JP2009036087A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly adjust the temperature of a particulate filter during the regeneration of the filter when an exhaust emission control device has a NOx catalyst and the filter. <P>SOLUTION: This exhaust emission control device of an internal combustion engine comprises a first exhaust emission control device 30 for eliminating NOx, second exhaust emission control devices 41, 42 each having a filter 41 installed on the downstream side more than the first exhaust emission control device 30, a bypass passage 6 for bypassing the first exhaust emission control device 30, a control means 10 for controlling the amount of the exhaust gas flowing through the bypass passage 6, a reducer supply means 5 for supplying a reducer from the upstream side of the bypass passage 6, and a downstream side temperature detection means 11 for detecting the temperature of at least a part of the filter 41. During the regeneration of the filter 41, the reducer is supplied. In this case, when the temperature of the part of the filter 41 is equal to or higher than a predetermined temperature, the amount of the exhaust gas flowing through the bypass passage 6 is reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

A technique is known in which an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) is disposed in an exhaust passage of an internal combustion engine. This NOx catalyst occludes NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reduces the NOx occluded when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present.

  There is also known a technique that includes a particulate filter (hereinafter simply referred to as a filter) and collects particulate matter (hereinafter referred to as PM) in exhaust gas. This particulate filter carries a catalyst having oxidation ability or is provided upstream. When the amount of PM collected in the filter reaches a certain amount, the reducing agent is supplied to the catalyst having oxidation ability, and the temperature of the filter is raised to oxidize and remove PM. This removal of PM is called filter regeneration or PM regeneration.

An exhaust cooling passage provided with a cooling device and a bypass passage that bypasses the cooling device are provided upstream of the filter. When the exhaust temperature is equal to or higher than a predetermined value, the exhaust from the internal combustion engine is used as the exhaust cooling passage. A technique is known in which exhaust gas is cooled by guiding it, and when it is less than a predetermined value, exhaust gas is guided to a bypass passage to prevent overcooling of the filter (see, for example, Patent Document 1).
JP-A-5-321640

By the way, a NOx catalyst, a bypass passage for bypassing the NOx catalyst, and a filter downstream of these are provided, and the temperature of the filter is adjusted by changing the ratio of the exhaust gas passing through the bypass passage and the NOx catalyst. Can be adjusted.

However, unlike the prior art, since the reducing agent reacts with the NOx catalyst, it is difficult to adjust the temperature of the filter in the same manner as in the prior art.

The present invention has been made in view of the above-described problems, and in the exhaust gas purification apparatus for an internal combustion engine, when the filter is regenerated when the NOx catalyst and the particulate filter are provided, the particulate filter An object is to provide a technique capable of adjusting the temperature more appropriately.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
A first exhaust purification device having a function of purifying NOx;
A second filter is provided on the downstream side of the first exhaust gas purification device, has a function of collecting particulate matter in the exhaust gas, and includes a particulate filter that supports a catalyst having oxidation ability or is provided on the upstream side. An exhaust purification device;
A bypass passage connecting an exhaust passage upstream of the first exhaust purification device and an exhaust passage downstream of the first exhaust purification device and upstream of the second exhaust purification device;
Adjusting means for adjusting the amount of exhaust gas flowing through the bypass passage;
A reducing agent supply means for supplying a reducing agent into the exhaust gas, which is provided further upstream than the location where the bypass passage is connected upstream of the first exhaust purification device;
Downstream temperature detecting means for detecting the temperature of at least a part of the particulate filter;
With
When oxidizing the particulate matter collected in the particulate filter, the reducing agent is supplied by the reducing agent supply means, and at least one of the particulate filters detected by the downstream temperature detection means at this time. When the temperature of the section is equal to or higher than the predetermined temperature, the amount of exhaust gas flowing through the bypass passage is reduced as compared with the case where there is no portion equal to or higher than the predetermined temperature.

The first exhaust purification device includes at least a catalyst for purifying NOx, and may be combined with another catalyst. By supplying the reducing agent to the first exhaust purification device, for example, NOx can be purified, the NOx purification ability can be recovered, or the NOx purification ability can be increased. Further, when the reducing agent is supplied to the first exhaust purification device, reaction heat is generated in the first exhaust purification device. Thereby, since the temperature of exhaust gas rises, the temperature of a particulate filter can be raised.

  The second exhaust purification device may be, for example, a particulate filter carrying a catalyst having oxidation ability, or may be provided with a catalyst having oxidation ability upstream of the particulate filter. That is, a catalyst having oxidation ability is also included in the second exhaust purification device. In addition, other catalysts may be combined. And the particulate matter currently collected by the particulate filter can be oxidized by supplying a reducing agent to the 2nd exhaust gas purification device. The first exhaust purification device and the second exhaust purification device are arranged in series.

  The bypass passage bypasses the first exhaust purification device. When the amount of exhaust gas flowing to the bypass passage increases during regeneration of the particulate filter, the amount of reducing agent passing through the bypass passage increases accordingly. Therefore, the amount of reducing agent that reaches the particulate filter directly increases. Then, the reducing agent reacts with the catalyst having the oxidizing ability of the second exhaust purification device, and raises the temperature of the particulate filter.

That is, by adjusting the amount of exhaust gas that passes through the bypass passage, the proportion of exhaust gas whose temperature has been increased by the NOx catalyst and unreacted reducing agent is supplied to the second exhaust gas purification device. Can be adjusted.

  Here, when the temperature of the second exhaust purification device is higher than the temperature at which the reducing agent reacts, the amount of reducing agent supplied directly to the first exhaust purification device is increased to the first exhaust purification device. Thus, the temperature of the particulate filter can be raised more rapidly than when the amount of the water supplied is increased. That is, when the reducing agent is supplied to the first exhaust purification device, the heat generated by the reaction of the reducing agent is consumed for the temperature rise of the first exhaust purification device, and accordingly, to the second exhaust purification device. The supplied heat is reduced. Further, since heat is released to the outside in the exhaust passage between the first exhaust purification device and the second exhaust purification device, the heat supplied to the second exhaust purification device is reduced accordingly. Therefore, when the reducing agent is supplied to the first exhaust purification device, the temperature rise of the second exhaust purification device becomes slower than when the reducing agent is supplied directly to the second exhaust purification device.

On the other hand, even if the reducing agent is supplied directly to the second exhaust purification device, the temperature is unlikely to rise upstream of the second exhaust purification device. That is, even if the reducing agent reacts on the upstream side, heat moves to the downstream side together with the exhaust gas. And since it becomes easy to react a reducing agent in the downstream which became high temperature, temperature becomes higher. Therefore, when the reducing agent is directly supplied to the second exhaust purification device, the temperature on the downstream side becomes higher than the upstream side of the second exhaust purification device. That is, the temperature becomes non-uniform in the particulate filter.

  On the other hand, when a reducing agent is supplied to the first exhaust purification device, exhaust gas having a high temperature flows into the second exhaust purification device from the beginning, so that the temperature of the second exhaust purification catalyst can be increased uniformly. However, the temperature rise becomes slow as described above.

  That is, when the temperature of the particulate filter is lower than the predetermined temperature, the amount of the exhaust gas flowing through the bypass passage is increased more than when the temperature is lower than the predetermined temperature, so that at least a part of the second exhaust purification device is obtained. The temperature can be quickly raised to the temperature at which the particulate matter is oxidized. Thereby, the oxidation of the particulate matter starts at an earlier time in at least a part of the second exhaust purification device.

  And when the temperature of at least one part of a particulate filter becomes more than predetermined temperature, the temperature of a 2nd exhaust gas purification apparatus can be raised uniformly by reducing the quantity of the exhaust_gas | exhaustion which distribute | circulates a bypass channel. Thereby, the particulate matter collected by the particulate filter can be uniformly oxidized.

  In addition, the predetermined temperature at this time can be set to the oxidizable temperature of the particulate matter.

  The adjusting means may adjust the amount of exhaust gas passing through either the bypass passage or the exhaust passage provided with the first exhaust purification device.

  In the present invention, the temperature of at least a part of the particulate filter detected by the downstream temperature detecting means is equal to or higher than the predetermined temperature, and the particulate filter is at least two of the part and the upstream side thereof. When the particulate matter deposited in the part when the area is divided into two regions is less than the predetermined amount, the particulate matter deposited in the part region is larger than the predetermined amount. Thus, the amount of exhaust gas passing through the bypass passage can be reduced.

  Here, when the amount of exhaust gas passing through the first exhaust gas purification device increases, the temperature of the exhaust gas flowing into the second exhaust gas purification device increases, so that the temperature rises on the upstream side of the particulate filter and particulate matter is generated. Oxidized. Then, the heat generated on the upstream side of the particulate filter moves together with the exhaust gas, and the temperature on the downstream side of the particulate filter increases. At this time, if the particulate matter is oxidized on the downstream side of the particulate filter, the temperature may further rise and overheat.

  On the other hand, if the amount of exhaust gas passing through the bypass passage is reduced after the particulate matter in the region where the temperature first rises with the particulate filter is sufficiently oxidized, the particulate matter is oxidized due to the rise in the exhaust temperature. Can be suppressed. Thereby, it can suppress that it overheats in a part of particulate filter.

  The predetermined amount can be set to a deposition amount that does not cause the particulate filter to be overheated by reducing the amount of exhaust gas that passes through the bypass passage.

In the present invention, the apparatus further comprises upstream temperature detection means for detecting the temperature of the first exhaust purification device, and when the temperature of the first exhaust purification device is lower than the temperature at which NOx can be stored at the highest rate. The amount of exhaust gas passing through the bypass passage can be reduced more than ever.

On the other hand, the present invention further includes an upstream temperature detecting means for detecting the temperature of the first exhaust purification device, and the temperature of the first exhaust purification device is higher than the temperature at which NOx can be stored at the highest rate. The amount of exhaust gas passing through the bypass passage can be increased more than before.

In this case, the temperature at which the NOx can be stored at the highest rate may be the entire first exhaust purification catalyst or a part thereof. Here, in the NOx catalyst, even if the temperature is too high or too low, the NOx occlusion ability is lowered. That is, the NOx catalyst has an optimum temperature for storing NOx. Even if the temperature of the first exhaust gas purification device is lower or higher than that temperature, the ratio of the NOx stored in the NOx catalyst in the NOx in the exhaust gas decreases.

On the other hand, when the temperature of the first exhaust gas purification device is lower than the temperature at which NOx can be stored at the highest rate, the first exhaust gas is supplied by supplying more reducing agent to the first exhaust gas purification device. The temperature of the purification device can be quickly raised. Thereby, NOx occlusion ability can be improved.

Further, when the temperature of the first exhaust purification device is higher than the temperature at which NOx can be stored at the highest rate, the amount of the reducing agent flowing into the first exhaust purification device is reduced, thereby the first exhaust purification device. The temperature rise of the purification device can be suppressed. Thereby, NOx occlusion ability can be improved.

  The temperature at which NOx can be occluded at the highest rate may have a certain range.

  In the present invention, when the temperature of at least a part of the particulate filter is equal to or higher than the threshold value, the amount of exhaust gas passing through the bypass passage can be increased as compared with a case where the temperature is lower than the threshold value.

  The threshold value can be a temperature at which the second exhaust purification device may overheat. By increasing the flow rate of the exhaust gas that passes through the bypass passage when the temperature of at least a part of the particulate filter is equal to or higher than the threshold value, the low-temperature exhaust gas can be supplied to the second exhaust gas purification device. Thereby, the temperature of the second exhaust purification device can be lowered below the threshold value. At this time, the supply amount of the reducing agent may be decreased, or the supply of the reducing agent may be stopped.

According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the temperature of the particulate filter can be more appropriately adjusted when the filter is regenerated when the NOx catalyst and the particulate filter are provided.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 and its exhaust system according to the present embodiment. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

An exhaust passage 2 leading to the combustion chamber is connected to the internal combustion engine 1. This exhaust passage 2 communicates with the atmosphere downstream. In the middle of the exhaust passage 2, an NOx storage reduction catalyst 30 (hereinafter referred to as NOx catalyst 30) and a particulate filter 41 (hereinafter referred to as filter 41) are provided in this order from the internal combustion engine 1 side. Yes. The filter 41 carries an oxidation catalyst 42.

The NOx catalyst 30 has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is low and a reducing agent is present. . In this embodiment, the NOx catalyst 30 corresponds to the first exhaust purification device in the present invention. In this embodiment, the filter 41 and the oxidation catalyst 42 correspond to the second exhaust purification device in the present invention. Here, the NOx catalyst 30 may be combined with another catalyst. Further, the oxidation catalyst 42 may be provided on the upstream side of the filter 41 without being supported by the filter 41. The oxidation catalyst 42 may be any catalyst having an oxidation ability, and may be, for example, a three-way catalyst or a NOx catalyst.

The exhaust passage 2 upstream of the NOx catalyst 30 is provided with a fuel addition valve 5 for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust passage 2. In this embodiment, the fuel addition valve 5 corresponds to the reducing agent supply means in the present invention.

  The fuel addition valve 5 is opened by a signal from the ECU 7 described later and injects fuel into the exhaust. The fuel injected from the fuel addition valve 5 into the exhaust passage 2 lowers the air-fuel ratio of the exhaust flowing from the upstream of the exhaust passage 2.

When NOx stored in the NOx catalyst 30 is reduced, by adding fuel from the fuel addition valve 5, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 30 is spiked in a relatively short cycle (short time). So-called rich spike control is executed. In addition, NOx
When the sulfur poisoning of the catalyst 30 is recovered, fuel is added from the fuel addition valve 5 to the NOx catalyst 30.

Further, a bypass passage 6 that connects the exhaust passage 2 downstream of the fuel addition valve 5 and upstream of the NOx catalyst 30 and the exhaust passage 2 downstream of the NOx catalyst 30 and upstream of the filter 41 is provided. It has been. An adjustment valve 10 that adjusts the flow path area of the bypass passage 6 is provided in the middle of the bypass passage 6. By changing the opening of the control valve 10, the amount of exhaust passing through the NOx catalyst 30 and the amount of exhaust passing through the bypass passage 6 can be changed. The control valve 10 may be provided on the exhaust passage 2 side where the NOx catalyst 30 is provided. Further, the exhaust passage 2 and the bypass passage 30 may be provided respectively. In this embodiment, the control valve 10 corresponds to the adjusting means in the present invention.

  The internal combustion engine 1 configured as described above is provided with an ECU 7 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 7 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.

In addition, an air-fuel ratio sensor 8 that measures the air-fuel ratio of the exhaust gas and an upstream temperature sensor 9 that measures the temperature of the exhaust gas are attached to the exhaust passage 2 between the NOx catalyst 30 and the filter 41. Further, a downstream temperature sensor 11 for measuring the temperature of the exhaust is attached to the exhaust passage 2 downstream of the filter 41. The temperature of the NOx catalyst 30 can be obtained by the upstream temperature sensor 9. Further, the temperature of at least a part of the filter 41 can be obtained by the downstream temperature sensor 11. Note that the temperature of the NOx catalyst 30 and the filter 41 may be detected by directly attaching a temperature sensor to the NOx catalyst 30 and the filter 41. In the present embodiment, the downstream temperature sensor 11 corresponds to the downstream temperature detecting means in the present invention. In the present embodiment, the upstream temperature sensor 9 corresponds to the upstream temperature detection means in the present invention.

An air-fuel ratio sensor 8, an upstream temperature sensor 9, and a downstream temperature sensor 11 are connected to the ECU 7 through electrical wiring, and output signals from these sensors are input to the ECU 7. On the other hand, the fuel addition valve 5 and the control valve 10 are connected to the ECU 7 via electric wiring, and the fuel addition valve 5 and the control valve 10 are controlled by the ECU 7.

  In this embodiment, fuel is added from the fuel addition valve 5 when the filter 41 is regenerated. At this time, the opening degree of the control valve 10 is changed based on the temperature of at least a part of the filter 41. That is, when there is no place where the temperature at which PM can be oxidized in the filter 41 (for example, 600 ° C.) is not present, the temperature is higher than the temperature at which at least part of the filter 41 can oxidize PM. Thus, the opening of the control valve 10 is increased. Note that the control valve 10 may be fully opened when the temperature of the filter 41 is lower than the temperature at which PM can be oxidized, and the control valve 10 may be fully closed when the temperature of the filter 41 is higher than the temperature at which PM can be oxidized.

  That is, when the temperature of the filter 41 is lower than the temperature at which PM can be oxidized, the amount of reducing agent that directly reaches the filter 41 is increased in order to quickly increase the temperature of the filter 41. For this purpose, the opening of the control valve 10 is increased so that more reducing agent flows through the bypass passage 6. That is, by causing the reducing agent to reach the filter 41 directly, the reducing agent reacts at the oxidation catalyst 42 and the temperature of the filter 41 rises quickly. In particular, since the temperature on the downstream side of the filter 41 rises quickly, the PM collected on the downstream side is first oxidized. That is, at least a part of the filter 41 may be on the downstream side of the filter 41. This downstream side may be the most downstream side, or may be the downstream side when the filter 41 is divided into at least two regions in the exhaust flow direction. Further, there may be another region further downstream than this at least a part of the region.

On the other hand, when the temperature of at least a part of the filter 41 is equal to or higher than the temperature at which PM can be oxidized, the amount of reducing agent flowing into the NOx catalyst 30 is increased in order to make the temperature uniform in the filter 41. For this purpose, the opening of the control valve 10 is reduced to reduce the amount of reducing agent flowing through the bypass passage 6. That is, by causing the NOx catalyst 30 to react with the reducing agent, the exhaust gas having a high temperature flows into the filter 41, so that the temperature on the upstream side of the filter 41 can also be increased. Therefore, PM collected on the upstream side of the filter 41 is oxidized.

  That is, the PM collected by the filter 41 can be oxidized quickly by changing the opening of the control valve 10.

  Next, FIG. 2 is a flowchart showing a flow of opening / closing control of the control valve 10 in the present embodiment. This routine is repeatedly executed every predetermined time.

  In step S101, it is determined whether there is a PM regeneration request. The PM regeneration request is issued when regeneration of the filter 41 is necessary. For example, it is assumed that there is a PM regeneration request when the amount of PM collected by the filter 41 exceeds a threshold value. If an affirmative determination is made in step S101, the process proceeds to step S102, whereas if a negative determination is made, the process proceeds to step S104.

  In step S102, it is determined whether or not the downstream temperature in the filter 41 is lower than 600 ° C., for example. That is, it is determined whether the downstream temperature in the filter 41 is a temperature at which PM can be oxidized. The downstream temperature in the filter 41 is estimated based on the temperature obtained by the downstream temperature sensor 11. If an affirmative determination is made in step S102, the process proceeds to step S103, whereas if a negative determination is made, the process proceeds to step S104.

In step S103, the control valve 10 is fully opened. That is, the amount of reducing agent that flows through the bypass passage 6 and reaches the filter 41 directly is increased. At this time, the control valve 10 may be opened on the opening side rather than being set in step S104.

In step S104, the control valve 10 is fully closed. That is, when there is no PM regeneration request, the exhaust gas passes through the NOx catalyst 30 in order to purify the NOx in the exhaust gas with the NOx catalyst 30. When the temperature on the downstream side in the filter 41 is, for example, 600 ° C. or higher, the amount of reducing agent that reacts with the NOx catalyst 30 is increased in order to increase the temperature on the upstream side in the filter 41. At this time, the control valve 10 may be set closer to the closing side than set in step S103.

  Next, FIG. 3 is a time chart showing the transition of the temperature of the filter 41 in the present embodiment. At the time indicated by A, a PM regeneration request is issued and the control valve 10 is fully opened. Further, at the time indicated by B, the control valve 10 is fully closed.

  “PM regeneration request” indicates whether or not a PM regeneration request has been issued, and is ON when it is issued, and is OFF when it has not been issued.

  “NOx catalyst temperature” indicates the temperature of the NOx catalyst 30, the solid line indicates the case where the control valve 10 according to this embodiment is controlled, and the broken line indicates the case where the bypass passage 6 is not provided.

  “Filter temperature” indicates the temperature of the filter 41, the solid line indicates the temperature on the downstream side of the filter 41 when the control valve 10 according to this embodiment is controlled, and the broken line does not include the bypass passage 6. The temperature on the downstream side of the filter 41 is shown. The alternate long and short dash line indicates the temperature on the upstream side of the filter 41 when the control valve 10 according to this embodiment is controlled, and the alternate long and two short dashes line indicates the temperature on the upstream side of the filter 41 when the bypass passage 6 is not provided. Show.

  “Control valve opening” indicates the opening of the control valve 10 and is fully opened during the period from A to B, and is fully closed during the other periods.

When the PM regeneration request is issued and the control valve 10 is fully opened at the time indicated by A, the amount of fuel that flows through the bypass passage 6 and reaches the filter 41 directly increases. The temperature rises quickly. On the other hand, when the bypass passage 6 is not provided, almost no fuel reaches the filter 41, and the fuel reacts with the NOx catalyst 30, so that exhaust having a high temperature flows into the filter 41. For this reason, the overall temperature of the filter 41 rises, but the temperature on the downstream side of the filter 41 rises gradually.

Even when the control valve 10 is fully opened, the heat generated by the fuel reaction on the upstream side of the filter 41 moves downstream along with the exhaust gas. Further, since the amount of fuel that reacts with the NOx catalyst 30 decreases, the temperature of the exhaust gas flowing into the filter 41 is not so high. Therefore, the temperature rise on the upstream side of the filter 41 becomes slow. On the other hand, when the bypass passage 6 is not provided, the fuel reacts with the NOx catalyst 30 and the exhaust gas having a high temperature flows into the filter 41, so that the temperature on the upstream side of the filter 41 also increases. However, since the temperature of the entire filter 41 is raised, the temperature rise is slow.

  In addition, when there exists a possibility that the filter 41 may overheat (for example, when temperature rises rapidly), it is good also as the control valve 10 fully opened. Further, the opening degree of the control valve 10 may be determined according to the temperature of the filter 41. At this time, for example, the opening degree of the control valve 10 is increased as the temperature of the filter 41 is higher.

In other words, when exhaust gas having a high temperature is supplied from the NOx catalyst 30 to the filter 41 when the control valve 10 is fully closed, if the PM collected in the filter 41 is oxidized all at once, the filter 41 is overheated. There is a fear. In such a case, exhaust of high temperature can be prevented from flowing into the filter 41 by fully opening the control valve 10. That is, the filter 41 can be cooled by exhaust gas having a low temperature at which the fuel does not react. In addition, a large amount of fuel flows into the filter 41. However, since the temperature rises with the fuel mainly on the downstream side, the risk of the filter 41 being overheated is small. At this time, the fuel addition amount may be decreased or the fuel addition may be stopped. Further, by determining the opening degree of the control valve 10 according to the temperature of the filter 41, an excessive temperature decrease can be suppressed.

Further, when the temperature of the NOx catalyst 30 is less than the optimum temperature for storing NOx, the control valve 10 may be fully closed. At this time, the control valve 10 is set according to the temperature of the NOx catalyst 30.
The degree of opening may be determined. For example, the lower the temperature of the NOx catalyst 30, the smaller the opening degree of the control valve 10.

  That is, when the temperature of the NOx catalyst 30 is low, the temperature of the NOx catalyst 30 can be raised by supplying more fuel to the NOx catalyst 30. Further, by determining the opening degree of the control valve 10 according to the temperature of the NOx catalyst 30, an excessive temperature rise can be suppressed.

On the other hand, when the temperature of the NOx catalyst 30 is higher than the optimum temperature for storing NOx, the control valve 10 may be fully opened. At this time, the control valve 10 is set according to the temperature of the NOx catalyst 30.
The degree of opening may be determined. For example, the degree of opening of the control valve 10 is increased as the temperature of the NOx catalyst 30 is higher.

  That is, when the temperature of the NOx catalyst 30 is high, the temperature of the NOx catalyst 30 can be lowered by reducing the amount of fuel supplied to the NOx catalyst 30. Further, by determining the opening degree of the control valve 10 according to the temperature of the NOx catalyst 30, an excessive temperature drop can be suppressed.

As described above, when the temperature of the NOx catalyst 30 is raised or lowered, it may be performed within a range in which the oxidation of PM in the filter 41 is continued. By doing so, the filter 41 can be regenerated while keeping the NOx purification rate high. For example, the rich spike control may be performed periodically while the filter 41 is being regenerated.

  In this embodiment, even if the temperature of the filter 41 is equal to or higher than the temperature at which PM can be oxidized, the opening degree of the control valve 10 is fully opened until the oxidation of PM collected downstream of the filter 41 is completed. Keep it.

  That is, if the control valve 10 is closed before the oxidation of the PM collected on the downstream side of the filter 41 is completed, heat is generated due to the continued oxidation of the PM on the downstream side, and the PM is generated on the upstream side. Exhaust gas whose temperature has increased due to oxidation flows downstream. Therefore, there is a risk of overheating on the downstream side of the filter 41.

  On the other hand, after the oxidation of PM collected on the downstream side of the filter 41 is completed, there is no heat generated on the downstream side even if exhaust gas having a high temperature flows from the upstream side. Overheating can be suppressed.

Next, FIG. 4 is a flowchart showing a flow of opening / closing control of the control valve 10 in this embodiment. This routine is repeatedly executed every predetermined time. In addition, the same code | symbol is attached | subjected about the step in which the same process as the flow shown in FIG.

  In step S201, it is determined whether or not the oxidation of PM collected on the downstream side of the filter 41 is completed. That is, it is determined whether the regeneration of the filter 41 is completed on the downstream side. The determination may be made based on whether the amount of PM collected on the downstream side of the filter 41 is equal to or less than a predetermined amount. For example, the amount of oxidation of PM is calculated based on the temperature on the downstream side of the filter 41 and the duration of that temperature, and the amount of oxidation of PM is subtracted from the amount of PM when regeneration of the filter 41 is started. PM amount can be obtained. The predetermined amount is set as a value that can be regarded as the completion of the oxidation of PM.

  If an affirmative determination is made in step S201, the process proceeds to step S104 in order to oxidize the PM collected on the upstream side of the filter 41. On the other hand, if a negative determination is made, the process proceeds to step S103 in order to continue to oxidize the PM collected on the downstream side of the filter 41.

  In this way, overheating of the filter 41 can be further suppressed.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its exhaust system. 3 is a flowchart illustrating a flow of control valve opening / closing control according to the first embodiment. 2 is a time chart showing a change in temperature of a filter in Example 1. 6 is a flowchart showing a flow of control valve opening / closing control in the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust passage 5 Fuel addition valve 6 Bypass passage 8 Air-fuel ratio sensor 9 Upstream temperature sensor 10 Control valve 11 Downstream temperature sensor 30 Occlusion reduction type NOx catalyst 41 Particulate filter 42 Oxidation catalyst

Claims (5)

A first exhaust purification device having a function of purifying NOx;
A second filter is provided on the downstream side of the first exhaust gas purification device, has a function of collecting particulate matter in the exhaust gas, and includes a particulate filter that supports a catalyst having oxidation ability or is provided on the upstream side. An exhaust purification device;
A bypass passage connecting an exhaust passage upstream of the first exhaust purification device and an exhaust passage downstream of the first exhaust purification device and upstream of the second exhaust purification device;
Adjusting means for adjusting the amount of exhaust gas flowing through the bypass passage;
A reducing agent supply means for supplying a reducing agent into the exhaust gas, which is provided further upstream than the location where the bypass passage is connected upstream of the first exhaust purification device;
Downstream temperature detecting means for detecting the temperature of at least a part of the particulate filter;
With
When oxidizing the particulate matter collected in the particulate filter, the reducing agent is supplied by the reducing agent supply means, and at least one of the particulate filters detected by the downstream temperature detection means at this time. An exhaust gas purification apparatus for an internal combustion engine, wherein the amount of exhaust gas flowing through the bypass passage is reduced when the temperature of the portion is equal to or higher than a predetermined temperature, compared to when there is no portion equal to or higher than the predetermined temperature.   The temperature of at least a part of the particulate filter detected by the downstream temperature detecting means is equal to or higher than the predetermined temperature, and the particulate filter is divided into at least two regions, the part and the upstream side thereof. Sometimes when the particulate matter deposited on the part is less than or equal to a predetermined amount, the bypass passage is larger than the case where the particulate matter deposited on the part of the region is larger than the prescribed amount. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the amount of exhaust gas passing through the engine is reduced. The apparatus further comprises upstream temperature detection means for detecting the temperature of the first exhaust purification device, and when the temperature of the first exhaust purification device is lower than the temperature at which NOx can be stored at the highest rate, the bypass passage is provided. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the amount of exhaust gas passing through is reduced more than ever. The apparatus further comprises upstream temperature detection means for detecting the temperature of the first exhaust purification device, and when the temperature of the first exhaust purification device is higher than the temperature at which NOx can be stored at the highest rate, the bypass passage is provided. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the amount of exhaust passing therethrough is increased than before.   The amount of exhaust gas that passes through the bypass passage is increased when the temperature of at least a part of the particulate filter is equal to or higher than a threshold value, compared to a case where the temperature is lower than the threshold value. Exhaust gas purification device for internal combustion engine.

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