JP2007315242A - Exhaust gas purification system for internal combustion engine - Google Patents

Abstract

In an exhaust purification system that has exhaust purification means such as an S trap catalyst, an oxidation catalyst, a filter, a NOx catalyst, etc. and purifies exhaust gas from an internal combustion engine, performance regeneration control for the exhaust purification means is efficiently performed, and At this time, the release of SOx from the S trap catalyst is suppressed, and a large amount of SOx is oxidized by an oxidation catalyst or a filter, and is prevented from deteriorating exhaust emission due to being emitted as white smoke to the outside.
An S-Trap 110, an oxidation catalyst 111, a filter 112, and an NSR 113 are arranged in series in an exhaust purification unit 10, and when performing the performance regeneration control, a first switching valve 12 is switched to a second position. The exhaust gas is caused to flow into the exhaust gas purification unit 10 from the NSR 113 side (second state).
[Selection] Figure 1

Description

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

  In an internal combustion engine, an exhaust system of the internal combustion engine is used to purify particulate matter (hereinafter also simply referred to as “PM”) such as soot and SOF (Soluble Organic Fraction) and nitrogen oxide (NOx) contained in the exhaust gas. Further, there is known a technique for arranging a filter for collecting PM in exhaust gas, a NOx storage reduction catalyst for purifying NOx (hereinafter also referred to as “NOx catalyst”), or a combination of a NOx catalyst and a filter. .

Here, the NOx catalyst occludes (absorbs and adsorbs) NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and occludes when the oxygen concentration of the inflowing exhaust gas decreases and the reducing agent is present. Releases NOx and reduces it to nitrogen (N ₂ ). In this technique, when the amount of NOx occluded in the NOx catalyst increases, the purification capacity decreases, so that a reducing agent is supplied to the NOx catalyst, and NOx occluded in the catalyst is released and reduced ( Hereinafter, it is referred to as “NOx reduction processing”).

  The exhaust also contains sulfur oxide (SOx), and this SOx is absorbed by the NOx catalyst by the same mechanism as NOx. When the amount of SOx stored in the NOx catalyst increases, the NOx storage capacity of the NOx catalyst decreases and so-called SOx poisoning occurs.

  Therefore, an S trap catalyst that absorbs SOx in the inflowing exhaust gas is disposed upstream of the exhaust of the NOx catalyst to suppress SOx poisoning of the NOx catalyst. Further, when the NOx catalyst is poisoned, the NOx catalyst may be heated and the oxygen concentration of the exhaust gas flowing into the NOx catalyst may be lowered to release SOx from the NOx catalyst for reduction (see FIG. Hereinafter, it is referred to as “SOx poisoning recovery process”).

On the other hand, in the above filter, when the collected PM increases, the exhaust pressure rises due to clogging of the filter and the engine performance deteriorates. Therefore, an oxidation catalyst is provided upstream of the filter. A technique for continuously oxidizing and removing PM collected by a filter at a relatively low temperature range by oxidizing (NO) into nitrogen dioxide (NO ₂ ) has been proposed (see, for example, Patent Document 1). ).

  However, in the configuration in which the oxidation catalyst, the filter, the S trap catalyst, and the NOx catalyst are provided in series, the NOx reduction process, the SOx poisoning recovery process, and the like (hereinafter also referred to as “performance regeneration control”) for the NOx catalyst. When the reducing agent is supplied from the oxidation catalyst side, the supplied reducing agent reacts with the upstream oxidation catalyst, and it is difficult for the supplied reducing agent to reach the NOx catalyst, and the efficiency of performance regeneration control deteriorates. was there.

In addition, when performance regeneration control is performed on the NOx catalyst in a configuration in which the S trap catalyst and the NOx catalyst are disposed adjacent to each other, SOx may be released from both the S trap catalyst and the NOx catalyst. In the configuration in which the released SOx can be supplied to the oxidation catalyst or the filter, a large amount of SOx may be oxidized by the oxidation catalyst or the filter and discharged as white smoke.
JP 2005-500147 A US Pat. No. 6,408,620 JP 2004-60596 A

  The present invention has been made in view of the above prior art, and an object of the present invention is to provide an exhaust purification means in which an S trap catalyst, an oxidation catalyst, a filter, and a NOx catalyst for purifying exhaust are provided in series in an exhaust system. In the exhaust gas purification system for an internal combustion engine, the performance regeneration control for the exhaust gas purification means is more efficiently performed, and at that time, the release of SOx from the S trap catalyst is suppressed, and the released SOx is white. It is to provide a technique for suppressing deterioration of exhaust emission due to smoke.

  In order to achieve the above object, the present invention is such that an S trap catalyst, an oxidation catalyst, a filter, a NOx catalyst, etc. are provided in series in the exhaust purification means in this order, and the performance regeneration control for the exhaust purification means is not performed. The exhaust gas purifying means introduces exhaust gas from the S trap catalyst side, and when performing the performance regeneration control, the exhaust gas purifying means introduces exhaust gas from the NOx catalyst side and supplies a reducing agent. To do.

More specifically, an exhaust passage that is connected at one end to the internal combustion engine and through which the exhaust from the internal combustion engine passes,
Exhaust purification means for purifying the exhaust that is provided in the exhaust passage and passes through the exhaust passage;
Reducing agent supply means for supplying a reducing agent to the exhaust gas introduced into the exhaust gas purification means;
Performance regeneration control means for performing control to regenerate the performance of the exhaust gas purification means by supplying a reducing agent to the exhaust gas from the reducing agent supply means;
An exhaust gas purification system for an internal combustion engine comprising:
The exhaust purification means collects an S trap catalyst that absorbs SOx in the exhaust when the air-fuel ratio of the exhaust is lean, an oxidation catalyst that has an oxidizing ability, and particulate matter in the exhaust and collects the particulate matter. A filter that prevents clogging by removing the collected particulate matter by oxidation, and when the air-fuel ratio of the exhaust is lean, it stores NOx in the exhaust and is rich in the exhaust and has a reducing agent. An NOx storage reduction catalyst that releases and reduces the stored NOx, and is provided in a state where the S trap catalyst, the oxidation catalyst, the filter, and the NOx storage reduction catalyst are arranged in series in this order.
The exhaust state can be switched between a first state in which the exhaust flows into the exhaust purification means from the S trap catalyst side and a second state in which the exhaust flows from the NOx storage reduction catalyst side. Further comprising an exhaust state switching means,
When the performance regeneration control by the performance regeneration control means is not performed, the exhaust state is changed to the first state by the exhaust state switching means, and the performance regeneration control by the performance regeneration control means is performed. The exhaust state is switched to the second state by the exhaust state switching means.

  In the exhaust gas purification system of the internal combustion engine configured as described above, when the performance regeneration control for regenerating the performance of the exhaust gas purification unit is not performed, the exhaust state is changed to the first state by the exhaust state switching unit. To be.

  Therefore, since the exhaust gas flows into the exhaust gas purification means from the S trap catalyst side, SOx contained in the exhaust gas can be absorbed by the S trap catalyst. Thereby, it is possible to prevent the downstream NOx catalyst in the first state from being poisoned by the SOx.

On the other hand, since the amount of NOx contained in the exhaust is absorbed by the S trap catalyst is small, the NOx flows into the oxidation catalyst on the downstream side when the exhaust is in the first state. Generally, NOx contained in the exhaust gas discharged from the internal combustion engine contains more NO than NO ₂ (for example, 60 to 70%), and the NO flowing into the oxidation catalyst is oxidized in the oxidation catalyst. As a result, NO ₂ is generated. Here, the NO ₂ can oxidize the PM even at a lower temperature than NO, and the generated NO ₂ is supplied to the filter further downstream in the first state.

Therefore, in the present invention, when the performance regeneration control for regenerating the performance of the exhaust gas purification means is not performed by the performance regeneration control means, the NO ₂ of NOx contained in the exhaust gas in the oxidation catalyst. By increasing the ratio, it is possible to promote oxidation removal of PM in the filter.

  In the present invention, when it becomes necessary to perform the performance regeneration control for regenerating the performance of the exhaust purification means, a reducing agent (fuel) is introduced into the exhaust introduced from the reducing agent supply means to the exhaust purification means. Etc.) are supplied.

  Here, in the exhaust gas purification system for an internal combustion engine that does not include the exhaust state switching means, the reducing agent (fuel or the like) supplied when the performance regeneration control is performed is oxidized by the oxidation catalyst, There are cases where the supply amount of the reducing agent (fuel, etc.) introduced into the NOx catalyst decreases.

  On the other hand, in the present invention, the exhaust state can be switched between the first state and the second state by the exhaust state switching means. Therefore, when the performance regeneration control is performed, the exhaust gas can flow from the NOx catalyst side, so that the reducing agent (fuel, etc.) supplied for the performance regeneration control is oxidized by the oxidation catalyst. Therefore, it is possible to suppress a reduction in the supply amount of the reducing agent (fuel, etc.) introduced into the NOx catalyst. Therefore, the performance regeneration control can be performed efficiently, and thus the fuel consumption related to the performance regeneration control can be improved.

  Further, when performing the performance regeneration control, even if the supplied reducing agent (fuel, etc.) flows out of the NOx catalyst to the downstream side by setting the exhaust state to the second state, it flows out. Since the reducing agent (fuel or the like) is oxidized in the downstream oxidation catalyst in the second state, it is possible to suppress the reducing agent (fuel or the like) from being discharged outside without being purified.

Further, even after the performance regeneration control is completed and the exhaust state is switched to the first state, the reducing agent (fuel, etc.) does not remain in the oxidation catalyst, so the amount of NO ₂ generated in the oxidation catalyst There is no risk of decrease. Therefore, after the exhaust state is switched to the first state, it is possible to efficiently promote oxidation removal of PM in the filter.

  Here, the performance regeneration control is performed in the exhaust gas purification system of the internal combustion engine in which the S trap catalyst is disposed between the filter and the NOx catalyst and adjacent to the NOx catalyst. In doing so, the reducing agent (fuel, etc.) supplied by the reducing agent supply means is easily introduced into the S trap catalyst. As a result, the temperature of the S trap catalyst also becomes high (for example, 600 to 650 degrees Celsius), and the air-fuel ratio tends to be a rich air-fuel ratio, so that SOx may leak from the S trap catalyst. In such a case, SOx leaked from the S trap catalyst may be oxidized in the filter or the oxidation catalyst, thereby causing white smoke.

On the other hand, in the present invention, the S trap catalyst, the oxidation catalyst, the filter, and the NOx catalyst are arranged in series in the above order, and the S trap catalyst and the NOx catalyst are arranged in series.
The catalyst is arranged apart. Therefore, even when the performance regeneration control is performed, the reducing agent (fuel or the like) supplied by the reducing agent supply means is difficult to be introduced into the S trap catalyst, and the S trap catalyst is unlikely to reach a high temperature. Therefore, it is possible to suppress the SOx absorbed in the S trap catalyst from being released.

  Further, even if the SOx is released from the S trap catalyst, the exhaust state is set to the second state when the performance regeneration control is performed, so that the SOx does not flow into the filter or the oxidation catalyst. Accordingly, it is possible to reduce the absolute amount of SOx flowing into the filter and the oxidation catalyst, thereby suppressing the generation of white smoke caused by the oxidation of the SOx.

  The reducing agent supply means includes a reducing agent addition valve that injects a reducing agent (fuel or the like) into the exhaust gas, and a fuel injection valve that sub-injects fuel during an engine expansion stroke or an exhaust stroke. Also good.

  In the present invention, the performance regeneration control may be a NOx reduction process in which NOx stored in the NOx storage reduction catalyst is released and reduced.

  The performance regeneration control may be a SOx poisoning recovery process that releases and reduces SOx absorbed by the NOx storage reduction catalyst.

  That is, when the SOx absorbed in the NOx catalyst needs to be released and reduced, the exhaust state switching means causes the exhaust state to be changed to the second state, and the reducing agent supply means to the exhaust gas. A reducing agent (fuel etc.) is supplied to the exhaust gas introduced into the purification means.

  Then, the air-fuel ratio of the exhaust gas introduced into the NOx catalyst is low, and the NOx catalyst is maintained at a high temperature (for example, 600 to 650 degrees Celsius), so that SOx absorbed in the NOx catalyst is released and reduced. be able to.

  In this case, if the S trap catalyst is an exhaust purification system configured to be disposed between the filter and the NOx catalyst and adjacent to the NOx catalyst, the same as the NOx catalyst, the Since the temperature of the S trap catalyst also becomes high and the air-fuel ratio becomes rich, the leakage of SOx from the S trap is more likely to occur. Further, since the S trap catalyst is provided upstream of the NOx catalyst in the first state, it is considered that the amount of SOx absorbed by the S trap catalyst is larger than that of the NOx catalyst.

  Accordingly, in the SOx poisoning recovery process for the NOx catalyst, it is conceivable that SOx is also released from the S trap catalyst. In this case, the released SOx is oxidized in the filter and the oxidation catalyst, and is white. There was a risk of smoke being emitted to the outside.

  On the other hand, in the present invention, the S trap catalyst, the oxidation catalyst, the filter, and the NOx catalyst are arranged in series in the above order, and the S trap catalyst and the NOx catalyst are arranged apart from each other. The Therefore, even if the SOx poisoning recovery process is performed on the NOx catalyst, the reducing agent (fuel, etc.) supplied by the reducing agent supply means is difficult to be introduced into the S trap catalyst, and the S trap catalyst has a high temperature. It ’s hard to be. That is, since the atmosphere around the S trap catalyst is unlikely to be a reducing atmosphere in which the SOx is reduced, it is possible to suppress the SOx absorbed in the S trap catalyst from being released.

Moreover, even if the SOx is released from the S trap catalyst, the SOx does not flow into the filter or the oxidation catalyst by setting the exhaust state to the second state. The absolute amount of SOx flowing in can be reduced, and thus the generation of white smoke caused by the oxidation of SOx can be suppressed.

Moreover, the following structures can be illustrated as an exhaust gas purification system for an internal combustion engine according to the present invention. That is,
The exhaust passage includes a first branch passage that branches from a branch portion provided in the exhaust passage and is connected to an end of the exhaust purification means on the side of the S trap catalyst; A second branch passage connected to an end of the NOx storage reduction catalyst side; a first exhaust passage upstream of the branch portion in the exhaust passage; and a second exhaust downstream of the branch portion in the exhaust passage. A passage,
The reducing agent supply means supplies the reducing agent to the exhaust upstream from the branch portion,
The exhaust state switching means connects the first exhaust passage and the first branch passage in the branch portion, connects the second branch passage and the second exhaust passage, and the connected state. The first exhaust passage and the first branch passage, and the connected second branch passage and the second exhaust passage are shut off to bring the exhaust state into the first state. Connecting the first exhaust passage and the second branch passage, connecting the first branch passage and the second exhaust passage, and the first exhaust passage and the second branch passage in the connected state; The exhaust state may be the second state by blocking the connected first branch passage and second exhaust passage.

  In such a configuration, if the state of the exhaust is the first state, the exhaust flows from the first exhaust passage into the exhaust purification means via the first branch passage from the S trap catalyst side, Next, the gas flows out into the second branch passage and is discharged to the outside through the second exhaust passage.

  On the other hand, if the exhaust state is the second state, the exhaust flows from the NOx catalyst side from the first exhaust passage to the exhaust purification means via the second branch passage, and then the second exhaust passage. It flows out into one branch passage and is discharged outside through the second exhaust passage.

  Therefore, according to the configuration of the present invention, the exhaust state can be switched between the first state and the second state with a simpler configuration.

  According to the present invention, in an exhaust gas purification system for an internal combustion engine in which an exhaust gas purification unit of an S trap catalyst, an oxidation catalyst, a filter, and a NOx catalyst for purifying exhaust gas is provided in series in an exhaust system, performance regeneration control for the exhaust gas purification unit When performing the above, it is possible to suppress the efficiency of the performance regeneration control from being deteriorated, thereby improving the fuel efficiency related to the performance regeneration control. Further, when performing performance regeneration control on the exhaust purification means, it is possible to suppress the release of SOx from the S trap catalyst, and a large amount of the released SOx is oxidized by an oxidation catalyst or filter to become white smoke. It is possible to suppress the exhaust emission from being deteriorated by being released into the exhaust gas.

  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. In FIG. 1, the inside of the internal combustion engine 1 and its intake system are omitted.

In FIG. 1, an exhaust pipe 5 through which exhaust gas 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 exhaust gas purification unit 10 that purifies particulate matter (for example, soot) and NOx in the exhaust gas is disposed in the middle of the exhaust pipe 5. Further, the exhaust purification unit 10 has an S-Trap 110 carrying an S trap catalyst, an oxidation catalyst 111 having oxidation ability, a filter 112 for collecting particulate matter in the exhaust, and an NSR 113 carrying an NOx storage reduction catalyst. Are arranged in series.

  Here, the exhaust pipe 5 is branched into a first branch pipe 10a, a second branch pipe 10b, and a second exhaust pipe 5b at the branch portion 15. Hereinafter, the upstream side of the branch portion 15 of the exhaust pipe 5a is referred to as a first exhaust pipe 5a. The first branch pipe 10a is connected to the end of the exhaust purification unit 10 on the S-Trap 110 side, and the second branch pipe 10b is connected to the end of the exhaust purification unit 10 on the NSR 113 side. That is, the first branch pipe 10a and the second branch pipe 10b are connected via the exhaust purification unit 10 to form a loop-shaped exhaust path. Accordingly, the first exhaust pipe 5a and the second exhaust pipe 5b correspond to the first exhaust passage and the second exhaust passage in the present embodiment. The first branch pipe 10a and the second branch pipe 10b correspond to the first branch path and the second branch path in this embodiment.

  The filter 112 in the present embodiment is a wall flow type particulate filter made of a porous base material. However, the filter 112 may have a configuration in which the NOx storage reduction catalyst is supported on the particulate filter.

  Here, the exhaust purification unit 10 corresponds to the exhaust purification unit in the present embodiment. Further, the first switching valve 12 for switching which of the first exhaust pipe 5a, the first branch pipe 10a, the second branch pipe 10b, and the second exhaust pipe 5b is connected to or shut off from the branch portion 15. Is provided. The first switching valve can be switched between the first position and the second position as will be described later. The first switching valve 12 corresponds to the exhaust state switching means in this embodiment.

  Further, in FIG. 1, on the upstream side of the branch portion 15 in the first exhaust pipe 5 a, fuel for adding fuel as a reducing agent to the exhaust during NOx reduction processing or SOx poisoning recovery processing of the NOx catalyst 113. An addition valve 13 is provided. The fuel addition valve 13 corresponds to the reducing agent supply means in this embodiment.

  Here, by setting the first switching valve 12 to the first position, at the branch portion 15, the first exhaust pipe 5a and the first branch pipe 10a are connected, and further, the second branch pipe 10b and the second exhaust pipe are connected. The pipe 5b is connected, and the two passages of the connected first exhaust pipe 5a and the first branch pipe 10a and the connected second passage of the second branch pipe 10b and the second exhaust pipe 5b are connected. Can be blocked.

  Further, by setting the first switching valve 12 to the second position, the first exhaust pipe 5a and the second branch pipe 10b are connected to each other at the branch portion 15, and the first branch pipe 10a and the second exhaust pipe are further connected. 5b and two passages of the first exhaust pipe 5a and the second branch pipe 10b in a connected state, and two passages of the first branch pipe 10a and the second exhaust pipe 5b in a connected state Can be blocked. The first position and the second position will be described in detail with reference to FIG.

  The internal combustion engine 1 configured as described above and its exhaust system are provided with an electronic control unit (ECU) 35 for controlling the internal combustion engine 1 and the exhaust system. The ECU 35 is a unit that controls the exhaust gas purification unit 10 of the internal combustion engine 1 in addition to controlling the operation state of the internal combustion engine 1 according to the operation conditions of the internal combustion engine 1 and the request of the driver.

Sensors related to control of the operating state of the internal combustion engine 1 such as an accelerator position sensor 36 and a crank position sensor 37 are connected to the ECU 35 via electric wiring, and their output signals are input to the ECU 35. ing. On the other hand, a fuel injection valve (not shown) in the internal combustion engine 1 is connected to the ECU 35 via electric wiring, and the first switching valve 12 and the fuel addition valve 13 in this embodiment are connected via electric wiring. It is controlled by the ECU 35. Therefore, the reducing agent supply means and the exhaust state switching means in the present embodiment may be configured to include the ECU 35.

  The ECU 35 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. The NOx reduction processing routine and the SOx poisoning recovery processing routine of the NSR 113 are also one of the programs stored in the ROM of the ECU 35. Therefore, the performance regeneration control means, the reducing agent supply means, and the exhaust state switching means in the present embodiment may be configured including the ECU 35.

  FIG. 2 is a conceptual diagram showing an exhaust path of the exhaust purification system in the present embodiment. First, the exhaust path when the first switching valve 12 is in the first position will be described with reference to FIG. As shown in FIG. 2A, when the first switching valve 12 is in the first position, the exhaust discharged from the internal combustion engine 1 passes through the first branch pipe 10a from the first exhaust pipe 5a, It passes through the exhaust gas purification unit 10 from the S-Trap 110 side, and then passes through the second branch pipe 10b and the second exhaust pipe 5b and is discharged to the outside. Here, the state of the exhaust gas flowing along the route R1 shown in FIG. 2A is hereinafter referred to as a “first state”.

  Next, the exhaust path when the first switching valve 12 is in the second position will be described with reference to FIG. As shown in FIG. 2B, when the first switching valve 12 is set to the second position, the exhaust discharged from the internal combustion engine 1 passes through the second branch pipe 10b from the first exhaust pipe 5a, and then the NSR 113. It passes through the exhaust purification section 10 from the side, and then passes through the first branch pipe 10a and the second exhaust pipe 5b and is discharged to the outside. Here, the state of the exhaust gas flowing along the path R2 shown in FIG. 2B is hereinafter referred to as a “second state”.

  By switching the exhaust state between the first state and the second state as described above, the direction in which the exhaust from the internal combustion engine 1 passes through the exhaust purification unit 10 can be reversed.

  Next, regarding the exhaust gas purification system in the present embodiment, control when performing NOx reduction processing on the NSR 113 will be described.

  FIG. 3 is a flowchart showing the NOx reduction processing routine according to the present embodiment. This routine is a program stored in the ROM in the ECU 35 and is executed at predetermined intervals while the internal combustion engine 1 is in operation. In this routine, description will be made on the assumption that the exhaust state at the start of the NOx reduction process is the first state.

  When this routine is executed, first in S101, it is determined whether or not a NOx reduction request has been issued to the NSR 113. Here, the NOx reduction request may be issued based on the integrated value of the intake air amount after the NOx reduction process for the previous NSR 113 is completed, for example. Further, a NOx sensor (not shown) may be provided in the second exhaust pipe 5b, and the second exhaust pipe 5b may be output based on the output of the NOx sensor.

  Here, if it is determined that the NOx reduction request has not been issued, the present routine is temporarily terminated as it is. On the other hand, if it is determined that the NOx reduction request has been issued, the process proceeds to S102.

  In S102, the first switching valve 12 is switched to the second position, and the exhaust state is set to the second state. When the process of S102 ends, the process proceeds to S103.

  In S103, a predetermined amount of fuel is added from the fuel addition valve 13. Here, since the exhaust state is switched from the first state to the second state in S102 described above, the fuel added from the fuel addition valve 13 is introduced into the exhaust purification unit 10 from the NSR 113 side, and the fuel is efficiently supplied to the NSR 113. Can be supplied. Here, the predetermined amount of fuel is the amount of fuel added from the fuel addition valve 13 in one NOx reduction process, and is an amount necessary for reducing and releasing NOx stored in the NSR 113. When NOx stored in the NSR 113 is reduced, the process proceeds to S104 when the process of S103 is completed.

  In S104, the first switching valve 12 is switched from the second position to the first position, and the exhaust state is set to the first state. When the processing of S104 is completed, this routine is once ended.

  As described above, in the NOx reduction process according to the present embodiment, by performing the exhaust state as the second state, the fuel added from the fuel addition valve 13 is introduced into the exhaust purification unit 10 from the NSR 113 side, Since the fuel can be efficiently supplied to the NSR 113, the fuel efficiency related to the NOx reduction process can be improved.

  In S103, even if the fuel added from the fuel addition valve 13 flows out downstream from the NSR 113, the exhausted state is oxidized in the downstream oxidation catalyst 111 in the second state, so the fuel flowing out from the NSR 113 It is possible to suppress discharge to the outside without being purified.

Similarly, even if the fuel flows out from the NSR 113 as described above, the fuel is oxidized. Therefore, even if the exhaust state is switched to the first state after the end of the NOx reduction process, the NO ₂ in the oxidation catalyst 111 is changed. There is no possibility that the generation amount will decrease. Therefore, after switching the exhaust state to the first state and returning to the normal operation, the oxidation removal of PM in the filter can be promoted efficiently.

  In this embodiment, since the S-Trap 110, the oxidation catalyst 111, the filter 112, and the NSR 113 are arranged in series, the fuel added from the fuel addition valve 13 in S103 passes through the NSR 113 and flows downstream. However, since it is oxidized by the oxidization catalyst 111 that has flowed out, it is difficult to introduce it into the fuel S-Trap 110.

  Further, since the S-Trap 110 and the NSR 113 are arranged apart from each other, the temperature of the S-Trap 110 is increased to a temperature (for example, 600 to 650 degrees Celsius) at which the bed temperature of the S-Trap 110 is released by the exhaust gas flowing out of the NSR 113. Is difficult to heat up.

  Therefore, even if the NOx reduction process for the NSR 113 is prolonged, it is possible to suppress leakage of SOx absorbed in the S-Trap 110. Further, even if SOx leaks from the S-Trap 110, the SOx does not flow into the oxidation catalyst 111 or the filter 112 because the exhaust state is the second state. Accordingly, it is possible to suppress the generation of white smoke caused by the oxidation of the SOx in the oxidation catalyst 111 and the filter 112.

Further, in the exhaust gas purification system for an internal combustion engine according to the present embodiment, the first switching valve 12 can be switched to an intermediate position between the first position and the second position. After being added, the first switching valve 12 may be switched to the intermediate position for a certain period until the reduction of NOx in the NSR 113 is completed. As a result, most of the exhaust passes through only the second exhaust pipe 5b having a low back pressure from the first exhaust pipe 5a and is discharged to the outside, so that the flow rate of the exhaust gas introduced into the exhaust purification unit 10 is rapidly reduced. To do. As a result, the NOx reduction reaction can be promoted by the fuel remaining in the NSR 113.

  At this time, if the state in which the flow rate of the exhaust gas passing through the exhaust gas purification unit 10 is decreased as described above, SOx absorbed in the NSR 113 may be released. However, even in such a case, the amount of SOx absorbed in the NSR 113 is small compared to the amount of SOx absorbed in the S-Trap 110, and according to the configuration according to the present embodiment, the S− Release of the SOx from the Trap 110 is suppressed. Therefore, it is possible to suppress the generation of white smoke due to a large amount of SOx being oxidized in the filter 112 and the oxidation catalyst 111.

  Next, regarding the exhaust purification system according to the present embodiment, control when performing SOx poisoning recovery processing on the NSR 113 will be described.

  FIG. 4 is a flowchart showing the SOx poisoning recovery processing routine according to this embodiment. This routine is a program stored in the ROM in the ECU 35 and is executed at predetermined intervals while the internal combustion engine 1 is in operation. In this routine, description will be made on the assumption that the exhaust state at the start of the NOx reduction process is the first state.

  When this routine is executed, first in S201, it is determined whether or not an SOx poisoning recovery request has been issued to the NSR 113. Here, the SOx poisoning recovery request may be issued based on, for example, an integrated value of the travel distance of the vehicle after the end of the previous SOx poisoning recovery process.

  Here, if it is determined that the SOx poisoning recovery request has not been issued, the present routine is temporarily terminated. On the other hand, if it is determined that the SOx poisoning recovery request has been issued, the process proceeds to S202.

  In S202, the switching position of the first switching valve 12 is switched from the first position to the second position, and the exhaust state is set to the second state. When the process of S202 ends, the process proceeds to S203.

  In S203, fuel is added from the fuel addition valve 13 to release SOx absorbed from the NSR 113. In this step, fuel is added from the fuel addition valve 13 so that the air-fuel ratio of the exhaust gas introduced into the NSR 113 becomes a rich air-fuel ratio. Thus, the air-fuel ratio of the exhaust gas introduced into the NSR 113 is low, and the NSR 113 is maintained at a high temperature (for example, 600 to 650 degrees Celsius), so that SOx absorbed by the NSR 113 can be released and reduced. Furthermore, since the exhaust state is the second state, it is possible to suppress the released SOx from being discharged directly to the outside. When the process of S203 ends, the process proceeds to S204.

  In S204, it is determined whether an SOx poisoning recovery end request for the NSR 113 has been issued. Here, the SOx poisoning recovery end request is, for example, that the air-fuel ratio of the exhaust gas introduced into the NSR 113 is rich while the bed temperature of the NSR 113 is maintained at the SOx release temperature (for example, 600 to 650 degrees Celsius) or higher. After the fuel is added from the fuel addition valve 13 so as to achieve the air-fuel ratio, the fuel may be output based on whether or not a certain period has elapsed. The floor temperature of the NSR 113 may be estimated based on a detection value by an exhaust temperature sensor (not shown) provided on the downstream side of the NSR 113 when the exhaust state is the second state.

Here, when it is determined that the SOx poisoning recovery end request has not been issued, the state after the process of S202 is continued. That is, the addition of fuel from the fuel addition valve 13 is continued. On the other hand, if it is determined that the SOx poisoning recovery end request has been issued, the process proceeds to S205.

  In S205, the fuel addition by the fuel addition valve 13 is stopped. When the processing of S205 ends, the process proceeds to S206.

In S206, the switching position of the first switching valve 12 is switched from the second position to the first position, and the exhaust state is set to the first state. As described above, in the SOx poisoning recovery process according to the present embodiment, the exhaust gas is added from the fuel addition valve 13 by performing the exhaust gas in the second state. Since the fuel is introduced into the exhaust purification unit 10 from the NSR 113 side and the fuel can be efficiently supplied to the NSR 113, the fuel consumption related to the SOx poisoning recovery process can be improved.

  In this embodiment, since the S-Trap 110, the oxidation catalyst 111, the filter 112, and the NSR 113 are arranged in series, the fuel added from the fuel addition valve 13 in S203 passes through the NSR 113 and flows downstream. However, since it is oxidized by the outflowing oxidation catalyst 111, it is difficult to be introduced into the fuel S-Trap 110.

  Further, since the S-Trap 110 and the NSR 113 are arranged apart from each other, the bed temperature of the S-Trap 110 rises to a temperature at which SOx can be released (for example, 600 to 650 degrees Celsius) due to the exhaust gas flowing out of the NSR 113 at a high temperature. Not warm.

  Therefore, even if the SOx poisoning recovery process for the NSR 113 is performed, it is possible to suppress the release of SOx absorbed in the S-Trap 110. Even if SOx is released from the S-Trap 110, the exhaust state is the second state, so the released SOx does not flow into the oxidation catalyst 111 or the filter 112. It is possible to reduce the absolute amount of SOx flowing in. As a result, it is possible to suppress the generation of white smoke that occurs when a large amount of SOx is oxidized in the oxidation catalyst 111 or the filter 112.

  In this embodiment, the control for the NOx reduction process and the SOx poisoning recovery process for the NSR 113 is exemplified, but the present invention can be applied to other controls. For example, when a large amount of PM accumulates on the filter 112, the present invention can be applied to PM regeneration control that oxidizes and removes PM in a concentrated manner.

  Further, the S-Trap 110 according to the present invention does not decrease the SOx absorption capacity even when the amount of absorbed SOx increases, and can sufficiently absorb SOx without performing performance regeneration control of SOx release. Although it is more preferable to use a trap catalyst, the present invention is applied even to an S trap catalyst that requires the above performance regeneration control to recover the SOx absorption capacity when the amount of SOx increases. It is possible.

  Next, an embodiment having a configuration different from that of the first embodiment of the exhaust gas purification system for an internal combustion engine according to the present invention will be described.

  FIG. 5 is a diagram showing a schematic configuration of the internal combustion engine according to the present embodiment and its intake / 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.

An exhaust pipe 50 through which exhaust from the internal combustion engine 1 flows is connected to the internal combustion engine 1 according to the present embodiment, and this exhaust pipe 50 is connected downstream to a muffler (not shown). Further, an exhaust purification unit 20 that purifies particulate matter (for example, soot) and NOx in the exhaust is disposed in the middle of the exhaust pipe 50. The exhaust purification unit 20 also has an S-Trap 210 carrying an S trap catalyst, an oxidation catalyst 211 having oxidation ability, a filter 212 for collecting particulate matter in the exhaust, and an NSR 213 carrying an NOx storage reduction catalyst. Are arranged in series. The exhaust purification unit 20 corresponds to the exhaust purification means in this embodiment.

  A first connection portion 25a is provided in the middle of the exhaust pipe 50. In the exhaust pipe 50, the upstream of the first connection portion 25a is referred to as a third exhaust pipe 50a, and the first connection portion 25a and the exhaust purification section. A portion between 20 and the end portion on the S-Trap 210 side is referred to as a third branch pipe 20a. Further, the fourth branch pipe 20b is connected to the first connection portion 25a, and the other end of the fourth branch pipe 20b is connected to the end of the exhaust purification unit 20 on the NSR 213 side.

  On the other hand, in the exhaust pipe 50, a second connection part 25b is provided downstream of the exhaust purification part 20, and the downstream of the second connection part 25b is referred to as a fourth exhaust pipe 50b. Further, the fifth branch pipe 20c is connected to the second connection portion 25b, and the other end of the fifth branch pipe 20c is connected to the end of the exhaust purification unit 20 on the S-Trap 210 side. In the exhaust pipe 50, a portion between the second connection portion 25b and the end of the exhaust purification unit 20 on the NSR 213 side is referred to as a sixth branch pipe 20d.

  Further, the end of the exhaust purification unit 20 on the S-Trap 210 side is provided with a second switching valve 22a, and the end of the exhaust purification unit 20 on the NSR 213 side is provided with a third switching valve 22b. The second switching valve 22a can be switched so that the exhaust purification unit 20 is connected to either the third branch pipe 20a or the fifth branch pipe 20c. On the other hand, the third switching valve 22b can be switched to connect the exhaust purification unit 20 to either the fourth branch pipe 20b or the sixth branch pipe 20d. The second switching valve 22a and the third switching valve 22b correspond to the exhaust state switching means in this embodiment.

  In FIG. 5, the third exhaust pipe 50 a is provided with a fuel addition valve 23 that adds fuel as a reducing agent to the exhaust during NOx reduction processing or SOx poisoning recovery processing of the NOx catalyst 213. Yes. The fuel addition valve 23 corresponds to the reducing agent supply means in this embodiment.

  Further, the ECU 35 is connected to the second switching valve 22a, the third switching valve 22b, the fuel addition valve 23, and the like in the present embodiment via electric wiring, and is controlled by the ECU 35.

  The ECU 35 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. The NOx reduction processing routine and the SOx poisoning recovery processing routine of the NSR 213 are one of the programs stored in the ROM of the ECU 35. Therefore, the performance regeneration control means, the reducing agent supply means, and the exhaust state switching means in the present embodiment may be configured including the ECU 35.

  FIG. 6 is a conceptual diagram showing an exhaust path of the exhaust purification system in the present embodiment. Here, as shown in FIG. 6 (a), the second switching valve 22a and the third switching valve 22b connect the third branch pipe 20a and the exhaust purification section 20, and the exhaust purification section 20 and the sixth branch pipe. When switching to 20d, the exhaust discharged from the internal combustion engine 1 passes through the third branch pipe 20a from the third exhaust pipe 50a, then passes through the exhaust purification unit 20 from the S-Trap 210 side, Then, it passes through the sixth branch pipe 20d and the fourth exhaust pipe 50b and is discharged to the outside. Here, the state of the exhaust gas flowing along the route R3 shown in FIG. 6A is hereinafter referred to as a “first state”.

  Next, as shown in FIG. 6 (b), the second switching valve 22a and the third switching valve 22b connect the fourth branch pipe 20b and the exhaust purification unit 20 and also connect the exhaust purification unit 20 and the fifth branch. When switching to connect the pipe 20c, the exhaust discharged from the internal combustion engine 1 passes through the exhaust gas purification unit 20 from the NSR 213 side after passing through the fourth branch pipe 20b from the third exhaust pipe 50a, and thereafter , It passes through the fifth branch pipe 20c and the fourth exhaust pipe 50b and is discharged to the outside. Here, the state of the exhaust gas flowing along the route R4 shown in FIG. 6B is hereinafter referred to as a “second state”.

  By switching the exhaust state between the first state and the second state as described above, the direction in which the exhaust from the internal combustion engine 1 passes through the exhaust purification unit 20 can be reversed. Therefore, also in the configuration according to the present embodiment, the above-described NOx reduction processing routine and SOx poisoning recovery processing routine can be applied, and the NOx reduction processing and SOx poisoning recovery processing for NSR 213 are performed. be able to.

  That is, even in the above-described configuration, in the NOx reduction process or SOx poisoning recovery process for the NSR 213, the fuel added from the fuel addition valve 23 is introduced into the exhaust purification unit 20 from the NSR 213 side, and the fuel is efficiently supplied to the NSR 213. Since it can be supplied, the fuel consumption related to the NOx reduction process and the SOx poisoning recovery process can be improved.

  Further, also in the NOx reduction process and the SOx poisoning recovery process of NSR 213 in the present embodiment, the S-Trap 210, the oxidation catalyst 211, the filter 212, and the NSR 213 are arranged in series in the exhaust purification unit 20, and the S-- Trap 210 and NSR 213 are separated.

  Therefore, even if the fuel added from the fuel addition valve 23 passes through the NSR 213, it is difficult to be introduced into the S-Trap 210, and the release of SOx absorbed in the S-Trap 210 can be suppressed. Further, even if SOx is released from the S-Trap 210, it does not flow into the oxidation catalyst 211 or the filter 212, so that the absolute amount of SOx flowing into the oxidation catalyst 211 or the filter 212 can be reduced. Accordingly, it is possible to suppress the generation of white smoke that is generated when a large amount of SOx is oxidized in the oxidation catalyst 211 or the filter 212.

  The above-described embodiment is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the spirit of the present invention.

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. It is a conceptual diagram which shows the path | route of the exhaust_gas | exhaustion of the exhaust gas purification system in a present Example. (A) is a conceptual diagram which shows the path | route of exhaust_gas | exhaustion when a 1st switching valve exists in a 1st position. (B) is a conceptual diagram showing an exhaust path when the first switching valve is in the second position. 3 is a flowchart showing a NOx reduction processing routine according to Embodiment 1. 3 is a flowchart showing a SOx poisoning recovery processing routine according to the first embodiment. It is a figure which shows schematic structure of the internal combustion engine which concerns on Example 2 of this invention, its exhaust system, and a control system. 6 is a conceptual diagram illustrating an exhaust path of an exhaust purification system in Embodiment 2. FIG. (A) is a conceptual diagram which shows the path | route of exhaust when the state of exhaust is made into the 1st state. (B) is a conceptual diagram showing an exhaust route when the exhaust state is set to the second state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Exhaust pipe 5a ... 1st exhaust pipe 5b ... 2nd exhaust pipe 10 ... Exhaust gas purification part 10a ... 1st branch pipe 10b ... 2nd branch Pipe 12 ... First switching valve 13 ... Fuel addition valve 15 ... Branch 35 ... ECU
110 ... S-trap
111 ... Oxidation catalyst 112 ... Filter 113 ... NSR

Claims (3)

An exhaust passage having one end connected to the internal combustion engine and through which the exhaust from the internal combustion engine passes;
Exhaust purification means for purifying the exhaust that is provided in the exhaust passage and passes through the exhaust passage;
Reducing agent supply means for supplying a reducing agent to the exhaust gas introduced into the exhaust gas purification means;
Performance regeneration control means for performing control to regenerate the performance of the exhaust gas purification means by supplying a reducing agent to the exhaust gas from the reducing agent supply means;
An exhaust gas purification system for an internal combustion engine comprising:
The exhaust purification means collects an S trap catalyst that absorbs SOx in the exhaust when the air-fuel ratio of the exhaust is lean, an oxidation catalyst that has an oxidizing ability, and particulate matter in the exhaust and collects the particulate matter. A filter that prevents clogging by removing the collected particulate matter by oxidation, and when the air-fuel ratio of the exhaust is lean, it stores NOx in the exhaust and is rich in the exhaust and has a reducing agent. An NOx storage reduction catalyst that releases and reduces the stored NOx, and is provided in a state where the S trap catalyst, the oxidation catalyst, the filter, and the NOx storage reduction catalyst are arranged in series in this order.
The exhaust state can be switched between a first state in which the exhaust flows into the exhaust purification means from the S trap catalyst side and a second state in which the exhaust flows from the NOx storage reduction catalyst side. Further comprising an exhaust state switching means,
When the performance regeneration control by the performance regeneration control means is not performed, the exhaust state is changed to the first state by the exhaust state switching means, and the performance regeneration control by the performance regeneration control means is performed. In the exhaust gas purification system for an internal combustion engine, the exhaust state is changed to the second state by the exhaust state switching means.   2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the performance regeneration control is a SOx poisoning recovery process for releasing SOx absorbed in the NOx storage reduction catalyst. The exhaust passage includes a first branch passage that branches from a branch portion provided in the exhaust passage and is connected to an end of the exhaust purification means on the side of the S trap catalyst; A second branch passage connected to an end of the NOx storage reduction catalyst side; a first exhaust passage upstream of the branch portion in the exhaust passage; and a second exhaust downstream of the branch portion in the exhaust passage. A passage,
The reducing agent supply means supplies the reducing agent to the exhaust upstream from the branch portion,
The exhaust state switching means connects the first exhaust passage and the first branch passage in the branch portion, connects the second branch passage and the second exhaust passage, and the connected state. The first exhaust passage and the first branch passage, and the connected second branch passage and the second exhaust passage are shut off to bring the exhaust state into the first state. Connecting the first exhaust passage and the second branch passage, connecting the first branch passage and the second exhaust passage, and the first exhaust passage and the second branch passage in the connected state; The exhaust of the internal combustion engine according to claim 1 or 2, wherein the exhaust state is set to the second state by blocking the connected first branch passage and second exhaust passage. Purification system.

Images