pressure upstream from the exhaust throttle valve, the exhaust can be released from the bypass valve, and the exhaust resistance increases. Reduction of engine output can be suppressed. The predetermined pressure refers to a threshold pressure at which the exhaust pressure becomes high enough to cause a decrease in engine output.

  According to the present invention, in an exhaust gas purification apparatus for an internal combustion engine, when two NOx catalysts are arranged in series, the temperature of the preceding NOx catalyst is easily raised, and the S poison recovery control for the preceding NOx catalyst is easily performed. it can.

  Specific examples of the present invention will be described below.

<Example 1>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied and its exhaust system.

  An internal combustion engine 1 shown in FIG. 1 is a water-cooled diesel engine having four cylinders, and includes a fuel injection valve that directly injects fuel into a combustion chamber of each cylinder.

  An exhaust passage 2 extends from the internal combustion engine 1. In the middle of the exhaust passage 2, two NOx storage reduction type NOx catalysts (hereinafter referred to as NOx catalysts) 3, 4 are connected in series upstream and downstream of the exhaust passage 2 in order to purify the exhaust discharged from the cylinders of the internal combustion engine 1. Are arranged side by side.

Here, when the air-fuel ratio of the exhaust gas flowing into the NOx catalysts 3 and 4 is lean (greater than the theoretical air-fuel ratio), the NOx catalysts 3 and 4 store NOx in the exhaust gas so as not to be released into the atmosphere. When the air-fuel ratio of the exhaust gas flowing into the NOx catalysts 3 and 4 is rich at the stoichiometric air-fuel ratio or less, the stored NOx is released. When the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio or rich, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust gas, it is released from the NOx catalysts 3 and 4. The nitrogen oxide (NOx) formed is reduced to N ₂ and removed.

  On the other hand, a fuel addition valve 5 is attached to the exhaust passage 2 upstream of the NOx catalyst 3 to supply fuel as a reducing agent into the exhaust gas flowing through the exhaust passage 2.

  An exhaust throttle valve 6 that adjusts the flow rate of exhaust gas flowing through the exhaust passage 2 is disposed in the exhaust passage 2 between the NOx catalysts 3 and 4.

  Further, a bypass valve 7 is disposed at a position where the exhaust throttle valve 6 is bypassed to the exhaust gas in the exhaust passage 2. The bypass valve 7 has a bypass passage 8 for bypassing the exhaust throttle valve 6 to the exhaust gas in the exhaust passage 2 between the NOx catalysts 3 and 4. The bypass passage 8 is normally closed and the bypass passage 8 is closed. It is a mechanical valve that opens when a predetermined pressure is exceeded. The predetermined pressure at which the bypass valve 7 opens is a threshold pressure at which the exhaust pressure becomes high enough to cause a decrease in engine output.

  The internal combustion engine 1 having the above configuration is provided with an ECU 9 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 9 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver. The fuel addition valve 5 is electrically connected to the ECU 9 so that the ECU 9 can control fuel supply and fuel supply stop of the fuel addition valve 5. The exhaust throttle valve 6 is electrically connected to the ECU 9 so that the ECU 9 can control the opening and closing of the exhaust throttle valve 6.

  Then, the ECU 9 performs control such as normal operation control for purifying exhaust gas, S poison recovery control, and NOx reduction control for the NOx catalysts 3 and 4.

  Here, in the S poison recovery control, the fuel is continuously and repeatedly added from the fuel addition valve 5 to raise the temperature of the NOx catalysts 3 and 4 to, for example, 600 to 700 ° C. and to set the air-fuel ratio of the exhaust to the stoichiometric air-fuel ratio or In this control, the exhaust gas is rich and SOx is released from the NOx catalysts 3 and 4. This S poison recovery control corresponds to the S poison recovery control means of the present invention.

  The NOx reduction control is a control in which fuel is intermittently added from the fuel addition valve 5 at a relatively long time, the exhaust air-fuel ratio is made the stoichiometric air-fuel ratio or rich, and NOx is released and reduced from the NOx catalysts 3 and 4. is there. Note that the NOx reduction control is repeatedly executed within a relatively short time.

  By the way, it is more difficult to perform the S poison recovery control on the upstream NOx catalyst 3 on the upstream side of the exhaust passage 2 than on the downstream NOx catalyst 4 on the downstream side. This is because although the latter-stage NOx catalyst 4 is likely to increase in temperature, the former-stage NOx catalyst 3 is difficult to increase because exhaust gas flows downstream.

  Therefore, in this embodiment, the exhaust throttle valve 6 is controlled to the closed side when the S poison recovery control is performed on the NOx catalyst 3 in the previous stage.

  According to this, by controlling the exhaust throttle valve 6 to the closed side, the exhaust is stopped upstream of the exhaust throttle valve 6 and the temperature of the NOx catalyst 3 in the previous stage is easily increased. For this reason, it is possible to easily perform the S poison recovery control on the NOx catalyst 3 in the previous stage.

  Here, when the exhaust throttle valve 6 is controlled to the closed side and the exhaust pressure exceeds a predetermined pressure upstream of the exhaust throttle valve 6, the flow of the exhaust gas stagnates, causing a decrease in the engine output of the internal combustion engine 1. However, in the present embodiment, when the exhaust throttle valve 6 is controlled to the closed side and the exhaust pressure exceeds the predetermined pressure upstream of the exhaust throttle valve 6, the exhaust can be released from the bypass valve 7. A decrease in engine output due to an increase in resistance can be suppressed.

Here, a control routine for performing control for causing the S poison recovery control to be performed on the NOx catalyst 3 in the preceding stage of the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 9 and is periodically executed.

  When the processing of this routine is started, the ECU 9 determines in S101 whether or not it is necessary to perform S poisoning recovery control on the preceding NOx catalyst 3 in the current operating state.

  Specifically, the ECU 9 reads a detected value of a NOx sensor (not shown) disposed downstream of the NOx catalyst 3 in the exhaust passage 2, and the NOx occlusion amount of the preceding NOx catalyst 3 is excessively reduced from the detected value. If it can be read, it is determined that the S poison recovery control is required for the NOx catalyst 3 in the previous stage.

  In addition to the above, the ECU 9 determines the accumulated amount of fuel injection in the internal combustion engine 1 or the travel distance of the vehicle on which the internal combustion engine 1 is mounted after the previous S poison recovery control for the NOx catalyst 3 in the previous stage. From the SOx occlusion amount calculated based on this, it may be determined that the S poison recovery control is necessary when the SOx occlusion amount in the NOx catalyst 3 becomes equal to or greater than the predetermined occlusion amount Qse. Here, the predetermined storage amount Qse is a value that serves as a threshold with which it can be determined that the NOx storage amount of the preceding NOx catalyst 3 may be excessively reduced.

  If the ECU 9 determines that the S poison recovery control is necessary for the preceding NOx catalyst 3, the ECU 9 proceeds to S102. Further, when it is determined that the S poison recovery control is not necessary for the preceding NOx catalyst 3, the processing of this routine is temporarily ended.

  In S102, the ECU 9 controls the exhaust throttle valve 6 to the closed side. Specifically, as shown in FIG. 3, the exhaust throttle valve 6 is opened from a map showing the correlation between the engine speed of the internal combustion engine 1, the fuel injection amount in the internal combustion engine 1 and the opening of the exhaust throttle valve 6. Determine the degree. Here, in FIG. 3, when the engine speed of the internal combustion engine 1 and the fuel injection amount in the internal combustion engine 1 are small, the opening degree of the exhaust throttle valve 6 is small and the opening degree is large. As the engine speed of the engine 1 and the fuel injection amount in the internal combustion engine 1 are increased, the opening amount of the exhaust throttle valve 6 is increased and the opening amount is decreased. The map shown in FIG. 3 is obtained in advance from experiments and the like, and is stored in the ECU 9.

  In S103, the ECU 9 performs S poisoning recovery control for the NOx catalyst 3 in the previous stage. That is, fuel is continuously and repeatedly added from the fuel addition valve 5 to raise the temperature of the NOx catalyst 3 at the front stage to, for example, 600 to 700 ° C. To release SOx.

  As a result, while the S poison recovery control for the NOx catalyst 3 in the previous stage is being performed, the opening degree of the exhaust throttle valve 6 is controlled to the closed side, so that it is upstream of the exhaust throttle valve 6. The exhaust gas is stopped and the exhaust gas is not allowed to flow downstream, so that the temperature of the NOx catalyst 3 in the previous stage is easily increased. For this reason, in the present embodiment, it is possible to easily raise the temperature of the previous NOx catalyst 3 to, for example, 600 to 700 ° C. Therefore, it is easy to perform the S poison recovery control on the previous NOx catalyst 3. it can.

  Further, during the S poison recovery control for the NOx catalyst 3 in the previous stage, the exhaust throttle valve 6 is controlled to the closed side, and the exhaust pressure reaches a predetermined pressure upstream from the exhaust throttle valve 6. In this case, the exhaust gas is released from the bypass valve 7 to suppress a decrease in engine output due to an increase in exhaust resistance.

  Then, after the end of this step, the processing of this routine is temporarily ended.

  As described above, by performing the S poison recovery control for the preceding NOx catalyst 3, when the two NOx catalysts 3 and 4 are arranged in series, the temperature of the preceding NOx catalyst 3 can be easily increased, and the preceding NOx catalyst 3 can be heated. S poison recovery control for the catalyst 3 can be easily performed.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention.

1 is a diagram illustrating an internal combustion engine and an exhaust system thereof according to a first embodiment. 3 is a flowchart showing a control routine for performing control for causing S poison recovery control to be performed on the preceding NOx catalyst according to the first embodiment. It is a figure which shows the correlation with the engine speed which concerns on Example 1, fuel injection quantity, and an exhaust throttle valve opening degree.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust passage 3 Occlusion reduction type | mold NOx catalyst 4 of a front | former stage NOx storage reduction | restoration type NOx catalyst 5 Fuel addition valve 6 Exhaust throttle valve 7 Bypass valve 8 Bypass path 9 ECU

Claims (2)

Two NOx storage reduction catalysts arranged in series in the exhaust passage of the internal combustion engine;
An exhaust throttle valve that is provided in an exhaust passage between the two NOx storage reduction catalysts and adjusts an exhaust flow rate;
S poison recovery control means for supplying a reducing agent into the exhaust to raise the temperature of the NOx storage reduction catalyst and lowering the air-fuel ratio of the exhaust to release the sulfur component stored in the NOx storage reduction catalyst;
With
When releasing the sulfur component stored using the S poison recovery control means to the upstream NOx catalyst upstream of the two NOx storage reduction catalysts, the exhaust throttle valve is An exhaust purification device for an internal combustion engine, wherein the exhaust purification device is controlled to the closed side. The exhaust passage between the two NOx storage reduction catalysts has a bypass passage that bypasses the exhaust throttle valve for exhaust, and the bypass passage is normally closed and the bypass passage exceeds a predetermined pressure. An exhaust purification device for an internal combustion engine according to claim 1, further comprising a bypass valve that opens.

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